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tdpole1

'29 Buick back firing and hesitating at speed

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tdpole1    1

My 29 Buick 6 cyl. standard has started backfiring and hesitating to the point of shutting down when running 50 +- on the road.  Still haven't gotten the speedometer working although I did find the correct cable but not the drive gear.  Anyone got a clue as to why the car would have started doing this.  If it quits running after backfiring and very jerky hesitating I pull off the road wait a minute or less and it fires back up.  It never does this when riding around town and 35 mph or so.  I think it may be flooding out due to the float not working properly.  I am still using the original fuel pump and do not have an electric booster on it.  Any Ideas?  If I need to rebuild the carb where do I find the serial number etc on it?  I can barely read the work Zenith on the side of it so the numbers may be long gone.

 

Thanks,

Tad

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raydurr    21

Tad , it could be several things causing this driving condition. A very common issue with the Marvel carb and heat riser is the development of pin holes in the heat riser tube. It is a sheet metal tube pressed into the heat riser housing. It allows exhaust to enter the intake charge. It will only get worse until the heat tube is replaced. The Marvel carburetors are prone to many issues as well such the venturi flap sticking. You will probably have to start a systematic elimination of all things ignition and carburetor/intake related to resolve the issue.

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pont35cpe    63

Check the points for the proper gap, when the points rubbing block wears down it will close the point setting, resulting in backfiring and hesitation under acceleration..  Tom

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Mark Shaw    381

I agree with Radurr..., but first disconnect the fuel line at the carb. to be sure you have full flow and are not just starving the carb. with dirt in the line.

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raydurr    21

I would like to add some of my experiences with my 29 Buick carb. If the car sits for several weeks  the jets seem to partly stop up resulting in the lean/ back fire pop. Sometimes it clears up with some aggressive driving while pulling the choker closed suddenly. Also the air valve tension controlled by the large 1 inch diameter screw may need a very slight adjustment. A little goes a long way here.

A steady, full volume fuel supply must be maintained. A weak fuel pump or blocked line can cause this condition. A fuel pump with an old rebuild can be affected by modern fuels. Distributor wear is a very real situation .Worn  or improperly adjusted points. Intake manifold gaskets should be checked. Check the heat tube. Last but not least , make sure all the fuel is fresh. Old fuel does not vaporize like fresh fuel does.

Good luck!

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tdpole1    1

Thanks everyone for the good ideas.  I have gone through the carburetor and cleaned a lot of crude out.  Filed and reset the points.  It seems to have solved the problem but I have not had the time to take it out on anything but residential streets yet.  Will know this afternoon ass I plan to go out where I can get it up to speed.

 

It looks like I am going to have to remove the gas tank, clean it out and use a sloshing compound as it is obviously rusty judging from the stuff the the filter and carb.

 

Still trying to get my speedometer working.  I found the cable and the speedometer head is working fine.  Ordered the gear housing from Bob's and now looking for the drive gear.  Anyone have a source for this scarce item?

 

Again thank you for the help on the back firing problem.

 

Tad

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