96 SLT780 - Poor throttle response

[johnsonmtz]

Here in Central Illinois we're not riding yet, but I'm trying to prep my ride for the summer. The engine was a brand new short block that was installed last year and ran pretty well. However, one thing I couldn't kick last season was a hesitation from a dead stop. If I would feather the throttle the engine would kick up fine and I could reach 50 mph at 6000 RPM. Also, the engine didn't want to idle well. If I didn't continually nudge the throttle it would die.

This seems like a fuel restriction of some sort. I suppose there could be junk in the carbs, but I'm sure the shop that installed the short block also went through the carbs. I have purchased a new fuel filter/water separator element that I will install this week. What other things should I look for to track down this problem?

Thanks,
KJ

[THEMOTORHUT]

Re: 96 SLT780 - Poor throttle response

Pull The Carbs Off And Clean Them. Check The Pop Off Pressure

[d.ginther]

Re: 96 SLT780 - Poor throttle response

I'd check the carbs also.
I'm not that familiar with the 780, but on the 1050, I'd start by checking the settings of the low speed jets.

How does the boat idle out of the water?

[johnsonmtz]

Re: 96 SLT780 - Poor throttle response

I had it out this weekend (finally hit the 80's) and it seemed to run OK, with the exception of the throttle response. It was responsive most of the time, but extended idling certainly made the response worse. I was able to hit right at 50MPH @ 6500 RPM. My Clymer's shop manual just arrived last week but I didn't have a chance to go through it thoroughly. My guess would be that 6500RPM is max on these?

I had installed a new filter/water separator element and that had no effect. When I'm idling the exhaust is pretty smoky, so now I'm starting to think maybe it's not lean, but rather it's running rich at idle and loading up?

I had it out this afternoon and it ran OK, but after about 15 minutes I was cruising @ WOT and suddenly lost power. I had the throttle open but was only going about 19MPH @ 3900 RPM. I didn't have a chance to troubleshoot anything, I just got to the nearest launch ramp, got a ride to my truck, and trailered it home. However, one thing I have noticed is the spark plug boots are very loose and they wiggle freely on the top of the plugs. Maybe I'm getting poor spark?

Wow, so many things this could be. The way it just lost power certainly felt like it dropped a cylinder. I'm going to tweak the plug connecters to get them fitting snug. Then I'll put in a new set of plugs. I'm sure I'll want to also check compression just to rule out a worst case scenario before I go out and lake test it. Hopefully all I've done is foul a plug(s).

Once I get it back running, I'll start into the carbs and try to track down this throttle problem.

[polarisslx1200]

Re: 96 SLT780 - Poor throttle response

sounds to me like your loading up if ya know anybody good at tuning carbs i'd have them take a look at them ......i got a 1200 and it generaly doesn't smoke too much do you run premix or oil injection????? maybe getting a tad too much oil????? those are just some things that first come into mind to me.....

[johnsonmtz]

Re: 96 SLT780 - Poor throttle response

No Pre-mix, I'm trusting the oil injection system. I suppose there are two possibilities. One is the low speed jets are too open and I'm loading up on fuel. Or the other possibility is maybe I'm over-oiling? I haven't really noticed excessive oil consumption. Do the oil injection systems on these fail often? Obviously I'd rather be injecting too much oil rather than not enough:D

Tonight I'm going to replace the plugs and work with the wires as I mentioned. Also, I'm going to test compression just to confirm the worst hasn't happened. From there I'll be able to tweak the carbs and get this thing running right.

KJ

[johnsonmtz]

Re: 96 SLT780 - Poor throttle response

This problem was eating at me, so I went home at noon to check the plugs. The rear most cylinder had a very clean, brown appearance. The front cylinder was brown in the center, but around the threaded area there was some carbon buildup. Sure enough, the center plug was carboned up and oily and the gap was closed. I can't tell if the closed gap was due to piston contact or what. The piston was at TDC and I couldn't see anywhere on the dome where it looked like it had hit the plug. Plus, the electrode didn't look smashed, it was just bent down against the center conductor.

Tonight I'll tweak the plug boots and check to see if I have spark on all cylinders. Also, I'll post a pic of the old plugs so you guys can see what they look like.

BTW, is there a specified torque setting for plugs? I'm wondering if maybe I overtightened the center plug and that's why there may have been contact? I looked high and low in the Clymer manual (it's not very well organized) and could find NO torque specs for the plugs. I would feel much better if I knew exactly how tight to make them.

KJ

[SBT-MNGT]

Re: 96 SLT780 - Poor throttle response

At this point you need to pull the engine and tear it own for inspection. You have internal damage and will only do more by trying to run it like this.

Pistons do not contact plugs unless you install the wron plug (too long). Gaps get closed due to debris hitting it and bendig it. It could be external debris, it could be a bearing coming apart, a ring snagged, part of the piston you can't see, etc. The bottom line is you have a situation you need to take care of before it gets worse and more expensive.

[SBT-MNGT]

Re: 96 SLT780 - Poor throttle response

One more thing - you said it was a bran new engine - what happened to the original that you needed a replacement, and what was done to specifically fix the cause?


Was it really brand new, or was it remanufacured? If it was one of ours, and you are still under the one-year warranty, pull it out but don't take it apart - call in to Julie for another engine.

[Wet Wolf]

Re: 96 SLT780 - Poor throttle response

if the engines OK. check the oil pump rod to the carbs. if this comes unhooke, then the oil pump arm rotates around to the full on position and will make the ski load up at idle, but then will clean out at wot.

[johnsonmtz]

Re: 96 SLT780 - Poor throttle response

BGLynn,
Ugghh, tear down the engine......man that's not what I wanted to hear. That will put a serious kink the summer fun

I don't believe this was one of your engines. The engine blew on the original owner in summer of 2003. He had the local shop, World of Powersports in Decatur, Illinois, install the new engine in January of 2004 when we bought the watercraft. I was not given any information why the original engine blew or what was so severe that they had to install an entirely new long block. I'm not sure what their source is for new/reman engines.

I didn't hear any unusual engine noise when this happened. I had just come out of a no-wake zone and accelerated to full throttle. I was running at WOT for about 20 seconds then the power just dropped off. No sounds, nothing, it just slowed down.

The plugs I'm using are NGK BPR8ES.

I think I might just punt and take it to the shop. I can diagnose a Johnson/Evinrude outboard pretty well, and this shouldn't be much different especially with a manual in hand. But, when it comes to internal stuff I know just enought to get myself in trouble.

Man, what a bummer. This is the last thing I need to have happen right now:(

[johnsonmtz]

Re: 96 SLT780 - Poor throttle response

Ok, I punted yesterday and took it to the shop. They were a little perplexed at the closed gap on the center plug.

The service manager told me that no-one installs new engines, they are all re-mans. Hmm, guess I was led astray by the original owner. Live and learn I guess....this is my first waverunner so I'm constantly learning new things and I'll just chalk that one up to experience.

Anyway, he told me they install a lot of SBT engines, so BGLYNN, it's quite possible this is one of your reman engines. They were pretty backed up with work, so it won't be until Wednesday or Thursday before they get a chance to look at. He said they'll check it out first and let me know what they find before the go ahead with anything.

I'm just surprised, if the piston did contact the plug, why the engine would blow so soon. It was only used from June to September last year (once or twice a week on average). It was pulling down oil from the tank so I know it was getting lubrication.

KJ

[Technical Support]

Re: 96 SLT780 - Poor throttle response

It sounds like you have no idea of the true history of the ski and/or repairs. It very well may be that the original problem was never corrected, maybe the ski was dumped on to you for a reason.

Bottom line is if you do not go through it completely and fix the root cause, history will repeat itself.

[johnsonmtz]

SBT engine is officially blown

The shop has confirmed there is play in the center cylinder connecting rod. THere is no scoring of the piston or cylinder wall and no signs there was insufficient lubrication, heat or a lean condition. In other words they have no idea. This is the same shop that installed the engine last January. Their suggestion was to just slap in another engine.

I called Julie and she said there is nothing she can do because the engine left SBT on 12/3/03 and it doesn't matter how long the craft sat unused. She offered to give me a $200 discount on another engine.

At this point I am extremely perplexed as to why an engine with less than 3 months of use, that was well maintained, has a loose connecting rod. That makes no sense to me at all. Last fall when I put this away I filled the tank with fresh fuel, added fuel stabilizer, ran the craft on the lake to full operating temperature, then fogged the engine with fogging oil. This spring I again added fresh fuel to the tank to top off, ran the engine at low/medium RPM to achieve full operating temperature before I ran out to WOT. I used double oil during the break-in period, varied RPM, and did not run at full throttle until after the double oil period. Also, I have used 100% synthethic oil after the break-in period was over.

So what could I have done to prevent this from happening? This is exactly how I have maintained my 2-stroke outboard engines for the last 15 years and I have NEVER had one of them blow up. I pull skiers, tubes, make long runs at WOT (5500RPM) with them and have never once had an internal failure. So if I'm maintaining those correctly and they are lasting for several years, how can this polaris engine blow after just one season?

I don't know who, or what, is to blame but I can tell you that I am totally ticked off that I am going to be out a significant amount of cash to get this thing running again. This engine should not have blown.

[Technical Support]

Re: 96 SLT780 - Poor throttle response

Well, I think there is a lack of communication somewhere. If the shop is telling you they have 'no idea' what the problem is, but they want 'slap another engine in it', to me that says either they are clueless, and you need to find a real shop, or they are lying and want your money - and you should find a real shop. Or you misunderstood something.

If you can post good pictures of all the parts, we can go from there and give you a good idea of what you need to do. Engines don't fail for no reason, and this is the third in the ski without anyone finding a cause (like a real mechanic is supposed to do) or any actual preventative measures being taken.

You can do all the regular maintenance on a ski you want - but if there is an unaddressed problem, it doesn't go away by fogging and flushing.