Personal Water Craft Forum banner
1 - 7 of 7 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 ·
After de-winterizing and getting my 1996 750 STS Jetski out on the lake, it ran perfectly with 2 passengers running hard for a half hour or so, then slowly started losing power, but had enough to return to shore.

Details: Like most 2-strokes, it misses a little in the low end as it gains rpm's and if I wait long enough under this new condition, it climbs in rpm a bit....almost sounds like it is running on one cylinder but not as rough, just smoother low power. i bought and replaced the 2 spark plugs and it ran great again (of course an hour later), but again after running it pretty hard another half hour or so, especially under load with 2 people and getting squirrelly it bogged down again. Letting it sit for another half hour or so (cooling off?), it works pretty well (maybe not 100%), but quite a bit of power. Just riding around slowly at 2000-3000 rpm alone or with one rider, doesn't seem to make it bog out. Single rider is best, but bogs down with 2-3 passengers and riding hard more quickly. I checked (and flushed) cooling and it's flowing well (flows well out pisser about 6-10"), have put in new premium gas, plugs, etc. Old plugs weren't really bad looking, but from last year. When it bogs down, it's gradual and you just notice it starting when you hit the throttle, it is really limited, then bogs down even more. Not jerky (like elec cutting out) and not like its running out of gas....just loses power and kind of stays there. It never dies or drops to idle, but remains at about 5-8 mph and therefore won't plane.

Could use some ideas before I have to trust a dealer with my wallet. Im the original owner and its never happened before. Im going to take it out and see if I can add a little choke when it does it, to see if that affects it which might indicate carburation. First time poster, Thanks for your ideas !
 

·
Premium Member
Joined
·
5,060 Posts
I hate to sound like a broken record because I keep suggesting this, but do a compression check. If things show good, then it is prob time to kit the carbs. Seeing the age, if you haven't yet, I would look at getting the oil injection lines replace as they are old and hard by now, and look at replacing the fuel lines as they might not be sealing 100% and might be sucking a little air. Also check the pulse line and make sure it is good, and check the zip tie down at the intake end of it to make sure it is tight.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #3 ·
Thanks Rodsatheart. I really appreciate your taking the time to share your knowledge. I'll borrow or buy a compression gauge and assume I should test it both when running well and when it acts up. Then I'll whittle down your suggested items as time allows. I haven't put a rebuild kit in a jetski carb before, but have done cars so I'll look for a kit online somewhere. I'll have to read up how to adjust the pop off pressure. Thanks again. Hopefully I can let you know what fixed it soon.
 

·
Premium Member
Joined
·
5,060 Posts
No, just cranking pressure is good. Keep the plug is the cyl. that is not being tested, plug wire grounded, and throttle wide open. These carbs are easy compared to automotive carbs. get a true Keihin kit. They are a little more, but worth the money. Much better components. Pop off is adjusted by spring length. Yours should be in the 25 psi range.
Document how many turns from seat each mixture screw is for each carb. They must be returned to that exact setting. Get a adjustment tool off amazon or ebay in case you have to set them low speed mixture screws, but you should be good returning them to orig. settings. Be sure and get the inlet screens clean.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #5 ·
Thanks. Cold cranking like you suggested was:
170 fwd
168 aft

I warmed it up for 10 mins (with water on) and tried again just for the heck of it.....took both plugs out, just for grins:
160 fwd
150 aft

3rd time, after 10 min cooling, one plug out at a time:
165 fwd
156 aft

From what I read, this seems to be normal if not pretty decent for a 20 yr old jetski. Right? Maybe the aft cylinder is wearing a bit, but certainly within the 10% and I should move to the next step and put a kit in the dual carbs, Agree? The gauge is pretty new and in good shape.

I'll order the carb kit and adjusting tool and take the next step. Anything other ideas, just let me know. Thanks
 

·
Premium Member
Joined
·
5,060 Posts
Not real fond of the 9psi difference, but the numbers are pretty good. If you document what the exact current setting of the screws is for each carb, it will go back together pretty close. make sure you get everything clean, and don't try to disassemble the fuel pump. It has anti tamper screws, and the kit will not have all the components.
Also, blow all the cooling lines out. Everyone of them, just to make sure there is not a water obstruction somewhere. Be careful when blowing back into the exhaust manifold.
 
1 - 7 of 7 Posts
Top