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Help! underhood heat problem

Hib Halverson

Technical Writer for Internet & Print Media
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71 04 12 19
I've gone back and read most of the posts in this thread.

The engine has no problem with the cooling system because the ECT never runs hot. You said perviously that you have 6-psi fuel pressure and you also said your running 10-deg initial advance and that as you raise the rpm the timing advances. The distributor is new and I assume the same about the plugs and wires.

I keep coming back to a lean air fuel ratio at idle and part throttle. That would make parts of the engine run hot.

The symptoms of lean AFR would be poor idle stability and stalling. Surging, bucking and misfire. Those problems would not be present after a cold start and might not be present during early warm up if the choke is slow to come off.

With that Edelbrock carb, you change the part throttle AFR by changing the primary metering rods.
 
Last edited:

dirtypants

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May 14, 2015
Messages
69
Location
Spokane
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81 4spd Corvette Blue dark met
Not to hijack but some of your ideas about gasoline are misguided. The octane rating of gas has no connection whatsoever to the quality, formula or quantity of additives. The octane rating is a measure of resistance to detonation (pinging) and absolutely nothing else.

I've been using E10 (10% ethanol) fuel in my Corvette (and all my other toys) for 20+ years with nary a problem. The sky-is-falling stories on the internet are out of control. Let's not beat that issue to death again.


ohhh there are so many "I have been doing this or that for years..""...stories: not wearing seatbelts, no helmet on motorcycles or bikes, .smoking, drinking heavily, cheap oil, hundreds of thousands of miles no oil change, eating fatty foods and living to 100, running fast on old tires....to each his own. By the way with all respect I did not say the octane was directly connected..it is however indirectly connected..and I did say that premium fuel is..well premium..meaning the entire formula is different. And there are plenty of sources for you or others to see what ethanol does to some metals, and certainly does to older rubber..in lines and diaphragms etc...and eventually the sky WILL fall!! But let' see if we can get this vette running properly. The long thread dialogues on fuel are elswhere...but I just had a motorcycle buddy with engine crapping out...and guess what it was..old ethanol fuel.
 

dirtypants

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May 14, 2015
Messages
69
Location
Spokane
Corvette
81 4spd Corvette Blue dark met
Edelbrock mods to 81 350

You don't have to remove it but you will have to remove the Radiator and a/c condenser.

If installing a cam, then a Good time to renew the radiator..and condenser if not in good shape..and of course to check the upper valve train bits....and the timing gears were replaced...the $bill keeps getting higher !!
FYI: Here is the Edelbrock intake/carb cam part of what has been done to my 81, as said all smog/catalytic removed.

Alumin 4bbl carb adapter Edelbrock A part 230232538770 $9.99
Intake manifold polished Edelbrock Performance: EDL 21011 $224.95, torque sequence see per Edelbrock, 25ft lb. Edelbrock parts EDE4222 $79.99: EDE4248 Short Elit $95.99
Edelbrock carb: Edelbrock Weber 1406 1734
Edelbrock Performer cam kit SBC, EDL 2102 $121.95, cam specs see PerformerPlus #2102. Use only sure seat valve spgs #5802 or 5809, use stock ratio rocker arms only. Use only link timing chain gear set #7800, Do not use late model sets.
timing set EDL 7802 $51.88, cam chnge kit MRG-4400 $19.95. Summit Racing
Intake gskt EDL7201 $16.88, ValveCvr gsk EDL7549 $21.95,
Edelbrock (K&N) aircleaner, tri-angle, 2.5 deep, 13.125 Across, can be cleaned, oiled. Summit Racing
The aircleaner just makes it..under the hood..after careful clearance checking with doublesided sticky weathertrips. Use a flat securing nut.
Distributor replacement also done, 8.8 Accel primary wiring ..and more.

Hey is good to see those of you with 81 vettes...my affordable (??) favorite, where seldom does one have to worry about strict originality and one can reverse the choking horsepower robbing of the early 80s.
 

Don61

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Joined
Jul 14, 2012
Messages
71
Location
Ohio
Corvette
1981 coupe white w/red int auto
I've gone back and read most of the posts in this thread.

The engine has no problem with the cooling system because the ECT never runs hot. You said perviously that you have 6-psi fuel pressure and you also said your running 10-deg initial advance and that as you raise the rpm the timing advances. The distributor is new and I assume the same about the plugs and wires.

I keep coming back to a lean air fuel ratio at idle and part throttle. That would make parts of the engine run hot.

The symptoms of lean AFR would be poor idle stability and stalling. Surging, bucking and misfire. Those problems would not be present after a cold start and might not be present during early warm up if the choke is slow to come off.

With that Edelbrock carb, you change the part throttle AFR by changing the primary metering rods.

The distributor is not new but the plugs & wires are new. I may replace the distributor just to be sure but like you, I keep coming back to a fuel problem. I haven't tried changing jets or metering rods but maybe that's something I should look at.
 

Peer81

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Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Is the part still under the vette that turns the cold air to the radiator?

Greetings Peter

Verstuurd vanaf mijn GT-I9195 met Tapatalk
 

Don61

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Jul 14, 2012
Messages
71
Location
Ohio
Corvette
1981 coupe white w/red int auto
Is the part still under the vette that turns the cold air to the radiator?

Greetings Peter

Verstuurd vanaf mijn GT-I9195 met Tapatalk

If you mean the front air dam under the front of the car, yes it's still there.
 

dirtypants

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May 14, 2015
Messages
69
Location
Spokane
Corvette
81 4spd Corvette Blue dark met
Do not think about changing cams until you have current problems fixed.
agree: keep variables to minimum until all is good and you can assess what you have as a starting point, check/do simple things first..this seems a process of elimination.
Nick
 

Don61

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Jul 14, 2012
Messages
71
Location
Ohio
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1981 coupe white w/red int auto
agree: keep variables to minimum until all is good and you can assess what you have as a starting point, check/do simple things first..this seems a process of elimination.
Nick

Agreed, I was just wondering.
 

Don61

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Joined
Jul 14, 2012
Messages
71
Location
Ohio
Corvette
1981 coupe white w/red int auto
Hey everyone,
Just wanted to pass along that I think I've solved the problems with my 81 vette!
After much discussion with a lot of you guys I did the following:
1. Replaced the fan clutch. Don't think it was the real problem but for $35 it was worth eliminating one of the4 variables.
2. Richened the metering rods & changed the step-up springs in the carb. Cost 0 since I already had the parts.
3. Checked the distributor. When I pulled the cap I noticed a lot of carbon build up & streaking on the rotor. The rotor & cap were new sp shouldn't have had any signs of wear. I decided to replace the entire HEI distributor with a new one from Summit. I installed it, reset the timing & adjusted the carb & it (so far) has run well without any of the aforementioned problems.

I can't thank you guys enough for your help! I keep you advised how it goes.

Don
 

dirtypants

Well-known member
Joined
May 14, 2015
Messages
69
Location
Spokane
Corvette
81 4spd Corvette Blue dark met
Don that is such good news..hooooraaaay ! Betting it was the distributor..
so..what distributor brand and model is it..?
was it a plug in and go..ready to run?
did you get the curve specs?
what timing specs did you set up.
and..is it all now off the computer..that is no computer ECC to either carb or distributor?
if..off the computer is your vac line to the manifold or to the carb port?

lotta questions because I am contemplating a distributor change as I go off the computer. I am "thinking" of the MSD 8365?? but am told (here on forum) the 8362 (economy chinese model) is fine,.

from what I can see in all the various forums..all the replacements sometimes have unhappy owners..as the dizzys had mfg problems..so hope yours does not..but watch for that if suddenly things go bad again.,.
 

Antz81

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Joined
Dec 21, 2013
Messages
936
Location
Auckland, New Zealand
Corvette
1981 4 speed
Good to hear it's sorted.
I'd put my money on the dizzy being the problem, the temps you were saying you were getting for you cooling and engine temps are about what i get with no issues.
 

Don61

Well-known member
Joined
Jul 14, 2012
Messages
71
Location
Ohio
Corvette
1981 coupe white w/red int auto
Don that is such good news..hooooraaaay ! Betting it was the distributor..
so..what distributor brand and model is it..?
was it a plug in and go..ready to run?
did you get the curve specs?
what timing specs did you set up.
and..is it all now off the computer..that is no computer ECC to either carb or distributor?
if..off the computer is your vac line to the manifold or to the carb port?

lotta questions because I am contemplating a distributor change as I go off the computer. I am "thinking" of the MSD 8365?? but am told (here on forum) the 8362 (economy chinese model) is fine,.

from what I can see in all the various forums..all the replacements sometimes have unhappy owners..as the dizzys had mfg problems..so hope yours does not..but watch for that if suddenly things go bad again.,.

The distributor is a summit racing model. It is SUM-850001-1 summit blueprinted hei distributor with vacuum & mechanical advance. It cost $90, no need to buy an expensive name brand. Was a plug & play, easy install, woks well. I think you can get the specs from summit. I set the initial timing at about 10 degrees. I have no way of checking total timing. The computer is completely unhooked from everything. The vacuum line is to a carb port. I do think the main problem was the distributor although I think the metering rods also helped.
Thanks for all the help!
 

Vettehead Mikey

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Joined
Aug 26, 2003
Messages
3,487
Location
Not that far from Ottawa
Corvette
1973 Coupe
Hang on to the old distributor as a spare. The reliability of the new discount price stuff from China is pretty dismal. As noted way up above, the most likely culprit was the HEI module inside the distributor an easy fix.
 

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