Linkert - LARGE - PUSH - Boomerang Throttle

This Snap-Back throttle linkage has been designed to retrofit to 3 & 4 Bolt Linkert "M" Series carbs with 1/4" throttle shaft and 5/16" mounting bolts commonly used on 1930-1952 Flatheads, 1936-1939 OHV Harleys and some Indians.

It will also fit Schebler DLX carbs with 1/4" throttle shafts, and 5/16" mounting bolts used on very early machines.

It does not fit Schebler HX Carbs, or Linkert DC carbs, I will have kits for them soon.

The LARGE - PUSH version is for throttles that PUSH the wire out at wide open throttle.  this LARGE design is specifically made for those people who DO NOT want the throttle sheath to move during operation.  the other SMALL version of my throttle linkage allow it to move by about an inch. 

The throttle cable must enter from the Timing Side with this product. 

You can order a handful of parts later on to convert it to a PULL throttle if you wish.

No more janky spring setups, no more flex, this thing is SOLID and is designed to look good against the period of the machined to which it will be fitted. 

I supply each linkage assembled to avoid confusion as it consists of a number of parts:

Rear Plate - Mounts behind the manifold, sandwiching the manifold between the rear plate and the carburettor using the stock mounting bolts that should already be on your bike (not supplied)

Lever - Drilled to 6.35mm (1/4") this is a very snug fit on purpose.  You can spread the opening a little if you want but I find there is rarely the need.  what I do is tap it in place with a mall drift, then adjust the butterfly position once installed.  The lever is further clamped in place with am M4x0.7x16mm screw and spring washer.  Only 1/2 to 3/4 of a turn should be required to lock it down.

Sheath Clamp - This is where your cable sheath enters the linkage.  On this LARGE - PUSH version the sheath clamp centrally located atop the Carb through a shouldered nylon washer.  It is held in place with a M1.6x16mm split pin.  The sheath is clamped in place with an M4x0.7x8mm screw and spring washer.

Cable Clamp - This is the component that holds the inner of the throttle cable.  On this LARGE - PUSH version the Cable Clamp clamp is towards the rear of the bike mounted to Lever through a shouldered nylon washer.  It is held in place with a M1.6x16mm split pin.  The sheath is clamped in place with an M4x0.7x8mm screw and spring washer.

Spring Bobbins - On this LARGE - PUSH version the extension spring is "Overslung" between the Rear Plate, and the Lever, on the Front side of the bike.  It is located by the two identical spring bobbins.  Each spring bobbin is held in place through a shouldered nylon washer, and then secured with an M1.6x16mm split pin.

Spring - One 25mm x 0.8mm x 10mm extension spring is supplied with Closed Double English ends to ensure it cannot come off!

Initial prototypes were shipped with 25mm, 30mm, and 35mm springs that were all 0.8mm Wire Diameter, and 10mm Coil O/D.  EVERYONE used the 25mm option so now that is all I ship. 

Throttle feel is subjective, very personal, and is also affected by cable type, length, and condition.  To that end I have made my Bobbins slightly undersized, and cross drilled them to allow you to experiment with rubber bands, 8mm springs (Tight fit), hook end springs etc etc.  This was done so as not to lock you into my preference, but also to allow you multiple options on the road to repairs.

Do not use 12mm diameter springs, they will be too large and could come off.

Carb Spacers (and how they affect spring length)

If you use spacers between your manifold and carb, rather than a gasket then you will need a longer spring.  Add the thickness of your spacer onto the stock 25mm spring length to get you close.  5mm Spacer, means a 30mm spring could be needed.

Mc Master Carr, and Ebay stock a wide variety of springs, this image is a quick filter of what was in stock on 27/04/2025

Installation 

Remove the Carb and Manifold.....your fingers will thank you.

Bolt the rear plate behind the manifold using the stock mounting bolts that should already be on your bike (not supplied), then you  Made from 316L Stainless steel it is built to last.  If you are using a three bolt carb make sure to take some time to ensure the plate is nice and level when tightened.  if it is not level your Idle and Wide Open Throttle (WOT) screws will not align with the Lever correctly. 

Next, Clean up your throttle shaft and remove any burrs, or corrosion. 

Align the lever and press it on the Throttle shaft till the base of the lever meets the carb.  Dont worry about butterfly position (that's not yoga!) untill the lever is pressed into position.  This lever is shipped to be SNUG and I often TAP it onto the shaft with a small pin hammer, in extreme cases I open up the clamping gap with a screw driver while tapping.

Now to set the CLOSED POSITION.  Hold the butterfly closed with your fingers, while adjusting the lever till the spring "Just" starts to open.  You need a very slight amount of spring pressure (where the coils just start to separate).  Camp the lever in place with its M4 screw.....DONT go nuts cowboy! You may need to work on this on the side of the road while you are high so just enough to compress the spring washer so it can do its job.

Now to set the WOT position.  Sight down the carb and set the lever into the WOT position, then wind in the WOT screw so that it prevents any over travel.  Now depending on your carb and your preferences the spring on the screw may be too long, jut trim it to suit with some side cutters.  If you want you can replace with any 5mm I/D spring that holds the screw to your liking.

TWEAK the IDLE.  Let everything go and the Lever should return the butterfly to the closed position.  Add two full turns to the Idle screw so that it adds some extra spring tension.  As with the WOT screw spring, I ship the springs over length so that you can trim to suit to get the the tension just right.

Remount the Carb.

FIT THE SHEATH Insert the Sheath into the Sheath Clamp and tighten the M$ screw so that it holds the sheath but does not hinder cable movement.  Remove any rubber sheath that you need to. If the sheath is too thick the M8 bolt may be too long to allow engagement of the spring washer, move to an M4x6mm screw (supplied) in this scenario.

FIT THE CABLE Insert the inner throttle cable into the Cable Clamp, rotate the throttle to closed, tighten the M4 screw on the cable clamp till it holds the cable in place.  If the Cable is to thick the M8 bolt may be too long to allow engagement of the spring washer, move to an M4x6mm screw (supplied) in this scenario.

Fire up the bike

Set the Idle

Hug your family, tell them you love them, then go for a ride.

Safety and Words of Wisdom

• It is YOUR responsibility to ensure the safe operation of this part and its legality on the roads of your country.  By building a custom bike you take on the responsibility for your work, respect that responsibility and show the next generation how to respect it so they continue the traditions!
• If you are not qualified to work on motorcycles please seen an approved professional to perform the work for you.
• I will not help you tune your carb, seriously! don't even call about that!
• If you loose a part, break a part etc.  I can sell you individual spares.  
• Some slight fettling of the part may be required.  My quality is consistent but the product will ALWAYS vary between production runs....small batch life baby!
• I'm one bloke in a shed, in Australia, with a Wife, Dog, and 9-5 Job.  I'm not a corporation, I'm not rich, and I don't intend to become rich of the backs of you lot so my profit margins are LOW so that you can do cool shit.  Please remember this when dealing with me, lets all work together.