951 Carburator Tuning

[dean thompson]

still cannot seem to get my rebuilt 98 GSX-L to run the way I want it to. There are two issues that I am having:

1. High idle out of water. If I set the idle at 1,500 in the water, it is ~4,000 or or more out of the water. I can adjust the idle to 3000 out of the water and it will stabilize and hold RPM. Put it back in the water and the RPM is lower than the required 1500 RPM.

2. Bogging up to ~1/3 throttle. The high speed circuit is crisp and responsive, however, there is bogging at low throttle position. The best way that I can describe the bogging is like a "gurgling" feel (and sound) with some hesitation.

Here are my current carb settings:
HSS: 0.5
LSS: 1.5
LSJ: 85
HSJ: 170
N&S: 2.0
Pop: 25 psi

I haven't done plug chops yet because I haven't achieved the rough tuning that I want. These are completely rebuilt carbs - very clean. The only reused part were the stock reeds. Actually, there are very few parts on this boat that are old. I really don't know what to do next.

[Technical Support]

Did you actually set your pop off or are you going off a chart?

[Bill O'Neal]

You are describing a motor that is too rich.

[dean thompson]

I do have aftermarket flame arrestors. The pop off stated is measured (with a gauge) not thoretical.

I will lean out the lows. What about the RPM issue. Now that I have it set at 3000 out of the water, I know I will be too low in the water. Can the rich condition affect that as well?

[Technical Support]

Yes, it makes the idle lower.

[thomas]

Do you have aftermarket flame arrestors?

[dean thompson]

I thought less gas took the idle up. Is it the other way around???

[thomas]

Yes, from the looks of it, your too rich on top. I always have trouble with a high idle out of water when I rebuild an engine. So, turn your idle down until the motor breaks in. Also, check that the carbs are synced and that the butterflys are closing all the way when the idle screw is backed off.

[dean thompson]

Thomas,

You think I am too rich on my highs, or lows?

[thomas]

highs

[dean thompson]

Thomas,

Help me a little because I don't understand. If most of the problems that I am experiencing are below 1/3 throttle, how can the high speed circuit be causing it?

Trying to learn ..........

[Blaine]

Here is my input .....

I have a basic set up , WCM jet kit w/ proks and a rossier head on my 2001 RX.

My highs and plug readings were GREAT on the highs ... no problem BUT I just could not get the bog out of the lows and I tried and tried, I turned them down until it hesitated then up 1/16th of a turn then it boged , I thought I would loose my mind [img]graemlins/cwm3.gif[/img]

Well it turns out those highs run just fine when to rich also ... I now have my highs CLOSED , I loose no RPM's in a 10 mile full throttle run and the plugs burn perfect. MOST of all I lost my what I though was "LOW END BOG" by turning my highs down.

Now this is my experience ... before you turn your highs completely shut make sure you go slow and take your time so you don't end up with a lean seizure ...

Good luck I hope I added some insite.

Blaine

[thomas]

Well, that was just an observation on your high speed jet numbers. Yes, lowering your high speeds might get you through a rich transition circuit better, but for the low bogging, I would look elsewhere. Did you use new needle & seats? What are your results when richening the low speeds screw? What is the result when leaning it?

[dean thompson]

Both carbs have brand new N&S and carb kits installed. One other notion that I am toying with is disconnecting the accelerator pumps.

To be honest, I have a phobia about going lower than ~1.5 on the LSS's. I probably shouldn't, but I put so much work into this ski I am a little paranoid. I can turn them down and then take some mid throttle plug chops.

The "rat-tat-tat-tat" bog doesn't seem to be at a transition point to the highs, but rather over the entire lower 1/3 throttle.

[thomas]

Although the Mikuni manual says, that you should not use the Low speed screws to cure a low speed hesitation, I have found that I can use them to diagnose a low speed problem. You will be able to tell immediately if you lower the low speed screws too much. It will gasp and die. Thus, you will know that lower limit. Engine damage will only occur at extended riding with an overall lean condition. Richening them over the correct setting will produce a noticeable stumble/gurgle before blasting off. As for the accelerator pumps, disconnecting them completely would cause poor power at takeoff. Are they both working properly, ie: does a dose of gas get squirted into each carb throat as you depress the throttle? You could turn in the accel pump screw adjuster to give less squirt and try that.
Also, is this low speed bog more apparent with a hard pull of the throttle? This would indicate more gas being squirted in than a gradual throttle application. Whew,
I am not an expert.

[ August 11, 2003, 11:49 PM: Message edited by: thomas ]