Carburetor balancing

[aroostok]

I('m ready to give up. I read all these posts and nobody seems to have any real problems. I don't have any idea what to do now except get the gun and put the B (and me) out of our misery.
I have a 76B that the PO literally gutted, taking the engine primarily back to a 71 or therabouts putting on 2 AUD326 carbs (these have the spring loaded needles). I have had no luck balancing or even adjusting these carburetors at all.
A little info: carburetors were rebuilt using the standard AAE spring needle (Vicky Brit), new float chamber components (all), etc. I have a Crane electronic ignition with which I have been able to set the timing and it remains rock solid at any rpm. With a little bit of coaxing I can get the B started relatively easy but have no success in adjusting or balancing the carburetors.
I have followed the SU manuals setting the jets 2 turns down from the bridge (each jet, in fact, at .084 from bridge) and throttle adjusting (idle) screw set at 1 turn open. No matter what I do, I cannot get the idle less than 1500 rpm adjusting the jet adjusting screws or the idle adjusting.
I have been using a "carb-syn" with no luck. When placed on one carburetor and adjusted, little happens after adjustment. However, other carburetor speed increases significantly when the carb-sync is used and no amount of adjustment makes any change.
There is a monza exhaust on the car.
I have been wondering whether maybe the needles need changed (these are HS4's, by the way) but other than that I'm at wits end. Ready to admit this was a bad investment.
Help, please. I had a 72B years ago and was the greatest thing since sliced bread. /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/confused.gif <font color="red"> </font>

 

[Mickey Richaud]

Hello, Aroostok -

Don't give up - you CAN beat this!

The HS4's are great carbs, but their jet needles need to be centered. If you haven't done that, you're spinning your wheels. Here's a pretty good site on SU's, and you might try Google for others:

https://www.gowerlee.dircon.co.uk/Tips.htm

Hang in there!

 

[Mickey Richaud]

Aroostok -

Check your private message.

Mickey

 

[Dave Russell]

[ QUOTE ]
No matter what I do, I cannot get the idle less than 1500 rpm adjusting the jet adjusting screws or the idle adjusting.

I have been wondering whether maybe the needles need changed (these are HS4's, by the way) but other than that I'm at wits end.

[/ QUOTE ]

The HS carbs have spring biased needles & as such, don't require jet centering.

The fact that you cannot get the idle speed down with normal adjustment would indicate that there is a large air leak somewhere in the intake system. Something not tight, throttle plates not fully closing, or the most likely - The throttle plates should have small spring loaded valve discs (over run valves) in them. If these valves develop leakage, which they frequently do, they let air pass through the closed throttle plates in spite of the plates being closed. The usual remedy is to permanently block these discs closed by soldering or epoxy. "JB Weld" works well.

You should then be able to adjust the idle speed & mixture as required. If by chance this is not the problem, check for vacuum leaks in other areas such as gasket surfaces & throttle shafts.
D

 

[jsneddon]

when you lift the pistons they should drop all the way back down with a nice healthy clunk. If they don't your jets are not centered and/or you've got binding the the dashpot.

Instructions for centering the jet are found on the page listed above. If they are still binding make sure that the piston moves freely in the dashpot cover with them off the car.

The pot and the piston are supposed to be a matched set so don't switch them around. And don't be tempted to sand out the insides of the dashpot with sandpaper.

I had one that the oil tube inside the piston was bent a little and it was binding on the oil cap as it went up and down. I was able to luck out by bending the tube ever-so-slightly back into a "true" position.

You might also get it started and then spray carb cleaner all around the carb, intake manifold, and especially the throttle linkage. If the engine speed increases then you have a vacuum leak and no amount of tuning will fix it until you adress the leak.

Also be sure that the butterflys are closing all the way and centered. With them off the car and shining a flashlight back from the engine side you should not see any light when they are fully closed (and the idle screw set out of the way).

Also there is some confusion regarding the brass washer just below the "lower jet bushing" and above the "gland" as illustrated on the website above. This is not a seal but a shim. When installed the lower jet bushing should just be a hair above the "locknut" so that the lower jet bushing is friction fit against the carb body when installed. If it doesn't stick up above the nut then the whole thing just spins when you turn the mixture nut.

I'm with Mickey - don't give up! They are GREAT carbs and once you get them set up you shouldn't have to fiddle with them for years.

 

[jsneddon]

Ooops. bad timing on the post. I was thinking H6 for some reason.

But the vacuum leak info still stands.

 

[Mickey Richaud]

[ QUOTE ]
The HS carbs have spring biased needles & as such, don't require jet centering.
D

[/ QUOTE ]

Well, I've done it again!

Just looked at the HS4 in your post, and didn't notice you said they had the spring-loaded needles. Earlier HS carbs didn't have them.

I'll go back to my room now!

/ubbthreads/images/graemlins/blush.gif Mickey

 

[beachbumbarry]

I don't know a lot about SU carbs but I know on other carbs If the float, needle and seat isn't adjusted to the proper level it can cause a lot of problems. If there is any forign patricals in the float bowl it can cause problems. Just some ideas you may have missed.
Hope you resolve the problem.
BarryE