Concentric again

Started by Mike Farmer, 05 May, 2020, 10:42

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Mike Farmer

05 May, 2020, 10:42
 :) :) :)
Hi and happy lockdown to you all.

I ahve a concentric carb with a throat size 27mm about 1+1/16th" Now the question is whether I am going to be able to sensibly run my a65 with this carb as its about 1mm undersize. Not my first choice but availavble straight away.

Mike 8) 8) 8)

AdrianS

#1
05 May, 2020, 11:32
Mike
Try it and see!
I've run different carbs on bikes in the past and they have run ok.
You probably are better running a fractionally smaller carb than a bigger one as the air flow won't be disturbed as much.  Remember you are running most of the time at partial throttle openings.
I would be prepared to fine tune jetting if necessary!
............just my opinion!

DAVE BRADY

#2
05 May, 2020, 11:52
Good morning,

It would be interesting to see how you get on especially if you can blend the carb to the manifold through the heat resistant spacer.
It may slightly increase the venturi affect of the carb resulting in more velocity taking the charge in to the cylinder.  Could be better at lower revs but run out of steam higher up the rev range.

Dave.

A10 JWO

#3
05 May, 2020, 17:23
I have fitted a 125 Carb on a 150 project, both two stroke applications, runs fine. 4 mm difference in size. Temporary measure. 

Allan G

#4
05 May, 2020, 18:01
The 27mm carbs were only ever made for the triples. Assuming you have fitted another carb top and made the correct changes for the slide. You will still have an issue where the spray tube isn't a 4 stroke one and there is most likely no slide adjustment screw.

Mike Farmer

#5
05 May, 2020, 19:49
 :) :) :)

Thanks guys. All very interesting stuff. It is probably not going to happen---but if it does I shall "jet" it per the normal 28mm with 3.5 slide and see where it goes from there. I worked it out and figure up to a 5% decrease in air quantity which will/may cause a minor increase in flow speed which will affect the mixture?????but not enuf to get upset about.
Amazing what a bit of knowledge can do----once upon a time, back in the day of honest politicians, I would have just shoved it on and run it, So you never know!!!!!!!!!!!!

Mike 8) 8) 8)

A10 JWO

#6
05 May, 2020, 22:19
Mike do you want to go flat out, will still have loads of power.

Mike Farmer

#7
06 May, 2020, 09:03
 :) :) :)

Thanks all. I have actually found a 928 which I shall sort out and see where it goes.

Mike 8) 8) 8)
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