Carb Linkage Install Questions

500LbGorilla · Post by **500LbGorilla** » Sun Jul 30, 2006 8:48 am

That's what I am putting the engine back in. My daughter is tired of pedaling.

Plastermaster · Post by **Plastermaster** » Sun Jul 30, 2006 10:21 am

doc wrote:Nice bike!

doc

That wagon looks like a bad boy too!

Ron

Post by **doc** » Sun Jul 30, 2006 10:22 am

I thought maybe she got a taste for the drags after Dad's recent success.

Here is a pic of the current state of affairs on my end. I think you can see that my threaded rods are not quite vertical. But they're close! Your tip was a big help.

doc

500LbGorilla · Post by **500LbGorilla** » Sun Jul 30, 2006 10:49 am

No problem. Vertical isn't KEY, but it reduces some fluctuations on ratio because of the geometry. Getting the angles the SAME is what is of primary importance. Looks great Scott.

Plastermaster · Post by **Plastermaster** » Mon Jul 31, 2006 1:03 pm

I was looking carefully at the linkage yesterday and noticed that the cross bar is not perpindicular to the carbs due to the offset. Therefore the arms are not going to have the same angle in relation to the carbs. On 3&4 the arm is turned in toward the carb and on 1&2 it turns away from the carb. What this does is make the distance from the top of the downshafts greater on 1-2 than on 3-4. If the downshafts are both vertical they will not be the same angle in relation to the carbs. It is not a matter of the angle being the same looking at the engine from the rear and then again from the side. Really I don't see how it can be made to work perfectly with this "designed in" difference in crossbar angle. Is there something I am not considering with the cross bar?

Ron

500LbGorilla · Post by **500LbGorilla** » Mon Jul 31, 2006 2:11 pm

What you need to do then is look at it from the angle perpendicular to the crossbar. In other words, let's say that your bar is sitting inch further back at the 1/2 side. If the crossbar is, say, 22.5" like the T1, then the angle of the crossbar is roughly 5 degrees. Given that, if you stand back 5 feet from the car to look at it, you need to be about 5 or 6 inches to the left of center of the car looking at the downrods. They should be perceivably straight up and down or perceivably the same angle if you need to have one. If they do not have offset at the brackets where they mount to the carbs, then other angles are automatically ok. If they do, measure the amount that the mount sits back further on the base plate from the other one, and your spacer for that downrod's mount to the throttle arm on the carb needs to be that long.

It may look a little goofy, but remember that the joints are socket joints and they don't really care about that angle as long as the downrods are at the same angles throughout the range, relative to each other, and respecting the need to be at similar angles with the crossbar.. That's what setting the angles of the downrods should do for you. If they have different angles at any given position, then the rate of change (due to the different components of motion) will be different and the carbs will spend some of their time out of synch.

Ephry73 · Post by **Ephry73** » Mon Jul 31, 2006 2:26 pm

Also, the longer the downrod, the "wider" the angle. try to keep the rod lengths as close as possible. It worked fo rme with the crossbar linkage.

One thing that helps is the extenders CB sales for the 3/4 side. This keeps your rods are about the same length.

E

Post by **doc** » Mon Jul 31, 2006 2:37 pm

Gorilla's comment about moving the threaded bars into the vertical position made me realize that the "optimum" position for the top of the vertical bars would be directly above the carb linkage connection. In both axes, front to back and side to side.

Holding that thought, I moved my hex bar arms out as far as I could toward the outside of the hex bar, getting as near to vertical as my setup allows. This was KEY and made everything much better and removed all the "stickiness" at the very beginning of the the throttle throw.

At this point, my threaded bars are at an angle in the side to side aspect, but moving the arms out reduced this angle to, say, 15 degrees or so. The little 1 inch standoff on the 3/4 side carb throttle arm just about accounts for the offset and evens up the side to side angle of the bars.

Now, I can't say that mine are correct, cause my motor is sitting on the bench, but I'd bet a dollar they're close. At closed, both carbs are sitting on the stops. At half throttle, the carbs appear to be, well, at about half throttle. At WOT, both carbs peg the stops at just about the same time.
Like Gorilla says, the heim joints, by definition, take up "system slack".

Seems to me the key elements in mine were:

1. Establishing linkage setup so it operates smoothly.
2. Move hex bar arms outboard to get as near "vertical" a set up as possible.
3. Tighten everything down really solid.

Just as an interesting comparison, my final hex bar length was 18 1/2 inches.

doc

Plastermaster · Post by **Plastermaster** » Mon Jul 31, 2006 2:41 pm

That makes sence about the 5 feet away and 6" to the left. That takes care of one angle. as for the other angle it appears the 1-2 (or is it the 3-4 side, (its not in front of me right now) should have an extention at the thottle lever pointing toward the rear so the downshafts are the same angle as you site down the cross bar. This would need to be something with absolutely no flex so that it does not absorb any movement.

I just scrolled down and saw Ephs post snuck in while I was writing this. I guess tht extention addresses it, but I woner why it isn't standard with the linkage kits.

Ron

Plastermaster · Post by **Plastermaster** » Mon Jul 31, 2006 2:46 pm

Ha! we're all posting at the same time here!

Doc, Youir right about the engione being on the bench. When you fire it up it becomes real obvious if it is out of sync at part throttle. When the engine has no load on it just a hair out of sync make s for very rough running. Its funny there is alot of infor out there on syncing your carbs at idle, but 90 % of the work is getting it right throughout the range with the linkage.

ROn

Ephry73 · Post by **Ephry73** » Mon Jul 31, 2006 3:02 pm

Plaster,

I guess it's extra money, and someone that cares enough about an actual working linkage. Most websites cator to tuning on the side of extra, rather than spot on. Plus, if they can get an extra $9.99 out of you(plus tax and shipping), they will.

CBs crossbar is not bad, add Jakes extensions, and the little extender bars and they get very, very close. I experienced with just adding the extenders on the 3/5 side, but the paly seems off a bit. Now that I don't have Jake's centerpull anymore, I will play more with the crossbar.

E

Plastermaster · Post by **Plastermaster** » Tue Aug 01, 2006 2:08 pm

I played around with my crossbar some more yesterday and got it even better. The fact that the geometry is not the same on both sides due to the offset makes it a bit hard to figure it out, but if you look at it in the 3D it makes it easier. Looking at it from the rear and then from the side, you will never get it the same (without the extender) If you look at each side as a cone with the point at the carb and the base defined by the possible locations of the arms on the cross bar, it opens up possibilities for the side to side location of the arms to compensate for the difference in how far the arms extend away from the carb front to back. Someone better at graphing equations could probably figure it out, but me, I just did it by trial and error. Also I found that any time you take the tops off the carbs, the linkage will be off adjustment when you put them back on due to the play in the mounting.

Ron

Post by **doc** » Tue Aug 01, 2006 3:52 pm

I got the aircleaner bases as part of the linkage kit. What goes on top? Just air cleaner and the top? What holds the top on? Long screws? I have to fit everything under the deck lid of a '63. How tall can the air cleaners be? Gotta order evrything from the air cleaner base up.

doc

Plastermaster · Post by **Plastermaster** » Tue Aug 01, 2006 6:24 pm

the air cleaner bases that anchor the cross bar is what I was refering to as the "top" as far as keeping things in sync. You have to remove those to change venturies of adjust float level. The bases should have 2 long allthreads polking up about 4.5" to allow for a 3.5" air filter element and the top that has 2 holes fore the althread. There are probably other set ups, but I am only faniliar with what I have. AFAIK the bases that come with the crosbar linkage are like I described. Maybe yours do not have the allthread?

Ron

Post by **doc** » Tue Aug 01, 2006 7:06 pm

No allthreads came with mine. Air cleaner bases sit on 4 short studs that screw into carb top. Guess a couple of those get replaced by the allthreads.

3 1/2" is what I thought, but 2 1/2 might have been the right answer. Thought someone would know. Thanks.

doc