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Old 14-03-2014, 17:44   #31
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Re: Mercury 3.5 hp outboard woes

Well the good news is that I finally got the motor running. I first pulled the old plug and poured some gas in the cylinder to clean out the oil that had spilled inside. I turned the motor over a few times, then put in a fresh plug. I did another carb clean, soaking the carb and components in carb cleaner for about 30 minutes then put it all back together. The motor started but seemed like it was running out of fuel. The motor just didn't want to run.

I was searching another thread for various possibilities as to why my engine didn't want to run and found a thread where the owner had the same problem. He found that the fuel filter (which is inside the line from the gas tank to the shut off valve) was clogged. I took the fuel line off, removed the filter and discovered that the filter had been crushed somehow. I took it out and decided to also bypassed the shutoff valve (which is very restrictive and is a bitch to get back into place) and hooked everything back up. Bingo! It started up and ran pretty good. It still needs some fine tune adjustments but otherwise it runs fine. I think I'll see if I can find a high flow in-line fuel filter and shutoff valve and go from there.

I would consider reusing the stock shut off valve if I can figure out how to get it back in position. I spent nearly an hour trying to get the damn thing back in it's hole and all the components lined up before giving up.
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Old 14-03-2014, 18:22   #32
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Re: Mercury 3.5 hp outboard woes

hopefully all of us here will have gained some useful knowledge from all of this. thanks for your efforts.

i've also got a couple of small outboards and have occasionally been stumped like you have. seemingly simple outboard (2 stroke) wont start or starts but runs badly or won't run at low throttle or won't run at high throttle, etc etc etc....
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Old 15-03-2014, 01:04   #33
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Re: Mercury 3.5 hp outboard woes

Now that you've got it running well, what I've learned is that you need to add an ethanol treatment to your fuel, premium only from a major brand and also don't allow fuel to sit in your carb when you are done . Always run your carb dry at the end of the day unless planning to use again within 2-3 days. Just turn fuel supply off or disconnect line and let the engine run til it quits. I've followed that advice and it always works well. Hope you gave a good season.
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Old 15-03-2014, 07:07   #34
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Re: Mercury 3.5 hp outboard woes

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Now that you've got it running well, what I've learned is that you need to add an ethanol treatment to your fuel, premium only from a major brand and also don't allow fuel to sit in your carb when you are done . Always run your carb dry at the end of the day unless planning to use again within 2-3 days. Just turn fuel supply off or disconnect line and let the engine run til it quits. I've followed that advice and it always works well. Hope you gave a good season.
Thanks Chris. Yes, I failed to mention that I also used fresh gas and a ethanol treatment. One of the reasons I want to put my fuel shutoff valve back in is to make it easier to run the carb dry.
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Old 15-03-2014, 07:11   #35
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pirate Re: Mercury 3.5 hp outboard woes

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Thanks Chris. Yes, I failed to mention that I also used fresh gas and a ethanol treatment. One of the reasons I want to put my fuel shutoff valve back in is to make it easier to run the carb dry.

OK, OK ... two Benjamins!
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Old 15-03-2014, 07:17   #36
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Re: Mercury 3.5 hp outboard woes

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OK, OK ... two Benjamins!

I'll meet you halfway at seven Benjamins.
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Old 15-03-2014, 07:32   #37
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Re: Mercury 3.5 hp outboard woes

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OK, OK ... two Benjamins!
Quote:
Originally Posted by Jcolman View Post
I'll meet you halfway at seven Benjamins.
HAAA!

----

OB's are maddening when they get like this.... At least you had a pint sized "pull-a-thon" trying~!
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Old 15-03-2014, 07:37   #38
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pirate Re: Mercury 3.5 hp outboard woes

Glad you got it going. I have a 3.3 2 stroke with an overflowing fuel bowl. I'm not worried. BTDT. Next nice day. ... Manana maybe ...
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Old 15-03-2014, 07:54   #39
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Re: Mercury 3.5 hp outboard woes

I don't recommend this but....

Was on a friends boat off St Thomas when a squall flipped the towed dink with a Merc 3.5, towed the damned thing upside down for almost an hour before we could get it upright. A few hours later we were on the mooring and got to work. The gas tank was completely full of salt water, water dripping out of the carb and so on, looked hopeless. Dumped the tank, pulled the plug, drained the carb and sprayed everything with CRC. A few pulls with the plug out to get the last of the water out, more CRC and repeat. Put it all back together with a new plug, filled with gas and... the damned thing started right up on the 2nd pull! That was several months ago and the owner says its running fine and in fact has never run better!

Boats.net has drawings of the carb and other parts of the merc 3.5 4 cycle. I found this a real help.
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Old 15-03-2014, 08:15   #40
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Re: Mercury 3.5 hp outboard woes

I have a 15 MERC also with few hours. I have had several over my lifetime. They can always be fixed. Every one of the ran well. My current 15 also came on a dinghy and had just been totally serviced according to the PO. It ran like crap until I found the air leak. Can you get the owners & service/shop manual for this? It would probably make life easy. No way a nearly new MERC should not run.

We get non-ethanol gas at the marinas - no problem. Also, if you may be able to buy at a small airport. Planes are absolutely not permitted to use ethanol.
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Old 15-03-2014, 08:17   #41
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Re: Mercury 3.5 hp Outboard Woes

Looking at the picture in the OP, you need a new float. The blistering likely indicates that someone put something in the fuel to "clean" it that eroded the float and it is likely not floating.

Good luck!
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Old 15-03-2014, 10:15   #42
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Re: Mercury 3.5 hp Outboard Woes

I have a 2011 Mercury 5 hp 4 stroke outboard extra long shaft. So far so good. I do add the stabil (izer) to the fuel and that's about it. Sometimes I run the carb dry, sometimes I don't with no problems. I'm using 6 month old 10% ethanol fuel at the moment.

Here is a link to the shop manual for the mercury 4-5-6 hp 4 stroke. (all 260 pages) It does come in handy at times. I couldn't find the one for the 3.5 mer.

Boatinfo - Mercury Service Manual for 4-5-6 hp
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Old 15-03-2014, 14:59   #43
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Re: Mercury 3.5 hp Outboard Woes

Thanks for all the tips and advice! If you read post #31 you'll see that I did get the motor running.
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Old 15-03-2014, 17:13   #44
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Re: Mercury 3.5 hp Outboard Woes

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I have a 2011 Mercury 5 hp 4 stroke outboard extra long shaft. So far so good. I do add the stabil (izer) to the fuel and that's about it. Sometimes I run the carb dry, sometimes I don't with no problems. I'm using 6 month old 10% ethanol fuel at the moment.

Here is a link to the shop manual for the mercury 4-5-6 hp 4 stroke. (all 260 pages) It does come in handy at times. I couldn't find the one for the 3.5 mer.

Boatinfo - Mercury Service Manual for 4-5-6 hp
Thank you for posting the service manual! It answered a few questions I had.
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Old 15-03-2014, 21:08   #45
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Re: Mercury 3.5 hp Outboard Woes

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Thank you for posting the service manual! It answered a few questions I had.
No problem. I'm glad it helped. It gives tons of detail, and I was very surprised that it was available online.
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