Main Jet Part Numbers

[Mike V]

This and my previous experience with other bikes has taught me that pilot circuits can have a significant impact on overall economy as they are still contributing to the mixture up to 1/4 throttle.  

Barry,
The graph you posted is fascinating and very informative. It's a great overall depiction of the circuits. Where did you find this? Did you create this yourself? I didn't see this in the Bing Manual.

[Barry]

Where did you find this?  

Mike

I honestly can't remember where. It's just something I saved - certainly didn't do it myself. I'll have a look when I get home from work.

There are a few of these graphs around and not all are applicable to CV type carbs. If the graph has a line for slide cutaway it usually means it's applicable to slide type carbs rather than CV's. That's a good one though.

[Bob_Roller]

The Bing manual has a much more simplified grahpic on page 11 at the upper left corner of the page, if anyone has a copy of it  .

[Mike V]

Barry,

It's an awful comprehensive graph. Very helpful as an aid if accurate. I question the height of the curve for the metering rod but I just wonder why we haven't seen something like this before. It was my understanding 1 notch on the metering rod equals about 2.5 jet sizes. Do you mind if I share this with some Airhead friends to get their opinions? Anyone else out there have any comments on the graph?

Bob I noticed the graph in the manual. The manual has several graphs (pg.3, 11, 15) and would be nice to have a composite like Barry posted to see overlapping functions.

[Barry]

Do you mind if I share this with some Airhead friends to get their opinions? Anyone else out there have any comments on the graph?

Mike, Sure it would be good to hear what they think. Couldn't find the original source but I am sure it represent a CV carb though probably not a Bing. That shouldn't matter as they all work the same in principle. The various graphs and diagrams around are very similar and who knows how accurate they are. For me they are an insight in to how the carb works.

Here's my take on each of the curves:-

Pilot screw has a diminishing effect from idle but still some small effect past 1/4 throttle - I agree

Pilot jet flowing fuel from idle up past 1/8 throttle. This is the most interesting curve because it's usually missing from other graphs and diagrams. - what this means is that the transfer ports which are not controlled by the mixture screw are still flowing fuel upto and past 1/8 throttle. I agree but not sure about the shape of the curve I would expect it to turn down again.

Needle diameter - Before the tapered part of the needle is pulled out of the jet this is contributing fuel flow upto 1/4 throttle.  I agree in principle and for me this equates to around 3000 RPM. Not sure about the scale of the curve though. I think you can only compare the height of this curve with the other jets that are contributing at 1/4 throttle and not with say the needle taper at 1/2 throttle.
 
Needle clip position - This one is confusing. I would have said that needle clip position simply moves the needle taper curve from left to right on the graph and to some exent up and down the graph because it determines at what throttle opening the needle taper comes into effect.

Main jet - Agree in principle but I would expect to see the curve extended down at least to 1/2 throttle and maybe 1/4 throttle even though it's effect down there would be very small.

[Mike V]

Barry,

Your graph is getting a lot of attention here in San Diego with very positive reviews.

[Barry]

Mike,

I look forward to hearing what they have to say.

[Mike V]

I've sent it out to a handful of close airhead friends here.  They all initially ask the same question about the source. But I have a feeling it's finding it's way into a lot of notebooks because of everyones high impressions of the comprehensive nature of the chart. I've tried some shots Googling to find it in some corner of cyberspace with no luck.  I may send it to Jan, Stoner, and others to get some expert impressions. Sorry to move away from the original Subject line, no disrespect intended. 

[Bob_Roller]

BTW how fast could you go at 1/4 throttle.  

1/4th throttle is around 38 mph

[Barry]

1/4th throttle is around 38 mph

Bob,

I was so intrigued with your result I went out and marked my throttle up again taking care to allow for the initial slack.  Ive just come back from a short test ride. What I did was to hold a throttle setting and then wait to see how fast the bike would go before I ran out of road. Here's what I got :-

Holding 1/8 throttle I can accelerate up a moderately steep hill to 40mph. On the flat this increases to 50mph.

Holding 1/4 throttle I can accelerate up a slight gradient to 60mph and on the flat this increased to 65mph. The Road ran out before I could go any faster.

These results are much the same as I got before and they are the reason why I'm a bit obsessed with the notion that pilot circuits on the carbs make a big contribution to MPG because I rarely seem to be using more than 1/4 throttle.

 

[Bob_Roller]

I rechecked the markings on the throttle housing and hand grip last night .

This morning I rechecked my findings, 43 mph for 1/4 throttle, and 73 mph for 1/2 throttle .

The surface streets around here have a 45 mph speed limit, and a stop light every mile, so the speed may well be higher for 1/4 throttle, have to wait until I get out on a deserted back road with no traffic to see for sure if it does change .

[Bob_Roller]

According to this article, we here in the US can expect to get lower fuel mileage if and when this goes into effect .

http://news.yahoo.com/s/ap/20100618/ap_on_bi_ge/us_epa_ethanol

[Barry]

Interesting, I suppose it can be put down to different engine , different carbs, maybe even different throttle cam.

The only other similar reference I can remember seeing is this from a guy called Mike Fishwick who was talking about tuning his R100 carbs

"Set up like this quarter throttle will give (with an RS fairing) 90 mph and 100 mph at half throttle"  

Sounds incredible that you can go that fast on 1/4 throttle but he was Technical Officer of the BMW club and not given to exaggeration.

[Barry]

According to this article, we here in the US can expect to get lower fuel mileage if and when this goes into effect .

Bob, the link didn't work for me but I assume it's about the proposed increase from 10% to 15% of ethanol. That's bad news. I should be grateful we are only on 5% ethanol blend in the UK.

[Bob_Roller]

Interesting, I suppose it can be put down to different engine , different carbs, maybe even different throttle cam.

The only other similar reference I can remember seeing is this from a guy called Mike Fishwick who was talking about tuning his R100 carbs

"Set up like this quarter throttle will give (with an RS fairing) 90 mph and 100 mph at half throttle"  

Sounds incredible that you can go that fast on 1/4 throttle but he was Technical Officer of the BMW club and not given to exaggeration.

I wouldn't doubt his results, the R100 bikes had different final drive ratios, I think it was set up for long distance and high speed, R100's get about the same fuel mileage as the R65 .

I'm sure an RT fairing  would gain you some extra miles due to streamlining the bike, lets face it, and unfaired motorcycle with a rider on it, isn't the most efficient shape, if I remember correctly an unfaired bike with rider had a coefficient of drag of a bit less than a flat plate .

The article was about the possibility of having 15% ethanol in the fuel supply in less than a year .

Owners manuals of most vehicles in the US state that fuel with ethanol content of more than 10% should not be used .

What's the final drive ratio on your bike, 3.89 ?

My R65 has a 3.56 ratio .