97 SPX 787 off idle hesitation/stumble

[RebuiltSeadooBaffles]

I am still in the break in period (1.5 hours in) on the rebuilt motor so there is extra oil in the gas tank, I do not know if this is causing my issue or not, I have done EVERYTHING possible (I am I mean everything) to make sure all is good, compression @ 152 psi, new fuel lines, in line fuel filter, vent check vlvs, all the stuff, carbs taken apart, completly cleaned, I did NOT change the N/S or the jets, the rubber on the needles had no grooves in it so I put them back in, settings are LSA 1 turn out, HSA 1/8 on both (for break in), pop off checked at 32-33 psi, holds all necessary vac/pressure in ALL checks of the carb like it should. My issue is only at 5-20% throttle and hard starts (have to feather gas to get started and "clear" it out after engine is warm), it idles fine but when given gas anywhere from 5-20% it hesitates/bogs and stumbles (pops/misfires whatever you want to call it), it will stumble the whole time if I keep it somewhere in-between 5-20%, it does not die, if I go over 20% it runs great, NO issues at all, its just down low. I am thinking of taking the carbs apart and replacing the N/S and jets (all OEM), you guys think this is my issue? Another thing is coming off the throttle from over 20% the motor sounds like it misses for a sec or two cause the vibration of the engine gets bad at that point (just for the second or two). I did not mess with the LSA when I was out yesterday, I prob should have a bit...

 

[manolocross]

The extra oil MIGHT be causing it. The combustion chamber might be oil slicked so you don't get a complete burn but also try richening up low speed 1/4 turn. Hopefully you are running XPS 2 oil.

 

[RebuiltSeadooBaffles]

The extra oil MIGHT be causing it. The combustion chamber might be oil slicked so you don't get a complete burn but also try richening up low speed 1/4 turn. Hopefully you are running XPS 2 oil.

I am running Quicksilver PWC Full Syn, from the research I have done (and im a internet junkie) the stuff is just as good as far as protection, etc goes

 

[manolocross]

Also forgot to mention to make sure oil pump is adjusted to spec. If not it can be injecting too much oil at idle causing stumble. Are you using oil pump or pre mixing?

 

[RebuiltSeadooBaffles]

All that stuff is good to go, carbs synced, oil pump good, verified flow, etc, I do have about a 60:1 ratio of oil in the tank for break in/first tank on top of the oil injection

 

[manolocross]

That is not a lot of extra oil... Maybe when more breakin is done the rings will seat, compression will increase and stumble might disappear. Lets wait for others to chime in.

 

[SabrToothSqrl]

that engine/setup has an accelerator pump, does it not? Is it functioning properly? hoses good?

You can't tell much from the over oiled first tank. Run it through, put in new plugs, then start looking into things.

I've never had carb issues using new carbs and 100% factory settings.

 

[RebuiltSeadooBaffles]

No accel pump on this year, compression is at 152psi, im taking it back out sunday to get this 1st tank break in done and get just gas back in the tank, if it still does it I have a 1/4 turn on the LSA's to play with, if thats still a no go then out the carbs come for new N/S's and jets...

 

[Dr Honda]

Well.....


A lot of the 800 engines I've played with have a stumble at the lower throttle settings... until it's cleared out. running the RAVES full tight helps.


But... are you running 97 SPX jetting? If you are... then your MAG high should be 0 and your PTO high should be 1/2. So... you are running one rich, and one lean.

 

[manolocross]

Well.....


A lot of the 800 engines I've played with have a stumble at the lower throttle settings... until it's cleared out. running the RAVES full tight helps.


But... are you running 97 SPX jetting? If you are... then your MAG high should be 0 and your PTO high should be 1/2. So... you are running one rich, and one lean.

Hey doc... Why the diff in high speed needle settings from pro to mag carb? I got both my HS set at 0. Seems fine, should I change it?? Same model and engine.

 

[Dr Honda]

Ummmmmm......


Let me go recheck the spec on that.....

 

[Dr Honda]

Sorry... I had to go verify, and refresh my memory.


For the 800:

In 96... generally... they ran the high screw at 0. (both carbs) But in 97 they ran the PTO carb at 1/2. I would imagine, that they had reports of stuck pistons... and the slightly rich mixture will help relive that issue. or they made a mechanical change, and they adjusted the fuel.


In '98... they ran differential jetting (larger main jet in the PTO carb) so they went back to 0.

Unfortunately... I can't remember if there was some other spec changes. (impellers, air intake, exhaust, ect) I guess I'll have to dig around to find if there was a mechanical change.


If you are running VERY hard, and down at sea level... then yes... it can't hurt to run the PTO a little on the rich side.

The quick check, is to simply look at your spark plugs. If the PTO is a little light... open the high needle a little.

 

[RebuiltSeadooBaffles]

Ok, well let me ask you this, is the low stumble a result of a lean or rich condition? I know I need to get through the 1st tank and change the plugs 1st but I do still have 1/4 turn in both directions to play with on the LSA.

 

[RebuiltSeadooBaffles]

Ok, well let me ask you this, is the low stumble a result of a lean or rich condition? I know I need to get through the 1st tank and change the plugs 1st but I do still have 1/4 turn in both directions to play with on the LSA.

Bump..........

 

[Vidgren]

it sounds to me like you have clogged pilotjets. replace or clean them.

it sounds like its running lean!

 

[RebuiltSeadooBaffles]

They are clean, plug color after 1.6 hrs of running is perfect, slightly richer on the PTO cyl.

 

[Bills86e]

Is it possable your rv plate is 1/2 tooth off? It happens to the best of us, when sliding it on the rv shaft splines. The plate can be flipped
over to get the 1/2 tooth mechanical timing closer.

 

[RebuiltSeadooBaffles]

I bought the engine from a reputable guy on this forum, I am sure its on there correctly but thats always a possibility, I put another hours on the motor today, it takes forever to get the ski over 2500 rpms but once its over that its good to go.

 

[RebuiltSeadooBaffles]

Ok, filled the ski up and took it out yesterday to put another hour on it, I opened up the LSA another 1/4 turn so I am at the limit of 1 1/4 turns out, its still doing some things, once started I cannot go over 10% throttle or it dies, I have to let it warm up for a good 5-6 mins at idle then very slowly apply the throttle till it goes over 2500 rpms then give it some primer gas and it goes, so I know its lean down low, once over ~2500 rpms it runs good, plugs look good so I dont think I have a issue on the high end of the circuit, just down low. I ordered a RV timing tool to check that out but if thats not my issue I may lower the pop off pressure to the lower end of the scale to see if that helps with the low end lean condition.

I just bought a OEM rebuild kit with new main and pilot jets (extra $12) and with 80G and 65G (extra $4) springs incase I need to lower my pop off to get rid of this low end issue, one thing I did not do is take the HSA and LSA screws out to clean them, I will now since the kit will have new o-rings for them. I did not order N/S's as mine had no issues with sealing and no grooves on the rubber tip.

 

[Dr Honda]

OK....


a "Low RPM Stumble" is totally different from it wanting to die. As I was saying before... the 800 needs to be cleared out... but that's from being a little rich... and it wont' die in that case.

When an engine shuts off from fuel... that's a lean condition. SO....


1) Make sure your pop-off is in spec. It could be a little high.

2) Your pilot jet is plugged. OR... more the case... the transition ports in the carb are plugged.

3) Your high speed check valve could be leaking. Make sure it's sitting flat.

4) High clearance in the RV

5) The RV is out half a tooth.



Generally... when I see this problem... it's #2. Also... numbers 3,4,5 will cause hard starting. SO... if it's starting easy... and will run full throttle, after getting it over transition.... I'm betting it's a pilot issue. (clogged jets, or ports)


I know in your PM... you asked about the pop-off. Personally... I would run it toward the lower side of spec. BUT... these skis will run, spot on, using the OEM settings.

 

[RebuiltSeadooBaffles]

Thanks for getting back to me, I will change the jets and make 100% sure ALL ports are clean and clear and set pop off at 25 or so.

 

[RebuiltSeadooBaffles]

OK....


a "Low RPM Stumble" is totally different from it wanting to die. As I was saying before... the 800 needs to be cleared out... but that's from being a little rich... and it wont' die in that case.

When an engine shuts off from fuel... that's a lean condition. SO....


1) Make sure your pop-off is in spec. It could be a little high.

2) Your pilot jet is plugged. OR... more the case... the transition ports in the carb are plugged.

3) Your high speed check valve could be leaking. Make sure it's sitting flat.

4) High clearance in the RV

5) The RV is out half a tooth.



Generally... when I see this problem... it's #2. Also... numbers 3,4,5 will cause hard starting. SO... if it's starting easy... and will run full throttle, after getting it over transition.... I'm betting it's a pilot issue. (clogged jets, or ports)


I know in your PM... you asked about the pop-off. Personally... I would run it toward the lower side of spec. BUT... these skis will run, spot on, using the OEM settings.

^It was this, no compressed air was coming out of the micro holes when sprayed through the piloit jet, sprayed some carb cleaner in and blew it out 3 or 4 times and bam, airflow, I bet this was my issue. I am still going to lower the pop off to about 25 psi and rebuild the carbs with the kit I ordered since I already have them apart again and parts will be here tomorrow.

 

[Dr Honda]

I'm going to bet your problem is gone, if you found them plugged.


Basically... the "Big hole" at the bottom... and that is under the butterfly, in the pilot system, is fed fuel, though the pilot jet, but is trimmed with the low speed needle. (so it's less fuel that the pilot jet) As you open the throttle... the low needle is basically bypassed, by opening the bypass holes, and by 1/4 throttle... you are using full "Pilot" fuel. (and the needle is no longer active)



SO.... when they are plugged... you are essentially trying to run the engine on a much smaller pilot jet.


Personally... I would NOT change the spring. (assuming it's the OEM in there now, and an OEM air box) Since you found the prob... you may start to over-fuel. 25 is at the bottom of spec... but if you are seeing 30~35... it WILL run.

 

[RebuiltSeadooBaffles]

I'm going to bet your problem is gone, if you found them plugged.


Basically... the "Big hole" at the bottom... and that is under the butterfly, in the pilot system, is fed fuel, though the pilot jet, but is trimmed with the low speed needle. (so it's less fuel that the pilot jet) As you open the throttle... the low needle is basically bypassed, by opening the bypass holes, and by 1/4 throttle... you are using full "Pilot" fuel. (and the needle is no longer active)



SO.... when they are plugged... you are essentially trying to run the engine on a much smaller pilot jet.


Personally... I would NOT change the spring. (assuming it's the OEM in there now, and an OEM air box) Since you found the prob... you may start to over-fuel. 25 is at the bottom of spec... but if you are seeing 30~35... it WILL run.

Makes 100% complete sense now, I will leave the pop off alone then as its at or around 32 psi but plan to check it again anyway. I will let you know what happens, thanks for the help.

 

[RebuiltSeadooBaffles]

I'm going to bet your problem is gone, if you found them plugged.


Basically... the "Big hole" at the bottom... and that is under the butterfly, in the pilot system, is fed fuel, though the pilot jet, but is trimmed with the low speed needle. (so it's less fuel that the pilot jet) As you open the throttle... the low needle is basically bypassed, by opening the bypass holes, and by 1/4 throttle... you are using full "Pilot" fuel. (and the needle is no longer active)



SO.... when they are plugged... you are essentially trying to run the engine on a much smaller pilot jet.


Personally... I would NOT change the spring. (assuming it's the OEM in there now, and an OEM air box) Since you found the prob... you may start to over-fuel. 25 is at the bottom of spec... but if you are seeing 30~35... it WILL run.

Went to the lake yesterday and completed the break in, the low end bog is gone, throttle response is crisp and it wont die going from 0-100% pretty quick, however if I am anywhere between 10-25% throttle it kinda sounds like its misfiring, anything over or under the 10-25% it goes away and runs great, pop off is 28-29 psi, adjusting the carbs LSA in or out 1/4 turn does nothing, adding primer gas does nothing (it will bog down after about 2 squirts), is this something the 787 just does down low or you think raising the pop off will cure it? Rave valve red caps are 1 turn in from the top...