Carb problem

sunshine

sunshine

Senior Member
How can I tell if a pwr. Valve is Bad ., other than a bad idle . Is ther a way to test them . Also is it true if you get a backfire thru the carb .your pwr. Valve is automatically shot . Thank You Sunshine.
 
first of all what carb im assuming its a holley yes the power valve is fairly robust but they do fail with age generally power valve failure will show up as super excessive fuel consumption
 
Thanks Cecil and Aussie . For the help , but I need to know if there is away to test them out of the carb. I am having a problem getting the 39 to ldle and run . I stated with an expert rebuilt carb. It backfired thru the carb.I have tried 3 other carbs. I need to check there pwr. Valves. Thanks Sunshine.
 
Take it out of the carb, Clean t off, put it in your mouth and suck. After you have created a vacuum in the unit, close it off with your tongue. If it sticks, it's good; if it doesn't, it's bad.
 
Hi Bob, I'd suggest contacting a member here who goes by "Charlie ny", aka Charlie Schwendler. He is very knowledgeable on the Holley type carburetors, and a great guy to deal with.
 

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Usually, a problem with the power valve is due to a backfire that damages the diaphragm. The easiest way to diagnose the problem is to replace the valve with a new or known good one.
 
Thanks everyone for your help,After using a vaciuum gauge it's showing a vacuum leak , after checking all of the obvious places I believe it is the valve guides , On a recent overhauled engine Thanks All. BOb.
 
Can you explain the "vacuum leak" a bit more? Not sure that valve guides are likely to be the problem. Loss/low vacuum can be caused by a number of things such as leaking or missing gaskets (don't ask), disconnected, loose or split vacuum hose, incorrect timing and other causes. Have a look at this chart, and it may give you an idea for where to look.


Sorry, the chart is not readable on this post, but google engine vacuum readings, and you should find a chart
 

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The vacuum needle quivers between 10 and 15 at idle I have checked all gaskets and the only two vacuum connections the one I am using for the gauge usally wiper by spraying starter fluid on them . The only change I get is when squirt MMO down the throat of the carb.the engine smooths out temporarily . Thank You. BOB
 
sun,
If it is one my builds send it back of course. Here is where I would address the issues you are having....the MMO

in the carb throat performing a temporary fix tells me that the throttle shaft / base
may be excessively worn. I build a fair number of 94's and came to realize the neg-
ative effect wear in the throttle shaft area can have on these carbs....especially idle
characteristics. OMHO.
Charlie ny
 
sunshine said:
The vacuum needle quivers between 10 and 15 at idle I have checked all gaskets and the only two vacuum connections the one I am using for the gauge usally wiper by spraying starter fluid on them . The only change I get is when squirt MMO down the throat of the carb.the engine smooths out temporarily . Thank You. BOB
Click to expand...


Check out the "Second Chance Garage"


http://www.secondchancegarage.com/public/186.cfm


Look at the vacuum gauge readings that
are displayed there. The depictions there
show the actual movement of the needle
and what it means. This is the best that

I've seen to figure out the problem.
 
Contact CharlieNY as suggested. He also had pv's that he has "massaged" the seats on for a better fit. Great guy, always helpful and will walk you through the problem. Chap
 
Guys,
'sunshine' and I had a nice visit. The carb is one of mine but the issue seems to be
else where. Great guy to talk to, he will update us accordingly.
Charlie ny
 
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