7.5 Mercury Outboard Trouble Starting

[dealdan99]

Hello, I recently bought a 1979 mercury 7.5hp. The guy said it ran but unfortunately it barely coughed. I rebuilt the carb and replaced a bunch of other parts but it still will not start properly. It will start and run beautifully with a little bit of starting fluid (I sprayed a bit of oil in the cylinder before doing that) but it will not start on its own. I was quite puzzled. I checked everything from the float level to the timing. Just recently I discovered that if I disconnect the bleed drain it starts just fine.

My question is, what is the bleed drain for and how important is it? I'm guessing that the check valve is bad but I really don't want to buy a new one. I've spent a lot of money on parts already and a new check valve is about $45. Can I just disconnect it and leave it run that way?

 

[racerone]

I can not see, hear or feel your motor.----The recirculation system is needed.----What bunch of parts did you replace ?-----Water pump impeller was replaced hopefully.-----Steps you need to take.------Post the results of a compression test.-----And does spark jump a gap of 3/8" on a test device , yes or no.-----Further help may follow.

 

[dealdan99]

I replaced all the gaskets in the carb, the float, the needle and a couple other parts that wouldn't effect the carb, ie the thermostat, the throttle lever, throttle cables etc. The guy before me said he replaced the impeller and it spits out water. I have not been focusing on that since it really doesn't matter if I can't even get the engine to run. I will probably check it once I get the other stuff figured out. The compression was about 120psi when I checked it. I do not have a way to check the spark but I took a spark plug out to check it and it shocked the heck out of me

 

[dealdan99]

Also what is the bleed drain for?

 

[racerone]

Oil / gas collects at the bottom of the motor.----The bleed hose returns it to the top of the motor.----You must have that in service.----Perhaps there are issues with crankcase compression.----Upper and lower crank seals.----Reed valves. ----And labarynth seal between the 2 crankcases.-----

 

[dealdan99]

Is 120psi not good enough compression? I was thinking about taking off that check valve and trying to clean it out. It seems like something must be restricting that since when I cover up the end of the tube with my finger the engine behaves similarly as to when the tube is hooked up.

 

[racerone]

I mentioned crankcase compression !!----I made no comment about the compression test in the cylinder.----Perhaps this is your first stab at diagnosis of a 2 stroke engine.----Time to read up on the basics.----Sorry to be so blunt here.

 

[dealdan99]

There is no need to be rude. I simply misread you're statement.

I took the check valve off and found it was stuck. I soaked it in mineral spirits overnight and it appears to be freed up now. The engine starts and runs great now