View Full Version : rough low end idle 97 GSX

05-29-08, 08:35 PM
Hi all. New to the forum and new to the sport. I posted an intro in the meet and greet and hopes that that will get me started. I have never owned a jet ski but my son wanted one for the summer. I checked around some and bought a ski local. I hope I didn't get burned. We did lake test the ski and the previous owner drove the ski. It has a 101 hours on it. It is very clean ski. He gave me receipts where he had the carb rebuilt,new gas lines,needle valve and etc. He convinced me that 2 strokes idle rough. Is this true? The ski ran good on the lake. It seemed to bog down on takeoff but ran good at a higher rpm.{Scared the heck out of me,insert old guy here}. I will be taking the ski to the lake for it's first outing this week. It also has new plugs in it. Whats next? What do I need to do and what should I expect? Thanks in advance. Probably the only help I'll be on this board is if it's in the welding field. Thanks TMP

robin savell lloyd
05-29-08, 08:54 PM
My boat engine seems to idle rough in the water I have not checked into it further yet.as it is new to me and I have been repairing other isues. I would not know if it was idleing rough if I did not look at engine while it was idleing as I do not feel it in boat. If yours is stock I would think you have a carb issue if you have a hesatation or a bog on take off. but I can be wrong. Good luck Robin. :cheers:

05-29-08, 09:13 PM
Sounds like your about to have fun....and your right, the 787cc motor in that thing will scare the living crap out of ya......(insert old guy here too!)

If you have all the papers, then you know what kind of maintenance has been done. But your problem sounds like a simple one. For the record, 2-cycles don't all idle rough. When was the last time the carbon deposits have been cleaned from the RAVE (rotax adjustable variable exhaust)?

This is an annual requirement on the Rotax engines that are so equipped. You can go to the boat section and look under the "General Discussion" and you'll see a post "a look inside the 787". There, you will see a picture of the RAVE, completly assembled, and apart. You'll also see what one looks like when it's clean. Check out the post. The carbon builds up on them and they stick, causing it to bog. Sounds like you have one stuck open, that's why you got good top end. Stuck open, it's bleeding off to much of your cylinder compression.

The one on the PTO (back cylinder) is easy to remove and clean, but the one on the MAG (front cylinder) has to be taken apart while in place to clear the exhaust. Take off the cap (careful, it's spring loaded) then, with a metric socket, loosen the center hex head (the cap to the rave bellows), then you can remove the 2 allen head screws on the side of the base plate. Pull the base and bellows out then the slide valve. Don't worry about the slide valve falling in, it has a stop on it so that won't happen.

Re-post if you have anymore questions.........welcome to the forum!...:cheers:

05-29-08, 10:11 PM
ok, first question seeing how I know absolutely nothing about these things. What are the little black round plastic things on top of the head and on top of the muffler. They have a red center in them that seems to adjust? I also found a plug wire boot at the black box that was busted. Surely that would affect the spark. Also is the carb adjustment screw at the top of the carb towards the back? Is that the air fuel or the idle screw if either ?

05-29-08, 10:26 PM
Ok, this is good! I've been a member 1 hour and already learned something. Mr. seadoosnipe I went to the boat section and read your tech article. Bingo the little black things are rave valves. The ones on my ski look to be new. Should I pull them and check anyway? Is the thing adjustable? Looks like the red button screws in and out. This is the place I needed to find. Thanks and please bare with me. I am a pretty decent car mechanic[building a 59 buick and a 27 ford coupe now. Both nailhead powered] OT I know. If I can get the to where I use the right words I think I can figure this out.

05-29-08, 10:42 PM
I'll be patient. If you've got mechanical apptitude, then it won't be long you'll have this thing in the palm of your hands.......

Be careful on the carbs. The upper screw is the high speed screw and should have a plastic cap that covers it so that it can't be leaned out by improper adjustment. They give us a quarter turn either way for fine tuning. The slow speed screw is on the bottom of the carbs. You'll have to open the throttle all the way to see them. I use a mirror to look up from the bottom. All good mechanics keep a mirror handy. Old mechanics anyway, that can't bend into these engines like they used to.....:rofl:

I'd stll check the RAVES, even if they look clean. Your looking for excessive buildup. If you think they may be o.k, then take out the one on the PTO side, since it's easiest, just to inspect it. The gasket should hold fast for you.

The other thing that can be causing some of the problem is "syncronizing" of the carbs being off a bit.

Look at the RAVE first. The red plastic cap should either be all the way in or adjusted out to about flush of the black plastic edge. These are adjusted for lower and upper end power.

Continue reading.....the 787 is an awesome engine. I love working on it. :cheers:

05-30-08, 07:29 AM
Snipe, thanks. As soon as I get off work I'll take the RAVE valves apart. This is a user friendly board unlike some of the hotrod boards I visit. Thanks for the kindness. All of the information will help. TMP:cheers::cheers:

05-30-08, 07:40 AM
Your welcome and we'll be waiting to see what you find out. If the RAVE's look fairly clean, re-post ASAP cause I got a couple other ideas. But without knowing how long it's been since they've been cleaned, thats where I'd start first..........

We'll await your re-post. :cheers:

05-30-08, 03:19 PM
SDS- you sir nailed the problem. The RAVE valve most likely has never been cleaned. I pulled the rear and it is totally black. I will now disassemble the front one and clean it also. I snuck in for lunch and pulled the valve. I will be very surprised if this doesn't fix the idle as bad as they are. I will report back this evening when I finish. Thanks. You not only saved me money but I enjoy learning new things. TP

05-30-08, 05:02 PM
Are the bevels on the raves pointed in opposite directions? I pulled each one seperate from the other. One faces one way and the other faces the opposite. Doesn't seem right to me. I am not going to start the motor until someone can answer me. Don't want to mess anything up. SDS where are you? I'm sure this is the way they came out. That might have been part of my problem if this is incorrect. TP:ack:

05-30-08, 05:28 PM
Sorry, I've been at work.....but all the boses are gone.

That's weird that they would have one way and one the other. I don't see how it could run. I hope it did hit the piston and do any damage.

Very easy to figure out. Look at the slide valve carefully. On the flat part of the slide, you'll see the word "top" stamped in the valve. Put the valve in with the word "top" facing up. If for some reason you can't see it, the beveled edge (longest point of the slide) is down. Imagine holding the slide at about a 45* angle. Well, the end of the slide rides flat surfaced to the side of the piston.

Let me know if you need anything else. Remember, I do work, so I may not be able to get right back to you. I try checking in on the forum while I'm here, ..........but man, sometimes it gets busy.

Good luck, clean them real good. :cheers:

05-30-08, 05:44 PM
I'm like a kid waiting on his neighbor to get home and play. I understand about the work. The one on the back side of the ski is the one that is in incorrect I believe. When I took it out I laid it down like it should go back in. The main housing has a gap in it . That goes toward the top also. It is not like that on the back one. So for me to put the part that says top in and the housing towards the top I'll have to take it apart. Proabably done wrong the last time it was worked on. If you are still on the board I'll wait a few minutes to see if you agree. TP

05-30-08, 06:00 PM
My mistake but thank you for clarifying the positioning. The rear one was correct. When I reassembled the front one, I put the slide in backwards. That could have been a disasater. Thanks TP

05-30-08, 06:27 PM
Make sure you clean out that small porting hole to the RAVE bellows from the cylinder. This is also a way of knowing which end is up when you go back with it. The hole in the base of the RAVE has to set on the hole in the cylinder head..........

I think you've got it. Now, I'll be curious to see how it runs.........:hurray:

05-30-08, 08:19 PM
Yes, I was a little confused on what it looked like. All is well. I put it on the hose and it's all the differance in the world. It would barerly idle before. It real crisp on throttle response now. I really appreciate the help. Like I said before this is a much friendlier board than some of the hot rod boards I visit. SDS are you a tech? I'm going to the lake tomorrow morning and I'll let you know how it goes. I am going to leave well enough alone for now. I drained the gas, installed a new filter and the plugs are new. What should they be gapped to? I'm anxious to see how it does. Now I have to go out and finish welding up the frame I fabbed for my 27 ford coupe. It like the ski is pure hotrod. [425 buick nailhead,2x4's,s/p 400 tranny,373 gear] I am comfortable working on it. thanks again. TP

05-30-08, 09:56 PM
Yeah, after making these changes, it would be a good idea just to see how it runs. If over the years, if they weren't cleaned, then the other owner may have adjusted the low speed screw open a bit.

Your spark plugs should be gapped to .020"-.024"....NGK BR8ES plugs or equivalent.

"Am I a tech?"........I don't know. In my day, we were called "shade tree mechanics". I see you've got some of that in your last post, 425 nailhead. My last rod was a 1969 C-10 with a 400cu.in small block, with forged pistons, a 486 lift and duration crane cam with the older model 2:02 heads. A 6" Offenhauser aluminum intake with a two inch spacer and cold can for my fuel line. I used a 650 cfm holley with vacuum secondaries for driving round town, and a 850 double pumper for the week-ends. I had hooker headers and a two chunks for my rear end. I had a 4:11 positrack and a 3:83. It would scream. If I had every penny I put in my HO motors, I'd be living in a 4000 sf home.........:rofl:

I've been a drag bike racer, built motors from lawnmower, chainsaw, motorcycle, outboards, cars, diesel truck, along with my trade of operating and maintaining steam generator equipment, boilers, turbines, pumps, compressors, heat exchangers, oil purifying equipement.............Man, I didn't know my knowledge base was so extensive. But you know what's funny. When in the forum, I'll base a decision on something, that in the past was logical, just to be corrected by a member that I was wrong. I don't mind admitting defeat, but when challenged, I will go straight to the source to find the answer. And 90% of the time, the ones that challenge me are right!....oh well, just goes to show in the world of the internal combustion engine, you can never stop learning about these things.

As my dad used to say, "a jack of all trades but a professor of none!"

Now, go out and have some fun!........let me know how it runs. If it runs kinda sluggish, adjust your red caps on the RAVES.......if you have them all the way down, then try them backed out flush to the black plastic cap.:cheers:

05-30-08, 10:04 PM
"Am I a tech?"........I don't know. In my day, we were called "shade tree mechanics". I see you've got some of that in your last post, 425 nailhead. My last rod was a 1969 C-10 with a 400cu.in small block, with forged pistons, a 486 lift and duration crane cam with the older model 2:02 heads. A 6" Offenhauser aluminum intake with a two inch spacer and cold can for my fuel line. I used a 650 cfm holley with vacuum secondaries for driving round town, and a 850 double pumper for the week-ends. I had hooker headers and a two chunks for my rear end. I had a 4:11 positrack and a 3:83. It would scream. If I had every penny I put in my HO motors, I'd be living in a 4000 sf home.........:rofl:

Now we are on the same page. I asked a young fellow the other day if he was a mechanisc and it insulted him a little. he promptly told me he was a TECH! I too have an old drag racing past. Build period correct customs and hot rods now as I can . Pipeline welder for many years and was a pro-bullrider and rodeo clown until I was 40+. hard on the body. I have always been an adreniline junkie. I think I will like the water crotch rocket

05-31-08, 06:25 AM
You think thrown by a bull is hard on your body, wait till this ski throws you. Hitting the water also hurts!..........

After getting the new boat, I went to the river. I decided to go "barefooting" as I did several years ago. I had no problem getting on my feet, but when they feel out from under me, it took 30 minutes for the "pain" to ease. The adreniline never stops flowing and the thrill for daring adventure is always there, but man, does it hurt more when things go wrong..........LOL

I dabbled in some welding. How can you work on "rods" without a little of it? I used a littel stick, hated the 6011's, my fav was the 7018........also did a little mig for aluminum with argon shield.

05-31-08, 08:04 AM
Snipe, we may be twins. I was made out of rubber when I was young. I think it's hard plastic now. Sure hurts alot more. I'm off to the lake. I have my vicoden with me incase I forget my age. Later TP:hurray:

05-31-08, 08:36 AM
I keep my bottle on me when out too. Never know when I'll be taking a "face plant" in the water!..........:rofl:

05-31-08, 11:46 PM
All is well except my body. I'm too dang old to take the obuse I had today. We had a blast.First rattle out of the box my son was driving ,he made a hard right and me and him made a hard left. I either broke my ribs or bruised them. Been years since I hurt like this. Going back tomorrow. Only problem I have the ski doesn't stay running due to a low idle settng. Runs and idles good on the hose but a little slow for the water. Whats the fix for that?Man that thing is fast. Good throttle response. I left the rave valves alone. They seem to be adjusted all the way down. What would it do if I raised them all the way up? Oh yeah, I'm sunburned. My legs havent seen the sun in probably 20 years. I see an addiction here. Thanks for all the help. TP

07-31-08, 01:49 PM
lmao.......man listening to you guys i dont ever want to get old.........hahahah. the gsx is a rocket, tks for the information on the rave cleaning. im going to give mine a shot, i think that might be the cause of the rough idle and the carbon black plugs. but ya even at 26 it still hurts hitting the water at 50 or so. especially trying to huck a backflip on an old 440. :cheers: