1993 VFR 750 running weak

Just finished my 1993 vfr750 resto. But one problem that i cant figure out. The bike runs alittle weak thru the rpm range,doesn't skip or miss,carbs are synced,two bros. full exhuast,dyno jet kit and k&n air filter. I eliminated the air injection pollution system. Any ideas??????????? Thanks , Scott
The bike only has 9000 miles and is in emaculate cond.

 

put in fresh plugs, run down the road at mid-rpm for awhile, do plug cut and check color; work from there to maybe find problem.

when eliminating air pump bits, some lines must be plugged, others left open to atmosphere, maybe the problem is there?

is the jet kit/pipe a recent change or something you ran before?

Have you been riding a V-Max recently??....no wonder your VFR feels weak!

 

I agree with squirrelman. Start by reading the plugs. Plugs that are just a little too cold will not foul, but will do exactly what you are describing. Plugs that are too hot will typically run strong through the midrange and misfire or feel lean on the top end.

I don't know VFR motors yet, so I don't know if your ignition timing is adjustable. If it is, it could be that the timing is retarded. That will also affect an engine in the same fashion.

 

Thanks for your input, that should get me started.
Scott

 

timing on VFR is inside CDI box code, not adjustable.

Let us know your improvements if any, Scott.

 

I had the same problem after I did my engine swap but, as soon as I changed the plugs it worked just as good as it did the first day it made its debut on earth. I also blocked the EGR valves and no problems there.

Good Luck

 

Hmm, sounds like a job one does on a Dyno if you ask me. right off the bat I feel a fuel issue is at hand, more lean than rich is my first guess. this will be a hard one to do by seat of the pants unless you have something to compare too, so seriously I'd look for a dyno that has a good tuner on hand. my .02 cents worth.

 

.........2 cents won't get far on a dyno, more like $200!

Certainly a dyno would be useful, but it is an extravagant expense for many, and the "tuner," running repeted tests, might want more than the bike is worth.
A competent, experienced mechanic could take the bike for a ride and provide useful info for almost free.












IN THE END, it's all trial-and-error; the dyno just makes it easier....

 

I have a hunch now that the prob. could be somewhere with the pollution garb removed. Or maybe its V Max withdrawals. Anyway thanks to are for the responces. Scott

 

I don't know if it is related, but late in the season my 93 felt weak to me as well, and no better after changing the plugs. Just recently doing winter cleaning and maintenance I found some electrical connectors under the right mid fairing that are scorched (??) going to have to investigate what they are for and if this may be related.