1990 150 Merc XR4 Power problems

[AlwaysBroke]

I have 1990 Mercury XR4 150 on 22' Baymaster will barely start, but once in gear runs to about 2200-2800 and wont go any faster. Just changed fuel lines, filters, plugs and thoroughly cleaned carbs. Revs fine in neutral but bogs in gear right before planeing out. Anyone have any suggestions, Thanks!

 

[Ram57]

Re: Need Help! Please!!

Re: Need Help! Please!!

Still sounds like a fuel issue, i would check vacuum before the fuel pump and pressure after the fuel pump. You could have a restriction in the tank or your fuel pump might need to be rebuilt. Hope this helps

 

[AlwaysBroke]

Re: Need Help! Please!!

Re: Need Help! Please!!

Disconnected fuel line from pump to carbs put in jug and cranked it, it will fill up the jug pretty quick, don't have any kind of pressure gauge to put on it though!

 

[Ram57]

Re: Need Help! Please!!

Re: Need Help! Please!!

Not sure if thats the best way to test since theres no restriction on the pump when pumping into a bucket. Another thing to check would be Carb float height. If Im not mistaken with those types of carbs, you should hold the bowl upside down and the float should be lvl with the bowl itself. Also make sure the needle and seat arent worn out.

 

[AlwaysBroke]

Re: Need Help! Please!!

Re: Need Help! Please!!

The boat was giving to me by dad he only had it about a year, had the shop go completely through it, the carbs were emaculately clean not even a speck of dirt or sand jets, needle valves, and floats looked great! I pulled all of the plugs out earlier, remember they are brand new, three on right side are burnt clean, three on the left are kinda wet fouled looking!

 

[CharlieB]

Re: Need Help! Please!!

Re: Need Help! Please!!

Spark test

Will run on 3 cyl but NO power, you may have an ignition problem.

 

[DutchMerc]

Re: Need Help! Please!!

Re: Need Help! Please!!

This could be a timing problem. In the spark is of-time, there will be no power, and it runs low on rpm. Could also be a spark missing. Check if all sparkplugs are wet, if only one, there is your problem...

 

[AlwaysBroke]

Re: Need Help! Please!!

Re: Need Help! Please!!

Can anyone tell me how to test the stator and switch boxes?

 

[AlwaysBroke]

Re: Need Help! Please!!

Re: Need Help! Please!!

By looking at the plugs after running engine for about five minutes it looks to me like the three plugs on left bank are not fireing properly. The three plugs on the right bank, are burnt clean, pefect look my opinion, moist to touch. The three on the left bank are black, look like they have been dipped in oil, then a splash of gas! So, that would mean that the 3 on left bank are not getting fire correct? So would that be the stator, or the outer switch box, which is the one that I believe controls those coils? Anyone know the correct way to test them properly? Thanks for all of the input it is greatly appreciated!!!!!

 

[Ed R]

Re: 1990 150 Merc XR4 Power problems

your motor has a 2 a stage stator, high speed coil , and a low speed coil . you can run on 6 clyinders at low speed, and run on 3 at high speed.

 

[AlwaysBroke]

Re: 1990 150 Merc XR4 Power problems

your motor has a 2 a stage stator, high speed coil , and a low speed coil . you can run on 6 clyinders at low speed, and run on 3 at high speed.

I am lost my engine has six coils? I tested stator and trigger with ohm meter, the stator reading were dead in the middle on the allowable readings by my manual, but the trigger had three test first and last were perfect but, the second one fell short, 1013ohms, required 1100-1400. Does anyone think that is my problem, or could it be a switch box??

 

[AlwaysBroke]

Re: 1990 150 Merc XR4 Power problems

Any opinions????????????

 

[CharlieB]

Re: 1990 150 Merc XR4 Power problems

Search this site for the instructions to make a homemade spark tester.

Test the ignition one step at a time to determine IF you have a problem.

The stator charges both ignition modules. The triggers trigger both ignition modules. Each module fires 3 coils.

Spark lose on one coil could be a coil or a module.

Spark lose on two cyl (one on each bank) could be a trigger.

Spark lose on one bank could be a module or a stator..

There is NO RETURN on electrical parts. Test twice to prove the fault BEFORE YOU BUY PARTS.

 

[Jugfisher]

Re: 1990 150 Merc XR4 Power problems

Just me but I would also check the compression on all 6 cylinders just to rule out the possibility of a dead one. I am sure that someone on this site can tell you what the correct compression should be or give you a link to a site that will tell you. I had an idintical problem and it looked like a fuel issue but it turned out to be I had a piston burn up

 

[j_martin]

Re: 1990 150 Merc XR4 Power problems

You can check the spark with a timing light. Just put the pickup clamp on any wire, and if it's firing, the light will flash. You could have your brother-in-law just grab the wire, and if he either hits the ceiling, or drops over, the spark is good.

If you find one bank bad, and the stator tests good. Do this
Disconnect the jumper wire between the two switchboxes. That's the bias sync wire. If it now fires on all 6, replace the box that seemed good. If it stays the same, switch the boxes, and if the misfire moves, you've isolated the box.

If you can find a known good pair of used switchboxes cheap, put them both in at once.

hope it helps
John