I need some help from the wizards please.

[Ryan Declark]

I have, by the book, aside from the timing, assembled a brand new js550 piston port motor. Fresh hone (not bore) within spec with new ADR crank, all new seals, pistons and piston rings. Super odd the the exhaust manifold bolts only want about 5 pounds of torque but I did it. Anyway, as I get everything hooked up with my newly purchased 44mm sbn I started cranking and realized I'm pulling air from the wrong direction, I can feel the air coming sucking from exhaust side. And and a very weak pull when I put my hand over the carb it pulls air from both sides basically

I've done minor reading on the subject as it's hard to find an exact article or video on setting a timing on specificly js 550s. I turned the stator counter clockwise about the width on a nickel. again this the first time I've messed with timing at all. My only thought is that perhaps when I pushed the flywheel on I pushed the keyway or Woodruff key out of the slot but I don't know how likely that is. The reason I suspect this is because I've heard of this being a cause of "back firing".

I don't even know if the timing is even an issue at this point. My understanding as of now is that the crankshaft doesn't need to be in any specific position, just as long as the stator is lined aligned correctly with the case, which in my case is the tiny hash mark on the stator and the parting line of the case, which has a raised metal tab indicating the timing mark.

I'm super bummed. I've ripped the engine out tonight and after everything was routed and back together nicely. I plan on opening up the timing cover and inspecting tomorrow after work, as I have a few more days before I set out to parkers run what you brung event.

I would appreciate any suggestions as to where to look or start. I'm running a million miles an hour and need some objective thinking.

Please and thank you.

 

[WFO Speedracer]

I replied to your PM but I decided to reply here as well , maybe it will help out someone in the future who reads this .

About the only way that could happen is if the pistons were installed backwards although on a PP engine with no boost holes it shouldn't matter that much , on pistons with boost holes they won't run in the water at all with the pistons in backwards.

Run a water hose up into the exhaust hose the exhaust pipe hooks to , turn it on, see what comes out the exhaust exit or you can put it in the exit and see what comes out the hose if the engine is out of the ski of course.

There is also the possibility of damaged baffles or a melted waterbox, I have also seen sections of exhaust hose that have delaminated inside where nothing would go through the hose, that was a fun one to find.

The Piston port engine depending on timing of course will still run in reverse , check the entire exhaust system for blockage , the exhaust pressure has to go somewhere if it can't go out the exhaust it's going to go backwards through the carb.

Not sure where you live but here we have dirt daubers , they look like wasps and they build nests basically out of mud in any hole they can find, in fittings , inside a hose, inside of a ski and sometimes on the inside of exhaust systems .

Over the years I have also seen shop rags and paper towels get stuffed into open exhaust hoses and sometimes into carbs, they have a way of blocking stuff up if they get left or pushed into the hoses and you will have lots of fun if they get left inside the carbs.

I know your ski is not running yet, it doesn't matter because running or not if it's spinning over and has compression it is producing exhaust pressure.

 

[Ryan Declark]

These

 

[WFO Speedracer]

Check the exhaust for obstructions before pulling anything apart

 

[Ryan Declark]

I'm not familiar with boost wholes. Can you give me a description as to what that is? Also I appreciate sharing the knowledge outside of the pm.

 

[Big Kahuna]

did your pistons have arrows on them, Are they pointed to the Exhaust Side?

 

[WFO Speedracer]

Bosst port pistons, the holes line up with boost ports in the cylinder , as I said piston port engines don't usually use them , the piston skirts determine the opening and closing of the ports.

 

[Ryan Declark]

did your pistons have arrows on them, Are they pointed to the Exhaust Side?

So I will verify once I'm done with work but after careful review of my assembly I destinctively remember saying to myself that I installed the chambers on the wrong way, so I turned the chambers and briefly looked at the pistons but can't remember if I had the pistons orientated the right way or not. I'm starting to feel like I installed the pistons in the wrong direction. Again I can feel pulling from exhaust side so not sure that there is blockage but I will run the water test to verify.


As a learning lesson to myself, can anyone explain why the pistons are orientated in a specific direction? Are the pistons crowned differently to pull and push air into a specific direction?

 

[Big Kahuna]

Terry (WFO) can explain it better, But it has to do with the way the porting works. With Reed cases and Cylinders, the Skirts act as windows to help with the flow of the fuel air charge. From the Intake Stroke to the Exhaust Stroke. On intake stroke, the skirting will block the exhaust port as the piston rises while sucking in the air fuel mixture, after the charge, and the stroke is going down, this opens the exhaust ports to start to push the burnt charge out. At the same time the intake side is sucking in the new charge down into the cases, then it gets forced up through the intake ports to the top of the piston......... Been a long time since I had to think of how everything works hand in hand!!!!!!!!!!!

 

[Ryan Declark]

Terry (WFO) can explain it better, But it has to do with the way the porting works. With Reed cases and Cylinders, the Skirts act as windows to help with the flow of the fuel air charge. From the Intake Stroke to the Exhaust Stroke. On intake stroke, the skirting will block the exhaust port as the piston rises while sucking in the air fuel mixture, after the charge, and the stroke is going down, this opens the exhaust ports to start to push the burnt charge out. At the same time the intake side is sucking in the new charge down into the cases, then it gets forced up through the intake ports to the top of the piston......... Been a long time since I had to think of how everything works hand in hand!!!!!!!!!!!

Ya well done. I understood "2 stroke" but I had a feeling as people started saying piston direction, I definitely recalled a time where I was unsure, as I was unsure about alot of things. Also just learning the function if the piston skirt too is huge. I never thought that deeply about it but only simply understood the actions included in the "2 stroke engine"
I work on diesel engines which are typically 4 stoke which include valves so this has helped a ton. Thank you.

 

[WFO Speedracer]

The biggest issue with installing them backwards is the locating pins for the rings will be in the wrong place, they have to line up with solid areas in the cylinder walls to keep the rings from getting caught in the ports.

A reed engine is just a piston port engine with reed blocks added to prevent reversion of the fuel charge , ON a rotary valve engine the rotary plate blocks off the ports to prevent this , on a piston port engine it's the piston skirts that do this..

Those holes on the left side of the pistons in the pic are most likely your issue if the pistons are installed backwards.

 

[Ryan Declark]

If I remember correctly I believe they did not have wholes in the pistons. So my bad on that but they were wsm pistons. They did not look special at all really.

Are their rotary jetski engines?

 

[WFO Speedracer]

The rotary valve which looks like a pie plate with a section missing rotates and opens and closes the intake port positively , they produce the most HP per CC of any two stroke engine setup , in this case 717 CC's 80 HP..

 

[Ryan Declark]

Okay so thier was a piece of tape stuck in the exhaust from the painter. That was fixed and it helped. Pistons orientated correctly. I've got 150 pounds of compression both Cylinders. I've got spark. Still no boom. This is what I've got right now.

 

[Ryan Declark]

Looks like one cylinder is pulling all the fuel other is completely dry? Bas

 

[Ryan Declark]

exhaust pipe was splashing with unburnt fuel. the base gasket was also wet. iv seen people use a little of 1211 on the base gasket but im assuming that a recipe for disaster or a Band-Aid on something that needs stiches. im not throwing in the towel just yet but tomorrow is my last day before i head off. that being said if anyones got any ideas whats going on im all ears. also my pilot jet is set at 105 right now with a 2.0 needle n seat with a black spring putting me around 23 pounds of popoff. what i really cant get over is that i can shoot a huge blast of ether in the carb and nothing, it seems like it just blows right back out. havint done a leak down test yet but tomorrow if i have time ill slap the bitch back together and do a leak down test, my hopes is that i dont have a warped cylinder base. i should have listen to @WFO Speedracer when he said "its not to late to give that ski back". but i aint no quiter, it just aint gonna happen this weekend most likely

 

[Ryan Declark]

After makingnm some calls someone has made the suggestion that even though I could be getting spark the ground wire on the stop switch might grounding out. Was told to unhook. Will try

 

[WFO Speedracer]

It's never too late to give it back.

 

[Ryan Declark]

It's never too late to give it back.

The hero Gotham deserves, but not the one we need.

Havint don't anything yet to engine. I likely flooded the engine like crazy trying to start it prior. Anyway it's gonna go with me, whether or not it's gonna be a river ornament or a running ski is gonna be if I can figure it out while I'm put their. I know I'm close. Also feel like I need to drop the pilot jet a ton thinking like 90. Will report if I can get it running.

 

[WFO Speedracer]

The hero Gotham deserves, but not the one we need.

Havint don't anything yet to engine. I likely flooded the engine like crazy trying to start it prior. Anyway it's gonna go with me, whether or not it's gonna be a river ornament or a running ski is gonna be if I can figure it out while I'm put their. I know I'm close. Also feel like I need to drop the pilot jet a ton thinking like 90. Will report if I can get it running.

I hear they make really good beer coolers , you know I am kidding right ?

From the post that mentions exhaust splashing with fuel it does sound like you may have flooded it out, PP 550's are often ridiculously hard to start to begin with . As far as the spark usually it does or it doesn't , put an extra plug in one spark plug lead leave the plugs in the engine, spin it over and see what you have, I have on occasion pulled the carb off the ski if it was flooded and started it without the carb on , it gets zero fuel that way and no need to hold the carb wide open , it will start rev way up then cut off if it's flooded out.