Question: Vacuum leaks

[Peer81]

The cam can be the problem but it's just an idea
Yes the ticking is the m/c solenoid, if it's far from 30 degrees it stops moving and no ticking can be heard.
The ECM only gives a rich or lean code if it's so far from perfect that the engine want to stop. If perfect is 14:1 A/F then mine gave a code below 4:1.

About the odd notice, I would also think it's running rich but it should be doing it again and again. I always use the vacuum port from the EGR to connect the vacuumgauge to

Greetings Peter

 

[Antz81]

Ok checked the torsional damper marks today (recommended by a guy at work) found it has slipped but only but not by much (at least in my opinion). Rechecked timing with a new (temporary) TDC mark, timing is at 10BTDC. I wouldn't think this is the cause of my rough idle but not certain. Obviously I'm going to have to replace the torsional damper regardless.

 

[Peer81]

I read somewhere that Lars says 90% of the carb problems the problem is somewhere in the ignition...

Greetings Peter

 

[Antz81]

Ok adjusted the timing to roughly compensate for the slipped damper (will order a new one on Monday), what a difference a few degrees makes, idle wasn't perfect, but was a lot better, no longer shaking the whole car and feeling like it wants to die at times. I'll still need to set the dwell (now sitting at around 40) and the idle speed, but I think I'm getting somewhere now. Did notice when I was doing the timing that there seemed to be an intermittent miss, so I'll have to look into that too, I'm guessing the HT leads are probably on the way out since I've done most (if not all) other things I can think of that would cause this.

 

[Antz81]

Ok so fitted the new HT leads, Idle speed dropped a little to what i thought was 650-700. (700 was where i last set it to) Connected my meter to adjust the idle speed, It was idling at 450-500!:L (In neutral as it's a 4 speed) Raised it up to 700, and it seemed much better.

Haven't replaced the balancer yet (waiting for a tool to arrive). and my vacuum is still down at 15inHg.

I've also noticed that my solenoid adjustment screws on the carb keep moving so I've ordered some new plugs for them which I hope should stop this. Checked the float level also, and that's a bit low (8/32nds) so will need to adjust this. (may do a rebuild as well since I have the parts)

 

[Antz81]

All is well (or so it seems, excluding manifold vacuum)
Replaced the balancer and reset the timing and adjusted the float level a few weeks ago.
The plugs for the solenoid adjustments finally arrived yesterday (they almost got sent back due to part of the address being cut off:L) so i was able to get them fitted today.
Idle speed is now set (although i had to set it a little high as when i tried to go lower it would drop right down to around 500) also set the dwell for the m/c solenoid.

Took it for a drive and all seemed well. Solenoid travel hadn't moved, dwell sitting at around 30.
Just that manifold vacuum sitting at about 15.5 at idle.

Anyone have any ideas why it may be low? Something i haven't checked? or does it always read around there when checking from the headlight port?

 

[Peer81]

Did you check the vacuum gauge to another one?
The other think you can do if pull a valve cover and check valve lift to see if the OEM cam is in there. If both turn out oke then i don't know

Greetings Peter

 

[Antz81]

Did you check the vacuum gauge to another one?
The other think you can do if pull a valve cover and check valve lift to see if the OEM cam is in there. If both turn out oke then i don't know

Greetings Peter

I will check my guage to another, but I think it should be fine. (It's not that old, but stranger things have happened)

At least that doesn't sound like too hard a check to do for the cam.

I do have a new evap cannister coming, as I rechecked it and found that a valve doesn't seem to seal properly.

 

[Antz81]

I must be getting very close . I'm still waiting for the evap cannister to arrive, but went for a drive to visit some friends (150mi one way) and averaged just ovrr 16mpg. No major problems on the drive. Except for the nut on the wiper motor coming off meaning my wipers stopped. (Not very pleasant since it was raining at the time, fortunately one a minute or so to fix) and the clip on the back of a door lock coming off. Overall a good drive though.

 

[Antz81]

I must be getting very close . I'm still waiting for the evap cannister to arrive, but went for a drive to visit some friends (150mi one way) and averaged just ovrr 16mpg. No major problems on the drive. Except for the nut on the wiper motor coming off meaning my wipers stopped. (Not very pleasant since it was raining at the time, fortunately one a minute or so to fix) and the clip on the back of a door lock coming off. Overall a good drive though.

Update. The drive down went well but a wheel bearing went on the way back. That's fixed now and I've fitted the new evap canister but still two more problems:
1. the brake on the rear wheel that had the wheel bearing fail is dragging (Have created a separate thread for this)

2. After i shut the motor off it tries to run on (Dieseling?) If i let it idle for a few minutes before switching the ignition off it's normally ok. I've tried running some seafoam (Well a similar product anyway as I couldn't find seafoam) through it but that made no difference.

 

[dougelam]

Hey Antz, what is your carb number?
Can you take some pics of the top of your engine. One from each side, some of us will be able to see something that might not be right.

Also you will need the thexton 370 Guage to adjust your carb properly.

Do you have access to a fluke multi-meter?
It's a must when diagnosing C3 systems unless you have an oscilloscope laying around

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[Antz81]

what is your carb number?

[FONT=Verdana, Tahoma, Calibri, Geneva, sans-serif]
Carb most likely the original. The number and date code match the engine block[/FONT]
[FONT=Verdana, Tahoma, Calibri, Geneva, sans-serif]carb number: 17081217


[/FONT]

you will need the thexton 370 Guage to adjust your carb properly.

I do have this.

Do you have access to a fluke multi-meter?

I have a 336 clamp meter, a 233 multi-meter (both fluke). also have a Brymen 869s (similar to a fluke 89) And a cheap meter for RPM, and Dwell

Now the photo's


Ignore the open vacuum port on the carb, it normally goes to the vac motors on the air cleaner.
Any help anyone can give would be great. This is the first carburetted car I've owned; so any ideas anyone has would be very helpful.

 

[bill81vette]

that is the correct carb for your vette...

 

[dougelam]

OK the first thing that I see is the original coolant temperature sensor, they were very unreliable. You need to update it with
GM Closed Element CLT / IAT Sensor with Pigtail
It comes with a new connector also, the old ones caused a couple of problems.

Second please tell me that those are not ignition wires zip tied to your wire harness!

Now, when spraying your wd40/carb cleaner around to find vacuum leaks it is sealing the leak so unmetered air isn't going into your intake hence it smooths out the idle. Spraying into your carb means nothing (at this point in the repair). As said before you need to isolate all the external devices that are controlled by a vacuum hose which in your case is the headlight doors, canister purge and thermac (air cleaner) if used. You Do need to have the correct PCV VALVE, a CV774C AC DELCO, not what ever the parts store wants to sell you. It is a calibrated vacuum leak and the wrong one will either allow to much air through making it difficult to correct with your MC solenoid or not enough and then it allows to much pressure to build up in your crankcase which unturn causes oil leaks.

I do not understand why Peer81 would use the EGR port for a vacuum check, it is ported (only has vacuum when the primaries are open, not at idle) you want to check Manifold vacuum at idle at the Manifold!

As for base ignition timing that was a good find with your TDC mark!
You didn't say if you by passed your EST (Electronic Spark Timing) when setting it
Check your ignition module, AGAIN if it's an aftermarket one it WILL NOT have the proper spark advance built into it. Less power or spark knock will occur.

Check your PROM (Programable Read Only Memory) some are better than others, you don't want one with California emissions!

And PLEASE post before or during your carb re-calibration, there is a lot more to it than what is printed on the rebuild kits instructions.

Provided that there isn't any mechanical problems with your engine I know we will have you up and running soon

Hang in there,
Doug

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[Antz81]

OK the first thing that I see is the original coolant temperature sensor, they were very unreliable. You need to update it with
GM Closed Element CLT / IAT Sensor with Pigtail
It comes with a new connector also, the old ones caused a couple of problems.

Good to know. I will order one.

Second please tell me that those are not ignition wires zip tied to your wire harness!

When I replaced them i simply put them back where they were. Thinking about it having, 20000v+ leads next to the 12V (and less) harness doesn't seem so bright. Have new retaining clips coming so I can re-route them the correct way. but have moved them away temporarily.

As for base ignition timing that was a good find with your TDC mark!
You didn't say if you by passed your EST (Electronic Spark Timing) when setting it
Check your ignition module, AGAIN if it's an aftermarket one it WILL NOT have the proper spark advance built into it. Less power or spark knock will occur.

I assume you mean by-passed it by unplugging the 4 pin connector on the distributor (which I did)
Having a little trouble working out if the ignition module is correct or not. Its GM (with a yellow dot), with 466 on the case as well as 617*0M28 . Can't tell if there is ment to be a digit where i put the *. Any ideas if this is the correct on?

Check your PROM (Programable Read Only Memory) some are better than others, you don't want one with California emissions!

Prom Number is 6084FN. (81 4spd fed emisions 1st design) So this seems fine.

You Do need to have the correct PCV VALVE, a CV774C AC DELCO

This is what i have, but i'm not sure on its age. I'll order a new one just to be sure.

 

[dougelam]

The factory ignition modules came with a yellow dot on it so to match the pole piece and coil which have yellow and white wires on them to designate a clockwise rotation.

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[dougelam]

You know what, I should have stated yellow and red. Sorry I've been out of automotive for 9 years so some things are a little sketchy.

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[dougelam]

Ant are you planning your carb rebuild anytime soon?
Living in Michigan, working for a Chevrolet dealership I was very lucky to be close to Warren.
There I was trained by GM DRC (Dealer Repair Center) technicians on CCC Control systems, that is a lost art and I am looking forward to helping you through it. When your done you will be really happy with the results.

Your 17081217 carb is not a fixed idle air bleed design which means it works very well with most changes you make☺

A heads up, get a new TPS (Throttle Position Sensor) with your Carb kit

Doug

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[Antz81]

Ant are you planning your carb rebuild anytime soon?
Living in Michigan, working for a Chevrolet dealership I was very lucky to be close to Warren.
There I was trained by GM DRC (Dealer Repair Center) technicians on CCC Control systems, that is a lost art and I am looking forward to helping you through it. When your done you will be really happy with the results.

Your 17081217 carb is not a fixed idle air bleed design which means it works very well with most changes you make☺

A heads up, get a new TPS (Throttle Position Sensor) with your Carb kit

Doug

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I have a rebuild kit (including a new tps). I don't have any plans to rebuild it yet though. If you think I should then I will.

 

[dougelam]

Once you think that all your vacuum leaks are corrected then that will be the icing on the cake!
Can you take a pic of your kit and the tools that you have related to the repair.


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