787 siezed up 1 time

[mully]

Ok I'll try to give enough info in this post to help get the answer. I rebuit my 97 xp with a 787 engine. I rebuilt the carbs. I have run the first tank of oil/gas through. I stopped using premix now. I think the oil pump is working oil goes down after running around some. The carbs are set at 1.5 low 0 for high. Compression was 150 both cylinders. I have melted a rave since the rebuild. I need to rebuild it, I have not yet engine is a little slow hitting top speed but it does. I will rebuild that now that I have some time and money. I have been running without air box so I can adjust neddle valves easier. The engine seized up 1 time after a day of hard riding (thank god for a rev limiter). I let it cool a minute restarted just fine, drove to shore, then pulled the plugs and fogged it real heavy, cranked it some and parked it. Now what should I do pull the oil pump for pre mix? I will fix rave valve, I will reinstall air box too. Is there something I should do special because of the possible seize damage? The plugs were a little dry but looked good. I know it seized due to being lean. Should I rich'n up the high some or will the air box slove that. I know a lot of questions but you guys can handle it.
:emoticonc

[Danny Roszell]

Re: 787 siezed up 1 time

Your carbs are jetted to run with the air box on. You will run lean if you ride with the air box off.

[mully]

Re: 787 siezed up 1 time

Does it the air box restrict the air flow that much to create a dangeous lean condition(without it)?

[1fastski.com]

Re: 787 siezed up 1 time

YES even if you put aftermarket flame arestors on you need to rejet . PWC are very picky when it comes to carbs and jetting .

[frankey01]

Re: 787 siezed up 1 time

is that 150 compression now after the seize or before the seize check compression for the answer of any damage to the top end after the seize

[mully]

Re: 787 siezed up 1 time

Yes compression is still at 150 each. Put the air box back on and the ski started to smoke some again. Drove it all day and no seize it actually ran a little better with the box back on. Looked down the rave valve holes and saw no damage to the rings or piston skirts. Guess I got lucky.

Found out when I pulled the melted rave valve that the valve shaft had cracked so the exhaust gas came up in the rave valve housing melting the plastic piston. I pulled the rave valve out and it was half gone melted away. I thought maybe it fell into cylinder but after rethinking it I think it sat low in the cylinder all the time I was boating and just melted away. Any thoughts?

Does anybody have a picture of the perfect spark plug mine seem dry. The procelin is dry and brown. The bottom metal of the plug is black and a little wet. Never mind I found a great article in the faq!

[Bill O'Neal1]

Re: 787 siezed up 1 time

You melted a rave valve, but you have no damage to the pistons? Wow!

That does not sound likely......... I have seen some very siezed pistons that still pumped 150 or better. As long as the top ring is not stuck, they will pump the number.

Brown plugs are what you want.

The reason it ran better with the airbox on is it is now drawing more fuel from the jets, you increased the vacume when you put it back on.

[mully]

Re: 787 siezed up 1 time

Gee thanks now I'm not gonna be able to sleep until I get the head off...:emoticond

I gave a hard look down the rave slot and saw no damage common sense says something got tore up but I'm a glass half full kinda guy.:emoticonw

[Bill O'Neal2]

Re: 787 siezed up 1 time

Maybe you will get lucky. But, how hot does it have to get to melt aluminum? Way too hot!