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-   -   Stock 40mm Bing jetting (http://www.advrider.com/forums/showthread.php?t=875584)

Hookalatch 04-02-2013 10:36 AM

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

supershaft 04-02-2013 04:20 PM

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!

Plaka 04-03-2013 03:12 AM

Quote:

Originally Posted by Hookalatch (Post 21091169)
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.

lkchris 04-06-2013 11:25 AM

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.

Hookalatch 04-06-2013 03:24 PM

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

Plaka 04-08-2013 06:30 PM

Quote:

Originally Posted by Hookalatch (Post 21124422)
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.

robtg 04-08-2013 07:21 PM

Quote:

Originally Posted by Plaka (Post 21139925)
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.

Plaka 04-08-2013 07:31 PM

Quote:

Originally Posted by robtg (Post 21140400)
....... 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.

robtg 04-08-2013 08:08 PM

Quote:

Originally Posted by Plaka (Post 21140507)
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.

Plaka 04-08-2013 09:05 PM

Quote:

Originally Posted by robtg (Post 21140829)
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.

This is true.

Would have been helpful if you either quoted (w/ the forum tools) or used quotation marks to indicate you were reproducing what someone else said.

robtg 04-08-2013 10:02 PM

Quote:

Originally Posted by Plaka (Post 21141272)
This is true.

Would have been helpful if you either quoted (w/ the forum tools) or used quotation marks to indicate you were reproducing what someone else said.


The way I posted it I thought it would be obvious.

Hookalatch 04-13-2013 03:29 PM

Quote:

Originally Posted by Plaka (Post 21140507)
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

Plaka 04-13-2013 04:32 PM

Quote:

Originally Posted by Hookalatch (Post 21178307)
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

Could very well be. I ain't been getting enough sleep. (:snore not)

Hookalatch 07-01-2013 01:16 PM

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

supershaft 07-01-2013 01:37 PM

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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