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

[IDoSeaDoo]

I've been scratching my head over this conundrum for two years now. I have a 97 stock SPX and it just won't stop bogging from idle. I've tried everything but new jets. I've tuned it to spec, 70 pilot, 142.5 mains, 1.5 turns on LSA and 0 on HSA. Pop off at 33. It bogs when you open the throttle, sometimes dies, sometimes (if you go slowly) it will work itself up to the higher RPM. Once in the higher RPM, it runs like a champ, strong and fast all the way up to like 6900RPM. Once it's running, the bog is not as bad, it doesn't die, just kind of stumbles, but still there.

I've cleaned out the transition ports, got new fuel lines, cleaned the fuel selector, water separator, checked the baffle, checked that the needles aren't leaking, verified that the engine holds pressure, got new carb gaskets. I've tried 26psi pop off, and 40psi as well, both giving me worse results. Tried new plugs. I've played extensively with the LSA screw, couldn't tune it out. Couldn't notice it getting better, just worse. I've tried unplugging the rectifier, but that didn't change anything. I've even put two carbs with accelerator pumps on, and set them up for a 99SPX. Runs terribly now, hard to start. The 99s had smaller pilot jets. I'm starting to think I need to go up a jet size, but how could that be??? If everything is set up to spec, how could I need to go up a size? I'm totally out of ideas past going up jet sizes, and ditching the stupid accel pump. It doesn't seem to help me at all.

 

[AdamXP800]

I have been battling this same exact issue. Hopefully someone will chime in here and help us out. Once going mine runs like a champ, when moving you can feel a slight bog when letting off the throttle then back on but its not very noticeable. if you come all the way to idle, then it bogs pretty nasty until it gets up there alittle in rpm. I have tried everything you listed above as well.

EDIT* I am running stock 96 XP carbs with no accel pump

 

[IDoSeaDoo]

Yea, I've read all the posts on the subject,and everyone just suggests the same stuff. The local shop said you tune it out with the LSA, but that didn't work (as I knew it woudn't). Also, the carbs with the accel pump seem to have made it worse. They run a lower pilot jet. I noticed also that the best way to start it or get it over the hesitation is to pull the choke. Strangely, priming the accel pump doesn't seem to have much effect for starting.

 

[AdamXP800]

I use a primer so I pump it once and mine usually fire right up.
Now on the water if I shit it down for a bit I have to use the throttle some to get it fired up. I did not replace my needle and seats, they might be leaking so I'm trying that next

 

[IDoSeaDoo]

You can actually test them: close the return line and pump them up like you're testing pop-off. They should hold 15psi for some time. That's how you tell if they're leaking.

 

[jhjesse]

Have had the exact same thing happening to my 96xp. I am currently using a set of carbs that have the accelerator pump. Working pretty good.

Some times these carbs just wear out and need replacing.
http://osdparts.com/index.php?main_page=product_free_shipping_info&cPath=595_602_1&products_id=75

 

[racerxxx]

The question I have is this.... When you guys go through your carbs what EXACTLY are you doing---every last detail. Are you replacing parts or re-using the old parts etc.... If replacing be HONEST which exact parts and brand? This is out of curiosity, I just want to know what or what not is being done to try and establish a pattern, possibly.......... We can all make suggestions on what to adjust but if there are components that are bad or on the verge of being bad all the adjustments in the world might not be enough to compensate. Or one of the little thin valves could be off just a little etc.... The other thing that makes it hard is you don't know who else has been in there before you and if you're putting stuff back together based on how it came apart you might be putting it back together wrong if the last guy did it wrong--that is what really sucks. I see it all the time with my equipment.

Sorry if I sound harsh, but I troubleshoot equipment for a living and I just love when guys leave out data and then give it to me hours later and I could have shortened the troubleshooting process with that info or pin pointed the exact problem, it can be a real drag some days.

 

[AdamXP800]

I rebuilt the carbs with all OEM mikuni kits. The needle and seats looked good so I reused those. New base gasket and all. I removed every removable part, cleaned with carb cleaner, compressed air and then dropped them in an ultra sonic cleaner

 

[IDoSeaDoo]

I have rebuilt the carbs a couple years ago, including N/S, but the problem started just after I rebuilt them and I've just been putting up with it since. When I take them apart to check/modify a setting, I go through and inspect the parts and verify that there are no holes where there shouldn't be, and that the filters are clean. All the gaskets seem good (not dry or cracked). I too spray carb cleaner and air, but no sonic bath. I've verified every part and its alignment according to the diagram in the seadoo manual. Everything seems spot-on, hence my confusion.

 

[Strizzo]

if you're adjusting the low speed needle, you can't just twist it and always see instant results. you have to make a small adjustment, see how it does, then go back and adjust further. especially when you're running rich on the bottom end, it takes a bit to clear out the excess fuel, so you might lean it out, and see no change, then go right back.

as for the accel pump carbs, have you verified that they are squirting when you hit the throttle?

also check your rotary valve clearance, it has a tendency to cause problems on the low end that act like a carb problem. CReynolds just found out his rotary valve was bent, causing a similar low end bog

 

[IDoSeaDoo]

BTW, I always used Mikuni parts in the rebuilds.

Also noteworthy is the fact that the plugs were BLACK when I pulled them today. Despite the ski running great at the top and the MAG jet being slightly smaller, the plugs still got super black. I guess that answers whether the accel. pump is working or not. Looks like it's working a little too well. I absolutely don't get this as I have to choke it to get over the bogging

 

[Strizzo]

if you have to choke it you're lean, pulling the choke makes it richer. is there any smoke out the exhaust when its bogging down?

 

[IDoSeaDoo]

See, that's what I thought too. I figured the accel pump would alleviate this issue by spraying that extra fuel in there right at the start of the throttle band, but it still bogs out and dies if you gun it. I wish this engine had just one big carb. Would be so much easier to tune that way, like my GTS...

 

[Strizzo]

the accel pump doesn't spray all the time, just for that first hit off idle. it allows the idle tune to be a little more lean, then the pump makes up the difference so the carbs can catch up when suddenly the engine wants more fuel.

 

[IDoSeaDoo]

Yea, that's what I was hoping for, but I'm having to do it's job manually. Once it gets used to running, it starts up and idles fine. But getting it to initially fire up, even after sitting for just a min, I'm forced to use choke. What would you do?

 

[Strizzo]

the 99 spx carbs should have a 95g spring in it and the pop off needs to be between 36 and 40 according to the manual. what do you have it set to right now with those carbs? you can run the pop off a bit lower i'd think. the pilot jets are just one size lower at 67.5, and the mains are almost the same, only the mag carb is a size leaner at 140. also might want to verify the correct needle and seat are installed too if you go back in. how far have you opened the low speed screw?

are the plugs black and wet or black and sooty?

have you had the intake manifold off? replaced the seal? really when carb adjustments don't make things better or worse, i want to start looking at other possible issues. if you have a set of feeler gauges try and check the RV clearance.

 

[IDoSeaDoo]

It's set to right around 40PSI on both carbs. The plugs were black and a bit shiny, not sure what you mean by sooty. They weren't wet, but they also haven't been run in a little while. I'm pretty positive the N/S are 1.5 but I did not check this time. I will check the RV clearance tonight. Do you guys use solder to check the clearance? I always feel like the solder doesn't squish as much as it should to truly reflect the thickness of the clearance.

 

[Strizzo]

solder is lead, which is softer than aluminum, so it will squish. you could use plasti-gage as well. there should be a version that covers .010-.014in that you need to measure.

 

[IDoSeaDoo]

Tested the accelerator pump last night to find that it was actually not working. It doesn't seem like these things can self-prime. I sat there with the motor not running and pressed the little pump for a few minutes with no results. I then took it apart, verified the diaphragm was in good shape, then put on some test hoses onto it. I put the inlet hose into a little cup of WD40. It didn't pump. It only started to pump when I dipped the outlet into the fluid as well. So I reassembled the carb and sprayed WD40 into both hoses and guess what? It works again Revving on the trailer, I can't feel the bog. Going to go lake test it today if the storms hold out.

Didn't get a chance to test the RV. I'll do it next time I have the carbs off.

 

[racerxxx]

There is also a specific procedure for making sure the arm and linkage is adjusted properly, look in the manual for how to set it or at least verify that your's is correct.

 

[AdamXP800]

What is the correct pop off spring and color of it for the 1996 seadoo xp carb?

 

[IDoSeaDoo]

IDK, but I'm pretty sure the manuals list the spec on that. I remember seeing a chart somewhere. Anyway, you should buy or build a pop-off tester. If you have an air compressor, all you need is an air valve (the kind you use to blow off things), a 3-way tee, a 60psi gauge, and a 1/4" fitting for the 3rd side of the tee. Set your air regulator on the compressor REALLY low, to where it's barely coming out and viola! I have a separate air regulator on my rig, works like a charm. Only bad thing is I can't take it to the lake and make adjustments out there.

 

[Strizzo]

the 96 runs an 80g spring and lower popoff.
[MENTION=32110]IDoSeaDoo[/MENTION] - i'd get a mini reg to be able to adjust the pressure at the end of the hose rather than at the compressor. probably go valve - reg - gauge - hose to carb. then you can shut off the air, hold the valve open and slowly turn up the reg to where it pops off.

 

[Dr Honda]

If everything is working properly... then these carb's aren't that sensitive. (small movements in the pop-off, and needles will still run) I've rebuilt (literally) 100's of seadoo carbs... and never had any issues. And... I can say with 100% certainty, they will run spot-on at the factory specs.


Here's the deal... If you are bogging off idle...

1) The bypass ports are plugged still.

If they are not open... then you don't get fuel as the throttle is opened.

2) The high speed check valve is leaking.

If it has even a light leak... then at idle, you will "Drain" the regulator, but the vac will be high enough to keep it running. BUT... when you open the throttle, and the main jet is supposed to feed the engine... there is a big air bubble sitting there... and the engine dies. BUT... if you feather the throttle, to get the RPM's up... then the regulator will refill, and the engine will run.

3) When you replaced the needle and seat... did you install the correct size? (1.5 is spec)

With that said....

1) Non Mikuni Needles, seats, and regulator diaphragms ALL SUCK !!!!! They DON'T work ! You can use aftermarket jets, and gaskets. FYI: the OEM hard parts will have a little window stamped into them. And the OEM diaphragm will have a red nipple.

2) Changing the jetting on a stock engine, in "Normal" altitude may get things to work.. but it's a Band-Aid, and could cause long term problems.

3) Other mechanical issues can cause problems that feel like carb problems.

a) High RV clearance.
b) RV timing off by half a tooth.
c) low compression.
d) leaking crank seal

Have you checked those?

 

[IDoSeaDoo]

I have checked everything but the RV clearance. That I checked some time ago when I last had this engine apart. I've only recently started maintaining digital records of my maintenance, but I still think would have remembered if the RV clearance was high.

Doc, how do I check to see if the High Speed Check Valve is leaking? I assume it's the one on that block above the jets? Those always look good to me, they're right between the two little dots, and never have any debris underneath them. Is there a way I can test it?