3/4 trhottle miss

[Richard Naugle]

hi folks i need a hand here with a 93 explorer it has the 580 motor and was running excelent last night when i put it away but this morning when we put it back in the water it has a miis at about 3/4 throttle but if i gentley ease it up on to plain givivng it thottle gently it will go wide open without a miss although the boat dosen't seem to be running as fast although i can't tell 4 sure as i don't have a speedo? any ideas??

 

[timmyboy76]

plugs?...cut the plug wires?...red cable condition?...carbs been clean?

 

[Richard Naugle]

got new plugs they are .. BR8ES they don't seem to sell the 7's around here. and i gaped them to .020 they keep looking gunky though.
as for the plug ends i'll do that now.. and the red wire i assume you are talking about is the main power cable? mine looks good... as for cleaning carbs that is not something i've ever done and would like to know the procedure and what to clean and how and what to leave alone.. any help is greatly apreciated th

thanks rick in the barn with the boat

 

[Richard Naugle]

pulled the boat out of the water and hooked it to a garden hose and when i crack the throttle wide open it dosen't miss..but was still missing in the water at anywhere past 1/2 open throttle.. pulled the plugs and the mag side plug looks to be alittle gunky while the pto side seems to be oily dry and clean.. did a compresion test after the boat was running in the yard on the hose for a few minutes and both cylynders are showing 70 psi.. is this right or should it be higher?? i can not find the compresion rate in my book.
any an all help apreciated

rick with the boat back in the barn...

 

[timmyboy76]

yeah, the motor will spool up no problem, out of water with that compression read'n, but in water, with load to pump, that compression read'n will make the boat go nowhere.

Time for topend, chief...:ack: 150psi is great, anything under 100psi, get the syptoms your get'n.

 

[Richard Naugle]

is there any thing other than a worn top end that will give me abad compresion reading like the rotary valve being out of wack or the timing being off with the oil injection etc.. just guessing and grabbing at straws because the boat was running so strong just 12 hours earlier??

 

[timmyboy76]

do another compression test, with throttle position at W.O.T., just to get "avg" read'n.

With it running awesome 12hrs earlier, could be a lean, which it'll run like a raped ape, until she blows. Oil injection could be the culprit.

 

[Richard Naugle]

nope on the oil injection as when i was running it on the hose it was readily apparent by the 2 stroke exhaust that it was operating..

I'll tell you a little story about exploring a river outlet the night before,while i was doing this and decided the river was to shallow i heard a kind of grinding clank 2 times and i assumed i had sucked a piece of wood debris through the pump..immediately after this the boat would rev up about halfway but not have anymore than 5 mph forward speed this lasted for about 5 minutes and then the boat proceeded to operate normally for the rest of the evening , about 2 more hours of riding..could this have something to do with my problem??

 

[kustomkarl]

No, it was probably just a stick or something in the jet pump/ impeller.

Here is some information on compression test;
To test compression, remove both spark plugs. Place spark plug caps on the plug cap studs near the cylinder head to ground the empty caps. This completes the circuit of the ignition electrical system and prevents any electrical problems from the caps being un grounded. Using the correct adapter for the threaded end of the tester,( same length of the spark plug threads length)screw in the tester in one plug hole. Hold the throttle wide open. Push the start button. Watch the compression gauge, when it peaks out at the most compression, let go the start button. Read the psi number. I would do it 3 times to be sure it is accurate. Check both cylinders the same way. The ideal compression is 150 psi per cylinder. If it is less, it's not a problem as long as they are close to being the same. If the psi is less than 90 it might need be time for a tear down and a rebuild. If the psi in 1 cylinder is say 140 psi and the other is 80 psi you need to tear down and repair. This difference is a lot then there is a problem. I hope this helps you.

The timing or rotary valve wouldn't have anything to do with the compression low

Karl

 

[Richard Naugle]

thanks karl

 

[kustomkarl]

We have parts available too. Click the "Parts" link at the top or in my signature. The parts link will give you a good break down of your seadoo too.

Karl

 

[Richard Naugle]

i have one other question about the cooling system if anyone can help..
the 2 jets of water coming out of the hull above the water line in the stern,are they both supposed to run hot?? one of mine, the one on the left ,as seen from the stern is running hot and the one on the right is running cold.