Engine Breaks Up at 4,000 RPM and above

So I recently put an 1166cc kit into my bike and have been working to dial in the carbs. My original guess of 135 Main and 40 Pilot were decent but definately was running rich. So I adjusted the needle and that seemed to clean up the transition between pilot and main but now my bike just falls flat as soon as I hit 4000 no matter what throttle position. I have since put it back to its original setting and I am still having this issue. I have checked voltage at the coils and I am 13 Volts so I don't believe it has to do with that. I have since dropped down to 37.5 pilots and 130 mains and it pulls strong to 4000-6000 rpm and then falls flat, exhaust pitch changes almost a fluttering sound to it. I pull the choke when it starts to do this and does nothing or makes it worse. I am guessing it's either something with ignition system or I am not getting enough air. I am inclined to think it has something to do with the carbs since I was messing with them. Could it be the diaphragms for the slides, I am not seeing any tears and i have tried reseating them and hasn't changed the problem? I am kind of at lost as to what to check next. Let me know you thoughts on what it might be and issues that cause this symptom

You didn't mention what kind bike, carbs, exhaust and air filter you have on there. If you're using pod filters with CV carbs--then good luck.

The problem you describe sounds a bit like fuel starvation--have you confirmed that your petcock/fuelfilter/fuellines are delivering a decent amount of gas? Have you confirmed your carb fuel levels?

I have BS34 carbs with Velocity stacks w/ 4-1 exhaust. Maybe it is, but you would think by using the choke it would improve a little

jeffw wrote: I have BS34 carbs with Velocity stacks w/ 4-1 exhaust. Maybe it is, but you would think by using the choke it would improve a little

The 'choke' means nothing at the rev range you're talking about...

130's seemingly should have been more than adequate for my 1100 with BS34 carbs (with the air box) :ohmy: , but until I put 132.5's in, it spat and popped at 6500 + rpm or so. Now its nothing but grrrr....past red line.

daveo wrote: 130's seemingly should have been more than adequate for my 1100 with BS34 carbs (with the air box) :ohmy: , but until I put 132.5's in, it spat and popped at 6500 + rpm or so. Now its nothing but grrrr....past red line.

I suspect that if going from 130 to 132.5 stopped spitting and popping.... You fixed something you didn't know was wrong and a seriously doubt it had much if anything at all to do with going up one step in main jet size. LOL!

missionkz wrote:

daveo wrote: 130's seemingly should have been more than adequate for my 1100 with BS34 carbs (with the air box) :ohmy: , but until I put 132.5's in, it spat and popped at 6500 + rpm or so. Now its nothing but grrrr....past red line.

I suspect that if going from 130 to 132.5 stopped spitting and popping.... You fixed something you didn't know was wrong and a seriously doubt it had much if anything at all to do with going up one step in main jet size. LOL!

Nothing else was changed at the time...

I believe you, but I can't accept that is what fixed it.

What bike and pics.
Steve

I think I have I have found the problem, one of the pilot caps had fallen off. The o-ring must be worn out so I replaced it and put it back together and it seems to work great again. I was also slightly lean on the main jet, I was always assumed that using the choke might help indicate lean conditions but that must not be the case here.

jeffw wrote: I think I have I have found the problem, one of the pilot caps had fallen off. The o-ring must be worn out so I replaced it and put it back together and it seems to work great again. I was also slightly lean on the main jet, I was always assumed that using the choke might help indicate lean conditions but that must not be the case here.

Just to clarify, when you say "pilot cap", you mean the plug over the pilot jet inside the carb body and not the anti-tamper plug over the pilot mixture screw on the outside of the carb body, correct?

Yep exactly