won't rev under load

[RFITZ]

99 GTS with 920 engine. Had 200 salt water hours on it with blown engine. installed new SBT engine, rebuilt carb,double checked ignition and valve timing. Won't nearly keep up witha friends GTI with same engine. When under heavy load, won't go to but about 3/4 throttle. As load lightens up, will kick up to full throttle. Can't pull a tube without this bog, but friends GTI pulls it fine. Can back into water on trailer and rev, revs up to about 3/4 throttle for about 1 second and then kicks up to full throttle. Revs fine out of water. Adjusting mix screws further doesn't help. Still carb problem? Driving me nuts...

[Bryan Glynn]

Who's kit did you use on the carb, what did you set the pop-off to, and where are your screws set at right now?

[Bill O'Neal]

You do mean 720 engine, right ?

It sounds like the carbs are not working correctly. Did you rebuild the carb and install a new needle and seat, or at least run a pop-off test to see if the old one leaks?

[John Kubiak]

Are you sure it's a 920, I'll bet it is a 720!!

What spark plugs are installed? Your ski calls for NGK BR8ES plugs or their equivalent resistor type spark plug. Non resistor spark plugs can cause this problem

What is the plug gap set to? It is supposed to be 0.022".

Most plugs come out of the box at about 0.030" You should always check the gap before installation!

Make sure that the spark plug caps are secured to the wires. They screw into the wires. If they pull off of the wires easily, you need to trim the wires back about 1/4" and re-install them by screwing them on to the wires.

[RFITZ]

Sorry guys, you're right, it's a 720, not a 920. Used a carb rebuild kit from the local Seadoo dealer. Set the popoff to 38, seems high but manual spec. (would higher or lower popoff help?). Didn't seem to leak around seat before popoff. Low speed screw at 1 turn, H at 1 1/2 (started at zero and this seems to run just ever so slightly, best.) Plugs are Nipendenso W24ESR-U, Supposedly replacement, but twice the resistance (6 ohm vs3.8 ohm). Assume that's not significant. Gap is at .022 and resistance plug cap to plug cap is to spec, so wires seem fine. Rebuild or replace carb? Send to local Seadoo Jock. I'm open to suggestions.

[Bryan Glynn]

Well first of all, put it back to the way it's supposed to be - highs 0 turns out, and put the correct plugs, NGK BR8ES back in. With so many variables in question it's very hard to narrow it down.

[RFITZ]

Put correct plugs in, right gap, reset Hi to 0. Didn't notice so much when cold but bog problem was there after we played a while. (1st time on the water this season.) Bog seemed to be at a lower RPM than I had remembered, though. Maybe at about half throttle or less. With light to medium weight load and full throttle standing start, takes off fine, goes to about 35% throttle, holds for a second or so (not actually a bog), then takes off smoothly to full throttle. If towing a load, stays at 35%. (Sorry, no tach on a GTS).
Still might be missing a little top end, but with 3 girls just becoming riding age, not too concerned with that yet.

[Bryan Glynn]

You are really close - sounds liek you just need to fine tune your low-speed screws, possibly clean out your carbs.

[hrichards]

Are you guys saying the the high speed screw is set 0 turns out? as in, it is not used because it is shut off?

[Bryan Glynn]

Sort of. As in, Sea-Doo set it up at the correct mixture through jetting, and doesn't want anyone messing around with it, leaning it out and blowing up the ski because of it.

[RFITZ]

Haven't done anything with lo speed mix but set it to best smooth idle, then set hi speed mix with plug check method. Is it normal to still have to adjust the lo mix further? Won't it sacrifice idle quality or starting? Didn't realize there was room to adjust lo speed for performance beyond idle. Open up a little?

[Bryan Glynn]

See our article here.

[RFITZ]

Took it out last night and started with lo screw at 1 turn. Tried everything fron 1/8 out to 2 out and still had the hesitation on takeoff at low speed, Maybe a little worse at less turns out. Wouldn't stay idling well when I got over about half turn from 1 in either direction. Not much other obvious change in performance.
Funny thing, when I put it in neutral-deflector down- to check rev during couple of the settings, it revved maybe a little slower to peak, but didn't have the hesitation. Try cleanout of lo speed circuit?

[Bryan Glynn]

What was your exact procedure for setting your pop-off pressure? Where did you put what parts, what did you do exactly?

The symtoms indicate it's too low.

[RFITZ]

Home grown guage. Hooked up a 0 -120 psi air pressure guage to a T hose and slowly bled compressed air into the port below the seat with a a valve(had a sea doo manual in front of me so assume it was the right port a year ago). Flooded with WD40 to watch for release pressure. Granted guage may not be most accurate in the world. Retested many times to confirm. Did have to stretch spring in rebuild kit slightly to reach pressure. Could be sticking? Exactly what fuction does popoff serve? If it could be too low, would that mean it's letting gas in too soon?