SPX starts but wont run unless I give it throttle

[avi8or3117]

Hello and good evening,

I just went through my entire fuel system and rebuilt the carbs, replaced the fuel selector valve, replaced all the gray lines, and cleaned out the filter. She started and sounds good. Sounds like a strong engine, but the only problems is that it dies if I dont give it throttle. I dont have to give it much throttle to keep it running, but it dies if I let it go. It sounds like the engine maybe idling to low. Is their a way to adjust the idle? If not then what should I try? Does it have anything to do with the low speed screw? I thought I tightened it to specs. Compression was tested about a month ago with 140 psi per cylinder. Any suggestions or help would be greatly appreciated.

Thanks

 

[Dr Honda]

Not a big deal... just raise the idle.

There is a screw at a 45 degree angle where the throttle cable hooks to the carb. Just twist it in a little.

 

[avi8or3117]

Thanks.

Worked like a charm!!

 

[avi8or3117]

I adjusted the screw and it idles fine out of the water. I went to put it in the water and had to re-adjust the screw to keep it running(I opened it more). Then I pulled it out of the water it was revving really high. It seems the load on the engine makes it die because it's not idling high enough but then I adjust the idle higher and when I pull it out of the water it sounds really high.
Is this right?

Also when I put it in the water and gave it gas, it started to bog down. It idled fine but just wouldn't rev up. What's happening? I just cleaned the carbs, adjusted the pop off pressure to specs, replaced all fuel, and cleaned out the filter and selector. Is their anything else I can to to fix this problem?

 

[6KJR]

Insure your carbs are set as per factory specs. All machines will rev high out of the water.

If theres no tach on your machine, you could order a tinytach like I did for mine. Gives you a decent reference.

 

[Dr Honda]

The spec is 3000 RPM's out of the water, and 1500 rpm's in the water. It's going to sound high out of the water.

Also, if your engine is old, and the compression is low, it's going to have a hard time idling in the water. (Check your compression)

A final FYI... you can't make any carb adjustments out of the water.

 

[avi8or3117]

ok thanks that makes sense. That is exactly what is happening. I have an SPX so it does not display engine RPM. How do I find out engine RPM? Is there a hand held device, like a tachometer, that I can hook up somewhere to read engine speed. If so how do I hook it up to engine? Do I have to cut into the spark plug cable wires??? Connect to spark plug??

Secondly, when tuning in the water, what specs should I follow? Are their guidelines? Or am I just listening to engine and throttle response? When I rebuilt the carb I tried to follow OEM specs from the manual. Low speed screw 1.5 turns and high speed screw slightly seated. Are these just starting points and know I have to fine tune. Like I stated before. It bogs down when I give it throttle, so do I need to adjust speed screws or just one? Which direction do I turn them? Leaner or richer?

My engine has less than 100 hours on it and i tested compression on both cylinders. 150/150.

Thanks again guys for all the help and advice!

 

[djredman99]

Not sure if you are using strictly the seadoo shop manual, but here is a link to the Mikuni Carburetor manual.

http://www.mikuni.com/pdf/sbn_manual.pdf

It gives you some insight as to how to adjust your carb. Also, it points out that both your idle stop screw (mentioned above by Dr. Honda) and the Low Speed Screw are used in conjunction to set your idle. As you turn the idle stop screw, it will affect your low speed mixture.

Be sure to follow the specs from seadoo and not any you may find in the Mikuni manual, they are just "rull-of-thumb" specs.

EDIT: I should clarify, when I say use seadoo specs, this is your starting point, assuming you left everything stock. Each engine is different and sometimes does require a little tweaking to get it perfect.

 

[djredman99]

How do I find out engine RPM? Is there a hand held device, like a tachometer, that I can hook up somewhere to read engine speed. If so how do I hook it up to engine? Do I have to cut into the spark plug cable wires??? Connect to spark plug??

6KJR mentioned he uses Tiny Tach (google it). Most add-on tachs that I have seen work by wrapping a wire coil around your spark plug wire. This picks up a signal on how often your plug fires and displays this as your RPMs. You can use them strictly on a per need basis, or install as a permanant option, running the cable and display to you instrument cluster.

 

[avi8or3117]

Thanks. I just ordered one and will set the RPMS accordingly.

Any answers as to why it would bog down in the water when I try to throttle it up? Im going to the ramp tomorrow and will play with the carb setting and try to fine tune it. Any tips??

 

[Dr Honda]

The actual RPM isn't super critical. Put the ski in the water, and set it where the engine is running relatively smooth, and isn't moving very fast. If you set it to a low idle, and it doesn't seem smooth, then adjust the low speed mix screw, but from experience with playing with SeaDoo's, they normally run well at the factory recommended settings, so only small adjustments may be needed.

If you have good compression, but it's bogging when you try to throttle up, there could be something else wrong. Are the plugs fouled? Did you check the pop-off pressure when the carbs were apart?

Even if you did... you may want to take the carbs apart again. You may have missed something.