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Holley carb vacuum leak at secondary shaft

21K views 8 replies 4 participants last post by  elano 
#1 ·
My friend's engine started acting up yesterday surging and basically acting like a vacuum leak. We've found a vacuum leak on the driver side of the secondary throttle shaft. The engine idles up when we spray it with carb cleaner.

Should he start looking for a NEW base plate or should we try to replace the plastic bushings on the shaft?
 
#4 ·
elano said:
I have the little white teflon bushing/bearings they give you in the rebuild kit, does anyone know if this will solve the problem? I havn't taken throttle shaft/butterfly assembly apart yet.
Maybe it will, maybe it won't depending on how bad things might be worn at that point. Be advised that there is never a vacuum tight seal at this point, all carbs leak a small amount around every shaft, and this is accounted for in the basic metering configuration of the carb. I would be looking somewhere else for the problem, especially if it just "showed up" out of nowhere.

Could be that the carb base gasket just happens to be leaking directly below the shaft??

The usual symptom associated with worn shaft bores is that the idle won't return to the same speed setting after each time the throttle is moved. Surging is something else.
 
#5 ·
Car was running like total crap. It had a crappy idle. It would stumble when you gave it any gas at all, It would shut off if you let off the gas on a hard acceleration, it would surge at low speeds, it would barely limp around on the road. Happened soon after I checked neadle and seats and found dirt in them.

I sprayed carb cleaner everywhere, already replaced the carb to manifold gasket. The only place that made it idle higher when sprayed was the secondary shaft.

The engine would also die when he stopped at a red light unless he put it in neutral. I was able to get the vacuum to go from 15 to 20 by unscrewing the idle neadles out. The one on the same side the leak was on gave the best improvement. I rebuilt this carb about a month ago and weve been having problems with it flooding out of the vents. Since he wasn't running a fuel filter, I pulled out the seats and there was a little dirt in both the primary and secondary. Is it possible that maybe some dirt got inside and is now clogging something up?

I've swapped carburetors and now it runs like a champ, but I need to fix the old carburetor since I just put one of mine on it temporarily.
 
#6 ·
elano said:
I've swapped carburetors and now it runs like a champ, but I need to fix the old carburetor since I just put one of mine on it temporarily.
On all the carbs I've worked on, a 2'ndary shaft leak has not been found to be a problem of such magnitude to cause all the driveability issues you've reported.

I would suggest that you bite the bullet, pull it back apart and re clean it- paying attention to the idle air bleeds, IFR's and the 2'ndary idle circuit as well as the floats/float level/needle and seat assemblies.

Good luck.
 
#7 · (Edited)
If you found dirt inside the carb needle and seat I would automatically expect to have to clean every passage in it. Metering blocks, main body, all of it. Get the fool to put a filter on it or it will happen again :rolleyes: . The fact that you had to move the mixture needles tells you that somehow the amount of fuel flowing past them had become lower, how do you figure that happened :mwink: Maybe clogged with dirt...?
 
#8 ·
ericnova72 said:
If you found dirt inside the carb needle and seat I would automatically expect to have to clean every passage in it. Metering blocks, main body, all of it. Get the fool to put a filter on it or it will happen again :rolleyes: . The fact that you had to move the mixture needles tells you that somehow the amount of fuel flowing past them had become lower, how do you figure that happened :mwink: Maybe clogged with dirt...?
Yeah I think I will pull it back apart. I was thinking that since it was running so lean (vac leak), the needles needed to be turned out a lot to put the mixture where it should be.
 
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