Poor mileage since Carb repair?

[jp9094]

Over the last 400 miles or so my mileage has been miserable. When I purchased the bike in May of 2016 (it's a 1983 r 65 LS ) I was getting around 200 miles before needing to go on reserve.

After my first (self) service in April of 2017 I got it up to 220 miles before going on reserve.

It has been 2000 miles since that  service. 400 miles ago I removed the left carburetor and replaced the butterfly axle and its O ring as they were worn. I replaced the Carb, adjusted the cables and reset the idle jet to the factory position (3/4 turn). Then tried to balance it and adjust the idle. Have it at 1500 RPM when warm and it sounds OK to my admittedly tone deaf ear.

I now only seem to get 150 miles before needing to go on reserve. I have scrupulously avoided touching the other carb. I also did not dis assemble at all the right carb ( did not even undo the float bowl)!

Any ideas as to what is going on. I Know I am coming up on a new service (fluids, valves etc) . Any and all advice appreciated!

Many thanks in advance.

[Barry]

So there are no changes in jetting and idle mixture screw is at 3/4 turns out. Is that where it was set before ? 

The butterfly is bevelled at the edges to fit correctly in the venturi where it sits at a slight angle when closed. Did it go back the right way around ?  Sighting against the light is the best method to ensure it's centred and fits in the closed position.

1500 RPM idle is a little high when hot. 1100 is as high as you should need to go.

It's easy to assume the needles were at stock position but they might not have been.  Did you remove them and if so did they go back in the same position.  I measure the needle length before removing them to be sure they go back in the same notch. Most big changes in MPG are down to needle position.

[jp9094]

Barry, thanks for the prompt reply. In answer to your questions, I made sure the butterfly was replaced in the correct orientation before snugging the screws.

As for the idle jet, I screwed it in to the stop (gently) then backed it out 3/4 turn. After a warm up ride I adjusted the idle the tweaked the jet by ear until it was at the lowest idle.

I take your point about 1100 rpm being ideal, so will re set the idle after a warm up ride and see what happens. I also plan on getting new float bowl seals and taking them off and cleaning them out. Will see what happens then.

Regards to all

[Barry]

After a warm up ride I adjusted the idle the tweaked the jet by ear until it was at the lowest idle.

Apologies if I've misunderstood what you did but slowing the idle speed using the mixture screw will guarantee a grossly incorrect setting. The mixture screw must be adjusted for highest idle speed and then the idle speed re-adjusted if neccessary with the throttle stop screw.

[Bob_Roller]

Do you have a manometer, or vacuum gauges to do a cab synch

[Tony Smith]

Sorry but this sounds like a major assembly error to me. If you haven't changed any other parts aside from the throttle shaft and O rings it beggars belief that you would so damage your mileage.

Others have asked how you balanced the carbs so I'll wait for your answer before weighing in on that topic.

My suggestion would be to revisit the throttle shaft and make sure that the butterfly is around the right way and that you didn't damage the O rings in installation.

I'll hold off on further comment until I see your responses.

[tunnelrider]

400 miles ago

Did the poor mileage start straight after the repair?  If so, like Tony and Barry said revisit the butterfly install.  If not I'd look at the spark plugs, if they are both sooty and the air filter hasn't been changed for over a year it may be from a blocked filter.

[jp9094]

Again many thanks for the replies. In answer to the questions posed, no I do not have access to a manometer, and I balanced the carbs by ear. Good point about the idle mixture setting and I will revisit it ASAP. Also will check the spark plugs as suggested. To revisit the butterfly requires ordering new screws which will take some time, but will be willing to do that after trying the above suggestions. Again may thanks to all who replied!

Best regards to all.

[Tony Smith]

I do not have access to a manometer, and I balanced the carbs by ear.

The cheque is in the mail;
Of course I'll respect you in the morning;
I'ts just a one time thing;

&

I can balance carbs by ear.


Are all untruths of about the same magnitude. A well trained ear can get carbs in the ballpark but that only thing that guarantees balance is a manometer (or mass flow meter if you must have better toys than anyone else)

Unbalanced carbs will cause amazing fuel consumption all by themselves.

[jp9094]

Tony,

Thanks for the received wisdom. As I do not have access to a manometer one does what one can. This all started when I organized for a local BMW guru to tune and balance my carbs. He pointed out, after I showed up for the appointment, the the butterfly shaft was defective. This is what lead to the current state of affairs ! Have re set the idle jet and idle. Will next check the plugs and air filter.After that, who knows. Thanks once again to all.

Regards

[Tony Smith]

As I do not have access to a manometer one does what one can.

Make one. It ain't hard, can be a bit of fun and costs cents.

https://www.youtube.com/watch?v=Y_WDF6glD5k

https://www.youtube.com/watch?v=0HfrHLmpHCY

https://www.youtube.com/watch?v=E2J_N4VVGGo

[Bob_Roller]

Here's a manometer that I made from bits and pieces from the garage .

[Barry]

And another one

[jp9094]

They all look great, but a bit cumbersome! Would aim for something a bit more restrained. Have re adjusted the idle mix and idle speed and it actually seems to run a lot different. After a warm up it just chugs along when at the lights. Plan on inspecting the plugs and air filter tomorrow when I am free. Thanks again for all the sage advice.

Regards to all!

[mrclubike]

Here let me straighten that for you
Nice collection by the way