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Old 10-22-2011, 04:44 PM
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Erratic idle issue I'm stumped!!!

Ok I'm having an erratic idle issue and I just can't figure it out!!!

It doesn't matter what gear I'm in but the rpms seem to bounce around. I've looked for vac leaks just rebuilt the carb played with timing I'm stumped.

Here is what I have:
383
800 eddy avs
Rpm air gap
ik200s
Roller rockers
Custom cam specs: 238/248 @50 600/570 lift 106lsa hyd roller
Pro billet msd part #85551
6al2 ign box


What could be some things that cause the erratic idle?
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Old 10-22-2011, 06:20 PM
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Bad/carboned cap or rotor, cam walking, play in the dist shaft/plate, worn timing gear or chain, come to mind on the mechanical side.
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Old 10-22-2011, 07:07 PM
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Quote:
Originally Posted by 68NovaSS
Bad/carboned cap or rotor, cam walking, play in the dist shaft/plate, worn timing gear or chain, come to mind on the mechanical side.

I have a brand new cap and rotor when I installed the new pro billet dist yesterday.

I have been thinking cam walk as well but wouldn't that mess with the timing? The timing is dead on.

I will check the chain and cam walk as a last resort because it's the most work.

Tomorrow I'm going to pull all the plugs and check them as well as the wires. I'm also goin to try setting the valves with the engine running. I have a weird feeling something is going on with the valves.
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Old 10-22-2011, 07:26 PM
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If it's doing this under light throttle cruise and you're using a vacuum advance, the vacuum advance may be supplying too much advance. Too much advance under these conditions will cause the engine to 'surge'. You don't want any more than about 46-50 max total timing including the vacuum advance. That means the vacuum advance should supply about 10-12.

You might want to check the rotor phasing as well. This usually isn't that common, but can a cause similar problem.
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Old 10-22-2011, 08:26 PM
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Quote:
Originally Posted by cobalt327
If it's doing this under light throttle cruise and you're using a vacuum advance, the vacuum advance may be supplying too much advance. Too much advance under these conditions will cause the engine to 'surge'. You don't want any more than about 46-50 max total timing including the vacuum advance. That means the vacuum advance should supply about 10-12.

You might want to check the rotor phasing as well. This usually isn't that common, but can a cause similar problem.

I have no vac advance on this dist. I have initial at 22* with 21* of mech which gives me a total of 43*

Phasing on the rotor? I don't believe I know what that is or I might have just not put that way before. What do you mean phasing?

It's a brand new dist with new cap and rotor. The dist part number is 85551
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Old 10-22-2011, 08:35 PM
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Total timing is too high. You don't need any more than 36 degrees. Running it this way is risking detonation, plus it won't make as much power as it will at 36 degrees or so.

Rotor phasing- http://www.msdignition.com/uploadedF...or_phasing.pdf
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Old 10-23-2011, 10:32 AM
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I will put timing down a bit lower and see how she acts the lowest stop bushing I have gives me 18* of advance. I will play with that see how she acts.

I am going to try a few other things today see if it helps at all with the rpms.
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Old 10-23-2011, 09:42 PM
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Download and read the directions from mallory or summit for this distributor.

For your specific custom cam:

You want to "lock out" the mechanical advance and set the locked out timing at 34-36 before tdc.

Swap the primary power step up pistons springs for light tension springs
3.5" or 4.5" vacuum rated

The primary metering rods must stay downin the jet - lean at idle.

This cam requires a high stall torque converter. Get a 10" 3500 stall.

max fuel pressure at idle 6psi 5 to 5.5psi best
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Old 10-23-2011, 10:24 PM
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Quote:
Originally Posted by F-BIRD'88
Download and read the directions from mallory or summit for this distributor.

For your specific custom cam:

You want to "lock out" the mechanical advance and set the locked out timing at 34-36 before tdc.

Swap the primary power step up pistons springs for light tension springs
3.5" or 4.5" vacuum rated

The primary metering rods must stay downin the jet - lean at idle.

This cam requires a high stall torque converter. Get a 10" 3500 stall.

max fuel pressure at idle 6psi 5 to 5.5psi best
I will definatly mess with the timing and the dist this week when I have time (busy work week)

I have the blue springs in there now 3" rating.

I have a 10" coan 3000 converter

The fuel pump is calibrated for this carb




I got the problem solved this thing is running like a whole new animal! There were a few things I did that I'm not sure if it helped and then a few things I did that were part of the problem.

Things I did that I'm not sure helped were messing with the plugs and wires. I pulled and cleaned all the wires are went from a 45 gap down to 35. I might go back up now that everything is solved. I also rerouted 5 and 7 wires there were no sings of them inner arcing but I moved them anyways.

Things I found that did make a difference were a vac leak and the booster check valve. The rubber groment was dried out and split apart. Then I went to the junk yard bought a set of valve covers cut the tops off and set the valves with the engine running. All the valves on the passenger side were fine. But number 7 exh was ticking and the same with number 1 and 3 int. once I did all that not one issue!!!

This thig is running like a really really good now!!!!
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Old 10-24-2011, 07:26 AM
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Quote:
Originally Posted by elcaminodragster
I will definatly mess with the timing and the dist this week when I have time (busy work week)

I have the blue springs in there now 3" rating.

I have a 10" coan 3000 converter

The fuel pump is calibrated for this carb




I got the problem solved this thing is running like a whole new animal! There were a few things I did that I'm not sure if it helped and then a few things I did that were part of the problem.

Things I did that I'm not sure helped were messing with the plugs and wires. I pulled and cleaned all the wires are went from a 45 gap down to 35. I might go back up now that everything is solved. I also rerouted 5 and 7 wires there were no sings of them inner arcing but I moved them anyways.

Things I found that did make a difference were a vac leak and the booster check valve. The rubber groment was dried out and split apart. Then I went to the junk yard bought a set of valve covers cut the tops off and set the valves with the engine running. All the valves on the passenger side were fine. But number 7 exh was ticking and the same with number 1 and 3 int. once I did all that not one issue!!!

This thig is running like a really really good now!!!!
Good going!

What did you end up setting the initial and total timing at?

Just for future reference, if you wanted to go w/more initial than the 18 allowed by using the 18 degree bushing (18 + 18= 36 total), you can take a look at THESE custom bushings. Using one of them will allow more initial (either 22 or 26) w/o the total going too high- which you want to avoid at all costs. Not only will too much total timing cost you power, it can destroy the engine!

Good luck.
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Old 10-24-2011, 11:24 AM
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Quote:
Originally Posted by cobalt327
Good going!

What did you end up setting the initial and total timing at?

Just for future reference, if you wanted to go w/more initial than the 18 allowed by using the 18 degree bushing (18 + 18= 36 total), you can take a look at THESE custom bushings. Using one of them will allow more initial (either 22 or 26) w/o the total going too high- which you want to avoid at all costs. Not only will too much total timing cost you power, it can destroy the engine!

Good luck.

That site has a lot of good info thank you

I have been looking at larger stop bushings like that in summit and jegs. My engine really likes 24* initial with it at 18* right now it's not to happy. But untill I get a larger bushing in there it's going to have to stay there.
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Old 10-24-2011, 11:56 AM
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Are you running a choke? If so, what kind?
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Old 10-24-2011, 12:08 PM
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Quote:
Originally Posted by elcaminodragster
That site has a lot of good info thank you

I have been looking at larger stop bushings like that in summit and jegs. My engine really likes 24* initial with it at 18* right now it's not to happy. But untill I get a larger bushing in there it's going to have to stay there.
It's a shame those bushings are so expensive, but if they work, that's the pay-off. Does Summit or Jegs have bushings other than the stock MSD bushings, cheaper than those from the link above? I'm not surprised it wants more than 18, I'm thinking either of the bushings will be pretty close to right- and you really want to keep the mechanical advance operational if at all possible. I also just wanted to say again that you don't want too much total timing.

I don't think this was already mentioned:

DETERMINING TDC will allow you to be sure the timing tab and damper are correctly indicating TDC.

MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, get one that matches the diameter of your damper.
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Old 10-24-2011, 04:42 PM
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Quote:
Originally Posted by cobalt327
It's a shame those bushings are so expensive, but if they work, that's the pay-off. Does Summit or Jegs have bushings other than the stock MSD bushings, cheaper than those from the link above? I'm not surprised it wants more than 18, I'm thinking either of the bushings will be pretty close to right- and you really want to keep the mechanical advance operational if at all possible. I also just wanted to say again that you don't want too much total timing.

I don't think this was already mentioned:

DETERMINING TDC will allow you to be sure the timing tab and damper are correctly indicating TDC.

MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, get one that matches the diameter of your damper.
Ya that's a bit expensive for 2 little bushings!!! I haven't looked at jegs and summit a of yet but I would imagine someone makes them.

I actually have a Sfi balancer with timing marks up to 60*

I'm most positive that my timing marker is dead in but I will still doubble check.
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Old 10-25-2011, 08:39 AM
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Well I can't find anyone out there that makes those bushings. Maybe I'm just not lookin in the right area. . .

Oh well I'm going to bite the bullet and buy them from the link you gave me. My car hates being at 18* right now.

Tho this thig is really torquey now that it's all running right little bit of carb tuning once I get the timing done and this thing will be dead on balls accurate!!! Lol
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