Seadoo 1996 GSX 781 won't reach max rpm plus hard starting

[Andrewdinsdale]

Ok so this is the third post about my GSX, various issues. Only starting a new post as this is a complete new fault I'm getting.

The ski is still flooding when NOT running, when its running it will run all day long and not flood but it is flooding. If you turn the fuel off, wait 30secs and it will fire right up, turn the fuel on then it runs fine up to roughly 6000rpm. (Feels fast par the cavitation if you accelerate quickly).

After 6000rpm, sometimes it gets 6500 and occasionally it will go to 7k before misfiring and basically cutting out. If I accelerate from a standstill it will hit the limiter for roughly 2 seconds then die?

I was 90% sure this was electrical so changed the plug caps etc. But theres nothing left I can really change. (It is not running to lean, the plugs are coming out perfect in colour). I've tried adjusting mixture screws as to the guide on this forum with no luck. Its silly as it runs great. Idles well, picks up perfect, not sluggish whatsoever.

Anyway this is what I have done so if theres anything I haven't done please let me know. Thank-you.

Here we go;

Carbs gone through, needles and seats changed, new kits in both carbs.

New fuel lines, got rid of my primer bulb, tried bypassing the fuel filter etc, cleaned fuel selector and checked o-rings etc.

New plugs, new ignition coil, new ht leads and new plug caps.

Replaced grounds etc in the rear electric box.

Tried swapping out the rectifier for a known good one.

Checked and cleaned the rave valves.

Checked and cleaned the stator, checked the rotary valve timing, checked the flywheel key.

All multipugs and connections opened up/inspected/cleaned.

As the ski is cavitating when I accelerate hard I've just ordered a new wear ring. I took the pump off today and could see it was quite badly damaged. I've got the old one out and am in the process of cleaning up the impeller, it has a few marks but overall very good condition.

When my wear ring comes I'll try it again but still am lost with it? A wear ring won't solve my starting issue but might help the top end?

Any ideas please help me.

Andrew

 

[mikidymac]

First lets address the flooding when not running.

It can only be the needle and seats leaking to cause this so......
1. Either your tank vent relief is not working and the tank is building up too much pressure in the tank.
2. The needle and seat are either leaking from being bad or something is holding them open.

With the carbs together and the return fitting plugged the inlet needs to hold 10 psi on the carb without leaking. If it does something is holding them open. Could be a piece of trash or the diaphragm or the lever.

 

[Andrewdinsdale]

First lets address the flooding when not running.

It can only be the needle and seats leaking to cause this so......
1. Either your tank vent relief is not working and the tank is building up too much pressure in the tank.
2. The needle and seat are either leaking from being bad or something is holding them open.

With the carbs together and the return fitting plugged the inlet needs to hold 10 psi on the carb without leaking. If it does something is holding them open. Could be a piece of trash or the diaphragm or the lever.

Thanks for the quick response.

1. Relief working fine, tank never builds up any pressure or *hisses* when you open the cap.

2. They are brand new mikuni needle valves so i presume they are ok.

I have read that if you don't use genuine mikuni carb kits the diaphragm can hold the needle open and cause hard starting after stopping the engines.

I couldn't get hold of genuine ones so went for patent ones. Shall I try putting my old diaphragms (ones with red centres) back in?

 

[mikidymac]

That is your only option. I guarantee it's the aftermarket diaphragms causing the flooding.

They are too stiff and hold the needle open just slightly.

 

[Andrewdinsdale]

That is your only option. I guarantee it's the aftermarket diaphragms causing the flooding.

They are too stiff and hold the needle open just slightly.

Ok since my last post, I got the carbs off, took the new patent diaphragms out and put in the old mikuni diaphragms.

Checked the internal fuel filters while I was at it (all good) put it all back together and left the fuel tap on for 2 mins, then tried starting it and it fired up fine. (had to shut it off quickly as its 9pm here).

Left it another 2 mins and fired up fine again. All seems good so far, I'll leave fuel ON overnight and give it a run in the morning on the hose.

Can't take it for a spin till the new wear ring turns up (hopefully I get lucky with a saturday delivery).

I'll let you know what happens tomorrow. Thanks

 

[Andrewdinsdale]

Ok so we have some improvement!

Like I said I changed the new patent diaphragms for the old mikuni ones and it's fixed the starting issue.

I fitted the new wear ring and cleaned up the impeller this morning.

I took it out this afternoon and started perfectly every time, idles great, runs up to 6k rpm perfect.

You can get it to go about 6500 now and it will sit there happily -but if you hold the throttle down (and don't let go) it will jump to 7000 then fall back to roughly (4-5000rpm) then pick up to 7k again and this carries on till you back off slightly.

I sat the bike at 6k for about 2-3mins then cut it while running at speed and checked the plugs, they were perfect in colour so I don't think it's running lean.

In my opinion it's fuel starvation at WOT but I don't know where I should be looking? Could this be a fuel pick up issue?

Thanks in advance for any help.

 

[mikidymac]

Sure could and sounds like fuel starvation too.