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Carb Mystery


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#1 Lauber1 OFFLINE  

Lauber1

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Posted April 13, 2012 - 02:13 AM

I've been working on a model N briggs built in 1946 this week. after getting all the bits and pieces together, i started it and readjusted the setting as normal to get it running right. After running for a while the motor would speed up and slow down every 30 to 40 seconds. At first i thought it was in my head, but i finally put the tach to the shaft and found it was going 2000, then 2500, then back to 2000. I had put it though the carb cleaner bucket as part ofthe rebuild, so i didnt think it was a dirt issue. looked at the throttle shaft to see if i had any extra play, and found that when the engine increased speed neither the gov, or the shaft moved. I was puzzled. Finally i noticed on the back side of the carb there was a spot that was wet with gas. Not enough gas that we had a drip, but just a coating over the metal where the to halves meet. I thought maybe the body was warped, but found that it was the gasket between them that was at fault. Appartently the gasket, an old NOS, one had a little dry rot on the edge and was breaking the vacuum inside the body, letting the engine surge, then slow back down. sometimes its the little things that cause the biggest problems. Hopefully a new gasket will fix it up.

Im posting this because i know others have had issues with surging that people have blamed on things like bad coils, dirt in the carb, misadjusted linkages, and other problems like that. Just because you have installed a new part doesnt mean its a good one, as even new stuff is prone to be defective, and old NOS one are worse.
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#2 HDWildBill OFFLINE  

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Posted April 13, 2012 - 09:42 AM

Your right, sometimes it can be the smallest insignificant part that causes the biggest headache's even if the part is new.




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