thunderbolt 850 runs great but won't start iteself

[blackmatch]

I have a Mercury Thunderbolt 850 ( not sure of year) the engine turns over great. choke on or not, will turn over till the cows come and not sputter once. The primer bulb gets and stays hard.
But when I spray gas/oil mix int either carb intake it will sputter and run, and after a couple second ( 5-6 sprays) it will stay running. neutral, forward, reverse all runs fine, idle and acceleration.
When turned off it will restart if left for only about 1 to 30 mins. any longer will have to respray mix into the carbs.
any thought?
thanks

 

[Wingedwheel]

Re: thunderbolt 850 runs great but won't start iteself

Your turning it over, but is the fuel pump actually putting fuel to the carbs? Take the fuel line loose at the carb and see if its pumping. The diaphram may be weak and will only work with the vacuum force of a running engine. turning it over may not be enough.

 

[Chris1956]

Re: thunderbolt 850 runs great but won't start iteself

Black, You need to choke the crap out of it, when first starting. Cold start lever all the way up, hold the choke button down and crank it until she starts.
If you choke is working, and she still won't start, you might check your compression. Low compression engines are real hard to start.

 

[blackmatch]

Re: thunderbolt 850 runs great but won't start iteself

Your turning it over, but is the fuel pump actually putting fuel to the carbs? Take the fuel line loose at the carb and see if its pumping. The diaphram may be weak and will only work with the vacuum force of a running engine. turning it over may not be enough.

we have, not sure how much should be squirting while turning over. It is about 5 drops per rev., should it be a stream? Also with the fule pump output line remove and squeezing the primer bulb gas squirts past the fuel pump so wouldn't that get pressure to the carbs right off the start no matter if the fuel pump is working or not?

Black, You need to choke the crap out of it, when first starting. Cold start lever all the way up, hold the choke button down and crank it until she starts.
If you choke is working, and she still won't start, you might check your compression. Low compression engines are real hard to start.

The comp. is around 115 on all 4. The choke restricts air flow at the intake, but there seems to be no cold start lever, what does it activate?

thanks for the replies.

 

[cannonford57]

Re: thunderbolt 850 runs great but won't start iteself

has it been sitting for a while?

 

[Chris1956]

Re: thunderbolt 850 runs great but won't start iteself

MerControls have a small cold start lever next to the choke button. It must be up for initial start of the day. Non merControls usually have a "throttle" only button where the throttle arm meets the body of the control. Push it in and advance the throttle 1" - 2" when cold starting.

 

[Wingedwheel]

Re: thunderbolt 850 runs great but won't start iteself

When was the last time the carbs were serviced?