1995 Mrec 50 could not go over 2000 rpm

[pnarakor]

I am a new member. The engine will start up, idle fine, but cound not accelerate to full speed. it won't stall, just won't get above 2000-2500 RPM. Backing the throttle to 2300-2400 RPM, keeps smooth running. It would get over 2000-3000 rpm on idle but not under loaded. New plugs, cleaned carbs, and new gas. Please help. Thank you.

 

[fishingdan]

Re: 1995 Mrec 50 could not go over 2000 rpm

Check in order:

1) Compression
2) Spark (most likely that you have one or more cylinders not getting spark)
3) Fuel system

 

[pnarakor]

Re: 1995 Mrec 50 could not go over 2000 rpm

FD - thank you for your help. I have read "related" problems here and have found that you have been very kind helping others.
I suspected the #2, one of the spark not firing. I am trying..
I will post my result soon. Hopefully, others may use same info.

 

[andy6374]

Re: 1995 Mrec 50 could not go over 2000 rpm

Trying having someone pump the primer bulb while attempting to get up on a plane, if this saves the engine from falling on its face then its time for a fuel pump rebuild.

When you cleaned the carbs did you dissassemble the carbs and clean or did you just spray carb cleaner down the carb throats?

 

[pnarakor]

Re: 1995 Mrec 50 could not go over 2000 rpm

Andy - I will try pumping the primer bulb next.

I cleaned the carbs using the spray cleaner down the carb throats. I don't know how to take it apart.

All 3 plugs gave good spark. I tested it one by one by having it rested on the block and turned the ignition key and stopped. Put plugs back in.

I then started the engine and let it idle for a minute. I then took each plug out. I saw that the bottom plug is clean, no black deposit, unlike the top 2 plugs. Please note that they are brand new plugs. Does the "black" indicate fuel+oil?

Is it possible that one of the IGNITION COILs is broken?

Thank you.
-phanom

 

[andy6374]

Re: 1995 Mrec 50 could not go over 2000 rpm



This ain't gonna cut it. By spraying the cleaner down the carb throats you are hitting non of the carb jets (idle or main).

You need to disassemble, soak in carb cleaner, blow out passages/orfices with compressed air, and reassemble with new gaskets.

Get a manual if you don't feel comfortable or just take some pics with the digital camera as you disassemble.

BTW: I wouldn't start any engine project with out an OEM manual.

 

[fishingdan]

Re: 1995 Mrec 50 could not go over 2000 rpm

phanom, purchase an inexpensive inline or inductive spark tester and see if you have spark while it is running. These tools are available at chain autopart stores, Sears auto departments or others. They should cost less than $10.

Andy is right about the carbs. You need to disassemble a carb to clean it. It isn't hard to do, but it may seem a little overwhelming if you haven't done it before. After you do it, you will find that there was nothing to it.

 

[pnarakor]

Re: 1995 Mrec 50 could not go over 2000 rpm

FD, Andy - First, Thank You very much.

Pumping the bulb did not help. I moved to the spark plugs area and...I found the problem. I have a bad switch box. The motor was only running on 2 cylinders.

On the bright side, I could save gas this way. There are car engines today that are designed to run on fewer cylinders while crusing on smooth and steady speed. Just kidding.

Finally, very good advice - I do need the OEM manual before staring the work.

I found a good site that provides very good pictures of parts for my Merc 50hp.

http://www.usboatsupply.com/Mercury_Mercruiser_Parts_Catalog3a.php?mc=01&ms=4100&si=571

Thank you,
phanom

 

[fishingdan]

Re: 1995 Mrec 50 could not go over 2000 rpm

Glad you diagnosed the problem.

 

[pnarakor]

Re: 1995 Mrec 50 could not go over 2000 rpm

An update:

After replacing the switchbox, the motor ran fine for a while. It sounded as if a cylinder is still missing.

At this time I got help from a pro. The stator showed "ok" reading. I am learning the reading as I go along.

There is a problem with the trigger coil. It showed 4 (too high), 1.5 (ok), and 1 (too low). I guess the ideal number would be 1.5?

I will provide more report later (as part is being ordered).

I hope this information would help others.

Thank you. -phanom

 

[pnarakor]

Re: 1995 MERC 50 could not go over 2000 rpm

Re: 1995 MERC 50 could not go over 2000 rpm

Last update:

Problem were Trigger Coil and Switchbox. After replacing them, motor runs very smooth. Also saw that the water came out better at the "pee hole".

Thank you. -phanom