Changed Impeller, need to re tune carbs? RPM dropping at WOT

[Krispy]

96XP- MPEM shows 240+ hours, stock from the air box to the water box. I am running a worx grate, sponsons, R&D trim tabs, 85/87 nozzle and all last season I used a Solas X0. I am using stock jetting and needle settings.

This year I changed it up a bit, I changed the impeller from a Solas XO to a Skat-Track (16/24?).

I went from running ~58 mph with the X0 at 6800 rpm to running ~57 mph at 7050 rpm with the Skat Track.

While full speed testing I have noticed that I will hit full RPM after about 10 seconds of WOT, but then the RPM's would drop slightly as if I let off the throttle. I have only noticed this problem this year and with the Skat impeller.

Is it possible that I need to adjust my carbs for the new impeller/RPM?

Also, I noticed after a long run at mid throttle ~5500 RPM my idle was about 600 RPM higher than where I normally set it any ideas why that would be?


Please give me a few things to check so I can try and figure out what is going on.

 

[LouDoo]

Changing the carb. jetting is not a good idea, the reason your rpm's are off a bit is the impeller. I would guess you're probably getting out of the hole a little faster. 57mph for a 96XP is pretty damn good, I wouldn't change a thing.

Lou

 

[Krispy]

Changing the carb. jetting is not a good idea, the reason your rpm's are off a bit is the impeller. I would guess you're probably getting out of the hole a little faster. 57mph for a 96XP is pretty damn good, I wouldn't change a thing.

Lou

I am just worried about being lean on the top end, dropping rpm while holding wot. For example. 1500->7000, then 6900, 6800, 6700 all while maintaining WOT

 

[AdamXP800]

You might try cracking the HS adjuster open just a bit and see if anything changes.

Have you done a WOT plug chop?



96 XP800!
Keep the 2 strokes alive!

 

[Krispy]

You might try cracking the HS adjuster open just a bit and see if anything changes.

Have you done a WOT plug chop?



96 XP800!
Keep the 2 strokes alive!

I haven't done a WOT plug chop. I could do one, but I find it hard as hell to pull the seat and plugs while bobbing around in the water one one of these.


Any one have insight to the high warm idle?

 

[jammin777]

agreed with lou, different pitch impeller will change the rpm wot but i bet it pulls harder on the low end. also do a plug chop head towards shore shut it down and drift a shore.

 

[Krispy]

agreed with lou, different pitch impeller will change the rpm wot but i bet it pulls harder on the low end. also do a plug chop head towards shore shut it down and drift a shore.

Shouldn't the WOT rpm be fairly consistent, not dropping off the longer I hold WOT?


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[jammin777]

yes you're right it should be consistent sorry read your post too fast.

 

[Krispy]

yes you're right it should be consistent sorry read your post too fast.

My title is misleading, not intentionally.

I even caught out the great [MENTION=31048]LouDoo[/MENTION]

Bump. Why is my RPM not consistent at WOT

 

[Shane0524]

You may be running lean. I believe that could cause your rpms to peak and then drop.

 

[Krispy]

So yesterday afternoon I got the ski pulled off the trailer and onto the stand in my shop.

After letting things cool off outside I went back out to pull the carbs so I could verify by settings.

When I lifted the seat I was hit with a strong gas smell, I continued to pull the airbox and take a look at the HS adjustment needles. What I found surprised me.

Apparently the MAG side carb return line had become detached from the nipple (possibly on a jump) and was leaking fuel. I guess it would be possible that this would limit the fuel available to the engine at high RPM causing my problem. I re attached and double checked everything and will go out and give it a test run tonight hopefully.

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[mikidymac]

Be sure to clean up the gas and let it air out. You don't want it to go BOOM!