engine height???

[jrocksho]

I have a 1985 15' performance thruster w/ 1985 mercury 115hp inline-6 with a 6" "Rapid Jack" jack plate. Please help with how to measure what height my engine should be? Some say prop shaft should be couple inches below pad, some say cavitation plate should be couple inches above pad. Which is best to go by? Also what S.S. prop size would be best for this set-up? I was running a 13x24 with 4700rpm wot at 51mph, changed to a 131/4x20 and gained hole shot but still 4700rpm wot at 44mph. I LOST TOP END!!! didn't gain rpm's at all. What else could be wrong?

 

[redjmp]

Re: engine height???

Well I have the same motor and it should spin to at least 5500. Try squeezing the ball at WOT and see if your revs climb.
You should pull and inspect plugs and make sure they are all a nice golden brown and not fouled.
You have to start with a compression test on all cylinders and they should be at least 125 and each should be within 10% of each other.
Then you have to do a spark test and make sure you are getting good spark to all 6 especially if you have any fouled or wet plugs. Never hurts to install new plugs.
Then check your link and sync and timing. There is a good sticky by Clams Canino in the FAQ area on how to do this. Many chickens were sacrificed to the Cods for this priceless info!
If everything still checks out, time to overhaul the carbs. Make sure to use some compressed air to blow out all the passages.

 

[tashasdaddy]

Re: engine height???

http://forums.iboats.com/showthread.php?t=168855

 

[jrocksho]

Re: engine height???

I have checked all that, good compression, good spark, had carbs done new fuel lines both from tank to engine and carb to carb, new fuel pump gasket kit, new plugs and wires. I had a mechanic do this for me when i had the 24p prop it would bog down during the summer on hot days, which is most of year here in LA. Now it don't bog on take-off with 20p prop so i think your right on the timing issue!! Where is the adjustable timing pointer supposed to be? To left, to right, or center? I also was recommended to another mechanic, I will ask him to link & sync. THANX