Linkage help

Ellis' Bug · Posted: Sat Oct 11, 2008 10:40 am Post subject: Linkage help

I did a search but didn't find what I was looking for. Im trying to adjust the linkage on my 48 dells. I have straigh manifolds and the off set carb tops with hex linkage. When I get both carbs to idle the same, they don't arrive at WOT at the same time. The left carb is completely open while the right carb looks to be about 1/4 inch from the stop. I started sliding the left carb arm down the hex bar........ but I keep remembering that the rods/heim joints should be straight up and down. It's making me crazy.
Any ideas? I have the Dell Superformance book, but it doesn't address teh streaight manifolds with off set carb plates, which i believe are causing this.

Scott Novak · Posted: Sat Oct 11, 2008 9:35 pm Post subject:

There is nothing that requires the linkage arms to be perpendicular.

However, the closer the linkage arms are to being perpendicular, the less effect expansion of the engine will have on the synchronization of the carbs from cold to hot..

CB performance supplies an extension to screw on the the carb arm to compensate for the offset. However, this adds considerable leverage to the carb arm and I have seen carbs arms that failed due to stress fatigue caused by this extension for the linkage rod. I suspect that this extension will also cause other problems with the carb throttle shaft and bearings.

Personally I think that the hexbar linkage is problematic, which is why I sold mine and bought the CSP bellcrank linkage. The bellcrank linkage isn't a perfect design either, but overall I think it's the least problematic of any of the dual carb linkages out there.

I also had Berg fan shroud linkage, which shares some of the same problem as the hexbar linkage when used with straight intake manifolds. However, the Berg linkage was the only linkage that didn't have any problems that needed to be fixed before it was installed. While there were some things about the Berg design that I didn't like, the Berg linkage will work was it was intended right out of the box. You do pay more for Berg parts, but they work!

Also, be absolutely certain that your left and right carb arms are identical, and that the heim joints are mounted the same. CB Performance supplies heim joints that have undersized studs for the holes in the carb arms that they supply with their linkage kits. You might even want to make spacers to center the heim joints studs in the carb arms to make sure that both carb arms have the same effective length.

Scott Novak

Dale M. · Posted: Sun Oct 12, 2008 10:44 am Post subject:

If you have that much difference the problem may be the distance between the throttle shaft to the hole where the heim joint connects on carb arm... You are converting linear motion to rotational motion, if ratio is not correct you will not get same conversion of motion.... The distance between the holes on the carb arms may be the problem.

Its all mechanics, not necessarily a "product" problem...

Dale
_________________
“Fear The Government That Wants To Take Your Guns"
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

Ellis' Bug · Posted: Mon Oct 13, 2008 7:33 am Post subject:

Would it make a difference if I moved the heim connection to the second hole on the carb arm? Because of the straight manifolds, the linkage angle is not the same for both carbs, which (I think) creates different downward motion.......resulting in the carbs not opening at the same rate. Hope I'm making sense.

Ellis' Bug · Posted: Mon Oct 13, 2008 7:40 am Post subject:

Oh yeah, this is a drag only engine, without the fan shroud so the berg linkage won't work. Perhaps I should just be concerned that both carbs are wide open at the same time, and not worry about them being the same at idle.

junior55 · Samba Member Joined: October 01, 2006 Posts: 941

You should be able to get both.. something isn't quite right.
I would stay with it till its good.

Dale M. · Posted: Mon Oct 13, 2008 10:23 am Post subject:

Changing heims to inner hole may not fix the actual problem it will just make it a "different ratio" so your throttle pedal will be come more sensitive to movement....

By changing hole center to center length on carb arm, you can change ratio to get full performance from idle to full throttle .... You may only have to change hole center to center by as little a 1/16 inch.... My take on this is arm on carb that will not go full open is to long (hole center to center) by a very small amount..

There is a old saying "the devil is in the details".... It may take time and patience and some work to get it right, but in end you will be happier with getting it right vs just close (like in horse shoes and hand grenades)...

The more meticulous you are with the small things the better and more reliable car will be...

Dale
_________________
“Fear The Government That Wants To Take Your Guns"
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...


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