Rochester carbs really getting under my skin...

[bbodie52]

I know it's just as it should be (new pcv valve too, and I've double checked to make sure the orientation is correct), but the best idle I've had so far was with the crankcase vent to the air cleaner plugged. To me that says its too lean at idle since it's under slight vacuum from the pcv.... but the other tests I did dont back that up.... I have to be getting something wrong... Just don't know what at this point.

When you say "new PCV valve too"......you know these cars don't actually have a PCV valve, it's just a pinhole orifice in that metal breather tube. You don't actually have a PCV valve on this car (like from a regular engine) right? If it were my car, I would also start by plugging every single vacuum port (even the crossover) and go from there.

Actually, 1960-1962 Corvairs don't have a PCV system -- just a Road Draft tube extending from the crankcase top cover through the bottom sheet metal cover on the right side.

Left-click on each image with your mouse to enlarge the picture for better viewing...

In 1963, a closed Positive Crankcase Ventilation system was introduced using a tube connecting from the crankcase top cover to both the right air cleaner and to the vacuum balance tube, regulated by a PCV valve. In 1964, the PCV valve and dual air cleaner assemblies were replaced by a single, center mounted air cleaner housing and a PCV tube that utilized a fixed metered orifice in place of the original PCV valve introduced in 1963. HOWEVER, engines with limited clearance above the engine, as in FC vehicles and passenger cars with an Air Conditioner system mounted above the engine retained the low-profile dual air cleaners coupled to a PCV system that continued to utilize a PCV Valve.

[scottydont]

(referring to Brad's suggestion about one idle circuit being clogged) Been down that road. I noticed the other day that the right bank exhaust was weaker than the left (I don't think it was always like that). I didn't pull plugs, but the right carb responds to mixture adjustments fairly well... so the idle circuit seems to be working. I also added propane and determined that bank was lean at the time the exhaust was weak, but in the past it hasn't been... That was several cycles of adjustments ago, so I'm not sure if the change is due to adjustments or something clogging the carb....

Also, in addition to dipping the carb bodies when I did the rebuild, I blew every passage that I could find. None showed any signs of clogging. I'd suspect gunk in the fuel line between the main filter and carbs, but the carbs have the brass filters in place as well so nothing should be getting through....

I'm ready to pull the carbs and tear them down again. Or replace them altogether... For me that's a drastic move, but I have never, ever had this much trouble tuning an engine. If I do go looking for replacements, are there any noteworthy performance, fit, or size differences between different models (IE earlier year, smaller hp carbs) and the '65 110 carbs?

[Augie]

My right carb was not running properly, removed the mixture screw, applied compressed air and bob is your uncle, better idle.... no more stalling

[scottydont]

Well, I'm homing in on things (slowly)...

My vacuum booster has a slow leak. So I disconnected and plugged it. That really didn't change things appreciably. So taking Augie's suggestion, I pulled the idle screws and blew the passages out with a compressor. After resetting the idle mixture I was able to back the idle screws out a bit and get the idle down to around 800. At this point it's starting easier, and idles pretty stable, but if I set to the highest vacuum reading it dies when the throttle snaps closed. If I richen the mixture (turning CCW on the idle screws here. I'm assuming the screws add fuel and not air) it starts to bog when revved, and and while it's better returning to idle, it still dies occasionally if the throttle is snapped closed hard....

Is there an adjustment for the accelerator pumps that might let me tweak things?

Also, what's the normal adjustment range on the idle screws? I live a 7K ft altitude, so the idle mix should be leaner than average, but I'm about 3-4 turns out from the seat on the idle screws. Does that sound right?

Thanks

[davemotohead]

sounds like you need to advance your timing.

[scottydont]

Base timing is 24 BTDC right now. I'm sure I can get away with more due to the altitude but didn't want to get too far beyond stock until I got the engine stable. But if people generally go beyond that at lower altitude, then maybe I should....

[davemotohead]

Did I miss something? is this a 110 or a turbo? base timing for a turbo is 24 BTDC a 110 should be 12-14 to start,look at brads chart above. I just went back and read thru,unless I missed something your timing is way advanced, back it off to about 14 BTDC,turn your idle mixture screws in all the way till the softly stop,then back each one 1 1/2 turns out and give it another shot setting the idle.

[scottydont]

Hmmm.....
I got the timing specs here:http://www.carnut.com/specs/gen/vair60.html. Per the chart, 65 110 base timing is supposed to be 24 BTDC, but other years show the lower advance.... Typo, or year over year difference?

Even with the altitude, 10 degrees beyond stock is a lot. I usually end up bumping timing by 4-5 degrees vs. low altitude.... Luckily its easy enough to change timing and check.

[davemotohead]

Must be a typo, look at all the other specs,only the turbos are 24 deg,turn your timing back to 12-14 and try again

[scottydont]

67 automatic 110's also show the 24 deg on that same chart. This was originally an automatic engine. Not sure if the dizzy for manuals and autos are different, or just the timing spec. Anyway, I backed it down. The change was marginal but seems to be positive.

The last few days Ive got the idle good enough that I could tell that one bank was firing weaker than the other, but the weak bank is changing from side to side (talk about a bizarre symptom!). Every time I think I've found the problem the change is marginal almost to be point that I question whether Im imagining it or not; but they're all adding up. At this point I'm more and more convinced that the remaining issues are related to idle circuit problems.

I've gone through several cycles of either blowing out the idle passages or revving the engine and capping the carbs with the palm of my hand to drive up the vacuum and suck any blockages through. I think that I've got it cleared out at this point, and the engine is finally idling pretty well and not stalling. But the highest vacuum is still at about 3 1/2 turns out on the mixture screws, and the idle speed screws are several turns past the baseline setting from the initial setup. Both of those seem excessive to me. For the sake of comparison, what would a "typical" engine set up at in terms of idle speed and mixture screw adjustments? I know there's a lot of variation, but I'd like to see if I'm in the same ballpark....

Thanks for all the help and support guys.

[bbodie52]

No Corvair initial timing specification in any model year has ever been 24 degrees BTDC, with the exception of the turbocharged 150/180 HP engine (which has a low compression ratio and actually retards the timing under boost). When it doubt, check the factory shop manual and supplements. The chart below comes from the 1965 Corvair Chassis Shop Manual.

1965 Corvair Distributor Specifications

Note that the chart does show some distributors bringing on up to 24-28 degrees full advance, but that is NOT the initial starting point at idle. The full advance figure includes initial plus centrifugal advance.

[scottydont]

I already backed it down so no worries. Right now I'm far more interested in how close to or far off from "normal" the settings that my carbs seem to have settled in at are.

It's still not behaving right. The idle went all to crap again this afternoon. I'm going to have to pull the carbs apart again and probe the idle circuits for blockages. I've run out of other possibilities at this point.

[davemotohead]

Have you looked down the carbs to see if you have and drips like the bowls are overflowing?

[scottydont]

You mean when the engine isn't running right? I've looked down the passages to confirm acc pump operation. Didn't see any drips or signs of dripping then, but I admit it wasn't my primary focus.

I can't look down the carbs with the engine running due to the configuration of the VW engine compartment. I'd end up with my nipples tangled in the belt and I'm just not too keen on that idea.

[scottydont]

Well.... I found the problem, but this really confuses me.

Something caused the fuel in the float bowls to gel. The fuel in the lines is good, no gel upstream of the sintered brass filters. but in the float bowls, and throughout the passages, there were globs of gelled fuel.

This isn't contamination from the tank or lines, and it's not left over varnish. I chem dipped and scrubbed the carbs and blew the lines out before rebuilding them initially. I also drained the tank and lines, changed the filters, and refilled with new gas at the beginning of this whole process. The only thing I can think of is some kind of chemical or microbial action that caused the gel... I've seen this with diesel, but never with gas. At least it explains the crazy shifting symptoms as passages blocked and cleared.

Anyway the carbs are all cleaned up and back on. Hopefully whatever caused the problem is out of the system. Time will tell.

[Swngaxl]

I heard a guy in my club say if you rebuild a carb, run the engine, and let it sit for three months, you will need to tear the carb down and rebuild again. The problem is the gas we get these days, particularly the alcohol gas. For mine, I use gas with no alcohol, very expensive, but seems to help. Not sure if this is what is happening, but maybe some Stabil would help?