Lack of power after warm-up

[Praetorian]

Hello All,

We have a 1997 SeaDoo GTI that has been through an engine replacement. When the new engine was installed we re-tuned the carburator and everything was great. Now here about 3 years later it starts up immeadiatly and seems to be fine, but after we get it on the water and ride it about 30 min to an hour it seems to lose the upper power band. You give it throttle and it attemps to rap up the motor and then just seems to bog down and not want to get on plane. I have 3 sets of spark plugs, completely emptied the fuel system and cleaned it. Attempted to check the carburator jet settings as best as I can and I am now a little stumped. Any help would be appreciated.

Tim

P.S. I have the appropriate shop manual for reference.

 

[seadoosnipe]

Info....

Could use just a little more info. What is your compression? Have you checked the wearing ring? What does your rpm max out at?

 

[Praetorian]

Hello,

It should be the factory compression. I haven't personally checked it, but the replacement engine has maybe 10 hours on it. Its possible that it was slightly bored (one to two thousandths) when it was rebuilt. The tech info sent with the motor did not specify.

RPMs usually max i think at about 3800(?) rpm. I haven't ridden it in a couple of years so I don't exactly remember. Top speed was about 46-48 mph.

My wife called our local shop and they recommended a replacement carb, which I don't think is the problem. Don't feel like blowing 400 bucks if its not necessary.

Thank You.

 

[njcowboy]

Hello,

It should be the factory compression. I haven't personally checked it, but the replacement engine has maybe 10 hours on it. Its possible that it was slightly bored (one to two thousandths) when it was rebuilt. The tech info sent with the motor did not specify.

RPMs usually max i think at about 3800(?) rpm. I haven't ridden it in a couple of years so I don't exactly remember. Top speed was about 46-48 mph.

My wife called our local shop and they recommended a replacement carb, which I don't think is the problem. Don't feel like blowing 400 bucks if its not necessary.

Thank You.

Don't spend the money on the carb until you prove it is not other issues
does it bog down and stall when you increase the throttle?
Check cold and hot compression. I had a 3 year battle with yamaha over an outboard. when the engine warmed up, it had a small crack that would allow pressure to release and the engine had no "balls"

They pulled the same crap and rebuilt my carbs 12 times (4 times 3 carbs each time) before they listened to me. They kept blaming E10 fuel

 

[seadoosnipe]

Performance....?

You say you haven't been on it in a couple years, then how is it that you know it's not running well?
Do not buy a carb. We'll go through the one you have on it if necessary.
What do the plugs look like? Do they show signs of leaning out? You said it runs good for a while until it gets hot, then the upper end performance just drops off. Does the engine still run smooth during this time? When you open the throttle, does it have this hollow sound in it, without acceleration?
Have you check the fuel circuit for vacuum?
If you can take it out and create this same problem, then as soon as it happens, you need to pull the plugs to see if there is any discoloration. Also, open the gas cap to see if there is a vacuum on the cap. I don't think it's electrical and with 10 hours on the motor, probably nothing major wrong in mechanical. Just something not quite in sync.
The 717cc engine has no balance shaft and no RAVE valves. So, this should be pretty easy to figure out.
What are the 2-cycle oil specifics that you are using?

 

[Praetorian]

More answers

You say you haven't been on it in a couple years, then how is it that you know it's not running well?

The last time we had it out was when these symptoms began. Haven't ridden it since and tore apart the fuel system last year to empty it out since it had been sitting for about a year at that point.

What do the plugs look like? Do they show signs of leaning out? You said it runs good for a while until it gets hot, then the upper end performance just drops off. Does the engine still run smooth during this time?

Engine runs and idles perfectly smooth, spark plugs show no signs of carbon build up, scorching, burning and generally have a slight tan to dark brown color to the electrode. Using the NGK guide it appears to be normal wear. On occasions there is a little dry fouling, but not common.

When you open the throttle, does it have this hollow sound in it, without acceleration?

Yup, that is exactly what it sounds like.

Have you check the fuel circuit for vacuum?

After I put the fuel system together after clean out, I haven't done a full vacuum check but up to the filter is good.

What are the 2-cycle oil specifics that you are using?

We are using the Bombadier/Rotax oil from the dealership. The low ash content.

 

[kustomkarl]

It sounds to me that it might be an over heating condition, as it takes about 30 minutes to cause the problem. Is the water coming out of the bypass- line out the rear? I would take a compression check just to eliminate any questions about the compression, or internals. It could be the internal filter in the carb, that might have some residue in it causing it to give you the 30 minute window. Let us know what the compression is, and than if it is good say above 125psi (150 psi is very good).If you not sure how to perform a compression check we can talk you through it. I would check all the screws and nuts and bolts around the carbs and intake to be sure of no air leaks. If it still has the same problem than it might be the small fuel filter in the carb. As a premium member you can check the manual for the proper procedure to clean them. Again if you have questions on the procedure let us know. I sure we can help solve the problem you having.

Karl

 

[seadoolover]

Lack of power after warm...

G'day Praetorian... you're saying the ski runs great for 30 mins to an hour then plays up.... this leads me to thinking that it wouldn't be the carbs as the ski would most likely play up almost immediately if the carbs were the problem... and you would think that it would only take about 5 / 10 minutes to reach E.O.T. ( Engine Operating Tempreature ) or start to overheat. You're saying you can get 30 / 60 minutes of good riding then the problem begins. Try this.... when the ski starts playing up get a spray bottle with a small amount of dishwashing liquid mixed with water and spray all the carbie gaskets taking care not to get any in the air intake. Spray the exhaust / intake manifold gaskets too if you can and also around the head gasket. If you see and unusually large bubbles forming this means you may have a gasket leak in that spot. Just thinking that after the ski gets warmed up then the problem occurs... it may be a leaking gasket. Let us all know how you went. :cheers:

 

[seadoosnipe]

Good responses....

These are all very good responses and it may take a little of all for you to find a solution to your problem.
When I mentioned the vacuum......that is, vacuum created on your fuel circuit if the vent line is stopped up. You can look over your fuel circuit for the problems discribed above but you also need to look at the collection of hoses at your fuel tank.
Where you see the four hoses at the tank, one of them is a vent line. Make sure its not stopped up. The hollow sound is usually made when there is a lack of fuel for ignition. Your opening the throttle plates and there is no fuel going in. So you may be vapor locking the carbs when the system gets hot, put under a vacuum, which is normally created from a stopped up vent line.

 

[ScubaDoo]

:agree: I agree with seadoosnipe. A plugged vent line will keep air from entering the fuel tank which will depend on how much fuel is in the tank. Then it will lean out the engine as it starves for fuel and eventually after a couple minutes stall. Check the vent tube as seadoosnipe recommends from the fuel tank.