Bill and ?, need tuning help...

[nb141fd]

Bill, you have recently been helping me try to find the source of my "hard-to-start-when-warm" problem on my 92 SP. The ski starts immediately when cold and runs great until you shut it down, then it takes forever to restart it.

The previous owner equipped the SP with a primer, SBN44 Mikuni, K&N flame arrester and a Coffman pipe.

What I've done:
replaced all fuel lines and filter
rebuilt the SBN44 carb including replacing the 2.5 N&S
replaced the fuel selector valve
replaced the battery with an odyssey dry cell
checked the rotary valve clearance (0.014) spec 0.009-0.014

Your last advice was heading in the direction of the carb settings. I have checked it and here are the settings:

2.5 N&S, 115 gram spring (gold)
Pop-off 20 psi
low speed jet- 117.5
high speed jet- 150.0
low speed adjuster- 1 1/4 turns out
high speed adjuster- 1 turn out

What do you think? Are there any changes to the carb that you suggest I try to get rid of the warm start problem? I also tried to get a hold of Coffman's to see if the jets were as they recommend, but they are on vacation until next week. Thanks Tony

[nb141fd]

Re: Bill and ?, need tuning help...

Bump

[Bill O'Neal2]

Re: Bill and ?, need tuning help...

Typical low and high speed jetting is more like 120 LSJ and 140-145 HSJ , 2.5 with 95 gram spring , 14 psi PO on a 580.

What do your sparkplugs look like? Could you post a picture?



Make sure the fuel tank vent check valve is allowing the air pressure to relieve itself from the gas tank. Too much pressure in the tank will force fuel past the needles and seats when you park it hot.

[nb141fd]

Re: Bill and ?, need tuning help...

Thanks for the reply Bill. I currently have the carb off with the SD in my garage. I was hoping to try some different carb settings, put it back together and head out to the lake for another try.

My manual says 22-29 psi PO for a stock 92 SP, so I thought at 20PSI I might be too low and fuel was getting by causing my hard warm starts. This is of course without knowing what the correct PO should be for the K&N and Coffman mods the previous owner added.

According to Mikuni, I could go to with a 2.3 N&S (staying with the 115gr spring) and get up to 22psi on the PO, or with a 2.0 N&S and 95gr spring I could get up to 25psi. Am I just chasing my tail or do you think Pop-off has anything to do with my problem? The other option I was thinking about and wanted to run by you was closing the low-speed adjuster (currently out 1 1/4 turns) in quarter turn increments to see if that would help. What do you think?

The last time I was out and had this problem, I opened the fuel cap to see if I could hear any sounds of pressure build-up. I heard nothing, so I assumed that my fuel thank check valves were working fine. If there is another test for this possibility, please let me know, and I'll check it out. I would post pictures of my plugs but they were last run on the trailer out of the water at slightly faster than idle. If you want to see them, I'll be glad to post them. Thanks again, Tony

[Bill O'Neal2]

Re: Bill and ?, need tuning help...

Wait a minute. Do you have a 44mm SBN on there, or a stock carb?

[nb141fd]

Re: Bill and ?, need tuning help...

Its a 44 Bill, the previous owner took out the 38 and installed the SBN44 as well as K&N arrestor and Coffman pipe. Tony

[Bill O'Neal2]

Re: Bill and ?, need tuning help...

So, why are you going by the information in the manual for a oem 38mm carb?

It is totally irrevelent to a 44mm SBN.

[nb141fd]

Re: Bill and ?, need tuning help...

Bill, I know what your saying, I'm just trying to get some foothold on what the settings (particularly Pop-Off) should be for my carb and the stock settings are the only numbers I can get ahold of for comparison.

Let me just ask you outright; what do you think of these settings on an SBN44 which is mounted on a 1992 SP equipped with a K&N flame arrester and a Coffman pipe?

2.5 N&S, 115 gram spring (gold)
Pop-off 20 psi
low speed jet- 117.5
high speed jet- 150.0
low speed adjuster- 1 1/4 turns out
high speed adjuster- 1 turn out

As far as my warm start problem, do you advise any changes to the above settings in an effort to improve my warm starting? Thanks, Tony

[Bill O'Neal2]

Re: Bill and ?, need tuning help...

Back up about three posts. I gave you the jetting numbers that I have had luck with on a setup like yours, except one thing. The Coffman 587 pipe is not as good as most other 580 aftermarket or oem performance pipes, so my jetting numbers might vary a little from yours, as I never use Coffman 580 pipes.

Do you have excessive RV cover clearances? Should be .010 to .014 with the valve and cover installed. Excessive clearance makes for hard starting.

[nb141fd]

Re: Bill and ?, need tuning help...

Bill, no RV clearance issues. You were helping me last week as I was just starting to try to solve this problem. Per your advice I did the following in order:

-replaced the N&S (2.5) I didn't have a pop-off gauge at the time and you thought the N&S might be leaking fuel by. I took it out to the lake and still had the warm-start problem.

-I replaced the fuel selector valve just to be on the safe side; no help.

-checked the rotary valve clearance using the solder method and got 0.014" (spec 0.009-0.014") you thought this was excellent for a 92SP.

This brings us to the carb settings. Mine don't seem that far from the ones you posted: You posted Typical low and high speed jetting is more like 120 LSJ (mine is 117.5) and 140-145 HSJ (mine is 150) , 2.5 with 95 gram spring (same as mine), 14 psi PO (I get 20psi on mine). It seems like I'm pretty close to what you use, except for the PO, therefore, I don't know what else to check or do to solve this problem. Any final advice before I blow this thing up?

[frankey01]

Re: Bill and ?, need tuning help...

yeah since you are in so cal take it to him or get right on his numbers as being off by 5 on the jets can make a difference.

[Bill O'Neal2]

Re: Bill and ?, need tuning help...

I'm sorry, I misposted the size of the spring. It should have read 65 gram spring, 14 psi pop off pressure.

I will need to see a picture of your sparkplugs right after idling for about 1 minute, and a picture of your sparkplugs after a WOT run, without any idling at all. Go full speed and pull the tether, stop and remove the sparkplugs, save them for a picture.

The sparkplugs must have at least 15-20 minutes of running time on them before you do the tests.

Also, take note of how the motor accellerates thru the rpm range and the maximum rpm that the motor turns. Does it loadup a bit after idling ?

List all aftermarket parts, and the impellor make model and size.

[nb141fd]

Re: Bill and ?, need tuning help...

Thanks again Bill, it will take me a few days to get the info, I'll get back to you. Tony