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Detonation - Hole in the top of the piston!
- Thread starter BoLongo
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This is scaring me as I just did the exact same setup except for the fuel filters.
Any chance that the pulse line being longer and further from the engine is causing it to not feed enough fuel to the pto carb?
The pto feed line would be slightly longer, but wouldn't think that would be a big factor. Just throwing out ideas.
Any chance that the pulse line being longer and further from the engine is causing it to not feed enough fuel to the pto carb?
The pto feed line would be slightly longer, but wouldn't think that would be a big factor. Just throwing out ideas.
snikwad003
Well-Known Member
What about the restrictiors in the return line right after the carbs, do you have them in there?
BoLongo
Active Member
Yes, if I was looking at this for the first time it looks like a (fuel problem) lean condition, but I have a different engine with a different oil pump and three different sets of carburetors all with the same results.
The fuel return after the carburetors is stock (no change).
The issue with the pulse line seems unlikely because I have the same setup on the engine right next to this one without any issues. I'm going back to the stock fuel line routing on both engines.
The fuel return after the carburetors is stock (no change).
The issue with the pulse line seems unlikely because I have the same setup on the engine right next to this one without any issues. I'm going back to the stock fuel line routing on both engines.
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BoLongo
Active Member
To chamfer or not to chamfer?
So now I have a dilemma, I hate dilemmas!
I have a great machinist that builds all the local racing go-carts in the area. He did a great job chamfering all the ports on my last top-end. He is leaving on a two week vacation next week and he cannot squeeze me in, so it will be at least four or more weeks for him to do the job.
I have a machine shop that I have been using for the last 8 years doing my engines. They do not specialize in two strokes but they do their fair share. I will not get the same chamfering work I would get with the guy that specializes in two strokes. But I will have the jugs back on Thursday.
Do you guys have the ports chamfered on your top end work?
So now I have a dilemma, I hate dilemmas!
I have a great machinist that builds all the local racing go-carts in the area. He did a great job chamfering all the ports on my last top-end. He is leaving on a two week vacation next week and he cannot squeeze me in, so it will be at least four or more weeks for him to do the job.
I have a machine shop that I have been using for the last 8 years doing my engines. They do not specialize in two strokes but they do their fair share. I will not get the same chamfering work I would get with the guy that specializes in two strokes. But I will have the jugs back on Thursday.
Do you guys have the ports chamfered on your top end work?
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snikwad003
Well-Known Member
You get a gold plated Rolls Royce as long as you pay for it:willy_nilly:
BoLongo
Active Member
Got my jugs back from the Machine Shop yesterday and started putting things back together.
Discovered that one of the RAVE valves was completely stripped at the valve piston. So when I was at ¾ to full throttle the RAVE Blade was free floating.
I’m not sure if this would cause the combustion issues I’m having but it cannot be good.
Discovered that one of the RAVE valves was completely stripped at the valve piston. So when I was at ¾ to full throttle the RAVE Blade was free floating.
I’m not sure if this would cause the combustion issues I’m having but it cannot be good.
BoLongo
Active Member
I got the carburetors back on today; I re-routed the fuel lines so they are closer to stock.
The problem with re-routing was the Mikuni high volume pump has two 1/4" outlets and the carburetors inlet is 5/16” so I could not just block off one of the outlets. I would have a volume issue. I got a brass 5/16” tee, forces two 1/4” lines onto the tee for the pump and one 5/16” line to the carburetor. Not pretty but it should solve any volume issues.
I was not willing to spend the money for stock OEM pumps, but if I were to do another SeaDoo boat I would buy the stock OEM pumps to start with.
The problem with re-routing was the Mikuni high volume pump has two 1/4" outlets and the carburetors inlet is 5/16” so I could not just block off one of the outlets. I would have a volume issue. I got a brass 5/16” tee, forces two 1/4” lines onto the tee for the pump and one 5/16” line to the carburetor. Not pretty but it should solve any volume issues.
I was not willing to spend the money for stock OEM pumps, but if I were to do another SeaDoo boat I would buy the stock OEM pumps to start with.
BoLongo
Active Member
Not blazing any trails, I spend a lot of time searching posts and forums to find things that work. I got the idea for the tee from an old thread on this forum, but there were no photos, so here is my contribution to the discussion.
A couple months ago I had a runaway engine on the trailer. I was frustrated because when I pulled the choke it should have killed it, but it kept running. I thought I had a huge air leak! I tore down the engine and pressure tested it and it held air. I was at a complete loss to why I could not stop the run away. Well today I found out that when I painted my dash last year I switched the choke pulls so when I was pulling the chock it was the choke on the engine that was not running.:banghead:
A couple months ago I had a runaway engine on the trailer. I was frustrated because when I pulled the choke it should have killed it, but it kept running. I thought I had a huge air leak! I tore down the engine and pressure tested it and it held air. I was at a complete loss to why I could not stop the run away. Well today I found out that when I painted my dash last year I switched the choke pulls so when I was pulling the chock it was the choke on the engine that was not running.:banghead:
BoLongo
Active Member
I got a used coil box from Westside Motorsports but the spark plug wires are a little bit short. Tomorrow I will be replacing the spark plug wires and reattaching them to the coil. I read a thread were you talked about how to replace spark plug wires. I often find RacerXXX posts in my searches. Thank you for sharing your knowledge it has helped me tremendously over the years. I might sound like I know it all, but the truth is I do a lot of research!
There are little spikes in the plastic holder, the holder.......it's like fine china.
I document a lot because when I got back into skis I felt like there wasn't enough documentation just a lot of chatter. MANY guys can look at a pic and figure out whats going on, there wan't enough pics. I have owned at least one seadoo over the last 24 years. And I'm creeping in slowly to 10K posts.
BoLongo
Active Member
I got everything put back together. The motor is popping very crisp. It feels like it wants to go. I’m taking it out on Sunday,
I so want to be excited that I finally got things right, but I have already done that the last three times I rebuilt the top end.
I think in the end those of you that thought it was a fuel problem will be spot on!
After rerouting the fuel lines the motor feel so much stronger. Splitting the fuel feed to each carburetor was a mistake.
I wish I would have listened to the more experienced guys on the board.
I would have spent more time in the water and less time in the garage wrenching.
I so want to be excited that I finally got things right, but I have already done that the last three times I rebuilt the top end.
I think in the end those of you that thought it was a fuel problem will be spot on!
After rerouting the fuel lines the motor feel so much stronger. Splitting the fuel feed to each carburetor was a mistake.
I wish I would have listened to the more experienced guys on the board.
I would have spent more time in the water and less time in the garage wrenching.
BoLongo
Active Member
Things did not go as well as I hoped; I put 30 minutes on the motors yesterday.
The starboard PTO cylinder is the problem child. The starboard motor would not rev past 5000 RPM. I think it was running on one cylinder at higher revs.
Here is what I did after installing a new top end:
I rerouted the fuel lines and removed the fuel filters for stock type filters.
I switched the carburetor sets between engines and checked pop off 38/40 PSI.
Take a look at the burn pattern on the pistons. The starboard engine is running wet/rich or the spark plug is not firing correctly causing the wet/rich appearance.
You can also see that scuffing has already begun after 30 minutes on the starboard PTO cylinder. Which in my opinion would mean water is working its way back through the exhaust port.
Question: if a cylinder is not firing (running on one cylinder) can water work its way back through the exhaust into the cylinder that is not firing?
Starboard PTO Cylinder (Problem Cylinder):
Starboard Mag Cylinder:
Port PTO Cylinder:
Port Mag Cylinder:
I used my WiFi scope to take these photos
The starboard PTO cylinder is the problem child. The starboard motor would not rev past 5000 RPM. I think it was running on one cylinder at higher revs.
Here is what I did after installing a new top end:
I rerouted the fuel lines and removed the fuel filters for stock type filters.
I switched the carburetor sets between engines and checked pop off 38/40 PSI.
Take a look at the burn pattern on the pistons. The starboard engine is running wet/rich or the spark plug is not firing correctly causing the wet/rich appearance.
You can also see that scuffing has already begun after 30 minutes on the starboard PTO cylinder. Which in my opinion would mean water is working its way back through the exhaust port.
Question: if a cylinder is not firing (running on one cylinder) can water work its way back through the exhaust into the cylinder that is not firing?
Starboard PTO Cylinder (Problem Cylinder):
Starboard Mag Cylinder:
Port PTO Cylinder:
Port Mag Cylinder:
I used my WiFi scope to take these photos
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BoLongo
Active Member
I’m confident that I have a short in the Starboard PTO ignition system. I’m not sure if the short is happening in the wiring or it is inside the MPEM.
Today I will be pulling apart the wiring loom and replacing the wires from the Mag to the MPEM and from the MPEM to the Coil Box.
After that the problem is in the MPEM.
Today I will be pulling apart the wiring loom and replacing the wires from the Mag to the MPEM and from the MPEM to the Coil Box.
After that the problem is in the MPEM.
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BoLongo
Active Member
My current (guess) diagnosis.
I think I have a short; more than likely a faulty ground. At higher RPMs the signal to the PTO spark plug is lost and stops firing. Without the combustion to push the gases out the exhaust, water works its way back into the cylinder washing the oil from the cylinder wall, which eventually leads to piston failure.
The cylinder is firing at idle because the engine will idle at 3000 RPM out of the water and 1500 in the water, but it will not rev past 5000 RPM and the PTO spark plug is wet.
I dug into the wiring harness today hoping to find a broken or corroded wire. I did not find anything wrong. I cleaned and tested the grounding blocks under the shifter, but I had cleaned them last year and they look fine once again.
My next plan is to run a ground wire from the battery to the coil box, MPEM and Mag housing. Hopefully this will resolve the issue if I am having grounding problems.
It could still be the MPEM but I have not found anyone with this problem that says it was the MPEM, so I believe it’s a grounding issue.
I think I have a short; more than likely a faulty ground. At higher RPMs the signal to the PTO spark plug is lost and stops firing. Without the combustion to push the gases out the exhaust, water works its way back into the cylinder washing the oil from the cylinder wall, which eventually leads to piston failure.
The cylinder is firing at idle because the engine will idle at 3000 RPM out of the water and 1500 in the water, but it will not rev past 5000 RPM and the PTO spark plug is wet.
I dug into the wiring harness today hoping to find a broken or corroded wire. I did not find anything wrong. I cleaned and tested the grounding blocks under the shifter, but I had cleaned them last year and they look fine once again.
My next plan is to run a ground wire from the battery to the coil box, MPEM and Mag housing. Hopefully this will resolve the issue if I am having grounding problems.
It could still be the MPEM but I have not found anyone with this problem that says it was the MPEM, so I believe it’s a grounding issue.
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BoLongo
Active Member
After reading the manual closer I have decided it is the micro-controllers inside the MPEM that controls the Starboard Engine.
I am going to replace the MPEM
From the 1999 Shop Manual:
Multi-Purpose Electronic Module (MPEM) The MPEM has 3 micro-controllers inside of its sealed case. One is basically responsible for the DESS (Digitally Encoded Security System), interpreting information, distribution of information, and as a timed/untimed power source. The 2 others are used to manage the ignition system (one for each engine). A relay is used to prevent discharge of the battery, through the ignition system, when the craft is not running. The relay is in the MPEM. The DC-CDI system within the MPEM receives the input from the trigger coil and signals the ignition coil when to fire. It also has the RPM limiter function built into its circuitry, as well as the ignition timing curve. Ignition Coil The ignition coil steps up the voltage input from the DC-CDI system and the end result is firing of the spark plugs. The coil is housed in the electrical box.
I am going to replace the MPEM
From the 1999 Shop Manual:
Multi-Purpose Electronic Module (MPEM) The MPEM has 3 micro-controllers inside of its sealed case. One is basically responsible for the DESS (Digitally Encoded Security System), interpreting information, distribution of information, and as a timed/untimed power source. The 2 others are used to manage the ignition system (one for each engine). A relay is used to prevent discharge of the battery, through the ignition system, when the craft is not running. The relay is in the MPEM. The DC-CDI system within the MPEM receives the input from the trigger coil and signals the ignition coil when to fire. It also has the RPM limiter function built into its circuitry, as well as the ignition timing curve. Ignition Coil The ignition coil steps up the voltage input from the DC-CDI system and the end result is firing of the spark plugs. The coil is housed in the electrical box.
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Your first paragraph is basically impossible. The only way water can get inside the cylinders is thru a leaking oring, a bad exhaust manifold gasket, a crack in the cylinder or the exhaust completely fills up from the water box forward back into the cylinders. Even if one cylinder isn't firing, the engine is still compressing air.....and exhausting it. Other than that, if I'm totally missing something please let me know.
If your losing spark, why not just buy a TTO tach and wire it to read the pto cylinder? I know your frustrated, but throwing money at ideas until something sticks is not the correct way.
If your losing spark, why not just buy a TTO tach and wire it to read the pto cylinder? I know your frustrated, but throwing money at ideas until something sticks is not the correct way.
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BoLongo
Active Member
I am willing to be wrong but I think combustion is what forces the gas out the exhaust port on a two stroke engine. On a four stroke you have valves that open and close to control the intake and exhaust pressure. If a two stoke is not firing there is no expansion and no force pushing the exhaust out the exhaust port
I will do a little research to verify.
I will do a little research to verify.
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BoLongo
Active Member
If a two stroke cylinder is not firing there is no exhaust pressure. The downward force of the piston will pressurize the crankcase which will allow fuel and air to enter the cylinder but without combustion the cylinder will not create exhaust pressure. If the exhaust manifold is pressurized by the other cylinder firing you could have a small bleed back into the cylinder that is not firing.
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BoLongo
Active Member
Last year you suggested the TTO Tach which I bought, it is connected to the Mag cylinder. I did not have the presence of mind at the time to move the tach to the PTO cylinder and verify that it was firing at higher RPMs.
I'm already causing cylinder damage so the boat is not going out again without a new MPEM or some sort of MPEM bypass. I will move the TTO Tach to the PTO cylinder so I can verify that it is firing at higher RPMs.
I'm already causing cylinder damage so the boat is not going out again without a new MPEM or some sort of MPEM bypass. I will move the TTO Tach to the PTO cylinder so I can verify that it is firing at higher RPMs.
BoLongo
Active Member
I agree that it is unlikely that water is being sucked back through the exhaust manifold. It could be that without the exhaust pressure I'm not getting enough fuel and oil to pass through the cylinder and as a result I'm getting a lack of lubrication.
I have not verified that I'm not getting a spark at higher RPMs but the engine will not go over 5000 RPMs; I pull the key and check the PTO plug it is wet like its not firing. The Mag cylinder is firing.
I have not verified that I'm not getting a spark at higher RPMs but the engine will not go over 5000 RPMs; I pull the key and check the PTO plug it is wet like its not firing. The Mag cylinder is firing.
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