Mercury 9.8 won't start cold

[gayle23]

I have a 1980 9.8 hp mercury which hadn't been used for several years. I rebuilt the carb and fuel pump, replaced the impeller, thermostat, and spark plugs, and changed the lower unit lube. The motor runs great as long as I start it by squirting gas into the cylinders. It also starts great when it is warm. But it WON'T start cold. I am thinking maybe the choke isn't working properly, or the ignition coils are weak and need to be replaced?

Please advise. Thanks.

 

[Laddies]

Re: Mercury 9.8 won't start cold

Look at the choke with the bonnet off if it's closing it's aright, the rings may be stuck from sitting around or a poor grade of oil so run some Mercury Powertune through it as directed on the can and see if that don't help.

 

[gayle23]

Re: Mercury 9.8 won't start cold

The choke flap is closing all the way. When I do get it started it runs like a champ for extended periods of time at various speeds so I'm thinking the rings are not stuck. Any other ideas? At the time of a cold start I must be having a spark or a fuel problem, which is resolved once it starts and keeps running. When the engine is warm it restarts on the first pull.

 

[gayle23]

Re: Mercury 9.8 won't start cold

O-K. I have done the PowerTune thing. Lots of gunk came out. The motor now runs like it is new at all speeds and really purrs. BUT, it still doesn't start without squirting gasoline mix into the cylinders. Also, even when I try extensively to start it, the spark plugs don't seem to be wet. How does the gas get from the carburator to the spark plug? This sounds dumb but the pistons are between the carb and the spark plugs so how does the gas get from one to the other? Also, I keep thinking the primer bulb maybe isn't working but it is new and does seem to work even though it is always hard, no matter what (I guess that is good?). Is it possible there is an air vent which is plugged which doesn't allow the primer bulb to force gas into the carb, but once the motor is running the fuel pump can pull gas through? It seems that pressing the primer bulb really doesn't do anything as it is alway hard, but doesn't seem to be, by itself, forcing gas into the carb. That is my best guess at this point as the priming thing doesn't seem to work, but once started the engine runs great. I am stumped but am VERY close to getting this thing working well. Thanks.

 

[Laddies]

Re: Mercury 9.8 won't start cold

The choke detent is on the cable make sure the butterfly stays closed when the knob is released and the detent is holding it, next some of the engines came with a 2 piece choke butterfly and the spring won't keep the cosed when the engine is cranked, if it has one of them either solder it or epoxy it so it can not flop open. The float level in the carb will cause starting problems if to low. Loosen the inlet cover on the side of the carb and make sure there is fuel to the carb. As far as fuel flow in the engine it is pulled through the carb goes through the reed valve (they act as intake valves to start the engine) into the crankcase and lubes the bottom end of the engine up the transfer pots and into the cyls. where the ign fires the mix.

 

[gayle23]

Re: Mercury 9.8 won't start cold

Thanks. I have now checked two of those items. When the choke is pulled out the choke plate is firmly engaged... does not flop or move at all. I loosened the inlet cover, pressed the primer bulb, and there is a good flow of gasoline reaching the carb. I will remove the carb and set the float higher. I am thinking that might fix the problem.

 

[gayle23]

Re: Mercury 9.8 won't start cold

O-K, now that I have the carb apart I remember I was concerned about the float level when I did the rebuild because the float's "tang (or whatever)" is plastic, not metal so if you try to make that adjustment it seems to go back to the position it was before. Is there a secret to this? Thanks.

 

[Laddies]

Re: Mercury 9.8 won't start cold

The float should have a metal tab to bend to set the float height at 1/4" to the bottom of the float when held upside down. If yours don't check out a replacement.

 

[gayle23]

Re: Mercury 9.8 won't start cold

O-K, but 1/4 inch from what? I don't have my seloc manual with me but I think it was something like the bottom of the float should be 0.040" from the top of the high speed valve thingy when the carbutetor was held so the float is hanging down. Thanks again.

 

[Laddies]

Re: Mercury 9.8 won't start cold

1/4" from the bottom of the float to the bowl mounting flange.

 

[gayle23]

Re: Mercury 9.8 won't start cold

Thanks. That really helps. I bought a new float and adjusted it per your directions (1/4"). It still doesn't start cold without squirting premix into the cylinders but other than that it is running better and better. I have been running it in a tank and think I will take it out on the water to see how it runs. Maybe running gas through the system will help??? Any other ideas would be appreciated. Thanks again. If this doesn't work I guess I will take it to a Merc. mechanic as I am probably missing something significant.

 

[gayle23]

Re: Mercury 9.8 won't start cold

BIG NEWS!! The motor starts without putting premix in the cylindars!! In fact, it really purrs. I will run it on the lake this week. This must be a result of the items you have suggested: decarbonization, and installing and adjusting a new float. This is very exciting as I don't think this engine has run for at least 10 years. I love this forum!!