Backfiring out of the carb

[charles@pricefarrington.c]

Took her out today. A few months ago, I had backfiring out of the carb I attributed it to blow by smoke in the engine. Since then I put in a PvC kit and all seemed good until today. It seems the engine runs fine; but putting it in full throttle; I don't have a tach; but at a level she seemed to run fine previous; she's now back firing out of the carb. She'll run fine at a little less throttle. Electronic ignition etc.. I have not check the plugs etc but I am running MM recommended plugs. I have to admit, I have not run MMO oil in the tank for at few tank fills, probably 25 hours.

Any thoughts?

[roadnsky]

Backfiring would, in theory, mean a serious TIMING PROBLEM...

Is there any reason for your timing to have changed?
Have you examined your plugs? Oily?
Are you certain you have the plug wires correct?

Try removing wires one at a time while the engine is running and see if you notice a change.

Sorry if these are obvious. I'm not intending to offend. Just "prime" the pump...

[charles@pricefarrington.c]

No problem. Basics are the best. I would not think that the wiring is incorrect since I ran her about 50 hours on a trip this summer with no issues other than blow by. Of course it's possible since i used the same order that was on the boat. Maybe that was off to start with. But it does not seem consistent. After sailing, we fired her up and I ran it hard for about 5 minutes and no issue...

[tenders]

Are the wires leaving the distributor and, reading clockwise and sequentially from the distributor, going to plugs #1, #2, #4, and #3?

Your symptoms sound as if you have two reversed. You're running on 2 cylinders, and at high speeds one of the other two are igniting the fuel on the exhaust stroke, much to the valves' surprise.

How's compression? I suppose you could also have a valve that's sticking open at high speeds.

[Marian Claire]

Sounds all too familiar. I could run at 2000 rpm but at 2200/2400 she would backfire out the carb and start to die. Drop the rpms and she was fine. Backfiring out the carb can be caused by a lean condition. My leanness was due to an air leak in the throttle shaft. My post “Persistence Pays” gives more details. Check for an air leak along with the other ideas. Is this your new carb? Maybe the carb PVC kit spacer connection since that is new??? Good luck. Dan S/V Marian Claire
More thoughts: The first thing Don had me do was back the main jet out a little. Is yours adjustable? If chocking helps stop the back fire and allows it to run at the higher RPMs then I would look for an air leak.
It is -4 here and I am stoking the fire and thawing out the kitchen cold H2O feed. So a little disorganized.

[charles@pricefarrington.c]

Yes, this is the new moyer carb. Does it have a main jet adjustment? Not sure. I will check the pvc connections and the wires etc...

[ArtJ]

Not sure this will solve your problem, but the flyweights in the
distributor are related to advancing of timing issues. It wouldn't hurt
to disassemble the distributor and check /free/ lubricate them. Check other
recent posts for more info on sticky flyweights.

Regards

Art

[Dave Neptune]

Charles, check the weights in the distributor as they could have broken loose and you could be way to advanced now if indeed that happened. If you haven't changed anything, no need to check on firing order.
It could also be a back-pressure problem in the exhaust unless it isn't to old.
Check the dist. weights first and be sure they move freely. Then do the poower timing, if the problem persists look at the back pressure.


Dave Neptune

[charles@pricefarrington.c]

How hard is that to do? Do I need to pull the distributor?

[charles@pricefarrington.c]

Ok, found this. I am hesitant to take the distributor out, this may be over my abilities, and it does not seem to say you have to correct?

Don has published on the forum several snippets from his newsletter compendium. Here's the info mentioned above. I'm not sure whether it's been uploaded in this form, but it is freely provided here:

INSPECTION AND SERVICING DISTRIBUTOR:

1. Note the mounting of the condenser and points, and remove them (one small screw for each).
2. Remove the points and the condenser mounting plate by removing the two small retaining bolts on each side of the plate.
3. Inspect, clean, free up, and oil the centrifugal advance mechanism. This is very important. Approximately half of the engines I disassemble for overhaul or for parts have their advance mechanism rusted tightly in place. Carefully take a small screwdriver and check the flat fly-weights for freedom of movement against their small springs. If both are free, simply wash the mechanism with gasoline, dry thoroughly and re-oil with a light oil. Marvel Mystery Oil works well.
If the mechanism is rusted, you’ll probably have to remove its two small retaining bolts and disassemble the mechanism for cleaning. The good news is that if you found your advance mechanism in this condition, you will be greatly improving the performance you have been getting from your engine. When these mechanisms are rusted, they are almost always stuck in the zero advance position.

REASSEMBLY OF THE DISTRIBUTOR:

1. Reverse the previous steps and replace the condenser and points....
2. With the mounting screw for the points slightly loosened, slide the lower plate of the points back and forth, so that with any one of the four lobes on the shaft holding the points at their most open position you measure a gap of .025” across the points for late models (Delco), or .018” - .020” for early models (Prestolite).

REINSTALLING DISTRIBUTOR:

1. With rotor installed and positioned as it was during removal, slip the distributor carefully back into its mounting hole.
2. Reinstall the hold-down plate and rotate the distributor so that the alignment notch lines up with the point of the rotor. Rotor should now be pointing generally away from the block as it was prior to removal.
3. Connect the primary lead to the negative terminal of the coil, and re-time engine as per Newsletter #5 (aren’t you glad now that you had that course first?).
4. Inspect and clean the distributor cap. If there is any indication of a crack or other damage, replace with a new cap.
5. You should now be able to crank up your engine and bask in a job well done....

[sastanley]

Charles, I found that the distributor removal was not hard...the biggest issue is remembering the rotor position..if you have a hand crank (i do not, but it is on my list for 'next purchase', and I will be drilling a hole in my engine box to accommodate access to the flywheel), I would recommend you set the engine @ TDC before removing the distributor...take special note of the rotor location prior to (pictures!!!) and then make sure it is the same when you re-install.

I yanked mine at 'wherever it was' and had to start from scratch. I have a C-30 so the flywheel is not really visible without a big hole in the dinette seat box...I used a small mirror on a stick to try and set up TDC. By the way - TDC is when there is compression at cyl #1 and the roll pin on the flywheel is vertical...there has been other discussion here on how to do that as well.

I am pretty sure I found all this data in the Moyer Manual..do you have one of those yet? The little distributor parts made me apprehensive also, but I had no trouble using the book as a guide, and I am sure mine hadn't been cleaned in many, many years, although they were not frozen. I cleaned mine up when I had the distributor apart installing the electronic ignition.

edit - incidentally, I think you can check the weights themselves with the dizzy in the boat..however, you probably have to remove the breaker/electronic module plate as they are underneath. I do not think I would attempt to disassemble past the plate in the boat though..a nice well lit workbench if I have to do more than that. Those pesky little screws get awfully small in the bilge.

[charles@pricefarrington.c]

Ok, I do have the manual. For some reason, messing with the distributor, yanking it out, causes me concern. I'll have to assess the matter this week and report back. Pictures are a good recommendation. So my list is:

1. Check wiring;
2. Check for leaks in fuel lines; connections; and
3. Check weights and springs in distributor, clean as needed.

[Dromo]

Maybe I'm missing something, But I don.t think you have to remove or move the distributor housing to service the weights
It just makes things easier
Rick

[rigspelt]

I found it was quite easy to remove and replace the distributor, but I had to learn how to reinsert it with #1 facing the right direction to set up the timing and make sure the alternator belt would not rub on the nearby distributor cap bolt hole nub. Much easier to service removed. Good education for me, actually.

[charles@pricefarrington.c]

Assuming the above stuff checks out, would the idle adjustment have anything to do with the carb backfire at high speed? and/or should I be thinking about purchasing an adjustable main jet?

I have not gotten back to the boat yet and probably won't this weekend, we are building a pinewood derby car for the race in the next two weeks, a little behind schedule on that project.....

[Dave Neptune]

Charles, by the time you are into the "hi-speed" circuits of the carb the idle screw will have very little if any influence to the mix. The adj. jet will not fix anything unless the "main jet is plugged" to begin with, it is just another goodie for dialing in the performance characteristics you desire.
You do have something amiss that is causing her to backfire out the carb, the first thing to check is the overall timing. If the timing is to far advanced, or in some cases a carbon trail inside the dist. cap will fire a spark while the intake valve is still open and she'll spit back out of the carb. If it is "JUST" the timing a simple adjustment to retard the timing a bit should work. If you have a carbon trail in the cap the spark can be diverted from the intended plug (cylinder) to another with less preassure (compression) and/or resistance causing this type of a problem in many cases. How fresh is the cap and how long since a tune up? This can also be caused by a crack in the cap as well. If you have not moved the dist and the centrifugal advance is moving freely the above seems more likely.
How did you fare in the Pinewood derby?

Dave Neptune

[charles@pricefarrington.c]

Great. Thanks for the comments. We've built the car and polished the wheels and axles. The derby is on the 29th. I'll keep you posted on the results.

[charles@pricefarrington.c]

Ok, I'm at the boat and opened her up and first thing I did was grab the distributor and oops, it moved pretty freely. The hold down bolt is loose. I am almost 99% sure this is the problem. I won't take her out today as it started pouring rain but I will take her out with the captain, my wife, this week and adjust the distributor and tighten it down.

I'll provide the final results upon completion.

[charles@pricefarrington.c]

I have not made the final tune on the distributor yet, but the results of the pinewood derby are in... my son took 1st in his den and 2nd in the grand finale out of about 35 cars. The one we made for the open class took 2nd overall as well. Fun stuff. He now wants to use his car for off road, but I have to remind him he gets to go to the regionals next....

[charles@pricefarrington.c]

Made it to the boat yesterday and played with distributor to no good result so pulled off the cap and here is what I found. Put on new cap but not a rotor and she ran a little better. The cap was a Niehoff DR-74, not sure about the rotor. My guess is neither part is correct given the damage to the cap I saw. I am going to order a set from Moyer. I am surprised she runs as good as she does with this cap.....

[ArtJ]

If you need the cap and rotor in a hurry, you can get them at any parts store
just ask for a cap and rotor to fit a 62 chevy nova 4 cylinder engine.

[charles@pricefarrington.c]

Made it to the boat yesterday and played with distributor to no good result so pulled off the cap and here is what I found. Put on new cap but not a rotor and she ran a little better. The cap was a Niehoff DR-74, not sure about the rotor. My guess is neither part is correct given the damage to the cap I saw. I am going to order a set from Moyer. I am surprised she runs as good as she does with this cap.....


Great. Does that work with electronic ignition as well?

[ArtJ]

The cap should be identical to the original part. By the way, the 62 chevy
is called a chevy 2. The Nova was a few years later I believe.

[ArtJ]

I am not familar with the ignitor distributor. If the cap is still the same
as the original delco cap, it will work properly.
The cap will definitely work with the original atomic 4 delco style distributor.( some engines had Prestolite distributors which would be different.)
The cap will also definitely work with the Indigo electronic ignition since it
is external to the distributor.
I have used these caps, rotors with my delco distributor and indigo for years.

[ArtJ]

From the moyer catalog, it looks like the Delco cap has been modified to work with the Petronix (sp?) distributor. Depending on how extensive the mod is
you may or may not be able to use the Delco cap. Suggest you find out what
the mod is. Perhaps that is what happened to your damaged cap?