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Well I posted about a year ago about my '68 GTO, in beautiful shape with a fairly new (1,000) mile rebuilt 400; mostly stock, but Doug's headers and I'm told a Ram Air III cam. Since day one, it runs GREAT, except at start on choke it runs a bit rich as seen by my white exhaust. Even so as soon as it comes off choke its fine, very responsive, etc. The only problem is, that sitting at idle such as in traffic for a cruise, it gets HOT - HHOOTT! I'm Talking 220+, warning lights, the whole bit... When I'm moving though it always drops below 180. So the battle started, and here is my story:

1) Ok, the obvious - what do I have for a cooling system - flex fan fits nicely in shroud, very new 4 core radiator. Water is very clean with antifreeze, and the thermostat is fine - I changed it out to a 160 for good measure. Base timing at about 14 degrees (I'll come back to that).

2) Changed out the water, thermostat - no help.

3) Water pump - bought a '68 Flow Cooler, painted it nicely, beat all the plates into submission clearance - installed nicely, no change.

4) Running out of options, I noticed my '68 was plumbed with ported vacuum advance. Changed it!

4.1) Set base timing back to 10 degrees, assume 10 more degrees on vacuum advance. She really didn't like to run at 10 degrees, but sounded much better when connecting vacuum (20 total now) - in fact far better than normal, although idel went up way too high.

4.2) Brought idle back down to around 750 - but it still sounded a bit strange to me.

I should mention now that this carb (quadrajet) has always been a bit suspect to me. Twice on a hard stop it flooded, and I'm now noticing a small amount of gas leaking under the base gasket.

4.3) Messed with Idle mixture, and as expected I needed to lean it a bit on both sides - not really an exact science, mostly by ear.

4.4) To deal with the rich idle, I bent the do-hickey that adjusts the actual choke flap pull off to get back to about .25"

Ok, so NOW I can't get it to get hotter that 180 degree at IDLE!!!!! At least so far, MUCH improved! Still messing with idle setting as it seems to need a slightly higher idle then before to stay stable, BUT it is also noticeably crisper off idle response!

So I'm not sure why they used ported for advance, but so far going to direct manifold seems much better, although it comes with complications such as idle setting, and mixture.

Also, I will pull the carb this winter and send to (??) to do a proper re-build. Throttle seems sticky especially after sitting a bit and then "brakes loose" (no brass sleeves) and i'm very suspicios that main well seal is leaking also (also on a hard accel, I smell gas).

So there you have it - more as it happens!

PS - Any recomndations on who to send my carb to for the winter re-build, complete with bushings, epoxy, etc? I here lots of critiqes on "hacks" but Cliff is already working on another carb for me (he isnt taking new entire rebuilds right now). I hear maybe Lars? Thanks!
 

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Ported vacuum was for emissions. Heat the motor up quicker and run hotter to reduce emissions.

Good job getting the temps under control!
 

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Discussion Starter #3
But wasn’t that like 1971 and up? Whoever rebuilt this ‘68 was confused! 😀
 

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But wasn’t that like 1971 and up? Whoever rebuilt this ‘68 was confused! 😀
I don't know about the rest of the country, but California started using ported vacuum in 1966. That's why there are two different tri-power center carburetors. The body of the CA carb has a fitting for ported vacuum.
 

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Mid sixties started some ported vac Inthink....sounds like you have fixed the cooling. Also you should check what your idle timing actually is as you said you “assume” you are getting 10 More degrees from the vac can. Unless you chnged deliberately to a vac can that pulls ten that is unlikely. Most pull way more 20+.....

Just put your timing light on it at Idle, don.t pull or disconnect the vac line,....then you will see your idle timing, which is base plus vac advance when you are hooked to full manifold vac.

good work on dropping that temp down sounds great now!
 

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May have learned something today! Conventional wisdom is that a car that runs cool on the road and hot at idle has an airflow problem. You fixed it with timing! Thanks for posting.

BTW white fog on a cold start isn’t “too rich”, it’s just condensate. Black smoke indicates too rich.
 
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