Mecury 150 xr4 turning 7200 rpms

[Turkey]

I have an old boat 17" bass boat with a 1989 Mercury 150 xr4 that is running a ballistic 21p prop and it turns over 7000 rpms...someone suggested that I have a modded motor. I am not sure that it is, but either way it runs like a scalded ape. It runs 65-70mph with two people in it @ 7100 rpms, knowing that, I know that should eat this motor at that speed I need some advise. At WOT it feels like it wants to go faster...I mean the motor is screamin a lil but it still seems like it wants to go faster. I have posts under the same name at iboats covering the same issues. Any advice would be more than wonderful!!!!!!!!!!!

[bigboy]

Maybe try a bigger prop...

[brotherxb03]

If you are turning up that much you better have the oil injection off that puppy.

[Turkey]

If you are turning up that much you better have the oil injection off that puppy.

I'm looking at changing the prop to a 24p 4 blade...I think I just happened into a jewel. I only keep merc 2 cycle oil in the tank, need to change the LU oil in 2 or 3 trips. I'll be happy to run it for anyone in the area.

[pyro]

With those kind of RPM's, the 24p would probably be a good place to start.

you should be in the 6000-6400 range for best power and longevity.

GET RID of the oil injection and premix, the system is prone to failure, ESPECIALLY with lots of wide open running. The crank drive gear for the pump tends to strip out. Use the search feature for more details on "oil injection removal".

[David]

My guess is that the motor has been modified, at a minimum the oil injection is gone (or it would have blown up by now), and the spark retard box is gone.

I could never get much more than 6200 out of my XR4 with any prop.

[JimMel]

Exactly what prop do you have, I might be interested in a trade.
Mine's a 23p, in classifieds

[Turkey]

Well I've tried different props and I think the 24p is the best place to start. I know the tach isn't working like it should but I also know what cavatation is. I'm still running the 21P 3bladed ballistic, still cavatating. It still runs like a scalded ape. I'm still looking for a prop...would like someone with some knowledge to take a ride and see...

[Turkey]

With those kind of RPM's, the 24p would probably be a good place to start.

you should be in the 6000-6400 range for best power and longevity.

GET RID of the oil injection and premix, the system is prone to failure, ESPECIALLY with lots of wide open running. The crank drive gear for the pump tends to strip out. Use the search feature for more details on "oil injection removal".

I run a 2.8 gallon oil tank plus the 2 pint tank under the cowl, I'm running really rich right now but it gives me everything I want, I just know there is more there.

The oil line runs directly into the fule line before the carbs...

[MODXR6]

Definitely get rid of the oil injection runnin at those rpm's (implosion waitin to happen)
What lower unit? Small hub 1.78? If so you definitely don't wanna be runnin those rpm's on a bass boat w/ it. (another implosion waitin to happen) When it goes it usually goes really fast & w/o any notice a all

[marquis4606]

a 26p trophy should put u around 6500rpm

[Techno]

I run a 2.8 gallon oil tank plus the 2 pint tank under the cowl, I'm running really rich right now but it gives me everything I want, I just know there is more there.

The oil line runs directly into the fule line before the carbs...

Your misunderstanding what the problem is. The oil pump itself will fail, then you have no oil injection. It won't matter how much oil, where its stored or where its injected if the oil pump isn't pumping at high RPMs.
The gear driving the oil pump is plastic!

[HillbillyRock]

I have a Black Max 150 2.4 and I got rid of the oil injection, I always premix 40:1, you can go 50:1 but 40:1 will keep that engine nice and lively running at higher rpms :)

[zstevens]

jimmel you still have 23p prop to trade? what model / brand is it ? thanks zach i have a 21p laser ll

[TD]

This guys been posting the same crap on other boards and doesn't take any advice. Either he wants to blow it up or he's full of chit.:eek:
TD

[Cp]

Thanks for the heads up, TD. I was thinking this smelled of Fish Story, trolling variety. If I'm wrong, he'll be back and sue me.

I hope he's got the bic-lighter sealed top pinners. He's gonna need um.

[HillbillyRock]

:eek: :eek: :eek: :eek: :eek:
:D :D :D :D :D

[jbf2002]

Yeah, make sure they are top pinned merc slugs and sell em' on new sealed top pins so it don't get them HOT-SPOTS and pop goes the weasel.

oooops,