67 Mercury Thunderbolt 500 Fuel Problem

[JWomack]

The motor was running fine since launching a week ago, but it recently started dying after idling for a few minutes. It would run fine at full throttle. Next trip it would remain running only while priming with the bulb after the fuel in the carbs was spent.

I changed to a different tank as the old OMC metal tank I was using had a loose connection on the tank end. It seemed to idle fine, so I took it out for a run. It sounded as though the plugs were fouling at low to mid RPMs, but would run fine at high RPMs and now didn't require any more squeezing on the bulb to remain running.

It's also been using an excessive amount of fuel, with quite a bit of unused fuel exiting the exhaust.

I thought to pull the fuel pump and carbs to clean and rebuild them, but I wanted some expert advice here first. Thanks for any help.

Jason

 

[merc850]

Have you set the low speed needles - 1 1/4 turns out then with motor in F and about 1200rpms turn each screw slowly in or out until the motor runs smoothly, rebuild the fuel pump first.

 

[JWomack]

I haven't reset them this year. I will try that first and go ahead and get those rebuild kits ordered. If the diaphragms are bad in the pump, can I get a kit with new ones?

I got this motor last year with the purchase of a 1964 Thompson Sea Coaster and the previous owner bought it at an auction. Judging from the state of the internal wiring harness when I got it, it hasn't seen much maintenance in quite awhile.

So far, new wiring harness, rebuilt water pump and new plugs.

Jason

 

[merc850]

A Mercury dealer should have the fuel pump kit, take your ser. Nr. with you. If not then here http://store.oldmercs.com/category_s/1449.htm

 

[JWomack]

Thanks for the help!

 

[JWomack]

Tried resetting the needles and it was still having the same problems. I pulled the fuel pump and quickly discovered a cracked diaphragm. Found a pump kit here(Ontario, Canada) for 8 bucks. Nice price!

Next, I pulled the carbs and just a bit of varnish build up and gunk in the filters. Floats and needle springs or what have you look good. Asked the local dealer to order a carb kit and I was quoted $103 a piece. Seeing as I have dual carbs this seemed a bit steep. The carb gasket kit was only $13 a piece.

Do needles and filters cost that much to replace?

He couldn't tell me what all it included, but didn't see any floats in the kit. Has anyone here bought a high priced carb kit for their old Merc?

 

[racerone]

The gasket kit should be all you need.

 

[JWomack]

Yeah, just picked up two today. Should have her back in the water in no time. Thanks for everyone's help.

 

[JWomack]

Newly rebuilt pump and clean carbs-runs great now!