Throttle linkage dismay

So I put a pair of Weber 32/36 DGV carburetors on my engine in my '82 280zx. Replaced the stock engine with another L28E out of a '78 280z after the old one gave out on me with horrific rod knock. I was having issues with the EFI system so I decided to just go carb'd since I had a source for them for very cheap. Right now though, I'm trying to figure out a reliable throttle linkage setup.

I went to my local junkyard today to try and go pick around the yard (I brought tools and cash) but got a big fat NO (insurance reasons they said)

Any suggestions for what to do next? I was previously trying to do a wire setup but after a bit more reading, a hard linkage looks much more reliable. Trying to figure out a bellcrank setup, get all the angles right and not have the linkages contact stuff is a bit of a challenge.

I got a bit more than I bargained for as this is my first car but it's required me to learn more than any reliable modern car would ever have! You can never go wrong with learning more about anything

I've run dual DGV's before and found that a linkage similar to these is the best way to go:

Another option would be to extend your throttle shafts and use some MG SU carb linkage connectors as shown in the picture below.

With this setup, it's important that the throttle linkage is actuated from in between the carburetors. If you pull on the end of the linkage it will have enough twist to knock the synchronising out of whack.

Shawn

Thank you this helps tons!!!

Find some old Mercedes. They have all the ball and socket joints you should need to rig something up.

Having rigged up/modified a dual carb linkage for a couple of engines that didn't have it (a dual SU converted Spit and a kludged Spit6 conversion w/ Z-S's), be aware of leverage ratios and how the leverage can change as it pulls the linkage.

On the Spit, I had to play with lever lengths and how the cable pulled the linkage in order to get 100% throttle when the pedal was floored. The linkage that came with the carbs would only net ~50% throttle with the pedal on the floor. When I first installed the carbs, we were thinking, "damn... this engine has less power than the single Z-S..."

On the Spit6, the leverage was all whacky, which made the throttle hard to hold at cruising throttle positions. It had a rising rate up until about 40% and then a falling rate to WOT. It made stop-and-go traffic fun... It was a linkage throttle carb set-up from an early GT6 in a cable throttle car (78 Spit). Fortunately, all it took to fix was repositioning one of the levers and extending a ball-socket rod. This changed the leverage to a more linear rate over the full sweep and made the car infinitely more pleasant to drive.

Cool_Hand_Luke wrote: ... I was previously trying to do a wire setup but after a bit more reading, a hard linkage looks much more reliable. ...

Sure, because the millions and millions of motorcycles designed and built never did get that bit right.

Bell cranks and such have inherent flaws and weakness:
What happens when the motor shifts on the rubber mounts?
Throttle opening vs pedal movement is inherently non-linear.
Every mechanical joint is another source of play, of failure, of adjustment.
Multi throat actuation is problematic.

In reply to erohslc:

Agreed. (I missed that in the OP). I would 100% go with a cable and keep the mechanical linkage to a minimum. Changing direction with a cable is easy. With linkage it's a PITA and requires a fair amount of underhood space. Plus, every joint is a potential point of wear and play.

Funny, my motorcycles use a mechanical bellcrank system to connect both carbs.

So does every factory automotive multi-carb system I've ever worked on.

Not saying cables won't work, just synching them up might be a bit harder.

Shawn

In reply to Ian F:

If you're using a cable to actuate the linkage, weber makes a handy little piece that looks like this:

It helps the cable pull to stay consistent which you can't get with a lever.

Unfortunately, it doesn't help much if the leverage problem is elsewhere in the linkage

In reply to Trans_Maro:

That's not what I'm talking about. Or erohslc, I think. I'm referring to how the throttle pedal pulls a cable, which then actuates linkage to work the carbs. Same as a motorcycle. It's getting that interface to work correctly that can be fiddly. Not sure what you are talking about.

That cam would be fine in a single carb install, but as mentioned, not so much in a multi install - unless maybe the throttle pulls a split-cable similar to how the choke cable works in my GT6...

Why can't that cam be used to actuate the middle of a dual-carb linkage with a cable. Like a lot of British cars already do with a lever.

I don't get where all the hand-wringing about wear in a mechanical linkage is coming from, it worked fine for the OEMs for a long time.

Sure, there's wear the linkage in an E-type Jag but it's also 40 years old. Is the O.P.'s car really going to be around long enough to wear out a heim joint or ballstud in the throttle linkage? Really?

Wouldn't it be easier to just fix the EFI at this point?

I've run dual DCOEs for almost 20 years with the socket & ball arrangement with no problems - it's a solid system, and pretty reliable once you get it dialed in. That said, if I was doing it from scratch I'd use the Weber version of that SU setup pictured above - single pull with the ability to sync the carbs individually. The Weber linkage kits can be seen here: http://www.piercemanifolds.com/category_s/223.htm . I don't know if the DCOE kits can be adapted to DGVs, but Pierce should be able to tell you what your options are.

In reply to Trans_Maro:

I'm not talking about the berking linkage between the carbs... good grief... nevermind...

In reply to Ian F:

Then quote the bit you were posting about and stop having a hissy fit.

Trans_Maro wrote: Funny, my motorcycles use a mechanical bellcrank system to connect both carbs. So does every factory automotive multi-carb system I've ever worked on. Not saying cables won't work, just synching them up might be a bit harder. Shawn

A 4-1 cable assembly, one cable to each carb (or throttle body), the threaded ferrule that the sheath fits into makes synching childs play.

Freed from the tyranny of mechanical linkages, you could even point the carbs in different directions (throwing gang signs:), or mount them in something other than a straight line, for packaging/clearance issues (a diamond shape, two high, two low).

I didn't know they made a 4-1 cable, I've seen the british twin ones before.

The two carbs on my CX650E are splayed with a goldbergian mechanical linkage between the two of them that links them together.

The linkage uses four ballstuds and a double-sided cam for the push/pull cables and looks like an engineers nightmare but is pretty easy to deal with.

Ian, help me out here, I get that you're using a cable but was your pull problem at the carb end or the pedal. I'm not trying to be a jackass, I just don't understand what you're getting at.

Shawn

bgkast wrote: Find some old Mercedes. They have all the ball and socket joints you should need to rig something up.

No kidding. I was under the hood of a 1972 280 last week and I found throttle linkage parts all over the engine bay. "Why does it go over THERE?"

Keith Tanner wrote:

bgkast wrote: Find some old Mercedes. They have all the ball and socket joints you should need to rig something up.

No kidding. I was under the hood of a 1972 280 last week and I found throttle linkage parts all over the engine bay. "Why does it go over THERE?"

It's certianly not the most pleasant situation. After fiddling around tonight with it, I realized I may have issues with it contacting the air cleaners

To clarify, the 280 I was fooling around with was a Mercedes. I don't know nothing about Datsun

Trans_Maro wrote: I didn't know they made a 4-1 cable, I've seen the british twin ones before. ...

I just sent a link to 4-1 a couple of weeks ago, can't find it.

Can make your own:
http://www.power-barn.com/servlet/the-1147/Cable-Splitter-2-into/Detail
http://www.power-barn.com/servlet/the-2004/Cable-Splitter-4-into/Detail

Trans_Maro wrote: In reply to Ian F: If you're using a cable to actuate the linkage, weber makes a handy little piece that looks like this: It helps the cable pull to stay consistent which you can't get with a lever. Unfortunately, it doesn't help much if the leverage problem is elsewhere in the linkage

Ooh, nice, got a part number (or what donor carb I can find it on)?

Trans_Maro wrote: Ian, help me out here, I get that you're using a cable but was your pull problem at the carb end or the pedal. I'm not trying to be a jackass, I just don't understand what you're getting at. Shawn

The pull problem was at the carb. Bearing in mind, I sold the car 4 years ago, so my memory is fuzzy.

First some background:

On a 1500 Spitfire, the pedal pulls a cable with the housing stopping in the top of the firewall next to the brake master. The cable then loops over the valve cover and pulls on a single Z-S carb with a stop bracket on the manifold and a sort of compounding linkage.

The GT6 engine was a MkI out of an early GT6 (my later MkIII GT6 also uses a cable). These early cars used a lever-rod throttle without a cable. Essentially, the pedal moved a leveer attached to a rod that goes across the firewall behind the engine which moves another lever (this is actually all one multi-bend rod) which pulls another rod attached to another bell-crank lever that turns the front-rear motion into up-down motion to work the carb linkage (I'm probably making it sound a lot more complicated than it is). Why did they change it on later cars? Probably for cost and ease of manufacturing: one cable could handle both LHD and RHD cars vs. two totally different pedal to carb set-ups depending on which side the driver sits.

So...

Whoever did the Spit6 conversion took the 1500 cable, swung it around the back of the engine, stopped it on a little bracket they made, and rigged a connection so the cable would function like the GT6 rod. However, they got the leverage wrong so the throttle was a bitch to control at partial openings (you know - where you spend 99% of street driving...). It didn't take much to fix: I cut and re-threaded the rod the cable was attached to and replaced the rod between the carb linkage and the bell-crank with one slightly longer so the way the cable was pulling the bell crank had a more even pull between idle and WOT.

I wish I had time to draw something up and post it, but I really have to get back to work...

Regardless, my experience really isn't meant to convey the benefits of any one way to connect the pedal to the carbs. It really doesn't matter. IMHO, if the pedal is already pulling a cable, it'll be easier to adapt that to work the carb linkage. The guy could have just as easily berked up the connection between an early Spit (which also used a rod-actuated throttle) and the carb linkage to get screwed up leverage.

So I made a bit of progress today

First off, did a little google search and made some phone calls. Found a trailer shop that sold steel super cheap. Got 10 ft of 1/8"x 1" flat bar and 10 ft of 1/4" round bar all for ~$15. I'm pretty stoked.

So after a little head scratching and whatnot I noticed a previous part of the linkage that had two roller bearings I could slide my round bar into. Measured twice, cut a 2 ft length and slid it in. I have a couple of those bellcranks with the ball on the end to attach the linkage socket. Lined some stuff up, tacked one of the bellcranks to the bar. Used a welding electrode to serve as a temporary linkage. Slapped some vice grips on it and she worked! (For the most part)

So my biggest question is where can I find some of those adjustable plastic socket bits and metal balls for the linkage? Junkyard is out of the question currently. I scoured ACE hardware today and couldn't find anything. Are they sold online?

Thanks for the help!!

McMaster-Carr: If they don't have it, you don't need it!

Here and here. There may be better options on their site, but those were the first two happened upon.