Horrible mileage - mixture screw setting?

[dewane]

Hi, so I got this R65 last year, and get 30 MPG. I've done the following (I've done other things but this would be relevant to mileage):

- Rebuilt carb with the carb kit (new gaskets and diaphragm)
- Blew out jets w/carb cleaner
- Checked timing
- Lubed bean can electronic ignition weights with triflow
- Replaced spark plugs, spark plug caps and spark plug wires
- Checked valve clearances (twice now since I've had it)

The last thing I can think of is to check the mixture screw(s). What is the recommended setting for those? I'd like to get a ballpark before I go messing around with them.

Also, is there more than one screw?

Anything else to check? Pipes look stock but the bike is kind of loud. It's always been hard to start (a bit better now that i replaced the original coils with a Dynacoil) and my seat-of-the-pants, raw gas smell when starting, and looking at the plug would say that it runs a bit rich.

[Lucky_Lou]

The mixture screws wont have a great deal of impact except on tick over they are generally set at about 3/4 to 1 turn open. You need to look at the needle position drop them a notch and see how you go after a 100 miles drop them again if need be. This can be done carb in situ if your carefull, just take the carb dome/top  pull the diaphragm out and use a pair of long nose pliers twist the needle through 90 deg and push down till it reseats about 1/8 inch.
Lou

[montmil]

Lou's correct about the mixture screws effect on mileage. He has a wee bit of experience, Lou does.

I would suggest checking all the jets to confirm that are to factory spec sizes; Needle jet in the spec'd position; Diaphragms fitted with the notch located correctly. There's a bit more involved in a Bing carb overhaul than just the gaskets and diaphragms.

A single strand of copper wire may be used to probe carb passages. The copper will not damage the internals. Shooting carb cleaner does not always guarantee clear passages.

Have you checked the air cleaner? Are the chokes -enrichment circuits, actually- functioning correctly with the discs refitted in the proper order? Could also be a simple cable maladjustment.

You did not mention the year of your R65 so we're guessing here, but both my R65s mixture screws are spec'd at 1/2 to 3/4 open from a gently closed position.

More checking ahead for improved mileage. BTW, my 1981 R65 turned in 48mpg after a very throttle cranking run of 200+ miles through the Texas Hill Country's Three Twisted Sisters.

Monte

[Bob_Roller]

The 'choke' may not be closing all of the way .

Check the cables that are moved when you move the choke control, with them closed, push down and see if they move more .

[Justin B.]

Maybe the chokes have been assembled incorrectly?  Seems the internals are "handed" and they will install onto the wrong side.

I had a choke cable return spring corrode enough to break on the R100 so check them as well as the choke (enricher) will stay wherever it was when the spring broke...

[dewane]

Hey thanks. Experience tells, the needles were in the lowest notch (in other words, raised as high as they could go). BTW I didn't have to take off the diaphragm (it's an '83), just removed a set screw in the slide and that exposed the needle.

I moved the clip down a couple of notches and rode it around. Seems to get the same power and the cylinders seem to be a little hotter, but no pinging. It's freakin hot in San Jose today - 98 degrees (those of you in the South are now saying, yeah right).

The chokes seem OK, I had to check the throttle settings and it's possible that one of the choke cables was maladjusted a bit.

I got a new air cleaner last year and it's got probably 3,000 miles on it, if that.

I don't believe the choke is installed incorrectly because it got the exact same mileage last time. But, I am a hack, no question.

I know I should check the passages but I'm a Sea Foam (read: lazy) kind of guy, so I'll try that first. Thanks for the tips guys.

[mimmo66]

Dewane ,
If you are wrenching or need any help I live in San Jose too.
Perhaps we can catch some ride together if you'd like.

Dom

[trolle]

The 'choke' may not be closing all of the way .

Check the cables that are moved when you move the choke control, with them closed, push down and see if they move more .  

Check both the choke- and throttle cables. If the  throttle cables aren't aligned properly the side getting most fuel/air will pull the most and thus have more work and use more petrol than necessary, while the other side won't use the alotted petrol efficiently because it doesn't pull. This will result in a consumption far above normal.

Earlier this month I did 200 miles at an average speed of 75 mph with badly aligned cables which resulted in a consumption of 26 miles pr gallon and a blackened left carburettor and cylinder. The right throttle cable was too tight by appr. 4 mm including slack.

Normal slack should be 1-1.5 mm

Check if the cables are bent at the fastenings as well, they should be straight.

greetings from a sunny but cold north

[dewane]

Dewane ,
If you are wrenching or need any help I live in San Jose too.
Perhaps we can catch some ride together if you'd like.

Dom

Thanks for the throttle adjust info, I checked both and they're at about 1 mm now.

Hey Campbell man, PM me and let's go for a ride some time, neighbor! This is the best time of the year in the Bay Area.

[Barry]

The mixture screws will have some effect on mileage if they are set excessively rich so they ought to be set correctly. The improvement will be nothing compared to the needles being 2 notches out though.

Worth checking the float levels too if the carbs have been rebuilt.