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T140D or E Single Carb Conversion #778661 07/14/19 10:39 pm
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Steven A Offline OP
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Hi All,

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

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Re: T140D or E Single Carb Conversion [Re: Steven A] #778663 07/14/19 10:44 pm
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Or why?


Amateur Loctite enthusiast.
Re: T140D or E Single Carb Conversion [Re: triton thrasher] #778670 07/14/19 11:16 pm
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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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778673 07/15/19 12:15 am
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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.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"

Re: T140D or E Single Carb Conversion [Re: Steven A] #778678 07/15/19 1:18 am
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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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778688 07/15/19 5:12 am
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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.


Amateur Loctite enthusiast.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778691 07/15/19 5:54 am
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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


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778693 07/15/19 6:13 am
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...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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778699 07/15/19 9:23 am
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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.


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Re: T140D or E Single Carb Conversion [Re: Tigernuts] #778704 07/15/19 11:54 am
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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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778720 07/15/19 4:43 pm
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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 .

Re: T140D or E Single Carb Conversion [Re: Steven A] #778728 07/15/19 5:41 pm
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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

Last edited by AngloBike; 07/15/19 5:44 pm.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778731 07/15/19 6:05 pm
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...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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778735 07/15/19 7:05 pm
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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


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778737 07/15/19 7:19 pm
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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.


Amateur Loctite enthusiast.
Re: T140D or E Single Carb Conversion [Re: HawaiianTiger] #778741 07/15/19 8:54 pm
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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.


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Re: T140D or E Single Carb Conversion [Re: Steven A] #778743 07/15/19 9:29 pm
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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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778744 07/15/19 9:32 pm
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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.

Last edited by HawaiianTiger; 07/15/19 9:35 pm.

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1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778746 07/15/19 9:45 pm
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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.


Amateur Loctite enthusiast.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778748 07/15/19 10:00 pm
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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

Re: T140D or E Single Carb Conversion [Re: Steven A] #778749 07/15/19 10:23 pm
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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.

Re: T140D or E Single Carb Conversion [Re: Steven A] #778753 07/15/19 10:42 pm
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...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...

Re: T140D or E Single Carb Conversion [Re: Steven A] #778759 07/16/19 1:27 am
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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 !

Re: T140D or E Single Carb Conversion [Re: Steven A] #778760 07/16/19 1:53 am
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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


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: T140D or E Single Carb Conversion [Re: Steven A] #778766 07/16/19 3:55 am
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"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!

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