Erratic Idle - Could it be the Distributor

[Freddie]

I have another thread on here about significant issues dialling in the carb. I've got that very very close now, just fine tuning.

However last 3 drives since I finally have the carb dialled in nicely at parked in Garage. Idle 750 RPM in drive. 1000 RPM in Park.

I drive the car for 10-15 mins, gets up to temp and the idle in park goes to 1500-1600 RPM and in drive 1200 and diesels on shut down.

No vac leaks (all checked multiple times)
I've pulled the carb and checked the butterflies aren't binding. Which they appear not to, but I will do an on car check when it's at 1600 rpm also
T slots are squared
even parked in the garage I can got Wot and it goes back to normal RPM.
It only has the higher RPMs after 10-15 mins of driving and at full temp

I really don't think it's the carb.

Engine was rebuilt before this new carb went on, and it sat for 2 years before that.

So I am thinking it could be sticking / binding springs in the dist. Weakened and not returning to fully seated. Dist is 11 years old

So I pulled the cap...holy crap so much corrosion.

MSD Pro Billet 85551 (tall Deck).

I know it can be cleaned, but I am thinking just replace.

1. Could this rust be an issue in my RPM not dropping back to set RPM when up to full temp?
2. Could weakened springs be the issue?
3. If you would you clean it and service it or replace it (cost to replace is circa $500

[HQM383]

However last 3 drives since I finally have the carb dialled in nicely at parked in Garage. Idle 750 RPM in drive. 1000 RPM in Park.

Just to clarify, is this ^^^^^ at full operating temp?

[Caprimaniac]

However last 3 drives since I finally have the carb dialled in nicely at parked in Garage. Idle 750 RPM in drive. 1000 RPM in Park.

Just to clarify, is this ^^^^^ at full operating temp?

Xactly…. Need stinking hot engine to set idle. Have a problem with a weber on a V6- it does not have a choke- mechanidm. So,idle at cold is not there, and need to play with rhe throttle at low temps.

Pic gives no worries. Look at the terminals in cap and rotor. Any corrosiob there and you need to replace or clean.

[Geoff2]

Lubricate [ lightly ] the centri weight mechanism. Easy to check if timing is varying after it gets hot. Check timing with a timing light when first started & then after a run.
You can buy a new p/up #84661. Shouldn't cost much. MSD doesn't charge extra for the rust........
Carb, let me guess. Holley or clone...

[Freddie]

Thanks all, to answer questions:

1. Yes RPM goes up at full I mean stinking hot operating temp. I was setting idle at temp (after thermostat opened). But car is way way way hotter after a 10 min drive
2. I didn't even think to re-check timing...LOL such an easy check. Will do that
3. I did a google search and found the part numbers for reluctor and springs and weights. Ordered all three (even if I don't need em)
4. Yes QFT 1150 2 Circuit

I pull the Dist just now, have hit it with some WD40 and sanded the rust off. Will put it back together in the morning and throw it back in the car.

I am also thinking I only checked the carb for vac leak. Might check manifold also. That said if there was vac leak it wouldn't start only when car is hot, I would have thought it would be there from the get go hence I wouldn't see such a dramatic swing in RPM warm to red hot

[mag2555]

I would rule out timing advance creep by removing the advance springs and replacing them with small cable tie's or mechanics wire to lock out the timing.
Light silver springs that come in most recurve kits give up the ghost fast and are even effected by engine temp!

[HQM383]

1. Yes RPM goes up at full I mean stinking hot operating temp. I was setting idle at temp (after thermostat opened). But car is way way way hotter after a 10 min drive

Maybe you have a cooling system issue to solve before going any further.

[Dan Timberlake]

sent in error

[Dan Timberlake]

Looks like there are some decent name brand distributors for way less than $500. Maybe $300 or less.

Regardless which route I went, I would include these steps.

I'd use $5 of the $300 to buy this to install on the damper with a verified TDC mark -
https://www.summitracing.com/parts/msd- ... gKdQPD_BwE
And add a /permanent witness mark across damper hub and outer ring to detect futire slip/failure at a glance.

I'm assuming you have a decent tach, so in about 20 minutes or less you could make a plot of the centrifugal only advance curve, and verify it 3 times, looking for excellent stability and repeatability.
==============.

None-the-less I'd check the distributor bushings for wear and clean all the mech advance parts, check them for wear. If all OK ( kind of doubtful) , lube, and re-assemble with a good quality module. (probably less than $50.)
I'm figuring One of these is needed too - 12 US bux -
https://www.summitracing.com/parts/mor-72310#overview

=========.

On the other hand ( the third one) This looks like a screaming deal.
https://www.summitracing.com/parts/sum-850030#overview
Hopefully someone can report their experiences with it.

[rp930]

My guess is timing is creeping up when hot. You will probably need stiffer springs. As stated on here timing is easy to check cold and hot.

[Freddie]

Alrighty just to update. Pulled dizzy cleaned it all up. WD40 on weights springs and moving parts. Took reluctor off and hit it with the dremel.

All back together and problem solved.

Idle 950 in park
780 in drive

Took it for 30 min drive and drive perfect

Must have just been binding

[mag2555]

...!

[lefty o]

rusty crusty junk can do amazing things.

[stealth]

Glad it’s solved....I was going to say All those rusty metal chips playing havoc with MAGNET pick up. Likely ozone trapped in cap caused the corrosion. Best to drill a few holes in the cap to vent.