Rejetted for elevation, also change prop?

Hello<br /><br />I have a 1968 55hp johnson, early this season I rejetted it to run at 7200 ft where I live and use it in the Rocky Mountains. I am wondering if I should also change the prop size or pitch too as I doubt I am running recommended wide open throttle rpms now with the smaller fuel jets. Also, I think my spark plugs are fouling, could this be related? Your help is greatly appreciated.

Re: Rejetted for elevation, also change prop?

How good is the motor. Has it been rebuilt since 1968? If you don't know how about taking a compression test and posting the readings?<br />If the motor is not worn and the fuel/air ratio and ignition is all right the plugs shouldn't be fouling. <br />At 7200 ft this motor would be down on power even if it was brand new.<br />Iwouldn't spring for a new prop until I was sure that everything else was in reasonable order, but that's just my personal opinion.

Re: Rejetted for elevation, also change prop?

Also live at 7500' -- cool in more ways than one!<br /><br />Bought 90hp 24' Pontoon that grew up in Nebraska. Would only get 4200 rpm WOT and sounded really burdened with 17" (pitch) prop @ 5500' (Platte valley).<br /><br />We bought 13" for valley use and 11" for Grand Lake. Both get to 5200-5400 rpm (analog tach) not sure that they aren't at rev limit because 11' has been used @ 5500 and held same rev max.<br /><br />Anyway, engine much happier at higher rpm and acceleration is superb. Original prop was like driving a car in too high a gear. Others on Iboats have said that laboring the engine is extremely bad for it.<br /><br />Have not messed with jetting because I don't want to cut back on 2 cycle lubrication. Would sure be interested in other's comments on this factor.

Re: Rejetted for elevation, also change prop?

thanks for the input so far. I brought it home this week and will try to get the compression readings soon as I now have a new problem. could not keep it running last time out at the lake. misfired at start and then died and could not get it started again. I thought plugs were fouling because it was missing at low rpms for a couple of tanks of gas. replaced plugs but it did not help. Hope it is a fuel problem and not compression. let you know what I find out

Re: Rejetted for elevation, also change prop?

Here are the results from my compression test.<br /><br />TOP = 85 PSI<br />Middle = 90<br />Bottom = 90<br /><br />Sorry but don't know cylinder numbering scheme so just listed positions.<br /><br />Seem ok?