compression on johnrude

[mikej]

what is the max compression you can run on a cross flow 2.4 johnrude with pump gas.

[Rickracer]

About 140~145 is all you can safely run on 93 octane, but even that depends on prop and load. It's critical that you be able to turn at least the factory rated rpms or you'll have problems. :eek: :confused: :mad:

[FCnLa]

and jetted fat enough.........and not too much timing:p

[Robbie B]

" not to much timing " What are your thoughts on max timing for an old 2.4 Johnrude running #140 - #145 compression on 93 gas??
What about avgas at this #??
Lots of recomendations on the board about 2.6's but not much about the good old 149's.
Still the odd one or two of us on the board tinkering with these little old antique treasures.
Havn't quite worked out why yet??????:D :D

[BenKeith]

Not trusting what comes out of the pumps and knowing how quick a tank of gas can loose octane sitting in boat during the summer, I don't run them over 135.

For timing, I start a little low and work my way up, letting the plugs tell me what the motor wants. Then I play with jetting, differnt heat ranges and different brands to get the mixture/heat range it likes best.

If you run it at 145, you had better make sure you don't leave much gas in the tank between trips so you can fill it up just before running it and by good, brand name gas.

I've never noticed enough difference in 135 and 145 to make me want to push the limit that close, but I run heavy bass boats, don't have one of these little surboards with a big ol go fast motor on the back.