---

1998 Johnson 50hp 2 cylinder 20" shaft. I picked it up used a month ago. It started and ran fine on the stand. Good spark, compression, very clean and seemed like a bargain. Here is the sympton:

will idle but when put into gear under load(in the water) stalls out.
will not idle very well in gear but when going back to neutral, stalls.
occasionally when started and run at above idle, will run away up to about 2500rpms

What multiple mechanics have done so far:
cleaned/rebuilt carbs, twice, verified they are the right carbs for the engine
new wiring harness, was some chafing on original
new fuel pump
new plugs
checked/verified correct timing, linkage
replaced choke solenoid due to small crack/leak
power tuned/engine cleaned twice, filled cylinders and let it sit overnight. Alot of carbon came out the first time


Compression is 145/135, engine runs great at higher rpms, just dies at idle. Next step is to pull the head and see if the rings are sticking, not allowing enough suction to pull the fuel in at low rpms.

Any ideas??

---

Have you check the fuel filter? Any fuel restrictions? Crimped fuel Line? Loose fuel line?

---

DP, it seems like you've just about covered all the bases on that problem. It seems to me like it has to be a fuel delivery problem......I'll defintely be waiting for finding out what the problem is.

Are your coils putting out what they should when under load??

---

I don't know know about the 2 cylinder carbs but are they actually taking the time to set the idle. My 3 cylinder 60 up recently rebuilt carbs but they idled horribly and loaded up. The idle screws werent adjusted properly.

---

Are the carbs syncronised and float settings verified to be correct? Fuel connector on hose or engine, o-rings in good order?

---

brand new fuel tank, lines and fuel filter. Carbs have been gone over 3 times, all verified that they are set properly by multiple mechanics( 3 at the same shop). It has become a personal issue with all 3, they are taking this as a challenge. We'll see what happens on Monday

---

Make sure freeze plugs in carb are not leaking air.

---

Well if they are good hounds then they will find it. Sounds as if the engine is running too lean as it sudenly takes off to 2500

---

What you are going through is one of my worse fears. Chasing phantom ghost issues is probably the most expensive issues we boaters have to go through.

I just sold my 1991 Honda Accord wagon and no one could find the idle issue I was having. I spent well over $600 trying to get it running as it always had but no mechanic could fix it. The guy who bought the car came by 3 days later and it was idling perfect. It cost him $12 and he replaced the vacuum lines and solved the issue.

Some times these problems are so simple we overlook the obvious and replace all sorts of expensive valves and other parts only to find a two dollar part was all it needed. Mechanics have it in their nature or from their employer to always start with the most expensive option and move on from there. Do the simple stuff first before you employ the costly mechanics and shops! Fuel lines, filters, vacuum lines and what nots just to be sure you actually do have a bad issue requiring further research.

Try a fuel tank you know is working right from a friends boat. If you have not yet replaced the fuel lines from tank all the way up to the carbs then do that too. It sounds to me like you have an air or vacuum leak somewhere.

---

TRY HAVING THE FUEL SYSTEM INCLUDING THE NEW COMPONENTS PRESSURE TESTED UNDER BOTH POSITIVE PRESSURE AND UNDER A VACUME,

---

Not sure if this will help. But I purchased a new EPA compliant 7.5 Gal Moeller gas tank. I noticed the vent on the gas tank not allowing enough air in the tank. The engine would idle fine until you gave it throttle. It would stall around 2500 RPMs. I removed the vent screw from the gas tank and the motor run like a champ.

I'm gonna call Moeller on Monday and see if it's user error or if I have a defective gas cap with vent.

---

Another thing to look into is to remove the carbs again, sorry, and remove the intake and reed box and examine the reeds very carefully for broken/cracked reeds as well as the gasket surface to the crankcase.

---

bottom cylinder is scored. I might have a deal on a powerhead, if not, I will probably fix it as the rest of the motor is looking pretty good right now

---

Did they find the scored cylinder, even though the compression was good, by using the leak-down tester like I mentioned to you on another boating forum?


http://www.thehulltruth.com/boating-f...umped.html

refer to post #5

---

no, pulled the head

---

Do you have any leads on a new powerhead??

If you do a search on this sitefor Northland Performance, you'll come across a place I used for my motor. They get their parts mainly from the cold freshwater areas of the northern US and Canada. If I can find the post, I'll link it here.

---

Was the motor either run without a thermostat or was the thermostat either stuck open or corroded away or the pressure relief valve stuck open?