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I purchased a 40 hp tiller with power trim electric start. Motor starts fine on first start but runs very rough. Put new plugs and checked for spark, all good there. So I went through and rebuilt both carbs. , still ran rough. Maybe suckling air or bad primer bulb, so I took another fuel tank that I run on another boat that I know is good and still runs rough. If I unhook the fuel line and let it run what's in carbs it runs perfect. It runs rough when fuel line is hooked up , when I disconnected it it runs rough for a few seconds then clears up and runs good threw all throttle positions until the carbs run out of fuel. Hook fuel back up starts up fine but stills runs rough. I'm stumped.
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Did you change/ adjust the idle air mix screws at all? Did you remove them for carb cleaning? Do you know what they are supposed to be set at, by the manual? Check what they (each one, and note what each carb is set at- don't mix up) are set at from lightly closed (do not tighten air mixture screws- can damage seats and screws). Also look at plugs for each cylinder (do not mix up plugs, they can tell a story).
post what you find. When able.
Good luck. -
The plugs are brown like they should be not white or fouled out. For the air mixture screws I didn't mess with them at all when I rebuilt the carbs I didn't see anything in the book that came with motor at where they should be set at.Comment
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There are a couple possibilities I can come up with from your diagnosis.
The fuel connector that you unplug may be leaking air because of a bad oring seal, when plugged together? If you ran the fuel hose directly to the fuel filter (bypassing the connector), you could tell if the connector was causing the idling problems.
Or, because you didn't remove the low speed jets (count the turns in till lightly seated, when removing) during carb cleaning, there may be some slight blockage in those low speed passages affecting low speed flow, of air, or fuel. For example, unplugging fuel hose, might create a restriction of fuel mixing with the amount of air being let in.
Good luck, post back if find anything.Comment
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Ok so I took the gas air screws (which are the ones one the side of the carb with the spring on them?) And cleaned out with carb cleaner were not dirty though. Took the fuel line and hooked it straight to the fuel filter. Neither have fixed it it still runs rough. I think it is something to do with the vro because on first start it smokes really bad and will only run full throttle and is dumping smoke. Then when I unhook fuel line it clears up smoke goes away and runs perfect from idle all the way to full throttle but as soon as you hook the fuel line back up goes back to rough running and smoke.Comment
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Ok. Then you may be right. I don't have the vro, so if you have a manual, can check there. Or, you might be able to post your question to the moderator here. Although, I haven't seen a moderator here helping anyone?
Someone else may have to speak up and help if they know the vro.
Good luck, sorry I couldn't help you more.Comment
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From the beginning of trouble shooting I figured it was something simple. Come to find out the red lever or manual choke on the side of the electric primer solenoid was set to choke so I turn the red lever in line with the solenoid or clockwise to run and she runs perfect now.Comment
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Yea that goes without saying, lol... Have to love those simple fixes.
Thnx for letting us know, you solved it.
Happy boating.Comment
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