Hi,

Can anyone help please...... My friend put a new motor into his manx, it's a 1916cc motor with Kadron carbies and Empi manifolds. The engine is running flat on cylinders 1 and 3 when idling. There is plenty of spark..... The engine seems to run fine on full speed, just seems to be flat when idling. Any assistance would be greatly appreciated

Cheers

start with mixture and try and get a carby balancer/vacuum gauge

Hmmmm....does it have a balance tube fitted??? Sounds like there might be a slight air leak.When started from cold,can you touch the extractors on cylinders 1 and 3??Do they get warm/hot at idle like 2 and 4?? Just curious how you determined they were not firing.

Plugs, points, leads, tappet clearance...?

What does 'flat' mean, exactly?





[ Edited on 2-11-2006 by VWCOOL ]

This is fairly common. The VW engine likes to idle on the rear two cylinders, especially with Kadrons.

As long as it still drives smooth, and doesn't really shake around at idle, then it is ok.

sorry for the slow reply, been busy.

I noticed it a little when I ran a stock carb, and more so when I ran kadrons. I figured the reason was this;

The VW firing order is 1432. Which is also 4-3 then 2-1. Basically the pairs of cylinders on each side fire in order.

So look at the drivers side kadron (cylinders 2 and 1);
* Air/fuel goes into cylinder 2 for 180 degrees of crankshaft rotation,
* immediately after air/fuel goes into cylinder 1 for 180 degrees of crankshaft rotation,
* then you have a whole 360 degrees of nothing,
* then air fuel goes into cylinder 2 again and the process repeats.

The same thing happens on 4 and 3.

So basically cylinder 2 starts the air moving in the carb. Because the air needs time to accelerate, cylinder 2 initally doesn't fill very well (at low revs like idle).

Then as soon as #2 intake valve closes, #1 intake valve opens. So now cylinder 1 fills really well because the air is already moving in the carb from cylinder 2 filling.

Then #1 intake closes, nothing happens for 360 degrees and the air flow in the carb stops.

This effect means #1 and #3 get a better intake charge at idle, and I think a slightly richer mixture than #2 and #4.

Did any of that make any sense

yep perfect sense - mine does the same (only idles on two - smoothly, but u can take a plug lead off and it makes no difference) and has done for about 15 years!

NEver thought of it like that, but explains a lot for me too.....

Wes u make no sense at all

Very common knowledge that kads idle on 2 cyl a bit, especially with a bit of cam.
Playing around with venturies, and jetting can help sometimes, but its nothing to worry about.

fixed my problem with 45 del's.... One Venturi per pot.

Tazz

he said he wanted a fix.....
sometimes its worth the expence.....
The results speak for themselves...


Tazz

Nope. Not worth the expense!

right.....
u win.... i spent good money on shit... and it doesnt rev or idle...

u caught me out...

Yes i was just trying to get someone to spend money on stuff that doesnt work.

VWCOOL seems to have all the answers and i will endevour to redirect any questions related to VW performance straight to you.

Tazz

Tazz, well if you spent money on stuff that doesn't rev or idle, maybe you should re-install your kaddies :P

Diego, this is from a US site but has good basic info:

http://www.lowbugget.com/adjust_idle.html 

Kool..... and then you can fix my Idle Problem..... Oh great wise one...



Tazz

forgive me for asking the obvious Tazz,

Do your dell's have dedicated manifolds to the twin ports or do they swirl it so each pot can grab from both barrels?

When your running dual webbers or Dell's each cylinder will have its own carby throat (They are not linked). Therefore the issue wes mentioned no longer exists........

Quote:

Did any of that make any sense

Now u got four throats to diagnose, not just two! And see in the pic how the manifold is... Oh, never mind! :P

So am I making a mistake selecting twin Kadrons to go on my warmish 1916?.. I need to know so I can get busy through next month..

Dells are the go.

How big is your cam, I had a similar problem with a 1916cc, 120 engle cam, sounded like a mack truck at idle.

Fixed the problem with a single 48 ida (which popped a little), then went to twin dells. Can't beat them for value and response (smooths the engine right out).

I've got a 110

Kadrons will be more than sufficient

Does anyone know if the same thing happens with a 40 dcnf webber