Idle Mix cylinders Different

KirkV · #1 (**permalink**) 04-14-2018, 12:17 PM

So I have my Inglese IDA system and installed it last fall. I have an issue I don't know how to resolve or if it is really an issue at all?
I set the velocity with the velomiter and got all cylinders balanced ok, but when I go to set the mix screws I started at 1 turn out on all of them.

The front 2 sets of carbs would stumble when starting to screw them in like I would expect. I opened them to about 7/8 open and they come back nicely.

Here is where it got weird, the rear sets of carbs when I screwed them in never went away like I expected. So I opened them more and the engine picked up rpm and idled smoother at about 1.5 to 1.75 turns open. I have tried different jet sizes and get the same results

I checked the air volumes again and they were all even. At this point I thought I had a intake leak so checked the whole thing over with raw propane and found nothing.

I have now pulled the intake and everything looked good on the gaskets and no issues found. I am trying to get rid of my stumble at 2000 to 2500 rpm by adjusting idle jets and air correctors but have a deuce of a time with it.

I am headed out to get new intake gaskets and start all over again, but does anyone have an idea of why the rear 4 pistons want more mix jet?

I have taken the webers off and examined the small holes that feed fuel in above the mix jet needle valve and found all of them to be open. The hole the needle valve screws into is open on all 8 as well.

I will get it reassembled tomorrow and try to set it up again, but I am at a loss??????

Thanks Kirk

Gaz64 · #2 (**permalink**) 04-14-2018, 04:10 PM

Kirk,

Can you post some pics of your linkage please?

Can you also supply your carb settings?

What happens when you swap one rear carb with one front carb?

Gary

KirkV · #3 (**permalink**) 04-15-2018, 10:12 AM

Gaz,

I have just set the intake manifold gaskets in place and need to let them cure before trimming the excess and starting the reassemble procedure. I have switched 2 of the carburetors to see if the issue travels or stays with the cylinders involved.
I currently have a 100 idle jet holder with a 70 jet and the primary is a F11 with a 170 jet.

Here are a few pics of the linkage.

KirkV · #4 (**permalink**) 04-15-2018, 10:21 AM

FD25CA28-F33C-415C-A65F-2D047CFBD977 - Club Cobra Photo Gallery

Heres the link to my gallery and you can see the linkage. Not sure whats up with posting them here

Gaz64 · #5 (**permalink**) 04-15-2018, 03:37 PM

Kirk,

I don't see anything unusual.

Have you got 2 or 3 hole progression?

And now while you are reassembling, we'll wait until you have it running to see what happens next.

Gary

KirkV · #6 (**permalink**) 04-15-2018, 05:12 PM

2 hole progression

Gaz64 · #7 (**permalink**) 04-15-2018, 07:23 PM

Are all the mixture screws the same shape at the pointed end?

Mixture screws are identical?

You will be swapping one or both rear carbs to the front?

KirkV · #8 (**permalink**) 04-16-2018, 04:42 AM

Yes Gary I checked and the mix screws are the same length and dimensions at the end. I will. E swapping just one carb set from back to front.
Kirk

Gaz64 · #9 (**permalink**) 04-17-2018, 04:02 AM

Ok Kirk.

We'll all be here for your next lot of testing.

Gary

KirkV · #10 (**permalink**) 04-18-2018, 08:27 AM

Well Gary it appears the problem has now switched from cylinders 3,4 to 5,6 along with the Weber set. It also seems to have an effect on cylinders 1,2 like it did on 7,8 when it was on 3,4.
So the cylinders directly across the manifold from it need more fuel in the mixing screw as well as the carb in question.
It must be leaking in air from someplace?
I have a call into Jim Inglese and am waiting on a return call from him.
Bummer but at least it is not the engine.
Thoughts?
Kirk

Gaz64 · #11 (**permalink**) 04-19-2018, 05:56 PM

Kirk,

I think Jim will say there is a carburetor issue with the carb that is now on 5 and 6.

If you look at your firing order, you can see how a carb that is not quite right at idle, can seem to affect other cylinders, since their individual vacuum levels drop just as they are called upon the produce power at idle.

Hope that makes sense.

Gary

KirkV · #12 (**permalink**) 04-20-2018, 09:42 AM

Seem to be having issues getting any responses from Jim hoping all is well with him?

byronpete21 · #13 (**permalink**) 04-21-2018, 12:57 PM

I talked with Jim Friday, and have a call scheduled with him Monday so I know he is around. I am following your post closely as I am having a very similar problem with my setup as well. Some of my mixture screws I can adjust to full close with no affect on idle, and some of them change the idle with a very small amount of adjustment. I too have chased air leaks and have yet to find one. My next step I think will be to check my float levels and re-check everything. I am also trying to sort out the same 2500 rpm stumble. Feel free to PM me if you would like. Maybe we can be of some assistance to each other.

Byron

65arboc · #14 (**permalink**) 08-05-2021, 10:10 AM

Quote:

Originally Posted by byronpete21

I talked with Jim Friday, and have a call scheduled with him Monday so I know he is around. I am following your post closely as I am having a very similar problem with my setup as well. Some of my mixture screws I can adjust to full close with no affect on idle, and some of them change the idle with a very small amount of adjustment. I too have chased air leaks and have yet to find one. My next step I think will be to check my float levels and re-check everything. I am also trying to sort out the same 2500 rpm stumble. Feel free to PM me if you would like. Maybe we can be of some assistance to each other.

Byron

I have been going over some old threads thying to find a solution to some of my problems similar to Byron. Why do some of these threads end without a final solution? Am I missing something?

Jim

1795 · #15 (**permalink**) 08-05-2021, 10:26 AM

I was having a problem with #8 not pulling anything and the idle screw having no effect. Took the carb apart, cleaned everything and it still was there. Talked to Jim a couple of times and as we took the carb apart again and looked at the jets my engine builder decided to run a wire up the idle jet holders (100's) and the wire ran all the way u to the base of the screw on #7 and only halfway up on #8. Called Jim and he said that it could be plugged with solder and to run a drill bit up it. Sure enough, some silver solder came out. The solder was blocking the air hole at the top of the idle jet holder. Not quite sure why it was there. It looks like there had been two holes on the idle jet holder and one had been soldered shut. Both idle jet holders were the same. Ordered a couple replacements from Pierce Manifold just in case and those idle jet holders only had one hole with no evidence of a second hole. The one hole that was there was in the same position as the filled hole on the ones in my carbs.

Re-installed everything and reset the idles screw, which was way out of line with the others, and everything worked fine. RPM's rose as I set that idle screw correctly and the engine runs consistent. Something to consider.

Jim

65arboc · #16 (**permalink**) 08-11-2021, 09:38 AM

Hi Jim,

Thanks for the update on your problem. I also run a 289 but not set up for racing. I have been chasing some similar problems with my set-up and have most things sorted out except very rich idle which I must keep set rich to avoid back fire on let-off and it helps the common hesitate at 2500-3000 rpm. I have found Jay at Pegasus has been very helpful even tho they are primarily VW tuners.
Thanks again,

Jim in Pa