1933 backfire questions- ongoing !

[Guest outlaw car man]

Hello -

Getting frustrated with this problem of backfiring in the muffler on my 1933 Buick.

Easy just to list what keeps going on. A lot of this has been posted before in parts.

1) car ran perfect till I had to remove the Marvel and it was covered with gum inside. Took it apart, cleaned it checked all the jets, set the float, new gaskets- Done this before on Marvels so kinda have an idea how to

2) I can get the car to idle real nice with a little manual throttle- Set the air V the same

3) smells like it's running rich, so backed the Air V to lean till it starts to die, then slowly turn back to a good idle

4) It runs up real well, but maybe not as fast as I remember, like it's slow to bring up RPMs, where before I could hand open the throttle and it would run right up. ( I think )

So, I run it up and it back fires no matter what I do. Seems like I can run it up slowly and back down with minimal backfire, sometime, but SLOW.

5) I tried pulling the Spark advance out, ran bad and backfired.

I can't think of much else to do , except take the marvel off AGAIN and check the high speed jets, maybe some gunk got back in- I can , unfortunately, do this in my sleep now !

Waddda think ?

Sandy Jones

Outlaw Car Man

PS- Hope all our Buick pals & gals are doing OK back East with Irene !!!!!!!!!!!!!!

[Mark Shaw]

Backfire is just about guranteed the instant you run out of gas. I still run the original vacuum tank fuel system in my 24 PU & when the system cannot keep up it backfires. This only happens at full speed when fuel demand is at maximum.

(I need to check again for vacuum leaks and double check the filter screen at the bottom of the vacuum tank).

I think you are running a bit lean. If your car backfires when you ramp up speed, I suspect it is fuel starved. I suggest you double check your carb settings and fuel filter.

Edited August 28, 2011 by Mark Shaw (see edit history)

[Bob Engle]

Hi Sandy: I missed all of the storm. Have you set up a vaccum gauge to see what kind of manifold vaccum you have? Low manifold vacuum will not vaporize the fuel and the droplets will cause a backfire. You might play with some different size jets to see what effect they have on the condition. Of course, poor ignition will cause the same problem. Check the timing and mechanical flyweight advance in the distributor.

Bob

[Guest outlaw car man]

Hi Mark,

Thanks- Haven't really checked the filter, just a visual inspection. It's running on the glass bowl filter on the dual pump.

Since I can't ramp it up with any good positive reaction, I'm thinking starvation, which leds me back to thinking the intermediate or high speed jets are AGAIN plugged. Which takes me back to the evaporation of the ethanol we have in our fuel. ( we've had a week of record high temperatures ) Really getting damn sick of cleaning 1933 Marvel carburators !!!! ( if this is the case again )

Also thinking fuel pump problems now which the ethanol also destroys. I rebuilt the one on the G-90 but haven't touched the one on the B-90-

just part of the deal with these old birds. Used to have the same problems with my 1933 Essex Terraplane 8, but a lot easier with Carter carb.

Thanks,

Sandy

I think you are running a bit lean. If your car backfires when you ramp up speed, I suspect it is fuel starved. I suggest you double check your carb settings and fuel filter.

[Guest outlaw car man]

Hey Bob, was thinking of you back there with your car collection. Great news-

OK, I haven't checked the vaccum as I don't have a vaccum guage. The wipers do work real well, my only clue. I've checked the jets, which are the correct size, in my Marvel parts book. ( little #s on the side of the jets), also they are/were open and clear-

Good idea to check the other side, see if one of the springs is catching or something on the flyweight, never done that, but heard it can be a problem.

I'm just getting frustrated with this ongoing problem, as you well know from the past.

I do have an ace in the hole, I have a spare Marvel that I rebuilt, that I can stick on too. Shouldn't have to this sort of semi-drastic measure....

thanks again, glad you guys are A-OK.

Sandy

Hi Sandy: I missed all of the storm. Have you set up a vaccum gauge to see what kind of manifold vaccum you have? Low manifold vacuum will not vaporize the fuel and the droplets will cause a backfire. You might play with some different size jets to see what effect they have on the condition. Of course, poor ignition will cause the same problem. Check the timing and mechanical flyweight advance in the distributor.

Bob

[jbbuick22]

Backfiring in the exhaust is usually ignition related, points, cond. coil etc.

JB

[Graham Man]

Sandy,

When did it run good last? If it was only after cleaning the marvel I would stick with that as the problem. I have been told the new ethanol fuel needs to run richer to get the same carburation results (airplane guys have lots of problems, my Carters run ice cold). I have rebuilt all my fuel pumps with new materials that will withstand the ethanol...had one die and that was enough for me.

Good luck,

Graham Man

[Guest outlaw car man]

I kinda have two posts going with the same issues, sorry about that, guess it doesn't matter- Heading back to the carburator. Car was running excellent till the last Marvel clean. That's next. ( again & again )

Thanks,

Sandy

Sandy,

When did it run good last? If it was only after cleaning the marvel I would stick with that as the problem. I have been told the new ethanol fuel needs to run richer to get the same carburation results (airplane guys have lots of problems, my Carters run ice cold). I have rebuilt all my fuel pumps with new materials that will withstand the ethanol...had one die and that was enough for me.

Good luck,

Graham Man

[FLYER15015]

Hi Sandy,

When I recently tuned my '40, after cleaning the plugs, I found her to backfire thru the carb when I cracked the throttle if the mixture screws were in too far (lean). At 3 turns open she does not backfire at all. At 2 1/2 she will cough a bit, and at 2 turns she'll send flame up the carb. So she's now @ 3 turns, and runs fine. I also validated ( with my harbour frt vacuum pump) that the vacuum advance line/diaphram/dist plate were working properly.

Just an FYI for you to consider.

Best Regards,

Mike Simpson

Buena Vista

[unimogjohn]

Sandy, agree with what everyone is saying, but check your spark plug wires. One might be loose or you might have a couple on the wrong terminal/distributor cap.

[Guest 1922 Buick]

Hi Sandy,

Check your distributor weights.

1922 Buick

JBK

1918 E45 Original car

1918 E45 Under restoration

1918 E45 Parts car

1920 K45 Parts car

1922 6-49 Restored, Seven passenger

1926 Model 20 Restored

[Guest outlaw car man]

That's about the only thing I haven't done- If you refer to my last post on the 1933 Marvel question on this forum , I've done most of this, timing, weight look new,manual spark advance set correct, points, plugs etc.

I pulled the Marvel off yesterday and it was gummed up AGAIN. ( see my posting about that )

If it quits raining, I'll fire it up. Since this has happened before, kinda thinking this is going to be an ongoing problem.

If it continues, I'll head to an intake valve and a vacuum check.

Then a stick of dynamite. ( never )

Thanks for all the comments. Keep you posted.

Sandy, agree with what everyone is saying, but check your spark plug wires. One might be loose or you might have a couple on the wrong terminal/distributor cap.

[Guest Straight eight]

Have you added any fuel suppliments to counteract the ethanol?

[Terry Wiegand]

I keep telling these guys that Marvel Mystery Oil is about the best additive that has ever been developed.

I add about a teacup full to every gas tank fillup. I have had absolutely no problems since starting that regimine. My Dad awore by the stuff and he was not wrong. Think about this - Marvel Oil was developed to help counteract the low octane fuel of the early 1920's.

The fuel was crap back then and it isn't any better today. Stay absolutely away from that ethanol or start running a mix of 50% aviation gas and 50% regular unleaded. I do not do this because we can still get straight regular unleaded gasoline in Kansas. Try the

Marvel Oil and report back to this forum about the results. You have nothing to lose except problems with your fuel system.

Terry Wiegand

South Hutchinson, Kansas

terrywiegand@prodigy.net

Phone - (620) 665-7672

[FLYER15015]

Hey sandy,

I've been reading your posts for a while now, and i've noticed "gummed up" jets comes up a lot.

What kind of fuel filter are you running ? Is the "gum" old evaporated gas, or foreign objects, like dirt or rust particles ?

If your carb is that sensitive in the jets etc., I'd try 2 or 3 filters in a row just prior to the carb, down someplace where you can hide them.

Just an idea.

Best regards,

Mike in Buena Vista

[Guest outlaw car man]

Gum, Marvel Mystery oil etc.

Thanks for the kind replys. I've been using Marvel Mystyery Oil for years, discovered it way back when I was flying an antique airplane. Great stuff for all sorts of applications, totaly agree.

Mike, it's gum that's coming through disolved in the gasoline, to my knowledge the inline filters will only go after solid particles. Someone should invent a filter that takes out dissoloved contaminents in gas.

I do use Stabil and Sea Foam too.

I'm now thinking Mark Shaw's comment about the ethanol cleaning out the car's system and depositing it in the carb may have some real significance.

I got the Marvel off, cleaned and back on , raining like hell out so haven't fired it up yet.

A friend of mine & I have been discussing this, the tank could have gummy stuff sitting in it and the alcohol keeps cleaning it out and bringing it forward, then gets left in the wonderful Marvel carb jets from evaporation.

The Marvel is spotless clean , sitting on the car, if the rain will let up, I'm going to fire it up and see if it backfires. If it does not, means the tiny jets are clean and not starving for gas and backfiring.

IF it doesn't backfire, I'll run it for a time and see what happens. IF it starts backfiring again, and the jets are all gummed up again, then it means a tank pull and cleaning. And Mark's theory is correct. The 1933 Marvel isn't helping matters either.

If it backfires with a clean Marvel, I go to vacuum checking.

It's only a machine, right ? HAAHA ( I think HHAAHA)

Sandy

[FLYER15015]

Sandy,

I think your going to have to pull the tank. Seafoam is a slow solvent, somewhat like Toluol paint thinner. I think what your doing is dissolving the "gum" in your tank and sending it straight to the smallest orifice in the carb, where it sits when you park the car. The ethanol in our gas just exacerbates the problem.

I got lucky w/ my '40 when I first got her, in that I noticed the gas tank straps were "paper" thin and needed to be replaced, and the fuel sending unit was not working. I pulled the tank, and took the sending unit out, and noticed a bunch of crap in the bottom of the tank.

My solution was first a mixture of 1/2 MEK and 1/2 Toluol (fast and slow solvents) from the hdwr store, 2 quarts each. Taped up the holes and let her sit for a day. Then a good cleaning @ the local car wash down thru the sending unit hole. Upon installation, I put the biggest see thru filter I could find @ Autozone right @ the tank.

I do have a glass bowl filter @ the carb, and I have noticed a "gel" in the bottom of it when I let her sit for a while.

Mike in B.V.

[Dandy Dave]

Watch that you do not have an exhaust leak that is reaching the intake of the carb. If it is hot enough, it will burn some of the fuel before it reaches the cylinders and cause a back fire. Dandy Dave!

[Guest 1922 Buick]

The list of ethanol-free gas stations in the U.S. and Canada.

Ethanol-free gas stations in the U.S. and Canada

1922 Buick

JBK

[Guest outlaw car man]

RESULTS:

After removing the 1933 Marvel, cleaning it, setting and reinstalled, the car runs better then it ever has.

Bottom line from this, is there is gum forming on the jets, impedding the flow of gas, thus causing backfiring.

Best cure, clean the fuel system, the ethanol has nothing to clean and bring forward and leave on the 33 Marvel jets.

Thanks for everyone helping on this problem, went full circle, but needed to, to find the problem.

Now, the other 90 !!!!

[JerryVan]

I had a gummed up Marvel carb too that gave me fits and was nearly glued together with gum. Had never had a gum problem before I began to use MARVEL MYSTERY OIL! Don't come with a mile of me with a can of MMO!

[Guest outlaw car man]

Jerry,

May have a good point here, I don't use that much in the gas, but cover the internals of the cast carb parts with it.

Doing a personal experiment with the two cars, with additives & without additives.

Got to do something, but one seems to be running OK now, that has the additives in it. Other , just got the left side done on the engine.

Thanks-

OCM

I had a gummed up Marvel carb too that gave me fits and was nearly glued together with gum. Had never had a gum problem before I began to use MARVEL MYSTERY OIL! Don't come with a mile of me with a can of MMO!