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I just finished up maintenance on my Marvel DD carb that is on my B48 Onan engine. Since there are so few pictures of the carb, I decided to take a few and share my experiences with this carb.

Below is a picture of the carb body with the cover off. Note the brass "jet". If this becomes occluded or clogged, the engine won't idle correctly. It will be too lean. If need be run some very thin musical instrument wire into the hole and wiggle it around and the blow it out.


Dirty - Time to clean it.


Much better

The next item to note is the fuel passages. The raw fuel enters the carb and passes through the rectangular hole on it's way to the needle and seat. If the gasket does not seal the area surrounding this passage, the crankcase will fill most likely fill with fuel. A bit of advice. If the bowl gasket is in the least bit damaged, replace it. New gaskets are about $5. If the old gasket fails to seal and the crancase fills with gas, just the cost of a filter and two quarts of oil will exceed the cost of the gasket by a factor of at least 3.




There are two ways to attach the needle to the float. Below is shown the WRONG way. With it assembled this way, the float will drop too low pulling the needle too far out of the seat thus causing the needle to never seat correctly. The result? Flooding and a filled crankcase.


WRONG!


Assembled correctly!

Float adjustment is fun and easy. All it takes is the right tools.

Below is a new float that was just installed. The float is a little off. The pontoon needs to be a little more parallel to the body. As near as I can tell the pontoon should be 1/8" away from the body at a point furthest away from the pivot point.


Unadjusted new float installed.

Below is the (hopefully) correctly adjusted float. The pontoon is so close to parallel to the body that if it was parallel it would not matter much.



Enjoy

Richard
 

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One more item. Before removing or installing the air filter housing on the carb, close the choke. A screw dropped down the throat of the carb could ruin your day.

This might be eligible for a sticky.
 

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Richard, this is great. Definitely should be a sticky.
 

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Discussion Starter #5
I saw a mechanic take the intake manifold off a V-8 because he dropped a nut down the carb.
 

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Great info Richard!
Heading out to the garage now to inspect and try again with your insight. Have been struggling to get my own b48 with a Marvel DD to perform under load...

Neither of the DD carbs I have disassembled contained the float assist spring that you have pictured, is that a factory item? Can these carburetors be used without the spring or am I missing a required item?

Was the foam to brass float switch required to rectify issues with your carb, or have you had success with the foam float?
 

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Just a note, this was posted on a 9 year old thread...
Seems like theres quite a few of these engines still in service today!

I have sent a PM to the OP aswell as started a new thread in the small engine maintenance forum labeled

"Marvel Schebler DD Troubleshooting"

Any insight on Marvel Schebler carburetor tuning would be appreciated
 

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Sorry, I don't know anything about the specifics of your engine, and you may not get a response to your PM to the OP, as he hasn't been logged into this site since 2018 (this is on member's profile page).

Good luck with fixing your carb.
 

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I have an 8163-T with B43M engine and Marvel DD13 carb. It has a spring on the float. When I was researching there were a number of threads related to carb float adjustment. Apparently, many of us have had troubles with adjustments of the floats. My float had leaks so I replaced it, but I used brass and not plastic (actually, I don't think plastic was available, but i could be wrong).

Hope that helps!
 
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