stumped after carb rebuild

[rustyscrew]

Still wrestling with a problem that has me stumped

Engine: 1994 120hp Evinrude OB

Problem: Starts up fine, sounds like all cylinders. Runs for a 30 seconds or so then starts to cough. Loses cylinders and can run for awhile but pretty sure its running on only 2.

History: Was having hard starts but ran OK. Figured it was time for carb cleaning. Usually I would clean and not replace any parts and it would always run better. This time ordered the kits and replaced all parts. That is when the problem started. Since then I have tried everything I can think of and stuff that this forum has suggested.

I am pretty sure I lose the both left-side (port) cylinders because the new plugs were quickly fouled and wet after one 2 minute running. WHAT might cause both of those cylinders to be bad?

What I have done:
1) Rebuilt all 4 carbs twice.
2) Checked for spark (with proper tool)
3) Checked compression
4) Replaced plugs
5) Replaced inline and spin on fuel filters
6) Tried alternative gas tank directly to fuel pump
7) Tested fuel pump pressure (5 psi and holds indefinitely)
8) Spray fuel into carbs while running. I can keep all cylinders running this way. Hard to tell exactly which cylinders it responds to. Definitely top-port.
9) fixed a busted wire in the computer on top (didn't change performance)

I was about to redo the carbs....then felt like that may not be the problem.

Any thoughts?!?

thanks

 

[Dhadley]

Re: stumped after carb rebuild

Make sure the butterflies are completely closed at idle. Those can be a little tricky but not impossible by any means. BTW - the port carbs supply the starboard cylinders and (obviously) vise versa.

 

[234rick]

Re: stumped after carb rebuild

Remove all plugs, hook up spark checker & check those two clys. to see if there's spark if there is then open throttle wide open( fast idle)(make sure timer base is fully advanced ) & check for spark. If there is spark I can't help, if there is no spark maybe I can help.

 

[clemsonfor]

Re: stumped after carb rebuild

i was going to say my 150 was running crazy and the butterflies all were not totally closed at idle causing caughing and sneezing at idle and up to like 2000 rpms and would die in gear and at idle and going to reverse, fixed it and now no problem.

Also could be a blown powerpack causing loss of spark? Do you have spark when it sounds like its only running on 2 cyls?

Another problem i had in the past is if you getting to much fuel to a cyl you wont fire. You can get this problem if floats are not adjusted right, causing flooding while just ideling (you can actually see fuel run out of the troats at idle) or i onetime has a piece of trash behind the inlet needle in the carb causing the needle not to close off. This made real easy cold starts (super fueled) but made it run rough at idle as well as hard to resart after a stop cause it would flood the carb into the cyl. Found this problem and it went away after messing with the floats like 3 times, i found the trash after i took them apart the last time. Cover everythink no matter how small, this happened right after a rebuild, the trash was a piece of OMC motor paint, i have no idea how it got introduced into the fuel system?

 

[Daviet]

Re: stumped after carb rebuild

Not much experience on that engine, but a few thoughs.
You said the plugs quickley foul on 2 cylinders. The cause of fouled plugs, to much fuel, lack of spark. You checked spark with proper tool, try using an inductive timing light, run the engine until the misfires happen and check and make sure all cylinders are firing properly.
Each carb has a fuel line coming off of the fuel manifold, maybe you could use a pair of needle nose pliers and pinch off one fuel line at a time and see if that cylinder cleans up just before it runs out of gas, thinking carb problem for that cylinder.
Just a couple of thoughts, may not be of any help.

 

[clemsonfor]

Re: stumped after carb rebuild

if it will run wide open run it WOt for 5 mins then cut it off (this on on water of course) and pull the plugs and see if they all have that amer color indicating correct firing. You ahve to pull them all on the water or at a dock to do it right.

 

[rustyscrew]

Re: stumped after carb rebuild

Really helpful, thanks for all the ideas. So- threw some more hours at it today. I rebuilt the one of the carbs that feeds one of the bad cylinders and replaced the needle-valve seat. Seemed to run better. would idle ok and not die. That was an improvement but still did not fire on all cylinders.

I retested for spark...set tester to 3/8 and one isn't firing!

Ok so that is good to figure out. not sure what the problem is though because I replaced the connector from the computer to the coil. It was rusted. also replaced the coil with one I had around. still no spark....

Is there is a way to test whether the coil is receiving current? voltmeter?

making progress...

also fixed a corroded wire from the computer (port back screws inside the black plastic housing) I don't know what they are for but thought maybe they were a problem since its the same side as the bad cylinder.

So looks like the spark problem is the priority now. any helpful tips for diagnosing where the problem stems from?

thanks...the advice on this forum is so incredibly helpful