'97 Challenger

[John Gillett]

I have the 787 110 Hp engine in my boat. I have recently replaced the carbs and the rave valve bellows and checked the compression of the cylinders. Out of the hole it revs out completely but once planing the revs drop off and sit at just over 6K and wont rev back up again to max. If I turn hard the revs drop off to 5K or pull the throttle back to about 5K revs then it sticks there and will not rev back up again to max revs when I push the throttle forward again. If I pump the throttle then it will go back up to just over 6K.

Which side is it? carbs or RAVE valves?

[Technical Support]

Re: '97 Challenger

Did this just start suddenly? was anything recently done, etc.? What is the history here?

[John Gillett]

Re: '97 Challenger

The sticking at 5K has been a long term on and off problem and was assumed to be related to the carbs, thus the change to some secondhand ones from Arizona off a 97 XP. These are in much better condition than the ones removed, one of which was badly worn down the barrel and very corroded. They didn't look like a piar, one was definitely older than the other. Both valve shafts were sticking in the bushes due to corrosion, seawater. When first put on the new carbs seemed to solve the 5K problem but it has now returned.

We have this year replaced the wear ring and impeller, NuJet Destroyer same as before.

Performance has been poor this UK summer season 6 trips so far(!) and may have been due to one of the RAVE valves having manged to undo itself from its plastic cap, and so wasn't moving, which made a mess of the cap which we have now replaced. No improvement afterwards.

We have now replaced the Rave valve bellows on the engine and water box and reset them to factory settings.

Performance described above is as now.

[Bill O'Neal2]

Re: '97 Challenger

First thing I'd do is try another impellor. You may be overloading the engine by having the wrong impellor in the boat. That would make tuning next to impossible and cause problems like you are describing.

Rave valves in a 787 are very simple. If clean and all the parts are in good condition, they will work fine.

A water regualator, on the other hand can be a big problem limiting rpm if they do not work correctly.
Do a search here and read some of the many articles I have written about water regulators and how to test them.

[John Gillett]

Re: '97 Challenger

Hi Bill, many thanks for your comments.

The NuJet impeller is the one for the boat and is the second one I've had and in general I have been happy with them. The first one lasted 4 years before I replaced it this year and really made a big improvement over the stock one that was on the boat when I bought it. Surely if the impeller was overloading the engine this would happen when accelerating out of the hole as well would it not?

This year's problem of the drop off in power is not isolated to turning but does happen when turning to the left, of course, when turning to the right it doesn't drop off at all. Its the fact that once straigthened out the revs stick at about 5K and will only come back up again with pumping of the throttle - again to a max of about 6-6.5K The problems really started happening once the shop got busy with the rave valves. Prior to that and after fitting the new carbs the engine went fine I was just losing alot in the pump unit with a damaged impeller and worn wear ring.

Understand what you say about the engine rave valves and the water regulator. On my boat would the settings for the RAVE valves be two clicks up from tight down for the exhaust RAVE valves and flush with the top on the water regulator valve? Can you direct me to your information on Water regulators and how to test them please?

Once again many thanks for your help from a rainy UK!

[Bill O'Neal2]

Re: '97 Challenger

I still think it is the prop.

For one, you should be seeing at least 6780-6850 at WOT. One of the ways we fought off the left turn syndrome was to lower the pitch of the impellor, which now you mention as another problem you are experencing.

If your water regulator was bad, you wouldn't see much over 6000 rpm.

It should not matter at all in rpm wether you have the raves adjusted in or out, they will still fully open at high rpms.