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Merc fuel problem

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lucky_d

New member
I have an early 80's 40 hp Merc. I pump the bulb to get fuel pressure, fill up the fuel filter, start the motor, and it runs until the fuel filter goes dry. I have replaced all the lines, put new seals in the fuel pump, and even tried a different carb. Could the fuel pump be worn out even though the gaskets and seals have been changed? I've tried changing the hose on my tank and both fittings. Any info would be great.

Thanks
 
You might have the check valves in assbackwards, or the diaphragm might be shot. Gas should pass through the pump easily as you pump the bulb.

Try this: Fill the carbs, remove the line TO the carbs, aim it at a bucket, and fire it up. Gas should shoot out. If not, it's a pump problem OR a restriction coming in.

I had a bad fuel line once that would 'lock up' on me--the outlet check in the bulb would just lock shut somehow. Drove me batty.

Jeff
 
Thanks for your help, when I get the boat out of storage I have a good place to start. I think that the pump might not be working properly, I could have messed it up putting in the rebuild kit. If It is not working, I think I will just buy a new pump instead of messing with this one anymore.
 
Pumps can get expensive, try what Jeff said, and turn the check valves around it it ain't pumping. This is worth a try before you spend anymore money.
 
I had a similar problem and it turned out to be a faulty vent screw on my fuel tank. I would unscrew it thinking I was venting the tank and it did not! Didn't take long before the pump couldn't pull against the vacuum that was created as fuel was sucked from the tank. As you can imagine I got just far enough from the dock each time to have to be towed back!
 
Ok I got the boat out of storage, still won't stay running, changed gas line and fittings, still runs for a minute then dies. I took off the fuel line and started the motor, the fuel pump pumps nothing. Took off fuel pump changed diaphram, and gaskets(including little gaskets on the valves) checked the picture in the manual to make sure valves went in correctly, still dies!!! I am ready to throw in the towel. Any other ideas on the things I should check would be great.

Thanks
 
I have a '76 Mercury 200 thunderbolt 4 stroke. I got it from my dad and decided to clean it up and sell it. It was stored in his garage for some time (about 8 years or so) without starting it. He can't remember if he changed the oil or fogged it up.
Anyway, there are a few things happening. I can't get the fuel running through the carb. I used a bit of throttle body cleaner and it started pretty good for a few seconds. I'm 'ok' at mechanical things, and don't want to tinker with it too much. I'm thinking of replacing the fuel hose from the inlet to the carb, but noticed that it was tightened on the end with a special crimping tool. Could I use pipe clamps instead? Or, is the tool inexpensive.
Since I'm looking at selling it to offset the cost of a used boat, I don't want to spend a whole lot bringing it to a marine tech.
What could the problem be. Please list as much as you can.
Secondly, what exactly is the thunderbolt ignition. There's a couple of wires going out from it.
Any replies would be greatly appreciated.
Ben
 
lucky_d said:
Did a compression test #1 cylinder 155 psi #2 cylinder 150. Is that good or bad compression?
Click to expand...
Your compression is great, can you borrow a tank assembly from someone. You can also bypass the quick dissconnect and hook directly to the fuel pump. Make sure you can blow into the fuel pump and threw to the out, and not the other way around.
 
boltonben said:
I have a '76 Mercury 200 thunderbolt 4 stroke. I got it from my dad and decided to clean it up and sell it. It was stored in his garage for some time (about 8 years or so) without starting it. He can't remember if he changed the oil or fogged it up.
Anyway, there are a few things happening. I can't get the fuel running through the carb. I used a bit of throttle body cleaner and it started pretty good for a few seconds. I'm 'ok' at mechanical things, and don't want to tinker with it too much. I'm thinking of replacing the fuel hose from the inlet to the carb, but noticed that it was tightened on the end with a special crimping tool. Could I use pipe clamps instead? Or, is the tool inexpensive.
Since I'm looking at selling it to offset the cost of a used boat, I don't want to spend a whole lot bringing it to a marine tech.
What could the problem be. Please list as much as you can.
Secondly, what exactly is the thunderbolt ignition. There's a couple of wires going out from it.
Any replies would be greatly appreciated.
Ben
Click to expand...
You should start a new thread from the top of the merc page. You will have to start from the beginning clean all carbs, check for spark and check compression. Failure to do so will waste the engine. If gas/oil cant make it into each carb and you run it, that part of the engine won't have any oil for lube. Think of each carb as a separate engine stacked on top of another.
 
I am a total MORON!!! I had the fuel lines hooked up backwards at the fuel pump!! Runs like a top now, just have to make the final adjustments, thanks for all the help.
 
Just an update and to say thanks. The motor was a 2 stroke and luckily I didn't spend too much time starting it. Took out the carb and cleaned it all out. New gaskets and reinstalled it. Added new plugs. Added the correct oil mix to the fuel. Changed the lower case oil.
After about a 1/2 days work, I got it running and woww, she realy purrs.
However, when I idle her close to top speed (with muffs), it misfires as it tries to cut out. After all of these years should I run it on a lower idle until things get properly lubed and 'warmed' up.
Thanks,
 
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