Question: Carb settings

[Antz81]

Any advice here would be appreciated.
I've been trying to track down the source of a rough idle problem. I've fixed a few vacuum leaks and am in the process of fixing the last one(I hope). However I did make one odd observation about the dwell readings on my mix solenoid. Everyone else reports a low dwell when they have vacumm leaks but mine is at 60deg (even before I started to fix any leaks).
today I noticed that my idle mixture settings on the carb appear to have been altered. could this be the cause of my high dwell? If so should I just return them to factory settings or should I have a much deeper look into things?
it has also been getting harder to start from cold with each leak that I have fixed.

 

[bill81vette]

Check 22229stingray's thread from last year,in the l81 section I think...see if that's what your looking for....
Or pm Gerry...

 

[Antz81]

Check 22229stingray's thread from last year,in the l81 section I think...see if that's what your looking for....
Or pm Gerry...

He had low dwell, which what you expected for a vacuum leak. But it a good source of information.
Also my ECM seems to be running fine, the dwell slowly increases to 60deg when it comes out of closed loop. And the mix solenoid does work.
i'll give Gerry some time to spot it then i'll pm him. I head away for a few days tomorrow anyway.

 

[Peer81]

Let me see, has been a few months since i last had the dwell meter connected.

It would be logical that if your carb is running way rich that each vacuum leak (extra air) is just keeping it alive. Now your closing all the vacuum leaks (which is a good thing) but the mixture is only getting richer with each vacuum leak you fix.
Best thing to do is reset the idle mixture to 3 turns out and start from there. After the mixture is perfect at idle then go on with the other settings including the choke.
Good luck, if you need me just send a pm or Gerry!

Greetings Peter

 

[Antz81]

Checked the idle mixture screws they were both set at about 3 1/3 turns. I had a look at where the idle air bleed screw was set, it's all the way in. Not sure how much of an effect that would have but I'm guessing seated is not right. Any idea of where it should be as a starting point for setting it?

 

[Antz81]

While waiting for a reply decided i might as well check a few other things.
Mix solenoid travel is just over 4/32 (by about 1/64)
TPS voltage 2.06v:ugh (for a while i thought i had done something wrong to get that voltage)

Looks like it might be a good time to open it up and have a proper look inside at what previous owners have done. I know one of them didn't even know the car had a ECM in it.:L

 

[Peer81]

4/64 for the mixture plunger is right set tps at base back to 0.56 (2.06 is like 40% throttle) so that is way off. But the Tps doesn't have a big impact on the carb so i would start turning back the idle screws to 3 or 2.5 and see the effect on your dwell meter.

Greetings Peter

 

[Antz81]

4/64 for the mixture plunger is right set tps at base back to 0.56 (2.06 is like 40% throttle) so that is way off. But the Tps doesn't have a big impact on the carb so i would start turning back the idle screws to 3 or 2.5 and see the effect on your dwell meter.

Greetings Peter

Not 4/64, it's 9/64. 4/64 would be 2/32 which is minimum travel. Currently it's just over the maximum.
any idea on roughly where the idle air bleed screw should be? Currently it's seated and that just doesn't seem right.

 

[Peer81]

Oke sorry looks like I forgot alot about the correct settings. Start with the screw half way and then work it up or down. Normally i set it with the special J staped tool so no idea what roughly it right. The shopmanual also gives a rough figure but don't have the book with me. See the idle air bleed as a fine tuning of the idle fuel screws.

Greetings Peter

 

[Antz81]

Oke sorry looks like I forgot alot about the correct settings. Start with the screw half way and then work it up or down. Normally i set it with the special J staped tool so no idea what roughly it right. The shopmanual also gives a rough figure but don't have the book with me. See the idle air bleed as a fine tuning of the idle fuel screws.

Greetings Peter

Yor eyes yes must be better than mine. I've never spotted anything about where the idle air bleed should be other than setting it to roughly 30deg dwell. I'll give it a try in the middle though and see what happens. won't be until Friday now but I see how I get on and report back.

 

[Antz81]

Success! (Well sort of)

Set the idle air bleed about 2-1/2 turns out (could have gone more, and might still do so) took it out for a drive and once it was warmed up I was getting dwell readings in the low 40s at idle.
Now I know that it does at least work correctly. Only problem I had was it almost died when pulling away at one intersection early into the drive. Any ideas what might cause this? Still had a rough idle, next I will confirm timing is correct, and set the tps correctly. After that try to find other vacuum leaks (if needed) would it be worth looking into the EGR? Currently it's just blanked off but could I still get an issue from it?

i also replaced one of the rubber fuel line that had I kink in it. (Fuel line to pump) had to bend the steel line back into place to do this. and had a look into what's causing the pull to the left when braking hard, have a leaky caliper on the right front (did put new seals on only a few months ago)

 

[jj_long81]

carb settings

hello. i had similar issue and turned out the balancer had slipped. would run but not right. then when it came to full temp it would hesitate and stall occasionally. even though i used a time light it would show it being correct but was timing to a mark that had moved.

 

[Antz81]

hello. i had similar issue and turned out the balancer had slipped. would run but not right. then when it came to full temp it would hesitate and stall occasionally. even though i used a time light it would show it being correct but was timing to a mark that had moved.

Interesting. I'll check on that when I check the timing.

 

[GerryLP]

I'm so proud of you guys. You figured it out, and although you are not there all the way, you are heading the right direction.

Once you correct the tps setting, you should see vast improvements. Zero point fifty six volts tells the computer the engine is at idle. But when the i item sensor is reporting an unexpected value, the computer tries to correct.

And yes, the more vacuum leaks Antz81 corrects on the induction system, the better it will function.

The "J" tool is the initial ballpark setting, but it is approximately the top of the air valve screw flush with the top edge of the horn where it sits.

One final reminder; make small (1/8) of a turn adjustments and wait two minutes for them to reflect on the dwell meter. You start chasing your own tale any faster or bigger adjustment than that.

 

[Antz81]

Once you correct the tps setting, you should see vast improvements. Zero point fifty six volts tells the computer the engine is at idle. But when the i item sensor is reporting an unexpected value, the computer tries to correct.

And yes, the more vacuum leaks Antz81 corrects on the induction system, the better it will function.

The "J" tool is the initial ballpark setting, but it is approximately the top of the air valve screw flush with the top edge of the horn where it sits.

Ok, I'm a long way from the top of the horn but I'm not done yet. Also reset the solenoid travel. Despite the initial travel being so close to acceptable it was still far off. The lean adjustment was 5 turns out! Not the 3-1/2 it should've been. I took it for a drive today still a bit of a rough idle. Must be more leaks somewhere. I should probably look into replacing all of the old hoses (I have found at least one has been cut and joined)

i did did say I thought I got something wrong when I checked the tps setting. I'd forgot to check the choke, it was still engaged from playing with things. Took it off the choke and checked it got two different readings, 0.54 and 0.58. I don't think I should touch it. It had a nice smooth increase up to 4.5v at WOT.