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Old 04-02-2013, 10:36 AM   #1
Hookalatch OP
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Stock 40mm Bing jetting

I am in the process of converting my 1984 R80RT into an S type model.
I am using parts from a 1982 R100RS. Presently rebuilding the 40mm Bings.
They are the correct carbs for a 82 RS according to the Bing book.
Bing calls for a 160 main, 45 idle jet, a 2.66 needle jet, and the needle on the 2 groove.
What I found in the carbs was a change to a 2.68 needle jet and needle on the 3rd groove,
The Bing book also states many models came jetted lean from the factory.
I need to replace the needle jet and needle and don't know if I am better off with the stock recommendations or increasing the needle jet size with or without moving the needle.

I am familiar with carb tuning practices but since I will have never run the bike with these parts I need a best guess starting point. I do not want to change the main or idle jets until I get the bike running. The needles were totally corroded and have to be replaced. I will go with Bing's recommendations on the 2.66 needle jet and needle on #2 unless the list experience indicates I would be better starting with with a 2.68 and richer needle position. I am using all stock R100RS parts from the airbox cover thru the cylinder and piston.

Chuck
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Old 04-02-2013, 04:20 PM   #2
supershaft
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Sometimes it's a toss up if they run best on the second or third clip. They never run best on the forth clip. Which clip it runs best on will determine your needle jet and viceversa. The needle jets effect mostly right off idle. The jet needle effects mostly low/mid rpm. I suspect you want to keep the jet needle on the second clip. What needle jet is going to work best? Just about no one figures out that jetting takes buying jets. You will just have to try them and see what works best keeping in mind that the leanest jetting that still works best is the best jetting.

Bing does not always now what they are talking about. The mains are often jetted rich from the factory. Put some 155's in it. Can't tell much difference? put some 150's in it and so on until you can tell a difference and then go back up one size. You will notice it revving much quicker IF it needed smaller mains. Remember. The leanest that works best makes most power and gets best mileage and keeps your engine running cleanest. Good luck!

They often need to be richer than stock just off idle with the needle jets and leaner than stock on the mains. Not always but there is only one way to find out!

supershaft screwed with this post 04-02-2013 at 04:46 PM
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Old 04-03-2013, 03:12 AM   #3
Plaka
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Quote:
Originally Posted by Hookalatch View Post
I am in the process of converting my 1984 R80RT into an S type model.
I am using parts from a 1982 R100RS. Presently rebuilding the 40mm Bings.
They are the correct carbs for a 82 RS according to the Bing book.
Bing calls for a 160 main, 45 idle jet, a 2.66 needle jet, and the needle on the 2 groove.
What I found in the carbs was a change to a 2.68 needle jet and needle on the 3rd groove,
The Bing book also states many models came jetted lean from the factory.
I need to replace the needle jet and needle and don't know if I am better off with the stock recommendations or increasing the needle jet size with or without moving the needle.

I am familiar with carb tuning practices but since I will have never run the bike with these parts I need a best guess starting point. I do not want to change the main or idle jets until I get the bike running. The needles were totally corroded and have to be replaced. I will go with Bing's recommendations on the 2.66 needle jet and needle on #2 unless the list experience indicates I would be better starting with with a 2.68 and richer needle position. I am using all stock R100RS parts from the airbox cover thru the cylinder and piston.

Chuck
I would set it up with the stock jetting for the R80 id you have an R80 top end. Just buy both needle jets if you are ordering, they're cheap. You want to want to run as lean as you can consistent with not overheating, knocking and making good power. Nothing like trying both. You can switch them in a moment by the side of the road.
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Old 04-06-2013, 11:25 AM   #4
lkchris
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You'll have to search pretty hard to find the correct jetting. It may take trial and error.

The intial jetting assumed 500cc cylinders, and 40 mm intake valves.

This won't be the same for 400cc cylinders and 32 (?) mm intake valves.

R80 jetting might be close, as the bike doesn't "ask" for any more air and you can bet your bottom dollar it wasn't being "strangled" by the 32mm carbs.

You understand of course that switching to 40mm carbs requires new hand throttle gearing and new throttle cables to match as the R80 items aren't the same as those used with R100 (40mm) carbs.
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Old 04-06-2013, 03:24 PM   #5
Hookalatch OP
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Thanks for the replies. I have the carbs done and ready to install once my cylinder heads are finished. I split the difference between the Bing book and what was in the carbs by starting with a 2.68 needle jet but leaving the needle in the 2nd notch. I know this may not be the final jetting but since I am completely reassembling everything with many parts new to the bike I want everything as close to good as possible.

I stated in the original post twice that I was using R100RS parts, not the R80 parts.

Chuck
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Old 04-08-2013, 06:30 PM   #6
Plaka
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Quote:
Originally Posted by Hookalatch View Post
Thanks for the replies. I have the carbs done and ready to install once my cylinder heads are finished. I split the difference between the Bing book and what was in the carbs by starting with a 2.68 needle jet but leaving the needle in the 2nd notch. I know this may not be the final jetting but since I am completely reassembling everything with many parts new to the bike I want everything as close to good as possible.

I stated in the original post twice that I was using R100RS parts, not the R80 parts.

Chuck
true, but you didn't say what parts.
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Old 04-08-2013, 07:21 PM   #7
robtg
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Quote:
Originally Posted by Plaka View Post
true, but you didn't say what parts.
....... I am using all stock R100RS parts from the airbox cover thru the cylinder and piston.......


Clear to me.
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Old 04-08-2013, 07:31 PM   #8
Plaka
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Quote:
Originally Posted by robtg View Post
....... I am using all stock R100RS parts from the airbox cover thru the cylinder and piston.......


Clear to me.
Well, yeah. it's your project. The idea is to make it clear to other people. If you are using 100RS airbox (flat top), carbs, heads, pistons and jugs, just say that. You're not texting here, you can write it out. I just said more in 10 words than you did in 11...

Now are you using the throttle gear and cam out of the RS too? I don't know if it matters, so long as the butterflies open all the way it shouldn't much.
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Old 04-08-2013, 08:08 PM   #9
robtg
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Quote:
Originally Posted by Plaka View Post
Well, yeah. it's your project. The idea is to make it clear to other people. If you are using 100RS airbox (flat top), carbs, heads, pistons and jugs, just say that. You're not texting here, you can write it out. I just said more in 10 words than you did in 11...

Now are you using the throttle gear and cam out of the RS too? I don't know if it matters, so long as the butterflies open all the way it shouldn't much.

I just pulled that line from the OP. You are responding to the wrong person.
The OP was perfectly clear, you missed what he was writing.
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Old 04-13-2013, 03:29 PM   #10
Hookalatch OP
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Quote:
Originally Posted by Plaka View Post
Well, yeah. it's your project. The idea is to make it clear to other people. If you are using 100RS airbox (flat top), carbs, heads, pistons and jugs, just say that. You're not texting here, you can write it out. I just said more in 10 words than you did in 11...

Now are you using the throttle gear and cam out of the RS too? I don't know if it matters, so long as the butterflies open all the way it shouldn't much.
Actually it is not Robert's project (although I unsucessfully tried to get him to do my cylinder heads), it is my project. I think he was just pointing out that it is clear to the average person. And yes I am using the 40mm throttle cam, the required cover, and the correct throttle and choke cables for the 40mm carbs, Didn't think I needed to list all that since my only question was about stock jetting for the carbs,

You often provide very useful advice. This wasn't one of those times.

Chuck
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Old 07-01-2013, 01:16 PM   #11
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Final jetting adjustments

In case anyone stumbles across this thread during a search I thought I would post my final (at least at this point) jetting changes. To recap- the engine is a converted 1984 R80 that is now basically a stock 1982 R100RS. The bike now has an S fairing and retains the stock R80RT 37/11 rear drive gearing. The 40mm Bings are stock for the 1982100RS engine.

Bing recommended 160 main jets and 35 idle jets. I am still using those jet sizes. They recommended a 2.66 needle jet and the needle in the second groove from the top. I went with a 2.68 needle jet and left the needle in the second groove. The carbs had already been converted to independent floats when I purchased and rebuilt them.

With this jetting the bike starts readily and idles fine. Acceleration was brisk and without a hiccup. Even with the lower R80 gearing the bike averaged 41-43mpg on some recent trips. The only issue was at steady throttle at about 4000rpm's the bike would occasionally stumble or surge. Felt like the first indications of needing to go on reserve. Strong headwinds or gradual inclines made the problem worse. Cracking the throttle open at these times resulted in flawless acceleration.

The way the bike is geared 4000 rpm is 60 mph and takes a very small throttle opening. I raised the needles to the 3rd notch and all surging and stumbling is gone now. This may decrease my mileage a little because most of the cruising done before was dangerously lean but the bike is running very well. I may play with decreasing the needle jet back to a 2.66 or changing the main but for now I am happy and will wait to see how the overall mileage gets affected.

Chuck
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Old 07-01-2013, 01:37 PM   #12
supershaft
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It sounds like you might be better off gong with a 270 needle jet and keeping the jet needle on the 2nd clip. If you do stay on the third clip you might be able to go back down to the 266's.

The mains are often better off leaner than stock. They jet them rich to be on the safe side. They jet them lean at idle and cruise for the EPA.

A huge factor in all this is the airbox top. I highly recommend trying the R80 one large/one small airbox horns versus the two large and remember that to give both setups an equal chance you might have to rejet for both setups. They make a BIG diff.
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Old 07-01-2013, 02:09 PM   #13
Hookalatch OP
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Quote:
Originally Posted by supershaft View Post
It sounds like you might be better off gong with a 270 needle jet and keeping the jet needle on the 2nd clip. If you do stay on the third clip you might be able to go back down to the 266's.

The mains are often better off leaner than stock. They jet them rich to be on the safe side. They jet them lean at idle and cruise for the EPA.

A huge factor in all this is the airbox top. I highly recommend trying the R80 one large/one small airbox horns versus the two large and remember that to give both setups an equal chance you might have to rejet for both setups. They make a BIG diff.
I don't think I have the ability to tell the difference in performance from an R80 to an R100 airbox top and probably not be able to tell the difference between a 2.70 or 2.68 needle jet. At least not without timing devices or an air/fuel mix measuring device. I can figure out which way to go to correct problems like the stumbling/surging but once things are pretty close my butt dyno isn't all that sensitive.

This isn't a good time for carb tuning anyway. It has been over 110 degrees for 4 days now and it is supposed to be 114 tomorrow. The good news is at least its humid!

Chuck
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Old 07-01-2013, 03:09 PM   #14
supershaft
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Can't tell the difference between night and day? That's the difference between those two airbox tops. It only take a minute to change them.
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Old 07-01-2013, 03:26 PM   #15
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If there is a big difference I could probably tell that. I just figured it would be a small change. Its a moot point anyway since I sold the R80 airbox top along with all the other R80 top end parts. I appreciate the suggestions anyway.

Chuck
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