6HP Johnson Seahorse – won’t idle

[peter sisa]

Rehabing late dad’s 6R78 sailboat motor. Rebuilt carb, new thermostat, new fuel pump, new coils — good spark. Starts and runs at high-med revs with 1/2 choke all day long. Can’t get to idle speed w/ choke in without choking to a stop. Out of ideas — compression issue perhaps (low vaccum for the fuel pump at low speed)? Have not yet done a compression check (that’s next) as motor seems to run strong and is very clean w/ low hours. Any other ideas? Thanks.

[crosbyman]

idling fuel is fed via the top drip chamber did you inspect /clean that out ?? a side chanel feeds fuel to the top half of the carb it is very important portant to have it clean and a wrong carb gasket can
fitted on the carb would block fuel flow to the top drip chamber by blocking the side channel …

picture shows an older carb but does show the upper drip chamber while you inspect the chamber confirm that the low speed orifice is not blocked or plugged from a broken needle tip
remove the LS needle and run some pressured carb cleaner front to back … it must enter the drip chamber

btw can it idle if you prime the bulb ?… probably not but test it vent open /working on the tank ?

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• This reply was modified 4 years, 1 month ago by crosbyman.
• This reply was modified 4 years, 1 month ago by crosbyman. Reason: type error

[Michael]

Carb idle circuit dirty or you need to adjust needles on carb. Have you done a link and sync?

[frankr]

If it runs, it has enough pressure/vacuum to operate the fuel pump.

[frankr]

???You say it runs at high speed with choke 1/2 way out? It should run too rich with the choke out. Check the high speed orifice plug. It is deep in the hole behind the hex drain plug. It must be absolutely positively CLEAN without a trace of any dirt or varnish in it. But don’t go jamming drills or wires through it. Too big is as bad as too little.

[crosbyman]

make certain you have this gasket …

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[Steve D]

I’ve worked on a couple of those 6’s from the 70s that had similar issues, even after doing all the usual ignition and carb stuff stuff. It turned out to be a bad upper crankshaft seal (too much air into crankcase). Any evidence of oil up under armature plate, points, flywheel?

[peter sisa]

Ran OK last night at high speed w/ choke pushed all the way in — but not at idle

[peter sisa]

Steve D wrote:

I’ve worked on a couple of those 6’s from the 70s that had similar issues, even after doing all the usual ignition and carb stuff stuff. It turned out to be a bad upper crankshaft seal (too much air into crankcase). Any evidence of oil up under armature plate, points, flywheel?

Thanks for all suggestions — I rebuilt carb w/ OEM kit — hope they provided correct gasket. Will continue to noodle away with your suggestions as a guide — and advise. Thanks!

[peter sisa]

What’s a ‘link and synch’ ? — is that the idler cam follower adjustment procedure? Not yet.

[Author]

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