were to drill the block to relocate peehole?

[ric67]

hi, got a 1991 johnny 70 horse-vj70eleie-i would like to do the update on the water tell tale but don't know were to drill the hole to relocate and is drilling the hole all that has to be done
thanks

 

[ezeke]

Re: were to drill the block to relocate peehole?

This was the subject of several Service Bulletins; click the thumbnail below:

 

[ric67]

Re: were to drill the block to relocate peehole?

thank you for the info. i siezed the middle piston, just got new piston and ready to put together. any other bulletins you know of that might help
thanks again

 

[Dhadley]

Re: were to drill the block to relocate peehole?

Did you determine why the middle piston siezed?

 

[ric67]

Re: were to drill the block to relocate peehole?

not yet. i took the carbs apart but did not really find anything pugged. cleaned and put new kits in them. the high speed jet was marked 5OD

 

[ric67]

Re: were to drill the block to relocate peehole?

using champion plugs ql77jc4 gapped at 30

 

[Dhadley]

Re: were to drill the block to relocate peehole?

Good choice. What grade fuel?

 

[ric67]

Re: were to drill the block to relocate peehole?

i'm in canada using 87 octane---once i ran a tank of husky that is 10% ethenal

 

[Dhadley]

Re: were to drill the block to relocate peehole?

OK, 87 is good. What's the top rpm you are capable of with an average load?

 

[ric67]

Re: were to drill the block to relocate peehole?

used to get 5600rpm normal load then up to 5800 when running lite

 

[Dhadley]

Re: were to drill the block to relocate peehole?

Ok, not bad. Your problem is not at all unique. We know those particular motors run fairly high combustion temps in the middle cylinder, especially in the mid range. When cruising around in the mid range you're running on full advance timing and not a lot of fuel. That makes for some high combustion temps. The longer you cruise the more temp builds up, especially in the middle cylinder.

We've seen motors do this even after all the changes outlined by the bulletins. What we do is richen up the mid range slightly. I believe the mid range jets on your motor are fuel jets not air jets. If we were doing it we'd richen up the mid range by at least 3 numbers, maybe 5.

 

[ric67]

Re: were to drill the block to relocate peehole?

thanks for the advise. how long do you think it took to burn up the piston?
does it happen after a few hours of cruising or does it happen slowly over a few seasons?

 

[Dhadley]

Re: were to drill the block to relocate peehole?

Both scenarios affect it. As combustion temps rise above normal the piston cannot get rid of the heat. That heat will eventually cause the piston to change shape. It might be a little at a time or on a long run it'll continue to change and at some point the piston will stick.

On a carb'd motor you can control combustion temps several ways. Grade of fuel, spark plug heat range and fuel flow. You're running the correct fuel grade and a (relatively) cool plug. What's left is the fuel flow.

I believe there is a bulletin about the high speed jet. But we've found the problem doesn't always happen at wot. We've had real good luck with fattening up the mid range.

 

[seahorse5]

Re: were to drill the block to relocate peehole?

There was a bulletin about changing jets and timing on the '91-'92 and some '93 motors.

The timing used to be 19? BTDC and was changed to 17?

 

[ric67]

Re: were to drill the block to relocate peehole?

hi, got my p/head back together and out for break in. ran sweet idled perfect but--when trying for full throttle it was cutting out/missing?? at 5300rpm would not go any higher. before i'm sure i would get 5500 at any time with my prop. have bigger main jets coming in tommorow- up 3 sizes to 53d. i don't know if the problem is fuel or spark problem. here is my plan--going to use timeing light to check spark and i was thinking to hit the primer when the cutting out happens and see what happens. will that tell me if it is a fuel problem or should i just pump the ball. i have not checked the max advance yet i don't have a test wheel and havent had calm water and enough guts to hang off the back of the boat yet. am i on the right track???