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Hi Everyone,
I'm having a heck of a time trying to "tune" my carbs (sync and set the jets). I'm curious -- how many flats out from completely in are you all setting your jets?
Mine are currently 20 flats out from completely in -- I suspect this is too rich, but the car seems to run well at this setting.
Some more detail -- I tried the approach of screwing in the jets until the idle gets rough, but I got them all the way in without much change. Screwing them out (richen) didn't seem to have much effect either. I don't have lifting pins, so I haven't been able to try the piston lift test. As a result, I've just been changing the jet settings, going for a test drive, set jets, test drive, set jets... rinse, lather, repeat. That's how I ended up at 20.
Idle also sounds high (1000 RPM?), but I don't have a tach, so I don't know the actual reading. Setting the idle lower results in a rough idle.
FYI, I started down this road because I was getting awful gas mileage (around 15 mpg -- I'm gunning for you, Repairman Jack!!) Also... because I screwed up the jet settings while doing other work...
--
Jerry | www.65brick.blogspot.com |
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The baseline setting for the HS6 is 12 flats (two turns) down from the uppermost position. When tuning, always work towards lean (up) not down. Achieve the leanest setting that does not produce a flat spot on acceleration.
The baseline assumes that the float levels are correct and that the needle and jet orifice are not worn, and that the throttle shafts do not leak air.
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Twenty flats out is a LOT. Before making yourself crazy trying to adjust something that may be too worn to get adjusted you need to check the throttle shafts and manifold for vacuum leakage with a spray of water or carb cleaner and to visually examine your needles and jets--look for scratched or flattened needles and jets that may have an oblong opening now. If all is satisfactory there (or after you've corrected any problem) the next step would be to loosen the carb links and then go to set the idle speed and mixture--twelve flats down is a good starting point and after making your idle speed/balance adjustment the linkage can be tightened. Mixture is always easier to determine if you go from rich to lean. The tendency going the other way is to way overshoot the ideal setting because the motor seems to run better and better until it's way too rich. Going towards leaness, a lean stumble tells you to take it back one notch. You can attain a reasonable alternative to the lift pins by lifting each piston with a screwdriver blade--you'll know it if you get it right.
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I think I'm sitting around 9 flats right now. Mileage improved substantially, but whenever I think I have the problem licked, then something else happens (on the same tank of fuel) to screw it all up. Witness my spark problem discussed in other threads,
Anyway, they say, go out 12 flats (two complete turns) and then move them in or out by 3 flats at a time listening for the engine speed to improve.
If you get no change at all when you adjust the nuts... you might have a needle/jet problem or the dreaded worn throttleshaft... I did find that too high of an idle tended to mask any change. What I thought was 1000 rpms by ear turned out to be about 1500 rpms (My tach was not working properly).
I invested in a $20.00 eqqus tach/dwell to take that variable out of consideration.
Good luck.
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Thanks for all of your advice, folks. I decided to buy a tach as well as a Uni-Syn (which, as it turns out, doesn't seem to be much more accurate than holding a length of hose to my ear), and give the carbs another try today. I also installed piston lifting pins.
After a good two hours of experimentation, I still ended up at 18 flats out on one carb, and 20 on the other. The car drives fine, but these settings appear to be rich, which leads me to believe I have the dreaded throttle shaft wear. I assume there's no fix for that except having them rebushed? (sounds expensive...)
Strangely, on the carb that's 20 turns out, the piston lift test doesn't seem to work -- no matter how rich I set it, the car wants to stall when I lift the piston. Is this a telltale sign of anything?
I ran out of time today, but think I noticed that the piston on the richer carb appears to have a series of notches in it. Travel feels smooth and it drops solidly, but I have noticed a weird hollow knocking sound at idle that sounds suspiciously like aluminum-on-aluminum. I'm going to investigate tomorrow, but this has me really worried.
Thanks!
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The only way to fix the shaft wear is to have the carb. bodies rebushed with new throttle shafts as well. It's not outrageously expensive, and will transform the way the car runs for the better.
I've never thought the lift pin is really necessary. If you push up on it completely, I think it lifts the piston too high for testing leading to a too rich mixture. It just doesn't seem like a well calibrated "tool" to me. I think the test height only around 0.030" additional to the idle height or so. Please correct that if necessary. I'll usually stick something in the carb throat instead. I find that more consistant than just lifting the piston by eye with a screwdriver.
--
Tom - '60 544, '68 220S, '70 145S, '86 745T, '06 Mazda MPV
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Stick your head in front of the radiator and see (listen) if the noise seems to emanate from the front of the engine, say just behind the timing cover (aluminum housing behind the fan) That's where your timing gears live.
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I finally had some time to work on the Amazon last weekend! I thought I'd run some of my thoughts past you all since I'm a shadetree mechanic, and an amateur one at that. (Apologies in advance for the long post.)
I think the "knocking" sound I was hearing was the transmission -- changed the lube in the transmission and diff, and it seems to have gone away. (Fingers crossed.)
re: Carbs -- I discovered that one of my jet needles was bent -- I straightened it out as best I could, and it seems to have helped a lot. I'm guessing I probably have to replace the jets and needles, though, as I imagine a bent needle would introduce a lot of wear in the jet/needle assembly? (I can see some scoring on the needle, but can't tell if the jet is ovalized.)
I'm currently at 14-15 flats out on both carbs now - improved from 18-20. After 1/4 tank of gas, it looks like I'm getting about 20 MPG - much better than the 10-12 MPG I was getting, but still not great! The engine still seems a little weak/low on power when I get to around 60 MPH (takes forever to accelerate from 60 to 65) or on hills (stumbles, drags). If I richen it up to around 17 flats (or pull out the choke) the power comes back, but I can smell strong fueley/exhausty fumes while driving. (Even at 15 flats, I can smell faint fumes, but my shift boot has a hole in it, so maybe that's part of the problem.)
I also tested for vac leaks with carb cleaner as suggested, and discovered that my front carb has a throttle shaft leak while the rear carb is OK. I'm guessing that's why the car seems to exhibit signs of being both too rich and too lean at the same time? For example - the front 2 plugs look good, but the rear two are dark and sooty. (Both carbs were adjusted equally for a while -- so compensating for the throttle shaft leak on the front carb probably richened the rear carb too much?) Might that also explain why the piston lifting test worked on the rear carb but not the front one? And why the carbs generally need to be set rich?
One last question -- I noticed that my front jet needle is longer (by around 1mm or 2mm) than the rear one. Both are stamped ZH, though. Is that normal?
Thanks in advance - I can't tell you how educational the posts here on Brickboard have been.
--
Jerry | www.65brick.blogspot.com |
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