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Help! Can't get my 96 Challenger 787 to rev past 5000!!

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mwestmstrum

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I bought this 96 Challenger last year and have had limited results so far! The motor idles well, starts good, and pulls ok up to 5000 rpms. I can't get it to get up on plane at all.

So far, I've removed and cleaned the carbs. I checked the fuel pump as well. The fuel selector has been bypassed at this point. The fuel bowl filter is clean and the final filter in the carb body is good as well. I pulled the raves and they seem ok as well. The fuel lines were replaced at some point. I checked the cylinder compression, and is was between 125-130.

Any ideas on where to look next?? This boat is making me crazy. We are at the cottage this week, and hope to get it working properly.

Thanks for any help on this....

Mark
 
Perhaps its not a fuel problem. Did you try: changing the spark plugs, checking the gear selector function/adjustment, impeller condition, wear ring, etc? If its lacking fuel, you can easily diagnose this by applying the choke just a little, and see if the RPM's go up. If they go down, your not starving for fuel. Could be a failing electrical system, but doubtful. Rev limiter of some sort?
 
Thanks for your reply Orion!

I have tried two new sets of plugs this weekend. I tried adding choke when it was sitting at 5000 rpm at wot, and it chopped the revs instantly. It didn't help at all. Carb adjustment for throttle and choke were decent when I had them off last week. Impeller and wear ring condition is ok visually although I haven't taken the pump assembly apart to inspect yet. The wear ring isn't worn,... I went thru that with my 96 XP.

Do you think that the compression is reasonable at 125-130?? Is the motor just getting soft and due for a rebuild?

Is there any chance that I have a learner key for this boat??

Still confused,...

Mark
 
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good call orion didn't even think about the raves, 787 has the raves. they are the 2 black caps with red adjusters in the middle, you slide the retainer off the black cap while holding the cap down cause there is a spring and some washers under there (should be) and lift the cap off and you can grab the rave and it should move freely up and down. just cause they move good dosent mean they are good. if you or a previous owner has been running tcw-3 outboard oil in it they are probably gummed up.
 
not to mention(I apologize if someone has...I didn't read all the posts) but on 9u there as a tsb to replace the early non slot rave valves. In certain instances it would limit the rpm to the 5k range.
 
Thanks so much for the input on my problem! Looks like I will start tomorrow by checking all three rave valves to see what sort of condition they are in.

I will update this thread with results (good or bad)!

Thanks again,

Mark
 
Daily update! I pulled the Raves on the engine, and cleaned them up. I set the tops of the raves flush. They weren't in too bad shape. I put in new plugs, and went out for a water test.

The engine was much more difficult to start today. The boat accelerated decently to 7000 rpm's and then settled in to only 5500 rpms. I had three on board, so I lightened my load, and the boat jumped on plane for once, but still only revved around 5500. I ran the boat for a little bit, and then returned to pickup my helpers. The boat continued to be tough to start, and I couldn't get it to get up on plane again.

I tried testing with the raves 2 turns in from flush, and 2 turns out from flush. No improvement.

I checked the fuel strainer, and if seemed tight with no leaks.

Once again, I'm at a stalemate with this machine......

Here's a pic of the plugs that I pulled after the last round of frustration

291.jpg


And here's a pic of the raves. Bottom valve in the pic is cleaned, and the other is 'as pulled'.
292.jpg
 
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A picture is worth a thousand words. I see an issue with what the spark plugs are saying. The PTO side almost looks like it's not firing at all or it is firing lean. Do you smell a lot of unburned gas when you are on the water?
 
Hmmm. Interesting, my wife (helper) said that she could smell unburnt fuel. It seems like I'm fouling the plugs. A new set helps for a short time only. Maybe I should snip the end of the spark plug wire.... It may be that simple??
The plugs in the pic have very little time on them.
 
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Every time you remove the carbs you have to go through the synchronization procedure because the distance between the carbs has changed.

Step #1 Adjust the throttle cable; I usually push the throttle all the way open and adjust the cable, so it is just opening to full throttle.

Step #2 Back out the idle screw and sync the throttle linkage.

Step #3 Adjust the oil pump cable, so the marks align

Step #4 Start the engine and adjust the idle speed.

You have to go through this proceed in this order every time the carbs are removed.
I'm not sure this will solve your problem, but that would be my first step.
 
I'm leaning towards the idea that the PTO cylinder is not firing or firing very weak maybe an ignition coil issue.
Yes snip the wire ends and see if that helps
 
Thx so much for your input Bolongo! I will take another swipe at this tomorrow! Snip the wire, and I will inspect the coils inside the boxes as well. The saga continues.....
 
A "surefire" way to see if a cylinder is firing, is to disable the other cylinder. If it runs, your cylinder is firing. If not, its not. If you are only running on one cylinder, that would obviously drop your RPM's and interfere with getting up on a plane.
 
I read the reply about the non slot raves. I will do some research about that issue.

Thanks for the tip about pulling the opposite cylinder. I'll use that tomorrow to help diagnose.
 
If you pull off the spark plug wire, make sure you ground the spark plug wire to the grounding post that is located on the front of the engine. (mag side)

s-l300.jpg
 
Daily update!! I trimmed an inch from the end of each plug wire and reconnected them to both the coil and plug caps. I inspected the ecm box and visually checked the coil. Everything was showroom clean with no corrosion or signs of tampering. I installed new plugs and set out for another sea trial. The motor was difficult to start, but that may be due to operator error. Once running, the motor ran marginally better, but would climb up onto plane and rev out to just under 6000 rpm. I did a plug check, and they are both very similar with a dark brown colour.

I was going to pull a plug wire, but I couldn't find the grounds. I do have a set on my XP, but I don't see them on this boat.

Sooo,... What should this motor top out at for rpm, and any other ideas to get the last bit of performance out of it so that it will plane quickly, and be able to pull a tube for the kids... Haha

Thanks to all for the help along the way!!

Mark
 
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I'm seeing some mixed advice here... so here's my thoughts.


1) The compression is low for an 800 engine. The spec is 150 psi. (open throttle, cold engine) SO... at 125 psi... you are reaching end of life. I would personally put in some new rings before a meltdown. (or at least verify your compression gauge)

2) The PTO plug in your picture is super lean. Even the PTO RAVE is showing lean. SO...

a) Lets verify you have good spark. Get an inline tester, and go for a ride, and have someone watch to see if the spark is dropping out. But, generally, if it is... you can feel it. (like a miss, or stutter)

b) Let's double check the compression on that cyl vs the MAG cyl.

c) The carbs need to come off again, and make sure that your PTO carb is good.
 
Another update! I haven't had a chance to get back to the boat. We have a packed weekend, and I might not get another chance to wrenching on the boat. I will certainly keep pushing to fix the boat when I get home and will post results. I'm interested to do another compression check and whip the carbs off again and reassemble properly. Thanks for all of the support and help along the way!!
 
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