[Cliff R]

Tks.

Couple of minor things to add.

Close to 8 out of 10 "carburetor problems" are part or fully caused by "ignition/timing problems".

When we "modify" carburetors, especially the idle system we are NOT making things richer far as A/F is concerned. 99 times out of 100 the choices made in the engine build REDUCE signal to the carburetor at idle speed. This does two things, It lowers engine vacuum AND the carb is not longer to able enough fuel to the engine via the idle system to make it happy.

We open up IFR's, DCR's, smaller IAB's, more bypass air etc simply so the carbs idle system can now supply enough fuel at the idle mixture screws based on the much lower signal produced at idle speed by the engine.

We do this in conjunction with MORE initial timing which helps burn a leaner mixture and it increases vacuum at the same time.

Doing one without the other very quickly gets the tuner into trouble.

For example, if your engine will NOT idle fully on the idle system, very little if any control with the mixture screws, etc, and opening up th e idle system helps you are most likely providing too much fuel to the engine at this point. What you should have done at the same time was to add initial timing to help the scenario AND went into the carb if/as needed.

Another thing folks get all caught up on is they believe that since they just built a much more powerful engine that you have to run a much richer A/F ratio or starting throwing more jet at it. More times than not (assuming good choices were made during the build for compression, squish, cam events, etc) the engine will need LESS timing and fuel to make it happy.

The other thing WAY too many people still do is to eliminate vacuum advance for street driven engines. It is a load sensing device and does nothing more than add a few degrees at very light engine load so you can use less fuel and effectively make optimum power with a leaner mixture. Only positives come from that deal, and i use VA here on all but the most powerful high compression full "race" engines.

I'll finish with a quick story as to how that works in the real World. A few years back I was hired to do a complete carburetor rebuild/restoration for a 455 Olds W-30. The car had been modified and raced for decades and the owner purchased it and was returning it to "stock". Well dumb-ars me didn't ask enough questions about the build but I was insured compression would be stock and the located a correct Olds W-30 camshaft for the build.

So I finished up the carb and tested it here, absolutely FLAWLESS as it should have been beind a factory "hot-rod" carburetor. I actually put it on my own 455 powering the Ventura at that time and ran the bag off of it, testing it intimately in every single area. I've never tested one that worked any better. So I ship it out and almost immediately the customer calls up bellyaching about it not working well. Says it idles perfectly, full control with the mixture screw and perfect anytime he goes to heavy or full throttl with it. The problem he's having is that it hesitates right off idle at very light engine load and "surges" slightly at cruise, plus "crackling" int he exhaust when he's driving very gently. (All symptoms of being a little lean in that range).

So he sends it back, and once again it's FLAWLESS here, so I call up and ask a few more questions. He insures me the cam was degreed correctly, squish and compression are right, and his initial and total timing are fine. Then I asked him how much vacuum advance is added? Vacuum adance? We (his Olds "guru" engine builder) and himself took that "crap" off WAY back in High School when the first started owning/driving these cars. He said he tossed the POS factory points distributor out and put in an MSD Billet distributor just like ALL the other muscle cars he's owned.

Well, I guess trying to discuss the need and advantages of VA aren't going to appoly here so fattened up a PERFECTLY tuned carb at light part throttle and sent it back. It was too rich and I lost that "clean/crisp" throttle response when tested on my 455, but it solved all the issue and the customer was happy with it.

I have many hundreds of stories just like that one, but at the end of the day what needs to happen is that the customer is happy. I've learned over many years of doing that that I'm simply NOT always able to educated them or help them make things as good as they can be..........but rest assured if/when you hire me to do some work I'm going to ask about your distributor and whether or not you are using VA or not!..........

PS: I did make a few minor spelling errors and one mistake in the previous response. Down where I'm describing how much timing the distributor needs to be set up for it should say:

The cure is simply to modify the mechanical curve for 10 degrees of advance (20 at the crank)