New style 4 bbl replacement that has a few miles and some serious backfires on it from the other engine Power valve was good-Checked it already.And I actually replaced it with a new one to be sure Screw the air/fuel screws in all the way and no difference in idle speed or vaccum readings. It idles O.K. but WTF ?? Suggestions? Oldmics
What size carb? What size motor? Lots of people have drilled small holes in the butterflys to combat this issue.
Needle and seat. Remove to see if o-rings have gone away. Use a magnifiying glass to see if the o-rings are nice and round. Mine were whittle down to flush. While bowl is off, check for debris.
4160 series 600 cfm on a fresh .040 over 390 Ford engine. I just found this info http://www.bob2000.com/carb.htm that explains the reasons for drilling holes in the throttle plate. Oldmics
Check the position of the secondary butterflies. Unless they've changed, you have to remove the carb and turn it upside down to access the stop screw that controls how far open the secondaries are when in the closed position. That's been the problem for me whenever I've run into one where the idle screws have no effect. They're designed to pull most of the idle air thru the secondaries, and if they're shut fully then you end up with the primaries open enough at idle to get it off the idle circuit where the screws then have no effect.
Could be a vacuum leak,just helped a friend find this.With the engine running use a propane torch[not lit]and go around the intake,if you don't find the leak inject the gas into the engine and see if the idle changes,if it does,you have an internal leak,usually intake gaskets.I agree with metlmunchr to check the secondary throttle blade settings,you should just barely see the transfer slots,if they are too open it will draw fuel,too closed and it screws up the idle circuits. ROY.
When you say "new style" is it an emissions type carb? The new ones have a reverse-idle adjustment. Screwing them in richens the mix. Counter clockwise is leaner.
I meant it as a new style replacement for the 4150 series. Its not one of the emission carbs. Good point ,however. Oldmics
you are off the idle circuit and on the transition circuit, so screws will not have any affect. Need to lower your idle, and check your timing. as this effects the low speed idle also. If your cam is diffrent from stock, you may need to drill some small holes on the top part of the plate to compensate for the lack of air do to having less vacuum in the engine.
I got ahold of a 600cfm 4160 in recent years that had a bum primary metering plate -was bleeding gas somewhere inside - gasket face or something. Make sure your power valve has the right gasket under it - some are strange due to "foreign influences". Set the idle transfer slot to be a "square" hole when you see it with the carb inverted. If you don't use that throttle blade setting, the transfer doesn't work right and hesitations abound. Fights using the idle mixture screws too. To set idle speed without resorting to the stonehenge method of drilling holes in the primary plates - Holley has this little screw that adjusts the secondary throttle blades (see below). I usually replace the tiny screw with a longer one that sticks down into sight right behind the operating lever for the vacuum secondary. and I turn it with needle nose pliers when adjusting it (I was raised in hill country). Runaway idle can be caused by big wide open PCV passages too - it can be pulling a lot of air out of the engine crankcase and valley - especially if you have some nice big free flowing breathers.
To easily adjust the secondary throttle screw, you can simply take a small pocket screwdriver (like the ones you used to get from service stations) and cut most of the handle off. The result will work with most intake manifolds, dual-plane or single-plane...
If you are turning in the A/F mixture screws and no difference then either the power valve is bad (which you said it isnt) or its the wrong size. To buy the correct PV you need to know engine vacuum at idle becaue it holds it close. I am sure your runnin rich at an idle as a result. Myself, I always plug the power valve and bump the jets up 2.
Ditto. Check with a gauge if you are having issues to make sure you have the right valve. It is usually an issue if the engine has a rough cam and low vacuum.
Some good advice from you all. Thank you ! Now for the next part of the delema. The throttle plates on the secondarys were as closed as possible so I adjusted the secondarys as suggested to slightly show the transfer slots. The primarys were opened too far and the machine was definatly off of the idle circuirt. Now I have adjustment with the A/F screws and smooth 19 inchs of vaccum BUT I cant get the engine to idle below 1100 rpm. Suggestions??? Oldmics
YEAH - Don't worry about adjusting for the transfer slot in the secondary - it just needs to be open enough to do the job. Do you have a PCV valve on there - or a plug on the carb opening for it?
Take out the secondary idle screw and turn it over,then went you want to adj open up the secondaries and turn the screw
Man,thats a chore easier said then done All told the secondary throttle plates needed exact adjustment. So the real question to ask is "How Many Times Do I Hafta Remove the Carb to get the Secondary Throttle Plates Adjusted"??? ANSWER- As many times as it takes. Thanks to everybody who played-She"s runnin like a kitten now.And best of all-I learned somethin. Oldmics
You can flip that sec/adjustment screw and screw it in from the top.... That way, you don't have to remove the carb to adjust it...
I've tried all sorts of schemes to make the secondary stop screw easily adjusted -changed screws and directions and all of that. The itty bitty piece of "all thread" sticking out the bottom worked the best for me. No burned fingers - no special screw driver in the bottom of the box - you can just about find it in the dark......
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