Non-restrictive flame arrestor

[IDoSeaDoo]

I have a 787 seadoo with a very non-restrictive flame arrestor, previous owner basically opened the retainers and pulled all the fine mesh out, leaving just one of the coarse screens. I just went thru the carbs and cleaned them up (they were already pretty clean) and made sure I didn't miss anything in the recent rebuild I did last fall. The ski hasn't ran since then, and was experiencing a terrible bogging from closed throttle to full rpms. I though due to my flame arrestor being basically a mesh screen, I'd need to drop the pop-off pressure, but when I checked it, it was at 25psi. I went back and set it to 35, made sure the High Speed check valve isn't stuck, that the three little high holes near the butterfly (under the Pilot jet) aren't clogged. Low Speed out 1 turn, High Mag:0 PTO:1/4

Should I go back and drop my pop-off lower? Anyone else have experience with low resistance flame arrestor?

 

[Dr Honda]

Dropping the pop-off will help, IF, the flame arrestor is the problem.

Have you checked your compression? Have you checked the rotary valve clearance?

 

[IDoSeaDoo]

Compression is a solid 150 on both cylinders. Have not checked the RV on this one. Wouldn't RV affect me through the whole RPM range?

 

[Dr Honda]

Compression is a solid 150 on both cylinders. Have not checked the RV on this one. Wouldn't RV affect me through the whole RPM range?

If the housing is warn, and it's not sealing correctly... then yes... it will.

Chances are, it's the carbs, but if you take them off to work on them... all you have to do is put a feeler gauge down the manifold, and check the clearance of the RV.

 

[IDoSeaDoo]

While working on the carbs, I noticed that my oil injectors are at the bottom instead of the top... that doesn't seem right... would the oil even get atomized this way? Should I pull the RV cover and flip it?

 

[IDoSeaDoo]

Would 35psi be too high for non-restrictive flame arrestors?

 

[IDoSeaDoo]

Left the pop-off at 35psi, (changed from 25 to 35) ski seems to bog the same way, maybe worse. Tried to enrich using the low speed adjustment, and the problem seemed to get worse. Ski starts right up, idles great, runs at top speed like a bat out of hell, but dies when you open throttle from idle... Do I just need new N/S? Could it be that my needles are moving too slowly in the seat body and giving me delayed fuel delivery? I recently went through the carbs and found nothing suspicious. This problem is a phantom... I'm getting very upset with people on the forums getting help on this issue and not posting what finally resolved the problem. Kind of irresponsible of them

 

[Dr Honda]

Did you check the rotary valve clearance?

If the engine will idle, and runs full power in the water...then no... you needle and seat are probably OK.


Is the bog when you open the throttle quickly, or can you find the dead spot while opening the throttle slowly?

If the filter is suspect... get a factory flame arrestor, and see if that helps.

The only other thing I can think of, is that you have a case leak. (possible crank seals)

 

[IDoSeaDoo]

Checked RV clearance before before put carbs back on, it's perfect :/ Case leak would be okay, a crank leak.... that would suck. The bog happens when I open quickly, but I'm pretty sure there is some dead spot as well... if it were crank seals, what compartments in the engine would I have to pressurize to test that?

 

[Dr Honda]

You would do a regular leak down test. Seal off the exh and int... and put pressure into the spark plug holes. (10 psi) if the pressure drops faster than a couple PSI over a few minutes... there is a leak. In a 2-stroke, a case leak will cause all kinds of issues... the worst of all is a melted piston from going lean at high speeds.


Do your spark plugs look different? (one lighter than the other?)

You need to take it out, and see if there is a dead spot in the throttle. Honestly, I think it's just a transition port that is clogged up.

 

[IDoSeaDoo]

Took the skies out today I actually MADE a tool to turn the low speed screws in and out, it was too freakin' hard to turn them back in by hand... Ironic thing is, I didn't even use it, was too busy having fun. Ski starts well, and runs @ top end great, just has a nasty dead spot in the throttle. Yes, pulling the choke half way does help the deadspot, which tells me that it's getting too much air. I was pretty resigned to the probability of having a case/crank leak until I took the ski home. As I was inspecting the plugs (which look perfect, and were very slightly different), I noticed that my RAVES were really nasty. This is a new (used) engine, and was freshly painted when I got it, with new RAVE boots. After today, there are black stains from where fuel/oil mix was evidently coming out. Took off the caps to discover that one of the plastic RAVE screw tops was really crooked, and the boot was completely off of it. I think I either forgot to put the retainer spring around the boot, or it broke, or I never screwed the cap down tight enough.

ALSO

As I was poking around in my engine bay, I also spotted my MAG carburetor gasket in the bottom of the hull. I don't think that would lead to a very big case leak, but it definitely didn't help my situation.

Tomorrow, I'm going to set my low speed screws back to 1 turn out, make a new carb gasket, and put on a spare RAVE cap and boot-spring. Will probably do a water test, I'm lucky enough to live 2mi from a lake I really hope that was all it was, wish me luck guys!!

(Oh and I also replaced the Autolites with NGK's, stupid Advance Auto doesn't stock NGK's in our heat range anymore... had to go to Autozone)

 

[IDoSeaDoo]

Put the carb gasket back on, and put on a new RAVE plunger where the old one was, reset the low speed adjustment back to 1 turn out. Still getting that terrible bogging, except I feel that it's even worse now. It takes forever to get the RPM's back up w/o choking it. Glad I didn't install those primer kits... Soooo I guess a pressure test is the next step right? Can I isolate exactly which seal it is (MAG or PTO)? I believe the PTO comes out w/o having to pull the engine, right? I really don't want to have to split the block. Could it be the inner crank seals? I have doubts that it is b/c isn't that area flooded with constantly? I mean, if those were leaking, wouldn't I be sucking way more oil and fouling my plugs with it?

 

[Dr Honda]

The leak would be the outer crank seals. (if they are leaking)

I really think you are fighting a carb problem. I know you've looked, and cleaned... but I've done carbs, and missed things in the past. Also... sometimes, cabs can be worn out too. Is there a lot of play in the throttle shafts? One other thing to look at... is one of the throttle butterflies bent? They are brass, and very soft.

 

[IDoSeaDoo]

I remember looking carefully at the butterflies, and they seemed perfect. I aligned them outside the ski on a spare RV cover I had. The shafts are a bit loose I guess, but I thought the shaft seal would take care of that. Are you saying I need new carbs? I guess used ones would have the same problem...

 

[Dr Honda]

Depending on the carbs... you may be able to change the seals. Also, some thick silicon grease on the shafts may help seal them up.

Unless the carbs are rotten, I would say you can make them work. I really think you have an internal leak, or plugged bypass ports.

 

[IDoSeaDoo]

If the bypass ports are the three tiny holes that connect with (I think the pilot jet), then no, those are not plugged. I watched as three jets of carb cleaner sprayed out of them, followed by 90psi of filtered/dried compressed air. Not the trans-ports. Could be the shafts, those were pretty loose, but I thought I replaced the seals on them. I'm going to build a test rig to pressure test those seals, basically cut out two pieces of plywood or aluminum, put some gasket material on it, put a port on it for my pop-off tester and see how much psi those shaft seals hold. Would it even matter if they leak though? I mean, I guess it all depends on where the leak is, before or after the butterfly...

 

[IDoSeaDoo]

Thank you Dr.Honda

BTW, I really appreciate all the insight and advise you give me Dr. Honda. Thank you!!

 

[IDoSeaDoo]

I was pondering about the crank seals leaking... If the PTO seal leaks, it's pulling air from the outside, right behind the flywheel, but if the MAG seal leaks, it has nowhere to pull from: the Timing Cover, Oil Pump, and Starter are all sealed with rubber o-rings. I have a hard time believing that I'm getting THAT much air past the actual crank seal AND past one of those other seals. If it really is my crank seal, it has to be PTO, which is removable w/o having to pull the motor

Could I do a leak down test by putting pressure to PTO spark hole and just plugging the exaust pipe outlet, the rv cover, and the water hoses?

 

[IDoSeaDoo]

Oh, another ?, if it one of my crank seals is leaking, would the plug on ONLY that side be lighter, or would it affect both cylinders?

 

[spx800]

do a plug chop. go for a ride, when it starts to bog, shut it down. pull the plug and see what it looks like. take a pic and post it.

 

[IDoSeaDoo]

Tried to do a pressure test with the exhaust still hooked on... too many passages in the water jacket. Will try again once I disconnect the upper exhaust pipe. I also kept the carbs on, and blocked the intake above the carbs. I wanted to see if the carb throttle shafts were leaking. This test did help me find a peculiar thing: MY NEW RAVE PLUNGER WAS AGAIN DESTROYED!! It seems that the Rave valve is getting too hot and melting the plastic, which causes it to come off the rubber plunger and makes my case leak through the little hole in the RAVE Valve body. Why would my MAG cylinder be getting so much hotter than the other one? Both of my plugs look too white, like it's been running lean, but the MAG side plug has a cleaner metal part, where the threads start. Other one is blacker. What could this mean? If I have a crank leak, would it affect one side more than the other??

My High-needle is turned all the way in, while the PTO is 1/4 out. Going to put on my last spare plunger and run it while spraying carb cleaner in suspect areas, hoping to find the leak when it surges.

 

[spx800]

did you ever get this resolved?

 

[IDoSeaDoo]

Sort of... I bought two new RAVE valves and one new RAVE housing (this was to see if they were any narrower than my old ones, and I don't really think they were, haven't pulled apart to note differences yet) and installed them onto the motor. Recently, I bought another ski, this one had a blown engine. I took the carbs off it, went through them and found that the throttle shafts seemed a lot more solid. With that in mind, I decided to try them out on my SPX: I put them on and the problem went away. So I've narrowed down my bog to two possibilities: either the bushings were shot and were leaking air, OR my rebuild kit had some POS diaphragms and they didn't work properly. I have new bushings, but want to rebuild that new motor and try my old carbs on it, then try to replace the bushings. I want to isolate my variables one at a time, so as to learn the most from this and help all you people out there