Carb not sucking air

[graysilm]

On my 2001 3cyl 2stroke 50hp mercury the top cylinder isn't sucking air in the carb. The sparkplug is wet with gas, but the carb just isn't sucking air. A mercury technician came by and looked at it and said he thinks its a problem with the reed valve. Does this sound right? Any ideas on what could cause this problem? Thanks

 

[Laddies]

Re: Carb not sucking air

If there is no vacuum then there is a good chance you have a bad reed.

 

[j_martin]

Re: Carb not sucking air

With a bad reed, it should suck and blow. No suction at all usually means a bad piston or broken connecting rod.

Pull the plug and look into the hole.

hope it helps
John

 

[graysilm]

Re: Carb not sucking air

I have pulled the plug and shined a light and didn't see any problems. I check compression and it is good. It just won't suck air.

 

[j_martin]

Re: Carb not sucking air

Is the throttle valve (butterfly) opening for sure?

Compression says piston et al is ok. Maybe I'm wrong.

John

 

[graysilm]

Re: Carb not sucking air

Ok, I have come to the conclusion that the mercury tech looked at my motor is wrong. The carb is sucking air, and when i put my hand over it it blows gas back out. The butterfly valve is opening. The motor is running like crap though, and I can tell by the plugs that it is the top cylinder that isn't combusting like it should, but the top plug is wet with gas so I have no idea whats going on. My cheap spark plug tester indicates spark. Any other troubleshooting tips?

 

[j_martin]

Re: Carb not sucking air

Ok, I have come to the conclusion that the mercury tech looked at my motor is wrong. The carb is sucking air, and when i put my hand over it it blows gas back out. The butterfly valve is opening. The motor is running like crap though, and I can tell by the plugs that it is the top cylinder that isn't combusting like it should, but the top plug is wet with gas so I have no idea whats going on. My cheap spark plug tester indicates spark. Any other troubleshooting tips?

Like I said, it sucks and blows. That's reeds. Compression would be good (doesn't care where it gets air, just measures the squish above the ports.)
would idle like crap, spit at you, probably run fine if it could be wound up to WOT.

hope it helps
John

 

[j_martin]

Re: Carb not sucking air

Just looked at the parts explosion for that engine.

The reeds aren't expensive, so for about 25 bucks in reeds, and about the same in gaskets, you can freshen it up like new.

Should be easy to work on, also. The reed plate is right behind the carbs. Use new carb base gaskets, and reed plate gaskets, and you should be good to go.

Be sure to get the manual and follow the procedures, such as torque sequence, torque specs, locktite, etc.

Once you have the carb off, you can probably look in and see the errant reed.

If you're new at this, a digital camera is priceless. Take detailed pictures of everything as you take it apart, then use it as reference for reassembly.

hope it helps

John

 

[graysilm]

Re: Carb not sucking air

thanks John. I've got my fair share of turning wrenches on two stroke outboards, although I absolutely hate fuel systems. I've rebuilt a few old OMC engines as well as a yamaha 25. I've got the clymers manual, all the tools, and a digital camera so I should be good to go. I'll just have to read up on seating the valve, that the only thing i'm worried about.

 

[j_martin]

Re: Carb not sucking air

Double Post

 

[j_martin]

Re: Carb not sucking air

thanks John. I've got my fair share of turning wrenches on two stroke outboards, although I absolutely hate fuel systems. I've rebuilt a few old OMC engines as well as a yamaha 25. I've got the clymers manual, all the tools, and a digital camera so I should be good to go. I'll just have to read up on seating the valve, that the only thing i'm worried about.

Usually the carrier will have a flat surface the reeds slap against that may get a little pitted and worn. A piece of very fine emmery paper, and a piece of glass window, and you're good to go for hand lapping. You don't touch the reeds themselves. V6's are a piece of cake. Don't know exactly what the 3 cylinder carrier looks like. It ain't rocket science, though.

There are thin and thick reeds for that engine. Why, I don't know. The thin reeds theoretically have better performance, and the thick better life. Maybe mic what's in it and get the same, or just go with the cheaper, tougher thick ones.

I don't think you'll have any trouble. Good luck

John