1998 Sportster 717 fuel starvation issue?

[thutch71]

I have a 1998 Sea Doo Sportster Jet Boat with a single 717 engine. The boat was converted to pre-mix at the same time a new engine was installed a year ago. The boat ran good for about a month. After a month the boat wouldn't get enough rpm's to get on plane. Every once in a while if hitting a 2 foot wave just right the engine would get past low rpm's and plane out. This worked for a few times and then hitting the waves just right didn't help anymore. Here's what I've done to the ski (jet boat) so far. Rebuilt the carb (filter was clean, gaskets and diaphragms looked good. New impeller was installed. All fuel lines where replaced and fuel switch cleaned out. In line fuel filter was replaced. New spark plugs installed (several times). The ski won't get past 1/3 throttle (about 5mph). When you throttle past that it dies like it's not getting fuel. Does changing to pre-mix have a bad effect on the carb operations since no oil is being injected? Does it mess with the fuel pump functionality? I'm at a loss on what to try next. Both cylinders have about 130 compression.
Any help is appreciated!

 

[Dr Honda]

ok........


First... if it's a new engine, and only has 130 psi compression... something is wrong. The spec on a new 717 engine is 150 psi. SO... you may have caused damage trying to run it with carbs that weren't working. (A lean run on a 2-stroke is death)

Second... If you decide to go Pre-mix... no... it doesn't really affect the fueling via the carbs. On that engine... the oil never enters the carbs... it is injected into the manifold.

Third... When you went to pre mix... did you keep the oil tank in place, and keep it hooked up to the rotary valve gears?


The oil injection on a Seadoo engine is SUPPER reliable, and there's no reason to remove it. Personally... I would put it back on. Also... NEVER continue to run a 2-stroke if the fueling isn't spot on.

So... if this was my boat... I would pull the carbs apart again... and verify that everything is right inside... and verify that all the internal parts are OEM Mikuni !!! All the aftermarket parts SUCK !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Then, I would verify the compression with a known good gauge. If it is down to 130... there's a problem.

 

[thutch71]

Thank you for the info and tips!

I rechecked the compression to find both cylinders are around 142 to 145. I think I didn't let the compression get all the way up when checking the first time.

The oil line is still hooked up to the return on the pump at the bottom.

I ordered and rebuilt the carb with a $17 dollar kit from ebay and you're right it sucked!!!!!!

I had to put back some of the old parts to get the ski to start.

I've ordered a new Mikuni BN40i which should arrive tomorrow.

I replaced the pulse line since it wasn't clamped down and seemed weak (one of the only lines I haven't replaced).

I cut back about 1/4" on spark plug wires to improve connection (the ends of the wires were crap before I cut back to fresh wire). I hope this helps. Waiting on new carb before I can try again.

Question: If I hook up the oil pump system can I still run premix for a while or will too much oil hurt the engine?

I saw a rebuild on youtube where a guy ran premix and the oil system on an old seadoo ski. It smoked like crazy but ran well.

As you can tell I don't do this for a living or I would be broke. I appreciate all input and things to check.

 

[ialonso]

Thank you for the info and tips!


I've ordered a new Mikuni BN40i which should arrive tomorrow.

As long as fuel is flowing freely, this will very likely fix your problem. What your fuel filter situation like? OEM Filters must have good o-rings with good seals , or the engine will starve for fuel. I have replaced mine with spin on filters that I have found more effective and reliable.

Best of Luck!

 

[thutch71]

A BIG Thank You for all the advice on this thread and the many others I've read with similar issues.

New carb arrived today. Installed carb and re-connected oil injection system.

Adjusted low speed screw to 1 1/2 and high speed to 0.

Jet Boat ran better than it ever has! :thumbsup:

I'm not sure if the issue was all carb related but I think the accumulation of all the improvements fixed the fuel starvation issue.

Cut back spark plug wires to make good contact.
Replaced all fuel lines and cleaned out fuel switch. Check one way valves for proper operation.
Re-connected oil delivery system after draining old oil out and cleaning lines.
Installed new Mikuni BN40i and set screws to OEM settings.

Since it's running good I'm going to upgrade to a high end fuel filter.
Going to continue to run premix until I'm convinced oil system is working properly.

Thanks again!

 

[Dr Honda]

With a fresh engine... you want extra oil anyway... so you are good there.


If you are going to use the oil injection... make sure it's been properly serviced. Replace the filter in-line on the feed hose, and make sure the small hoses between the pump, and manifold are good. (replace them with new tygon hoses) and make sure the nipples in the manifold are clear. (they can be cooked over from backfires)