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Getting mixture right for emissions test

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BrandonBJ8

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I'm trying to lean out my car to get it right for my failed emissions test. I've gone a step hotter in the plus and now I am working on the carbs.

It's hard for me to tell where I am when I tune the carbs. Right now, I have the slow run valves turned in all the way and the car is still idling at 1300rpms. However, it's smooth. Is this okay or should I try adjusting it more?

Thanks!
-Brandon
 
Brandon

I got a Gunson Gastester, because I never knew when the mixture was correct. If you want to be "sure" before the emissions test, you need to beg, borrow or steal some sort of gas analyzer to set the mixture.
 
So how much do you think shipping would be on a Gunson Gastester from Wellington, FL to Phoenix, AZ? /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif
 
Hello Brandon, I have HD8 carbs on my BJ7, so here is what I do. To adjust your slow run screw, which is basically your idle mixture control screw, your throttle plates must be "COMPLETELY" closed. This is different than any of the other SU carbs where-by the throttle plates do control idle. The Reason is that on the HD8 carbs the slow-run screw is adjusting a passage that flows a mixture of fuel and air directly off the main jet. So if your throttle plates are not completely closed you will be introducing more air flow and hence more volocity to suck fuel out of the main jet and you won't be able to get an idle. If your throttle plates are not closed, you may have to loosen the throttle shaft interconnection clip between the carbs. do so close both throttle plates and then retighten the clip.
With the plates closed, you may be able to turn completely down the slow-run screws and still have an idle speed at about normal rpms or even alittle higher. This happens on old carbs because they suck air from everywhere. Be that as it may, with the plates closed and the slow run screws turned in, then adjust the jet adjusting screws to get the mixture for each carb where you want it. Turn the jet adjusting screws clockwise to richen a carb and counterclockwise to lean it. Check the mixture by lifting the pin to raise the inner piston, if the engine momentarily increases in speed and returns to normal then the mixture is about right.(although that could be alittle rich for emission testing). If the engine stalls apon lifting the pin the mixture is too lean.
 
[ QUOTE ]
Check the mixture by lifting the pin to raise the inner piston, if the engine momentarily increases in speed and returns to normal then the mixture is about right.(although that could be alittle rich for emission testing). If the engine stalls apon lifting the pin the mixture is too lean.

[/ QUOTE ]

/ubbthreads/images/graemlins/savewave.gif excuse me for interrupting, this is about as clear a description as I've seen for adjusting these carbs...I just want to know, to which "pin" are you referring to, to lift the inner piston?
 
HI Dar100, This little pin is called the "piston lifting pin". If you approach you car from the left hand side reach directly behind the rear carb and just below the bell/body joint you will feel a pin hanging down. A similar one exists on the front carb but is harder to access. If you will lift up on this pin it will lift the piston inside the depression chamber. Should the pin not move up with gentle lifting force it has become crudded up. The pin can be freed by removing the bell, using a bit of carb cleaner on the pin's recess in the carb's body while applying gentle pressure on the bottom of the pin.--Fwiw--Keoke
 
About $10.88 one way. I should warn you that my unit is a bit tricky to use as the hoses fall off at will. You are welcome to borrow it.
 
They sell a paint can opener with a tab sticking out on one end and a loop looking line an old fashion bottle opener on the other (about $.67). It works great for the hard to reach (tight spaceing on a BJ8) pin on the forward carb. It seems important not to push the pin all the way up. I think only 1/8 inch I read somewhere.
Vette, great explaination.
 
[ QUOTE ]
It seems important not to push the pin all the way up. I think only 1/8 inch I read somewhere.
Vette, great explaination.

[/ QUOTE ]
Not quite as easy as it sounds though. There is frequently some slack in the pin (lifter). the pin is spring loaded to the down position, & doesn't start lifting the slide (piston) until after the pin is raised a bit. The 1/8" is from the point of pin to slide contact. If you just lift the pin 1/8", the slide may not lift at all.

Probably a good idea to do the pin lift a few times with the air filter off so that you can watch the slide lift. After doing this a few times, you can feel the additional resistance of the slide return spring when the slide starts to lift.
D
 
/ubbthreads/images/graemlins/iagree.gif w/everyone. The front pin especially hard to work. I use a very small flat screw driver with a 90 degree bend. Get the blade under the pin and pull up. I cheat every way I can when I adjust these carbs because they are so hard to reach. (certainly not a spridget). One of the ways I cheat is to do it with the air cleaners on. That way hopefully I won't have to fuss with the choke cables. If you take the air cleaners off, you can lift the inner slide/piston with your finger down the throat of the carb. Alot easier than the pin. But then you have all the fussing with the air cleaners.
 
[ QUOTE ]
I'm trying to lean out my car to get it right for my failed emissions test.

[/ QUOTE ]

Hi Brandon! /ubbthreads/images/graemlins/thumbsup.gif

I have to deal with rubber bumper MGs all the time and qualify of testing in ILL.

One thing I found a LONG /ubbthreads/images/graemlins/blush.gif time ago that generally makes passing easy (after leaning out carb /ubbthreads/images/graemlins/grin.gif):

Fill your tank with SHELL (ONLY!!!!) and go for a LONG drive. Re-fill and repeat. Re-fill and go DIRECTLY to Test Station. Do NOT allow to sit and idle.When you re-start, rev the heck out of it before sniffer pipe insertation.

"Generally" works!!! /ubbthreads/images/graemlins/angel.gif

I repeat, SHELL ONLY!!!

/ubbthreads/images/graemlins/cheers.gif
Ed (who's Elky just passed doing same thing!! /ubbthreads/images/graemlins/grin.gif)
 
Interesting about Shell. When I had a BMW every dealer and survice person told me to avoid Shell becouse of the carbon build up on the valves or injectors. A Unical dealer friend told me all the fuel was about the same and it was only the additives added that made any difference. What does Shell do for the EPA tests?
Maybe Brian can straighten me out on this. I believe you have a service station in Santa Cruz?
 
" What does Shell do for the EPA tests"? Gets "U" by.---Keoke- /ubbthreads/images/graemlins/grin.gif
 
Vette,
Thanks for your good description. I used it and the owner's manual and the service book today to adjust the carbs. I was surprised to find that the car would actually idle faster with the slow run screws all the way in. I guess that was due to the mixture being extremely rich when I started. In fact, that is why I played with them. The car was running very rich....
After leaning the mixture, the car seemed to run hotter than before . I guess with the mixure extremely rich, it was helping the car run cooler ?
Before I tweak them further, I wanted to ask a question; Does the setting of the slow run screws contribute to the overall fuel mixture when not at an idle ?
Or is it completley out of the picture when not at an idle ?
 
[ QUOTE ]

Before I tweak them further, I wanted to ask a question; Does the setting of the slow run screws contribute to the overall fuel mixture when not at an idle ?
Or is it completley out of the picture when not at an idle ?

[/ QUOTE ]
The idle circuit will supply enough fuel for a correct idle mixture. As the load/speed become greater, the main jet will supply progressively more fuel while the idle circuit continues to supply it's relatively small portion. IE- There will be an engine load window from idle to part throttle where the idle circuit is supplying part of the mixture, but the percentage of the whole that the idle supplies will become progressively less as more throttle is applied.
D
 
Friday is the day that I will be having it tested again. It's running much leaner right now but I will test it using the pin method. I didn't know where it was lcoated so you're descriptions are great!

Ed - I plan to use your method before testing. I'm a bit worried of the excess traffic and the fact that I haven't driven the Healey for longer than 10 minutes in quite a few months. But hopefully it will be okay.

ThomP - If I fail again, I may take you up on that. Thanks!

Thanks everyone!
-Brandon
 
Ed K., I agree with Dave Russells response. The passage way that the slow run screw seats into comes out into the carb venturi or throat on the down stream side of the throttle plate. That passage pulls its mixture from the main venture area downstream of the jet so that what ever mixture is derived from the adjustment of the jet is what is passed thru the idle passageway. Thats why you get the old contraption to run with the throttle plates completely closed. /ubbthreads/images/graemlins/wink.gif The venturi effect and suction from air being pulled down the bore is what draws the fuel out of the idle circuit. As Dave said, as the throttle is openned, the amount needed to come out of the idle passageway is inversely proportional to what is coming thru the main venturi.(i hope you engineers abouts here don't shoot me over this, I'm using some darn big words here.) One thing that is important to remember with HD carbs is that you get the jet adjusted right for leaness/richness and that is what comes thru your idle passage. If your jet is too rich or too lean, then you will be trying to set an idle with the wrong mixture. (other SUs the idle is set by openning the throttle alittle. /ubbthreads/images/graemlins/cheers.gif
 
You're welcome (as long as you only borrow it) :>}
 
Thank you Vette and Dave.
I thought that " might be " the way it was working and now that you both have verified it for me, I think I can go back and tweak both adjustments until I get them right.
I am also starting to believe that these cars want to be adjusted a little on the rich side to keep them running smoothly and also running a little cooler. I really noticed a change in engine heat after leaning the carbs. They had been adjusted way too rich before I started.....
Before I forget, MERRY CHRISTMAS to you and everyone on the BCF !
/ubbthreads/images/graemlins/cheers.gif
 
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