DCOE 45 install

[dscoff]

Now that the carbs are installed and running fairly well, I thought it would be helpful to share the process!

I originally planned on purchasing some DCOE45's over the winter to go along with the motor I'm planning on rebuilding (10.5:1, bigger valves etc). A pair was for sale on FAQ recently however and I couldn't help myself. In order to finance the 45's I needed to sell my 38/38, meaning the 45's would have to go on now.

Preparation:

I decided to use an electric fuel pump (Mr.Gasket) along with 5/16" steel line run under the car. I was able to mount, wire and plumb everything ahead of time, so when the carbs arrived all I'd need to do is attach the tank and carb ends of the line. 5/16" wasn't exactly easy to work with, but it also wasn't impossible. Just took my time and did as much pre-bending as possible. The pump is mounted just below the rear seatback with a relay under the rear seat and wired to a switch on the console.

I ordered all the necessary coolant re-routing hardware from Blunt (of course) as well as gaskets and mounting hardware. From TEP came some soft mounts and their cable linkage (more on this later) and another FAQ-er sold me some nice Ti manifolds. Finally I ordered an Ireland Engineering mechanical advance dizzy; not only are there no ports for vacuum lines on the Ti manifolds, but my vacuum retard dizzy's diaphragm was NFG and the unit was generally pretty tired.

The 45's I bought included rebuild kits, which the units needed. This was an easy process with the additional help of the Haynes Weber book. With some fresh washers, gaskets and lube they were as good as new. The previous owner hadn't used the carbs on an M10, so using tips from FAQ (mainly dapbmw and Lee) I bought some baseline jets including 4.5 aux venturi's, 130 mains and 45F8 idles. Note that my motor is stock and slightly tired with IE headers and 2.5" pipe being the only performance bits.

Mounting:

This was the easiest part and probably took 3 hours. Drain coolant, old stuff off, some crevice cleaning, then new goodies on. I preassembled the carbs to the manifolds with the soft mounts and used some heavy silicone brake grease on the o-rings to hold them in place and ensure they sealed. Linkage on, carbs on, fuel lines in, done and done! I crossed my fingers and twisted the key..... braaaaaap! Fired up on the first try! Now for the hard part...

Trouble shooting/tuning:

The linkage has caused me the most grief. The first issue was cable friction. Even with an auxiliary return spring (see photos) the car didn't want to idle. After some reading and diagnosing, the majority of the friction came from the lower housing boss being too high and creating an "S" in the cable's path. I cut the mounting piece that bolts to the booster mount and extended it with 6" of 1/8" steel plate, as well as some creative bends to contour it around brake lines and get the housing aiming as directly at the pedal as possible. This and plenty of lube cured most of the friction. The second linkage problem stemmed from the tab on the "master" link being too long and binding on the "slave" link. The fix was easy but removing the link requires removing at least one carb. I'm still dialing in the final part: tightening the throttle shaft nut. All the tech books say "finger tight" however this lets the master link twist sideways slightly resulting in a high idle (15K-2K). I've been tightening it bit by bit and getting rid of the issue, but I don't want to overtighten it and bind the shaft.

The second problem was more complicated, but is also what I love about the dual sidedraft setup: just start from square one, think about the specific problems and trace them to specific carbs, parts or circuits. The car popped like nuts off throttle, but not at idle, and there was a flat spot around 2-2.5k. It also shook like crazy at idle like a cylinder (or two) was missing, but arcing the plug wires to the head confirmed spark and there was plenty of fuel. Removing plugs 3 and 4 however didn't change the idle. Changing the mixture screws on 1 and 2 had immediate results for the worse, with 1/4 turn on either almost killing the motor. Screwing in 3 or 4 improved the idle but turning them even to the seat wouldn't kill the motor. Figured it out? Leaking needle in the aft carb and overly lean idle jets! With the idle mixture screws set the same as the front carb, fuel was POURING into the cylinders, drowning the spark, and basically sealing the mixture screws leaned out the leak to the point where it would run. The flat spot and vast majority of the popping were both cured by 50F8 idle jets.

While we're on the subject of fuel bowls, I made two "standards" for measuring float height out of aluminum. They're just to pieces of 1/8" aluminum, cut to the high and low float heights (cut and filled to within 0.05mm and square) with a notch cut for the seam in my brass floats. WAY easier than eyeball measuring or the drill bit method.

Filters/horns:

I wasn't planning to run a Ti booster, but one came available locally so now it's on my workbench! I'm not a huge fan of Ramflo or pancake filters, so I started to build a plenum out of .090" aluminum that would feed both carbs and feed from a big panel filter sitting where the battery used to be. It's still in the works (although it was originally designed around the standard booster so it will probably never make it past "prototype") but yesterday at a local 02 gathering, a fellow owner sold me some gorgeous horns! I may run socks on them but with a rebuild in the next few months, I'm not super concerned with dust in the motor. Version 2 of the plenum is shaping up to be a bigger one that will fit the Ti booster, have these airhorns inside and have a hatch for accessing the attachment bolts... again to a big panel filter.

Whew. It's a awesome feeling to have the aforementioned issues ironed out and get to tear around listening to the carbs howl (and not constantly diagnosing in your head).

Jonathan

[M3M3]

nice write up..you should add it to the dcoe install faq in the faq under construction zone!

what chokes are you using?

[dscoff]

Do I just copy and paste it as a reply to the FAQ article? Btw, that article was a great source of part numbers for nuts/washers/gaskets/coolant parts.

I've got 36 chokes, which probably don't yeild the best idle, but they're awesome above 4k and will be great once the carbs go on a rebuilt motor and head with a hotter cam etc...

Jono

[M3M3]

yup!

36's should work well. i have 38's in a set of 45's i intend to install on my engine. might be scary at low rpm's. engine is build to 9.5:1 pistons, balanced crank, 292 schrick. i currently have 40's with 32mm chokes. runs great up to 4k rpm. power is gone by 5k.

[dscoff]

Cool! The 45's will be great! One more small tip: wire your aux venturi and choke retaining screws with safety wire. I've lost two aux screws held in with the bendable retaining tab, causing the venturi to rotate and stop delivering fuel. Surprise!

Jono

[vintage_car]

these engines just look so bad a$$ with dual webers... I miss my 40's badly! Happy tuning

[mossyboy6]

I would love to see more pics of your throttle cable / linkage setup and specs.

Im just starting to build one and need some tips!

[Slackey]

Hello,

Just about to do this same thing. Do you remember what the thread pitch of the second sensor hole on the water divider was? Cheers,

Daniel

[vintage_car]

I don;t know if this helps or not, but here are a few pics of the linkage I had on my 40's before I got rid of them. I thought it was a nice linkage setup.

[dscoff]

Thanks for the pictures! I think I'll be heading in the direction of a rod linkage...

The plug for the water neck was a BMW part:

Screw plug 07119919228

I'll follow with some pics of my linkage shortly.

Jono