High Idle Issue

[76chevyc20454]

So i have a problem lol, when i go out in the mornings and start my truck is misses pretty bad. Its a 76 c20 454/th400. It only misses when the motor is cold. once it warms up to about 190 it stops. The other day i figured i would try something so i pushed the fast idle cam down and zip tied in place to open choke all the way and drop idle down and it ran just fine, no missing. What could this be? Could it be getting to much fuel on high idle? Also i got told that HEI dizzy need to have spark plugs gaped to .45, mine are .35, could that be it? I'm confused. Can someone please help.

 

[MadOgre]

The spark plugs them selves determine what gap is used. which spark plugs do you have? Should read on the white porcelain what type they are.

 

[rich weyand]

Let me guess. You have an open element air cleaner, your vacuum advance is connected to ported vacuum, and your base timing is set to about 4* BTDC. Right?

 

[firebane]

The spark plugs them selves determine what gap is used. which spark plugs do you have? Should read on the white porcelain what type they are.

Not necessarily. Two key points are whether you are running points or hei.

Points requires .030-.035 where hei requires a MINIMUM of 0.045.

 

[76chevyc20454]

The spark plugs them selves determine what gap is used. which spark plugs do you have? Should read on the white porcelain what type they are.

I have ac delco r44t gaped at .35

 

[DoubleDingo]

Not necessarily. Two key points are whether you are running points or hei.

Points requires .030-.035 where hei requires a MINIMUM of 0.045.

This is true. I looked up plugs for a 1972 350 and a 1981 350 and they both say the engine takes the same exact plug, and the 72 is gapped at 0.035 and the 81 is gapped at 0.045. Only difference is points and HEI.

 

[DoubleDingo]

I have ac delco r44t gaped at .35

Could also use R44TS, or CR44TS.

 

[firebane]

This is true. I looked up plugs for a 1972 350 and a 1981 350 and they both say the engine takes the same exact plug, and the 72 is gapped at 0.035 and the 81 is gapped at 0.045. Only difference is points and HEI.

I only know this because of this exact thing. I ordered plugs for my 74 and it came gapped for points because in 74 hei didn't exist.

And basically the truck had absolutely NO power and stall out in power around 1800-2000 rpm.

 

[MadOgre]

I have ac delco r44t gaped at .35

1976 350 with R44T plugs is gapped at .035"

A 1976 454 should be using R45TS gapped at .045"

 

[MadOgre]

Yes all engines 1967-74 are gapped at .035"

75' and on vary, such as..... in 1975 all engines were gapped at .060" 76' and later vary between .035"-.045" depending on which plug is used.

And it does matter which plugs are used as eg: In 1985 the 350 was offered in light duty and heavy duty. The plugs are gapped the same but differ in length. So that they would sit further in or out of the combustion chamber.

 

[firebane]

Yes all engines 1967-74 are gapped at .035"

75' and on vary, such as..... in 1975 all engines were gapped at .060" 76' and later vary between .035"-.045" depending on which plug is used.

And it does matter which plugs are used as eg: In 1985 the 350 was offered in light duty and heavy duty. The plugs are gapped the same but differ in length. So that they would sit further in or out of the combustion chamber.

See this is why people get so confused for and its not necessary. SBC engines like R44T plugs gapped at 0.045 if you run HEI or 0.035 if you run points.

They did try to run .060 for awhile but discovered it really didn't do any good and just said stick with 0.045.

All the research I have done regard what plugs and gap to run on a HEI system for our trucks is R44T with 0.045 and nothing else. Some people have reported to run a wider gap but apparently only helps if you have a seriously beefed up igntion system.

 

[76chevyc20454]

Let me guess. You have an open element air cleaner, your vacuum advance is connected to ported vacuum, and your base timing is set to about 4* BTDC. Right?

Im not sure what timing is don't have a timing gun, and vaccum advance is hooked up to ported vacuum. Im not sure what you mean by open element air cleaner, its the factory one with the snorkle looking thing coming out of the side of it.

 

[firebane]

Im not sure what timing is don't have a timing gun, and vaccum advance is hooked up to ported vacuum. Im not sure what you mean by open element air cleaner, its the factory one with the snorkle looking thing coming out of the side of it.

Get a timing light and check your timing and put your distributor on manifold vacuum.

 

[MadOgre]

See this is why people get so confused for and its not necessary. SBC engines like R44T plugs gapped at 0.045 if you run HEI or 0.035 if you run points.

They did try to run .060 for awhile but discovered it really didn't do any good and just said stick with 0.045.

All the research I have done regard what plugs and gap to run on a HEI system for our trucks is R44T with 0.045 and nothing else. Some people have reported to run a wider gap but apparently only helps if you have a seriously beefed up igntion system.

Well then research it again cause your wrong

 

[76racetruck]

I think that your choke pull-off isn't working. the choke should open about 1/4 inch as soon as the motor fires. If not you are actually giving the motor too much gas. Try opening the choke a little bit as soon as the motor starts.

I hope this helps.