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Post by Smitty on Mar 31, 2010 10:34:20 GMT -5
Got a rough rundown on Carb removal on the MC 54B? Is it a big job on the MC 54B? -- (JCL 250A)
The scooter runs good but at times the idle will hunt from 1500 to 1000. Also it started to surge at light throttle. This morning I looked in there and there is fuel dripping out and running down the side of the carb. I am going to remove and clean the float needle and would like to check the float level adjustment.
I could find no specs on the web. I'll check and set the float to be level or in the middle of the bowl. Does that sound about right?
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Post by earlwb on Mar 31, 2010 10:39:29 GMT -5
I think you are close to being correct. There are no specs on it. Usually on a 250B with the pulse fuel pump, the float bowl is marginally full at higher speeds, and can go empty when trying to go up a hill in a headwind at 50mph or faster, so having the float a little on the high side is usually the norm. If you have an electric fuel pump, you can set the fuel level a little lower.
What happens is every once in a while, like when there is a blue moon, the fuel inlet valve in the carb can get a little off kilter or a tiny piece of debris keeps it from closing. Sometimes the metal tab on the float gets off to one side or the other and jams up against the support post.
Most always, you take it apart and look at it, scratch your backside thinking WTF and put it back together and it works fine.
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Post by Smitty on Mar 31, 2010 10:52:20 GMT -5
I will check, scratch and set the level about level as i already have the electric pump. I'll quit putting it off and get it in there now.
Thanks Earl
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Post by dukeofyork on Mar 31, 2010 20:30:52 GMT -5
There is a very easy way to check your float level by using clear tube , put it on the float bowl drain and raise the loose end above the top of the carb. If it's any higher you'll need to pull the bowl and make an adjustment.  If too much fuel is entering the engine, the float valve may be set too high allowing fuel to enter the throat of the carb. Another sign of this may be fuel running from the drain tube. Sputtering and misfires may result. If not enough fuel is getting to the engine the opposite may be true. Typical symptoms are poor running and no power when throttle is opened. If fuel slowly leaks from the bowl lip, the bowl gasket is probably torn and needs replacing. |
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Post by JR on Mar 31, 2010 21:34:24 GMT -5
Man I just would like to know how it can go dry going up a hill or at higher speeds, still have OEM fuel pump after 5800 miles and absolutley no problems like this at all! As long as the valves are adjusted correctly and no vacuum leaks or bad vacuum hoses the vacuum fuel pump works great! Yes one needs to make sure the float is adjusted correctly and on the 30mm carb for the 250 it's about 19mm if I remember correctly, I'll look it up! If the float is wrong an electric fuel pump will do nothing for the problem, low is low no matter what form of delivery! Aso if you have fuel coming out of the overflow it's set too high and the electric fuel pump is not going to solve that either! Got to set the float! You think the pump is weak or bad replace it with a Mikuni and you'll be glad you did! 1/3 of the work, cost and headache of the electric! JRR www.aircraftspruce.com/catalog/eppages/mikunifuelpump1.php |
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Post by JR on Mar 31, 2010 21:49:47 GMT -5
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Post by earlwb on Apr 1, 2010 14:02:49 GMT -5
I have had the engine run out of fuel and stall out going too fast or up a hill into a headwind before. Actually quite a few people did. I switched to a electric fuel pump and no more problems with it.
Basically, with the throttle opened up towards WOT, the intake manifold pressure pulses (or vacuum) become weaker and weaker. Thus the fuel pump doesn't pump as well and the carb float bowl starts to empty out. When the fuel level drops below a certain point the engine dies. You coast off to the side of the road and crank the engine some to get it started and it usually fires back up Ok after the fuel starts getting into the carb again.
Anyway I posted some articles about it and videos with results showing how the intake manifold pressure or pulses get weaker as the engine is reved up faster or put under a load.
But usually this means you might have a intake vacuum leak someplace, or the intake and exhaust valves need readjusting, or the fuel filter might be clogging up or worst, the pulse pump is going bad. Mikuni pulse pumps have rebuild kits the OEM pulse pumps do not have rebuild kits. generally the inside diaphragm or one way valves have stiffened up or deteriorated causing the problem. A few years ago the internal pump parts on the pulse pumps deteriorated fast due to our usage of ethanol in the gasoline. it was bad for the pumps.
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Post by JR on Apr 1, 2010 20:34:00 GMT -5
With a proper PDI and getting rid of the problems associated with poor vacuum the OEM pumps do fine and don't think for a minute that the ethanol doesn't eat up the little electric pumps also and the difference is you throw it away and buy another again at least twice the cost. My scooter has been running fine with the original OEM fuel pump since Sept 08 and absolutley no fuel starvation and no running out of fuel on mountains not hills;  It all adds up to do you want to properly set the scooter up out of the crate or just start replacing things like the fuel pump without getting rid of the other possible problems associated that can cause the same problem, Hose and fixing leaks, putting on a proper fuel filter and porting out the pitiful manifold intakes are not only cheap to do but make the scooter perform better overall period. Even if putting on an electric pump keeps you from stalling out it doesn't mean that you have the scooter running at it's peak performance if it was just as simple as a bad hose causing a vacuum leak. Too many times folks just throw up their hands and say "oh it's the vacuum fuel pump" when all along it was something else. But to find these and fix them sometimes takes some time and effort and doesn't go along the lines of the quick fix other solutions. JRR |
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