too much gas

[fastgranpaw]

I have a 4412 that is said to have been "reworked", at idle the driver side idle needle works like it should, the passenger side I have run it in till it bottoms out and the idle does not change and gas is pouring out of the venture, would this be a float level problem? jet problem ?(76) . the lowest idle I can get with out dying out is 1300 rpm. thanks for any help.

[racer61]

Sounds like someone drilled out the metering plate too much. Might check the bleed hole size in the butterflys also. If they are too big the idle will never come down.

[jwmbishop]

fuel comes out of the venturi for all circuits EXCEPT idle, transfer and acc pump (idle circuit fuels thru the transfer slot). The fuel comes out of the venturi whenever the air pressure at the air bleed (atmospheric) is higher than the air pressure at the signal port (under the venturi, above the butterfly). If you have more airflow on right side (vacc leak on left of split plenum manifold etc.) - that side will "tip in" to the main and PV circuits faster! You are either A) tipping in due to throttle position and airflow, tipping in due to the rework being not on target for your app or C) tipping in due to mechanical mismatch of parts or failures (Power valve below). Either way you will not get it to run at a lower RPM because its running too rich to get down there with the mains tipped in!

 

Eliminate float probs by running without the sight plug - nothing should come out.

 

Swap jets left to right to check for a bad jet (doubtfull - the jet size should be irrelevent to the point of tip in)

 

A blown power valve can over fuel the main circuit - and irregular signal (pulsy vacc guage reading) can limit the excess to one side. Plug the pwr valve for testing - or at least check the PV you have - also make sure you have enough vacc to hold it closed - a 65 pv needs 6.5 inches, a 75 needs 7.5 etc. Two above is best starting point (if idle vacc is 7.5 - use a 55 pv etc). If I was doing the testing I would use a plug or a 45 just to make sure.

 

Try changing the metering body first - most "reworking" is done to the bleeds, signal ports and passages in the main body. A carb builder I once used taught me to keep as much as of the carb as "off shelf" as possible to make track repairs easier - and the metering body itself is one of those! Thats not to say your builder follows the same theory - compare the metering body to an unaldulterated one and see what differences you have.

 

Give it a controlled vacc leak to allow more air and thus be able to close the throttle more - then check to see if the pass side is still tipping in.

 

If none of the above seem to be it - you have either an overdrilled air bleed (nearly impossible to tell without some seriously expensive tooling), or you are having to open the throttle past the transfer slot to get enough air to run (the sweet spot in the slot is large enough that it should be able to to overcome left to right variation in air bleed pressures).

 

Pull the carb after setting it to the lowest sustainable idle speed with no vacc leak (don't worry about mixture yet) - and look at how much transfer slot is exposed on the manifold side of the butterflies - more than .040 inch and you could be tipping into the main circuit - which could have more signal on one side (especially if the air bleeds are drilled uneven to make a "left turn" carb - which I hardly recommend for anyone not extremely familiar with the circuitry of a carb) - and equal on both sides - if not equal you could have a twisted throttle shaft - one side would be in main circ while other side is still in idle\transfer. If you ARE more than 040 - drill a hole in the front of the butterflies - lined up with the transfer slot. Start with a .080 and step up in .010 increments (the biggest I have ever needed is .125) until you acheive that 040 exposure about at +\- 250 of target idle rpm. The hole allows air to flow in with the butterfly closed further - and forces the transfer slot to do its job. If after this you can not get the idle lean enough - you may have to widen the transfer slot - VERY tricky and best left to someone with a diamond file and holding fixture - I have only had to do this one time with a whole lot of cam on a drag race engine (even after all mods we could not get it to even run under 900 rpm - the air was just to "lazy" to get a good signal to the carb and the vacc was below 8)! If you are at or below .040 transfer slot and at or below .120 air hole in butterfly - and still tipping in - then the "rework" is not conducive to your engine, cam and manifold setup (or is junk with the airbleeds and signal ports not working together).

 

I do not reccomend running with the butterflies you drilled - rather once you know the size of hole - order them predrilled from JEGS or Summit - the machining is more precise and smoother air flow both over and thru the hole will help a lot in transitioning thru circuits (plus you eliminate the possiblity of one hole being larger than the other - or further from the transfer slot - either of which could ALSO be a one side tipping into main circ before the other issue). Just be sure to grind off the exposed threads of the old screws before removeing them - and do not forget to locktite and spike the NEW screws (do not reuse the old ones) - I sent a car to the wall at WOT once when the butterfly dropped just enough to offcenter and hold the thing open. Not fun for driver (or my reputation)!!!!

 

EDIT: here is a link to some well written points on holleys - the circuit description under theory is a very good!

[fastgranpaw]

I took the carb completely apart, cleaned and blew out all holes, reassembled and installed on car, fired it up and same thing, just for kicks a put a timing light on it and found it was a 0 degree. advanced it to 16 and every thing smoothed out, it idles at 950 rpm, but now I have a stumble at fist aceleration. WTH? damn gremlins.

[jwmbishop]

I have a stumble at fist aceleration.

Cool deal (I assumed you had already set ign - in the future remember that most carb problems are not really in the carb - but rather in the ign (which drastically affects the "signals" the carb uses to meter the fuel - get that right - including the advance curve - before you tweak the carb!!!!) - sounds like the lack of timing had you opening the throttle past the transfer to make it idle. Don't know if your typo is FIRST or FAST.

 

Either way I think you now need to tune your power valve and pump shot (usually this is all you need to tune going from one engine to another - unless the cam in the engines are way different).

Power valving is harder to tune than the pump shot - but you need to be close there first - run a vacc guage to where driver can see it and accelerate to avg mean RPM staying out of the range of the valve (ie 55 valve dont let vacc go under 6.0") - check plugs - set your main jets to be right on without the PV tipping in - once mains are set do another run WITH the valve just tipping in (5.0' vacc for a 55 valve etc) and if rich go down a number - if lean go up a number. Once you have good plugs with main and PV just tipping do a run at (WOT) and fine tune with the main jet size (or consider a two stage PV if this requires more than one or two jet size - some guys just plug the PV and run larger mains - I do not). Then its time to fine tune the acc shot.

 

Use only the 50cc acc pump - its easier to take fuel away from the curve than to try to add beyond whats available. Make sure the shot lever is not loose (drag racers let em run loose so that idle rump does not cause an unwanted shot or dribble - circle racers do not hit the throttle from a true idle - they hit it from a high vacc decell and a delay in shot is way more noticeable) - it should just be barely loaded. As a starting point - a good pump shot generally squirts immediatly when the throttle is moved any at all - and a quick idle to WOT (engine NOT running) should produce around 3/4 to full second of squirt. Then start her up and make a few hole shots - if the stumble hits immediatly when you open the throttle (or backfires in carb) give it a larger cam (or larger nozzle) - if it jumps and then stumbles give it longer cam (or smaller nozzle). (acc pump works on both amount of fuel delivered and time of delivery). Acc pump is what tunes you for throttle opening at the apex - a burp of the throttle just before the apex can fix flat spot so its not as critical as the power valve for WOT operation - but when its right all ya gotta do is hit your mark and come down on the throttle at the same rate every lap!

 

This is where a dyno is so sweet!

edit - check to make sure the body has a blow out preventer - when you are looking at the bottom of the carb the BOP is a steel ball set in a hole between and slightly off center from the bores - this will prevent a backfire from blowing out the power valve - and it does not effect operation of the carb!! Holley makes a retro kit for older throtlle plates that do not have em already.