Britbike forum
Posted By: Steven A T140D or E Single Carb Conversion - 07/14/19 10:39 pm
Hi All,

Has any body converted a parallel port head to single carburetor? If so, how?
Or why?
Posted By: Steven A Re: T140D or E Single Carb Conversion - 07/14/19 11:16 pm
Originally Posted by triton thrasher
Or why?


Because my mechanic (amongst others) of decades of experience reports how marvelous the dual to single carb conversion is."Transforms then", his words.
Posted By: Jon W. Whitley Re: T140D or E Single Carb Conversion - 07/15/19 12:15 am
Originally Posted by Steven A
Hi All,

Has anybody converted a parallel port head to single carburetor? If so, how?



The only option for you to be able to run a single carb on your T140D is to find a TR7 head and bolt on intake manifold. I would just try my best to properly sync the dual Amal Mk II carbs first.
Posted By: DMadigan Re: T140D or E Single Carb Conversion - 07/15/19 1:18 am
Not exactly the only way. The inlet stubs being threaded in makes it more complicated. You could make stubs with a circular flange, thread them into the head then mark, drill and tap them for the adapter holes. Make the 2:1 adapter and bolt it on.
Or you could cut off the existing steel stubs leaving 1/4" or so beyond the head, thread it and make circular plates to match then do the same as above.
Originally Posted by Steven A
Originally Posted by triton thrasher
Or why?


Because my mechanic (amongst others) of decades of experience reports how marvelous the dual to single carb conversion is."Transforms then", his words.


But this super mechanic, who reports such a transformation, doesn’t know how to do it.
Originally Posted by Steven A
Originally Posted by triton thrasher
Or why?


Because my mechanic (amongst others) of decades of experience reports how marvelous the dual to single carb conversion is."Transforms then", his words.


Not necessarily true. Due to port biasing, you could end up with a bike that has a much rougher motor. And in my experience, twins carbs have the ability to provide for much more fuel efficient running, ie better fuel economy. It has mostly to do with how the right hand functions, though. Twin carbs make for more top end power and when matched with the proper cams and cam timing, make for a more fun ride.
It's all in the combination. The early 70's TR6's has what I think of as the perfect match, but the Bonnies were good, too. In fact, the move to 750cc's wasn't necessarily a good move or even necessary. The TR6's and Bonnies are more fun to ride than the 750's of any stripe.
My two cents.
Cheers,
Bill
Posted By: reverb Re: T140D or E Single Carb Conversion - 07/15/19 6:13 am
...man; except the 500 racers the definition of the bonneville is the twin carbs...
In most models with the splayed ports look fantastic and perform good as HT is saying and you have this idea? Honda four with one carb? cmon

HT; possibly more fun in small trip with curvy roads etc but I have a buddy here with a T120r and they say that they are not perform better in longest runs at top speed (too much for the 4 gear) etc
He has also a 78 750 fitted on a mid 50s frame and he say that is faster.
More RPMs to keep the same speed and that is too much rpms in my book to keep constant 120-130km/h for 2 or 3 hours as I do.
Posted By: Tigernuts Re: T140D or E Single Carb Conversion - 07/15/19 9:23 am
Instead of demanding to know why you're asking the question, I'll have a go at answering it. The T140E head is the same casting as the TR7 head. Triumph modified the TR7 head to fit a pair of Amal MkII carbs by threading the inlet ports and fitting adapter stubs. If you offer up a TR7 manifold to an E head with the stubs removed, you can see what needs doing to make the manifold fit properly. Unfortunately, the manifold's mounting stud holes coincide with (or at least, overlap) the threaded ports, so some building up with weld followed by careful machining to even the ports out and then drill & tap for the studs would be needed.

Not a difficult task for a skilled welder / machinist with their own equipment, but probably a bit expensive to get someone else to do it. But the TR7 heads are rare, so possibly worthwhile? Despite what some people seem to think, the single carb heads make for a sweeter running engine with plenty of torque and surprisingly little difference to top speed, even with everything else left standard. If you improve breathing with straight-through exhausts and fit a better exhaust cam, they're faster than a standard twin carb version.
Posted By: Steven A Re: T140D or E Single Carb Conversion - 07/15/19 11:54 am
Originally Posted by Tigernuts
Instead of demanding to know why you're asking the question, I'll have a go at answering it. The T140E head is the same casting as the TR7 head. Triumph modified the TR7 head to fit a pair of Amal MkII carbs by threading the inlet ports and fitting adapter stubs. If you offer up a TR7 manifold to an E head with the stubs removed, you can see what needs doing to make the manifold fit properly. Unfortunately, the manifold's mounting stud holes coincide with (or at least, overlap) the threaded ports, so some building up with weld followed by careful machining to even the ports out and then drill & tap for the studs would be needed.

Not a difficult task for a skilled welder / machinist with their own equipment, but probably a bit expensive to get someone else to do it. But the TR7 heads are rare, so possibly worthwhile? Despite what some people seem to think, the single carb heads make for a sweeter running engine with plenty of torque and surprisingly little difference to top speed, even with everything else left standard. If you improve breathing with straight-through exhausts and fit a better exhaust cam, they're faster than a standard twin carb version.


Thanks Tigernuts. A model of constructive advice, unlike some.
Posted By: quinten Re: T140D or E Single Carb Conversion - 07/15/19 4:43 pm

I see brand new LF Harris 750 TR7 heads
Available online ... from $800 to 1050 ..
From a number of different vendors... [Linked Image]
$1050 is for the complete head wirh
Kibblewhite Valves , guides and springs .
Posted By: AngloBike Re: T140D or E Single Carb Conversion - 07/15/19 5:41 pm



https://www.ebay.co.uk/itm/TRIUMPH-TR7-1973-83-10-STUD-CYLINDER-HEAD-71-7505-BRAND-NEW-UK-MADE-STUB-PORTS/183557760635?hash=item2abce5267b:g:an4AAOSw4m9b~f4a


And sell the original head on, or keep it
Posted By: reverb Re: T140D or E Single Carb Conversion - 07/15/19 6:05 pm
...may be ALL the brands are wrong fitting multiple carburetors in their engines...is a myth that a single carburetor works better on the top end; also looks no better more in a Triumph Bonneville.
With constructive criticism in mind, the switch from twin carbs to single carbs has a lot against it. However, if you must do it, say, just for the fun of it, spend all your hard earned cash on modifying your head and be prepared to be disappointed in the results.
The parallel port head was a move that Triumph SHOULD have made many years prior. Tuners in the fifties and sixties spend a lot of time and money correcting the inlet port shapes to get power and efficiency from this motor. Triumph apparently never looked at their results.
Re-angling the inlet ports was one of the things they did to help correct the tendency for these motors to detonate or experience pre-igntion.
What you have with the parallel inlet head is the final product of Triumph finally bending to winds of change and now you want to mess that up.
Go figure.
For the fun of it, Sure, have at it.
For practical reasons. Money is better spent doing other things to your bike.
Cheers,
Bill
The strange thing was they never stopped making parallel port 650 and 750 heads- they just didn’t put twin carburettors on them until the T140E.
Posted By: Tigernuts Re: T140D or E Single Carb Conversion - 07/15/19 8:54 pm
Originally Posted by HawaiianTiger
The parallel port head was a move that Triumph SHOULD have made many years prior. Tuners in the fifties and sixties spend a lot of time and money correcting the inlet port shapes to get power and efficiency from this motor. Triumph apparently never looked at their results.
Re-angling the inlet ports was one of the things they did to help correct the tendency for these motors to detonate or experience pre-igntion.
What you have with the parallel inlet head is the final product of Triumph finally bending to winds of change and now you want to mess that up.


This just isn't how the parallel port heads came about! The only reason for them was to be able to easily use the Amal MkII carbs, which would enable Bonnevilles to keep on being saleable in the USA. It was an easy fix because the Tiger head was easily adaptable for the parallel inlet stubs, which hold the carbs nice and close and able to be supported by the airox directly behind them. If it had been feasible to carry on using the V head with MKII carbs, Triumph would have done it.

There is nothing remotely special about the E heads. The fact that they happen to work OK is testament to the overall brilliance of the engine design, rather than to any clever engineering of the inlet ports. A lot of racers go for the V head due to better results at top end.

If you want tractability, consistent smooth running, low maintenance and no noticeable loss in performance unless you're racing, a single carb head is a sensible move. I agree that twin carbs are better, if you want every ounce of horsepower at full throttle, but few riders of old Triumphs care enough about that to even notice.
Posted By: Stein Roger Re: T140D or E Single Carb Conversion - 07/15/19 9:29 pm
IMHO the perceived superiority of the single carb head is caused by the smaller ports, not the single carb as such.
One of the loveliest Triumph engines I've sampled was a TR6 to which I fitted a Webco twin carb conversion last year.
While I liked it with the single carb, I loved it with two. Beefy power all the way.
Like Bill, I like the long rod 650s better than the 750s but the British weeklies of the day got more speed out of the TR7 than the T140.
Putting a single carb on a T140 head will probably end in tears though.

Yes I know I'm banging on about the small port virtues, but I haven't come up with this all on my own- I stumbled on it when I built a fearfully quick TR7 a long time ago, and I've read John Healy and Pete R relating their views on it. In the Norton community it's a well known fact that on the 850 an RH10 head the 30mm ports makes for a much beefier midrange than a 32mm port RH4 head. And so on.
TT has a good point. The TR6's were always essentially parallel port. That's one of the reasons that folks are after the earlier ones. The other is that the ports were smaller increasing charge velocity.
Before I get too far out of my depth here, there has to be some changes to the head, since it obviously isn't a TR6 head with two carbs on it.
Also, it's perfectly within the expectations from Triumph to make changes with some unexpected and unintentional benefits. Seen that before...
However, my statements with regard to the Bonnie heads stand. Angling the incoming charge away from the spark plug is a dumb idea, but that's exactly what Triumph did until the parallel port T140 head came out.
So, it's likely that welding up the existing head for single carb is much less of a good idea than just buying a single carb head. That's exactly what I'd do.

On a slightly different slant....I've been toying with the idea of getting a couple of Webco bolt on inlet stubs and running two carbs on my old Thunderbird. I would be after a bit more power, but I also believe that I could tune my motor to be smoother, which is something I like even more than the power.

Cheers,
Bill

PS Edit. I wrote my response before I read Stein's. We tend to think alike regarding these things. However, I would search old PeteR (rip) posts to see what he has to say about this subject. When he came on the scene years ago, most of us just sat back and listened. He was brilliant.
B.
Originally Posted by Hawaiian Tiger
.I've been toying with the idea of getting a couple of Webco bolt on inlet stubs and running two carbs on my old Thunderbird.


I used a plate a bit like this to mount two 928s on my T110.

[Linked Image]

The best part of the improvement is the midrange response.
Posted By: reverb Re: T140D or E Single Carb Conversion - 07/15/19 10:00 pm
Hello HT; a buddy with a 78 splayed head T140V engine fitted in a mid 50s frame with the STD camshafts, 18 wheels; you know a bits bike performs very similar like my 79 parallel ports 32 Mikuni dual plug heads with spitfire camshafts...just saying
Posted By: Stein Roger Re: T140D or E Single Carb Conversion - 07/15/19 10:23 pm
Yes Bill, once again we seem to think along the same lines. Midrange and good throttle response beats a few bhp on top any day.
There's a bunch of info on this forum alone, if one looks for it. I hope I'm not infringing on anyone's copyright by offering this quote from John Healy.
What he doesn't know about these bikes, I certainly don't!

John Healy in an earlier BB post:

"Actually Kevin Cameron submitted an article on this subject for the next issue of Vintage Bike which is at the printer. We were discussing this, he was a Triumph/Kawasaki dealer in the sixties (though he spent most of his time in the cellar porting TZ750D's) and he penned a few words on the subject.

My previous comments, or theory as it where, is based on tests performed at Triumph's Baltimore facility where they were trying to find out why a T110 would go 110 mph and a 1970 T120 wouldn't go over 95mph. They were swamped with consumer complaints and set out to find the missing power.

The task was left to Tom Gunn and Cliff Guild. They tried everything and as a last resort fit a 1963 head, with smaller ports, to the bike. Right up to 110mph.

The stock 1970 ports didn't come into their own until they increased the bore (the relationship to the piston area to port size is a factor in flow) and made it a 750.

Now most people outside of the US don't know who Kevin Cameron is. I suggest you google his name... Trained as an automotive engineer at Massachusetts Institute of Technology, he has worked for Kawasaki on the World GP circuit tuning the TZ750D, is a technical editor for Cycle World magazine, and has written several books and numerous technical articles.

Actually one of the nicest street Triumphs I have ridden lately was a 1970 TR6 with an 750 kit, 5 speed conversion and a single JRC PWK carburetor. 

It is owned by Bill Getty of JRC Engineering. It reminded me why I like these Triumphs so much: it went, stopped and turned."


My conclusion, as regards the OP's question, is: Don't bother with altering your T140E to take a single carb, get a TR7 head instead. The T140 has 1 1/8" (29mm) ports compared to 1 1/16" (27mm).
A TR7 head with TT's manifold maybe? Pete R used to favor twin carbs for individual tuning and best midrange.
The advantages of a single carb are convenience (no synchronizing issues) and a lighter throttle, and to be honest they're usually fast enough too.
Posted By: reverb Re: T140D or E Single Carb Conversion - 07/15/19 10:42 pm
...please go ahead all to buy the single carburetor bikes and let all the Triumphs, Hondas, Kawa, BMWs, you know all with multiple carbs for the dumb rest. Again, I really doubt that ALL the factories are wrong. Small or bigger ports all put 2, 3, 4 or more carburetors in the big bikes. Or may be you need an HD. Those have one big carburetor...
Posted By: JakeH Re: T140D or E Single Carb Conversion - 07/16/19 1:27 am
I made a single carb Manifold for my T140E dirtbike. I have the T140E enigne in a dry frame, and no way to put GOOD airfilters in the MK2 Amals.. So i made up a manifold that mounts a single 930 out the left side with a triumph paper air filter. This was also an experiment. one runner is longer than the other so the Mixture at low throttle openings is off a little. Not a huge deal for what it is.
This is a T140E which i know was De tuned some.
Stock with 2) 30mm Amal mk2s the was 35 Hp and 40 torque.
Removed that set up and installed 1) 30mm Mk1 amal and...... 34Hp and 41.5 torque!!! All of this happened before 5500 Rpm.. The engine started to nose over at 5000.

So for a dirtbike i was happy! better air filter and better torque!! i can notice the imbalance some, but its not an issue!
Just something to think about !
That manifold TT showed us just might be the ticket. I was thinking of this setup.
[Linked Image]
But these put your carbs out in the breeze, not nicely tucked in like the one above.
.....and I have a set of used carbs laying around..... a set of anodized throttles, some cables and air filters and I'm there.
Cheers,
Bill
Posted By: Steven A Re: T140D or E Single Carb Conversion - 07/16/19 3:55 am
"Actually one of the nicest street Triumphs I have ridden lately was a 1970 TR6 with an 750 kit, 5 speed conversion and a single JRC PWK carburetor. "

Well how about that!
That has more to do with the 750 kit on the long rod motor than the single carb. It's something every Triumph enthusiast should experience at least once. Like Mr. Healy states, once the cc's are up to 750 the head starts to work.
I've had a long rod 750 myself, but with twin carbs and hot cam. The throttle would not tolerate rough treatment....the front end would shoot straight up in the air.
However, having said that, the bike was near unridable because of the vibration. It's something that I began to address in my bikes a few years after I had this one. I know I could build an engine with a 750 kit that would be tolerable now, but then I hadn't discovered the secrets.
Also, the five speed isn't really necessary on these bikes either. They're just a much nicer shifting gearbox than the four speed.
Finally, Bill Getty knows how to build a bike that works. I have a Command built by him in the early 80's that still hasn't had the bottom end or gearbox apart and has been in continuous service since then.
Cheers,
Bill
Originally Posted by HawaiianTiger
That manifold TT showed us just might be the ticket.
Bill


It took a couple of attempts to seal the carbs onto it.
Posted By: Hillbilly bike Re: T140D or E Single Carb Conversion - 07/16/19 10:51 am
In 45 years of Triumphs, the nicest one is the parallel intake ports T140D with Mikuni flat slides I ride now...I also had a 67 TR6 than ran very nicely...It's my opinion a dual carb bike tuned properly and with a rider who know how to roll open the throttle properly, gives up nothing to the single carb bike at normal road speeds and is faster at high speeds..And dual carbs just looks better...
Posted By: Irish Swede Re: T140D or E Single Carb Conversion - 07/16/19 6:34 pm
Fastest street Triumph I ever saw was a '66 TR6R with a Routt 750 kit and ONE BIG Mikuni carb.

Even with a lengthened swing arm, that TR6 would pull the front wheel up when the rider hit second AND third gear.
Posted By: Tigernuts Re: T140D or E Single Carb Conversion - 07/16/19 7:05 pm
This has turned into one of the most interesting and informative threads for quite some time - please keep the carb / heads/ ports stories coming!
Posted By: kevin Re: T140D or E Single Carb Conversion - 07/16/19 7:56 pm
Originally Posted by Hillbilly bike
In 45 years of Triumphs, the nicest one is the parallel intake ports T140D with Mikuni flat slides I ride now...I also had a 67 TR6 than ran very nicely...It's my opinion a dual carb bike tuned properly and with a rider who know how to roll open the throttle properly, gives up nothing to the single carb bike at normal road speeds and is faster at high speeds..And dual carbs just looks better...


i just rode this T140D of tony's a week or so ago. it's fantastic.

don't listen to tony. he complains about bogging. he's way picky. his bike has instant throttle response, absolutely zero hesitation on the slides in normal to enthusiatic throttle openings. it's like a correctly-tuned harley-- open the throttle, boom. it's made me look really hard at the VM mikunis i've used for years, that always seemed so much better. until i rode this machine with correctly-set up TM carburetors.

and there's no reversion in his bike either, at least none that anybody but him could detect.
Posted By: MarksterTT Re: T140D or E Single Carb Conversion - 07/16/19 8:16 pm
The parallel port head is only parallel on the outside, once inside you have the angled ports of the TR7 aiming the intake charge at the spark plugs. The TR7 head in turn is just a TR6 head with a modified casting for the 10th bolt hole, added material to the outside of the inlet entry ports to allow room for machining and threading for the steel carb stubs, (which are parallel) and a chamfered combustion chamber lip to match the larger bore of the 750.


The new TR7 head castings as seen on line appears to be the parallel inlet port head casting with the extra intake material still there but machined for the single carb manifold...might be a good head to have for some custom dual carb mods or a... straightened out port … single carb head for better flow than short stock single carb manifold. I wouldn't mind having one with the KB valves and guides and springs but just wonder about the quality of the valve/guide job? Just thinking about things.


Back to the original poster...it would be fairly easy to weld in a couple of flush aluminum plugs to replace the steel threaded in stubs, line up a stock TR6/7 inlet manifold, drill and tap for the manifold studs or use the stock steel stubs and do as Dmadigan suggested. Nothing at all wrong with a torquey, responsive TR6/7 around town which will usually outpull 99% of the ill tuned Bonnies you're likely to come up against.
Quote
Nothing at all wrong with a torquey, responsive TR6/7 around town which will usually outpull 99% of the ill tuned Bonnies you're likely to come up against.


In what imaginary world are there TR7 riders torquily responding around town, “coming up against” 99 Bonnevilles!
I'll challange any of you with a single carb 650-750 to a 2000 rpm in high gear roll contest...
Posted By: Steven A Re: T140D or E Single Carb Conversion - 07/16/19 10:41 pm
This has been a good thread.
Posted By: MarksterTT Re: T140D or E Single Carb Conversion - 07/17/19 1:51 am
Originally Posted by triton thrasher
[quote]Nothing at all wrong with a torquey, responsive TR6/7 around town which will usually outpull 99% of the ill tuned Bonnies you're likely to come up against.


In what imaginary world are there TR7 riders torquily responding around town, “coming up against” 99 Bonnevilles!
[/quote

Maybe I should have said 'Back in my day' a good stock TR6 could take a not so well tuned, poorly synched twin carb T120 a good percentage of the time...just keep turning corners and stay off the freeway. I used to piss off my buddy on his kawi H1 triple with my basically stock stripped downTR6 TT bike, of course I was geared way down so wouldn't even look at a straightaway but in our then undeveloped but paved neighborhoods I'd out drag him from block to block then just turn a corner.

I just wanted to let Steven A know that there is a lot to be said for a good single carb 650 or 750 Triumph twin, one of the best running Triumphs I rode in the 60's was a TR6 Rickman Metisse scrambler with a Chantland 750 kit,34mm vm mikuni and desert torque cams, can't remember the grind and it did run out of steam on top end but anywhere else just open the throttle and go sideways. Nowadays add a little hotter cam and a flatslide and you'd have a fun streetbike.
Posted By: Steven A Re: T140D or E Single Carb Conversion - 07/17/19 7:11 am

[/quote
I just wanted to let Steven A know that there is a lot to be said for a good single carb 650 or 750 Triumph twin, one of the best running Triumphs I rode in the 60's was a TR6 Rickman Metisse scrambler with a Chantland 750 kit,34mm vm mikuni and desert torque cams, can't remember the grind and it did run out of steam on top end but anywhere else just open the throttle and go sideways. Nowadays add a little hotter cam and a flatslide and you'd have a fun streetbike.[/quote]

I appreciate your contribution.
Posted By: reverb Re: T140D or E Single Carb Conversion - 07/17/19 4:40 pm
...seeing your comments seems that depends on what the rider or user is looking. Seems too that most only use the bikes at barely mid range speed or into town and for few kms, hence the perception that the single carbs are better.
I always admitted that the later Triumphs are the best in functionality for the street use. Not the best looking though. The factory was down but they tried to squeeze all of the design, so disregard all that is somewhat dumb.

Then you have the opinions Tony and Kevin here, that are tuning these bikes since long time and race them, then my opinion that is from a daily rider, strong mid range rpm user and "long" distances user. Then you have the opinion of HT that is wrenching the older stuff and some of these and then you have almost all the factories that made all the big engines with multiple carburetors...
Posted By: Tigernuts Re: T140D or E Single Carb Conversion - 07/17/19 10:24 pm
Originally Posted by reverb
...Seems too that most only use the bikes at barely mid range speed or into town and for few kms, hence the perception that the single carbs are better..



I mostly use my singe carb 750 for fairly high speed (80 - 85mph) cruising for hours on end in France with occasional 100mph+ overtakes. Not exactly 'barely mid range speed or into town stuff. I find it performs excellently and gives great fuel economy too. But if anyone chooses to disbelieve, its no skin off my nose.
Posted By: Hillbilly bike Re: T140D or E Single Carb Conversion - 07/17/19 10:56 pm
Originally Posted by Tigernuts
Originally Posted by reverb
...Seems too that most only use the bikes at barely mid range speed or into town and for few kms, hence the perception that the single carbs are better..



I mostly use my singe carb 750 for fairly high speed (80 - 85mph) cruising for hours on end in France with occasional 100mph+ overtakes. Not exactly 'barely mid range speed or into town stuff. I find it performs excellently and gives great fuel economy too. But if anyone chooses to disbelieve, its no skin off my nose.


Ok 100 mph overtakes? That wold be a stock engine with you riding up right?
Posted By: quinten Re: T140D or E Single Carb Conversion - 07/17/19 11:10 pm
There is an old "60s" magazine comparison test ... drag race . ( cant seem to find it )
Where they raced a TR6 against a Bonnie .
The Bonnie won the quarter mile by 2/100 of a second ... @ 98mph
Thats a clear win on a drag strip
That amounts to , I think , ... about 28"
On the street , if you need to get to the post office 2/100 of a second faster ... you need 2 carburetors .

On the other hand
TR6's ruled California desert racing in the mid sixties
And scored a major win as late as 1970 ... if there's a desert between you and the post office ... take the TR6

Triumph continued to make the single carb TR7 up till the end of Co-op production
Triumph even won a road rally race
In the Pyrenees in 1981
On a single carbed TR7T
This last small hurrah garnered
The Triumph Co-op some much needed export orders .
... if you're ever in the Pyrenees , ride whatever is offered .




Posted By: Hillbilly bike Re: T140D or E Single Carb Conversion - 07/17/19 11:54 pm
Originally Posted by quinten
There is an old "60s" magazine comparison test ... drag race . ( cant seem to find it )
Where they raced a TR6 against a Bonnie .
The Bonnie won the quarter mile by 2/100 of a second ... @ 98mph
Thats a clear win on a drag strip
That amounts to , I think , ... about 28"
On the street , if you need to get to the post office 2/100 of a second faster ... you need 2 carburetors .

On the other hand
TR6's ruled California desert racing in the mid sixties
And scored a major win as late as 1970 ... if there's a desert between you and the post office ... take the TR6

Triumph continued to make the single carb TR7 up till the end of Co-op production
Triumph even won a road rally race
In the Pyrenees in 1981
On a single carbed TR7T
This last small hurrah garnered
The Triumph Co-op some much needed export orders .
... if you're ever in the Pyrenees , ride whatever is offered .





.....98 mph in the 1/4 is way faster than any other road tests...Usually low 90's in the low to mid 14's. And every road race and flat tracker with a B engine had dual carbs...I believe Cycle magazine tested a 73 Tiger that ran a 13.6....As did the off road 60's straight pipe on each side single carb 650 when geared low..
Bring them screamin single carb stock bikes over to my place near the beautiful Finger Lakes...Go to Tommy Hillbilly bar for the best hamburger and then we'll do a two lane blacktop contest of speed...Like I said, 2000 rpm in high gear roll to show me how those torque monster bikes perform... wink
Posted By: HawaiianTiger Re: T140D or E Single Carb Conversion - 07/18/19 12:04 am
What I'm getting from all this is that twin carbs rule, but the Triumph twin carb head sucks. So, if you put twin carbs on a single carb head especially an early small port one, you get the best of both.
Sound about right?
I'd like to do some experimentation myself, but money and time are issues at this point.
It beats all the work you would have to do to make the twin carb head work.
Cheers,
Bill
Posted By: Mike Baker Re: T140D or E Single Carb Conversion - 07/18/19 10:37 am
It all comes down to how carefully a motor was put together and tuned I think. Back at the factory and now.
I've spent enough time with the Halls to conclude that these are all over the map. Their dyno gets used a lot and they are always willing to test a new tuning strategy, whether theirs or anyone's. 650's with single carbs from mid 20's HP to high 30's and low 40's. Twin carbs from the 20's to around 50.
How fresh is the motor? How are the cams timed? What size carb? Exhaust? Gearing? Even from the factory, I bet no 2 bikes were identical. I've never found any evidence that they dialed in camshafts. How many combinations could that result in?
Bottom line IMO is a careful build and the small details matter.
So, Tony, I have a pretty fair running 650 with 2 carbs. How bout it?
Posted By: Hillbilly bike Re: T140D or E Single Carb Conversion - 07/18/19 11:00 am
Mike, yeah, it runs pretty fair .....................
Posted By: Tigernuts Re: T140D or E Single Carb Conversion - 07/18/19 11:52 am
Originally Posted by Hillbilly bike
Ok 100 mph overtakes? That wold be a stock engine with you riding up right?


I didn't say it was a stock engine but that is sitting upright, and it does have a single carb. My point was that single carb head 750s don't have to be slow. I know that if I was to fit a twin carb head (if I did it would be a V head, not an E one), it would increase the top end somewhat but for road use, albeit not hanging around, I can't see the need.
Posted By: Hillbilly bike Re: T140D or E Single Carb Conversion - 07/18/19 12:39 pm
An honest 100 mph in an upright position? Naked frame or a fairing? What is done to the engine? I never said a single carb is slow, I said a dual carb can be faster..
Posted By: Tigernuts Re: T140D or E Single Carb Conversion - 07/18/19 1:07 pm
Well I agree with you on that. It was Reverb, I think, who seemed to imply that single carbs were only good for pottering around slowly (sorry if I misunderstood you on that Reverb). The engine has a 70-9989 exhaust cam, 71-7017 (standard) inlet cam, 9:1 or so compression, T140D exhaust system without any silencer (I recommend this setup - releases a lot of otherwise stifled power), carb jetted to suit. No fairing, 'western' bars and me hanging onto them in my Belstaff coat like a parachute! I've had it over 110 on the clock, but that is a fraction over 100 in reality. I never crouch down for extra speed as that reminds me of kids on mopeds.

I'm building a similar engine but with a twin carb head in racer style. This will have a small (Ducati 900SS style) fairing, clip ons, rearsets etc. It'll be interesting to see how fast that'll go. I reckon well over 120 with the right gearing.
Posted By: Dibnah Re: T140D or E Single Carb Conversion - 07/22/19 5:51 am
Keep the twin carb, buy another bike with a single carb.

Motorcycle Mechanics (and others) used to publish bhp and torque curves for bikes tested, that would provide the answer to "which pulls better at lower revs". As I recall, the single carb Tiger was well regarded by magazine testers in the mid-1970s; suitable testing attire being leather jacket plus fireman's boots with fisherman's socks turned over.
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