Starts fine,idles good,20 seconds later bogs,misses

[cranstkc]

My 3.0 inline 4 Merc. I/O engine only has about 60 hours on it. Always ran like a champ till one day just staled out and would not start back up. The first thing that came to my mind was fuel. So I removed all the gas, added that dri fuel stuff and put a couple gallons of 93 octane in to try, nothing. Had the Carb rebuilt, same thing, and yes its getting good fuel pressure to the carb. What i mean by same thing is, its will start just fine and idle just fine with good throttle response for about 30 seconds then just bog and shake and idle at like 100 RPM. So then I check the distributor, cap and rotor are fine, new spark plugs, wires are good, new coil. Same thing. I dont know what would make this happen but maybe yall do. Not an expert on timming but i would think the timming is ok since it starts and idles fine for the first 30 seconds and when it does bog down it wont die or back fire.

 

[danond]

Re: Starts fine,idles good,20 seconds later bogs,misses

Still sounds like it might be water in the fuel. Friend of mine just went through the same thing. He was "certain" he'd pumped all the water out of the tank (left the gas cap off in the rain).

If you think you may still have water in the fuel, disconnect the fuel line from the carb, disconnect the coil and point the fuel line into a clear cup. Turn the engine over until you have gas in the cup. Let it sit, see if it separates.

 

[cranstkc]

Re: Starts fine,idles good,20 seconds later bogs,misses

Yea, couple of my buddies told me the same thing so i disconnected the fuel line from the carb and pumped it all out to clear the line. filled up a gas can with supreme and had it feeding from that to try to eliminate the possibility of whatever is in the tank is the problem. Same thing

 

[danond]

Re: Starts fine,idles good,20 seconds later bogs,misses

You sure you got the right coil when you replaced it?

 

[Kevin215]

Re: Starts fine,idles good,20 seconds later bogs,misses

Cranstkc, Scroll down the list till yesterday, probably page 2 or 3 by now and read "Engine Dies" by Kevin215.

Hope your back on the water soon,
Kevin C.

 

[cranstkc]

Re: Starts fine,idles good,20 seconds later bogs,misses

Yes its the right coil. What about fuel pump. Would a bad fuel pump cause it to start fine because of the choke and then cause it to run so rough 30 seconds later?

 

[JRose_1989]

Re: Starts fine,idles good,20 seconds later bogs,misses

Mine was doing the same thing. Take the cove off the carburetor, start the engine and look down in side the barrels of the carburetor. When the engine starts to bog down, look to see if you can see fuel running down inside of the carburetor. If so it is probably a float problem, if not then check to see if your idle screws are correctly adjusted.

 

[Maclin]

Re: Starts fine,idles good,20 seconds later bogs,misses

Kevin, yours has an electric fuel pump, this one has a mechanical fuel pump.

 

[Maclin]

Re: Starts fine,idles good,20 seconds later bogs,misses

Cranstkc, I just wanted to make sure yours has not been modified and is still stock with a mechanical fuel pump......

 

[cranstkc]

Re: Starts fine,idles good,20 seconds later bogs,misses

Yes, it is a mechanical fuel pump, Ive been trying to see if the timing was just a hare off or something and it is not the case. i also checked the filter once again and its clean. Im still leaning on it being something electrical.

 

[Don S]

Re: Starts fine,idles good,20 seconds later bogs,misses

Merc has been using a 3.0L engine for over 30 year, lots of things have changed.
What year is yours?

 

[romy624]

Re: Starts fine,idles good,20 seconds later bogs,misses

i have a 1987 forester with 165 3.7 that is doing same thing and im finding that there is seawater getting into back cyclinder works good at hiher rpm but missis at idle im not right sure how sea water getting into that one cyclinder?

 

[Don S]

Re: Starts fine,idles good,20 seconds later bogs,misses

romy, have deleted on post on this thread. IF you have a queston on your engine ask it in a new thread, not someone elses.

 

[buggiedad_67]

Re: Starts fine,idles good,20 seconds later bogs,misses

My 3.0 inline 4 Merc. I/O engine only has about 60 hours on it. Always ran like a champ till one day just staled out and would not start back up. The first thing that came to my mind was fuel. So I removed all the gas, added that dri fuel stuff and put a couple gallons of 93 octane in to try, nothing. Had the Carb rebuilt, same thing, and yes its getting good fuel pressure to the carb. What i mean by same thing is, its will start just fine and idle just fine with good throttle response for about 30 seconds then just bog and shake and idle at like 100 RPM. So then I check the distributor, cap and rotor are fine, new spark plugs, wires are good, new coil. Same thing. I dont know what would make this happen but maybe yall do. Not an expert on timming but i would think the timming is ok since it starts and idles fine for the first 30 seconds and when it does bog down it wont die or back fire.

you said you checked the cap rotor and and replaced the plugs, what did the points look like, might want to do a tune up, sticking points or bad cond, can do this also, did you check you distributor shaft for any side to side play, is your choke working right, unhook your interrupter swicth and make sure its not shorted out on the inside. as a after thought have you checked for a vacum leak around the carb base, easy way to do this, is to spray wd 40 or carb cleaner around the mounting base and see if it smooths out.

 

[CharlieB]

Re: Starts fine,idles good,20 seconds later bogs,misses

What is different from the original in the carb and/or the fuel pump?

I made the mistake of swapping carbs only to tear out my hair for weeks to discover that the fuel pump 'vent' was plugged into a vacuum port, effectively stopping the fuel pump from pumping once the motor started.

Tested fine cranking, no vacuum cranking, running and fuel flow stopped, killing the engine.


(Even I have my 'Homer' moments, D'oh)