Fighting with this 440 idle!

[Macdon221]

Good Day All,

In need of some guidance.

As the title says....been fighting with a 440 to get it right. It's a newly built engine in the last year or so. A little bit of porting, comp cam #21-223-4. Nothing too crazy. Stock Heads.

The engine ran good, not perfect...a stumble off the line but that's about it. Idled ok after warm. Choke was not set up. It makes tons and tons of power. Stock intake. Stock original carter avs carb. Also had original dist with a pertronix pick up with the standard coil....extra wire ran to the ballast resistor. Started and idled ok.

I like things back to stock...just my thing....so I replaces the carb with a newly restored correct CARTER AVS carb. Same carb just restored. Same jetting. Stock 101 primaries and 95 secondary's. Spring set installed allows the to sink on idle and pop up when throttle is blipped.

I removed the correct original numbered dist that was installed, which is the original one to the car, and installed a correct numbered newly restored dist with points and condenser. No pertronix pick up.

Choke all working fine. Car will start, warm up no issue. Smooth idle. Idles done to about 650-750 in gear no issse. Can get lower if needed.

Dist has been set to about 15 initial. Have FBO limiter plate installed to ensure all in no more than 34. Reeving up and checking the timing confirms this. Dwell set to 30...checked with feeler gauges for the ballpark and with a dwell meter.

Removing the vacuum advance at idle makes no difference to the timing....so at idle the vacuum advance is not influencing the timing.

Now here is my nemesis....start, warm up, drive, all good. Tons of power through all ranges. Zero hesitation from off idle. Very responsive. Gear shift points are good. Start, stop, idles good. BUT.....after about 15-20 mins of driving and the car heats up....the idle rises to about 1500. If wont go back down. The throttle is closed and back on the stop screw...same as where we started at. It also wanders a from back to 1000 and then back to about 1500. I have repeated this cycle 3 times now...let it cool...next day...same thing. Great at the start...but after a good warm up the cars idle is again not correct.

So....I have changed the carb to another avs carb while car still warm...restart...same. Changed the carb base gasket multiple times, 4 hole, open ...same. I have switched the coil when warm to cool coil....same. I have capped all vacuum sources while warm....choke diaphragm, pvc port, vacuum advance port, brake booster port on engine, and vacuum headlight (69 charger) port....no change.

I have tried to find an carb or intake manifold leak with water, and propane....no luck.

Where from here?

1. Should I go back to the original dist with the pick up? Try a new condenser? New points?
2. Ballast resistor?
3. Continue to look for an intake leak and how?

I really appreciate all your guys/gals help. I love it when my car is working perfectly....and I need help for this one.


macdon221

 

[1967coronet]

I would swap the points plate and condenser into the 1st distributor that has the pertronix set up.
I would not put the limit plate in.
It sounds like you have figured this out , the problem being in the distributor.
I run a pertronix set myself with their 1.5 ohm coil , I have bypassed my ballast resistor though and ran a switched 12 volt to the coil.
I understand wanting everything back to stock.
To me the warm / cold idle difference would seem choke linkage related.

 

[toolmanmike]

Is the carb bleeding over? When it acts up what is the fuel pressure. ANything over about 5# will cause issues.

 

[AR67GTX]

Do you have power brakes? Maybe something like a vacuum leak in the system although I can’t think of why it would be OK cold and warming up but then leak when hot?

It doesn’t sound like an ignition system issue to me unless somehow the centrifugal weights are hanging up and not pulling back in. If when it starts to happen, if you shut down and restart the motor is it still idling high? If so I would pull the distributor cap and see if it looks like the weights are hanging partly open. You could also secure them in with a rubber band and restart the engine to see if it idles properly. I have 2 of those FBO limiter plates in cars without issue but maybe the weights/advance pins are dragging on yours for some reason.

 

[Dave6T4]

It sure sounds like a vacuum leak, but you have been all around that. What is your fuel pressure? Carter's do not like anything over about 5 psi.
Toolmanmike beat me to it

 

[Macdon221]

Fuel pressure....no idea. no way to read it. I just have the stock fuel mechanical pump. Wasn't an issue before.

Yes...I have power brakes...with the high idle I have then removed the booster hose and capped it. No change. Again...only occurs after engine is warmed up nice and not after about 20 mins and a run on the highway.

If I shut it down and its idling around 1500 rpm...yes when i start it it is the same.

I now have a thought here...it may be the weights...It has only started after I have "lit er up" to check out power etc. May the weights are sticking open giving the higher idle cause the advance is in. Maybe. And when i shut it off it makes a funny noise sometimes from the high idle. Anyone add?

Is there another way to check an intake leak? Maybe under the intake? Is is possible the leak shows up after its heated? Again it did not do it before.

 

[Mick56]

Is there a heat riser flap in the exhaust? Could be stuck closed, heating up the intake. Do you have the insulator pad between the intake and the valley pan?

 

[Macdon221]

No Pad. Heat Riser Flap removed.

 

[Macdon221]

Any other ideas?

 

[Orig69]

Did you try the propane in between the intake manifold and the cylinder head right where the intake ports are located?

Maybe there is some extra paint there.

 

[turbine68rt]

When the idle gets up to about 1500 did you verify that the linkage is in fact resting against the stop screw?

 

[Don Frelier]

Did you check the base timing when it idles high?
Maybe the advance is sticking after it gets warm.
My plymouth definitely idles higher when fully warmed up but that's where it's tuned.

 

[lewtot184]

Primary spring in the distributor may be too light and the fbo plate could be causing a hang-up. Im not a real fan of those fbo plates. Take the distributor apart and make sure the weights are lubed.

 

[Geoff 2]

I think the ign timing is changing. When the engine is cold, idle is normal, check the timing. Then check timing again when the rpm has increased.

 

[lewtot184]

Something else I've noticed is these new repop vacuum advances have too light of a spring in them and the one I have doesn't have good, if any, adjustment. It's typical aftermarket garbage and would create havoc with a high vacuum engine.

 

[Macdon221]

So...an update.

When I got home I took the distributor out, cleaned and regressed the weight pins, and all of the areas that would be rubbing. Has a light and heavy spring. The heavy spring has the bigger loop on one end, so the weight with the heavy spring swings open first and is free to move without any rotation. Placed a thin layer of grease on both sides of the fbo plate as well. Vacuum advance will swing with suction applied.


Reinstalled, started the car when I got home yesterday....base timing, vacuum advance unhooked and plugged set to 16 degrees with dial back light. Idle set at around 750 no issues. Throttle applied vacuum advance still plugged and advance all in around 2500 at 32-34 degrees.

Engine at idle 750 rpm....Vacuum advance hooked up...no change in base timing. Throttle up to about 2000 rpm steady and the timing now in around 45 degrees. Go back to idle and timing settles right back to 16 degrees.

Test ride time....went out for about 30 min. Everything about the performance is perfect. The engine just purrs in cruise and no issues at all from the stop light with any amount of throttle application. Smooth as silk. A few hard accelerations and everything is working fine! Maybe I have this beat....then on the last hard acceleration....as soon as I let off the gas....bingo here we go. Back to the high idle again and just running very poorly. Its instant...right after that last acceleration.

It has to be either something in the carb sticking open or the distributor. I cant think of anything else.

Limp back to the garage...Turbine....yes the throttle is all the way back to the stop even at the high idle.

I failed to check the timing when back in the garage with the high idle. I should of. Also Maybe the secondary's are failing to close fully when warm?? I didn't look at that either. I was just deflated and went in the house. lol

I think I should take out that FBO plate and see if that is the issue....just base time it for 34 all in without the plate maybe and see what happens. Could it be that case the fbo plate is causing the clearance to be not enough for the springs to bring the weight's back because it is clearance is just not enough? The little C-clip goes back in the top no problem though...can I move the collar down on the shaft just a bit to give it a bit more wiggle room?

 

[AR67GTX]

It might be that heavy spring with the big loop. I never quite understood that set up but I guess they used a heavy enough spring on the other post, to be able to pull the advance plate around and the cam action with the shaft football would retract the weight with the big loop spring to close it. Change the regular spring out for a lighter one and it no longer has enough tension to pull the cam plate around and allow the cam action to retract the other weight. I would find another medium weight spring to replace the one with the big loop and try that.

Ultimately it’s probably the best approach to use 2 springs of equal tension that will still allow you to reach full advance by 3,000 to 3500 rpm for the street. The lightest springs in the spring kits are usually no good for the street. Two medium tension springs usually work well but they have to be of proper length. You might check with Halifaxhops as he occasionally has Mopar performance spring kits for sale.

 

[Macdon221]

I have no doubt the springs are correct. It's a fresh dist from Hallifaxhops all tested and curved.

 

[lewtot184]

Check to make sure there aren't any snags in the throttle cable and make sure you have enough throttle return spring.
That cam closes the intake valve about 10 degrees sooner than a stock cam and that's significant! I feel very confident that your engine doesn't need an aggressive timing curve. I've found on stock or near stock engines they don't need a fast timing curve. Keep in mind a fast curve is just a crutch for low rpm inefficiency in the engine. You shouldn't have that problem. I'd try a heavier primary spring and limit initial timing to 10btdc at most. I use a 13 degree plate with 36 degrees total and the engine drives nice and burns reasonably clean. Look at the number on your stock advance plate. Most people on this website push a high initial timing. That's OK if your cammed up and vacuum is low but you shouldn't be experiencing any of that with a short cam. Don't let your butt dyno fool you.

 

[turbine68rt]

Back to the high idle again and just running very poorly.

Sounds like the secondaries may not be fully closing. When it hangs up in high idle, manually verify that the secondaries are fully seated and see if it changes anything or stays the same.