Stumped, one cylinder seems dead

[marley42]

Hi Guys, new here, but I am not new to engines or especially 2 cycles. Owned Johnson 50-60 hp, multiple snowmobiles and now own a 1991 25 HP Yamaha. The issue; top cylinder runs prefect, bottom is dead. The real issue, both compressions within 2 lb's, spark is so hot you can disconnect and the arc shoots from the boot to plug, spray fuel in through rebuilt carb, nothing.
Never seen anything like it, ideas or giggles..

If you got the time, thanks in advance 1991 25HP Yamaha ELRP

 

[99yam40]

check the fuel pump.
if the diaphram leaks fuel into the crankcase it will cause that cylinder to run too rich.
I am guessing #2 is what provides the pulse for the pump on your motor.

 

[marley42]

Thank you! Sometimes its easy to think too fast and miss the problem. I pulled the carbs to rebuild yesterday, moderate junk in there, blocked main jet on #1, So I thought lets rebuild this fuel pump long as its off. First thing tomorrow, I'll take a look, did I mess up in the placement of seals and diaphragm? Also, just something to run by you, I pulled reed valves out as well, checked them and took a peek inside, long as I'm there. You think a bad gasket could effect the vacuum inside the cylinder, maybe replace that gasket as well, it is a 1991 after all, Cheers! Never talked to a fleet Admiral before..

 

[brodmann]

If you damaged the seal for the reed valves, you could have lost the vacuum needed to suck gas and air through the carburetor. I hope you had fun with your exploration of this motor! I understand your curiosity. Now it's time to order some gaskets, fuel pump (or fuel pump rebuild kit) and maybe some carb gaskets. While you're at it, how long has it been since you replaced the water pump, or at least the impeller?

 

[marley42]

Brodmann, Thanks for helping out. So far I have done the carbs, head gaskets, water jacket gasket, fixed the Bendix ( wasn't extending) I picked up the reed gasket as well have not done that yet. The Fleet Admiral above nailed the problem, so fuel pump is rebuilt now. Starts before you can get your fingers off the Key, thanks Admiral.

Now I have a intermittent water pump, I just reinstalled it for the 4th time it pumps for a bit, shut it off, start again and no pump, cleaned out every water passage, 80 psi air and trimmer line, thinking it was a blockage, about at my wits end. Came in for a little libation to soothe the savage beast and saw your post.

I like this place, newer or in my case re-owners need to be here just to read the thread advice!

Best !!

 

[99yam40]

make sure the key is in the slot on impellor and the impellor is not spinning (broke loose from the shaft collar)
always buy the OEM pump kits and replace it all
just to let you know I am a Backyardian that bought a Used Yamaha back in 2008 so I joined this site myself to figure out what I needed to do

 

[marley42]

Bought the whole kit, installed and spent the afternoon o nthe lake with the wife. Thing runs like new, need a prop with lower end bite and I am good.

Thanks for the advice guys!!