From what I understand this motor is one of the low compression motors that were made back in the mid 80s that is why you lower numbers. Maybe these motors where not made to run 55mph or 5600-5800 RPM, but I have no idea about that. I will say this motor runs like a top and has been very little trouble.

Could it be that my tach is off and just not showing the correct RPM? The tach is only about a year old. The MPH I am stating is from my GPS readings, I don't trust speedometer numbers.

If this is all this motor is capable of running then I'm fine with it. I tend to baby the motor because of the age and even though I get 5200 out of it I tend to run it around 4800 because it really sucks the fuel when I go WOT. I am just kind of confused about what I should expect from my props.

it is a 90 degree loopcharge built for higher torque and a little lower rpms but i have never heard of a low compression 2 stroke built that way, 2 stroke gas thrive on compression and at 6/6.5:1, i would say its on its last leg, yes the tach could be off but you trying 2 diff 19p props and both loaded up the engine and no speed difference i would just go with the 21p to allow the rpms to come up and just run it, it may be controversial, but you could try running high octane to help, i have noticed a difference on a well seasoned engine

Ok, thanks for the insight. I'll be happy with what I'm running at then.

i had a 83 and 85 rude 150 and both had around 110 compression. wot was 5500 and it ran about 55 with full load and two men.the were both on a 370 ranger. i ran a 14.25/24 raker. hope this helps

Thanks for the info whybass.

One more question for the group. I have no idea what brand or manufacturers prop I am running. I do know they are all SS and the four blade is aluminum. Does manufacturer make a difference when running a prop? These props I'm running are just props that came with the motor or I have acquired over the years.

If you are saying the 21p gets you 5200, and the 19p gets you 4800, you don't have something set right. Throttle cable my be out of whack like others have said

Post a pic up of them! Do they not have a brand name on the side?

Motor issue---That 150 should turn a 24p prop at 5600 on that boat with no problem.

that 19p prop may have dropped the rpms and speed because it's not lifting the bow.
causing excessive drag and a loss of more speed and rpms.


what 150 rude is that. an xp ? or fastrike?

i'd say it's an xp motor, and only can turn a 22p raker that is in great shape.
5500 to 5700 is all i'd turn an xp motor anyway.

Like Steve is saying you probably have more issues than just prop pitch size going on. Give me a call and we can sort thru it to get you setup and running where you should be.