engine is acting up

[alanyluan]

I recently purchased a 91 FZR-600. The previous owner put in a new motor maybe about 1000 miles ago and I don't know what maintenance has been done on it since then. I've been riding it just around town for the last couple weeks and everything has been fine.


Anyways, the last couple days i've been riding it, I've noticed something weird when I apply throttle - the engine seems to ride kind of rough and it cuts out on power and chugs along pretty roughly. I don't know how else to describe it other than its just really choppy whenever I apply the throttle.


If you have any ideas of what it could possibly be, that would be much appreciated. I might just have to take it in to a local shop just to get it checked out but who knows how much that is gonna cost. Thanks a lot and I am definitely still learning here so again I appreciate it.

 

[TownsendsFJR1300]

I recently purchased a 91 FZR-600. The previous owner put in a new motor maybe about 1000 miles ago and I don't know what maintenance has been done on it since then. I've been riding it just around town for the last couple weeks and everything has been fine.


Anyways, the last couple days i've been riding it, I've noticed something weird when I apply throttle - the engine seems to ride kind of rough and it cuts out on power and chugs along pretty roughly. I don't know how else to describe it other than its just really choppy whenever I apply the throttle.


If you have any ideas of what it could possibly be, that would be much appreciated. I might just have to take it in to a local shop just to get it checked out but who knows how much that is gonna cost. Thanks a lot and I am definitely still learning here so again I appreciate it.

Being its a carbureted engine and the carbs probably have some varnish built up in them clogging the jets. As its still running, you may luck out by putting in either a heavy dose of Chevron Tectron or Seafoam (or both). Both are fuel stabilizers\fuel system cleaners... You may need to run a tank or two thu for best results. Also, check any fuel filters/clean as necessary. There may also be a vacuum line off the fuel valve at the gas tank to one of the carbs, make sure that is intact, NO CRACKS/LEAKS, or the fuel valve will shut off (no fuel). There should be a drain screw on the bottom of each float bowl. Drain each bowl into a small container(I use a clean tuna fish can) and watch for what junk comes out..

If all else fails, the main/idle jets in the carbs are probably clogged. The entire 4 carb assembly will need to come off as ONE ASSEMBLY. You can get to the jets from there. If your not familiar with carbs, a shop manual is a must. If you can't get that, bring up a parts fisch for you bike, it'll show the breakdown of the carb and exactly where the jets are. They MUST BE FULLY REMOVED FOR CLEANING. You should be able to see light thru ALL ORIFICES...

DO NOT UN-BOLT THE CARBS SEPARATLY FROM THE MOUNTING / ALIGNMENT RAILS, its not necessary and will cause more problems than its worth. Also possible is a diaphram vacuum leak for the slide however I'd check the jets the first as there more likely to clog. Also check for any cracking around the rubber intake mounts (between the carbs and the head). You can run the bike, spray a little carb cleaner around the rubber while running and listen for changes in the idle (rising). If that happens, your looking at dried out intake mounts causing a vacuum leak.

The below first site shows your carbs broke down.

Good luck..

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[1/2%normal]

might also be the valves. If you dont know the maintenance then its a good chance there is some damage done regardless of what the previous owners says. Have it checked out by a local shop. Compression and leakdown test can tell you what it is. might just be as simple as your carbs or more serious like bad bearings (from bad or old oil used in the past).

 

[YZF73]

I'm with Townsend on this one, The carbs would definitely be the first thing I'd be considering, the approach Townsend has described is probably your best move :rockon:.

Yamahaboyz

 

[FinalImpact]

^^
Agreed -

Along that same line of thinking is this:
Not sure how well fuel is handled in those parts, but water in the petrol could easily cause some of the performance issues you speak of.

Can you drain the float bowls safely? Is there a plug/bolt at the bottom?

If possible, drain the float bowls into a clear container to look for seperation of water and petrol. If detected, Remove all petrol from tank and add fresh from another source. Add fuel dryer in the proper proportion for the volume of petrol being treated.