6000rpm & falls flat on face!

[pinkchev71]

We are working on a buddy's bike and did regular maint, jet kit in carb, replaced spark plugs, etc...the bike runs great until you hit 6000rpm, then spits and sputters and falls flat on her face! WTF? We tried another "known good" CDI box since thinking that might be a problem, but we are still having the issue. What are we missing? Any suggestions?

[Dragon]

Think it's your jetting... now u need to tune the bike....

[mrfreeze5]

Sounds like jetting. Check your needle placement and main jet size.

More details on the bike like intake and exhaust mods, elevation, ambient humidty, etc can help us diagnose your issue.

[yamaha_george]

Sounds like jetting. Check your needle placement and main jet size.

More details on the bike like intake and exhaust mods, elevation, ambient humidty, etc can help us diagnose your issue.

Our new Mod has spoken +5 on knowing details of the air intake to exhaust what is stock & what is not.!

When you did the carbs you did a full balance , float height check etc?

[pinkchev71]

'94 FZR 600 Stock airbox, stock filter, 3 jet kit carbs-jet is set at 126 main jet, a/f screw 3 turns out, full muzzy exhaust.. Any help is appreciated!

[sweekster]

By chance, have the carbs been synched?

[pinkchev71]

Yes, carbs been synched & balanced, floats ok. We are at this point in time... Hubby's a mechanic and can't figure it out! Ugh...

[M in KC]

Agree with all previous, fuel delivery or fuel management issue. What do the plugs look like after a plug chop? I'm aslo assuming the fuel pump is able to keep up with fuel demand at that type of load or beyond.?

[ragedigital]

It certainly sounds like jetting to me. Any idea what brand of jet kit it is? Know what jet needle clips are set on - should be 5 or 6 groves (start from top)?

[mrfreeze5]

'94 FZR 600 Stock airbox, stock filter, 3 jet kit carbs-jet is set at 126 main jet, a/f screw 3 turns out, full muzzy exhaust.. Any help is appreciated!

I think a stage 3 is a bit much for your setup running a stock airbox. 126 seems WAAAAAYYY too big for that setup. Try a 110 or 112.5 main, and tune from there.

[ragedigital]

I think a stage 3 is a bit much for your setup running a stock airbox. 126 seems WAAAAAYYY too big for that setup. Try a 110 or 112.5 main, and tune from there.

Sounds like a DynoJet kit which a 126 is probably the right number. I ran a 130 and it was perfect.

[mrfreeze5]

I think a stage 3 is a bit much for your setup running a stock airbox. 126 seems WAAAAAYYY too big for that setup. Try a 110 or 112.5 main, and tune from there.

Sounds like a DynoJet kit which a 126 is probably the right number. I ran a 130 and it was perfect.

I thought about that after I typed it. I avoid dynojet mainly because of their funky jetting numbers.

[knightrider092]

Hey guys,

its pinky's husband..just typeing in an update...stock air box and stock filter...full muzzy exhaust.....carbs are set as such...130 dynojet main jet..dynojet needle set on 5th slot per instructions...a/f screw set to 3 turns out per instructions...the slides have been drilled out per the instructions
I warmed the bike up to normal operating temp,(till the fan came on). Road tested bike on back roads as well as on the highway. I was lucky to get to 75mph. The bike run ok on the back roads,(easy to moderate throttle below 6000-7000 rpm's). Rpm's will go higher if i'm easy on the throttle,but still wont go to redline. after racking my brain for about 45 minutes,I've decided to go back to the begining and cross all the T's and dot all the I's. I would like to say thanks for all the help, any further info that you guys can give would be great...I'm starting to think that it my be too large of a main jet,causeing the engine to load up when the needle is pulled up higher..any thoughts? THANKS AGAIN GUYS!


Steve

[thatkid]

We are working on a buddy's bike and did regular maint, jet kit in carb, replaced spark plugs, etc...the bike runs great until you hit 6000rpm, then spits and sputters and falls flat on her face! WTF? We tried another "known good" CDI box since thinking that might be a problem, but we are still having the issue. What are we missing? Any suggestions?

was the bike running ok before the jet kit, spark plug replacement etc? (wondering why you tried a different known good TCI) if so id back track, easiest would be to replace the old plugs (could be a faulty new plug/plugs) any reason you cant go back to the stock jets? to see if it runs ok.

One day i'd 24,000 mile serviced a MKV Ford Cortina took it for a test drive it ran great, 500 yards from the garage the engine cut out and wouldn't start. i walked back got the truck and towed it, All the other technicians ribbed me like hell . I hooked it up to the SUN 1080 tester (1980's), all the electrics/ignition checked out fine. The damn fuel pump had packed up, nothing at all to do with the service, i didn't even look at it .

Sometimes you gota look outside the box, could be nothing to do with what you've done, but a different underling problem. Good look in solving the issue.

[ragedigital]

Set the needles down 2 more clips and ride the heck out of it... emulsion tubes are shot.

darrin