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concentric carb on pre unit #785919 09/30/19 9:13 pm
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Michel1990 Offline OP
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I would like to use a Concentric on my pre unit Triumph.
And i was hoping someone could suggest a staring point for main jet, slide number, etc.

I was thinking about buying a wassell carb anyone have any experience with these carb`s?
and should i go with the 30mm or 32mm?

Engine specs:

Triumph 650
T110 iron head
7:1 pistons
E3134 cams
air filter

Regards
Michel

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Re: concentric carb on pre unit [Re: Michel1990] #785920 09/30/19 9:15 pm
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triton thrasher Offline
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28 or 30 mm.

I prefer 28.


Amateur Loctite enthusiast.
Re: concentric carb on pre unit [Re: Michel1990] #785923 09/30/19 9:42 pm
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HawaiianTiger Online Content
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Too bad you can't test a 928 vs a 930. My bike is set up exactly like yours but it has a Monobloc 389 on it. I had a 376 1 1/16 but when I put the 389 which is slightly larger bore, it ran much better.

#3.5 THROTTLE SLIDE, 230 MAIN JET & 106 NEEDLE JET SPECIFICALLY FOR SINGLE CARB BSA / TRIUMPH

These specs were taken off the Bonneville Shop's web page for 930. I agree with the 3.5 slide unless you're at some altitude.
The Main jets can vary a bit....It would be foolish to use a standard Concentric when the excellent premier is available with all it's upgrades.
I've found that the normal 1.5 turns out from closed pilot adjustment to be not very accurate. I usually end up with closer to one full turn maybe a bit less. I think some bikes could stand a richer pilot jet than what is supplied.
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: concentric carb on pre unit [Re: Michel1990] #785996 10/01/19 6:20 pm
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Michel1990 Offline OP
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Thanks Bill, those are the same specs for my 1970 Tr6 i was thinking that would be a good starting point.
air screw on my tr6 is not even open a full turn
and i think the 3,5 slide will be ok because i life in the netherlands no mountains here
i think i have some main jets so ill think ill start out with 1 size bigger just to be safe

could you explain triton trasher why you prefer the 28 over the 30 mm?

Michel

Re: concentric carb on pre unit [Re: Michel1990] #786002 10/01/19 6:56 pm
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triton thrasher Offline
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Going oversize on carburettors means the throttle is not open so far at a given speed or acceleration rate. That means the mixture is being metered by the pilot jet and the throttle slide when it should be on the needle taper. I find that makes it harder to get the mixture right in the lower ranges.

The original carb was inch and a sixteenth, which is just over 27 mm.

I can’t tell you whether you’ll get more power with a 930, because I’ve been using twin 928s on my T110 for almost 20 years. I don’t think they are too small, because the bike has held a genuine (not just speedometer) 106 mph for a few miles at a time. Maybe it would do 107 mph (maybe not) with 930s, but who cares? The midrange pull is very good .



Amateur Loctite enthusiast.
Re: concentric carb on pre unit [Re: Michel1990] #786007 10/01/19 7:22 pm
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TR7RVMan Offline
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HI Michael, Pretty much seems everyone that gets Wassell is disappointed with it. Pretty much every part I've gotten from Wassell has low quality issues somehow. Just had to return primary chain tensioner. Pad glued on crooked & bends at end were terrible.

On the other hand AMAL Premier has proven quite good overall. If you choose AMAL make sure it has .019 idle jet. The new Premier is different casting & they do much better with the 019 jet. This has shown true on both Tigers & Bonnies. You can buy direct from AMAL & they will assemble to your specs with all parts including top & banjo fitting. They didn't charge me extra. Email Phil at AMAL. I found him easy to work with. I would start with the other jets & slide sizes Hawaiian Tiger posted.

Also float level on Premiere is above float bowl, not lower like earlier Concentric. Don't lower it. Idle jets are easy to get & not costly, but I'd still start out with .019 idle jet.

I've found lowering compression ratio doesn't seem to effect mixture, meaning putting 7.1 pistons in unit 650.

I don't have experience with your motor, but I've found on T140 even going from 930 to 932 doesn't run as good overall. I've been personally involved with that.

I would tend to go closest to size of the original carb. Over sized carbs generally only work at the very highest RPM which is only good for racing at high speeds. Going fast on public roads it will often run worse pulling out of turns in real life speeds etc. The 932 on the T140 was disappointing. The price of Premier is not cheap, but worth it. However I see you want to get it right the first time. Smart move!
Don


1973 Tiger 750
Re: concentric carb on pre unit [Re: Michel1990] #786058 10/02/19 3:56 am
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reverb Online Content
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...very interesting what you say HT. Possibly the problem with these carburetors that I have in this 79.
I think that you are right TR7RVMan.

Re: concentric carb on pre unit [Re: Michel1990] #786697 10/10/19 11:41 am
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Dick Harris Offline
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Bill, when you swapped the Monobloc 376 for the 389, di you open out the manifold? I am about to try the same modification on my '57 TR-6. and I would think that would be necessary. Thanks Dick

Re: concentric carb on pre unit [Re: Michel1990] #786702 10/10/19 1:30 pm
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Hillbilly bike Offline
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My experience with larger carbs is it all depends on the engine tune and how the rider treats the throttle...A 750 with it's stupid stock intake cam timing has near too much carb with the original 30mm's.....Correct the cam timing and it's a different story.. I had 32 MM Concentrics on a 650 with a 750 kit and it never felt over carbureted..But I don't snap open the throttle, I roll it open no faster than the engine can handle....Sometimes ya got to be smarter than the engine when you use non standard stuff and you may see more performance....But if more performance isn't the goal, stock sizes usually are best I suppose


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: concentric carb on pre unit [Re: Michel1990] #786721 10/10/19 6:26 pm
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HawaiianTiger Online Content
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Dick, I didn't touch the manifold. I don't remember even checking it, to be honest. It could have already been done, and that would explain why the larger carb ran better than the smaller one.

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: concentric carb on pre unit [Re: Michel1990] #786781 10/11/19 10:50 am
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Dick Harris Offline
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Thanks Bill , is it possible that the carb throat being larger than the manifold, could cause a bit of extra swirl in the incoming mixture which might be an advantage. It's a thought. Dick


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