Greg, I found that you are correct that lifting the piston on one carb
makes the engine run on the remaining carb. I guess that is why I have not
been totally happy with the carb adjustments I have made in the past!
Thanks for bringing this up!
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 Sun, 31 Mar 2002, Patrick J. Horne wrote:
> Greg,
>
> I don't recall that the piston lifting tells the state of tune of the
> opposite carb.
>
> As I understand it, raising the piston on one carb will lean out the carb
> that you are raising, which will make the 2 cylinders that run off that
> carb run a bit leaner than they were. If the carb is set correctly the
> engine should speed up a bit, then drop to a speed lower than what it was
> before lifting. If it speeds up and stays high it is running lean and if
> just drops in speed it is running rich. This is from memory, so I guess my
> car needs to have its carbs adjusted in the next couple of days! What
> better Easter present for it could there be!
>
> Now where did I put my bunny ears?
>
> 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, Vicki Burrows wrote:
>
> > 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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>
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