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

[IDoSeaDoo]

I'll have to compare it to yours next time we're out there together. Looks like tomorrow will be ugly at least for the 2nd half of the day. I'm going to try and sneak down to Jordan for a few hours in the morning then, see if greasing up those throttle shafts stops my lean bog and start breaking in the GTI.

 

[IDoSeaDoo]

Well, I forgot to bring my laser temp sensor, but I feel like the cooling system is working okay. The top of the head on the 787 is mildly hot, and the pipe was more bearable this time also. Overall, the ski ran great, ripped like a monster. After greasing up my throttle shafts real well and blocking any air that may be leaking past those rubber throttle o-rings, the bog went away a tiny bit, but I'm now starting to think that my idle wasn't properly tuned. I realized that idle should be tuned in conjunction with the low speed jet. I opened the jet some, and opened the throttle a bit. It idles around 1700 and the bog is a lot less noticeable now, almost gone, but still a tiny bit present. I tested everything and that carb is spot on. Holds pressure in all the right places, for all the right durations. At this point, I'm just going to tune the top end based on RPM and plug color.
NC guys, when are you going to be back on the water? I need to compare the exhaust water injection spring with someone. I'm pretty sure it's almost right, I plan to tune for the slightly collapsed spring by screwing it in a little (after all, it is an adjustable component)

 

[suke]

Well, I forgot to bring my laser temp sensor, but I feel like the cooling system is working okay. The top of the head on the 787 is mildly hot, and the pipe was more bearable this time also. Overall, the ski ran great, ripped like a monster. After greasing up my throttle shafts real well and blocking any air that may be leaking past those rubber throttle o-rings, the bog went away a tiny bit, but I'm now starting to think that my idle wasn't properly tuned. I realized that idle should be tuned in conjunction with the low speed jet. I opened the jet some, and opened the throttle a bit. It idles around 1700 and the bog is a lot less noticeable now, almost gone, but still a tiny bit present. I tested everything and that carb is spot on. Holds pressure in all the right places, for all the right durations. At this point, I'm just going to tune the top end based on RPM and plug color.
NC guys, when are you going to be back on the water? I need to compare the exhaust water injection spring with someone. I'm pretty sure it's almost right, I plan to tune for the slightly collapsed spring by screwing it in a little (after all, it is an adjustable component)

I have friday off from work, not sure if you guys do, thought about hitting the lake then. Also I'm pretty open after work this week. I still need to test my carb settings too.

What did you use to grease your throttle springs? You just put some bearing grease on the springs on the shaft?

 

[IDoSeaDoo]

I'll be out there sometime this week for sure. I need to figure out the carb situation on my GTI still. It starts hard and acts like it's running lean.

 

[CVFD1314]

I'll be out there sometime this week for sure. I need to figure out the carb situation on my GTI still. It starts hard and acts like it's running lean.

Did you ever get the hard start figured out on your GTI? I'm in the same boat (literally, I have a GTI also) as you with hard start. I believe I have mine narrowed down to the RV cover having too much of a gap as my carb and accelerater pump have been re-done. I'm having a heck of a time getting mine to start in the water

 

[IDoSeaDoo]

You know, I was chasing this bog on my 787, and when I suspected the RV, I had actually developed a method to shave the mounting ears on the RV cover to bring it back within spec. Well, it didn't change anything. For my GTI, I took my carb off and changed the pop-off pressure to ~30psi. Also, I found that the manual was wrong on about the needle specs. Low is supposed to be 1.25 out and high 1.5 out. Seems strange how high the high speed jet is turned out, but it is a single carb feeding two 82mm cylinders creating 85hp. That's a tall order for one carburetor. Going to put it in the water today and test it. My GTI doesn't have an accel pump though, so my specs will likely be different from yours. Also, think about this, when you start it, your carb wants a certain amount of air. This comes from the idle stop screw. This, however has to be tuned in conjunction with the low speed jet. I used to just crank one or the other, but now feel like you have to adjust both. I take it you've already gone through all the other potential problems, like a fuel line leaking air? The last 3 feet of fuel line feeding my is clear tygon, and I can see bubbles entering (if I have a leak, which I don't). Also, check your fuel tank vents. Make sure they're all letting air in/out as they should. Refer to the manual for that procedure. Do you have a way to test if your carb holds pressure? I found that if you take the carb apart, the fuel body doesn't always come back together tight. Sometimes it can leak air (as verified by me pressurizing it to 10psi and spraying it with soapy water). That solid flap that goes over the big o-ring separating the chambers doesn't always make a good seal, esp. if it's old. You can make a pop-off/pressure tester for ~30 with typical hardware store parts.

 

[CVFD1314]

I never thought about the idle stop screw being in sync with the low speed jet. I would set my idle stop screw to the correct idling RPM only and leave it at that. I have eliminated just about everything fuel related, my work this summer so far has been:
- replaced all grey fuel lines
- rebuilt carb w/ a mikuni kit (same needle and seat, looked perfect)
- new fuel selector
- 2 new check valves
- cleaned carb, jets flowing good
- pop off @ 40 PSI, holds pressure for 10 minutes at 30 PSI
- same jets and needle & seat.
- pressure tested fuel system, holds fine and no leaks

I have a pop off tester I made and tested the carb apart and after I put it back together. I feel like I've got everything covered that's fuel delivery related. Started ok about a dozen times on the trailer, and once I put it in the water she fired right up. Rode for about 15 minutes, parked for about 5 minutes, then would take for ever to start back up once it was warmed up.

SO I'm thinking my rotary valve cover is over it's .014" gap making it hard to start. It is the original cover, I didn't put a new one on when I dropped a new motor in last year. The valve was new but not the cover. Looking at them on SBT's website and going to order another to see if that's my hard start issue.

 

[IDoSeaDoo]

I had the exact same problem with my GTI this weekend. I had rebuilt the carb and put in a spring that made it pop off at 30psi. I thought it was not getting enough fuel with the one carb. Well, it HATED the 30psi spring. Almost ruined the battery this weekend trying to start it. No one else could start it to save their life. Yesterday I put back in the 45psi spring and starting got A LOT better, but it still seems to load up at the NO WAKE zones. Also, it doesn't like reverse. Tends to die if I stay in Reverse any amount of time. My LSA was out 1.25 turns. When I screwed it in a tiny bit, it seemed to start worse, so I feel like I needed to close the idle screw a bit as well. Those jetting screws seem extremely sensitive.

 

[IDoSeaDoo]

Will, I figured out the gti problem, I used a 787 o-ring to seal the rv. Put the right one on it and voila. But the spx still stumbles. Also, I noticed that when I first rebuilt it, it ran like a raped ape, but now it's slower on takeoff and more sluggish to start. This same thing happened to me last time I rebuilt a motor...

Sent from my SCH-I545 using Tapatalk

 

[AdamXP800]

I've been battling a off idle bog forever. I have replaced every part possible in the carbs to no avail. I finally broke down and got a new set. Runs perfect now



96 XP800!
Keep the 2 strokes alive!

 

[CVFD1314]

I've been battling a off idle bog forever. I have replaced every part possible in the carbs to no avail. I finally broke down and got a new set. Runs perfect now



96 XP800!
Keep the 2 strokes alive!

A new set of carbs?

 

[IDoSeaDoo]

Adam, have you tried going up with the low speed jet any? I've tried reducing the pop-off, but that didn't fix me.

 

[cykrus]

IDoSeadoo, I am trying to sent you a private message but you have your inbox full. Please clean up some messages and let me know. thanks and sorry for the off topic but there was no other way to let him know.

 

[IDoSeaDoo]

unresolved threads are a pet peeve of mine when I'm trying to diagnose an issue and finally stumble across someone who has the same issue, so here goes my resolution: new carbs. Bought a set off the internet off a similar ski. They came looking fresh and shiny. The paint was still good on them, and they even had grey lines on. I replaced the filters on them and verified alignment of the cross bar and went for a ride. Low End bog GONE! I still don't know why my old carbs were causing this, as EVERYTHING was good on them. New carb kit, clean transition ports, new N/S... everything in the world was new on them, but still they were performing like garbage. Put these on with the same specs and voila. So there you have it.