I just responded to Jon's earlier message about carbs, then I read this nice
write
up. However, is it not true that when you push up the plunger on the bottom of
the
carb you are actually checking the air/fuel mix on the opposite carb? Pushing
up
the plunger in essence "turns off" that carb, making it run on only the other
carb. That was always my understanding, then again, I run Mikuni's...
Greg Burrows
67 2000
"Patrick J. Horne" wrote:
> Before you adjust the carbs it is best to be sure that the rest of the
> engine is in good shape. Make sure the valves are adjusted correctly, the
> ignition (points, plugs and condenser and timing are correctly set (Points
> and condenser are not on your new distributor. Check the plug wires to be
> sure they are good.
>
> Once you know everything else is correct it is time to adjust the carbs.
>
> Remove the air filter and reach into the throats of the carbs and lift the
> pistons up as high as they will go. Let each one fall and listen for a
> "click" when it reaches the bottom. A "thud" or scraping sound, or the
> piston not dropping all the way means that you need to center the jet.
> This is a time consuming bit of trial and error until they are set
> correctly. I prefer to raise the jet as far as it will go to do this
> adjustment so the fattest part of the needle is as high as possible.
> Record the settings of the mixture so you can set them back where they
> were after you are finished. Loosten the nut above the mixture adjustment
> and lift/release the piston to see if it will drop all the way down. (the
> nut doesn't have to be really loose, just loose enough to allow the jet
> holder to move sideways a little. Tighten the nut and check again. Keep
> doing this until the carb "clicks". Reset the mixture and move to the
> other carb.
>
> The reason that you have very different readings with the unisyn is that
> the throttle butterflies in the two carbs are set differently. Disconnect
> the dumbell linkage from both carbs so that the throttle linkage is
> disconnected from both carbs. Make sure that the cloak linkage is not
> holding one of the carb jets down a bit. Start the car and adjust the idle
> speed adjusts (on the linkage for the butterflies) until the unisyn shows
> the same reading on both carbs. You may have to change the settings on
> both carbs until they are the same and idling at about 700~800 RPM. The
> readings need to be the same with the unisyn adjusted the same for each
> carb. By adjusting the unisyn you are changing the range of the unisyn.
> That should get the carbs in sync at idle.
>
> Next connect the throttle linkage on one carb. The unisyn should still
> show equal readings. Now adjust the dumbell for the other carb so that the
> length of the dumbell matches the location of the ball on the carb
> linkage. Just for fun check the balance again.
>
> Now it is time to set the idle mixture. There is a lift pin on the
> bottom of the carb, just below the throat, I believe on the side
> opposite the float bowl. Use this pin to lift the piston for a
> second or two. If the engine revs up a little, then slows down to a
> bit less than what it was running at idle, it is about right. Try
> the same with the other carb and go back and forth until they are
> the same. Adjust the nut around the jet on the bottom of each jet to make
> mixture admustments.
>
> Open up the setting on the unisyn and have someone rev the engine up to
> about 3000RPM. Check the balance again, it will probably be off by a bit.
> Adjust the dumbell until they match. (The idle balance will probably be
> off a bit, but not much.
>
> Go through the settings again and keep at it until it is running right.
>
> After spending the better part of a day going through all of this it is
> time to take a spin to see how your handwork did. Upon return treat
> youself to a beverage of you choice and relax!
>
> Peace,
> Pat
>
> - Support Habitat for Humanity, A "hand up", not a "hand out" -
>
> Pat Horne, Network Manager, Shop Supervisor, Future planner
> CS Dept, University of Texas, Austin, Tx. 78712 USA
> voice (512)471-9730, fax (512)471-8885, horne@cs.utexas.edu
>
> On Sat, 30 Mar 2002 WisslerJon@aol.com wrote:
>
> > Gary,
> >
> > You were absolutely correct. I was adjusting the damn air mixure screws and
> > not the idle screws. I finally figured out what the hell was going on.
> > Fortunately for me, a neighbor who restores old Mercedes stopped by and told
> > me I had to adjust the Unisyn to get a reading (as you said) and voila !!
> > Now the only problem is no matter what I do I can't get both carbs to get
>the
> > same reading. The rear carb, when covered by the Unisyn, causes the motor
>to
> > stumble a bit. I have the air mixture screw baily opened on that one. The
> > front carb barely gets a reading practically no matter what the heck I do.
>I
> > have it opened SEVERAL turns. Does this mean that my carbs are essentially
> > toast do you think? Despite the fact I probably have the SU's nowhere near
> > tuned, I went out for a test spin and WWWWWWWOOOOOOOOOWWWWWW !!!!! The car
> > absolutely hums !! No more stall at low RPM's, and if I punch the throttle
> > there is INSTANT response. Major improvement. Thanks again for such a fine
> > product, the excellent instructions, and the follow up advice. The wife and
> > I will heading out to dinner in the sunset tonight and I may be scaring the
> > hell out of here with my driving.
> >
> > 69 2000 (With the most excellent Gary Boone EI dizzy)
> > 69 510 Wagon L20B (With the dash removed waiting for a dash clock)
> > 69 Chev C10 4x4 307 2bl (HEI, Edlebrock manifold and carb waiting in the
> > garage)
> >
> > (I think I have too many things going at once !!!)
> > NOWROC
> > Troutdale, OR
> >
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