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Mercruiser 305 hard to start hot and cold

jjvb

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"I have a Mercruiser 305 with

"I have a Mercruiser 305 with a Mercruiser 2-barrel carb. I replaced the fuel pump last fall as it left us in the middle of the lake. I took it out today for a test run. Dang thing would not start worth a darn. Then when it did, it would gradually run slower and slower until it quit. About the only way I could get it started was to start it with the throttle lever all the way forward. I turned up the idle a little which helped keep it running. It ran great at anything above idle. Pulled well, etc. My thought is that the idle mixture may be too lean. I at least want to try that before taking it in to the shop. Your thoughts would be appreciated. Thanks."
 
John.
I'm not clear on th


John.
I'm not clear on this but here a few things. If the throttle must be wide open for it to start.Most of the time it means the engine is flooded. This also is what it sounds like it is to me by what you said it did when it is running. It is getting to much fuel and is slowly flooding out. But it could be a number of things.
These are a few things to check. Is the choke opening after it starts? If not could be dirty/sticking or bad thermocoupler. Is there any sign of fuel leaking around the carburetor or over flowing into the carb from the float bowl vent. If so could be dirty/sticking float/needle & seat. When the engine starts is it slow to gain speed from starting or does it rev right up? If it is slow it is flooded. This will have black smoke from the exhuast and smell like fuel. Do you need to pump the throttle for it to start? If so then it is lean and not getting enough fuel. If this is the case it would gain rpm fast from starting and would most likely stall very fast at idle. On the other hand you may need a tune up. It may need spark plugs. Do you know what a engine that is not hitting on all of its cylinders sounds like? Please do not get mad that I asked that. I have no idea of what you know about engines. For all I know you have no idea of what I am talking about but I hope you do.
Without hearing the engine it is hard to tell.
But best of luck with it.
 
"Thanks for your repoly. I wi

"Thanks for your repoly. I will check on the choke today. No sign of fuel leaking anywhere. Cannot smell fuel like you normally can with a flooded engine. No hesitation on transition from idle to full throttle. Good strong hole shot. Definitely hitting on all cylinders. No black smoke. Doesn't miss a beat running around the lake at anything above an idle.

I do have to pump it to start it. I left it all the way forward to start it, but it probably would have started at half throttle too. I will experiment more with it today. I am going to check on the choke, make sure fuel is pumped in the carb when the throttle is pumped. I am also going to mess with the idle mixture. I can always put that back where it was."
 
"Ok, more info. I took the fl

"Ok, more info. I took the flame arrestor off and the choke was open. Should be closed when cold. I fiddled with it and seems the choke was hung up on one of the linkages. They insert the round control rod (wire) through the linkage then crimp the end to keep them in place. One of the crimped ends was wedged into one of the holes. Seems like all of the carb linkages have a lot of play. I freed this and oiled all off the connection points . I pushed open the choke and had my son pump the throttle. Two very nice streams of fuel were shot into the carb. Started the engine. It idled very well. Let it run for a while then shut it down for five minutes. Started immediately with just the key. Let it sit for almost 2 yours and it restarted immediately again. I think the choke was not functioning properly due to the linkage getting stuck. For now it is working as it should. Thanks again."
 
John.
Sounds as if you have f


John.
Sounds as if you have found the problem. If it does it again you may need to replace the linkage rod or find a way to tighten it up so it can't jam up in the hole.

Best of luck.
 
I will know for sure after nex

I will know for sure after next weeks trip to the lake. We are driving 600 miles and would be annoyed if the boat wasn't running properly. You got me thinking about the choke. I appreciate your response.
 
"Great repair John! I suggest

"Great repair John! I suggest a small e-clip on that linkage. It might hold it in place. Your cleaning and oiling will go a long way though is my guess.
"
 
"..."No sign of fuel leaki

"..."No sign of fuel leaking anywhere. Cannot smell fuel like you normally can with a flooded engine."

You never will with a marine carb, for they deliberately flood inwardly to prevent gas in the bilge.

If the choke fix doesn't do it, get the carb rebuilt.

Jeff"
 
I have a spare carb from my 4.

I have a spare carb from my 4.3 I removed last month. It might be a bolt and go for your app. I went to an eddy 4 barrel. Never gave me any problems. If you need one let me know.
 
"We spent several days at the

"We spent several days at the lake last week. I believe that the choke issue solved the running at idle problem. However, it is very hard to get it started without the throttle lever all the way forward. It must be flooding. With the lever all the way forward, it takes about 4-5 seconds for it to start. Exhaust smells like it was flooded. Also, it has started dieseling. Sometimes for about 10 seconds after the key is turned off. I figure my next move is to check plugs, timing and may need a new float. I rebuilt the carb about 10 years ago and put in a brass float. Wouldn't think that would leak but who knows. Any other things I should check? By the way, it ran flawlessly once started. Thanks again.

Bill, don't think I need a new carb, but will keep you in mind if I do.

John VB"
 
"hi, I have a 305 in my baylin

"hi, I have a 305 in my bayliner that would not idle, it turnred out to be corrosion in the distributer cap, I cleaned it up and have had no problem since, just some food for thought that the carb is not the only reason an engine runs poorly at low rpms"
 
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