NEW MERC 3.5HP 4-STROKE WONT IDLE - The Hull Truth

Rock Hall · 07-26-2008, 02:55 PM

Before I tak this motor back to the dealer (because I probably wont see it again till Winter) I thought I'd run this by you guys. I recently bouoght a new 08 Mercury 4-stroke 3.5hp outboard for my fishing boat. The first 2 times out with it, it ran flawlessly. I had it out last weekend, ran great then shut off. I usually run this motor out of gas then fill from a small can I carry with me. When it shut off, I assumed it was out of gas, so I put about a pint in to finish up the day. After I filled it, I noticed it was really hard to start. I had to full choke it to get it started. I let it run for 10 seconds or so then cut the choke. It shut off. I finally got it running again, but it would not idle. As soon as I let off the as, it would shut off. It seemed to run normally as long as I was giving it gas.
I have had some issues with water in the fuel on my lawn mower etc. So I thought this might be what was causing the problem. So, I drained the tank, drained the carb. Dumped all the gas from the can into my truck. I then rinsed the can with dry-gas and ether to make sure no water remained. Then put an ounce of Stabil in and filled i back up with fresh gas at the gas station.

I took the fresh gas and ran it throughthe fuel system on the motor. Left the carb drain out and let some fresh gas go through. Then closed the drain and put about a pint of new gas in the tank. Had to choke to start. The motor ran great as long as I was half choked. Even after warmed up, as soon as I killed the choke, the motor shut off. I was also able to get the motor to run buy starting it in a higher throttle position. As soon as I returned to idle. It shut off.

A couple things I dont know. Does this motor have a fuel filter hidden somewhere?
After break-in does the idle need to be readjusted? I doubt this one because it happened very suddenly. I do not have a tach to tell you what the idle speed is. I just know it ran perfect with the throttle all the way back before.

I hate to take ths to the dealer. For one, I doubt I'll get it back in time to get any use out of it again this year. 2nd they always seem to find something that is not covered and charge me $200.

Any ideas of anything else I can check? I have a minimum selection of tools at this location.
Thanks
Mark

Reel A Lure · 07-26-2008, 07:20 PM

Had essentially the same problem with my merc 6hp 4 stroke. Did a search and found this: http://www.marineengine.com/cgi-bin/...79&page=170132 After reading it I went down and bought a can of carb cleaner, removed the carb and dis-assembled the float bowl and emptied the can of carb cleaner into every nook and cranny I could find in the carb, float, etc. Reassembled it all and reinstalled with the same gaskets (I was careful with them and they looked fine). Has run perfectly ever since. If you are mechanically inclined I would give it a try. Might just do the trick!

Rock Hall · 07-26-2008, 07:45 PM

Reel,
Thanks much! Now I dont feel so all alone. Geez, had I known how problematic this motor was going to be, I would have done something different. The reason I bought it was because my 2-stroke 25hp was giving me a problem I couldnt figure out and I wanted something reliable. The only thing I am concerned about is the warranty. I've only had it about a month and I guarantee the shop I bought it from will try to nix my warranty if they know I took it apart. I am a big Sea-Foam fan and use it in my cars and my big boat. In fact it's about the only thing I didnt try today. I have a can in the truck. I think I will try to run some through. I might get creative with how I get it in the motor. I like to get it into the intake in a strong dose. It has worked miracles on my other engines. If that doesnt work, I'll call the shop and explain what I read and ask them if they want me to do it, or if they will do it under warranty. I keep this boat at my weekend get-away on the Chesapeake. Motor is totally exposed to the elements and my gas can is outside but covered. Hot, cool, hot, cool, rain. and this state requires 10% ethynol in all fuel so you can imagine the problems with water even with stabil. I've rebuilt many carbs, so that shouldnt be a problem as long as Merc doesnt mind.
Thanks Again, Even though it wasnt real positive on 4-strokes, it was encouraging to know it is common and easily fixed.

A1 Outboard · 07-27-2008, 06:18 AM

Gummed up carbs are not a warranty situation anyway so don't worry about that part of it.

4-stroke carbs are the worst for getting gummed up on stale gas. Thier passagways and jets are very tiny and sometimes hard to clean. Some places don't even mess around with trying to clean a varnished one, they just put a new one one as the price is not that much more considering the labor involved and the parts prices. Some places use an ultra-sonic cleaner with good results and that seems to clean things out very well. Just spraying a solvent on the carb parts doesn't seem to work well except on the larger holes inside a 2-stroke carburetor.

Rock Hall · 07-27-2008, 08:28 AM

Stale gas is an issue, I'm sure. I am only here on the weekends and everything sits in the weather all week. I'll try the SeaFoam today and see if I get lucky. If that doesnt work, Then I will take the carb apart and hopefully be able to rectify the problem
Thanks for the help.

Rock Hall · 07-28-2008, 04:47 PM

I ran a pretty heavy dose of Sea Foam through for about 30 min yesterday. It might have helped a little. It seems like I can get it to run a little slower than before. It can be running for 10 min then just die. And the speed is not entirely steady. As I was workng on it I remembered I had some stuff at home called Nautique or something like that. You spray into the intake. This stuff has worked miricles for me in the past, so I'm going to give it one more try with that stuff then tear the carb down. I guess I should get a rebuild kit for it also. I need to try to locate a drawing or something also. I hate it when little parts fall out and you have no idea where they came from. I'm really starting to wish I hadnt bought this motor. I bought it because my other motor was unreliable. I used this 2 times and now it doesnt work.

Reel A Lure · 07-28-2008, 08:06 PM

Here is the breakdown of a carb on the 6 hp outboard: http://www.marinepartsplus.com/catalog/mercury/serial/4+H.P.+(4-STROKE)/803599006/11768-70 I'm sure if you search on that site you can find a diagram for yours. Personally, after my experience, I would try a can of carb cleaner after you get it apart before I would commit to a rebuild. Good Luck!

rlbrown · 06-23-2009, 09:47 PM

I had the same problem on 2 of these engines and it was the ignition module on both.

squinn92 · 08-02-2009, 11:47 AM

I have a 2001 6HP 4-stroke and had the same problem. After checking out the filter and fuel pump, I found a clog in the low speed needle. It comes out from the top of the carb (very easy to get to and no risk of breaking gaskets). After a quick cleaning, she's running great again.

Steve