J-3 with 85 horse

I have a J-3 with the 85 horse continental and a McCaulely 1b90-cm7146 that has been repitched to a 42.

I can only get 2300 rpm flat out at at 1700 ft. This seems abit low as the 85 don't develop full hose power untill it reaches 2525
I am looking for better climb performance what pitch should I use.

Scott

Hi,
That prop looks like a 90hp -11 prop. I think I had a Sen. 76\46 AK-2,
ie.74-42, it worked good for me.
Dave.

On my T-craft with C-85 I have a 39 pitch that came off a J-3. It works great.

Check the Type Certificate Data Sheet for the proper prop. Then check your static RPM and see if it meets the TC. Also Univair has a prop guide which tells which prop and pitch for cruise or climb for a particular A/C. If you are losing the cam it will effect the RPM. I would check the pitch angle first though.

Scott,

My first question is "How correct is your tach?"

I've gone through several years of checking mags, fighting with dogs, overhauling the carb, chasing wing monkeys and (wrongly) repitching the prop only to find that the real problem was a tach that was badly out of calibration on my C-90 powered clipwing Cub.

The best way to check is with an electronic tach checker. If your engineer doesn't have one here are several alternatives:

Do you have a friend that flys RC planes? He may have a checker.

At night run your engine where you can look through the prop at a
flourescent light. I forget what RPM exactly, but you can check several
settings.

Run up or fly in trail of another plane whose tach you know is correct.
When you "stop"your prop your RPM is the same is his.

Find one of those old "twangy" tach checkers. Your mechanic will know
what I mean.

These are cheap or free things you can do to increase your RPM for "free".

Good luck,

John Scott

The TC says static rpm- not over 2350, and not under 1950, for the 85. It also says - not over 72", and not under 70". I know people have run the 74" on the 85's. A friend runs a 7242 on an 85hp champ and it twists real good. I pulled a 65hp with a 7443 to put a C75-12 in my cub. It had been converted to 85hp with the bigger venturi and main jet. Didn't want to buy a new prop, so called it a 75hp. It wouldn't turn 2350 rpm static, but flat out it would turn 2550 and indicate 105. A friend told me my airspeed indicator was off, but power off, it didn't stall till 35 to 40 mph. The airplane only wieghed 775 lbs. Had the original application for airworthyness from piper in 1940, and it wieghed 635 lbs at the factory with a 65 Lyc.
Wilbur

delete

Good advise to check the tach first before one starts chasing ones tail,
this I will do.
I re checked the book that came with my plane aircraft specification no A-691 and the specs I find for the 85 with my prop are not over 2550 not under 1950
What I wouldlike is to know is what rpm static others are getting with the same combo or with any of the other pitchs say a 40,or 38

Scott