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Unable to get low speed adjustment correct

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bluemg

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I have a 100-6 with a 3000 block and two HD6 carburators. I can not get it to idel less then 800 rpm's, and thats fully lean and the slow run valve fully closed.
I have rebuild the motor and carbs.
The throttle disc seem to closes fully, but a slight amount of light can be seen around the edges in the closed position.
The choke stop does not activate them.
The Jet assembley is new, it goes to the top of the Jet bearing, which is even with the bottom of the casing.
Using a small hose and blowing into the float chamber passage way when the piston and needle is down, the airway closes.
Same with the slow run valve, when it is screwed down tight no air passes throught it.
The pistons are moving freely, new needles, I have expermented with moving the shoulder of the needle a few 16th further down, making the needle longer, no difference.
The motor starts quickly runs smoothly, it just will not idel down. Making the mixture richer takes only a couple turns, and makes noticable carbon smoke when the motor is reved.
I have adjusted the fuel pressure regulator up and down,
The choke is not activated anywhere. The pistons have a brass pin which is about 1/32 or so from the bottom of the piston, and holds the piston up that little amount from the bottom of the casing, could this be the cause?
I do not believe air is getting through the throttle shafts I looked for an intake leak unsecussfully.
What have I done wrong???????
 
The piston does not need to be all of the way down & the brass bumper which is spring loaded WILL hold it up slightly.

The throttle butterflies SHOULD be completely closed. The slow running valve bypasses the butterflies.

I think you have a vacuum leak somewhere. Could be around the throttle shafts - likely, at the carb mount flanges, at the manifold to head flanges, or via one of the manifold vacuum connections. With the engine idling, spray some carb cleaner on all possible leak locations & look for changes of engine speed.

The only thing you cannot check this way is the butterfly closing. If they will not completely close look for the problem, something binding?

I know you have done much of this, but try it again. With the butterflies fully closed & the slow running valves closed, you should be able to slow the idle to a stop.

BTW, 800 rpm isn't a bad idle speed.
D
 
It's probably not your issue, but when I was trying to set the idle speed on my BJ8 I couldn't get it to tick over smoothly below 800 although (unlike you) I could slow it down. Spent ages convinced it was carburation until after a few days frustration decided to temporarily give up, and move on to looking at the distributor. When I rebuilt the dizzy and lost the play in the cam bush all of a sudden tickover at 500 rpm was possible !
 
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well...here I've been happy with about 1100!

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---Yeah, Dar100, 1000 RPM 0n the Tach is about par for the course. Checking the car Tach against against my Pensky shop analyser comes out to about 800 RPM.---Keoke
 
900-950 for me on my 1960 BT7
 
Thank you all for your comment, My 800 rpms comes from my flee market engion anlyser, does volts, dwell, points and rpms. It seems pretty fast for 800.
Dave I thought about the vacume leak and after checking the carbs, put a gasket on and mounted them direct to the intake, without the heat shild to see if something was leaking. I will try the carb cleaner on the shafts and intake at the block.
The light I was seeing at the butterflys was the thickness of paper around the top and bottom, would that make that much of a difference???
Is there a difference in the diaphram jets of the HD6 carbs and the HD8 carbs? they have a different part number in the catolog? Maybe I got the wrong ones????
Also I started to play with the timing as the battery went dead yesterday, I will experment with that some more.
Thanks everyone......
 
[ QUOTE ]

Is there a difference in the diaphram jets of the HD6 carbs and the HD8 carbs? they have a different part number in the catolog? Maybe I got the wrong ones????

[/ QUOTE ]

Yes they are different sizes and if you ordered HD8's you have the wrong ones.---Keoke
 
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