Pierce manifold/ Mikuni Solex carb linkage

[DKB59]

Has anyone successfully engineered a throttle linkage for this combination? 1600 (stroked), Pierce manifold (Weber type), Mikuni Solex 44 PHH carbs. Pictured is my first attempt using modified original 1600 linkage pieces. The accelerator pedal cable action is too stiff and not easy to gradually increase throttle action. I think the angles of the bell crank are too severe not allowing the carb linkage to pull straight upward. The manifold had to be ground considerably to allow the arm connected to the carb arm ball to clear the manifold. If anyone has figured out this linkage I would appreciate all suggestions!
Thanks
Dave

[Gregs672000]

Not an expert here, but I'm wondering if you need to set it up just like a U20 or similar using a U20 bell crank attached to your main rod to ease the motion of the cable.
https://www.racingbeat.com/RX7-1975-198 ... 16622.html

[Solex68]

Talk to PREMO as I think he has some experience making the Canon linkage and maybe the Pierce manifold linkage work better as well.

[roadstermike]

I made this setup for my stroker years ago. it worked great. One problem with the long rod set up is it has too much flex and mine broke in half, twice. So i made setup. I used parts from the su linkage and some simple fabrication.

[DKB59]

Do you have any photos you can post?

[david premo]

Hi Dave,
I’m on the road right now and will be back next week, and yes I have worked out the linkage issues. I should be able to show you what I’m doing when I get back after Tuesday.
Dave

[DKB59]

Thanks all for your input! Looking forward to Dave Premo’s solution. Roadstermike: your approach is in line with my thinking. The long rod that comes with the Pierce manifold kit is really designed for the end linkage Weber carbs, not the center pull Mikuni setup. I was surprised to see how much it flexed. How did you attach your bell crank assembly to the manifold? And where did you mount your cable arm?

[JT68]

Thanks all for your input! Looking forward to Dave Premo’s solution. Roadstermike: your approach is in line with my thinking. The long rod that comes with the Pierce manifold kit is really designed for the end linkage Weber carbs, not the center pull Mikuni setup. I was surprised to see how much it flexed.

This is pretty much correct. The pierce manifold is a very poor casting and the linkage was never intended for Solexes. That rod assembly does work better with webers, but it's isn't a good design overall and has a number of issues.

Dave is certainly the best solution short term. He can fix you up!

Fortunately for the long term, we are working on a much better R-manifold that will work well with webers, mikunis and efi.

It will definitely cost more than 400$, but you get what you pay for. It will be a much better casting and a complete linkage setup specific to each style carb/body. We should have casting prototypes this year, then build the linkage, then production probably next year.

(We'll make the manifolds available to Dave as well since he is such a big help to the community! )

If anyone wants to try out a functional prototype later this year, give us a shout, we'll see if we can make that happen

[DKB59]

JT,
As we discussed earlier this year, I “acquired” this project with this Pierce manifold so it’s what I’m stuck with currently. I will definitely be interested in your manifold and linkage when you get it developed. If it’s as good as your exhaust that I purchased from you then I know it will be excellent. Looking forward to it!
Dave

[JT68]

Thank you Dave!, I'll post some photos as things get closer

[david premo]

Alright I’m back so I will try and explain all the problems that have to be solved with the manifold. I’ll attach all the pictures at the end of this post and you can look at them carefully.

The first problem is that the manifold was drilled without putting the carbs in alignment and the rear carburetor is mounted at an angle to the front carburetor. This causes the center pull linkage to bind and high idle when the engine warms up. If you run separate linkage for each carburetor then there is no problem, however the carburetors are still not aligned. The insulators that are supplied are also a problem for Mikuni’s as they cause a vacuum leak on each carburetor where they fail to seal to the bores of carburetor. So the way I correct the poor alignment between the front and rear carburetor is I had a plate made that aligns the ports and centers the carburetors. I then drill out the existing holes and put in inserts that convert them to 8m X 1.25 metric threads for studs instead of the 5/16 thread that’s drilled and taped in the manifold.

The throttle linkage and shaft supplied are far too small and flex significantly. My solution here is to use a 10 millimeter shaft that utilizes the stock 1600 cable drum and pull. I also use the stock 1600 cable stand for simplicity and bolt it to a plate I mount using 8 millimeter coupler nuts. I also make thick, 3/4 inch insulators between the manifold and carb’s which helps with the linkage angle. To make mounting easier I use 8 millimeter stainless all thread to make my studs and no worries about plating as they will not rust after I cut them to length and de-burr them. The final thing I do is to use torsional throttle return springs that actuate off the center of each carburetors throttle shaft. 44PHH type 2 carbs used them, and I had them re-produced years ago for my race and roadster customers.

[DKB59]

Great information. A lot to review here. Thanks for posting. Interesting point that the manifold does not align the carburetors. I have been fighting the center pull linkage alignment and high idle when the engine is warmed. Could not figure out why the linkage arm was not fully touching the idle adjustment screw. The thick insulators will also alleviate the interference with the linkage rod and the manifold. Need to digest all this and redesign my approach.

[david premo]

I repair them for others, we can talk about that if you want. I also sell the thick insulators.
Dave

[Gregs672000]

Nice work Dave... wow, what a cluster f...

[david premo]

They didn’t do anybody any favors with this manifold, it’s a very poor design and product.