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post #1 of (permalink) Old 08-19-2004, 04:46 AM
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looking for carb help

I recently rebuilt an atc70 carb using a moose utilities division carb kit.

Before the rebuild it ran perfect, started first pull cold (I would pull the string and bump the throttle a few times and she reved like she had just been shut off) . Why did I rebuilt it then? The atc sit for 15 years untouched and figured why not rebuild it, now that its running again.

Here is my problem, now with the first or second pull of the string it will start (with choke off) but the second you hit the gas it dies, pull string again it will start right up but you have to ease into the throttle and eventually it'll let you rev it up.

Another problem, the idle kinda sounds like its missing every once in a while and idles higher than I recall. (I reinstalled the old idle screw and spring and set it back to the stock setting and it still seems to idle higher than it did before.)

If you give it full throttle when riding and let off, every so often it will have a quiet backfire through the exhaust.

One thing I noticed, if riding and your cruising half throttle turn the choke on, it flat dies, I would expect a slow bogging down until it died but this is instantaneous. Probably means nothing just an observation.

I am kinda at this point thinking its too rich. I have reinstalled all the old parts that I replaced with the kit, just to see if I could get it to run as it did before using the old parts..the only exception being I am still running the new main jet and needle, I am sure I set the needle at the same height/notch as the stock one was set at. I even reset the idle screw back to almost one turn out as it was stock, the other screw to the left of the idle screw (unsure of name) was turned all the way in. I installed the old screws and springs to be sure they were as they were stock.

Another thing, when you rev at idle, sometimes, it will run on just a tad bit, instead of more throttle - more rpm, less throttle - less rpm, with less throttle its still at the high rpm just for a second longer than it should be....kinda like its delayed...so I am thinking too much fuel is getting in somewhere.

ONe last thought, when first starting the atc, as previously mentioned it fires right up but you have to ease into the throttle and hope it doesn't die a few times to get it going, one thing I have noticed was during this process it smells very rich but there is no smoke.

I will check the needle and main jet tomorrow, probably lower the needle to lean it out some but feel free to give me ideas and thoughts. Thanks
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post #2 of (permalink) Old 08-22-2004, 12:40 AM
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Re: looking for carb help

Sorry, I have no idea what your problem is, but if you think it's running rich, why haven't you pulled the plug out and checked? [img]images/graemlins/confused.gif[/img]
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post #3 of (permalink) Old 08-22-2004, 07:07 AM
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Re: looking for carb help

Good point, after I was finished asking for assistance, thats exactly what occured to me. I let it idle for 5 minutes or so, pulled the plug and it was black as coal, with a thick coat of dry soot all over it. I reinstalled the old needle and main jet (as well as every other old part) and so far the problems assosiated with the new parts/kit are gone. I tried to rev the atc cold and it would sputter and die, I changed the main jet and needle back to stock parts and started the engine and it reved just fine and drove just fine, this was all in a period of 5 minutes so I am almost 100% sure it was the faulty kit parts. If someone wants to rebuild their atc70 carb then I would recommend they not purchase the moose utilities carb kit, if they need a kit for 78-82, chances are the idle jet and main jet will be useless, being they may be the wrong ones. thanks for the reply
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