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3rd cylinder is running rough (1995 Mariner 50hp)

T

tyfab

New member
Hi,

I have been trying to fix the 3rd cylinder running rough when revving.

I have:
- Changed fuel line,
- checked fuel pump - pumps fuel
- Added Water separator
- Changed filters
- Clean fuel and Used Can of Wurth to remove any water
- Removed the Carby and checked overall condition inside, No apparent gum
- Disconnected Rev Limiter
- Swapped Coils to see if the coil was burnt - Nothing
- Changed spark plugs
- checked reeds - all good, clean and closed
- Checked compression - 100 PSI on each cylinder

I removed the link arm between carbies and ran each separately. 1 and 2 cylinders run perfect but the first one cant rev.

I then saw a technique to see if the jet is clogged by vacuuming the carby with your palm.

I tested the 3rd cylinder by vacuuming it so that there is more fuel sucking into the carby. the Carby gets flooded and run really rough but suddenly works perfectly! but then goes back to running rough.

The thing that I also discovered is that the primer bulb isn't hard when running the engine

Here is a video to understand the issue and the vacuum technique.
https://youtu.be/38f6X6Y9_3M

Any thoughts?
 
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My thought are that your carburetors are not CLEAN....

A carburetor as simple as it appears is a very complex, highly engineered, block of metal with VERY small passages.

Start with buying 3 gasket kit.

Take them off, and then take them apart ONE at a time.

Soak then, over night in some quality carb cleaner (I personally ultrasonic clean mine in this step, it is quicker).

Then take a very fine brass wire and feed it through all the very small hole that you find in the throat of the carburetor (this is where all the highly engineered magic begin). It doesn't take much crud in the very small passages to change the way the carburetor functions.

Now it is time to rinse the parts in very hot water.

As you remove the parts from very hot water, blow them off with compressed air drying the parts and back pressurizing all the very small passages that you just cleaned.

Time start reassembling the carb with the fresh gaskets that you purchased. Be sure to check the float level before you put the bowl back on. When you have the float bowl back on you should give the partially assembled carb a shake. You should hear the float freely move in the bowl.

Finish re-assembling the carb. Move on to the next one and repeat.
 
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Primer bulb fills the carburetors with fuel.----When running the bulb does nothing .----And it does not need to be hard at all.----What are the actual compression numbers ?----Does spark jump a gap of 3'8" or more on all leads.
 
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