1995 Mercury 150XR6 No RPM past 4200

[Big Sexy]

I have the 1995 MERC150XR6 (SN:0G228702) mounted on 1995 Nitro 17 1/2 foot running a 22P prop, can not get past 4200RPM feels like it surging. So far I have done carbs 2 times, new reed valves, fuel pump, fuel hose, external fuel tank, plugs, link and sync, timing. Any ideas or help would be great I'm hitting a wall here.

 

[sam am I]

Compression?

 

[Big Sexy]

Sorry compression is 120-125 all 6 cylinders also did leak down and it was good.

 

[Dukedog]

has it been this way since day one of your ownership or just started actin' up?

checked fire ta all six?.. sounds like a switch box....

 

[Big Sexy]

Bought it used has done it since I've had it I was thinking switch boxes guess I'll invest in a couple and try it thanks

 

[Faztbullet]

1) Check the timing as if bad advance box will retard timing on top end...2) if its a 2.5 block you could have a sleeve/s turned...fairly common problem.

 

[JDusza]

Yes, sounds like timing isn't advancing for acceleration. Before you spend any more $$ (you've spent enough) I would get a DVM with peak hold and a DVA. These tools along with the CDI Ignition troubleshooting pages, you'll become an ignition expert. You'll pay for these tools with your first diagnosis.

http://www.cdielectronics.com/troubleshootingguide/

J

 

[Big Sexy]

Hopefully not a turned sleeve I'm going to get a flex light from my buddy and see if can see if sleeves turned. I'll know more in a few days and post the findings. Thank you for info all

 

[Dukedog]

its tha XR4 (pre fat block) that's known for tha sleeve movin'.. 2.5 block would be very, very rare...........
XR4 was merc's first attempt at a steel sleeve 2.4 and they missed it a tad on some of tha production motors

 

[Faztbullet]

I have had three 2.5 blocks turn #6 sleeve

 

[Dukedog]

between bobby and myself we've done over 400 2.5's since '96 and never saw one.. probably 10 ta 12 older (pre fat block) xr4's with almost all of 'em turned...and not jus one hole either.... must be something in water in tha southeast part of tha country...............

i will say this though... we did see a coupla 2.5's turned but they had been replace by a **** poor machine shop... only ones and were tha cause of them comin' to our shop..... none that were original...............