General backfiring question - 1930 60 series.

[michaelod]

Just have a general question related to backfiring in a 1930 Model 68 with the 331 6 cyl. engine. My car starts OK but seems to backfire repeatedly. I am not referring to a thunderous explosion that alarms the entire neighborhood, but rather a series of repeating popping noises coming from the exhaust along with some roughness in the engine while running. Any clues on what to look for?

Thanks,

[unimogjohn]

Michael, do you seem to need more choke to keep her smooth also? If yes, it is a dirty or plugged venturi. It sounds like your carb has some dirt/debris causing some restriction.

[Guest OLBUICKS]

Sounds like the distributor cap may have a small crack or moisture, or clean rotor, the tips under the cap, or points need cleaned or replaced and adjusted...

[michaelod]

John,

First let me thank you for your assistance. I don't think it would be an issue with a dirty carb due to the fact that I just rebuilt the carburetor a couple of weeks ago, making very sure it was thoroughly cleaned before putting it back together. I have the air valve set at the factory setting and that is the only adjustment available on the 1930 Marvel carb for this engine.

The distributor cap is brand new, as well as the rotor and condenser. I haven't changed the points yet so that may be a good place to start.

Thanks,

Edited January 25, 2010 by michaelod
text (see edit history)

[Guest mclbuick2002]

Michael

If it is popping around carb area it could have an air leak in heat riser or air valve could be set too lean. Check to make sure air flapper moves freely and you have the correct length of spring. Start with knurled knob flush with pointer. Then turn in to the right a 1/4 turn at a time until engine rolls.Then turn to left [leans] until engine hesitates. Turn screw back to right 3 or 4 notches at a time until engine runs smoothly.

My 331 runs best at 1 full turn to right from end of pointer.

Stan

[michaelod]

Stan,

Thanks for the tip on the carb setting. I pressed in a new heat riser when I recently rebuilt the carb and am pretty certain it is well sealed. The air valve spring is one found in the rebuild kit I purchased from Bob's, so I hope it is correct. At this time I have the knurled knob set flush with the pointer and have not yet experimented with adjusting it, however I will be sure to follow your suggestion in this area. The popping noise seems to be coming from the exhaust (I think) and is most noticeable around the rear of front pipe where it enters the muffler. I came across a message on the 1930 Buick group on Yahoo where a previous owner noted the same backfiring problem during the brief period he owned the car and I don't think he was able to resolve it. When I replaced the spark plugs that were in the car when I bought it, they appeared somewhat oily and very sooty and based on these it looked to me that the car was running too rich rather than lean. At this point I am thinking of installing some new points, properly timing the engine and adjusting the valves. In addition I will run a compression check. I think the engine is suffering from a general lack of maintenance at a minimum.

I just got the engine running about a week ago after having sat for about 4 years, so I am at the point now of just trying to figure out what I actually have. I am not able to run the engine for any length of time due to an overheating situation. A previous owner has removed the thermostat that control the radiator shutters and they are now unable to move to the open position. From what I have been reading, it might be best to fix them in the open position for adequate cooling, so I think this will be the next task to accomplish.

Thanks,

[trp3141592]

Hi Mike,

I had a similar problem with a Brand X-mobile several years ago. Do the spark plug wires in your Buick run parallel and bunched together at all? If so, the wires may be "talking" to each other by induction, especially if they are old, greasy, or cracked at all.

That was the case on my X-mobile. New wires installed so as NOT to run next to each other solved the problem.

--Tom

[Guest OLBUICKS]

Speaking of spark plug wires make sure you don't have one crossed... This car is a little older than ones I have, but it all works the same.. Firing order 153624?

[michaelod]

The spark plug wires are an issue that I have not addressed yet. I did replace the distributor cap and just swapped in the old wires from the old cap, being very careful to insure each wire moved over to the new cap in the exact same position. This however makes the assumption that they were correct in the first place. Although I think the firing order is correct, it is probably worth going back and check just to be sure.

My spark plug wires look OK, but they appear to have been on the car for a while. I see many cars of this vintage restored with some nice yellow fabric covered plug wires and am wondering if anyone knows where these can be purchased. I don't see them listed in Bob's catalog, but perhaps I missed something.

Thanks,

[Guest brh]

Sounds as though you may have some very minor issues to resolve and you'll be on the road to recovery. I'd replace the points, condensor and wires. This needs to be done anyway. If your engine is overheating while you have it in the garage, Dad and I used a box fan in front of the car to blow air through the radiator and keep engine temps down when working on our 34 Olds. You might try that if you can.

[Guest OLBUICKS]

Does it seem to back fire every time of a every revolution? You said it has not been started for 4 years,, I was wondering if a exhaust valve may be sticking..

[unimogjohn]

Michael, re the plug wires. Go to Rhode Island Wiring. They have several 7mm color wires from which to choose. Make sure you get the connectors (front and rear) to go with them. You will have to tell them how much in feet of the wire you want. They you just make up the wires yourself. An easy and fun little project. Rhode Island Wiring Service Inc.

On your carb, don't you have a little wheel on the bottom of the carb? If yes, close it all the way and open it until the notch on the wheel lines up with the post on the carb base. This is the factory setting. I have this wheel on both my 23 and 28.

[Dwight Romberger]

Hi Michael,

I got those pretty yellow fabric covered wires from Bob's page 14.

Dwight

Edited January 26, 2010 by Dwight Romberger (see edit history)

[Dwight Romberger]

once again

[michaelod]

John, I don't seem to have any wheel on the bottom of my carb and it does not appear that it ever had one. The only adjustment is at the air valve.

Dwight, Is your '30 the same as mine with respect to the carb?

Just went out to Bob's in an attempt to order those wires that are on Dwight's motor (which is looking outstanding by the way) and the new website is 'up' but not functional. I emailed Bob and asked if there is an alternate method of accessing his catalog online and he said the guy working on it 'broke' the old site in the process of bringing up the new.:mad:

[michaelod]

OLBUICKS,

The backfiring seems constant but rather random at this point. There does not seem to be any pattern to it.

Thanks,

[Dwight Romberger]

Michael,

No wheel on the bottom of mine.

The Marvel section of the Buick Master Parts List has different parts numbers for the 40's and 60's model's carbs. But I don't know how they are different. No pics in the parts list book. Maybe someone with a Marvel catalog could tell you.

Dwight

[Dwight Romberger]

Michael,

My unprofessional analysis of your backfiring is that is that one of the cylinders is not firing everytime (bad plug, plug wire, dirty rotor contact, bad points, etc i.e. an electrical problem) The unburned gas vapor is finding the proper oxygen concentration in the exhaust pipe and heat flash pushed out of the next cylinder expolsion. It gives you a semi-regular POP between the exhaust mainifold and the muffler.

If you can get a little richer mixture, you can blow up the muffler. That's real cool! Been there, done that. Model T's are notorious for it!

Dwight

[Barney Eaton]

I don't remember anyone above saying anything about an exhaust valve that is not closing or burnt. Run a compression check to eliminate that problem.

It could be you have two plug wires mixed...running to the wrong plug. Something is ignighting the fuel in the tailpipe.

[michaelod]

I just wanted to express my appreciation to all those who responded to my question about the backfiring problem. There are a number of good ideas here that should help me resolve the issue.

Thanks again,

[Dandy Dave]

I would also opt to check the valves. Also, take off the radiator cap and see if you see air bubbles are comming up in the water when you first start it and it is cold. If so, you could also have a bad head gasket, or a crack in something. This will make the car overheat rather quickly. These leaks will not always allow water to go back in the engine, but will allow air, under compression, to come out. Dandy Dave!

[michaelod]

Dave,

Thanks for that tip on the possible crack or head gasket problem. I will investigate that issue, although I certainly hope there are no cracks. A head gasket would be a relatively simple fix compared to the other situation.

Thanks again,

[Mark Shaw]

Michael,

I tried to look up your phone number in the BCA roster, but you are not listed....

[Dandy Dave]

Dave,

Thanks for that tip on the possible crack or head gasket problem. I will investigate that issue, although I certainly hope there are no cracks. A head gasket would be a relatively simple fix compared to the other situation.

Thanks again,

One other thing that came to mind. Be sure that there are no exhaust leaks that are blowing in the direction of the carburetor. I've seen this several times in the past on various cars and equipment. The leaking exaust will burn the fuel out of the intake before it gets to the cylinders. Dandy Dave!

[Guest ZondaC12]

Michael,

The unburned gas vapor is finding the proper oxygen concentration in the exhaust pipe and heat flash pushed out of the next cylinder expolsion.... ......If you can get a little richer mixture, you can blow up the muffler. That's real cool! Been there, done that. Model T's are notorious for it!

Dwight

Oooooo....I wonder if it was YOU that originally corrupted me. :eek: Maybe not, all I know is that trick I learned from someone on here that claimed to have "once owned a model A back years ago". I've become a rather eeeevil person over the last few summers with that. *snicker*. The height of it has definitely been this summer, I heard about my actions directly. A buddy of mine was eating with his date at the same Cheesecake Factory I decided to drive by and "liven things up a little" and he texted me later that night when I was back at the McDonald's parking lot (the essential local fri/sat night hotrod/rice rocket hangout) asking me WHY THE HE-DOUBLE-HOCKEY STICKS I did that!!!! I actually got like 5 people together from "the lot" and showed them what I was talking about. The 38 was the life of the party that night....ugh I miss summer!!!!

My exhaust is *still* composed of nothing but cheap-o flex pipe. It and the $19 special muffler have withstood these shenanigans amazingly.

[Dwight Romberger]

I didn't do it on purpose! But it was LOUD!