Motor hesitates at high RPMs

[rjwenzel]

Still have not done anything

Ok then, I'll take the carb appart this weekend and change the float level. I'm sorry I don't have more time durring the week but work gets in the way . . .
Here's a side view of the current carb position. The way I had it before was tilted quite a bit more to the front (left in this photo).

 

[rjwenzel]

No Luck

I took the carb appart and bent the clips a bit so that it pretty much puts the float at the top . . . and it did nothing! I guess the next thing that I'll do is put the motor back in the same position it was in before I started to have this problem.

 

[userix]

Pardon the necrobump, but I am having the same problem as the OP. Was running perfectly fine, decided to remount the engine in attempt to lessen vibration, and now whenever I hit WOT, I get hesitation and sputtering. It was running perfectly fine before and nothing else changed or broke. I have now tried to remount the engine like it was before, but it's still hesitating and sputtering at WOT.

 

[crassius]

that could be a vibration problem that is foaming the fuel in the bowl - does it feel like it is running out of gas for a sec than come right back as soon as it slows a bit?

 

[userix]

Yeah, If I slow down for a bit, it runs again fine. The vibration is pretty bad once it gets up to max speed. How would I alleiviate this foaming gas problem? I just find it weird how it does this after only remounting the engine slightly different. I made sure every bolt is tightened down and not loose

 

[crassius]

different parts of the frame will vibrate at different levels - I usually try to get the motor as low as possible in the frame & use a bit of PVC between motor & frame

 

[KCvale]

Just a few things...

You don't adjust carb angle by engine angle.
The engine has only 1 way to mount properly, that is the back mount metal to metal at a 90 to the seat post, period.
You can go up and down to help with the front mount but unless it's a V frame with the right size downtube, get a http://SickBikesParts.com front mount.

Do 'THE test' on your mount...
Hold your top bar with one hand, the top of the head with your other, and push back and forth AS HARD AS YOU CAN, if the engine moves AT ALL that is a fail and where your vibrations are coming from, hence the good front mount.

I suggest you get an NGK 5944 (BPR7HIX) Iridium spark plug while you are there as well, I put them in everything I build.

And remove that useless boost bottle and plug the intake hole, that could very well be causing your problems at high RPM's.

Just tips.

 

[rjwenzel]

Ok guys, I've pretty much had this thing parked since I failed on the last attempt. But now I have to fix it because I'm moving and I need to sell it (because I'm not going to ship it). Thanks crassius and KC! I'll mount it lower, more solidly, and I'll pinch off the boost bottle. I was going to pull the boost bottle anyway but it's good to know from an expert that that might be causing the problem. When/if I have time to fix it, I'll post back here.

 

[Ridin clean]

I have a lil of the same problem, almost feels like the spark plug gives up. Before i changed the carb, WOT,i would do 33mph,back off (just lil) and would hit 35ish. Another question, moving the needle down means raising the clip?

 

[Nino]

Hi Guys,

I have the same problem too with my motorcycle a 155cc Honda bike. I change the carb to size 28. after that. My bike sputters in high RPM. And Some time if I am going to force it to the top speed the bike dies. with a sputtering sound. This problem is more in the carb.but some would say it might be. Pistons. don't know wich one is correct.