Max RPM for 2 strokes?

**freightguy** · 03-10-2016, 02:31 PM

The info I am finding online is telling me 5500 RPM's in the max for my 1988 Mercury 150, but when I get on plane and go WOT its up around 7000. My prop is in really good shape so I do think I have a problem there. I am wondering is there something that is supposed to limit the RPM's or is it on me?

**ssv1761982** · 03-10-2016, 03:10 PM

What boat and prop? Speed? Check the tach.

**90 5.0** · 03-10-2016, 03:26 PM

Need more info. Could be tach off could have been modified in the past.

Regular black max 150 or XR-2 150??

**j_martin** · 03-10-2016, 08:26 PM

88 would be an XR4 if it has the small lower. Vertical reed motors tend to fall flat over about 6000 RPM. You can make em spin faster, but you don't gain any power. Horizontal reed is another animal.

A lot of parts interchange, so we need details to figure it out.

**90 5.0** · 03-10-2016, 08:40 PM

I thought 87-88 Were xr2 and 89 was XR-4?

**Dave Strong** · 03-11-2016, 02:40 AM

Those motors had a crazy timing module, not sure about the XR-2 but the XR-4 module did idle timing. Then once a set rpm was hit would advance the timing, then when you exceeded a set rpm would retard the timing. Advance modules are an accident waiting to happen. JMO.

Dave

**tlwjkw** · 03-11-2016, 03:30 AM

Originally Posted by 90 5.0

I thought 87-88 Were xr2 and 89 was XR-4?

think they "over lapped"...... were both built in last year of xr2 and first year of xr4... either '87 or '88... don't remember which?

**freightguy** · 03-11-2016, 08:43 AM

I believe its a regular black max 150. There are no other markings on it. Its does have the timing module.

**freightguy** · 03-11-2016, 07:44 PM

Originally Posted by j_martin

88 would be an XR4 if it has the small lower. Vertical reed motors tend to fall flat over about 6000 RPM. You can make em spin faster, but you don't gain any power. Horizontal reed is another animal.

A lot of parts interchange, so we need details to figure it out.

Whats that mean to fall flat?

**freightguy** · 03-11-2016, 07:46 PM

Originally Posted by Dave Strong

Those motors had a crazy timing module, not sure about the XR-2 but the XR-4 module did idle timing. Then once a set rpm was hit would advance the timing, then when you exceeded a set rpm would retard the timing. Advance modules are an accident waiting to happen. JMO.

Dave

I recently had a guy working on the motor that suggested removing the module, but he was not showing me he knew what to do with the timing after removing it, so I did not go for it. I have also been told to remove the oil injection but I like it.

**David** · 03-11-2016, 09:14 PM

88 Merc brochure shows 2L 150 XR2 and a 2L 150. Recommended rpm 5500-6000 and 5000-5500.

i have no experience with either.

**Markus** · 03-12-2016, 01:58 AM

Originally Posted by freightguy

Whats that mean to fall flat?

That it does not get any stronger as the revs increase.

Until you have it figured out, increase the oil mix ratio to 1:40.

**Dave Strong** · 03-12-2016, 02:19 AM

Originally Posted by Markus

That it does not get any stronger as the revs increase.

Until you have it figured out, increase the oil mix ratio to 1:40.

Got to loose the oil injection to do that.

Dave

**Markus** · 03-12-2016, 11:52 AM

Originally Posted by Dave Strong

Got to loose the oil injection to do that.

Or put some extra oil in the fuel.

**perfmarine1** · 03-12-2016, 12:09 PM

Originally Posted by freightguy

The info I am finding online is telling me 5500 RPM's in the max for my 1988 Mercury 150, but when I get on plane and go WOT its up around 7000. My prop is in really good shape so I do think I have a problem there. I am wondering is there something that is supposed to limit the RPM's or is it on me?

Wait what? What boat, what prop pitch, what speed. That could make it easy to figure out!