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end of back--firing but no power Marvel


rwolf
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After checking and re-checking everything related to the ignition on my '24 4-cly I decided to put back the original carb. It solved the evasive back-firing problem but the car has much less power than with the replacement carb. Can somepone advise me how to adjust the Marvel carb? confused.gif

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Have you tried putting a vacuum gauge on your engine?

Few engine testers are more useful and versatile than a vacuum gauge, yet very few of us shade tree mechanics use them. A vacuum gauge can pin point valve and valve spring problems, carburetor and timing problems and more. Check out this site: http://www.secondchancegarage.com/public/186.cfm to learn all that this inexpensive tool can do for you.

Let us know what the gauge tells you! wink.gif

Whitney

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ok,

if the engine has no power, it's not getting gas.

the wheel at the bottom of the carb is for idle. open it up 1/2 rotation, and increase 1/4 turn until you get a smooth idle. under 25mph, the low port powers the car.

Next, if you are getting a popping noise in the intake as you try to go fast, you are to lean.

these car only have to carb ports. low and high speed.

the high port only takes over after 25mph. there is no adjustment on this.

so.... run it with a lot of choke and see if you get power.

if you do, your air flap valve is to lose, or the spring is stuck. the air valve is suppost to be 1/16" off the valve body wall when the car is off. you have to pull the heat riser off to check.

if you do pull your heat riser off, check for holes in the innner pipe. if you have hole, your exhaust is getting sucked into your intake, and that could be your problem.

all else fails, take the bottom off the carb and blow thru your ports and see if they are clogged. you can make your own gaskets, any air leak will prevent the fuel from being sucked into the intake.

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  • 2 weeks later...

I've adjusted the carb as suggested and idled it for close to an hour with Marvel Mystery Oil. The vacumn went from a fluctuating 14-16 " to a much more steady ( but still vibrating ) 15". I think I'm on the right track getting those valves free but now I have an overheating problem when driving. I havn't really had a chance to check it out.

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Robert,

Retarded spark will cause over heating. Advance the spark and you should see the vacuum increase. Try to get 17"Hg.

I'm getting my Marvel back from the rebuild shop soon and will be hoping to get my ol' gal ('23-4 cyl) fired up after a 40 some year nap.

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  • 4 weeks later...

I have a Radco tune-up manual from which I can scan the relevant pages for you if you are still in need. The late Duesenberg expert Jerry Gebby told me the story from the time he was involved with Buick why they changed from the fixed head engine with valve cages, to a detacheable head in the early 20's, if anyone is interested.

Ivan Saxton

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