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M is back firing now, please help

B

BigTone

Member
took the carb apart again, replaced the gasket, and the motor is now firing, but as it starts it either immediatly dies or as im starting it, it back fires. I'm lost guys, is it getting to much gas? should I reajust the float? I could really use some help, thanks, anthony
 
Sounds like a timing issue. If you have had plug wires off you might check that firing order is correct, should be stamped on side of the block.
 
Sounds like a lean fuel mixture. If you use the choke, how does the situation change?
For a starting point, I bottom out the idle AIR screw, then back out 1 1/2 turns.(in is richer-out is leaner)
The main or hi speed FUEL screw is backed out 3 1/2 turns or so. (in is leaner-out is richer)
NOTE THE DIFFERENCE BETWEEN THESE 2 ADJUSTING SCREWS.
The float is set at the factory recommended setting. (don't recall the distance at the moment)
Is there an air leak between the manifold & the cylinder head?
With the spark timed at TDC, the engine should run well enough to make additional adjustments.
Send me an e-mail noting your location.
 
I did it all, I think im going to get a new float because I may have messesd that one up. should be no leak at the manifold, brand new manifold and gaskets. its close to timed, I was going to fine adjust it once its running. Gas tank is full of crap from sitting, im draining the gas, replacing the filter. Ill re check those adjustments to make sure. I also had the #2 and #3 plug wires switched so I think that was my problem all along. thanks for the help, anthony
 
I had the #2 and #3 wires switched, im going to do a little maintaince to the fuel system, change the float and try again. thanks for the help. anthony
 
Shouldn't need to change the float unless it is dented or has a pinhole leak and is filling up with gas. If it is dented I have heard that you can sometimes pop the dent out by sticking the float in hot water but have not tried that myself. Try shaking the float, if it leaks you will hear the gas slosh in the pontoons. If no dents and no hole I would not buy a new one, ou likely just need to adjust it.
Zach
 
how do you adjust the float? do you bend the tab on the hinge? The hanger has a hole on the far side, and a hole with a vertical slot on the near side, do I do something with that, the directions in the carb kit were vauge. thanks
 
You need four things to make an engine run;

1. Air
2. Fuel
3. Compression
4. Timing

Your timing may be off our you have a leaky intake valve, from being burnt or valve clearance set too close.
 
Assuming all else is fine - carbs can be frustrating.

Sometimes you just have to find a very narrow sweet spot for the mixture /idle adjustments.

Do as somebody here pointed out the 1 1/2 turn out or whatever it was as the starting point.

Then make SMALL adjustments from there. Like 1/8 turns.

I've found some carbs you can be within 3 turns of where it wants to be and it'll run fine - others have a very tiny window where the balance has to be just right.

You'll get it.
 
something else just occurred to me - a friends M was having a lot of weird carb issues.

Drove me crazy trying to clean it/adjust it. Kept dying under load.

Turns out the metal fuel line was kinked. It LOOKED like it was flowing enough gas - but after I swapped in a new line, it ran like a champ.

Just something else to keep in mind. Sometimes an "ok" flow isn't "ok" enough.
 
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