The Best Carburetor Option Yet?

If you’ve read my blog over the years you know how fickle carburetors can be. I’ve tried several options; rebuilding existing ones, buying lightly used ones, buying a new Bing, using a Jetex- you name it I have tried it. In the spirit of trying to get my car to be the best it can be I have tried another option, and I’m happy to report results that are worth passing on.

Here's the carburetor: a 30mm Tiawanese OKO carb made for 250cc quads. I’ve put several hundred miles on one in a variety of conditions and I’ve been pleased with it. This carb solves several issues for me. Installation is not too hard (but not necessarily easy) but well within the reach of anyone who tinkers with their car on a regular basis (and who doesn’t; It’s a Heinkel!)

Here’s the carb as I bought it off of EBay:

Carb purchased from e-bay

Here are the issues with my existing setup that I hoped to solve, and how this carb stacks up:

Problem	Solved?
Poor idling	yes
Flat spot on acceleration	yes
Running rich (black spark plug)	yes
No bodywork modifications	yes
Accelerator pump?	yes
Easy to get parts	yes
Easy to tune	yes
Inexpensive	yes
Easy access to make adjustments	Mostly (use stubby screwdriver for idle)

General overview of the carb:

This is a 30 mm CVK Carb. It has a 30mm orifice with a 36mm (exterior) manifold mount.

Air intake view

Manifold side

Accelerator pump is cylindrical piece on left bottom

Electronic choke is in upper right hand section in this picture

It has an accelerator pump like the original equipment Pallas 22mm. It also has an electric choke, which means you don’t have to pump the gas to start it. It has a 46 mm intake opening for an air filter.  Don’t be embarrassed if none of these stats are familiar; not one of them is a standard Heinkel measurement.

Installation:

Installation is a 5 step process: I've gone through each one below with plenty of photos.
The steps are:
1. Make a new throttle cable
2. Run a wire to power the electric choke
3. Make an airtight seal from the carb to the existing Heinkel intake manifold
4. Make a supporting bracket for the carb
5. Install an air filter

You may also need to re-jet the carb, but I'll talk about that at the end of the post.

Making a new throttle cable: The Oko carburetor has different ends than a Pallas. Not to fear, you can make your own cable quite easily. I used a Venhill U01-4-101-BK Universal Motorcycle Throttle Cable Kit - 5mm OD, made in the UK. Cost was $16.99 delivered to my house. The only trick is here is to determine the proper length of the inner cable. Loop the outer cable up and over the engine and then down into where the carb will sit. Then measure the distance from the top of the adjuster to one of the cable holding holes on the carb. That’s your distance.

Running a wire for the electric choke: The electric choke replaces pumping the throttle when you are starting the engine cold. The electric choke is temperature activated by an electric current that comes from the ignition circuit. The other end of the wire runs to ground. The easiest place to pick up the ignition circuit is where all of the black wires meet up under the dash, so you need to run a wire all the way back to the dash. I setup my carb with electrical disconnects so I could easily take it apart if necessary (and it has been necessary a few times).

Disconnects for electronic choke

You can see the black wire under the tube. It would be a tight
 fit in the tube but you could do it if you had time

Making airtight seals: The Heinkel carb intake manifold has a 28mm outside diameter. The new carb has a 30mm opening. There are two ways to bridge this gap- make a custom manifold adapter or find some off the shelf component. Luckily there is an off-the-shelf solution (sort of). I poked around my local motorcycle salvage yard and came up with a “spigot manifold”. The manifold solves the carb side of the problem. Here's an example of one I purchased from Amazon that is an exact fit:

Perfectly sized spigot manifold

Installed on carb

The other end I solved using 3 o-rings slid over the end the Heinkel intake manifold. I used 1 1 1/8” inside diameter 1 3/8” OD O-rings, which are a common size in the US and cost 50 cents each. I assemble everything with screw clamps and got a great fit.

1 3/8" OD O-rings - 3 required

Put one on the manifold

Put two more inside the spigot manifold

Installed - a really nice fit

Supporting the Carb: While the airtight fit was great, it was so flexible it would fall off quickly from vibration. The solution was to make a carb “exoskeleton” to support it and prevent if from falling off. I made a bracket. You can weld up one like I did or assemble one with nuts or rivets. Here’s a picture of mine. This is version 2.0: the first one allowed the carb to fall backwards off of the manifold, so I made an extra support piece that sits atop the speedo housing to prevent this from occurring again.

Welded L-shaped bracket 

Top of bracket attached to convenient throttle spring mounting holes

Extra support keeps it from tipping backwards

Installing the air filter: This is easy! Just buy a standard Chinese 46mm ID air filter from eBay and mount it on to the end of the carb. In an ideal world you would actually run the air intake up to the original spot, but I tried to make an adaptor for this and the air cleaner kept falling off. They are only $5.00 each but that adds up after a while!

The air cleaner- 2 for $8.99 on Amazon

Air cleaner from back- I safety wired the air cleaner to keep it from falling off

My abortive attempt to connect the air cleaner to the original housing; it kept falling off!

Jetting the carb: I spent time jetting the carb to avoid flat spots and hesitation. Jetting is a bit time consuming, Paul Spakov has a great series on YouTube on how to tune GY6 carbs(a reference to the ubiquitous Chinese engines that use this type of carb); here's a link to one: https://www.youtube.com/watch?v=6EYTQsi1YJc&t=7s  that explains the process.
I think I'm running one size of jets down from the stock. Chinese carb jets are standard and super cheap (at least compared to a Heinkel Bing jets); I think a whole set was $12.

Get this Jet Set along with the Carb

Performance: I've been running the carb since April and it has met all my objectives. I have yet to do a top speed test yet, although I have run it up to 45mph and felt there was still more power available if I needed it. I've been getting about 50mpg (US) which might be a little less than I used to get, though when I check the plug the color is good.

Plug color is light brown- a good sign

 On the whole I'm happy and would recommend this improvement to anyone.