88 katana 600 mid range hesitates

[invisible4good]

so the midrange in my 88 gsx600f hesitates low range is good, mid range just hesitates and slightly sputters, but if i go full throttle it clears out and will hit the rev limiter easy. so far ive done an oil change, fresh gas, new NGK plugs, compression text (155 PSI in all 4 cyl), carb adjustment, carb cleaning, and carb syncing. now before i get too much further into this... the previous owner deleted the vacuum line for the tank, and kept the original petcock on prime and installed an in-line petcock. so is it possible that without gas being PUMPED its not getting enough to fill the carbs?

[XXWoodmanXX]

Absolutely.

I had a 95 750 with a bad petcock I had to leave on Prime, and it would 'buck' thru the mid-range and just show all sorts of power loss here and there. Then I replaced the petcock, and had much more power than I really cared to try to wrangle. Ended up trading the bike for a shaft-drive cruiser. lol

Embarassing, yes. But that should tell you just what a night and day difference a properly operating petcock makes.

[invisible4good]

guess i know what im doing tomorrow haha

[Kreylyn]

so the midrange in my 88 gsx600f hesitates low range is good, mid range just hesitates and slightly sputters, but if i go full throttle it clears out and will hit the rev limiter easy. so far ive done an oil change, fresh gas, new NGK plugs, compression text (155 PSI in all 4 cyl), carb adjustment, carb cleaning, and carb syncing. now before i get too much further into this... the previous owner deleted the vacuum line for the tank, and kept the original petcock on prime and installed an in-line petcock. so is it possible that without gas being PUMPED its not getting enough to fill the carbs?

OEM petocock does not pump anything. It's vacuum operated in that in the On or Reserve positions fuel will not flow unless vacuum is applied to the back side. That back side has a diaphram with a spring. The spring pushes the plunger closed sealing off fuel flow. Vacuum on the diaphram pulls the plunger open, allowing fuel to pass by it. It does not pump it for force fuel past at all.

I don't think it's a fuel flow issue. If it was, then the issues would increase and get worse the higher rpms. Simple process of higher rpms = more fuel used.

I would revisit the carbs for mid range adjustment issues.

Krey

[invisible4good]

hmm. i ordered a brand new oem petcock today just because i dont want the hassle of the inline shutoff valve. im noticing now im almost sure its gotta be a fuel delivery problem im having only because when i let it idle for a bit, it will rev out nice and smooth for a second or two. then midrange hesitates again. i wonder if the inline fuel shutoff is restricting flow somehow possibly; however like you said, full throttle would be affected too. the carbs air/fuel mix screws were originally around 2 turns out. i tried 1 and 3/4 and that didnt fix anything. then i heard for these bikes 2 and 1/2 is good. so i brought them to that, and still no change. man this things confusing :/

[Kreylyn]

hmm. i ordered a brand new oem petcock today just because i dont want the hassle of the inline shutoff valve. im noticing now im almost sure its gotta be a fuel delivery problem im having only because when i let it idle for a bit, it will rev out nice and smooth for a second or two. then midrange hesitates again. i wonder if the inline fuel shutoff is restricting flow somehow possibly; however like you said, full throttle would be affected too. the carbs air/fuel mix screws were originally around 2 turns out. i tried 1 and 3/4 and that didnt fix anything. then i heard for these bikes 2 and 1/2 is good. so i brought them to that, and still no change. man this things confusing :/

If you have not checked, this wear issue would have the exact symptoms your describing.

http://www.factorypro.com/tech/needle_jet_wear.html

Krey

[invisible4good]

no kidding huh. the only thing im curious about is wouldnt the engine run richer if the needle had worn? in my case, a little choke slightly helps eliminate the hesitation

[invisible4good]

ok so when i got the bike a noticed the muffler tips had holes drilled in them (about 9 holes each, plus the big original hole near the top). so i decided possibly the holes are messing with jetting so i welded them shut. and i got the new petcock in the mail today (which is slightly different than mine in the way of it having two fuel outlet nipples and mine has one). should i be hooking this up a certain way? what i did is block off one outlet and attached the other. so something between the new petcock or the muffler drilled holes being welded shut, something is wrong as the bike runs worse than before. i can get it to idle but it wont rev at all now. it just bogs and dies. ideas?

[invisible4good]

ok so after i spent hours yesterday working on the bike i finally fixed it. took apart the carbs completely and looked closely. carb number 3 was missing the screw that holds the float needle seat down so the seat was sitting higher than it should be. also adjusted the float heights as they were way out of wack. then noticed water in my carbs... which meant water in my tank. so it got a good flush and fresh gas. carbs were blown through with air. put back together mostly, resynced the carbs, cleaned the plugs, got a new battery put in her and put her all back together and she runs perfect!