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Author Topic:   Problem with 4-stroke Outboard After Long Lay Up
lakelanier posted 10-04-2003 05:50 PM ET (US)   Profile for lakelanier  
The 17-Standard I just bought has a 50-HP 1996 Mercury 4-stroke. The motor has not more than 100 hours and was laid up for probably at least a year before I bought it.

First time out it would not idle in neutral and would sporadically drop a cylinder. My shop found that the carbs were way out of adjustment and synchronization. I had the [repair shop] properly adjust them. The motor then idled smoothly, and it would run up to about 5500 RPM, although there was still a rough spot at about 2000 RPM. At higher RPMs it ran sweet.

After about a 45 minute run (at about 4500 RPM) it again seemed to drop a cylinder. I limped back to the ramp on 3 cylinders and back to the shop. Their next step is to take the carbs apart for a clean and rebuild. That is looking like a $400--$500. job. Anyone out there have a similar problem with this motor.

mnboater posted 10-04-2003 11:54 PM ET (US)     Profile for mnboater  Send Email to mnboater     
lakelanier--The problem you are experiencing with the motor is the result of improper storage preparation. The carbs need to be drained. The use of fuel stabilizer would have helped for the short term but not suffice for a year layup. The fuel has varnished and possibly, with some level of moisture, created white corrosion in the fuel bowls. All fuel system components on the carb side of the engine fuel filter need to be cleaned and flushed extremely well. This includes the fuel lines and fuel pump.

I speak from experience as I have a 25-HP, a 50-HP, and a 100-HP, all 4-stroke engines. I purchased each of them used within the second or third season of use. All very low hours of use and most likely, not properly prepared for the 7 month layup we have in Minnesota. All have required complete fuel system overhauls. I started just cleaning the carbs but soon learned that the fuel lines harbored flakes of varnish that would soon plug another jet. In fact, my 100-HP has tiny filters at the carb inlets that ended up partially blocked starving #1 & #3 cylinders above 4000 RPM. I don't mind tackling the first cleaning but it gets very old the second or third time.

I'm sure some people are concerned that these problems show up with 4-stroke's more than 2-stroke's. I would have to agree.

The 4-stroke jets are much smaller and the carbs have more intricate fuel passages requiring the extra cautions in fuel filtering and steps to prevent fuel varnish from forming. The 4-stroke owners that use their motors limited times and set for long periods will experience fuel delivery problems. I'm fortunate as I can do the motor work myself. It is much cheaper to take the precautions than pay the dealer for service that is preventable.

mn boater

jimh posted 10-05-2003 09:21 AM ET (US)     Profile for jimh  Send Email to jimh     
mmboater--Thanks for the excellent advice. Good information like that is much appreciated.
lakelanier posted 10-05-2003 10:07 AM ET (US)     Profile for lakelanier    
Thanks for the heads up. I will be sure that the shop cleans the entire fuel system.
Dick posted 10-05-2003 12:19 PM ET (US)     Profile for Dick  Send Email to Dick     
As mn boater said the 4 stroke jets are very small. In addition to replacing the fuel filter once a year I add OMC 2+4 to every tank of fuel. After 4 years my Merc 50 4 stroke has had no carb problems.


Royce posted 10-05-2003 02:11 PM ET (US)     Profile for Royce  Send Email to Royce     
I have a Suzuki-evinrude df 70 EFI. What is the best way to prepare it for winter? Does the EFI suffer the same problems of the carbed models?
Dr T posted 10-05-2003 08:55 PM ET (US)     Profile for Dr T  Send Email to Dr T     
A note on the recovery process: I had a very similar problem on a motorcycle: a 4 cyl. 4-stroke Suzuki. I was advised by a mechanic at the dealer to add a bottle (about 6 oz.) of STP fuel treatment to a tank (about 4 gal.) of fuel and go for a hard fast ride to remove the varnish. It worked.

The active ingredient of that fuel treatment, I believe, is acetone.

Does anyone one know if such a "field cleaning" process will also work on an outboard?


Bigshot posted 10-06-2003 01:49 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
$4-500 to clean carbs....YIKES. Usually about $40-50 per carb.

Techron does wonders to clean up a fuel system and so do inline filters. I advise to run techron every 50 hours or so. Inspect or replace filter at 50 as well.

Dr T posted 10-06-2003 08:25 PM ET (US)     Profile for Dr T  Send Email to Dr T     
I agree, Nick. It is great stuff, especially for fuel injected engines.

That is why I brought up the STP gas additive trick. I wonder if a concentrated dose of Techron would have a similar effect. At less than $10 a bottle, it may be worth a shot. Just mix up a cocktail in a portable tank and see what happens.

As I recall, the Fuel Injection cleaning process uses a similar procedure...


lakelanier posted 10-13-2003 07:54 PM ET (US)     Profile for lakelanier    
Update. I ended up having all 4 carbs rebuilt on this 50HP four stroke. My initial estimate of 400. to 500. turned into $940. I was told that there was far more labor than anticipated because these mercury carburetors had a large number of soft parts in the rebuild kits. (Rebuild kits were $50. each).
I have done business with this shop for the past 7 years and I have a fair amount of trust in them but I can not help but to think that this bill is a little high. This is the first 4 stroke I have owned so I do not have experience with there maintenance costs compared to a two stroke.
I am not through discussing this with the shop owner and would be thankful for any thoughts anyone has regarding the fairness of this bill. Thanks

RJM posted 10-13-2003 08:27 PM ET (US)     Profile for RJM  Send Email to RJM     
Bigshot, after reading a number of replies where you recommended Techron, I recently bought a couple of bottles and used it in my carbed 150 Mercury. It is now running the best it ever has. It idles smoother and I think it got rid of a mid rpm vibration. Thanks for the tip!
Bigshot posted 10-14-2003 11:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Rebuild kits are not cheap and $50 is about list price.....You do NOT always need them for a cleaning, I rarely do unless I break a gasket. All I can say is that $940 is OUTRAGEOUS bu what can you do? Net time try the Techron and again....find another mechanic or make him show you where the factory tech manual shows you the amount of labor for that job. Hell call 4 other dealers and ask them what they would charge.
tabasco posted 10-14-2003 01:54 PM ET (US)     Profile for tabasco  Send Email to tabasco     
You would have been better off to add the $950 and your motor and traded it for a new one with a warrantee
hooter posted 10-14-2003 03:29 PM ET (US)     Profile for hooter    
You old hands know all this, but for the newer lads, because Ah get by on little whenever Ah can, Ah'm always pickin' up old motors that's been set up, usually for some years. Even when Ah don't plan to do a carb rebuild mah self, as increasin'ly seems to be the case, Ah ALWAYS remove the carbs, get to the bowls and see what's what before doin' anythin' else. The whole story is often in there. If the bowls is heavily varnished up or gunk full, plan on a total rebuild of the carbs. Otherwise, a soak overnight in Varsol or mineral spirits and a shot of compressed air can most often do the trick of cleanin' her out without a complete take-down. That goes double for an engine only set up a year or so. Follow up with Techron in the first gas tank-full. But don't EVER attempt to start that old baby without knowing what's what inside. Sure ticket to many more problems once you succeed in pullin' a bunch o'crud through the carbs and beyond.
lakelanier posted 10-19-2003 09:21 AM ET (US)     Profile for lakelanier    
Well the rebuilt carbs made a huge difference. Almost seemed worth the price--that is until the engine failed in a big way. See separate thread under Repaire-Mods for this tale of woe (Blown engine- why?).
jimh posted 10-19-2003 09:34 AM ET (US)     Profile for jimh  Send Email to jimh     

for the continuing and sad story.

lakelanier posted 10-19-2003 10:32 AM ET (US)     Profile for lakelanier    
Yes it is indeed a sad tale, but I am trying to rally and stay of good nature. After all this is boating--if it were easy everyone would be doing it!

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