Problem with an 87 700 running correctly at speed

Hey everyone. Please don't shy away from this long post as I'm really at a loss.

Thank you in advance for those that read it.

I'm hoping to get some help with this problem as I'm at a loss for what to do. I bought an 87 700 with 25000 on it about 2 months ago. It didn't run when I bought it however it turned over. Since then I've cleaned it up and gotten it running. All it took was a good carb cleaning and a little fiddling with the fuel pump. It runs great at idle. I can't hear any knocking or top end noise and it revs clean throughout its range. As you could expect I was ecstatic and quite pleased with the bike. Then came the test ride. Everything seemed to be going fine until I got the engine speed up to about 3000 rpm and had it bog down on me. I don't know how else to describe it. It's not a loss of power that causes the bike to slow, its as if the bike doesn't want to run any more and is resisting you. I can push the bike past 3000 rpm into higher rpm but it likes to resist. This behavior is also very inconsistent. Sometimes I'll ride it and it'll rev smooth to 5000 then bog, other times it'll bog at 3000. However, you can push the bike through this most of the time and it seems to bog less at higher rpm. The bogging event is also inconsistent. Sometimes the bike fights you hard while others its like a fish. Meaning it has spurts of fight from 3000-6000 where it bogs, picks up a little, bogs, and so on.

Now for what I've tried and first I should say that I have another 87 700 that runs great. I use parts off the running bike to try and fix problems with the poorly running one, thus eliminating the chance that the parts I'm throwing at the bike are bad.
So, I've gone through the carbs completely. Every jet is clean, the floats, needle and seat, and diaphragms are good. The carbs have been synced by hand and the idle mixture screws have been set to stock. The stock settting was assumed to work because the bike has had no other modification.
The carbs are good. And too double check this face, the carbs off the running bike were put on this bike to find the problem still persisting.
The gas in the bike is good and new.
The fuel pump is good as is the fuel relay and the rectifier.
The spark unit has been switched with one off the running bike to no avail.
The Engine stop switch seems to be in working condition with no problems.

In conclusion, I'm at a loss. I'm left thinking that it might be something in the top end. I thought that top end issue would cause a more consistent problem thought.

Please help me!

Any info at all would be helpful and greatly appreciated!

Thanks for everyone's time and i apologize for the lengthy post.

Nick

 

sounds like youre having the same problem as me:chaingun:

 

Did you run a fuel pump volume test? It sounds like you have a fuel delivery problem.

 

Or your spark is not strong enough to deal with the rpms. Plugs, wires or ground? Seeing you changed the spark unit. Known good?

 

No volume test performed, however I've taken the fuel pump off my running bike and put it on this one only to have the same problem. So I can eliminate the fuel pump.
As for the question of spark, I can't be sure. I've changed the plugs multiple times, but I haven't messed with the wires. That might be next.
As for the ground on the bike. When I first got the bike the ground was completely unwrapped. It was just the bare wire. Being that I didn't have any rubber wire wrap, I wrapped the ground in multiple layers of electrical tape. I don't think the tape could be the problem, but perhaps I didn't ground wrap the wire completely? then again being that the ground is attached to the frame I wouldn't think it would matter if the bare ground wire touched the frame in another place.
The spark unit that was tried is known to be good.

 

can you "tach" the bike out in nuetral? or do you have to fight it to rev up?

 

The bike revs fine parked in neutral. I've never tried reving it in neutral at speed.

 

Sounds like fuel flow, tank vent/ petcock, did you swap the tank from the good running bike? Exhaust restricted? Oil fresh? fuel in oil will cause weird problems.