Carter YH Vacuum Port?

[frez]

Hi everyone,

I had a good day above and below the car, she is sounding great. I am looking to fine tune the fuel/air mixture on the carb more then just by ear. I have the RPMs at the 850 or so and it sounds fine, but I wanted to hook up a vacuum/pressure gauge and I am not sure if there is a place on this carb to do that. I have the book by Bob Helt, but he makes no mention of using the gauge.

Is there a port on this carb, if so can someone please enlighten me.

thanks

[cnicol]

For the purposes of idle mixture adjustment, you can use the "vacuum" line that goes to the distributor pressure retard. That will provide the needed vacuum signal for peaking idle vacuum. There are no vacuum ports on the YH, though it can be modified to add one (See CORSA Tech Guide for procedure). You don't need to do that for the mixture adjustment procedure though.

[Nickshu]

If you can find someone with an exhaust gas analyzer that would be the best bet for tuning the idle mixture. Above that your best bet is to install a wideband O2 sensor such as the one that comes with the safeguard unit. But yes I have used a vacuum gauge on the pressure retard port in the right cylinder head as Craig suggested.

[notched]

Best bet is to buy a digital wideband gauge. They can be had all over Ebay for under $150 now with the sensor. No need to buy a $500+ system just to get a wideband.

[cnicol]

Re Wideband... I'm going to pushback a little on one of those as a tool for idle mixture adjustment. While it will tell you your AFR, the AFR target for idle conditions isn't a given or known number, in my experience.

On the other hand, peaking the idle vacuum tells you where your particular engine is happiest. In my experience the WBO2 might indicate 12.5 or 13.0 at best idle; not an AFR target I've ever seen published. The best way is to use a 4-gas analyzer but who has one of those laying around?

Idle adjust ment, my order of preference: (in order of result & practicality)
1) Peak vacuum
2) Ear
3) 4-gas
4) WBO2 (last choice)

For cruise and acceleration mixture adjustment
1) WBO2 (cruise & acceleration)
2) Spark Plug (Cruise)
3) G-Meter (acceleration)

[frez]

Ok so I checked the vacumm by pulling the line to the a/r it was low around 15 and shaky. No matter how I dialed the fuel mix and idle. The best I can do is get it to be pretty stable at the 15. When I rev and let go it jumps from 0 to 22 and then back the 15. From what I see on line that say bad rings. Which might make sense with the other symptoms. It start and runs, I can drive it around but it has a rough idle kinda like a sputter I can some times rev the engine and it will stall. And after a hot start which I have to give it some gas to get started it wants to stall. I have to keep revving the engine until I can get it into gear then after I drive down the road the stalling stops but there is hesitation in the acceleration. I have good gas in there. Do I have bad rings if so does that mean the rings on the top of cylindar or the o rings on the lower valves? What do you suggest I try next? Already have new a/r, plugs, wires, distributed cap, electric ignition and coil. Timing looks good; 18 with hose off the a/r 28 with it on.

[cnicol]

14-15" of vacuum is about par for the course on 140 and turbo Corvairs. Bad rings usually present first with excessive crankcase blowby and then finally with blue smoke out the exhaust during acceleration. I don't think your car's issues have anything to do with rings.

It sounds like you fitted a Clarks/Dale advance-retard unit? Most of those installations involve modification of the carburetor for a vacuum port or an electric vacuum cutoff unit to stabilize idle. It sounds to me like your engine needs its carburetor and ignition system straightened out. For purposes of troubleshooting, I would recommend temporarily trying a good points-based turbo distributor with pressure-retard (in other words ALL STOCK) and seeing if the problems go away.

[flat6_musik]

You guys didn't mention adjusting for peak idle RPM....that's how I adjust the mixture. I also make sure that my idle speed hasn't crept up too. If the ideal idle quality is a tad "fat", so be it. As long as my engine's happy and smooth and doesn't have a case of the "nervous shakes".
You might want to do a compression check on your engine, just to see where it stands.

[frez]

Thanks guys. Yes the a/r is the clarks-dale. Funny thing is I got rid of the points and put on an electric ignition and electric choke