New engine will not idle - HELP?!?

oz · Jul 13, 2004

Greetings,
I rebuilt my '69 302 this spring and fired it up recently. I can not get it to idle properly. The engine shakes like crazy at anything less than 2000 rpm. I assume I have a carburator problem.

This is the combo:
302 bored +0.030; stock heads - ported, new guides, new edelbrock springs, screw in studs, full roller rockers; Edelbrock preformer RPM package - intake, cam (#7122 290/300, .496"/.520", 112 lsa), valve springs, 600 cfm carb w/ electric choke conversion; stock distributor rebuilt w/ pertronix and recurved by Mike Ulrey; headers, 8mm wires, etc...

The problem:
Engine shakes like crazy below 2000 rpm - the lower rpm the worse. I only have 8 - 10 inches of vacuum at 900 rpm. The idle mixture screws don't seem to do anything. From one turn out to 7 turns out, the idle does not change. Choke comes off shortly after start up so this is not a problem. This really seems like a massive vacuum leak but I can't find any.

Possible Causes:
Initially had timing off 180 degrees (rotor pointed wrong way) so engine backfired through carb a few times...
Carb was purchased slightly used from a friend. Worked when it came off his 289 5 years ago... been sitting in the box since then - has original Edelbrock jetting in place now. Could either of these things cause the problem?

I've tried:
Squirted starter fluid around the intake gaskets abd carb base to rule out intake leak - found no leak. Checked to make sure all plugs were firing with inductive timing light - all ok.

Things I will try:
Plug power brake booster vac line to see if booster is still good.
Plug all other vac ports.
Make sure there isn't a vac port on the edelbrock choke that is open (I guess Holley has a vac port on their choke - not sure about Edelbrock???).

I don't think I have a compression or cylinder leak issue but I can check that also....

What else should I try?

THANKS!

dodgestang · Jul 13, 2004

I would check that you wired the engine with the firing order from the cam card...which may or may not agree with the firing order from places like a Chiltons manual.

oz · Jul 13, 2004

99% sure I did but I will consult the card again....

If it was the wrong order, wouldn't I be able to hear it in the intake? I would think that the 4 cylinders that were firing wrong would be backfiring through the runners.

I'll check again... it wouldn't be the first time I did something that stupid

Thanks!

Any other suggestions???

geegee · Jul 13, 2004

Fellow Mustanger ('66 vert) had his engine rebuilt by reputable firm. Had similar problems as you describe. After a string of trouble he got down to checking everything. Found he had 351w cam installed. When he changed the firing order to 351w, the problems disappeared. Its worth checking.

Bonestock2k · Jul 13, 2004

I like where your going with things you are going to try - sounds like vaccum/carb problems to me. Do you have access to another carb you know is good that you could bolt on to rule out that possibility?

Max Power · Jul 13, 2004

Sounds timing related to me. Either the distributor a tooth off or the firing order problem.

That a good amount of cam. It's not going to idle like a sewing machine, so you may not be that far off.

oz · Jul 13, 2004

Thanks for the replies.

Just to rule it out, I am going to change the firing order and see if it runs (even the Edelbrock tech guy said that I have it right but that 'stranger things have happened').... only if Summit sent me the wrong cam I think.

Edelbrock tech suggested checking fuel pressue, possibly rebuilding the carb (since gaskets can crack, etc) in addition to changing the firing order.

I may just change the fuel pump because the only problem the car had before was a strange habbit of not starting if it sat for a week or more. I'd have to crank and crank it... probably fuel evaporation but could be the pump I guess (?)

bull999999 · Jul 13, 2004

Did you try rebuilding the carb since it's a used one that's been sitting around for 5 years?

Also, if you take a look at my "Mystery Engine" post, you'll see that in my case, it was due to the firing order.

2nd Mustang · Jul 13, 2004

I have a Holley that one day, all of a sudden, wouldn't idle unless I held the rpms up at a minimum of 1500 rpms. Rebuilt the carb, now the sweet sounding lumpy idle is back to normal at around 900 rpms.

oz · Jul 14, 2004

Last night I:
- tried the 351 firing order... that is not the problem
- tried using the manifold vacuum on the distributor instead of the 'delayed' vacuum... this didn't help
- rebuilt the carb with the Edelbrock kit. The carb was spotless inside.
- reduced the gap on the plugs to .040" - since I am using a Pertronix and Flame Thrower coil, I was running an extra .010" of gap vs stock.
- did a compression test - compression was evenly distributed between 135 and 146. The battery was having a tough time keeping up so the cranking speed may have a little to do with the (relatively low?) numbers.

The engine didn't shake quite as much at idol but I still couldn't pull more than 10 inches of vacuum. I am going to try a different port and see if I am just not seeing full vacuum.

Bought a fuell pump for it too but didn't have time to all the above and install it last night.

Thanks.

rfedd · Jul 14, 2004

If the plug gap chance improved the situation, go down a bit more to .035. You might be on the right track, at least it appears that way. On the 4 corner idle mixture screws...run them in until you hear a change in idle...idle should come up bit, and then back off an 1/4 turn. Do that on each corner until it runs right. At that point it may be idling to high, so then lower the idle, using the idle screw.

From what I read you were trying different settings and then starting the car?

Do it with the car running. Mine are almost closed.

ron

Pakrat · Jul 14, 2004

For what it's worth, I have a 69' 302 also, and when I recently put in the pertronix and flamethrower, I left the plugs at .034 which is dead in the middle of the stock range still.

I'm sure you didn't make this mistake but I figure it's worth mentioning that Pertronix does make two V8 kits for distributors with and without a vaccum advance, so since you seem to have a vaccum issue problem, maybe they gave you the wrong one???? Just a thought.

2nd Mustang · Jul 14, 2004

I didn't catch what plug gap you were at and are presently at. With my Unilite conversion, Mallory coil and MSD6A box, I run a .045 gap. I heard of people running as high as .050 on their plugs with an electronic ignition.

My Holley looked clean inside too, but I cleaned out every orifice with compressed air. My vacuum did drop a little when I had the idle problem, can't remember the reading, but even with my mild cam, I get 14 inches of vacuum at idle, just barely enough to operate the power brakes.

As other poster mentioned earlier, the best way to verify the carb is probably to temporarily run a known good carb to see if it cures your idle problem. Good luck.

oz · Jul 14, 2004

Pakrat said:
I'm sure you didn't make this mistake but I figure it's worth mentioning that Pertronix does make two V8 kits for distributors with and without a vaccum advance, so since you seem to have a vaccum issue problem, maybe they gave you the wrong one???? Just a thought.

I did not know that... I had Mike Ulrey rebuild the distributor, recurve it and install the Pertronix. He is a pro - I have seen his name more than once in Mustang Monthly articles as the guy who built their distributor so I a want to give him the benefit of the doubt.
I may give him a call tomorrow to talk about my difficulties.

It is an Edelbrock (Carter AFB) carb so there are only two idle mixture screws. Everything off idle is done with jetting.

I will definitely change the plug gap back to .035".... since the carb was clean and the only other change was plug gap - maybe the spark was being blown out(?)...

what a moron I will feel like if that is the problem... I don't think so at this point because the shaking is better but the vacuum is still very low.

Thanks

pabear89 · Jul 14, 2004

I'm a holley guy, But does the rear throttle plate have an adjustment screw somewhere?
It sounds like a holley that has the rear blades open too much or a fuel leak internal, Float setting or pwr valve.
When the mixture screws Show no affect, It is drawing the fuel in off idle or leaking the fuel.

What is your base timing at without vac attached?
PB

blown65 · Jul 14, 2004

9" on that cam seems kinda low. Did you by chance ask Edelbrock what Vaccum you should see. Maybe the gaskets under neath the intake are messed up. If it wont run under 2000 Id still say you have some sort of vaccum leak.

Do this, start it up, and get it to idle as low as possible running like crap. Dont let it run long. Now check your header pipes one by one and see which ones are hot and which ones are cold. If they are all hot or are all about the same temp, then the vaccum leak may not be the problem via intake gasket. If you have a cylinder or two that is cold and the rest are fine, then check with a timing light to verify spark, interchange wires/ plugs and eliminate the wires. If all that checks out, Id check the valve train and make sure a valve isnt being held open slightly causing bad idle or low vaccum. Lastly, just may be that intake gasket.

oz · Jul 15, 2004

I wanted to make sure what I was saying was true about the idle screws.
When I turn them in almost all the way, the engine dies.

I thought maybe there was too much air being drawn throught the PCV so I plugged it - didn't change anything.

I also unplugged the brake booster when the car was running and that nearly killed it but when I plugged it, it was back to about 10" vacuum.

I tried the vac gage on the brake booster port (in case it wasn't getting full vacuum from the other port). No effect - same 10" vacuum.

Base timing is 10 BTDC but (as expected) if I advance it at idle, the engine speed increases and smooths out a little.

Checked the water for bubbles - when the water is really hot there is sort of a super thin layer of 'foam' (not really foam, perhaps the result of turbulance). I am using the fluid I took out before the rebuild so I can flush it out and any funk that is in there too. Not using any water so I don't think I have a head gasket issue (and I have even compression 135-146)

When I rebuilt the carb I thought the floats were a little low so I adjusted them.

The Edelbrock guy was concerned about my fuel pressure.... I got the old (very new looking) pump off last night but did not get the new one on.

Neither the heads nor the deck needed to be machined so the intake runners and water passages should line up well...

I am about ready to tear the intake off and put new gaskets on... even though I did everything right when I installed it (used guide studs, good torque wrench, sealed water passages, RTV on the ends, ARP bolts, etc....).

rfedd · Jul 15, 2004

Make sure to also use gasket cinch. I have seen 2 cases of the gaskets creeping in the last 3 months. They were torn at the bolt location and seperated on the bottom side, so you could not see the cracks.
They block the runners and performance is affected. Also re-torque the intake bolts after a 1/2 dozen heat cycles.

Ron

blown65 · Jul 15, 2004

rfedd said:
Make sure to also use gasket cinch. I have seen 2 cases of the gaskets creeping in the last 3 months. They were torn at the bolt location and seperated on the bottom side, so you could not see the cracks.
They block the runners and performance is affected. Also re-torque the intake bolts after a 1/2 dozen heat cycles.

Ron

ya, thats what happened on mine and dropped a cylinder. At idle it just ran like crap sucking in air. Thats why I asked him to run it for a short time and check the exhaust pipes for one or two cylinders not firing.

oz · Jul 16, 2004

I talked to Mike Ulrey (the guy who built the distributor) and he said there are really only two things that will cause low vacuum at idle.

One was a big vacuum leak. There is not really a vacuum in the crank case if the PCV is removed so I really doubt the gaskets are leaking along the bottom.

The second was that the cam was cut/installed retarded too much... He said only a little will have a huge influence on vacuum. I used a Cloyes timing set that did not have any extra keyways for advance / retard so I know the cam is installed straight up. I did not degree the cam though to confirm the timing relative to what the cam card said.... Mike said to advance the base timing up to the point that the engine no longer increased in speed and then see if it detonated when accelerated. Since the car does not have a front end on it right now (no body or bumpers, lights), I can't take it out the road.

The distributor was set up with 36 degrees total advance at 3500 rpm so I think I may have a few degrees to play with but not much.

Would you take the intake off first and redo the gaskets or the front cover to check the cam???
Intake leak or Cam problem - which is most likely - intake leak, right???

New engine will not idle - HELP?!?

oz

dodgestang

Active Member

oz

geegee

Bonestock2k

Member

Max Power

Active Member

oz

bull999999

New Member

2nd Mustang

oz

rfedd

Pakrat

2nd Mustang

oz

pabear89

Active Member

blown65

oz

rfedd

blown65

oz

Similar threads

New engine will not idle - HELP?!?

Active Member

Member

Active Member

New Member

Active Member

Similar threads

Privacy & Transparency

Privacy & Transparency