I have a 1998 speedster with twin 787's. This weekend the starboard engine started running a little rough and then began backfiring in the middle of the rpm range (but runs fine at the upper rpm range). I visually inspected the engine and do not see anything out of the ordinary. Motor fires right up and will idle but a little rough. I have not worked on this type of motor before, so any guidance would be greatly appreciated. Thanks!
98 speedster - engine problem
- Thread starter Daystar40
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robin savell lloyd
Active Member
I would start with new spark plugs. :cheers:
robin savell lloyd
Active Member
You could buy a cheap compression guage and give it a compression test while you are changing plugs. No it is not normal for plugs to foul that quick. but it can hapen and if the plugs make it run beter then you know that you may have a carb or other problem. you need to look at the old plugs that you remove to see how the engine is burning fuel. :cheers:
I pulled the plugs and one looks darker (and more wet) than the other plug but neither look terrible. I haven't checked the compression but it was 150 across both engine in June so I hope it hasn't changed. Any ideas where to look next or what the difference in the two plugs is telling me? Also, can the 1998 be hooked up to a diagnosis computer? - I believe their is a port on the drivers side under the helm pod (or whatever its called).
timmyboy76
New Member
due comp test, could be 150 today, and 50 tomorrow,...install new plugs, and cut plug wires back 1/4in from boots side, then reinstall boots, and fire ur up...
Over time the wire will become corrosive and need to have a fresh end to handle the electric load. It wouldn't hurt on an older machine.
Karl
Karl
Thanks for all the help. I checked the compression and it is 150 across the board. I also changed the plugs and gapped them to .022. I did not cut the wires because they are only 3 months old. The engine starts right up, idles strong but still gets rough at mid-rpms. I want to put the boat on the trailer so its easier to work on but will I still be able to get the rpms up on the trailer to test it (without the rev limiter kicking in)? I have never hooked it up to a hose before. Any other guidance?
You can still rev it up to the full speed if you put the selector out of neutral... but it isn't recommended. The hose water doesn't cool as well as if the boat was in the water. But if you have access to a launch that isn't busy and it's close by to your house, you can try it out of water then back the engine into the water and keep it on the trailer and run it like that. Remember that it'll idle at around 3K out of water instead of 1500...
Looking back to the original issue, I'd say it can't be fuel delivery because it would be worse at the top end, not better.
Check the rave valves to see if they are dirty, and then you might be thinking about a carb rebuild.
Karl has a great writeup on the rave valves, take a look here
Let us know how it progresses!
Looking back to the original issue, I'd say it can't be fuel delivery because it would be worse at the top end, not better.
Check the rave valves to see if they are dirty, and then you might be thinking about a carb rebuild.
Karl has a great writeup on the rave valves, take a look here
Let us know how it progresses!
Forgot something that might be of interest.
Check the low speed and high speed adjusters on both carbs of the motor having touble, it could be that one cylinder is running richer than the other. Verify that they match the spec on your motor.
For the 1997 (i'm looking at the '97 shop manual) it is all the way in (JUST until it stops, don't overtighten as it'll ruin the needle valves in the carbs) then turn it back out 1 turn on the low speed screw and 1 1/4 turns on the high speed screw.
Since it runs out fine at top end, i'd look at the low speed screws first.
Check the low speed and high speed adjusters on both carbs of the motor having touble, it could be that one cylinder is running richer than the other. Verify that they match the spec on your motor.
For the 1997 (i'm looking at the '97 shop manual) it is all the way in (JUST until it stops, don't overtighten as it'll ruin the needle valves in the carbs) then turn it back out 1 turn on the low speed screw and 1 1/4 turns on the high speed screw.
Since it runs out fine at top end, i'd look at the low speed screws first.
This is the correct carb settings;
The High Speed screw is set to "0". These have a plastic cap on them to keep them from being turned any more than 1/4 turn. The Low Speed screw is set to 1 1/2 turns. The screw has a pin through it. If you need to adjust the idle speed do NOT use the low speed screws to adjust it. Use the IDLE Screw to adjust both carbs at the same time. When adjusting the carbs be sure both carbs are in sync.
Here is some more usefull info; You can hook up the hose to the seadoo and have it run for up to 5 minutes to flush it out. Connect the hose and start the seadoo. Turn on the water after it is started. Turn off the water, than shut down the seadoo. This way it won't allow water to back flow into the engine through the exhaust due to no back pressure from the engine not running. The bearings and seals on the impeller jet pump are cooled from being in the water. When it is on the trailer it doesn't have that cooling effect so they will get hot after about 5 minutes.
I pre start my seadoo's, dry before I leave for the launch, but just for a second or 2 to be sure it will start at the launch. Peace of mind is worth a lot.
Karl
The High Speed screw is set to "0". These have a plastic cap on them to keep them from being turned any more than 1/4 turn. The Low Speed screw is set to 1 1/2 turns. The screw has a pin through it. If you need to adjust the idle speed do NOT use the low speed screws to adjust it. Use the IDLE Screw to adjust both carbs at the same time. When adjusting the carbs be sure both carbs are in sync.
Here is some more usefull info; You can hook up the hose to the seadoo and have it run for up to 5 minutes to flush it out. Connect the hose and start the seadoo. Turn on the water after it is started. Turn off the water, than shut down the seadoo. This way it won't allow water to back flow into the engine through the exhaust due to no back pressure from the engine not running. The bearings and seals on the impeller jet pump are cooled from being in the water. When it is on the trailer it doesn't have that cooling effect so they will get hot after about 5 minutes.
I pre start my seadoo's, dry before I leave for the launch, but just for a second or 2 to be sure it will start at the launch. Peace of mind is worth a lot.
Karl
That's great news,.....Yes, let us know how its running.
Karl
Karl
Had the boat out this weekend and with the expection of one issue, its running better than it has ever run. Great hole shots and pulls very hard (better than ever) through top speed (58 mph on gps). All the info did wonders - Thanks! However, it doesn't seem to like to be at idle for very long. After about 5 minutes of a no wake area, it starts to run rough and if I firewall the engines right out of the no wake area it hesitates (almost stalling) and then goes like you know what (if I throttle up slowly, the problem appers to be lessened). Do I need further adjustment to the low speed screw or is it something else? Thanks again for all teh help!!!
I would adjust the low speed screw a 1/4 turn in and try it. Be sure to adjust both carbs so they are in sync. If it worsens, adjust it out to add fuel. If either adjustment helps it might be the accelerator pump might be plugged in the carb. To check it with, the engine off remove the carb cover Put the shifter in forward, and look inside the throat of the carb. Than push the throttle linkage to full throttle and you should hear and see a squirt of fuel go into the throat of the carb. If not than the fitting is probably plugged. You will have to remove the carbs to blow compressed air into it and unplug it.
Keep us posted on your progress.
Karl
Keep us posted on your progress.
Karl
let us know how it goes.
Karl
Karl
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