Love this boat ..but still minor issues any thoughts?

[Danosll]

First thanks to everybody on this forum .both to people who replied to my questions and posters who threads I have read. It's what has pointed me in the right direction to get this boat running so well.
787 challenger single.
After I installed new impeller motor would only rev to 5500rpm. Now after going through carbs ,raves, and water regulator on exhaust . Will turn 6800 rpm .
Idles great But still has bad miss at 1/4 throttle, and after extended idling through no wake zone will only rev to 5500 rpm.after a couple minutes with finally start to pull strong up to 6800rpm. So my issue is basically mid range.
150+ compression. rebuilt carbs pop off equal and within specs . Low speed adjuste 1 1/4 high speed turned in fully clockwise (with cap on right?) I didn't record low and Hs jet sizes.but I rember pop off spring silver and 1.5 seat. Fuel pump tested good according to manual.Ran fuel line directly to pick up baffle by passed selector valve. Cleaned rave valve,replaced 1valve and piston,bellows.adjusters turned in all the way. Check water regulator valve and adjuster flush. Plugs are always a good colour. But I never checked colour after pinned at 5500 rpm but I assume it is rich.
Running injector with semi synthetic low ash non tw3. Was running full synthetic but had to change . Seemed to run better with full synthetic . So I will change back when low.
What do you think? And thanks

 

[Waterluvr]

I think your Rave valve's will look like the insides of a black powder cannon after a few hours of running anything but full synthetic injection oil. The guys running motors without the Rave valves can get away with those blended oils so long as they have the right salt additives for ash content but it's a deal breaker for your 787 motor to stray from the XPS-II oil.

I would also be wary about how the seals (specifically the inner and outer crank seals) would respond to having exposure to different oil blends on older seals that have been in service for a while.

Outside of the world of Rotax engines I have seen numerous crank seal failures on outboard powerheads that occurred very suddenly sans some of the typical warning signs of an atmosphere leak in the case that affects tuning and smooth power range operation. Many of those cases involved the owner having switched oil brands or a subsequent owner dumping in the cheapest grade of Dino oil on top of the synthetic blend or premium synthetics the original owner used from day one.

Your issue with the engine loading up and hitting a point of 5500 rpm's after extended idling and then clearing out and making WOT after a short time would seem indicative of the needle and seat allowing in to much fuel to soon. I would verify the pop off pressure and set the arm to the correct height and clean the Raves and test.

 

[Danosll]

Thanks waterluvr idid the pop off test although I don't remember the exact figure it was quite high 32psi I believe. But I was kind of hoping I would not have to remove carbs again but it seems all indications point to either pop off or jet. When I read "to turn in high speed jet all the way" that is with black plastic caps still on right?.. My supplier ran out of full synthetic so I kinda got stuck and had to use semi. I will go back to full.
The raves are clean but seem really loose in there bores. can't find specs on tolerances. I even have some old ski doo manuals that also don't really give much info on raves other than to clean them regularly . I have them tightened to max. Thanks

 

[Waterluvr]

No, pull the black plastic caps off to expose the slotted adjuster on the brass and seat it lightly all the way in. That plastic cap is a limiter designed to allow only about 1/4 turn of adjustment until it hits the stop on the cap. You have no way of obtaining a baseline for how it was set previously unless you remove the cap and see how far if any you can actually seat it.

Back that low jet out and check the size when you're in there, hard to tell what someone did prior to you having the boat. I find all kinds of out of spec needle and seats and jet sizes that are pretty far out of bounds for the intended application.

If you need some help with that pop off or adjustment I'll be glad to help you.

Aside from that, I have come to think the Rave valve's have a much larger impact on performance than what the technical specs call for. Or in other words, I think they have the ability to impact rpm transition over a wider range and lower numbers than expected.

I think it's a very good investment to replace the Rave housings and all the soft parts on a boat this age that's seen anywhere near typical hours of seasonal use in our part of the world. My concern lies in wear and tear on the housing from heat exposure and the ability of the o-ring to do it's job and keep heat and carbon out. At some point that is going to have an impact on the bellows and springs doing their job and regulating the valve operation.

Your boat may well benefit from this, I can share that a complete rebuild of my Rave valves made a night and day difference in performance from the 4500K rpm range and up upon hard acceleration with everything in the carbs being as close to perfect as I could get them.

 

[Danosll]

Okay so I should leave the Hs needle seated? That's I error I have made in not removing caps.
One valve is new, as are piston and bellows both orings. Wish I could find specs because the excessive play appears to be in the actual bore that the guillotine rides in. One valve was actually broken at the shaft. Valves are the 353 model.

 

[Waterluvr]

Okay so I should leave the Hs needle seated? That's I error I have made in not removing caps.
One valve is new, as are piston and bellows both orings. Wish I could find specs because the excessive play appears to be in the actual bore that the guillotine rides in. One valve was actually broken at the shaft. Valves are the 353 model.

The factory spec is seated, on my boat the pto cylinder responded better with just a slight adjustment off seated equal to less than 1/8 of a turn open.

Regarding the play in the Raves, this is why I believe the housings should be replaced with new one's on both sides with all the soft service parts new as well. They will be adversely affected over time by heat effecting the ability of the o-ring to seal out contaminants that gum up the works in the bellows and warp the housings.

 

[Danosll]

Thanks waterluvr. I will remove plastic caps and see what kind of difference that will make. After I change my rave housings .

 

[Waterluvr]

Thanks waterluvr. I will remove plastic caps and see what kind of difference that will make. After I change my rave housings .

That made the difference in my boat, had just a very slight hesitation in the 4200-5500 rpm range from a dead on the peg idle taking the throttle directly all the way open and new Rave housings cured that for me. I transition from 1500 rpm to 7000 in about 2-3 seconds now with zero cavitation pulling a brand new factory impeller and wear ring and I'm liking it a lot!

These boats are never ending fun when you get them dialed in right and it doesn't break the bank to see 40+ mph over water with them on fuel costs.

 

[Danosll]

My housings are original and I was the first to remove them. The valves were pretty gummed up. One was broken. The play really seems to be in the bore itself guillotine to cyl. Play. There must be some way to find specs for that? And adjusters turn in all the way is better for mid to high right. ? And thanks waterluvr to take the time to help me.

 

[Waterluvr]

Yes Sir, all the way in on the adjusters is where you want them but not to tight you should still be able to move them up and down by hand with relative ease. I suspect on my boat only one of the Rave housings was somehow compromised thus not sealing and allowing proper operation of the valve.

 

[Danosll]

rave valve housings really worn. With one broken valve .so judging by the wear on the valve the valve bore must be damaged also. couldn't really see down it is behind exhaust manimanifold ordered all new parts. Housings,valves ,diaphragms,pistons .question is. If valve bore is badly worn will a new valve with a new housing. Break right away. This little boat has given the kids so much fun over this summer and there is only a couple weeks left. I would like to replace valves housings and tear it apart over winter. Any thoughts? I mean even if valve breaks again it can't really do anymore damage.

 

[Waterluvr]

The only contact the Rave valve should have is on the inner radius of the housing bore, from the bottom of the housing bore the rest of the valve should be floating at all times no matter if it's open or closed.

I have seen a wear specification for that housing bore tolerance but I'm not having any luck finding that in the manual right now, I'll keep looking for it as it may been published by a third party source.

 

[Waterluvr]

Found that reference for clearance, the source was cited as having been copied from the Sea Doo racing handbook:

"Move the valve side-to-side while it's in the housing. If it moves more than 1/4" either way, you must replace both the valve and the housing. If you continue to use the valve, you could wear away the cylinder clearance for the valve. If you are really mechanically inclined. Take the removed valve and stick it into the port. Take a 0.17 feeler gauge and put it in-between the valve and the cylinder. If there is more clearance than 0.15", then the cylinder has too much clearance for the valve to function at it's peak level. If this is so, then the cylinders must be completely replaced if you wish to get the maximum amount of power you can out of the valve."

 

[Danosll]

Thanks waterluvr I myself have searched high and low for the actual specs. As I have mentioned in my previous posts. Even my SKI-doo racers handbook lightly skips over any specs for the valve itself. So even though my bore is worn as long as I replace the housing I should be ok although my valve won't allow the motor to achieve the utmost performance. ? And the valve broke because of the excessive clearance in the housing and valve stem? I thought about installing brass bushings into the housings .

 

[Waterluvr]

Well, in my minds eye a worn housing bore also equals a worn valve shaft providing both of those components have been wearing in unison over time. You put a fresh housing into service with a worn valve shaft and day one your tolerances are off and wear is increased all over again at a higher than normal rate.

For a 17 year old 787 Rotax with original Raves start over with all new housings, components and valves and clean them every 30 hours or so and use a new o-ring and gasket each time. Using the proper oil to combat heat and wear those should last through the next engine rebuild and the remainder of the boats useful lifespan up to the point where the upper and lower portions of the hull and deck implode at the rub rail seam when the rivets give way.

 

[Danosll]

I am changeling valves and housings my concern was the valve bore in the cyl. But as you said it floats so I should be good. Just the increased tolerances for the valve blade itself won't allow the engine to produce max power . Which makes perfect sense. I do find the odd rivet in the bilge . But this boat has had a hard summer. Thanks again waterluvr

 

[Danosll]

OK new rave valves ,housing s ,pistons gaskets orings. Big difference!Pulls really strong .first day would pull good and hard right up to 7200 rpm and stay there. Now on day three still pulls strong but I only see 6500rpm. Gradually rpm started to taper off. Drained oil and am running full syn xps. So I took apart raves everything looks good. Did a hispeed spark plug run maybe a little lean on PTO so I'll back out hs adjuster. Next week I'll verify compression. Was 150+ at start of season. Too bad it ran better then ever after rave housing swap. But we still had a great weekend. Does any body now of a good method to verify flow of fuel pump .

 

[Danosll]

this is other plug

 

[Danosll]

Any body have any thoughts on my plugs? Too lean? This is after running wot 6500 rpm

 

[Waterluvr]

I just got your PM, it ran amazing and now performance has suddenly dropped off? I don't like the mostly white appearance of the plug insulators at all that's more than just a little lean.

Again for you and other reader's, small 2 stroke engine 101 when you have a performance issue the very first first place you look to is compression number's. When lean seizures occur in a 2 stroke it's often recanted by owner's that it ran the best it ever did right before it dies.

Fully charged battery with both plugs removed, ground your plug wires and with the throttle wide open crank the engine to an 8 count. Rinse and repeat and post your numbers we can go from there I hope your engine wasn't damaged by finally achieving WOT operation only to find carbs flowing less than 100% or a crank seal leak.

 

[Danosll]

Boat is at cottage and my compression gauge in city. That was my next test after I checked rave valves were still good. The performance increase was immediately after I replaced faulty rave assemblies. And power tapered off over the weekend. As opposed to a lean seizure or melted piston which is more of an immediate lack of power. Right? My issue is similar to what happened the first time I serviced valves .ran great at first then power tapered off. I'm thinking fuel supply filter or pump itself. Engine seals usually would cause backfireing, hard restart and would be one lean plug only? Right?. I was frustrated to not have my compression gauge with me. I had every other tool but. Thanks

 

[Danosll]

Maybe I will order a high volume fuel pump. And if the compression numbers are good . I'll just install with new filter.

 

[Waterluvr]

I'm not going to sugar coat it for you, we'll hope for the best but those plugs indicate running in failure mode. When your motor starts a series of lean seizures the very first thing you'll notice is power tapering off just as you describe it.

What did the piston skirts look like when you had the Raves out again?

 

[Danosll]

Didn't think to check skirts. Sun was setting and was in a rush to get back to city .first day of new school year for the boys. I'll check compression this weekend. And post numbers. Thanks waterluvr for the help once again . What I asked about the seals make sense? More of a fuel issue then sucking air ?

 

[Waterluvr]

A small leak at an outside crank seal won't just backfire right away, if you had an ear for listening to and tuning 2 strokes the onset of such a leak often times has the cadence of an engine with to much timing advance but they run like lightning at WOT for a little bit before bad things happen.

Far as a fuel issue, today I worked on two sets of Mikuni carbs that were supposedly just cleaned and kitted a few weeks ago and the boat still had issues falling off at about 5000 rpm. Things didn't look right when I sprayed through the circuits so out came the jet's and in the small sonic cleaner they went. I changed out the fluid for each individual carb body and it looked like cake batter in there when the cycle was done, those carbs had been fixed just enough by a hack to get them working to the point where the motors would self destruct in short order if run that way.

let's see where your compression numbers are and go from there.

These carbs have got to be right or the engines lean out badly at WOT operation, while leak and pop off testing is an important part of the service process it's what people don't see that get's them every time.