1965 Corsa clone, but a sweeeeeet one

[Gregory_Miller]

I think I have all the fittings I need to plumb engine vacuum to my new MAP sensor. Plug wires may get here as early as today. Need to refresh my understanding of the operation of the SDS-4 ignition system portion. I have tested the crank angle sensor pick-up before, but will re-verify. Looking forward to getting it running on the triple coil pack. I made an angle bracket, need to paint and install to support one corner of the coil pack amd get it installed.

[JohnnyBoomBoom]

Greg, I really like those dual air cleaners. How much do you know about them. Did they come with the car ? Are they Clark’s parts ? If you know, what other modifications are necessary to replace the stock air cleaner ?


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[Gregory_Miller]

They came with my car, but they are the Clark's version. The 140 crankcase ventilation tube was rotated and a hole with a grommet was plumbed into the passenger side air cleaner so crankcase gases are run back through the engine. The only thing I would improve is to move the orifice tap to the other side if the metal tube so that big black vacuum hose could be re-routed less conspicuously. I am tapping into that big black hose with a T to route vacuum to my under-car MAP sensor. I had the incorrect sized fittings (needed 3/8 had 5/16) going into this weekend, that has been corrected. I have some new plugs for my 1999 Nissan, and the old plugs are going to be used for testing the new system, firing the old plugs mounted into a piece of metal plate, grounded to the car so it can run on distributor system while I figure out my new system.

[Gregory_Miller]

Oh, and you either have to notch the rubber hose material they use to connect carb to air cleaner or remove the tabs from the carb tops that the old air cleaner tube clipped to with the J bolts. I went with the latter eventually when I had all 4 carb tops powder coated. The old hose had the notches in it. I bought new hose removed the tabs and had them powder coated then replaced the old hoses with the new. Another thing to note is the thickness of the hose and the clamp can interfere with the operation of the choke linkage/pulloff if you are not careful.

[Gregory_Miller]

Backed the timing off a tiny bit, helps tame the surging under low RPM/high vacuum all in ignition timing situations. Haven't done anything but drive it lately.

[Gregory_Miller]

I had a occasional hot start problem recently, and I think I found the issue being a slightly sticky primary float. I also did some minor adjustments on choke tangs on the throttle attachment so both primaries are open the same amount when on the same fast idle tang. One was clearly not opening as much. I also noted some cracking in my insulators and one actually broke when I attempted to remove it. I had spares for all the things listed above.\
I also unplugged the fuel supply to my secondaries, removed the floats so they don't bounce around in empty bowls, and reinstalled the block-off plates so now they are vacuum tight placeholders while I make sure all is good in my primaries, which do 95% of the work anyway. Removed the secondary actuator linkages and temporarily went back to the stock accelerator linkages while I dial in idle mixture and speed, balance and choke settings. Once I'm totally happy, Roger's gear goes back on. I'll get to finish balancing later this afternoon and test drive after that. I did re-fill the primary bowls and checked for leaks, all that looks good.

[Gregory_Miller]

Balanced the carbs, and now I also have a LOT more fast idle when cold that I did before, when the section of the throttle link that touches the fast idle cam gap was different between primary carbs so only one was really even touching the cam when the chokes were shut. Have turned the choke links down 1 turn to help them open a bit quicker and I might re-gap both of the links a bit smaller gap to reduce the fast idle a bit. Turned down idle speed screws a bit and reduced the idle mixture on both carbs about a half turn since I have no vacuum leaks around my blocked-off secondaries. Car is running great right now, just tweak the fast idle a bit more now that I have more than I need instead of not enough. Good day working on my baby yesterday, and driving it today.

[Gregory_Miller]

I decided to adjust the fast idle a bit and turn the idle mixture screws in a bit more this morning, and drive the car to work to see how it liked the changes. I could tell something was off beyond a possibly slightly lean idle mixture. Had no time to troubleshoot before work, but suspect the "new" float set I grabbed to replace the sticky one has a pinhole in one of the two and it took about 24 hours for it to become apparent. I have a couple more sets so no biggie yet. 30 minutes work should determine if I am correct in my suspicionating, as Tigger would say... I'll get on it after work tonight.

[Gregory_Miller]

The solution was mundane.. when I squeezed the u shaped gap on the primary carb that controls the fast idle to decrease it and lower the fast idle, the upper part moved both down and out, rubbing against and handily removing the lower retaining clip from the throttle link. I was trying to accelerate on one carb. Oops. Easy fix though and glad I ran my fuel pump and checked for venturi drips on the passenger side primary before tearing it down. Once I'm happy with how it's running, idle, balance etc. Roger's linkage goes back on the primaries. I think I'll leave the secondaries as empty vacuum leak free good looking placeholders for now, as I only get into the secondaries, well, not often enough anyway.

[bbodie52]

...I was trying to accelerate on one carb. Oops...

Do you have a Unisyn airflow gauge? My suggestion is to use it to synchronize the primary carburetors using the Unisyn at BOTH idle speed AND at partial throttle. Doing this would reveal a throttle linkage problem like you described.

The Uni-Syn Carburetor Balancing Instrument is a tool that I remember as far back as the 1950s and 1960s. It was designed for use in multi-carburetor automobiles, motorcycles, etc. that were initially common in European vehicles, but were later found in American vehicles like the Corvair.

The Uni-Syn is an airflow gauge that must be calibrated to match the specific engine airflow moving through the carburetor throat. The flow control in the center of the Uni-Syn is mounted on a threaded pin. Rotating the flow control raises or lowers it, which increases/decreases the air gap, which impacts the air velocity passing the oriface that allows some airflow to pass through the gauge. With the Uni-Syn held firmly on the carburetor intake with the engine idling, the flow control is adjusted so that the plastic float is approximately centered in the glass sight tube. Once calibrated, the Uni-Syn can be moved back and forth between the two primary carburetors to compare airflow at idle. The goal is to play with the idle speed screws to get an even airflow level that matches between both carburetors, and at the same time produces the desired idle speed. Before fine-tuning this idle balance with a Uni-Syn, the ignition system, idle speed and idle mixture should have been adjusted following the standard procedures as described in the factory shop manual. The balancing step with the Uni-Syn gauge is added at the end of the tuning procedure to measure actual airflow though both carburetors at idle, and balancing that airflow using the airflow meter as a measuring tool, rather than simply relying on a physical balanced "calibration" using a strip of paper to detect initial contact between the idle speed adjustment screws and the carburetor linkage, followed by counting the screw turns needed to obtain the desired idle speed (and ensuring that the same number of screw turns are applied to each screw). That procedure achieves a fairly close initial setup. The use of the Uni-Syn airflow gauge as a final step ensures balance between the two carburetors by measuring actual airflow.

Once the balanced idle airflow and desired idle speed have been achieved, a similar procedure can be used to synchronize the airflow when the carburetors are held open at a faster engine speed by the throttle linkage. Again, the shop manual procedure can be used to set the initial mechanical balance between the two sides of the throttle linkage. The linkage segment connecting the accelerator pedal to the cross-linkage between the two carburetors is temporarily disconnected, and a turnbuckle is temporarily attached to hold the throttle opened against the pull of the throttle return spring.

The turnbuckle can be adjusted to hold the throttle open at approximately 1500 RPM. The Uni-Syn center flow control is readjusted to re-calibrate the float to a position somewhere in the center travel of the sight tube, based on the increased airflow through the carburetors at the higher steady RPM maintained by the turnbuckle arrangement. As with the idle synchronization procedure, the re-calibrated Uni-Syn is used to measure the airflow moving through the two carburetors. The goal is to fine-tune the threaded portion of the carburetor actuation linkage so that the same airflow reading is attained on each carburetor, but this time with the throttles held open by a pull on the throttle linkage, instead of by the setting of the idle speed screws. When the airflow has been balanced using the throttle linkage adjustment, the balancing procedure has been completed and the normal accelerator pedal throttle linkage can be reconnected.

TIPS & CLARIFICATION...

With the engine at idle, you want to open the Uni-Syn flow control as much as possible, but still keep the float in the sight glass at about mid-level. Then check the other carburetor, which you want to read the same flow rate. You may have to adjust the flow control a few times as you adjust the carburetor settings. Just remember to check each carburetor with the flow control set at the same point, and to keep the sight glass in the vertical to prevent the float from hanging up in the tube.

The wheel in the Uni-Syn venturi controls the flow through the tube, or in other words how high the bead is in the cylinder for a given engine speed. You need enough flow to not strangle the engine, and the bead works just as well in the lower third (which still lets good air flow through). Make sure the idle speed doesn't drop when you place the tool on the carb: if it does, open it up.

Before setting the carbs, make sure that the ignition is right: points and timing set, good wires and plugs. Poor running is often blamed on carbs when in fact it's a weak, retarded spark. Check the throttle shafts: loose ones let in air and lean the mixture, raising idle speed, as well as throw off the linkage action. Check the linkage that connects the carburetors. if it's loose, one will open before the other. Make sure there are no vacuum leaks.



With a twin carburetor set up, disconnect the linkage that connects one carburetor to the other. Set the idle speed with the linkage screws first. Use the Uni-Syn to check that each carburetor is drawing equally at idle. This may take a few tries until you get both drawing equally at the speed you want. Blip the throttle to see if they come back to those settings (worn throttle shafts can fool you). Set the idle mixture screws in accordance with the shop manual instructions. Check the balance again. Hook the linkage back up. If one carburetor now draws more, adjust the linkage until it's back to roughly equal.

Once the carburetors are drawing equally at idle, hold an engine speed: at about 1500 RPM. This checks that the mechanical linkage is pulling equally. You'll need to open up the Uni-Syn center wheel to draw more air and bring the bead down in the tube. If both carburetors are within a bead's thickness of each other, that's good. If one is definitely off from the other, the higher flow carburetor's linkage is being pulled more than the other. You'll need to figure out why that's happening mechanically to rectify it.

[Gregory_Miller]

Yes, I do have the uni-syn and I do check balance both at idle and off-idle. Just didn't open it enough there to spot the clip removal goof. It's all good now. I will return to Roger's linkage now that I have everything working well on the stock linkage.

[Gregory_Miller]

I found that while I was balancing the carbs, as things warmed up more to full operating temperature, the driver's side carb was no longer closing fully. Adjusting that linkage 1 turn then made the car almost stall, so up the idle set screws on both carbs equally till happy. Uni-syn says things are good. I have not gone with the turnbuckle test before but I may when I convert back to Roger's linkage. Might still need to adjust fast idle a bit more, bit it's running really well now.
I plumbed in the hose for the manifold vacuum sensor that is mounted under the rear seat package area above the transaxle. Because the crankcase vent pipe has been rotated to plumb into the passenger side air cleaner, the nipple with the orifice faces out towards the fan, and a big fat sweeping hose attached to the vacuum balance tube. I found a 90 degree fitting to attach to make the big fat hose less "sweeping" across the top of the engine.
NOTE: After I took this picture, I rotated the hoses so the letters on them no longer show.
EDIT: Figured out how to rotate the picture.

[Gregory_Miller]

Haven't posted in some time. Occasionally post on other Corvair forum, but wanted to bring this one back up to date. Been mostly driving my car for the last year occasionally. I needed a torque wrench for my DD Saturn Ion's needed clutch replacement, so I decided to drive the Corvair down to get one. Once the chokes came off, it would not idle. Finally discovered after "suspiscionating" idle circuit problems in one carb, popped off the tops and removed the venturi clusters to discover one fully blocked, and one partially blocked. Had a piece of non-ethanol rated fuel line between engine and body metal fuel lines. Threw it away before cutting into it but thanks to someone on the Facebook Corvair pages mentioning it. Turns out one of them had been plugged for some time, and the other was filling up with gunk until it just wouldn't idle on 3 lean cylinders. I've also had an issue with "bucking" at part-throttle for a very long time that I thought was the price to pay for my "fat cam". Turns out that while it would idle on 3, it won't make power with only 1 idle transition slot passing fuel. Once I put it all back together after cleaning out the crud in the idle siphon tubes and re-adjusting the balance and idle mixtures, it runs SO nice at 2000 RPM and throttles barely cracked on a residential street, for example. Wish I'd figured it out sooner, but better late than never.

[Gregory_Miller]

I went home, checked the oil, washed the cat prints and dust off, and brought it to work. Hot afternoon ahead, but I'll likely survive. Car is running really well now so pretty happy, but:
I might be able to lean it out 1 jet size, it still smells kinda rich. I do have Ray Sedman's WB O2 sensor, just been delaying putting it in until the ignition and carb issues are resolved, and where to put the meter is also been keeping me from pulling the trigger. I have a spot with the port welded in with a dead O2 sensor in it to plug it up in the exhaust just south of where they both join in my big single.
Anyone know if there's an A pillar 1 or 2 gauge replacement that fits a Corvair out there? I'd put it in the A pillar if there's something available that would fit without a lot of work.
So I had both carb issues and a cranky coil (A Bosch not a stock coil, never researched to see if it wanted 12v unballasted...) that I didn't figure out was pretty bad while chasing my tail with multiple issues. Thanks to the Facebook Corvair folks who mentioned non ethanol fuel line as a likely culprit clogging my idle siphon tubes once again.

[Gregory_Miller]

Looking good today.

[doug6423]

Looks good!


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