• This site contains eBay affiliate links for which Sea-Doo Forum may be compensated.

787 bogging from idle, do I need higher jets??

Status
Not open for further replies.
When I got this jet ski, it ran great. No hesitation, no hard starting. The thing just ran, and ran well! Put a huge grin on my face every time. Then, the needle bearings at the wrist pin let go and killed the piston, rotary valve and brass gear. After some tears, I got another rotary valve, RV cover, brass gear and pistons, but ever after, I was battling this damn problem. The main thing that changed was the RV cover.

I went out and measured it last night, I was able to stick a .33mm feeler in there and BARELY get a .4mm in there, but that was REALLY tight. So I popped it off and put some thin solder in there. It squished to about .36mm That is about .05mm out of spec. Is that really all it takes to ruin the performance of these boats? I don't have any other RV covers that are any good, so I'll be shaving down the ears on the existing one with valve grinding compound against the block till it's back within spec. Looks like I'm also going to have to heli-coil at least one RV bolt hole on the block. yippie... I love manually drilling out aluminum with a T-handle.
 
Did you reposition the gear on the crank when you did all of that? It most likely has been shifted.

As for your question, from the manual:

NOTE: If the clearance is below 0.25 mm (.010 in) this could create an overheating situation and if the clearance is over 0.35 mm (.014 in) this could create a hard starting situation.

Edit: did you remove the o-ring when checking?
 
Last edited by a moderator:
I always position the gear according to the manual. I tried reversing it and chose the side that gets me closer to the book. It's on there how it's supposed to be, as far as I can tell. It even lines up with the fine scribe mark someone else put in there.
Just reread the manual. Last night I thought the clearance should be .25mm Now I realize that it should be .30mm +/- .05mm. Mine's at about .36mm I can't believe that that tiny difference is making it this hard to start. I'm going to file it down to about .30 and try with stock carbs, POP OFF at 33psi and no accel pumps. I get the feeling that it's not the RV afterall...
 
I always position the gear according to the manual. I tried reversing it and chose the side that gets me closer to the book. It's on there how it's supposed to be, as far as I can tell. It even lines up with the fine scribe mark someone else put in there.
Just reread the manual. Last night I thought the clearance should be .25mm Now I realize that it should be .30mm +/- .05mm. Mine's at about .36mm I can't believe that that tiny difference is making it this hard to start. I'm going to file it down to about .30 and try with stock carbs, POP OFF at 33psi and no accel pumps. I get the feeling that it's not the RV afterall...
 
Ground the RV valve to about .32mm. Tested with and without the o-ring. My RV cover has been through some battles. There is a gouge right near the MAG port where something got caught and bit into the aluminum. Some time ago I must have shaved that part down. The gouge is about .5-1mm wide, and about .5mm deep and extends about 1cm into the face, then it smooths out. Also, the RV cover has a couple fine grooves (maybe .01mm deep) going around it. Could this cause me problems? It's always been my opinion that the seal happens between the block and the RV plate, and the cover is just to maintain a tight clearance.
 
A lot of covers end up with some grooves, but deep grooves and scratches that stretch between both ports can cause the cylinders to steal from each other similar to high rv valve clearance. The gouge you're talking about in your cover is probably from when you stripped your gear. Keep in mind that you can't just file down the rv cover, you also need to be able to machine the o ring groove so it tightens the clearance down.

Assuming your rv valve is in good shape, id recommend a new rv cover.

My quote above comes straight from the fsm, so I guess you can believe it, or not...
 
Yea... I'm starting to feel the same way about needing a new cover. I realize that the o-ring groove has to be machined also, but I ground it only .04mm. I think the o-ring can squish a just THAT little more. When I checked the solder with the o-ring, it was the same thichkness as without the oring. As for the groove going around the circumference... I wonder if it even can steal from the other side as that side should be closed at that time. But who knows...
 
The groove between ports can steal charge from the other cylinder, or pull air through the other carb, reducing the velocities in both carbs and throwing off fuel mixture. It affects the quality of the seal at the port.
 
Well, I'm still having this issue. RV clearance didn't fix it. This year I rebuilt the engine, and want to get the carbs purring perfectly, as I believe my engine runs very lean at low RPM. During break in, my pipe got VERY hot, I could only hold my hand on it for 2 sec or so. What's scarier is my lower end felt even hotter. I'm worried my new crank will suffer teh same fate as my last one (broken connecting rod). I read a forum post here where a member had the same problem and like me, checked everything. His carbs came from Dr. Honda, so they definitely were good. He fixed his problem by putting grease around his throttle shafts. Turns out his bushings were allowing excess air. I'm going to try that on my ski soon. Hope that finally kills my 5 year old gremlin.
 
The engine getting that hot all leads to the cooling, did you check/rebuild the water regulator? Being a little lean wouldn't make your pipe that hot or engine for that matter. That sounds like cooling to me
 
Hmm, I didn't rebuild the water injection rave. I did examine the bellows though, and they are fine. One of the coils of the spring has essentially collapsed, so the spring is about 1/8 or so inches shorter, but I don't think that affects it much at all. I have one washer in there, and it was turned out about 4 turns from stop. I pulled the hose coming off the reg and had a little bit of water coming out of it (at idle), pulling the hose from the barb at the manifold yielded more water, so that's draining fine. The lake water was very warm to the touch, I'd say it's somewhere around 85F or warmer. I know that cooling is relative to lake water temperature, but does anyone know what temperature it's supposed to be at? I'm going to bring my laser thermometer next time and see what it's at.
 
SWEET! So the SPX is back up and running at least? Sounds like we need to do another weekday run to Harris. :) I need to get mine out and do some testing too, but have been too lazy when I get home to hook up my ski and drag her down to the lake....even though it's like 5 mins away. HA!
 
Yea man, it's mostly together. I repainted the hood this year, and going to buff her out. I went and sanded her down lightly with some 1200grit. She's got a lot of battle scars, but looks good enough after a little buffing. My biggest concern is the hesitation and temps. Would be good to go out with you guys and get some temp readings on your motors to compare. I haven't finished the break in yet (have about 2 heat cycles and 8 gallons of fuel to go) but I should be out somewhere this weekend with both my GTI and the SPX. Probably Jordan.
 
787 properly cooling you can hold your hand on the head pipe at idle for just about as long as you want to. If any part of the pipe is turning colors that is an indicator.

Sent from my SGH-T889 using Tapatalk
 
IDoSeaDoo said:
Yea man, it's mostly together. I repainted the hood this year, and going to buff her out. I went and sanded her down lightly with some 1200grit. She's got a lot of battle scars, but looks good enough after a little buffing. My biggest concern is the hesitation and temps. Would be good to go out with you guys and get some temp readings on your motors to compare. I haven't finished the break in yet (have about 2 heat cycles and 8 gallons of fuel to go) but I should be out somewhere this weekend with both my GTI and the SPX. Probably Jordan.
Click to expand...

Nice! I'll be visiting my parents this weekend, but after that I'm free. Also can be free most weeknights. I replaced some parts myself so went back to the tuning specs that worked for me to see if i actually had an air leak. So I still have some testing to do. I'm hoping all is well now, cause the first day I was out with yall it ran amazing!!
 
So if you ever wanna just poke around harris one evening lemme know. I'll def be doing some tweaking. So ride and stop quite a bit to make sure I don't burn up my motor.
 
Suke - yea, I'll be out there, probably tomorrow evening. I need to put my GTI together and break it and my spx in. Just got the last part for the GTI in from the machine shop yesterday. Need to assemble engine and pressure test it. The carb just passed all tests so fingers crossed that it just RUNS! :)

Racerxxx - the cooling seems to be working, all the lines are verified to be clear, and the jugs stay only warm. Could the hot ambient/water temps be causing it to just SEEM hot to me? I know my perception of heat is different than that of the engine. I never went above 1/4 throttle and most of the time, the ski was plowing water.

Anyone have a laser thermometer to offer some figures?
 
JMHO,
The elbow going to the tuned pipe from the WCV is calibrated. There should be a number stamped on the side 22, 24, 48. (see chart on page 105) That elbow is calibrated to allow the proper amount of water in the tuned pipe. The elbow has a larger inlet diameter with a slightly smaller outlet diameter.
The spring inside the WCV is also calibrated to allow the proper amount of cooling according to the amount of throttle you are giving it.
The WCV should be screwed all the way down then turned counterclockwise 3 complete turns. A properly calibrated WCV delivers 0.4 gallons per minute at WOT.

If any of these criteria are not met serious engine damage can occur. page (106 in my manual)

You mentioned that one of the coils of the calibrated spring was collapsed, therefore the spring is no longer calibrated. Not good in my opinion. You also mentioned 4 turns out from the stop. Should be 3 turns.

FWIW I can lay my hand on the tuned pipe all day with no problem with a properly calibrated WCV. Hope this helps.
 
Last year, I had an issue with not reaching max RPM, it ended up being diaphram in WCV ( water control valve/water regulator ) was pierced by its rusty clamp as they all do, and the spring was broken that was inside. I snagged the parts off my 96' gsx and there you go all done. So I would definentely get the right spring in there. The WCV spring is longer than engine RAVEs.

Now as for the cooling. I was out riding 2 weekends ago on a very hot and humid day, I had gotten back from a 20 min ride, varying rpms but mostly at 5k rpm cruise. When I pulled seat it was warmer than normal but I kept riding rest of day. When I got home I went ahead and checked all cooling lines for blockages. It was good to go, no blockages. Ski still performs great, but I know the long run I took it on and the hott day attributed to its higher operating temp that day.

Have you grounded your temp sensor with engine off and lanyard on after double clicking the red start button to awaken the gauges? Remember me and [MENTION=59515]suke[/MENTION] were testing that last year on his xp? We took my screwdriver and grounded the temp sensor wire to the head. Then verified the loud "beeeeeep" and red overtemp light on in multifunction gauge. I would do it just to know peace of mind that it does work incase your engine does get too hott. Im thinking about coming out to Jordan if you guys wanna ride saturday. We can see how warm my 787 gets against yours after an equal length ride in same temps.


Rob
 
Well my wife now wants to go furniture shopping Saturday, and seeing as how it looks like tstorms half the day, I may indulge her. I might come out for the 2nd part of the day. I have to finish breaking in the spx and start breaking in the gti.

As for the cooling rave in the back, the diaphragm looked good. I think I can compensate for the slight collapse of the spring by turning it in a little. I'll show you when I see you next, it's not bad, and it's Def not rave spring. This are skinnier.

Sent from my SCH-I545 using Tapatalk
 
[MENTION=20888]jhjesse[/MENTION] I believe the elbow to be the correct one. I will double check, but I think it's right. However, having a properly configured water regulator would only account for the expansion chamber and waterbox temperatures, no? The part of the pipe that seems to be too hot is the waterjacketed part, above the injection fitting. The heads however don't seem too hot, but the lower case and pipe did. I will definitely keep an eye on that and get some real surface temperature figures this weekend. I'll also compare them with my 720.
 
The water box spring should be stiffer, longer, and thicker than the rave spring. If not, you got the wrong one in there
 
Here is a pic from my missing RPM thread last year...the spring on left is bent and too short, it is what was in my water regulator.

The spring on right is the one from 96' gsx and fixed my problems. It is the correct spring for 787 setups.

Ratchet and socket there for size reference.

photo 4.JPG
 
Status
Not open for further replies.

Similar threads

L
96 GTI 717 bogging, losing power after warming up
Replies
0
Views
118
lilstrudel717
L
TurnerBFC
Here we go again… Seadoo bogging down in water
Replies
10
Views
655
mikidymac
mikidymac
B
HX Issue I can't solve. Help!
Replies
12
Views
663
gp1200x
G
B
97 sea doo xp no spark.
Replies
1
Views
274
lavasioux
lavasioux
S
1996 SPI - Engine Problems After 7 Years of Running Great
Replies
6
Views
275
manolocross
manolocross
Back
Top