1997 SPX (787 motor) bog/hesitate at 5% to full throttle or constant 15%.

[gtsdrs]

Hope that I'm posting/positioning this question correctly. I'm an original owner of a '97 SPX. Had very little problems with it. Has probably 200 hours. This summer riding it more and had problems with the carbs. I've got it running as good as ever (or new) but now I want to fix a problem it has always had.

Problem -

From idle, if you go 100% throttle, ski hesitates for 1-3 seconds, kinda half running (not dying), then pulls strong. It has always done this. Very annoying for pulling a skier (which I've done a lot). If you run at 20% throttle for few seconds and then go 100%, it pulls hard. I've tuned / played around with jetting/mixture on 2-4 stroke dirt bikes, so I have a little experience. It seems like it is running lean, not getting enough fuel (like it is hurting for an accelerator pump!). Another condition/symptom is that it "four strokes" from 10-20% (like 5-15mph range). Not sure of the right terminology for it but I always thought this was just a characteristic of 2-stroke seadoo, now not so sure it needs to be this way. BTW - running near sea level, 400ft (austin, tx).

Here's why I'm thinking it is lean -
If I go from idle to partial throttle, then back, then 100%, it seems a bit better.
If I hold at 10% throttle, it doesn't run great either. If I shut the fuel off while it does this, the motor doesn't ever "clean out" or lean out and pick up, it just eventual loses all power (out of fuel).
Changing low side needle valves doesn't seem to have any effect (i've moved them in out probably 1/2 turn either way).


Background -----

Here's what I've done this summer -

New fuel lines.
Clean tank.
Clean fuel valve.
Tested tank, fuel valve, lines under pressure (for leaks).
Disassemble clean carbs.
Very carefully (and completely) cleaned both hi/lo jets.
Rebuilt fuel pump (was the specific problem this summer).
Tried rebuilding carbs with cheap rebuild but found parts worse then original so cleaned original parts.
Fixed a flooding problem due to fuel slipping past o-ring pop-off valve (new o-ring).
Set High side needles to "half-way". There is a cap or something on valve so you can only rotate it about 70-90 degrees.
Set Low side needles to 1-1/8 turn.
Measured pop-off. Valves hold pressure then "pop-off" just under 30psi, then bleed down to 20-22psi and stay there.


I've done nothing with Rave Valves. Kinda scared to because seems to run mostly good. Had a problem with these originally and actually received a new boat (in 1997) because original wasn't running right. They found out what was wrong after giving me a new boat (under lemon law).

Things I haven't done but will/can do:

Check the oil pump calibration. Do this next time apart. It is possible a little rich (oil wise) that could be causing, but doesn't seem to be a problem anywhere else in power band.
I have a set of 75 pilot jets coming in the mail.
When I put jets in, I'll recheck/clean the 3 tiny holes from pilot jet to intake.
I haven't but will remove low side needle and clean it (I didn't do that when cleaning carb).
I have pulled plugs to try and determine rich/lean condition, but it is super difficult, especially with oil injection adding to the mix. I'm familiar with the process, but always felt like it is a little more art than science.

I'm reluctant to think that just cleaning the carb will change anything because this boat has always had this dead spot at initial acceleration. After you're moving, say 10mph, punching it give full thrust.

If you are still with me, bless you! Ski is running as good as I ever remember. Idling nice, starts easily without choke. Top end feels good (maybe a hair rich), but clocked at 55mph (GPS) on not the best of water and without trimming it perfectly. Basically, I feel like the top end is almost new spec.

So - anything I've missed? I'll take any suggestion. Don't really want to spend $100+ on rebuilding kits yet, especially because it's always done this.

Thanks for reading!!

 

[Mraw]

I would rebuild your carbs with only genuine mikuni kits incleuding new needles and seats
You could also run the RES line from the tank directly to the carbs to bypass the fuel selector and fuel filter

 

[Mraw]

Before that though I would verify that your accelerator pump is working, look down the throats of the carbs, when you press the throttle their should be a splurge of fuel

 

[etemplet]

What I am suggesting is JUST THE OPPOSITE. No need to rebuild the carbs. You are RICH. Too much fuel and when the engine burns off the excess fuel it accelerates just fine. You can verify this by pulling the choke out slightly. It if runs worse you are rich.

So... close the low speed adjusters 1/2 turn.... IN. See what happens. Also, a lower pop-off pressure will cause the same thing or a combination of both. If you pull the carbs, check that the 3 holes in the carb throat are spraying forcefully. Visit Mikdymac's carb thread. I find the 787 runs best in my area with a 37psi pop off pressure. Also make sure your needles are not leaking.

I spent a lot of time with these carbs on (2) 787 GTXs side by side. I started at 23 pop-off pressure because that is what the initial springs gave me. I increased to 27psi. then to 30 psi. I got to 33psi and it did much better. Finally I bought the correct spring and replaced the needles and seats (Genuine Mikuni). After that replacement the pop off pressure for both skis (4 carbs) was 38psi. Both skis ran great. So.... I"ve been down your road. Hope this information helps or gives you some things to think about.

 

[gtsdrs]

Thanks to both of you....

Mraw - I'm not sure these carbs have accelerator pumps? If so - I'm just not seeing them. I totally could have missed them, but I'm familiar with them on automotive/motorcycle applications (many motorcycles also don't have them). If you are sure they exist, please tell me, and I'll recheck/verify.

Etemplet - Excellent idea on choke. I'll definitely try that. My experience with the choke is that it gets way rich quickly (at least at idle), and also that it doesn't need choking when starting as long as motor is warm at all - I realize that absolutely could be an indication of being on the richer side. As I mentioned, I HAVE tried shutting off fuel and trying to get the boat in the 'sputtering' range to see if it acts differently. It's very possible that it goes from rich to completely out too quickly for me to notice an improvement/difference. Also - I have turned in the low side 1/3-1/2 turns and didn't really notice it being better or worse. My thought is that where I'm experiencing this problem is past where the low side needle will make a difference?

I was out on the boat again today, and it was running exceptionally well - with the exception of this one spot in performance (10-20% throttle). Starting, acceleration, top end is all really good otherwise. That combined with it always running this way has me thinking that rebuilding the carbs, while not hurting anything, probably won't change it either.

I'll do a little more testing first. Thanks again. After owning this thing since new, I'm now ready to try and get this one little thing worked out. It's just so much harder to do than a motorcycle that you can ride, adjust, re-jet, etc in your driveway.

 

[etemplet]

I have a 1997 SPX outside in my "to be worked on" section and I'd be awful surprised if it has an accelerator pump. As I stated the choke is just a check. I'd suggest you read Mikidymac's carb thread. There are 3 small holes in the carburetor barrel that must be checked. If these are not flowing properly you ski will react the way yours is acting. Not a bad process to check the pop-off remove the low speed jet and do the test. Good Luck.

 

[POPPS]

I dont think you have an accelerator pump on that, turning out the high speed screwwill make it run richer, which is why they have caps that prevent you from leaning in more than 1/4 turn to closed...they are set for all altitudes...The fuel selector cannot really be cleaned, there is a diaphram in there that eventually becomes "mushy" and is not serviceable, and unfortunately not replaceable, the whole unit has to be replaced.,,,And yes,,,check that the low speed jet orifce and 3 bypass holes are clear.,,,If turning out your pilot screws from factory stock slightly improves your low end response, then that usually means up stream fuel leanness/delivery issues, or down stream carb efficiency, (fuel delivery issues).

 

[gtsdrs]

So here's my latest 'test'. I changed from 70 to 75 pilot jets. Seemed to about 1/2 solve the problem. Still slight hesitation if you go 100% if you are starting at idle-15% throttle. Hesitation lasts about 1 second.

The pilot jets helped. BTW - rechecked/cleaned low speed circuit (including 3 tiny holes) when I changed jets out.

So...Using the choke method to test lean/richness. I can completely eliminate hesitation if I pull choke out and immediately release at exactly the same time as going from 0-100% throttle. Doing this makes the fueling/power seem perfectly modulated. If the timing is off just a bit (like holding choke open for more than an instant), then doesn't work as well.

I'm pretty sure this is all indicating that i'm running just a hair lean for just that instant when I dump the throttle. I'm not sure increasing pilot jet or low speed needle is good because it would run too rich at idle?

One last thought, if anyone wants to comment - what impact will the Rave valves have on this condition? I have not had them apart for cleaning / checking. I kind of understand that they reduce airflow at lower RPM, but I don't want to adjust them not knowing how they will react.