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Question for those of you that know motors better than I do
I have an older Johnson 85 HP, it's an '80 model. Question is, at WOT it runs 35MPH by GPS at 5200 RPMS pushing a 17" glass Crappie Master with 2 people in it. I'm happy with this, but was wondering if this is in the optimal performance area.
Any comments welcome.
Thanks
I'd imagine you've got a few hundred RPM to be had. Maybe try going down an inch on your prop size or adjust the trim. Check to see what max RPM is for your motor. Most 2-strokes like to run WOT.
Yeah...that ol' johnnyrude 90 degree is lugging. You need to have her above 5500rpm...That engine will be very happy in the 5600 to 5700 rpm range. What type of prop and pitch are you running?? A renegade in a 19 or maybe but probably not a 21 degree pitch. Where you are running is going to coke up your rings and cause carbon buildup in that engine pretty quickly. 5500rpm with a avg to heavy load would be good. That way when you are a bit lighter you can get on up there a bit. As said before...two strokes like to run...and its way better on them. You have to remember that you are starting off in overdrive...no gears...so if your lugging at WOT...you are lugging when taking off....when easing around...all the time your lugging. You may also want to see how deep in the water your motor is...engine height has ALOT to do with performance. I would think you should hit 40 in that rig. You may also have some wet foam...just some things to check out.
Engine doesn't sound like it's lugging at WOT, matter of fact it hums like a sewing machine. as to prop size I don't have a clue, I've looked all over it and can't find any numbers on it. I guess I could take it off and there's a good prop shop not too far from me that could tell me. Looks like it might be the original, but at 30 yrs. old I doubt it.
I would suggest playing with the tilt/trim function before spending the $$ on a new prop to see if you can get any better performance out of the motor. I run my little 60 2 stroke merc at 4200 to get 29mph on the gps on my tracker pt175 with a light load (me and < half a tank of gas). You can gain a couple hundred rpm thru the trim function and a mph or 2 or well. If you're happy, why change it out?? Mine goes fast enough for me completely stock.
probably won't change out, mostly wondering if it was anyway near optimum performance and it sounds like it is close and at 35 MPH that's plenty fast enough for me.Quote:
Originally Posted by jimp
no, it may not sound like its lugging...I don't mean the lugging you hear a truck is loaded and won't gain any rpm going up a hill...you won't here this. Anything under 5500 rpm @WOT is lugging that engine. Just FYI. Be sure you run seafoam...as it will coke up over time. Look at your prop hub...around the nut...you should find numbers there. Those are great engines...take care of her!! :)
How and Why to decarb
Check out that thread and you'll get a little insight on rpm of 2strokes. Just my opinion on it. Hate to see something happen to that johnnyrude...they are my favs!!
Thanks Scrapper I'll look inside the hub for #'s that's the only place I haven't looked.
I run Sta-Bil and Seafoam, wouldn't be without it in the gas.
Yes it's a sweet running motor, wouldn't want to loose it.