Saturday, September 13, 2008

Swapping Carburetor Bodies @ Matt's Place

Today was the day I was scheduled to ride Brigitta, my 1987 R80 Beemer Airhead, down to Colorado Springs to Matt Parkhouse's place for him to swap the damaged carb body Brigitta came with for one I got from

Matt Parkhouse is one of the recognized gurus of the Airheads Email List which is used to spread wisdom/knowledge/fixes/info amongst Airheads all over the world. I just lucked out in that he agreed to help with me with the swap and that he was close by.

I got there a little after 1030am, having had to return shortly after leaving home to retrieve my camera. Just as well I was running late since Matt was tied up with another Airhead owner of a stripped down 1977 R90S. It was part of a ground up restoration and I'll cover the pictures I took of them working on that bike in a later posting.

A bit after 1200 or so, Matt was finally free and ready for me. I rode Brigitta into Matt's yard and next to his shop. He got to work immediately and within a minute or so had the carb off the left side of the bike and into the shop.

Matt has done hundreds of these carb jobs so he moved fast. I tried to keep up with photos but really, I was trying to actually see him do the actual work for when I do the rebuild next time they're due. He made it look so easy but I was comforted to see even he used an assembled carburetor as a guide when it came to putting things back together! In fact, as I'd read online somewheres, he also recommends keeping one carb assembled while you work on the other when doing rebuilds. It prevents mixing parts up since some of them are "handed" in that they are made to be on the specific side's carburetor, otherwise you reverse their function/range of motion which is not good.

The part of the swap process, the removal of the throttle plate and the peened mounting screws which I'd feared doing alone the most, proved anticlimatic as the screws appeared to Matt not to be peened. He did start dremeling one of the them so I got to see how that's done. In the end though, not much dremeling was needed.

Here's the left Carb without the cover

Disassembly begins, note the broken end on the mounting post that caused all this to occur

Most of the parts, removed, they were cleaned as they were taken off

The new carb body

Most of the parts on the new carb body

Old floats back on, new pin in place as the old one was bent

Carb Needle and old float

Old and New Diaphragms comparison, old is near top of pic

New Carb Body in place

Matt Parkhouse/Guru and Brigitta

Matt's wife's R100/7, note the well worn seat! This one has 107,777 miles on it, Matt's got another airhead with over 440k on it! He rebuilds the engines about every 100k miles. You can bet this bike is in much sounder mechanical condition than mine is!

Matt made it all look easy but I am sure its all a result of years of experience and practice/learning on his part with great mechanical talent thrown in.

Once he had Brigitta put back together, there was some tweaking of the carb floats to be done as I'd bent them before to deal with the vagaries induced by the bent mounting pin for the floats. He got that squared away easily enough though and I took Brigitta out for a test ride to warm her up prior to Matt doing a carb sync.

Once I got back I watched Matt do a carb sync by shorting each spark plug in turn as he made adjustments to the opposing carburetor. It was simply amazing how he did it. His method, he says, is more accurate since it balances the whole power process and not just the vacuum as the manometer method I use does. He's made from a couple of used /5 spokes, two rods which attach respectively on each spark plug end, the other end connects to the spark plug cable. To short out the plug he wants to short, he just touches the rod with a screwdriver! Cool stuff. I wish I'd thought to take pictures of them.

He got the idle correct using these tools, now I know you're supposed to adjust it so that the respective carburetor just barely stays running. Again, he made it look so easy.

He then ran up the rpms to about 3000 with a throttle lock and quickly switching between spark plugs with his shorting screwdrivers balanced the carbs at speed as well! Amazing. No pics, I was just barely keeping up with him just watching and I did not want to miss the Master at work! He works fast since its not good to run the engine without air moving over the jugs!

Brigitta is running sweetly now, her throttle response is snappier I think and I'm having to relearn my shifting/throttle operation due to the changes for the better. She sounds great, a bit throatier actually. Matt did preemptively replace both carb diaphragms since they were coming close to needing replacement.

Not expensive either, the whole thing came to $139! Labor and parts! Matt will probably be the guy I take the transmission on Brigitta for rebuild when that's due. He's a great teacher and mechanic and I can see why he's recognized as a Guru amongst Airheads.

Thanks Matt!


xobule said...

Very nice bike!

Jessie said...

Hi Domingo, I've been reading your blog for a few years but never commented before. I live in Denver and have gotten a lot of good ideas for rides from your blog. I went back to this old post because I remember your description of the carb balance that Matt Parkhouse did. I've got an 82 R100 that I just learned to do this on. Bought some nice secure adaptors from Northwoods BMW to do the job. They came with good directions that match up with Snowbums on-line directions. It's pretty easy. Are you now balancing your carbs this way or do you use your manometer?

redlegsrides said...

Hello Jessie

thanks for reading this stuff and commenting.

I still use the manometer as I've never pursued the shorting method I saw Matt Parkhouse use. What was the p/n from Northwoods BMW that I can use to order the adaptors you have?

Jessie said...

I don't see a part number, the site is not that advanced, just offers useful tools and you just send an e-mail and ask for it. The site is at
Be warned though, our favorite BMW mechanic will tell you in very strong terms not to use the shorting method on an electronics ignition bike (1981 on??). So now I'm thinking of using the manometer next time I need a balance, though shorting is really easy. It hasn't harmed my bike (that I know of). I guess since Matt Parkhouse and Snowbum use the method for EI bikes it can't be all bad.

redlegsrides said...

Hi Jessie

wasn't aware that you're not supposed to use the shorting method on bikes post-81 with EI, figured as you that if Matt Parkhouse did it, it was OK.

you're welcome to come by and check out your "balance" with my manometer... you can reach me at