FR 125 stalls when taking off

[EJ Korecky]

Runs strong all thru the power band after take off, but stalls when leaving the line if you don’t feather the throttle – if you give it full throttle, it stalls almost immediately. Float heights were set at 5mm, dropped it to 3 – planning on testing next week to see if this cures the issue. Any other ideas or suggestions would be appreciated.

PV 8 clicks, 162 main, 2 1/2 turns air screw. Max EGT 1250, Max RPM 12800, Max water 146, Plug BR9EIX – looks spot on, battery fresh/full charge always, Reeds intact. Could this be a sign of a weak coil?

Thanks,

ej

• This topic was modified 5 years, 4 months ago by EJ Korecky.

[William Martin]

Might try turning in the air screw a bit. Does it gag on the stand if you give it full throttle from idle? If so, turn the air screw in about a 1/4 turn and try again, repeat until you get decent throttle response. Hope this is useful!

Bill

[EJ Korecky]

On the stand, holding the brake and flooring it causes it to stall. I am assuming that it is rich on the bottom – wouldn’t closing the air jet richen it more? I will give it a try though.

inner pilot B45, outer pilot 50, needle K22,

 

Thanks for the reply,

 

ej

[William Martin]

Not familiar with what “typical” jetting is for that engine/carb combo, but if the plug looks good I wouldn’t change float height or main jet. It may be that your pilot jet is too big, and the air bypass has to be adjusted way out to make it idle. The fix for that is a smaller pilot jet and turn in the air screw a bit. I’m just going on a prior experience with a Honda shifter that developed a terrible bog when going full throttle. What had happened was the air screw had vibrated loose to where it was about to fall out… as soon as I put a new O-ring on the jet and set it back to where it was happy before, all was well with throttle response. You can easily try turning in the air screw, don’t worry about good idle, just keep it turning fast enough to not stall while you do your search for correct air screw setting. The important thing here is to stay on the safe side with jetting changes…go slowly!

Bill

ps: just fyi, if it runs good at full throttle, it isn’t weak ignition parts.

[EJ Korecky]

Did some testing today…started with air screw at 1/2 turn, and went  in half turn increments to 3 turns with no change whatsoever. Tried the needle in clip in every position – no change. Tried leaner pilots – no change. Tried a new battery – no change. Without feathering the throttle at take-off, it stalled every time.

 

Thanks for the ideas and suggestions,

 

ej

• This reply was modified 4 years, 11 months ago by EJ Korecky.

[William Martin]

Wow, that’s a strange one. Just out of curiosity, has it always behaved this way, or is it a recent change? It would be really good if you could borrow another carb & swap the whole thing out to see if the problem goes away. Just hate to go buying a new carb without that one sanity check!

 

[EJ Korecky]

Not a new issue – has always struggled off of the line. I took 2 pics, but not sure how to post them here.

 

ej

[EJ Korecky]

 

https://youtu.be/AqMkE8L5K-s

• This reply was modified 4 years, 11 months ago by EJ Korecky.

[EJ Korecky]

Just wanted to post a follow up of an additional change I made…

Engagement RPM has always been very low – around 2600 with new stock shoes and springs. This, coupled with the carb issue really made this engine struggle off of the bottom. I machined the shoes and got the weights down to 53 grams each (stock shoe weight is 64 grams). Engagement is now at 3700, and it is a completely different engine off of the bottom. Was considering the new EVO clutch, but with this change I no longer see the need.

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