92 GSXR 1127 engine into 750F Katana, [sick]

[Buffalo Bill]

Kan't get the idle below 4000.
Kinda stumped at this point.
Made sure of all possible vacuum leaks:
New O rings.
Tight hose clamps.
Tight cap on #4.
Idle screw adjusted to 0.
Could it be the 750 CDI box advancing the ignition too far? This don't seem likely to be the issue.
I see conflicting opinions about CDI compatibility.

[posplayr]

I think you want an 1100 Ignition that matches that engine and not the 750.

[pete]

I'd tend to agree with that but... is it possible there's something hanging the throttle cable a touch? Just enough to keep the butterflies open? Assuming they're CV's of course...

Have you completely unwound the idle screw so it does nothing? If it still sits there after that, then there has to be something still holding them open just a touch at least...

Edit: Quick additional thought... disconnect the throttle cable(s) entirely and operate it by hand... that will definitely tell you if something is hanging it up.

[Buffalo Bill]

The cables aren't hanging up.
After the engine cooled down for an hour I took the airbox off and started it up just to see whatever.
No choke, it started instantly and as it warmed up the RPMs climbed with it.
I'm thinking it's too rich, after installing 120 main jets and the Dynotune needles.
Tomorrow, I'll turn the idle jet screws in from 2.5 out, down to 1.5 out and drop the needles to their lowest setting.
I'll continue to lean out the idle circuit and see what happens.

[Buffalo Bill]

The thing about CDI boxes is at this vintage they ain't doing much.
I been around long enough to have tuned point ignitions with mechanical advance. Not much going on there.
Then I converted one to electronic, just as the GS has been. Still had mechanical advance: 2 weights that swing out regulated by coil springs.
These late 89-92 CDI boxes replace the capacitor, points and mechanical advance, plus an RPM limiter.
Still not much going on there. No fuel injection, no Oxygen sensors, no sensors anywhere.
Nothing much is different from engine to engine that needs special calibration.

[posplayr]

The thing about CDI boxes is at this vintage they ain't doing much.
I been around long enough to have tuned point ignitions with mechanical advance. Not much going on there.
Then I converted one to electronic, just as the GS has been. Still had mechanical advance: 2 weights that swing out regulated by coil springs.
These late 89-92 CDI boxes replace the capacitor, points and mechanical advance, plus an RPM limiter.
Still not much going on there. No fuel injection, no Oxygen sensors, no sensors anywhere.
Nothing much is different from engine to engine that needs special calibration.

Well you know the rev limiter is going to be different and the advance curve is available in the manuals. The discussion of weights and springs is pretty much irrelevant. But you are probably correct that you don't have to worry about AFR map compatibilities.

[Buffalo Bill]

Making some progress, but not there yet.
I've turned the pilot mix screws to; 2 turns out, and lowered the needles one notch to where they are on the OEM needles.
I've synchronized the carbs.
Idle is down to 2500 RPM.
Thinking of trying some cheap tricks to solve a possible air leak at the intake pipes, gasket goop or silicone.

[Buffalo Bill]

Looks like for my 750 carbs to work right, I need to install the pilot and air jets used in the 1989 GSXR1100 carbs.
The 89 GSXR1100 used the same carbs: BST36SS.

[trippivot]

modified bikes = modified problems to solve.

I love this project -if it was a 600 chassis/body that would really make it a sleeper...

What ignition signal generator are you using? Have you checked where the spark is happening during the runaway idle? possibly your carbs are ok and the starting position of the ignition is too advanced . just a thought. idle speed advance has to be lower than 13 degrees BTDC

TPI boxes from 88 - 92 gsxr 750/1127 interchange.. The 88,89 600 katana is the most aggressive advance curve and makes a 1127 SCREAM.

I know on the GSXR1100 wiring harness there is a "wheelie wire" it is Red/Black doubles as the neutral switch wire - prevents full advance in 1 gear - split the circuit ground the box connection and make the neutral indicator light work properly - I've never combined these two units that you are doing -

sorry for this obvious statement but carbs are carbs- even 750s' on 1100 engine when the butterflies are closed AND the fuel mixture screws are at zero from seated the engine should not run.

[Buffalo Bill]

Thanks. I had the mix screws down to 1 out and it would die unless I blipped it up to 2500. It just won't idle in between 0 and 2500.
With the 750 carbs I figured I would get normal idle and power up to 5000rpm, and only need to be rejetted for wide open up to red line.
Wish I could get the same advice from 2 different people, everybody has their own opinion.

[trippivot]

You say that as if you are setting every cylinder mixture screw to exactly the same position across the board.

[Buffalo Bill]

For just getting one step closer to final tune, isn't that the right way?

[trippivot]

that is the just the starting point- lean idle drop tune each cylinder individually with the mixture screw only - looking for a positive response on each of the 4 cylinders. and then idle speed should become controllable.

#1 get it running #2 idle drop tune #3 set idle speed #4 synchronize #5 idle drop a second time for super fine tune - OR repeat #2 and #4 until you can control #3 IF NOT you have a different prob.

if you still cannot get the thing to idle, this is the point where you should be able to identify if you have a - fuel control problem , an air leak, or a mechanical linkage problem or a ignition timing problem-

[Buffalo Bill]

Sounds right, thanks!
Bummer they moved the idle screws under the carb throat. On the older GS it's at the top and easy to reach.
For that reason I haven't tried turning them as the motor is running, kinda hard to reach.

[Buffalo Bill]

I love this project -if it was a 600 chassis/body that would really make it a sleeper...

What ignition signal generator are you using? Have you checked where the spark is happening during the runaway idle? possibly your carbs are ok and the starting position of the ignition is too advanced . just a thought. idle speed advance has to be lower than 13 degrees BTDC

TPI boxes from 88 - 92 gsxr 750/1127 interchange.. The 88,89 600 katana is the most aggressive advance curve and makes a 1127 SCREAM.

TPI: Throttle Port Injection? You must have meant CDI box.