rongold

Hi guys,

My 67 427/435 is running so rich, it burns your eyes and stinks you out. It’s basically stock with a faster advance curve, full time vacuum to the vacuum advance can, and about 20 years ago, I increased the jets in the center carb from #64 to #66 (which should only affect the mixture at full throttle). I run about 16 degrees initial advance and there is 24 degrees built into the distributor for a total of 40 degrees at about 3200 RPM + about another 15 degrees of vacuum advance. I looked in the center carb, and the boosters are not dripping. Both mixture screws are between 1.5 and 1.75 turns out, and I can stall the engine by turning either one in, but it does not lean out the idle. The idle is rock steady at 800 RPM, and there is no bogging or flat spots—the car runs great, but it stinks like nothing you’ve ever smelled before.

The end carbs have no dripping either, and are passing a minimum of air when closed as they’re designed to. However, I noticed that in order to idle at 800 RPM, my throttle blades on the center carb are about 50% into the transition slots. If I pull the vacuum advance hose, the idle drops about 200 RPM as I would expect, so there is not too much advance at idle. I can imagine how it would smell if I left the vacuum advance as ported, as I would have to open the throttle even more and expose more of the transition slots.

This problem showed up about 2 years ago. This engine used to idle very clean with a minimum of stink, but now it has become unbearable. How can I keep the idle speed up and close the throttle. I never had to run it with the transition slots exposed---this has only occurred in the last few years. I know the old trick of drilling holes in the throttle plates to flow more air at idle, but I really do not want to do that. Something has changed, but I can't put my finger on it. This car ran great with no stink a few years ago---WHAT HAPPENED ???

Hoping for a solution,

427435

When was the last time you rebuilt the carbs??

mel e foye

Great detail Ron. Rock steady idle, runs great, stinks at idle, gradually getting worse, 50% transition slots open and likes 40 to 55 degrees total init, cent and vac. Old gas stinks real bad but this has been happening over time. B4 I did anything with the carb I would be 100%sure of my initial timing as in a bad timing light or the dampner slipping. Late timing can cause the plates to be opened too much just to get the idle speed up. Fuel stinks because some of it is passing through being unburned.
An easy try would be at idle advance the initial w/o cent or vacumn in play till you reach 800 rpm again and see if you can reduce the throttle opening. Now bring in the vac. adv. and reset to 800 rpm. Repeat as necessary. Remember it takes a little time at idle to clear the unburned gas smell out of the complete exhaust system. If it is the dampner I would not want to drive one of these high-reving bad boys till I got a new dampner.
Don't worry if I am wrong as I have been there b4. Mel

KM1959

Sounds like a blown (ripped, torn, whatever) power valve.

rongold

Well, I took the center carb apart yesterday, and I don't see any problems. The power valve was good, no ripped gaskets, not even any "green goo" from sitting 2 years with the ethanol laced gas. I guess I'll pull the end carbs and look for problems, but there's not much in the end carbs that can go bad. The only thing in the end carbs that can cause rich running is if one of the metering plates has come loose. Meanwhile, I rebuilt the center carb, and will reinstall it over the weekend.

KM1959

Hey Ron, I must've missed the part where you said that you could stall it with the idle mixture screws - that is usually not the case with a blown PV. The drilling of the throttle plates is supposed to help only for big cams so at best that would be a band aid.

Maybe there is something blocking one of the mixture ports internally? It wouldn't hurt it to pull it apart and give it a good soaking. I have a Demon on a 502 that gave me fits until I did that - too much garage time. If I can remember anything else I did I'll pass it on.

rongold

Well, the center carb is rebuilt and reinstalled, and even though I found nothing wrong, it does run much leaner and doesn't stink as bad. I guess I'll leave the end carbs alone for now. The only thing I can think of is that one of the passageways in the main body or metering block was clogged. CONDITION CORRECTED !!!