218 rough idle

[ol'skool]

Been dealing with an idle issue since a rebuild and modifications. List of modifications,

1. Dual Carter B&B carbs on a stock split intake

2. 12v negative ground

3. Petronix conversion

Stock engine rebuild. Block is dated 1952. 218ci from a Plymouth.

What's been happening is the idle is poor. Rough.

It smooths out very nicely, accelerates nice and smooth and car cruises very nice.

Timing is set at 2-3 degrees.

Vacuum reading was 13

Can't set idle less than 525-540. Anything less, it stalls. Fire right back up.

I advanced the distributor and idle smoothed out and sped up. However, the dizzy is turned as far as it can go in the slot. I know the timing is probably in the 10 BTDC. I haven't checked it to get an exact number. Using a stock 12V coil, no ballast.

I ordered an original replacement distributor breaker plate with points/condenser. Thinking about changing back to points. I've had issues with pertronix in the past.

Distributor is an IAP-4103A if I remember correctly.

Trying to get an idea of where to start. It idles great now but the timing is too far advanced. Don't want to drive it until I get it dialed in. The vacuum now reads 17 -19 range.

Any ideas?

[Jerry Roberts]

 "Trying to get an idea of where to start. It idles great now but the timing is too far advanced. Don't want to drive it until I get it dialed in. The vacuum now reads 17 -19 range. 

Any ideas? "    So are you saying that everything is fine now or that the timing is too far advanced causing it to run bad at higher rpm's ?  If everything is good ...  take it for a drive . 

[ol'skool]

If I set the timing back to the recommended range, it doesn't idle, and I have to set it(timing) well above the recommended setting just to keep it idling on its own. By advancing the timing, it helped but the underlying issue is there.

[deathbound]

Can you be more specific with the vacuum. If it fluctuates from 17-19, something is wrong.I believe there is a screw holding the bracket to the dizzy, which may have some more adjustment.

Here's a link on vacuum readings:http://www.secondchancegarage.com/public/186.cfm

[ol'skool]

The gauge moves a little bit. From what I could tell it was in that range. It wasn't fluctuating like it was before I advanced the timing. It did hold fairly steady.

[suntennis]

Had a problem with a rebuilt engine not running right with the vacuum 17-19. One odd thing with my problem was when I pulled spark plug wire number 5 at idle, it made no difference in rough idle. The same thing also occurred when I pulled spark plug wire number 6 (this was done one cylinder at a time). The 17-19 vacuum is one indication of a sticking valve. When the valves on cylinders 5 and 6 were checked, it was discovered that one of the two valve keepers on number 6 exhaust valve had fallen off during assembly and was laying next to the valve spring. Normally when a plug wire is pulled while the engine is at idle it causes a noticeable miss. Hope this helps

[Don Coatney]

Have you  done a compression check? How do your spark plugs "read"? Is your engine running hotter than normal? Have you synchronized your carburetors using a synchronization tool as pictured below? 

 

[ol'skool]

Carbs are synced.  Running 180 degree t-stat.  Aluminum radiator-New.  The temp runs 170-180 and the 25 miles I drove it last year didn't go above 180.  Yes, it was idling poorly then also.  I had tuned everything that I could the best that it would go last fall.  I will be rechecking carbs, setting idle mixtures, checking compression, checking plugs.  I don't know if this maybe the cause and that is I read there is a difference between the IAP and IGC distributor caps or something like that.  Might have that mixed up. I know mine doesn't feel like it's secured on the distributor. I have to check into that.  What is the difference between the caps, they look identical?  Thanks Don, I have 2 of the Uni-Sync synchronizers.  Right now with the timing advanced, it idles really good but I know I can keep it that far advanced.  Is there a chance the lower crank pulley is off.  Mine has a slight wobble to it.  Still trying to locate one.  Could the outer ring have slipped, it didn't feel like it could have when I inspected it.

Edited March 13, 2016 by ol'skool

[dpollo]

Check your distributor cap.  The  IAT cap is noticeably smaller than the IGS and uses a rotor with no counterweight.

 

It fits tightly.

 

I ran into this problem on a 50, which was the change year for the distributors . The symptoms were similar to yours.

[ol'skool]

Check your distributor cap.  The  IAT cap is noticeably smaller than the IGS and uses a rotor with no counterweight.

 

It fits tightly.

 

I ran into this problem on a 50, which was the change year for the distributors . The symptoms were similar to yours.

 

I will check into the rotors.  I know the distributor is a donor from another car.  The one that was in mine was rough so I got a donor out of a 51 or 52.  If I remember right, I have the rotor without the counterweight.  These are the 2 that are available from rock auto as they get credit for the photos.  I'll have to check.  I see the rotor without the counterweight is for an IAT distributor, mine is an IAP so that could explain.  So if they both fit the distributor, why would the one cause an issue with idling.   

Edited March 13, 2016 by ol'skool

[Jeff Balazs]

If the cap does not fit securely then that is where I would start.

 

Jeff

[dpollo]

make sure it is the correct cap.  They do fit securely.  

[Plymouthy Adams]

ol'skool, on 13 Mar 2016 - 09:15 AM, said:

 

Carbs are synced.  Running 180 degree t-stat.  Aluminum radiator-New.  The temp runs 170-180 and the 25 miles I drove it last year didn't go above 180.  Yes, it was idling poorly then also.  I had tuned everything that I could the best that it would go last fall.  I will be rechecking carbs, setting idle mixtures, checking compression, checking plugs.  I don't know if this maybe the cause and that is I read there is a difference between the IAP and IGC distributor caps or something like that.  Might have that mixed up. I know mine doesn't feel like it's secured on the distributor. I have to check into that.  What is the difference between the caps, they look identical?  Thanks Don, I have 2 of the Uni-Sync synchronizers.  Right now with the timing advanced, it idles really good but I know I can keep it that far advanced.  Is there a chance the lower crank pulley is off.  Mine has a slight wobble to it.  Still trying to locate one.  Could the outer ring have slipped, it didn't feel like it could have when I inspected it.

 

you have two synchronizers....are you using them both at the same time as in one on each carb and if so have they been balanced to each other?   I recommend only using one unit when balancing, rules out the time factor in balancing the two at both idle and high speed for proper baseline and linkage adjustment.  Use of a piston stop/dial indicator in access hole at #6 can help you determine if you damper timing indicator is correct. 

[Jerry Roberts]

Your distributor cap must fit snug and it should feel like it drops into place correctly . Time to purchase another cap using your distributor model number .  

[ol'skool]

I've been thinking about checking the timing like that Plymouthy Adams.  I did remove the plug but there is debris plugging up the hole.  I'm debating about drilling small hole through the stuff but don't want to push the crud down into the cylinder.  My comment to Don was that I have 2 uni-sync and I even have a 3rd type synchronizer.  I know not to use them like that.  The idea had crossed my mind that I do that but I would have to calibrate them both on the same carb and then go from there but it seemed like time was wasted that way.  Might have made it easier to sync.  

[Don Coatney]

The distributor cap is "keyed" with a slot in the housing and a protrusion in the cap as pictured below. When installed correctly the cap should not spin independently of the distributor body. If your cap does not lock in place you have the wrong cap.  

 

 

[ol'skool]

That is correct Don.  Mine does that.  I'm wondering if the metal hold downs have lost some of their tension.  I did come across an old article about that on these IAP distributors.  Here's part of it:

 

•DISTRIBUTOR CAP POPPING OFF CORRECTION

(Early "IAP" & "IAR" Distributors):

May be caused by one or both of the following conditions and can

be corrected as indicated:
Distributor Cap Hold-down Spring Clips Incor-

rectly Formed—Lip at upper end of spring clip fit- ting into recess in cap may have too large a radius to permit spring to seat securely in cap recess. Cor- rect by pinching the spring together at the end.

Ruptured Vacuum Control Unit Diaphragm (al- lowing fuel vapor to collect in distributor and blow cap off when ignited by spark)—Install new vacuum control unit and make certain that mounting brack- et has ventilating hole on underside (see illustra- tion) . If bracket does not have this ventilating hole, drill a 5/32" hole at this point.

NOTE—This ventilating hole provided in produc- tion on later distributors. 

[Don Coatney]

Cap should lock in place with a slight down hand pressure before the spring clips are installed. Once locked in place it takes very little pressure from the spring clips to hold it in. I have never had to pinch the spring together at the end on any distributor I have ever worked on. 

[soth122003]

Are the timming marks on the damper in line with TDC on the #1 piston? If you have a 17-19 reading on the vacuum gage and idle is good, then I would suspect the timming marks. What is your idle speed currently?

[ol'skool]

The cap and rotor are correct for the car.  They are older so I ordered new ones today.  I'm going to change out the coil to a similar one to the pertronix flame thrower.  Just thinking possibly the coil I have is internally reduced.  I couldn't find anything on that when I looked it up and there isn't any printing on it stating either way.  I know the pertronix likes a full 12V to it.  They say bypass, get rid of any resister.  Also going to locate TDC and check reference to the timing pointer/marks.  That will be tomorrow though.

[Jeff Balazs]

Having a matched coil is an important part of doing the Pertronix conversion. Most of the problems I have heard about with this conversion are caused by mismatched components and not following the instructions carefully.

 

Jeff

[ol'skool]

Yes, that's what I'm thinking part of the problem may be.  I fried a pertronix last fall on an old pontiac.  It didn't have a ballast resister so I didn't worry about it until I came across an article that they used separate wire that reduced the voltage to the coil.  It was too late for the pertronix by then.  Put the points in with a ballast resistor and the car ran so much better. 

[Jeff Balazs]

I have a 6 volt positive ground system with the Pertronix trigger and matched coil.

There has been some naysayers.......but I have to say this set up is as good as it gets.

It gets a big thumbs up from me. Mine has been absolutely faultless.

 

Jeff

[ol'skool]

Finally, was able to check for TDC.  Mine is dead on between the marks and number 6 cylinder check.  I can set the timing at 4 degrees and set the idle at around 500-525 and it runs ok, stumbles off idle then smooths out.  Any lower idle or timing then it runs like crap and starts to stall out.  I got a new breaker plate with points.  I think I'm going to put that back in and see if it improves.  First, I'm going to check the vacuum advance and make sure that's working properly.  My understanding is that it's a ported vacuum source from the carb.  

[Jeff Balazs]

You may also want to check what sort of vacuum reading you are getting at idle.

Jeff