97 Sport Jet rebuilt and won't idle well and run in water????

[76Vector]

I rebuilt this engine (97 175 XR2 sport jet mercury power head) this past winter in my free time from college and it came out well and everything went smooth until I got to firing it up and timing it. It will not idle unless you manually hold the timing advance lever all the way and even then it is still rough. I have reset the timing several times with a timing light and have had no luck. Everything is rebuilt and started at the factory specs from the service manual but I am out of ideas and troubleshooting tricks! It also has a rap in it that sounds like a timing issue to me but I have no more options to test???? Any help is greatly appreciated. The sooner I get this done, the better I will feel and the more antique outboards I can bring back to life!!!

 

[Dhadley]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

Start with the basics. Did you bore it? What pistons did you use?

 

[76Vector]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

It has one cylinder bored to .020 over if I remember that number correctly. That has a new wiseco piston and ring set in it with the others all having new rings installed.

 

[Dhadley]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

Did you hone the other 5? If so what was the finished bore size? How worn were the other 5 pistons (has to do with skirt to wall clearance)?

 

[76Vector]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

All other 5 were honed lightly just to deglaze the walls and they were all in good clearance when I checked them before assembling this winter.

 

[76Vector]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

The boat had maybe at the very most 200 hours operating time when it blew. So everything was in pretty good condition when it was apart and there was almost no carbon buildup on the piston skirts and ring lands. It failed due to a lead foot girl who has no respect for mechanical items!

 

[Dhadley]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

So what was the finished bore size after it was honed? What did the used pistons measure?

 

[76Vector]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

Standard cyl. bore is 3.501 with a .020 oversize bore. Making that 3.521 inches after machining. I do not remeber the piston size off hand but I know it was correct when I checked everything this past winter. The number excapse me at this time.

 

[Dhadley]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

We know what the book calls for but we need to know the actual cylinder size after the 5 were honed. We'll assume the bored cylinder has the correct skirt to wall clearance for the moment.

 

[76Vector]

Re: 97 Sport Jet rebuilt and won't idle well and run in water????

That works for me. I am not going to rule anything out but I am more after the externals and timing along with carb synchranization.