Spark Plug Melting

[jr86]

Well, I have replaced the engine and went out Wednesday. The unit ran well, but I wanted to look at the spark plugs for grins. I found the rear cylinder plug to be melted on the tip. (Look at pic) They are both heavily carboned, but the melt is my concern. I looked at the piston, there does not appear to be any damage.

Any help would be appreciated.

 

[derek]

i think rear cyl is too hot. i don't think the piston will survive long. options are; retard timing. richer jets rear carb. thicker base gasket to drop compression a little. the theory is the crank flexes under load, and the rear piston comes up retarded (late). the timing is still where it thinks the rear piston should be. therefore too advanced. detonating or bordering on it. creating too much cyl pressure and heat. that is believed to be the reason most engines lose rear piston and front still looks fine. i think somebody should assemble cranks with rear cyl advenced about 2 degrees. then when it loads up, it is right where it belongs. but i don't build cranks, so i can't try it.

 

[kustomkarl]

2 questions...1)what plugs are you using and their gap? 2) what is the compression now?

Karl

 

[jr86]

Plugs

The plugs are NGK from SBT. (I did not record the number.) I set the gap at .036". The compression in the rear cylinder is 150 and the front one is 147. I have adjusted the high speed crew on the carb richer by about 1/16 of a turn. I will be hopefully checking it out today.

 

[kustomkarl]

The Spark Plugs should be NGK B8res Gaped to .020 -.024 in. The high speed screw can be adjusted to 1/4 turn from "0". Keep us posted. Be sure the engine is getting enough oil...is it premixed or still injected? Double check the timing marks too, so it isn't over advanced.

Karl

 

[jr86]

Oil

It is premixed as SBT recommended this first. I went through the oil injection pump and thought it was ok. The rear cylinder is getting oil, at least the line is now full and without bubbles. The front one does not appear to be putting oil into the cylinder.

I will stick with the remix and richen the high speed a little.

 

[kustomkarl]

First you need to adjust the carburetor idle so the speed adjust touches the adjustment plate. Turn the screw 2 more turns. Turn the cable adjustment screw to align the marks on the Injector pump. Look closely and you’ll see the marks on the cable disk and the pump. Use a mirror if necessary. The throttle and oil injector must be synchronized to react at the same time. This adjustment is the same on single or dual carb models. Be sure the oil is in the lines to the carburetors. (Use a helper in the next step) Start up the seadoo on the garden hose, be sure it is running before you turn on the water. Push the cable disk( pump lever) to full oil while the seadoo is on the water hose. DON”T REV THE ENGINE, let it idle, while you getting the oil to the carburetor hoses. Turn off the water and shut down the engine. Recheck the adjustment of the cables.

Karl

 

[Mirage]

What's the word, is it still together??? I know it would be sometime before I went away from premixed fuel!!!