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Motarded659

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hey guys I'm still messing with my muggy. i got it tuned pretty good now it still starts kinda hard but thats ok. anyways i run it for about 3-5 minutes and it starts to run lean then will quit. it loses its prime in the line. i take the line off the exhaust and start to prime it and it will not hold the prime it keeps wanting to suck all the fuel back in the tank. i waited awhile and it started working ok again. just wondering if anyone has run into this and if so what do you change i was thinking maybe a bad gas tank or something wrong with the carb. any comments would be very greatful
 

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You have an air leak somewhere in the system. Make up a soap and water solution to test the system. Drain the fuel tank and spin the engine a few times to expel any fuel. Brush a little soapy water around the carb, HSN and LSN, backing plate, and tank/fuel lines. Remove the pressure line from the exhaust and blow in it. Any bubbles marks the spot where your leaks are.
 

olds97_lss

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Sounds like your running it too lean and getting it too hot. When it's really hot and you try to prime it, the carb boils the fuel and pushes air into the fuel line.

Try what RC Addict suggests, then set the carb back to factory and tune from there.
 

Motarded659

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thanks for the suggestions ill try to check for an air leak today and post up any findings.
 

Scrogg

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Sounds like your running it too lean and getting it too hot. When it's really hot and you try to prime it, the carb boils the fuel and pushes air into the fuel line.

Try what RC Addict suggests, then set the carb back to factory and tune from there.

X2! THe Mach engines will boil the fuel at 250F like clockwork. Keep it under 240F. To get it to start when it is warm, attach the ignitor, plug the exhaust and crank on the spinstart until it forces the fuel into the carb. Watch the fuel line closely., don't overdo it.
Another trick is too keep a can of compresssed air handy, hit just the carb with it briefly to cool it down.
 

Motarded659

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rc addict i did as you said but i dont see any external bubbles. i can hear a little air but its just coming out of the hole in the carb where the fuel enters is there a certain way to do this. am i checking it wrong? or could it be leaking at like the crank seal area and should i take out the motor?
 

Motarded659

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so i checked pretty good for an air leak on the motor and the gas tank and couldnt find any. it ran pretty good for longer today. on another note now when i gas it and let off the throttle it still wants to take off for a second or two then will return to idle. any suggestions?
 

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rc addict i did as you said but i dont see any external bubbles. i can hear a little air but its just coming out of the hole in the carb where the fuel enters is there a certain way to do this. am i checking it wrong? or could it be leaking at like the crank seal area and should i take out the motor?

Guess I should have been a little more specific. You need to remove the air cleaner and put your thumb over the carb inlet for the test to work. As you found out, if you don't seal the carb all the air goes right out the inlet...
 

Motarded659

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so i dont think i have an air leak, i looked as good as i could and couldnt find anything. so i guess ill just run it til she blows. thanks for the help
 

olds97_lss

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on another note now when i gas it and let off the throttle it still wants to take off for a second or two then will return to idle. any suggestions?

To me, that would suggest your a bit lean on the HSN and possibly a bit on the LSN.

When you run it up to higher RPM's, all the fuel reserves in the crankcase blow through and get burned. When you let off the gas, the engine still needs a decent supply of fuel or it runs lean for a few seconds until it can build up a bit of a reserve/over rich mix in the crankcase again. This is the reason they get "loaded up" when you let them sit and idle for more than 15-20 seconds. The air/fuel mix in the crank case gets overly rich while idling.

Running a bit richer on the HSN means it's scavenging less when you let off because there's a richer mix in the crank case at WOT. If richening the HSN a bit doesn't help, then richen the LSN a bit to help compensate.

I usually tune the HSN so the idle drops down pretty quick after a WOT run. I also tune the LSN so it doesn't load up to bad after sitting for 10-15 seconds at an idle.

Some engines are more forgiving than others for idling. My old reliable OS21RG can sit and idle all day long and only get a little rich when I take off. My LRP is a bit more finicky and loads up, then stalls because the glow plug gets too damp to stay hot. It will still sit and be ok for 15 seconds or so and only die if I let it sit for a around a minute or more. But it usually doesn't die until I go to take off. All that rich mix in the crank case floods the glow plug and flames it out.
 

Motarded659

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well after some bashing this weekend i came to the conclusion that it all boiled down to some bad fuel. I was using some old fuel (maybe a year old, sealed tight) figured it was ok cuz it still ran just very sporadically as you have read. so, i finished off what i had then ran 1/2 tank of my buddys fuel and it ran great :) temps were down and was tons smoother. if it wasn't for me breaking the diff carrier id still be driving. thanks for all the help guys. even though it was all user error- i think.
 

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