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SpeedyMitch
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Joined: 12-17-2009
Location: Hailey, Idaho USA
Posts: 83
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New to me JH 12827 (73 Mk 1) was running 'just fine' last May according to the PO. For me it starts and idles as normal, but only for several seconds (about 10-30 seconds). When time is up the motor just stops. It seems that if I keep the revs up it will run longer, sometimes.

Suspecting the original SU fuel pump I replaced it with a simple Carter 2-4 PSI unit from Napa and inspected the fuel filter (located in the trunk, after the SU pump, and oriented in the 'wrong' direction). The filter was clean but I replaced it anyway. The new pump does not seem to have made a difference.

Currently, there is no filter between the fuel line and the dreaded, soon-to-be-replaced, plastic 'T' between the carbs.

Next I inspected and removed the carb dash pots. The diaphragm for the forward carb has some small wrinkles that have split while the rear carb's diaphragm looks OK.

I'm guessing it is time to order the ZS rebuild kit? While I'm at it, what other tools, parts, fittings, etc should I order? Does the rebuild kit have decent instructions or is there another manual that would be beneficial?

Thanks in advance for any help, guidance, or advice,

Speedy Mitch

Judson Manning
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Joined: 03-14-2005
Location: Atlanta, Georgia USA
Posts: 406
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Sounds like a fairly typical issue. Floats may be stuck and/or gross-jets may be clogged w varnish, etc. A full rebuild may not be necessary, but a good soaking in carb cleaner probably is.

SpeedyMitch
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Joined: 12-17-2009
Location: Hailey, Idaho USA
Posts: 83
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SpeedyMitch wrote: New to me JH 12827 (73 Mk 1) was running 'just fine' last May according to the PO. For me it starts and idles as normal, but only for several seconds (about 10-30 seconds). When time is up the motor just stops. It seems that if I keep the revs up it will run longer, sometimes.

I have found the source of this problem. Turns out there is a short or faulty circuit in the ignition switch. If I keep just a bit of pressure on the key after starting the JH runs fine. I squirted a bit of contact cleaner into the lock and that seems to have helped, but not solved, the problem.

How do you remove the cowling around the lock to inspect it? It seems that I would have to take the steering wheel off first???

Thanks in advance,

Speedy Mitch

 

Jensen Healey
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Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 976
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Hi Mitch,

90% of carburetor problems...

My cowl seems to have been cut to allow easy removal after the steering wheel is off.  I have no idea what the original looks like.



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