Acceleration problem 1991 Katana 750 after sitting 4 years - Motorcycle-Journal Forums

gmeriaux · 05-11-2004, 09:11 PM

Hi,

I just bought a 1991 Katana 750 that sat without running for 4 years in a garage. The bike has only 4700 miles and has never been modified.
Things that I did:
- Drain tank and carbs and replace with new 91 octane fuel
- Replace air filter with new one
- Change oil and oil filter
- Replace the Spark Plugs with new ones
- Checked the coils and they are OK
- Removed and cleaned the carbs

The bike will start fine and idle OK, but if I accelerate it goes up to 4000 and then gets stuck there or runs very roughly up to 6000. Above 6000 rpm it will run better.
Looks like the problem is mainly between 4000 and 6000 rpm.

Does anyboby has an idea of what the problem can be ?

Thanks,

**87gsxrnut** · 05-12-2004, 11:20 AM

Check your slide diaphrams. They might be pinched, have holes in them or installed incorrectly. (You DID pay attention to that when reassembling that didn't you)

Make sure they slide up and down with no stiction. Your midrange acceleration is tied to the needles/diaphrams not operating correctly. Make sure they are pulling cleanly and not sticking. Being totally stock, this should be a pretty simple fix. It is when you have all of the jet-kit/pipe crap that it gets to be a pain in the arse.

General carburetor rule:

Idle to 1/4 throttle - Pilot jet
1/4 - 3/4 throttle - Needle jet
3/4 - full - main jet

This is why so many bikes run incorrectly. Many people think the main jet is always the culprit. BUT, most of the CV carb problems I have found were due to incorrect needle height when the jet kit was installed. (no worries w/stock though)

My 1100 race bike is going on the dyno this weekend. Need to get my carbs totally sorted out now that the motor is broken in.

- Nut

**Uncle Bob** · 05-12-2004, 02:14 PM

Well this isn't very technical but after 4 years of sitting it probably just needs to run some.

Before spending money or time why not try some gumout in your gaz for a tankfull or two and see if that helps, if not you're looking at rebuilding your carbs.

gmeriaux · 05-13-2004, 08:51 PM

Thanks for your answers.
I checked the needles and diaphrams. Everything seems to move nicely and I cannot find any hole in the diaphrams. Look like the next best thing to do will be to rebuilt the carbs.
Where is the best place to buy a rebuilt kit ?
What does the rebuilt kit needs to contain ?

**87gsxrnut** · 05-17-2004, 07:07 PM

I don't know about the rebuild thing. Sounds like you might need to adjust the needle height a bit maybe. Did you make sure the needle spacers were installed correctly?

- Nut

dirtyfingers · 05-17-2004, 10:55 PM

If it has a jet kit, (evident by multiple notches at the top of the needles) try raising the needles a notch or two. If it still has the stockers get yourself some small washers/shims to raise them.

gmeriaux · 05-19-2004, 11:46 PM

Thanks for your answer.

I think I will order the K&N Stage 1 Kit. It look like a nice upgrade and should fix my problem.

05-11-2004, 09:11 PM	#1 (permalink)
gmeriaux Newbie Joined: May 2004 Posts: 6	Acceleration problem 1991 Katana 750 after sitting 4 years Hi, I just bought a 1991 Katana 750 that sat without running for 4 years in a garage. The bike has only 4700 miles and has never been modified. Things that I did: - Drain tank and carbs and replace with new 91 octane fuel - Replace air filter with new one - Change oil and oil filter - Replace the Spark Plugs with new ones - Checked the coils and they are OK - Removed and cleaned the carbs The bike will start fine and idle OK, but if I accelerate it goes up to 4000 and then gets stuck there or runs very roughly up to 6000. Above 6000 rpm it will run better. Looks like the problem is mainly between 4000 and 6000 rpm. Does anyboby has an idea of what the problem can be ? Thanks,

05-12-2004, 02:14 PM	#3 (permalink)
Uncle Bob Site Admin & Squeegee Boy Joined: Dec 1969 Bike: 2003 Volusia SE Location: Montréal, Québec, Canada Posts: 107	Well this isn't very technical but after 4 years of sitting it probably just needs to run some. Before spending money or time why not try some gumout in your gaz for a tankfull or two and see if that helps, if not you're looking at rebuilding your carbs. __________________ Yadda yadda yadda, whatever, they ain't going to listen anyway.

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05-12-2004, 11:20 AM	#2 (permalink)
87gsxrnut Ho Dog Joined: Dec 2003 Bike: 867-5309 Location: Terror Lake Posts: 4,224	Check your slide diaphrams. They might be pinched, have holes in them or installed incorrectly. (You DID pay attention to that when reassembling that didn't you) Make sure they slide up and down with no stiction. Your midrange acceleration is tied to the needles/diaphrams not operating correctly. Make sure they are pulling cleanly and not sticking. Being totally stock, this should be a pretty simple fix. It is when you have all of the jet-kit/pipe crap that it gets to be a pain in the arse. General carburetor rule: Idle to 1/4 throttle - Pilot jet 1/4 - 3/4 throttle - Needle jet 3/4 - full - main jet This is why so many bikes run incorrectly. Many people think the main jet is always the culprit. BUT, most of the CV carb problems I have found were due to incorrect needle height when the jet kit was installed. (no worries w/stock though) My 1100 race bike is going on the dyno this weekend. Need to get my carbs totally sorted out now that the motor is broken in. - Nut

05-13-2004, 08:51 PM	#4 (permalink)
gmeriaux Newbie Joined: May 2004 Posts: 6	Thanks for your answers. I checked the needles and diaphrams. Everything seems to move nicely and I cannot find any hole in the diaphrams. Look like the next best thing to do will be to rebuilt the carbs. Where is the best place to buy a rebuilt kit ? What does the rebuilt kit needs to contain ?

05-17-2004, 07:07 PM	#5 (permalink)
87gsxrnut Ho Dog Joined: Dec 2003 Bike: 867-5309 Location: Terror Lake Posts: 4,224	I don't know about the rebuild thing. Sounds like you might need to adjust the needle height a bit maybe. Did you make sure the needle spacers were installed correctly? - Nut

05-17-2004, 10:55 PM	#6 (permalink)
dirtyfingers Ditch Magnet Joined: Mar 2004 Location: Chicago Posts: 167	If it has a jet kit, (evident by multiple notches at the top of the needles) try raising the needles a notch or two. If it still has the stockers get yourself some small washers/shims to raise them.

05-19-2004, 11:46 PM	#7 (permalink)
gmeriaux Newbie Joined: May 2004 Posts: 6	Thanks for your answer. I think I will order the K&N Stage 1 Kit. It look like a nice upgrade and should fix my problem.

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