Angler Don
Cadet
- Joined
- Jul 21, 2004
- Messages
- 13
Hi all. Been fiddling with this for 2 seasons now. 2000 40hp 4 stroke. 3 cyl, 3 carb.<br />OG993964 Bigfoot. Has a miss at idle. At idle only. One cylinder begins 'dropping out' slowly, and gradually gets worse, until it has one last solid misfire, a shake of the motor, then smooths out momentarily and begins this cycle all over again. Very repetetive. The whole sequence repeats every 5 - 8 seconds. All day , every day, hot or cold. Get some excessively rich exhaust. Never backfires or pops, though. History : new Mercury fuel line & bulb, fuel filter, oil & filter, 2 sets correct NKG's. Thermostat. Ohmed all 3 coils & wires. Tried 87, 89, 92 octane and non-oxygenated fuel. Tried Seafoam and Mercury Quickleen. Carbs cleaned 3 times. Passages blown out with compressed air, etc. Synchronization is perfect.I did it myself using my own synchronizer. Took to Merc dealer, they did their carb " power purge " cleaning & re-synched the carbs ( which I told them not to change ) Did not help the misfire, but caused other problems. Hard start, bogging, stalling. So I re-synched the carbs, runs well again except for miss at idle. In all other respects, this thing runs like a dream. Tap the key, and it starts right up, accelerates smoothly throughout all RPM ranges, top end good @ 40mph, <br />Dependable, quiet, fuel efficient. Carbs do not have an idle mixture adjustment, they have a fixed idle jet inside the carb. Only one jet size is available, as I understand it. I tend to think there is an idle circuit issue with one of the carbs, I may try a propane enrichment to determine which one, if so. I may end up replacing one of the carbs. Serial number OT17500 and up carbs do have a mixture adjustment. But at $260.00,I want to check with you first. Any recalls, service bulletins or known problems I should check out first ? I think I have covered the basics. Any suggestions are greatly appreciated !<br /> Thanks, <br /> Don 