1994 GSXF 750 wont run right

[94Kat750]

**The Bike**
I am the proud new owner of a 1994 GSX750F Katana. Picked it up Last Friday from a buddy of mine who drove the bike daily and never had any major mechanical problems. I Spent that night cleaning the carbs, oil change, cleaned air filters, replaced spark plugs and new tires, clutch cable and new battery. The bike fired right up with a little choke , I threw on my gear as it warmed up, and after several min I jumped on and gave it a spin.

**The Issue**
As i hit 3rd gear I gave the throttle a good twist to go through the gear quickly but @ about 4500 to 5500 rpms i got a violent back fireing that repeated it self as long as i held the throttle. The engine would not make it past 5500 rpms no matter how long i held the throttle open. It would just sputter with the needle bouncing off of 5500rpms. As i came to a stop sign and put it in Neutral the bike idled so low it wanted to cut off.. but other times it would idle around 3500ish. I've cleaned the carbs over and checked everything i could but cant find the problem.
Someone suggested that it is a Diaphram on top of the slide in my engine, so I took the air filters off and sure enough when i reved the 2nd slide from the left most carb did not move up and down when twisting the throttle.
I would like a 2nd opinion is this enough to cause violent back firing and sputtering. **Should i order a new set of 4 diaphrams??

Tonight I rode for about 15 min to listen to the engine and the more i drove.. the more power i lost and eventually i had no throttle response. I am new to working on street bikes and would appreciate anyones input on whats possibly wrong.

[Kfreak]

Could be a number of things. You changed the plugs. did you put the wires back on the right cylinders? Check them and go from there.

[94Kat750]

Any suggestions on where I can find the correct wire sequence?

[md86]

Well , the left coil goes to 1/4 , the right goes to 2/3 . Sounds like your plugs were fouling more & more as you rode / Gotat figure out WHY . Whether it's a ful , spark ,or compression issue . Pulls plugs , see which (if not ALL) are black . Should give you some clues where to start ....

[Wild-Bill]

Bothers me that the #2 slide didn't raise. first, try sticking your finger in the throat of that carb and make sure the slide will move - that it isn't frozen up. If it moves then pull the top off that carb (Watch for one little o-ring under the vacuum port and the long spring that will try to throw the cap at you.) and pull the slide out. Hold the diaphragm up to a light and see if there's any holes/tears in it. You don't have to replace all 4 diaphragm-slide assemblies as a set. It'd probably be better if you did, just to keep all 4 carbs working the same but they're expensive little boogers.

If the slide is OK I'd start looking at vacuum. There's a passage that passes vacuum from the intake to the tops of the diaphragms. There's an o-ring at the top of it, under the cap and the diaphragm seals up between the bottom of the cap and the top of the carb body. Vacuum from the intake feeds the top of the diaphragm which pulls the slide up against the pressure from the spring, pulling the needle out of the emulsion tube which allows more fuel to pass through the main jet. No vacuum, no mains. No mains, no power. No power, no happy!

[Trackerrrr]

**The Bike**
I am the proud new owner of a 1994 GSX750F Katana. Picked it up Last Friday from a buddy of mine who drove the bike daily and never had any major mechanical problems. I Spent that night cleaning the carbs, oil change, cleaned air filters, replaced spark plugs and new tires, clutch cable and new battery. The bike fired right up with a little choke , I threw on my gear as it warmed up, and after several min I jumped on and gave it a spin.

**The Issue**
As i hit 3rd gear I gave the throttle a good twist to go through the gear quickly but @ about 4500 to 5500 rpms i got a violent back fireing that repeated it self as long as i held the throttle. The engine would not make it past 5500 rpms no matter how long i held the throttle open. It would just sputter with the needle bouncing off of 5500rpms. As i came to a stop sign and put it in Neutral the bike idled so low it wanted to cut off.. but other times it would idle around 3500ish. I've cleaned the carbs over and checked everything i could but cant find the problem.
Someone suggested that it is a Diaphram on top of the slide in my engine, so I took the air filters off and sure enough when i reved the 2nd slide from the left most carb did not move up and down when twisting the throttle.
I would like a 2nd opinion is this enough to cause violent back firing and sputtering. **Should i order a new set of 4 diaphrams??

Tonight I rode for about 15 min to listen to the engine and the more i drove.. the more power i lost and eventually i had no throttle response. I am new to working on street bikes and would appreciate anyones input on whats possibly wrong.

First thing I suspect is that you either pinched or didn't get the #2 diaphram seated properly when you reassembled the carbs. If they ran fine when you bought it and crappy after you worked on it, that's a clue.

Second, you refer to air filters, not air filter. You most likely have pod filters then right? Ditch them and go with a stock air box and filter, your bike will be a much happier bike. Kats like vacuum to work right. There are a few on the board that say they got them to work right so you might hit them up for advice if you are set on keeping the pods.

Third, you say you continue to lose power til the bike won't run and no throttle response. Check your fuel lines for kinks and pull the plugs and check them also. If they are black and sooty, clean them and reinstall. Did you reinstall the petcock vacuum line properly also, should run from back of petcock to #4 carb to work right. It almost sounds like your bike was fuel starved. Make sure the spark plug boots are screwed onto the wires good too, they do come loose sometimes.

[94Kat750]

WOW thanks so much for all the feed back guys. I checked everything and today after taking the tops off to check the O-rings on top corner of all 4 carbs, looks like the slides are working great. But now the bike wont even start and run. The RPM needle is jumping everywhere then sputters til it dies for a few seconds and wont stay on, the fuel lines seemed to be unkinked and I'm getting major back fire when reving to 5k-6k in neutral. the fuel dial is missing but there is a flat spot on the rounded peg that sticks out from under the tank to turn the fuel on / off. The positions are 12o'clock, 9o'clock, and 6o'clock but i only know that up is off. Could someone tell me what the other directions are (*?? RES , ON??*). I will be dropping the bike off to a local bike shop (not dealership, but a old school, bike parts everywhere shop) and based on what I told them on the phone, theyre estimating that about 200 will fix her up. ANy other suggestions are welcomed, I would hate to spend the money if this is a simple fix.

[scottynoface]

There is no off on the petcock, "ON" is actually off as fuel only flows when the engine is on, the vacuum pulls it in. RES and PRIME are gravity fed.

[steves]

http://katriders.com/wiki/index.php5?title=Petcock

You are probably running too rich. Is the bike jetted?

When you pop the top off the carb, and remove the slide... does the needle have grooves and multiple positions with an e-clip?

[md86]

And you still ain't pulled them plugs yet , have ye ?

[Wild-Bill]

How old is the gas? Pull the plugs like md86 suggests and give them a cleaning with a toothbrush. You've probably fouled them. Then make sure you've got plenty of fresh fuel before you try again.

One of the problems with buying a used bike is that the PO is generally going to have left the bike sitting for quite a while before finally deciding to sell it. Human nature but it's very bad for the bike. Now you've got to figure out and fix whatever went wrong that convinced the PO to sell plus deal with the consequences of letting the bike sit. Don't be surprised if you have to disassemble and clean the carbs. Pilot jets get gummed up pretty regularly and the only real fix is to pull the carbs off the bike, yank the jets and soak them.

[md86]

Not just the jets that get plugged , but the little holes in the carb bodies . I find more crap in THOSE than the jets .

[Wild-Bill]

Yup!