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RESTO seadoo project gtx 787

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shendershot731

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I am working on a restoration. Bought as a basket case. The good it starts and runs. The Bad on hose wont go over 5k rmp, and occasionally backfires out exhaust and coughs out intake. so list of parts new and replaced. coil, new battery, rotax plate and gasket ( verified the timing 146.5 from top dead on mag side), rectifiers test done and replaced for good measure, tried a different mpem, replaced fuel lines, converted to premix, new plugs, when building engine passed pressure test. so i have attached a short video running on hose
. My best guess I have a lean condition. As I never foul plugs unless i pull choke and kill it. Taking to lake to test and try and adjust carbs. ( popoff pressure is black springs sitting at 27-32)
 
also compression is 135-140 for both cylinders. I have some spare jugs I might throw on it at some point. Not trying to go 50mph just 25-35mph make it last and give kids a ride.
 
Ski should run close to 50mph and if it doesn't something needs to be addressed. From the look of it the ski seems to be a 1996 or a 1997 GTX Carb ski. Your compression isn't bad so I couldn't focus on that for the current problem. Did you rebuild the carburetors with Genuine Mikuni parts? Replace the needle, seat, and correct spring? If the carbs are not clean and all the ports internally not flowing the ski will not run as it should. I'd pull the carbs and take a long hard look at them. There is an excellent carb rebuild thread on the forum. Looks like you did a good job and now just chasing down the loose ends. This is typical of these skis. Good Luck !

Also, check your rave valves and make sure they are free and functioning.
 
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ok just had at lake and more mystery to my madness that is this gtx. so idles great never dies. will go up to 2700rpm then start to bog down and never over 3krpm. so I tied turning out ls to 2.5 turns out .5 a turn a time and wait 5 min between each idle up to the 3k. no difference. re set back to one turn out and tried hs screws to 1 turn out no difference. tried by passing the fuel filter ended up with a bunch of air in the fuel lines. so my last ditch effort test. one i got most of my air out of the lines. held at 3k rpm then slowly eased the choke close to half and then 3/4 and it wouldn't rev up just died. tried twice. but would always restart. I will post videos with the go pro. also interesting note. I was checking for leaks around intake area with wd 40 and no chance in rmp. but I started with carb cleaner and it did slow stumple to a stop. if i had a leak i would expect a increase in rpm. I sprayed alot so not sold on crankcase leak. but is a possibility.
 
I'd pull those carbs. Turning screws and nothing happening is a sure sign they have issues... to me. :)

Did you check your exhaust hose? It might be collapsed.
 
video from last night. ordered a genuine carb kit. could it be my pressure relief valve for the vent tube not letting pressure into my fuel system? I will check my exhaust hose from waterbox later and report back.
 
Did you connect two spark testors for the spark plugs to check fire? Just to make sure. They are cheap. Try snipping a 1/4 off the plug wires and reconnect the boots.

Hopefully doing the carbs will solve your problem. Good Luck.
 
yeah the coil is brand new. and had same problem with previous coil and snipped off the ends. I assume since increasing the choke and the engine didn't climb is more fuel was not being pulled into the engine. It still really feels like a lack of fuel issue.
 
ok I may have found my problem. so I don't think it is carb related, but I disconnected my t split hose from the vent line and had like a 3 sec suck of air back into the gas tank. Anyways my problem might be vacum pressure not lets air into the tank to rev pass 3k rpm. hence seems like a lean fuel issue. I did a quick test to see my gtx would go over 3k real quick and it went to 5k rpm. progress I will take and verify tomorrow night on hose then at the lake. might even go Register the ski tomorrow.
 
ok so the phrase one step forward two steps back. so runs and idles now goes over the 3krmp limit and even saw 5k rmp on the hose. but starts backfiring. i think something is sucking air into the fuel lines. getting lots of bubbles. mainly from fuel selector and fuel filter. the ls adjuster is actually. affecting the way the engine runs. better at 2 turns out then one.
 
Wonder if there is a gasket or seals that could leak on fuel selector. How about rave valves are they been apart or cleaned function. I had bellow go on rave valve and was hard to get motor to rev up. Usually if below goes you will see oil residue around them. Plugs do not look bad. Starts great. Probably carb problem.
 
Check the ground wire that goes from the battery into the black box.n7mber 2 there is a exhaust bung that is right above the electrical connector on mag housing.run with gas cap loose or off slightly pull the choke and see if rpms pick up.a novice tuner won't notice a difference changing low speed screw a half turn.also put a volt meter on battery and try it.make sure you have correct voltage while running.
 
so same with bypassing the fuel filter and selector. volts while running were 13.5 if choked back firing stops and will get up to 4k rmp. so conclusion is needs oem carb kit should be here wed. will report back.
 
Almost where it needs to be. so carbs rebuilt with oem mikuni kits. put in lower pop off pressure springs. it will pop and back fire at the 3500 rpm. but past then it will run smoothly and strong 4k to 5k rpm mark. adjusted low speed adjuster to a smooth idle at 1.5 turns out. I still feel like carb issues. I need to take to lake put airbox on and see it will smooth out. I did get registered. so low speed should be for up to 1/3 throttle right. so i must need to adjust those more on the water with resistance on the motor. pop off was at 24# for one carb and 27 for the other. any suggestions would help if you got some. only thing I haven't checked was race valves. I did a thought cleaning when putting those in. also did check and I have strong blue spark.
 
Update took to the lake to try and tune carbs. so again won't go over 3k rpm. I can change ls adjuster and the engine will smooth out and or stutter. It seems like the carbs are not opening the fuel needle to let more fuel in to go above 3k RPM. choking it just dies. plugs aren't dark and covered in oil. Tried by passing the fuel selector and filter same results. I am trying to not get frustrated and just take a step back. out of the water max rmp is 4k rpm. won't ever go above. i have the smaller springs that came with mikuni kits. to get a lower pop off pressure. I was hoping that was going to fix my problem.
 
Please stop swapping carb springs and messing with the screws.
Your ski will run perfectly with the 80 gram springs and stock settings if the carbs are correct.

The fact that you can't get to redline 6,800 rpm out of the water shows that you have something major wrong as with no load that engine should hit redline at 1/2 throttle out of the water.

Now that you have the correct Genuine Mikuni kits except for the correct 80 gram springs as they do not come in the kits you need to get everything back to stock baseline.

If you are worried about the gas tank not venting or building pressure just crack the gas cap open a little.

The fact you are seeing air in the fuel lines even bypassing the filter and selector is not normal either.

Finally, you can't clean the fuel selectors, they go bad with age and have to be replaced or they will suck air.
 
well last night I actually wasn't having any air bubbles in the lines. i will go back to the 80gram springs and set carb to defaults. so when you say major wrong what you thinking? carb bad? electrical? or port still clogged on carbs? or what I fear is a bad engine?
 
It is hard to say.

The only time I have seen backfiring is if it is running really rich or there is an electrical issue.

You need to have the airbox on for the carbs to work correctly.
 
ok got carbs apart followed your carb rebuild to a T. the only thing I wasn't sure on was needle and seats. to be safe I have some on order. Passes all popoff pressure tests. 32 and 35 for pop off . hold pop off for 5 min and doesn't drop. Install black pop pressure springs. still not going over 4 k rpm on trailer. ok so trying to think of what else it could be. compression is 135 both cylinders.
- electrical. tried different things. disconnect red wire on rectifier. no change.
- new coil as ground was a little corroded.
- new plugs.
- i have a different mpem. no change
- different cdi box no change.
- verified the rotax plate timing and replaced with a new one and seal.
- checked rave valve clean and red cap is flush and installed top side up.
- fuel is good. using premix. at 35:1
- new battery and fully charged.
- it does show a sign of a exhaust leak. a small amount of smoke will appear every one in a while.
- exhaust hose is not collapsed when testing.
- starts right up.
- spark plug gap was checked.
Might get spark plug checker to see if it drops off at higher rpm.
plugs when i pulled were a little rich last night.
- stator and pickup has not been replaced.
I feel like i have gone through this entire thing twice.
Only thing I can think of is a bad engine?
might just have to save up for a new engine.
 
Well cleaned the rave valves it runs up to 5k rpm but is not smooth in that aspect. so took to the lake to do the carb adjustment. set the idle at 2200k rpm out of water starts right up. put on water starts quickly goes to a smooth idle. but won't go over 3k rpm. so in testing yo try and figure something out. plugs are wet and black doesn't die with wide open throttle. seems like my manifold pressure isn't opening the fuel needle when engine is under a load. any suggestions? checked compression when i get home and it is 135 on each cylinder. I still think something is wrong. probably need a new engine.

 
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