I have a 150 Rude on a 18ft Skeeter. I currently have a 21p prop that is getting me to 5200rpm and only about 43mph. Should I try a 23p? Will that get me up to 5600 rpm and a few extra mph? I'm worried my hole shot might suffer if I go up any higher.

each inch of pitch is worth around 200 rpm and you would need to go down in pitch in order to go up in rpm. id check motor height as well. are you running a jackplate? if not it might help get you in the right direction.

Yep I have a jackplace and my motor is sitting 3.5" below pad. I have a 19p but it only gives me 4800rpm and 38mph on the gps. I also have a four blade aluminum prop 19p that gives me 4800rpm but 42mph. I'm all confused on what I should trying now

something is wrong with that b, i'm not thinking about it right now, i haven't had my coffee yet and i don't want to hurt myself, lol

Check and make sure your throttle cable is set right........something ain't right.......

I had a merc 150 and I ran a 23p with no problems, may want to try that out.

taller props (more pitch) will reduce WOT RPM, if a 23P make 5200 rpm, your 19P should be bumping the rev limiter if running the jackplate at the same height and trimmed the same and they are similar props.

23p @5300 & 43mph should be in the mid 50s
19p @4800 & 38/42 mph this sounds right

I am far from a prop expert, but in trying to prop my boat correctly I have learned more about them than I cared to

I'm not a prop expert either but something is not right. I have a Merc 115 on a 19ft Tracker and running 50mph GPS @ 5800rpm, loaded with fuel, gear and two big boys. I changed over to a SS and that helped on my hole shot. Someone on here will have the answer you're looking for.

It very well could be I don't have my throttle cable set correctly. I have always felt it the handle could got down another half inch or more. How do I go about checking that out and making an adjustment?

i would ask for yr/make/model of engine/hull, do you know your hull weight. it makes no sense to drop pitch and loose rpm. i would start with a compression check, check throttle linkage, including the plastic roller to make sure the butterfly plates are all the way open at full throttle, check spark, good spark will ark an inch or so, check all six too, what do the plugs look like?

take the air box off to watch the butterfly plates, at wot, they all should be completely horizontal and in exactly the same position

1986 Rude 150 on a 1984 bug. Compression on all six is 87-90. Link n sink is perfection. Plugs are brand new and firing clean. Butterflies are horizontal at wot. Only think I have that is not OMC is the rubber roller but it has is within Tolerance. I have the OMC manual for this motor and have my work checked by a certified mechanic. We just went over the timing because of another issue I recently had with the carbs. My mechanic is kind of scratching his head too so I thought I might bring the problem to the forum to get a different opinion.

It really does not bother me but i would not mind seeing if I could get a few more RPM. And MPH

What is your motors max RPM rating and these speeds you're posting, are they gps or from the speedo?

You need the prop that will give you the top of the RPM range at WOT. You can prop up to get more top end if you want to hot dog, but you'll dog it down on the low end and possibly cause motor damage. It's shouldn't be all about how fast can I make it go, but how fast should I make it go.
I could be wrong, but your compression seems a little on the low side.

although the engine pressures aren't great,(2 strokes like good compression) it runs, you need to start looking at the props then, new/reworked/damaged? that would be a need to see but a need to know why your losing rpms when you reduce pitch. i would think that engine should be turning up to 5600-5800 light loaded and above 5000 loaded to the gill. my opinion- the engine isn't that strong, the 19p 3 blade has a little more diameter and both 19p may have more bite loading up the engine compared to your 21p that may have more slip to allow for more rpms