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Desperate4answer plz help!!!!

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Desperate4answer plz help!!!!

Postby KneeDeepInSnow » December 30th, 2001, 10:46 am

hey, i just rebuilt the carb (tillotson (hr?) on my '73 tnt (7* 250single free flow...).
starts easy, runs pretty well although i'm in the stages of adjusting the mixture screws.....

seems to idle ok, but the problem is that when I throttle up it revs up, runs for a second or two, then dies down and then revs back up again...
the only thing that i can see is that its running kinda cool ( I know my snowblower does that when its cool and you back off the choke) but i let it warm long enough i think( 1-4 mins)....

*******just a few things to note********
-when i rebuilt it I uniplugged the fuel line return because it was plugged by i am asumming the previous owner with a paper clip and silicone(orange stuff) and looked like it had been bronzed back together.

-i installed a bulb primer in the fuel line instead of using the original and covered the lead that goes into the flange neck peice with tape..***I THINK IT MAY STILL BE SUCKING IN AIR**

ANY IDEAS?????????

*This Message was edited on 31-Dec-01 10:23 AM by powersports*
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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby Campy4 » December 30th, 2001, 11:42 am

Sounds like you might be right with your guess. When there's enough suction in the fuel line, it begins pulling air in through the primer flange, which causes the engine to die out due to an extremely lean condition. When the revs drop below a certain point, there is not enough suction to pull air through the taped up flange, and it begins to rev up normally again... but then the suction becomes to great, and it pulls air through... thus, the cyclical effect you're describing...

Maybe if you used duct tape?
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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby KneeDeepInSnow » December 30th, 2001, 12:05 pm

tried with the line off.. same thing
tried with finger plugging it...same thing...don't feel suction....
tried with screw plugiing in... same thing

still not sure what it could be.... it's mix still hasn't been adjusted...working on it...kinda hard though when you can't get it revving long enough to adjust it

put 2 filters in when i replaced the line, but i don't think thats the problem(slow fuel movement) because theres plenty of fuel going through the return...


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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby PowDar » December 30th, 2001, 4:35 pm

hmm... that's gotta be the longest title for a post I've ever seen...

Well, lemme give ya what I got. My old lawnmower (ACK!! LAWN BAD!!) used to do the same sorta thing. Rev up. Die. Rev up. Die... etc. I mucked around with fuel lines, and throttle linkage for a couple of days. When I finally decided to put some time and effort into fixing it (hey, it sorta ran! Grass cut = good) I took apart the carb and had a close look at the all the little bits and pieces. Well, what I ended up finding was that the last time I put it together, I must've bent the the little clip that holds the float in its place in the float bowl. This caused it to move erratically. Can't remember exactly, but it would move to far, or stay put when it was supposed to move and since this controls fuel intake, well I'm sure you get the picture.
Well, all I had to do was bend it right (Careful!!!) and now it seems to work better. Still revs up and down a bit when it's cold, but runs smooth as briggs and stratton should after 5 minutes. Hope that idea helps.
----------------------------
I can't think of a good signature so this will have to do for now.
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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby JOHN327 » December 31st, 2001, 12:16 am

KNEEDEEP SPRAY AROUND ENGINE WITH CARB CLEANER IF REVS P/U MAY BE A LEAK IN GASKETS OR CRANKSEALS HOPE IT HELPS YOU
JOHN
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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby JOHN327 » December 31st, 2001, 12:16 am

KNEEDEEP SPRAY AROUND ENGINE WITH CARB CLEANER IF REVS P/U MAY BE A LEAK IN GASKETS OR CRANKSEALS HOPE IT HELPS YOU
JOHN
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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby KneeDeepInSnow » December 31st, 2001, 1:53 am

hey thanx for the sugesstions guys...
anyway i think I know what happened....there is a flange gasket between the engine and the carb and i think it's in bad condithion or i gotta use somthing to seal it... I think thats where its sucking in air....
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Desperate4answer plz help!!!! engine "cycles" revs up when put to wot, dies down, then picks back up

Postby Rotax700x » December 31st, 2001, 3:48 am

Ck that gasket kneedeep, If I remember right, there is a crankcase pulse hole there which accuates the "pump" side of the diaphram stack.
It sounds to me like this is blocked or maybe the low speed circut in the carb is blocked.
Try opening both high & low speed needles 1.5 turns and start from there..................R7
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Desperate4answer plz help!!!!

Postby tuna5 » December 31st, 2001, 7:51 am

is your pulse hole lined up or is it an xternal pulse line?
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