Wednesday, January 9, 2013

CV Carburators

Temperatures have been dropping since the weekend and now hovering around -20°F. Sunrise is slowly starting to get a little earlier. This sunrise photo was taken at 10:48am about eight minutes after sunrise. 

Yesterday evening, I pulled the Bing carburators off of the bike and this evening I'll be taking them to a longtime friend and fellow Airhead member who offered to help clean and overhaul. Since I've had the bike, the gas mileage has been in the mid-40s to low-50s. On my trip last summer, the mileage was pretty steadily in the mid-40s from Fairbanks through Canada. Shortly after crossing the border, the mileage started dropping and leveled out in the mid-30s ever since then. I'm thinking that this may be due to old rubber parts in the carburators softening and cracking due to the ethanol in the gas. In Alaska, all of the gas sold now is ethanol-free so it hasn't been an issue. I've replaced other rubber components within the fuel system but never dug into the carbs. I've had a rebuild kit sitting on the shelf for over a year but the bike has never exhibited any fuel related symptoms.

I think the last time I overhauled a carburator was back in the early-70s when Delco Quadrajets and other four barrel carburators were common and most people didn't keep their cars for more than 100k miles. Cleaning and rebuilding carburators and doing tune ups was a great way for a high school kid to make a few bucks. But I have never taken apart a CV (Constant Velocity) carb before. A new experience. I did not pick up the ethanol resistent float kit just the basic set of gaskets, o-rings and diaphragms.

Now is the time to get my hands dirty...

13 comments:

Coop a.k.a. Coopdway said...

I'm all ears. Having only put less than 300 miles on my RT, mileage for 2 fills was in the mid-40's.

When I brought mine home there were no leaking carbs. After the first ride, bike on side stand left a small puddle. It's been on the center stand since then and I don't see or smell anything.

With your winter riding, what weight oil? What ambient temp is the bike at when you start it?

SonjaM said...

Can't help you with the carburator obviously but I thought I let you know that I admire your new header picture.

Unknown said...

Richard:

Hard to compete with you and DOM with snow photos. I know nothing about carbs either nor anything about CV or reg carbs. I am on a first name basis with my mechanic and he smiles everytime I see him

hope the rebuild cures the MPG problem

bob
Riding the Wet Coast
My Flickr // My YouTube

redlegsrides said...

I've done some work on the carbs but not full overhauls ... Rejets, swap diaphragms, blow them out, but no actual taking apart the throttle mechanisms......take lots of pictures!

RichardM said...

I still have the synthetic 20W-50 oil that was in there at the end of the summer. Before I start riding in the winter, I'll change it to something lighter like 10W-30. Last year, I rode on a couple of 12°F days and the bike didn't want to crank very fast but it started up just fine. At home, it resides in a heated garage.

Sticking fuel inlet in the carbs is a common problem. Do you have inline filters on the fuel lines?

RichardM said...

Thank you, Bridget took the picture last Saturday. I'll let her know...

RichardM said...

I don't have anything on Dom. The scenery in CO is incredible. I hope to find that the diaphragms are cracked. But they are pretty grimy as this is probably their first rebuild ever....

RichardM said...

I suspect that with your altitude, you've had to rejet any carbureted vehicle you've had. One benefit of EFI.

My friend implied that this is a quick and easy job. No more than a few hours.

Coop a.k.a. Coopdway said...

There aren't 3rd party filters there, not sure if there are OEM integral filters. I just got a used Haynes manual on Ebay and it looks very comprehensive.

I've noticed a momentary pause when I push the starter button. Battery seems up and even when warm, there's a lag as if it might have second thoughts about wanting to turn the starter. The old ST2 Ducs were known for having too small a wire from the battery and suffered the same sort of lag. I installed a larger gauge cable and it helped immensely. Sound familiar at all or might it be something else?

RichardM said...

No built in filters besides the screens in the tank. Most of the BMW parts places such as A&S have small, cheap inline filters. Be careful of some of the torque settings in the Haynes manual. They are too high and you'll damage the threads. The airhead list or the BMWMOA forums are a good place for information like that. I had that problem with starting a few years back and simply replaced the starter relay which completely eliminated that problem.

VStar Lady said...

Richard I'd be lying if I said I knew anything about a carburator, except that I have heard of them ... I'm with Bob - love the sunrise snow photos though.

Coop a.k.a. Coopdway said...

Thank you!

RichardM said...

The header photo is taken near high noon. At this time of year, that's how high the sun gets. The winter sunrises are pretty nice.

Carburetors are one of those things that make a bike repairable just about anywhere. EFI systems start easier, are probably more reliable, get better fuel mileage, run cleaner, etc. but I can't fix it if it stops working. I still like to tinker with this stuff so it's a good fit and I completely understand why folks like the new stuff.