Odd frustrating US-41 problem.
 

'Lo all.

Friend of mine has a US-41 I just sold him. Ran fine on my P-51 but I needed to upgrade (and so did he).

Fast forward 6 months later and he's putting the 41 on his Robinhood 99. Problem is, it won't start! Occasionaly if you squirt just enough fuel in the carb it'll fire but run really rough. It is never consistent, and doesn't turn near the RPM's I turned using even a slightly bigger prop than his (when it runs).

Carburator is cleaned and re-cleaned. Needles are all factory. Mag is on good, gotta good spark. Fuel system is all setup good. Just doesn't seem to want to draw fuel.

Possible compression problem? Timing bumped?

Help needed![sm=drowning.gif]




Also, when he took apart the carb first time, there was a small "bb" or bearing laying in the carb. There was a rocker arm in it that the bearing apparently fit into at some point.................?

RE: Odd frustrating US-41 problem.
 

I think that "BB" might be your fuel check valve for the diaphragm pump. You need it in there. You can get carb kits from bennettbuilt.com or ask them questions about the carbs.

Jim

RE: Odd frustrating US-41 problem.
 

I don't remember any bb in the carb...Look for a leak under the carb in the gasket or block...

RE: Odd frustrating US-41 problem.
 

Where, it the carb, was the BB. The fuel pump side, the metering diaphram side, or the throat. Just trying to pinpoint where it came from.

RE: Odd frustrating US-41 problem.
 

I believe it was the diaphram side.

Will the BB just pop back in, and is the cause of the problems?

RE: Odd frustrating US-41 problem.
 

THIS CLEARLY A CARB PROBLEM. EITHER THE NEEDLE SETTING IS OFF OR THE GASKETS FOR THE CARB ARE DEMAGED, THAT I WON'T SUCC ENOUGH GAS INTO THE ENGINE.

IF YOU HAVE ANY QUESTIONS, DON'T HESITATE TO CALL IN.

US ENGINES, INC.
CUSTOMER SERVICE
WWW.US-ENGINES.COM

RE: Odd frustrating US-41 problem.
 

Hey all, just found out that the carb is most likely OK. The likely cause now is a leak somewhere around the crankcase and jug. Looks like some of the gasket material fell out, causing the engine to have almost no compression.

This would explain why it ran fine for me and degraded over time till now. Also, if the engine happened to get enough fuel in it, the gap would open and close during the vibration, making it run very rough and also very intermittently.

We'll know more after tonight as he is going to put the carb off of this 41 and put it on another tried and true 41 and see what difference it makes.

RE: Odd frustrating US-41 problem.
 

OK I think we have the problem figured out.

Thanks all!