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Old 09-21-2010, 05:54 PM
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Need Help with rough idling. 383

Okay I got my 383 engine running. Yeah! It sounds mean idling, but I have not been able to take her for a spin yet.

I feel I'm chasing my tail getting it set up correctly. I can't get it to idle below 1000rpms and at 1000rpms it wants to idle at 35* BTDC! I have the vac cannister on the HEI disconnected and the port on the carb plugged. So it's just initial plus any mechanical that's in by 1000rpms. Manifold vacuum is around 18". I have a Lunati 60133 Solid Roller Cam.

When I take it down to 800rpms and 15* BTDC it chokes and coughs. If I then very slowly open the throttle I can get it to rev up. If I blip it it coughs and sometime back fires. When I keep the timing up at 35* it it much smoother and I can blip it pretty hard. If I floor it all the way quickly it stutters.

Proform 750CFM race series with 4 corner idle adjustment and vac secondaries. I have all four corners at 1.5 turns out. Floats are set with fuel just visible in sight glasses. Fuel pressure at steady 6psi.

Why does it want so much advance at idle?

This could be unrelated but my alternator seems to not be putting out enough power at idle. I have a see though cap on the HEI and as the engine runs and idle drops, the sparks change from white/blue to yellow/red. Rev it up and they get hotter again. I have a streetfire ignition.

I can post a video if it would help diagnose. Thanks!

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Old 09-21-2010, 06:01 PM
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Why by all means post a video for us to see. We like videos May help solve your problem faster.


Cole
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Old 09-21-2010, 07:02 PM
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Trying to upload a video now but utube is being a butt.

Vacuum was higher last night.

In the past when I have adjusted a distro, rpms went up to a point and then things died again. Right now I can keep advancing, and advancing the distro and rpms still climb. Could my distro be off a whole plug and still run. And if so how would the timing light still work?

As a side note right before the video I turned in teh 4 idle screws to see if it made a difference. Seem to be worse. I put them back to 1.5 turns for now.
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Old 09-21-2010, 07:14 PM
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Was the cam degree'd in there, maybe its retarded some. TDC verified on damper? just think'n out loud.
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Old 09-21-2010, 07:19 PM
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Crate engine. I didn't install cam. I sure hope it was. Hate to have to take off the front end to check. Is there a way to tell looking at the rockers compared to the balancer TDC mark?


I had them install the cam as per the cam card recommendation. I believe it was 4*.

If cam is off, all I would have to do is remove the timing chain and reinstall off one or two teeth to set right? Doesn't the lunati cam have a mark to line up when installing at 4*?

Hoping it's something simpler, especially since it seems vacuum is down from last night. Could a vacuum leak cause this issue? Maybe I didn't torque the carb down? I only have 3 vacuum lines. The large one to brakes, one to distro that is plugged and one straight to vacuum gauge.
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Old 09-21-2010, 07:51 PM
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Quote:
Crate engine. I didn't install cam. I sure hope it was. Hate to have to take off the front end to check. Is there a way to tell looking at the rockers compared to the balancer TDC mark?
A piston stop is used to find TDC and verify your 0 timing mark

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I had them install the cam as per the cam card recommendation. I believe it was 4*.
If thats what in am think'n its 4 deg ground in if degree'd on the given cam centerline

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If cam is off, all I would have to do is remove the timing chain and reinstall off one or two teeth to set right? Doesn't the lunati cam have a mark to line up when installing at 4*?
depends on the type of timing gear set, most times the crank gear has multiple key ways, some cam sprockets also have bushings/slots for placement. I can't advise you with any confidence on the best way to check the cam placement for adv/retard once in the motor but I am sure some around here will be able to provide some input
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Old 09-21-2010, 07:53 PM
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Pulled a plug and it's covered in black powdery soot. Not sure if it's that rich or just sucking the backfires back in.

Here's the video. Hope it works.

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Old 09-21-2010, 08:07 PM
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I really think you need to bring it back TDC. Pull #1 plug bring it up top and check where you are at on the distributer. And go from there.
You haven't done that yet have you? Start back tracking yourself.


Cole
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Old 09-21-2010, 08:20 PM
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Couple of ideas

In the past I have been a tooth off at the distributor and still able to run but not able to get "dialed in". You can try retarding it a tooth to see if things improve. To check for vacuum leaks I have used a can of ether/ starting fluid, but with due care and caution! FLAMMABLE! First of all never on a fully hot motor, two I put a red squirter tube on the spray nozzle, (the kind like on a WD-40 or Brakekleen can) to make a more direct shot. If you have a leak at carb base plate of the edge of an intake manifold to head gasket, the motor will rev up some from the (small) shot of fluid. Just keep them small.. to the point... and don't get all crazy with the stuff.
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Old 09-21-2010, 08:20 PM
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I had the distro in and out several times trying to get her to fire.

Here's my thought though which could be wrong.

If it's in and running, and the timing gun is working off the #1 plug wire, indicated advance should be correct. Right?

I lined up my timing tape with the mark on the balancer. Balancer had only one cut mark and no degrees. Maybe the balancer is off? I assumed the balancer mark at zero on the timing tab was TDC. I thought the balancer was keyed and only went on the crank one way.

I just went out and plugged the port to the brakes. So only vac line is straight to the gauge. Still ran the same. Did notice vacuum drops as it warms up.
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Old 09-21-2010, 09:17 PM
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Couple thoughts..

Do I need more accelerator pump shot since it back fires when quick rev'd?

Also this was a "lightly" used carb when I bought it. Never thought to check the jets. Could it be jetted way too small for my 383 causing a lean backfire and hesitation when rev'd?

I will verify TDC tomorrow after work to make sure my timing tape is accurate. It actually backfires more with less advance, so maybe it's running real lean. The black soot on the plugs could be from the back fires.
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Old 09-21-2010, 09:33 PM
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Quote:
Originally Posted by Landshark928
Couple thoughts..

Do I need more accelerator pump shot since it back fires when quick rev'd?

Also this was a "lightly" used carb when I bought it. Never thought to check the jets. Could it be jetted way too small for my 383 causing a lean backfire and hesitation when rev'd?

I will verify TDC tomorrow after work to make sure my timing tape is accurate. It actually backfires more with less advance, so maybe it's running real lean. The black soot on the plugs could be from the back fires.
What are the cam specs? What is the idle vacuum and what does the vacuum gage needle look like at idle?

The advance at idle can be increased by hooking up the vacuum advance to manifold vacuum. You don't need more than 10-12 of advance from the vacuum can. If it gives more, adjust it if you can, or use a Crane #99619-1 Limiter Plate.

Then use around 18 of initial (or whatever is required to get good off idle response) and 36 or so of total- depending on the heads you have. Fast chambers like Vortec run fine w/less total.

The popping back when you wing the throttle is the accelerator pump. It's either not adjusted to give an IMMEDIATE shot, the shooter needs to be bigger or less likely you need a different pump cam.

You need to be sure the primary throttle blades aren't open too far to get a good idle speed. This will overexpose the transfer slot and that causes a bad idle, too rich usually, and causes the idle screws to become ineffective. You said the idle screws respond to adjustment, so you should be OK there.

Sort the timing out first.

Last edited by cobalt327; 09-21-2010 at 09:55 PM.
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Old 09-21-2010, 09:35 PM
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Quote:
Originally Posted by Landshark928
Couple thoughts..

Do I need more accelerator pump shot since it back fires when quick rev'd?

Also this was a "lightly" used carb when I bought it. Never thought to check the jets. Could it be jetted way too small for my 383 causing a lean backfire and hesitation when rev'd?

I will verify TDC tomorrow after work to make sure my timing tape is accurate. It actually backfires more with less advance, so maybe it's running real lean. The black soot on the plugs could be from the back fires.
1st ??- possibly, very likely if timing is correct, but retarded timing will cause backfire too.

2nd ?? - they would have to really have made then insanely small. Jetting does virtually nothing below 3000 or so rpm, not until airspeed is up and fuel is flowing from the boosters. Low speed and idle is idle and transition circuits.

Sounds like you may not have enough ignition spark energy, either from distributor or due to poor plug wires. I noticed the yellow wires in another pic, what are they?? hoping you don't say ACCEL. What spark plugs, brand and heat range??

Have you run through the valve lash yet, just to check?? This could be related to vacuum loss as it warms up, I would expect vacuum to increase as it warms up.

Soot on plugs can be also be from low rpm misfire, due to cam overlap causing charge dilution from exhaust combined with lack of enough spark energy. You may need a multi strike ignition to clean it up.
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Old 09-21-2010, 09:39 PM
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Another thing, carbs with a sight glass generally need fuel level to be in the mid point of the glass. Different than the "dribble out" setting for solid type sight plugs, due to glass size and placement.
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Old 09-21-2010, 10:09 PM
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Cam specs: Voodoo 60133 .585/.600" lift. 279/285 Duration. 249/255 @0.50" Solid roller with lash set at 0.016" when built.

I have not checked valve lash. Engine did sit for 4 months. Would lash setting loosen up?

Plug wires are Jegs 8.5's.
Distro is ProComp and may be the issue.
Should be stock jets in carb, I believe 74s primaries and 84 secondaries.

First thing I'll do tomorrow is swap out gas. Kinda of a brain fart moment. I am burning the same gas the was in the tank since last October. Return fuel line in engine compartment was not shut off. We were the rainiest city int eh US this year. I may have water in the gas. Thinking I may have bad gas on top of trying to get the rest of the tuning right.

With fresh gas I'll set the floats a little higher. Then I'll try setting initial timing again for around 18-20*. At 1000rpms I may already have a couple degrees of mechanical in the mix? I'm getting a spring and bushing kit tomorrow and will try to use the lightest springs and get the bushing to limit mechanical to 18* (36* total). I'll keep vacuum advance off for now. I'll also see if my speed shop has bigger nozzles for the accelerator pump and a cam kit.

I'm thinking bad gas along with not enough initial timing for a decent sized cam, plus lack of juice in the accelerator pump is causing the hesitation and backfiring. I'll also verify TDC to the balancer mark and my timing tape.

If that doesn't help, I'll check valve lash and finally cam timing.
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