Help Yamaha Zeal - hesitation below 6000rpm

I have a similar issue, I think it happens coming off the throttle (if you pull the clutch in the engine stops), when you go to accelerate it is sluggish. The plugs very clean after nearly 2000km:


I was told it could be the seal for jet housing, but how do I tell? Do I just increase the jets and lift the needles? Rebuild the carbies? Also, the power cuts under full throttle above 11,500rpm (power is great when you back off a bit) - this appears to be just too small of a main jet, despite everything being standard.

 

maybe a stupid question but did you check your airfilter ?

 

Not sure why the air filter would affect it, it runs fine otherwise. And as for the fuel filter, that would only affect it at high speed and full throttle, but it recovers immediately and seems problematic immediately, too. I'm thinking it's either jetting or the housing seals, but the fact it runs well (apart from full throttle at full revs and after braking, or accelerating hard and pull the clutch as you close the throttle - engine stalls), makes me think it could be something else. From memory, these carbies have a needle tube with the emulsion tube junction in at an angle, I'm wondering if that is loading with fuel and dumping under braking? And did up take so long to recover? It seemed to only happen once, too. He was 2-up and trying accelerate in third from low revs, then down to second and still struggled before finally clearing. He said it was bogging down, which would point to overfuelling, right?

 

Have had issues with my zeal regarding fuel flow. Make sure fuel lines are as short as possible and no twists or kinks in them, and that all lines are the same size.

Also check that the carbs are synced.

Litetek carb kits are a good investment.

 

Engines need FUEL, AIR, SPARK, COMPRESSION.

If you've changed coil packs, they're in the right order and you've got good spark then that's one covered. FZR's are notorious for carb issues and the Zeal is basically an FZR so I'd be looking for blocked jets in the bowls. Clean them out, easy enough done. You might have some issues with the floats etc but I wouldn't jump to complex theories about carb syncing and that sorta jazz - in my opinion you should only need to do that when you completely rebuild your carbies.

 

Mm the fuel octane wont affect it. E10 might though id avoid that. Cleaning out carbies would have sorted it i think.

 

91 leaves residue (gum, lacquer) in carburettors, especially if the vehicle is not in use for an extended time. I have (and I'm sure many others on here) have had to deal with the stinky stale 91 fuel and cleaning the carbies, both mechanically and chemically. I have done enough to tell people to use 98 in their bikes. And watch out for other companies selling high octane, United fuels had a 100 octane fuel that contained ethanol. If you ride daily, maybe it is fine. Maybe compounds vary between countries and climates, too.