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q-jet issues

L

leadfoot067

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im having a problem with the power piston in my q-jet....its sticking,sometimes it sticks open and sometimes it wont open at all...its a not very old jet stage 2 q-jet...the piston is clean so is the bore it rides in,ive changed springs to both stiffer and softer,ran some emery cloth in the bore and on the piston..even tried a different piston...still sticking....anybody have this happen? and solve this problem ive run out of ideas on this thing... :confused:
 
You mean the accelerator pump I suspect?

It sounds to me like the accelerator pump shaft is binding on itself. If I'm not mistaken it's two pieces, one slides into the other as it's compressed, that's the only bind point I can think of, either that or the tip that sticks out of the carb is sticking on the hole in the casting itself for some reason. (angled load from the accelerator pump arm?)
 
Installed one way, but sometimes you'll see it installed with the gasket riding the power piston assembly. I'm sure you'd have seen it like that if it were, when you were in there before.

You say it's sticking, is it possible to make it do this with the air horn off just pushing on it, or is it something you know is happening, and when you pull the air horn off you see it?
 
it can happen either way...i also know it does it when its running..i can stick a paper clip down the hole..and watch it move up and down when its working..then ill go for a drive and it will backfire thru the carb cause its stuck(leans out when it doesnt open)..or when it stuck open it will black smoke at idle..in the past ive seen them stick from carbon buildup and stuff..but this carb is close to new...no carbon in there at all,and the passage for vacume that operated the piston is clear....im simply lost as to why it sticks...i took another piston and emery clothed it for a long time...its real small in the piston bore and it still sticks...
 
OK, so how about the little plastic piece that holds the top of the piston assembly in place? No binding on that?

If you remove the needles, does it still stick? (definitely the power piston itself)
 
Jon V

Alcohol content is high in some of todays fuel. (oxygenated fuel for cleaner emissions). The alcohol can cause the rubber seal on the piston to swell. When you take it apart, the alcohol evaporates, the rubber shrinks back, the piston moves without binding. You can tell by the rub marks on the cylinder. Change gas; maybe a new piston has newer better rubber.
 
ok saturday i took the carb apart again..checked the plastic thing,gasket,and everything else...I GIVE UP NOW...selling the jet stage 2 q-jet....
 
Not like it's right next door, but you are welcome to come over to my place and we could play around with it and the multitude of rebuildable Q-jets/parts I've got laying around, see if we can find/fix the problem.
 
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