1989 FJ1200 "Flat Spot" around 3500 rpms... V&H Supersport to blame??

[lumberjack2277]

    Hey All,   I'm new to the board! ;-)    I have a 1989 FJ1200.  Starts right up, a little cold natured though.  All works great, has great power, except it has a flat spot right around 3500 rpms.  The bike has a Vance And Hines supersport 4-1 and unifilter individual carb air cleaners.  I dont know if its ever been jetted or not.   ANy advice?  I know its kinda' broad of a question... thanks for any input. 

[weymouth399]

Pull carbs, clean carbs, and then find out whats in them for jets. We will be able to help you with a little more info. These bikes LIKE fuel and factory jetting is slightly close at best, if not plugged by years of rust in the tank, varnish or what ever.
But if I had to put a guess I would say you need a adjustable needle or a bigger pilot jet. Or a combo of both.

Bob W

[andyb]

Naw, that's the jetting.  There is always a flatspot with a 4-1 pipe, but it's generally up higher and pretty subtle, probably between 6 and 7k, right before it tears your arms out.

[fj11.5]

ive wrong  before, but try raising the needles in the top of the carbs a notch, if they have them or a thin washer under each ,should be detailed pics on here if you do a search

[racerman_27410]

my supertrapp pipe had a similar flat spot but the jet kit i bought had an "optional" air correction jet 44 or 45(?) that pretty much cured it.   the air jet screws into the back of the carb at the air inlet opening.




KOokaloo!

[SlowOldGuy]

my supertrapp pipe had a similar flat spot but the jet kit i bought had an "optional" air correction jet 44 or 45(?) that pretty much cured it.   the air jet screws into the back of the carb at the air inlet opening.
KOokaloo!

That would be the optional (richer) 144 air jet that a DynoJet kit includes as opposed to the stock 155 air jet.

DavidR.