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Tue Jan 17, 2012 12:52 pm

ok so i was reading a thread on timing and someone mentioned that dual single barrel carbs like ICTs and Kadrons idel on only 2 cylinders usually 2 & 4, but when reving up the engine will fire on all 4. is it just me or does that not sound correct. heres the link to the thread:

http://www.thesamba.com/vw/forum/viewtopic.php?t=495524

about half way down is where it is mentioned. can someone please explain this.

thanks
kam

Tue Jan 17, 2012 1:00 pm

very common issue. The VW firing order is 2 on one side, 2 on the other, etc.

Basically with dual 1bbls, the first cylinder uses up the air/fuel and there's nothing left for the 2nd one on that side until the throttle is open a bit.

This is not the case with dual 2bbl carbs, nor center mount 1bbls.

Tue Jan 17, 2012 1:08 pm

oh ok now that makes a little more sense thanks john, but why is that centermount 1bbl carbs dont have the same problem?

Tue Jan 17, 2012 1:10 pm

A single two barrel can act the same, in some cases

Tue Jan 17, 2012 3:35 pm

I think if you put the notch [across the intake ports] in the manifolds like factory did to stock DP end housings it will help with the Idle problem, I have a extra set of ICT manifolds I think I will try it on.

Casey

Tue Jan 17, 2012 3:49 pm

The intake manifold volume evens those pulses out. One cylinder can't suck the whole intake dry when it is feeding 4 cylinders. Think about how much volume is in a 1bbl dual carb intake compared to a 1bbl 4 cylinder intake.

In dual 1bbls the balance tube does help some, but a lot of guys omit it and don't really pay attention to the problems caused by this. Some don't care.

I've seen a lot of cars that ran like chit that guys thought "ran great".

Tue Jan 17, 2012 5:12 pm

The larger the duration the worse the idle miss gets. I have started removing the division between the intake runners in the manifold to help with this idle anomolly and it does help.

If you are going to run big duration you should use IDF or HPMX style dual 2 throat carbs to completely solve the problem.

Kadrons work excellent with the manifolds modified. The more common plenum before the intake valve (think single port) the better the dual single barel carbs will run.

Gary.

Tue Jan 17, 2012 5:57 pm

have any pictures of a modded manifold? :)

Gary Massin-Ball wrote: Kadrons work excellent with the manifolds modified. The more common plenum before the intake valve (think single port) the better the dual single barel carbs will run.

Gary.

Tue Jan 17, 2012 6:02 pm

My 34 ict's ran what i thought was pig rich at first start on the stand. So i changed the idles from 55's to 57.5's I had a good used stock cam and lifters on the motor so i was not concerned about the standard 2000 rpm break in procedure. So i throttled up from my 750 rpm to 1250 and it went away, came down to about 850 and it started stinking again. No balance tube used. The moral to the story is at idle you might have some unburnt fuel but just past that they run good.

Wed Jan 18, 2012 10:06 am

lots of great info thanks for the input. i think i will be picking up some manifolds for my kadrons and do some experimenting :)

Wed Jan 18, 2012 10:09 am

Just curious why if you thought it was pig rich on the stand, you went from 55s to 57.5s? Wouldn't that make it worse?

bsairhead wrote: My 34 ict's ran what i thought was pig rich at first start on the stand. So i changed the idles from 55's to 57.5's I had a good used stock cam and lifters on the motor so i was not concerned about the standard 2000 rpm break in procedure. So i throttled up from my 750 rpm to 1250 and it went away, came down to about 850 and it started stinking again. No balance tube used. The moral to the story is at idle you might have some unburnt fuel but just past that they run good.

Wed Jan 18, 2012 4:57 pm

Your right John, I said it backwards, must have been that last brandy. Right now I'm on my first. Point is i thought it was rich but it was just not firing on all four at idle.