Introduction and fuel consumption

[Db7gtgrigio]

Hello there, Chris from Sydney signing in...

Have just bought a 1983 R100RS in Alaska Blue. 98,000 kms extremely original except for Staintune exhaust and Ikon shocks plus some hideous green fuel hose and awful cheap fuel filters. This is my third airhead in 29 years of riding (previously R65LS 1991-93 and R90S 2000-2002). Very pleased with the bike and am working through the small niggles you always get when buying an old bike (front brake hydraulic lamp switch inoperative, new rear tyre, brakes need servicing, fixing wiring to the illumination bulb on voltmeter) but engine has strong performance, seems to use negligible oil, box shifts very nicely (for an airhead). Compared to my other bikes (all Italian super sport stuff) it is supremely comfortable and serene (which is exactly why I bought it).

However, I did a round trip to Newcastle (400km) last week which highlighted very poor fuel consumption (I think). On the freeway I was travelling at 130-140 or 80-85 in the imperial. Of the 400 km, about 250 was freeway the rest was town riding. I achieved 38mpg. IMPERIAL. My 1970s Italian bikes 850cc and 750cc achieve 45-50 mpg ridden in a similar manner, so I'm not happy with 38mpg.

I think there is a fault and a clue may be that the bike starts easily. WITHOUT CHOKE. It won't start if any enrichment is applied. I have ordered a carb rebuild kit including diaphragms but would appreciate any comments. I have checked the float levels and they shut off the fuel when the floats are parallel to the carb base, so I think they are OK. The bikes pulls strongly and revs all the way to the redline freely. When my R65 suffered a split diaphragm it just would not rev so I am not suspecting split diaphragms in this case. Exhaust tips covered in hard black residue. Looks like running rich, however plugs nice brown/grey colour....

I do suspect the enrichment devices in each carb, but any advice from this group would be much appreciated.

[SteveD]

Welcommen aboard. Congrats on the new to you RS. Is it one like this?



Ever heard of the Blue Duck Inn? viewtopic.php?f=17&t=9222 Last weekend this month Friday and Saturday night! Oz Boxerworkers get together and talk shite! Blokes from Dubbo and just below Woollongong heading down.

Fuel.
Probably need new needles and needle jets. They're consumables that are worth changing every 30-40K kms. They wear and consumption rises.

[Bob Bennett]

Welcome to the forum Chris, go with Steve's advice re the needles and needle jets mate, not to
be confused with needle and seat. My R80 went from 13km per Ltr to about 17km per Ltr with
just that change, a lot more Ks on my bike though.

Regards Bob.

[Kurt in S.A.]

Does 38 MPG (Imperial) convert to about 45 MPG US? If so, that sounds pretty good to me.

Kurt in S.A.

[barryh]

Quite likely to be worn needle jets but might also be float levels too high. Even if the you are replacing the needle jets the floats levels should be checked to establish a baseline as the fuel level has an affect on mixture across the range. Before ordering any bits for the carbs I'd have the floats off and weigh them accurately. New floats are 12.5-13 grams, anything up to 15 grams can be made to work with some adjustment. Over 15 grams are close to sinkers and I'd bin them.

[melville]

Does 38 MPG (Imperial) convert to about 45 MPG US? If so, that sounds pretty good to me.

Kurt in S.A.

No, it's the other way. 38 mpg IMP => 32 mpg US.

[Kurt in S.A.]

Does 38 MPG (Imperial) convert to about 45 MPG US? If so, that sounds pretty good to me.

Kurt in S.A.

No, it's the other way. 38 mpg IMP => 32 mpg US.

Kurt in S.A.

[tsa]

Congrats with your new RS, Chris; I particularly liked your comment that it is supremely comfortable

+ 1 on the advice to get new carb needles & needle jets. They are consumables. Worth checking the carb enricheners as well; their gaskets, that they are assembled correctly, and that the lever returns them back fully to the closed position. Also get a new air filter, unless you know it has been replaced recently.

I also plan to replace the needles & n.-jets on my recently acquired /5, also due to higher than expected FC. I plan to examine my new and old N & NJ under a high magnification glass to checkout any differences. Would ber very interesting to see if someone else also could correlate a shift to acceptable FC with a somehow quantifiable visual wear of those needles & jets.

[Ken in Oklahoma]

. . . I think there is a fault and a clue may be that the bike starts easily. WITHOUT CHOKE. It won't start if any enrichment is applied. I have ordered a carb rebuild kit including diaphragms but would appreciate any comments. I have checked the float levels and they shut off the fuel when the floats are parallel to the carb base, so I think they are OK. The bikes pulls strongly and revs all the way to the redline freely. When my R65 suffered a split diaphragm it just would not rev so I am not suspecting split diaphragms in this case. Exhaust tips covered in hard black residue. Looks like running rich, however plugs nice brown/grey colour. . .

Welcome to the forum, uh, however your handle is pronounced . . .

I have another possible culprit for you to consider, that you may just not have listed. You set the float parallel to the carb casting, but if you have a heavy (gas soaked) float it will float low. Since you're experienced with airheads you've probably experienced this already and took it into account.

Ken

[Major Softie]

I have another possible culprit for you to consider, that you may just not have listed. You set the float parallel to the carb casting, but if you have a heavy (gas soaked) float it will float low. Since you're experienced with airheads you've probably experienced this already and took it into account.

Ken

Note Barryh's post....