340/S - no spark

[jdjock]

I’ve got a 340/S with no spark on number 1 cylinder. Recoil side. I’ve tried all the tests in the service textbook with not much results. Tried 2 other cdi boxes; one new and one used with the same result. Tried a new coil but old one tested ok when I switched the wire to the coil. I’m guessing it’s the timing ring/trigger but I don’t have another one to try. Any other suggestions or does anyone have a used one that is good or a new one. I’m frustrated with this one for sure. Seems like I’ll have lots of time to work in my shop.

[Green and Gold]

Doesn't the 340/s use the same prestolite ignition design as the 76-78 Lqui/Cyclones? If so, check out the stator. If you have a multimeter, Scott Hewett has the resistance information on his web page.

[jdjock]

Thanks for the reply, but no they are not the same ignition system. The 295/s and the 340/s systems are unique. Especially the timing ring and cdi. Timing ring cannot be converted to work. The 76-78 sleds are in their own class.

[Green and Gold]

Sorry for the distraction....didn't know if it was just plug/pin configurations that got them a different P/n.

I had a bunch of Sno and Trail twisters along with a few Cyclones. Bought a some new Deere pick up rings for the Cyclones thinking they'd also work on the Mercs. They didn't; the diameter was different. I still have timing ring for a Twister sitting on shelves. I could measure the ID and OD if you'd like to compare it to yours. Merc started using it on their 74 S/T, so maybe?

[HoosierDeereMan]

I'd check the wiring where it goes through the rubber grommet and into the engine case. Might also pull the flywheel and check the wiring to the trigger and stator. It's possible it may have rubbed and is shorting out. Are you sure the stator isn't bad or weak? If it's weak it may not be generating enough juice for the cdi to fire the coil? Those old electrical systems break down after years of heat cycles.

[jdjock]

Green and gold,
The ID and OD are the same as the cyclone. So I assume it would not fit. Thanks anyway.
Troy,
I’m going to pull the flywheel and look things over. Brock Weber mentioned the same ideas also when I talked to him. Stator was new about 5 years ago so probably not that, but will check it out. More thinking a pinched wire like you suggest. Haven’t run it in 2 years because of this problem.

[HoosierDeereMan]

You mention the stator was new about 5 years ago. Was this a 40 year old NOS stator or a rewound stator? I haven't had much luck with the old OEM Prestolite CDI boxes and stators. With age they just don't hold up to the heat and break down. Also are trying to run surface gap spark plugs or the electrode style? Some of the old Prestolite CDI's won't fire a surface gap plug.

[jdjock]

Troy, the stator was an old nos unit but ran good until 2 years ago. I just don’t understand how the system could just quit working while sitting in my shop over the summer. The wires all look good on the stator and trigger. Has anyone tried to use the stator and trigger from a 77 or 78 machine with the round plugs. I have both from a 77 liqufire. The flywheel measures the same on the inside. If one coil fires strong, I don’t think it could be a bad stator could it? I’m not very good on diagnosing electrical issues. Tried both types of spark plugs also.

[harleysportster]

Possible causing of only only one cylinder spark:
Bad spark plug, stop using surface gap plugs
Bad coil-switch with other side, see what happens
Ohm coils, compare to hewtech specs
Bad timing ring, compare to hewtech spec
Plugs,coils,timing ring good-replace cdi with hewtech fireplug.

[harleysportster]

PM for instructions to use a multi meter

[jdjock]

I still haven’t had any good luck with my no spark problem. Tried 3 different timing rings and still no spark on number 1 cylinder. Ordered a Hewtwech cdi and adapter and will try them. I’m hoping that will end my frustration. I’ll post later and hope the news is good

[jdjock]

I finally got to the bottom of the problem. It was the cdi box that was faulty. Or should I say all the cdi boxes I tried, even the so called new one still in original box. Box a Hewtech from Scott and an adapter, spliced in the wires and spark on both cylinders. Luckily I was able to test it before I installed the engine back into the sled. Had to mount the hewtech box in a slightly different place because the two coil wires were two inches short. But it all looks good and runs like it should. Thanks all for the help. Especially Scott at hewtech, who said if it didn’t work I could return it.

[jdjock]

Just a follow up on the 340/S. Glad I took the engine out so I could get to the carburetors. They were somewhat gummed up and needed a good cleaning. Anyone with this sled knows how difficult they are to get out and work on. With he engine removed they are just hanging there on the airbox..Anyhow after cleaning and reinstalling them; ready for the choke cable install, I just happened to flip the choke lever and lo and behold only 1 cable moved. Lucky find there.had to replace and reinstall. All good .