Challenger single 787 surges will not go pass 5000rpm

[pwrtech195]

Help! I am working on my uncles 1997 Challenger Jet boat and it is not achieving full rpm for more than a second or two.I give it throttle from any speed and it revs out to 7000 for only a second and drops to 5000 rpm then it will surge/hunt. I have checked the gas and no water, fuel lines have been changed to black (fuel separator was removed?), carbs cleaned and rebuilt, rave valves cleaned and checked. Before the rave valves being cleaned it would only go 15mph and only rev to 3000rpm. Spark plugs have been changed and are looking grey/brown on the tips. I noticed water leaking from the front cylinder at the cylinder/exhaust gasket near the bottom and it looks as though it has been leaking a while. The exhaust manifold connection with 4 bolts to the muffler looks like it has been removed (red RTV) I am going to remove the exhaust and replace the gaskets but I don't think this could be it could it?
The engine revs great out of the water on the hose.
Will not rev (rev limiter) when in nuetral.
Checked the "rave looking valve" on the muffler can and it is freely moving and lines are clear (Water regulator).

 

[Dr Honda]

That's a carb issue. They need cleaned.

Reving out of the water won't tell you anything, since there isn't a load on the engine.

 

[pwrtech195]

How clean is clean?

How clean do you mean? I tore these down ,soaked them in Yamaha carb cleaner (hour) cleaned them with gumout, blew all passages clean, rebiult with new kits. checked pump vac and pressure by mouth but could not get enough presure to check pop off of inlet needle. Used same color springs on inlet needle as original. Do you have any tips on getting them cleaner or is there something else that could cause this?
I thank you for any help I hate to use dynomite on this boat.
P>S> I took off exhaut manifold and the gaskets looked like they were leaking everywhere and someone had put RTV on them did they use this at the factory?
One other note, when I took off the front Rave valve it did not have any carbon on the angle (tip) like the back one did and that is where the water leak was on that cylinder.

 

[pwrtech195]

ok, I recleaned the carbs and tested the pop off pressure and found it to be to high so I replaced the springs with less stiffer ones but still no improvement. I replaced the exhaust gakgets that were leaking and then when that didn't work a new coil. Still no change. Now I am going to replace the rave valve diaphrams to see if that will help. running out of good weather here in Michigan.HELP!

 

[Comp]

When you had the carbs apart did you replace the little filters in them?

 

[pwrtech195]

Yes I replaced the small filters as well as everything else. I used a new rebuild kit in the carbs.

 

[newly]

i know this might sound dumb, but check to make sure the RAVE housings are not upside down. This will also cause the problem of not staying above 5k. That or one of the Valves in the RAVE has "let go" of the cap by stripping the threads out. Had one of each of these scenarios on each of the twin 787's in my challenger.

Also, as a side note... I have seen posted on here that a leaking water regulator can cause similar symptoms. (RAVE looking piece on the water box exhaust)

Hope this helps

 

[pwrtech195]

I thank you I have ordered new parts to rebuild the Rave valves, running out of options. I am a little confused by how the housings could be upside down? Do you mean the threads of the center peice of the cap?

 

[newly]

The aluminum housing can be upside down, even if the "Valve" is upside right, The cap that the valve screws into can spin if the spring that hold s the bellows to the cap is loose at all, I had this happen to me on one of the valves, ...stupid mistake..., if the housing is on upside down, it blocks the little blow by hole that goes up into the housing, thus not allowing the exhaust gases to push the valve open. I had the same kind of scenario where it would surge to 7k at WOT, but then would drop back to around 5k after a few seconds... This might not be your issue, but it wont hurt to clean the RAVE's anyway, Just make sure the valve is staying attached to the cap when you put them back together, one of the caps on mine had stripped out all the threads, and the valve wasn't opening on that one either....

Again, Hope this helps

 

[newly]

here's a pic of the housing, you'll notice that the "cut out wedge" (marked in red), on the housing is to the bottom. mine had been installed with that cut out to the top...

 

[pwrtech195]

Thank you I see what you are talking about. Mine are in right but I am going to replace the bellows. I am thinking that maybe the water regulator could be a issue I have not taken that apart, thinking how could that be the issue. I am getting frustrated I have: rebuild the carbs (3) times, new gaskets in exhaust(water leaks), new plugs and ignition coil. Compression is 150/148psi. After this I am thinking computer.

 

[parrothd]

You sure you're not cavitating?

 

[pwrtech195]

Yes it is a RPM issue.It revs to 7000 then drops and surges from 5500 to 6000rpm.

 

[Flightfollowing]

Did you figure out what was wrong?? Cmon guys, you need to add conclusions to your threads so when people actually do search for a problem, they don't need to start a new thread, they can just read yours. Conclude!

 

[Seadoobuddy]

I agree but this is Monday and maybe they went away for a long weekend.
Give them until Tuesday then shoot 'em.

(just kiddin')

 

[newly]

my next suspision would be the fuel pump, maybe a leak in the pulse line, or a leak in the pump diaphragm. If you have the pump that stands by itself, (not part of the carb unit), I don't believe that they are rebuildable, but I think the ones that are part of the carb unit are.... almost sounds like it revs to7k when the accel pump squirts, then drops down with the lack fuel.

Just another thought

 

[pwrtech195]

Not fixed yet

I have still not found the problem, waiting for time to check water regulator. Fuel pump is working fine I checked and rechecked this thanks for all of your help.

 

[pwrtech195]

just pulled water regulator and will replace to see if it will fix this pile of crap.

 

[pwrtech195]

Hello everyone, I replaced the water regulator and finally go to take this out and test it. There was no difference. Help please this was my last resort any more Ideas?

 

[CaptSteve]

I had a similar problem on my 2001 with a 951 engine. It turned out to be an air leak in the pulse line from the engine to the fuel pump on the carb. I went through everything you did and finally replaced the pulse line and that fixed it. I don't know if your problem is the same, but this is what worked for me.

Good Luck.