1997 xp falls on its face at WOT, then surges....falls on its face.

[murray1886]

I can't seem to get full throttle for more than a sec, it keeps surging. All new lines/ carb filters. I bought it with a blown engine so I have no Idea how it ran before and I didn't adjust carbs. seems to run fine except when I try for WOT

 

[RebuiltSeadooBaffles]

Need to properly go through the carbs, verify prroper jets and N/S, FULLY clean them, check them for proper pressures, etc, clean fuel selector, check compression ratio

 

[murray1886]

Need to properly go through the carbs, verify prroper jets and N/S, FULLY clean them, check them for proper pressures, etc, clean fuel selector, check compression ratio

did all of the above... just didn't adjust because I don t know the proper settings. Does it sound like a fuel problem to you? running lean at wot? Could it be plug wires or would that just cause a miss?

 

[bell99man]

Surging is very often fuel. Spark tends to be apparent more than just WOT. Since full throttle is fuel controlled, I would verify fuel flow first. HS screw should be all the way in and LS should be close to 1 1/4 to 1 1/2 turns out from closed. But this will not likely fix you trouble.

 

[- BiRkS_]

Take it for a WOT run. After about 20 secs bogging, pull the lanyard at WOT and pull the plugs. See what they look like. They should be equal. If one is lighter coloured than the other, then that cylinder needs more fuel. Personally, it is better starting off rich and tuning from there. If you run it lean for too long, you will roast the engine. Did you clean out the fuel selector valve?

FYI is this a brand new rebuilt engine? how many hours? You shouldnt be doing any WOT runs until after break in.

 

[Strizzo]

did you clean/replace the small filters inside the carbs? you'll also need to replace the grey fuel lines with new and clean/replace the fuel selector valve, the additives in modern fuel breaks them down and clogs the filters in the carbs, which causes fuel starvation and the surging you're talking about.

 

[murray1886]

The engine has a new top end. I 've ran it for and hour or 2 and it should be broke in. all new lines, new filters in carbs, new main filter, fuel selector cleaned as well. I checked the hs and Ls adjustments, HS was all the in on pto and out about an 8th on the mag side, Ls was 1 and a quarter out on the rear and I lost track of where the front was when the screw driver slipped. I set both LS screws to 1.75 out sense I saw that on another thread. We'll see how it does in the AM.

 

[Sportster-2001-951C-Stock]

Pressure test your fuel line all the way back to the tank if you haven't already, you could be sucking air. Are you sure the fuel pump pulse line isn't leaking? Of course you verified your low and high jet sizes are appropriate?

High power lean out is not something you want to push too much obviously, most risky place for seizure. Maybe this is what wiped the previous engine? Fuel pickup is clean, fuel shutoff isn't plugged, all that same stuff.

 

[murray1886]

Pressure test your fuel line all the way back to the tank if you haven't already, you could be sucking air. Are you sure the fuel pump pulse line isn't leaking? Of course you verified your low and high jet sizes are appropriate?

High power lean out is not something you want to push too much obviously, most risky place for seizure. Maybe this is what wiped the previous engine? Fuel pickup is clean, fuel shutoff isn't plugged, all that same stuff.

good point...I did not pressure test the fuel lines or check the pulse line! I will do this today. Thank you!

 

[Sportster-2001-951C-Stock]

Ha, yeah, I'm obsessive about having clean fuel so I can't tell you how many times I've cleaned the fuel filter bowl and not gotten a good seal on that cup o-ring. So now after putting the cup back on I make a habit of removing the fuel line from the carb, shutting off the fuel selector, and doing a quick pressure test.

I think I'm done with that for awhile though, not finding trash in the fuel filter anymore.

 

[Cmills8907]

Ha, yeah, I'm obsessive about having clean fuel so I can't tell you how many times I've cleaned the fuel filter bowl and not gotten a good seal on that cup o-ring. So now after putting the cup back on I make a habit of removing the fuel line from the carb, shutting off the fuel selector, and doing a quick pressure test.

I think I'm done with that for awhile though, not finding trash in the fuel filter anymore.

how are yall doing pressure test on fuel?? I need to check mine too...

 

[Sportster-2001-951C-Stock]

I'd recommend taking the fuel line loose from the fuel pump and from the tank, plugging one end and then pumping not more than two PSI of air into it.

As a quick test, I just blow as hard as I can with my mouth and hold it to see if it leaks down. Don't swallow that gasoline. You can test all the way back to the tank or just back to the fuel shutoff by turning turning the shutoff valve to the closed position.

I've gotten to the point I test back to the shutoff valve each time I clean my fuel filter cup, to make sure the o-ring doesn't leak. I take the fuel line off the fuel pump, shut the valve off, and blow in the line.

 

[murray1886]

OK, I checked all clamps (some seemed questionable), checked fuel filter o ring, and turned out HS 1/8... not sure which one fixed it....but it runs like a champ now. Maybe a little rich at idle though, I have the LS out 1.75... may crank them in an 1/8 and see what happens. Thanks for all the input, sometimes it just takes a different point of view to see the obvious!

 

[Strizzo]

OK, I checked all clamps (some seemed questionable), checked fuel filter o ring, and turned out HS 1/8... not sure which one fixed it....but it runs like a champ now. Maybe a little rich at idle though, I have the LS out 1.75... may crank them in an 1/8 and see what happens. Thanks for all the input, sometimes it just takes a different point of view to see the obvious!

factory setting for the LS needle on the 97 xp is 1 turn out from closed, so you should be way rich at idle.

 

[murray1886]

factory setting for the LS needle on the 97 xp is 1 turn out from closed, so you should be way rich at idle.

where did you find that at? I'm reading that a 97 LS is supposed to be 1.75...

 

[murray1886]

forget my previous post.... I was looking up 787 engine thinking the carb settings were the same for all boats.
I just pulled the manual...you're right.
The 1.75 setting is for sp/gs/gsi...
Thank you for saving me some serious tuning head aches!!
I'll turn them in tomorrow