Rough Running

[tkmichael11]

I have a Mercruiser 228 that I can't seem to figure out what's wrong. I had it out today and it fired right up and ran great. We stopped for a few hours and caught some fish. When it was time to head back, the boat was harder to start. It would idle fine, but as soon as you put it in gear, it died. I was finally able to get it running in gear but it ran horribly. Spit and Sputter the entire way back to the dock and finally stalled again. Same thing, it would idle but as soon as you put it in gear, it dies.

Anyone know where I should start? I was thinking carb, but it was just replaced about three months ago ( after doing the same thing twice before)?

 

[ne7800]

Re: Rough Running

when was the last time you did plugs, wires, cap, rotor, points, condenser, fule filter

 

[Don S]

Re: Rough Running

Pull the spark plugs and check for signs of water. may be failing manifolds or risers.
A compression test would also be handy, when was the last tune up? Have you checked the fuel filters for water? Plug wires ok? Coil tower maybe have a crack?

 

[ne7800]

Re: Rough Running

looks like me and don where thinking the same thing

 

[tkmichael11]

Re: Rough Running

Well, this all started about the middle of summer. It has been doing the same thing everytime I take it out. I started by doing the full tune up. i.e plugs, wires, cap rotor, timing adjust, points adjust and dwell.

Then I took the boat out and it did the same thing again. This time I replaced the carb. Took the boat out and guess what?!? Same thing. I am completely befuddled (if that's a real word).

Also, when its running, it runs great under no load. I can run it to full throttle and it runs great. Once I put it in gear, though, it stalls and spits and sputters.

 

[Don S]

Re: Rough Running

Do some vacuum tests. A gauge hooked up to the intake manifold can tell you a lot.

 

[tkmichael11]

Re: Rough Running

Can the compression test be done with the exhaust manifolds off? I was looking into some other posts with the same problem and some of the fixes included a clogged fuel pickup. Does this make sense? Also, when the boat is idling, and i'm having the problems getting it to run in gear, I look down into the carb and the port side of the carb is spraying a constant spray into the carb and the starboard side of the carb is not showing any fuel. Is this normal?

 

[Maclin]

Re: Rough Running

At idle you should not be able to see fuel spraying unless it is the spray from the accelerator pump when the throttle is opened up, and that spray is only for a second maybe, and it should visibly spray in both sides during that short time.

Either way it sounds like a carb problem again now. And because this happens after a while with a new carb there must be a fuel filter or fuel contamination or rusting problem somewhere.

 

[tkmichael11]

Re: Rough Running

I have added an inline fuel filter, thinking dirt might be causing the problems, but that was added prior to this last attempt on the water.

 

[Maclin]

Re: Rough Running

If the stuff is already in the carb the only thing to do is remove it (carb) and take it apart and get everything clean again.

 

[tkmichael11]

Re: Rough Running

Thanks for the help. I will pull the carb and clean it. After that, I will do the vacuum and compression checks and hopefully figure this thing out.

 

[tkmichael11]

Re: Rough Running

I just had the carb apart and cleaned. It is doing the exact same thing. This makes me think that maybe this is normal? Don't know. All I do know is that it idles like a brand new engine (which has always been the case when its cold). Tomorrow is hopefully going to be the compression and vacuum checks.

Can someone tell me exactly where to do the vacuum check? what numbers am I looking for? where should I connect the vacuum guage? etc.

 

[Maclin]

Re: Rough Running

That was a pretty quick carb clean, did you remove all the parts and soak it and blow out all the passages?

 

[Don S]

Re: Rough Running

I just had the carb apart and cleaned. It is doing the exact same thing. This makes me think that maybe this is normal?

NO, it is NOT normal. So don't try to convience yourself it is.
I have rebuilt a lot of carbs that still didn't work. They get replaced with new or remanned.

 

[tkmichael11]

Re: Rough Running

I didnt soak anything, just spray carb cleaner, but it was torn apart, cleaned, and put back together.

 

[tkmichael11]

Re: Rough Running

What could be causing this and how do I fix it? (the carb problem)

 

[tkmichael11]

Re: Rough Running

The carb is being shipped out today for a rebuild. I talked with the technician who told me that when the carb was tested, it was tested with mineral oil and not gasoline. Gas is thinner and since the right venturi is leaking, it would not show up with the heaver medium. I will be installing the old carb just to get the compression and vacuum checks completed and fix any issues there. That way, when the new carb comes back, the boat will be ready to water test (as long as the snow isnt flying yet).

 

[tkmichael11]

Re: Rough Running

Ok, I borrowed a carb to put on the boat so that I can run some vacuum tests. Where should I connect the vacuum guage to give me the readings I am looking for?

 

[Don S]

Re: Rough Running

There should be a pipe plug (3/8"NPT) on the intake manifold just aft of the carb. Put a fitting in it that will adapt down to the hose for the vacuum gauge.

 

[tkmichael11]

Re: Rough Running

I spent the last few hours running some tests on Compression and Vacuum. Here are the results:

Compression: 1-130, 2-132, 3-130, 4-150, 5-130, 6-140, 7-110, 8-130

Vacuuum: Warm engine at 900 idle and the guage is jumpy between 12 and 17. It doesnt fluctuate rapidly but it slowly goes within that range but the needle is not smooth. At wot the guage is steady at 20. When I go back to idle, the engine stalls. Also, when the engine is idling and the vacuum guage drops to 12, it stutters like its going to stall and then jumps immediately to about 17 and continues the cycle all over again.

When the engine does stall, it is very hard to start again.