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Discussion Starter #1
Hey guys, I recently made a post about the car not running right when it got hot, and now the engine is surging at idle once it warms up.

302
650cfm holley 4150
462 heads, big valves
comp cam 236 @.050 .495" lift
~12:1+ compression, has stock 67' 302 pistons
weiand open hi rise intake
1/2" wood carb spacer

ill tell you everything I have done:

- Initial timing is 14 w/o VA, total is 36
- floats are adjusted correctly
- no vacuum leaks (im positive)
- idle mixture screws have been in every position, but my baseline is 1 1/2 turns out
- valve lash is adjusted good
- carb is brand new, no dirt or junk in the needle and seat, cleaned out the mixture screw passages
- transition slots on carb look good
- fuel pressure good, does the same thing with gas cap on or off

Can someone please tell me what the timing should be set at, and what my idle should be? Maybe I can get a better baseline, but the car runs good when it is cold, but once it starts to warm up it wont run right, it is surging really bad at idle, sounds exactly like a blower engine.

I was just driving the car a few weeks ago, and now I cant even get it to idle right, everything ran great on it untill I tried driving it one time, and its been a ton of problems.

anyone have ideas on what i can check next?
 

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‘67 RS
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Is it surging with vacuum advance connected? Possibly not enough vacuum to pull the VA can all in.
 

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I have a 327, see sig for specs. I have 20 initial timing and 16 mechanical. 36 total at 3200 rpm. Had it setup By FBO Systems on Oregon on a distributor machine. Mine idles at 1100 rpm in park and 900 in gear.
 

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My first thought would be that you may not have enuff fuel or air in idle circuits. You said you were adjusting mix screws in or out , , Does this change idle speed? If not I would suspect jets out of range or your PV trying to open ?

How much vacumn do you have at idle?

Have you adjusted this while reading a vac gauge going for highest vac read?

Is your idle vacumn below the PV set points to open? I use rule of thumb , 2" below idle vacumn read..

Have you checked to see what the secondary throttle plates are doing?

I think your initial timing is ok, maybe go to 16° and idle at about 950-1000? Sounds like you have a little race motor with that compression.
 

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Have you milled the snot out of the heads? How do you get 12+ to one compression with stock pistons? Should be about 11:1
Just asking, as that is not likely your problem. Now to your issue, as I know this kind of thing can be maddening.

Hmm...read this: "I was just driving the car a few weeks ago, and now I cant even get it to idle right, everything ran great on it untill I tried driving it one time, and its been a ton of problems." That tells me your choices of parts is not the issue, unless something was changed recently.

I know this may just piss you off, but... any time something goes wrong, I always work backwards.

Did you do ANYTHING to the car between the "ran great" and the "tons of problems"?

You have already checked for vac leaks. Does your dist have a vac advance? (I am not familiar with the "streetfire") If so, try disconnecting it and see if the surge goes away. If so, then it is in some way connected to that. Either the can is bad, or you don't have enough vac to keep it pulled open.

If that doesn't pinpoint, I would SUSPECT a bad power valve. Used ethanol fuel lately?
 

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Discussion Starter #9
Is it surging with vacuum advance connected? Possibly not enough vacuum to pull the VA can all in.
It was surging with the vacuum advance connected to ported, full vacuum, and not hooked up at all. But once the engine gets to about 2000 rpm it runs fine.

I have a 327, see sig for specs. I have 20 initial timing and 16 mechanical. 36 total at 3200 rpm. Had it setup By FBO Systems on Oregon on a distributor machine. Mine idles at 1100 rpm in park and 900 in gear.
Thanks, will the car idle at any lower of an rpm?

My first thought would be that you may not have enuff fuel or air in idle circuits. You said you were adjusting mix screws in or out , , Does this change idle speed? If not I would suspect jets out of range or your PV trying to open ?

How much vacumn do you have at idle?

Have you adjusted this while reading a vac gauge going for highest vac read?

Is your idle vacumn below the PV set points to open? I use rule of thumb , 2" below idle vacumn read..

Have you checked to see what the secondary throttle plates are doing?

I think your initial timing is ok, maybe go to 16° and idle at about 950-1000? Sounds like you have a little race motor with that compression.
Yes, the idle mixture screws are working. before the problem my idle vacuum was around 10", but right now the vacuum is going from 5" to 10" from the surging. I cant adjust the screws for the highest vacuum because of the surging, but thats how I was doing it before this problem.

Have you milled the snot out of the heads? How do you get 12+ to one compression with stock pistons? Should be about 11:1
Just asking, as that is not likely your problem. Now to your issue, as I know this kind of thing can be maddening.

Hmm...read this: "I was just driving the car a few weeks ago, and now I cant even get it to idle right, everything ran great on it untill I tried driving it one time, and its been a ton of problems." That tells me your choices of parts is not the issue, unless something was changed recently.

I know this may just piss you off, but... any time something goes wrong, I always work backwards.

Did you do ANYTHING to the car between the "ran great" and the "tons of problems"?

You have already checked for vac leaks. Does your dist have a vac advance? (I am not familiar with the "streetfire") If so, try disconnecting it and see if the surge goes away. If so, then it is in some way connected to that. Either the can is bad, or you don't have enough vac to keep it pulled open.

If that doesn't pinpoint, I would SUSPECT a bad power valve. Used ethanol fuel lately?
When I first got the engine the block was milled, not aure about the heads, but when I rebuilt the engine the block needed to be milled down due to rust around the cooling holes on the deck, and also when I got my heads redone they were milled. I actually put a different spark plug in because I had one that was misfiring, and the piston hit it and closed the gap. I dont know exactly what my compression is, but its just a guess.

the only thing I have changed was that I installed a 1/2" wood carb spacer, last time i was driving the fuel was boiling in the carb, and it was not running right, and started surging, i thought the wood carb spacer would help but it didnt seem to do anything.

I'm using a mix of 110 octane and 93 "up to 10% ethanol" gas

yup, that would be it!
 

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If it started surging before the spacer, it isn't likely contributing.

10% ethanol may be a problem.
I think you have either:
power valve issue, or
little piece of rubber clogging an idle circuit.

Unless you have all new fuel lines designed to run ethanol, little bits can almost dissolve, the re-form in the carb. Kind of like a varnish deal, only it is the rubber.
 
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