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Joined: Nov 2003
Posts: 51
Shade Tree Mechanic
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OP
Shade Tree Mechanic
Joined: Nov 2003
Posts: 51 |
My 1933 Master Engine when running at idle speed will have a distinct backfire through the carb. Its a small popping sound. Its not big but it does blow back through carb. It is not uniform but may do it once then not again for 20 seconds then next time is 5 seconds. The motor is in time and runs smoothly except for the little backfires. I think it must be ignition issues since it is not uniform. Could this be a condenser issue?
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Joined: Jan 2002
Posts: 30,701 Likes: 141
ChatMaster - 25,000
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ChatMaster - 25,000
Joined: Jan 2002
Posts: 30,701 Likes: 141 |
This is usually caused by an intake valve problem. The valve may be sticking in the guide, adjusted too tight or just plain leaking. Also could be a broken valve spring.
The first thing I would do is slowly pour some Marvel Mystery Oil or ATF through the carb. throat with the engine running at a fast idle. This should free a sticking valve. If that doesn't help do a compression test.
Gene Schneider
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Joined: Nov 2003
Posts: 51
Shade Tree Mechanic
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OP
Shade Tree Mechanic
Joined: Nov 2003
Posts: 51 |
Started the motor and put some Marvel Mystery Oil through carb and when the smoke cleared no backfire at all. Let it run 15 minutes and it sounds great. I appreciate the experience of this forum so much. Thank you for helping me again.
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Joined: Jan 2002
Posts: 30,701 Likes: 141
ChatMaster - 25,000
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ChatMaster - 25,000
Joined: Jan 2002
Posts: 30,701 Likes: 141 |
I would add a generous amount of MMO to the gas . You have a varnish build-up on the intake valve stems.
Gene Schneider
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Joined: Jun 2007
Posts: 1,894
ChatMaster - 1,500
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ChatMaster - 1,500
Joined: Jun 2007
Posts: 1,894 |
Is it deposited from the fuel side or from oil running down the valve stems?
Any way to prevent this varnish buildup?
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!)
1975 4-speed L82 Vette
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Joined: Jan 2009
Posts: 935 Likes: 12
ChatMaster - 750
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ChatMaster - 750
Joined: Jan 2009
Posts: 935 Likes: 12 |
Did I not read a while back in the Chat site that MMO is nothing more than Kerosene with color and a aroma agent added ? If so, why not just add straight Kerosene which should be a cheaper way to go?
dick
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Joined: Jan 2002
Posts: 30,701 Likes: 141
ChatMaster - 25,000
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ChatMaster - 25,000
Joined: Jan 2002
Posts: 30,701 Likes: 141 |
If the car had older gas in it it would be varnish from the gas.
Oil running down the valve stems builds up carbon on the stem and can also cause valves to stick. Note that the shop manuals often say to squirt oil on the valve stems before adjusting the valves. That is why I prefer to add some type of an oil shedder under the valve spring/cap.
The old motor oils left more of a carbon deposit than modern detergent oils.
I am the one that said MMO is mostly a keresene like mixture with a dye snd flavor added, If I were to use kerosene I would mix a little ATF or oil with it.
Gene Schneider
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Joined: Jan 2002
Posts: 30,701 Likes: 141
ChatMaster - 25,000
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ChatMaster - 25,000
Joined: Jan 2002
Posts: 30,701 Likes: 141 |
Some modern cars with direct fuel injection (directly into the combustion chamber) are having problems with carbon building up on the back of the intake valves. Port type F.I. injects the gas in and it passes under the intake valve to keep it clean. The additives in good modern gas contain good detergents to keep the carbom from forming. Then to top it off if the engine is turbo-charged carbon cleaning agents can not be induced through the air intake so the heads need to be removed and the intake valves cleaned. I have seen this on a number of Ford 3.5 Ecoboost engines.
Gene Schneider
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