89 gsxf 750 Issues

[xvpx]

This may be a bit much for a first post but here goes.

I bought an 89 gsxf 750 and am having an incredibly hard time getting this to run, properly. It runs but after about 10 minutes the plugs foul up extremely bad. I will start with the choke on and as it warms up it runs with no choke, but then stalls out after a short time (5 Minutes) Then I need to clean the plugs again. I have cleaned the carbs according to the carbs guide on the wiki. I replaced the o-rings, measured the floats, bench synced them. So I have a few questions to ask.

I need some clarification on some of the things I have read on the various carbs related topics.

1. What are people referring to when they say "Main jets"?
2. The A/F screws, which direction of turning does what?
3. Is there a way to tell if the jets are OEM or After market?
4. Which notch on the needle inside the diaphragm is the standard position for the c-clip?
5. I have read different things on what the different c-clip positions do, any clarification?
6. Could weak coils be causing the fouling? How do I test the coils?

[600FY-Hank]

I'll answer what I can, and hopefully someone else will chime in with the rest.

1. The mains are what the needles seat into.

2. Clockwise on the A/F screw would close the passage off, or make the engine run lean; counter-clockwise would open the passage, or make the engine run rich.

3. The stock jets should have a Mikuni number stamped on them, somewhere around 135 or so, IIRC, with larger jets on the outside. I'm probably wrong.

4. The stock needles shouldn't have multiple positions, but I'm probably wrong.

5. The lower the position of the clip, the higher the needle will sit when closed, opening up the jet, and allowing more fuel into the engine. The higher the position of the clip, the lower the needle will sit, closing the jet, and allowing less fuel into the engine. This covers the whole travel of the needle, and as such, the whole vaccuum range of the engine.

6. Possibly, however as the state of the carbs and their adjustments are in question, I'd look at those first.

[Kreylyn]

This may be a bit much for a first post but here goes.

I bought an 89 gsxf 750 and am having an incredibly hard time getting this to run, properly. It runs but after about 10 minutes the plugs foul up extremely bad. I will start with the choke on and as it warms up it runs with no choke, but then stalls out after a short time (5 Minutes) Then I need to clean the plugs again. I have cleaned the carbs according to the carbs guide on the wiki. I replaced the o-rings, measured the floats, bench synced them. So I have a few questions to ask.

I need some clarification on some of the things I have read on the various carbs related topics.

1. What are people referring to when they say "Main jets"?
2. The A/F screws, which direction of turning does what?
3. Is there a way to tell if the jets are OEM or After market?
4. Which notch on the needle inside the diaphragm is the standard position for the c-clip?
5. I have read different things on what the different c-clip positions do, any clarification?
6. Could weak coils be causing the fouling? How do I test the coils?

1. Main jets are located in the bottom of the carbs, under the bowls. OEM size for your bike is...

Type BST36SS
Main jets

• US, cylinder no. 3 110
• All others 105

It's going to be the larger one sticking down, has a slot for a flat head to remove it. It screws into the bottom of the emulsion tube.

With the bowls off, make sure you have the rubber stopper in the hole covering the pilot jet. Make sure it's sealing off well also. This could cause an issue with running rich if not.

Click the wiki link above, search carbs 101. At the bottom of the carbs 101 is a link to a PDF. Download that as it has pics of the full process on cleaning the carbs. These pics includes locations of parts and such.


2. Out from seated is adding fuel. More turns = more fuel. 2.5 is a general starting point for stock. If you have a stage 1 kit with full exhaust system you might need more in the 3+ range depending on the jetkit and exhaust your using.

3. OEM jets have a design on them next to the size. The OEM design is a box, with a smaller box in it in one corner. See above for size.

4. OEM US needles do not have multiple options. Jetkits will, and generally the starting point is 3rd from top. Adjust from there to fine tune the 5-8k rpms performance range.

5. The needle primarily controls the fuel/air mix for the 5-8k rpms range. The needle tapers to the point, so the further out of the emulsion tube the needle is, the more fuel that will mix with the air thus "richen" the mixture more. The slides generally will be in the same posistion at those rpms, so by adjusting the needle eclip, your fine tuning the fuel mix for that rpm range.

6. The manual has a full test procedure on how to check the coils. Click the wiki link above, and download it.

Also check the voltage going to the coils. You should have a minimal of 11v to the coils (turn key on, check voltage at the orange/w wire plugged to the coil).

[xvpx]

Ok well thank you both for the information, won't get to this until next weekend. I will download the material you suggest and do some reading. I will check back in when I have had a chance to look at it.

Thanks again.