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Old 06-08-2012, 12:17 AM   #1
GodOmelet OP
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Standard Carb Jets on the R100/7 at almost sea level

Hi Everybody,

In untangling the mystery running issues with my bike I discovered today that the idle and main jets are not spec. The PO had 50 idle jets and size 160 mains. Anybody care to offer up their own numbers on a similar bike? Mine's an early 77 (April I believe). The original owners manual I didn't know I had until recently states 45 idle and 150 main is spec.

Should I swap forthwith? I'm starting to suspect both bad gas and bad floats on my bike that I had recently disavowed any carb issues could be possible with. Also found all kinds of black sooty crap coating the enrichener circuit and slide. Weird.

Forgot to mention these are the 32mm column-top 64-32-19/20 Bings.

GodOmelet screwed with this post 06-08-2012 at 01:32 AM
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Old 06-08-2012, 01:02 AM   #2
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Flat top carbs?

BING book says:

Carb 19/20 with hard tip float needle....MJ is 150. IJ is 50

Flat top carb 219/220: MJ 150. IJ 50
Flat top carb 223/224: MJ 145, IJ 45
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Old 06-08-2012, 10:26 AM   #3
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What bb said. Usually the difference in idle jets is more than made up for by readjusting your mixture screw to each idle jet size. In other words, the different sizes don't make any difference unless your mixture screw is at real close to it's limit in or out. Most say at three turns out simpley because that is where the spring tension on the screw might let it back out. Your mains could probably be reduced to 135's for more power, less carbon build up, and better mileage. Most all the later models run 135's from 650's to 1000's. SO many people up their jet sizes like someone did on your bike thinking that it is going to make more power and run better but reality is just the opposite. Of course, be careful! Best power, economy, and engine longevity is real close to melted pistons. That's pretty much why most never go that direction. You have got to know what you are doing!

IMO the only jet that usually might need to be richer is the needle jet. Smaller mains and bigger needle jets often gets you a great performing bike. Even after a LOT of mods and performance increases.

supershaft screwed with this post 06-08-2012 at 10:33 AM
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Old 06-08-2012, 12:20 PM   #4
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Thanks. That's great info. FWIW, the needle jet is 2.68. I'll order some smaller mains just to see what's what.
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Old 06-08-2012, 12:22 PM   #5
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Mine aren't the flat tops. What is a hard tip? Mine wiggle in the holder.

Quote:
Originally Posted by boxerboy81 View Post
Flat top carbs?

BING book says:

Carb 19/20 with hard tip float needle....MJ is 150. IJ is 50

Flat top carb 219/220: MJ 150. IJ 50
Flat top carb 223/224: MJ 145, IJ 45
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Old 06-08-2012, 03:23 PM   #6
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Look at the opening of your needle jets. Are they round? They wear out and cause rich running off idle. They are a wear item and should be replaced.
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Old 06-08-2012, 03:31 PM   #7
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Float needles come in several styles. Two styles are common in Bing carbs used on our bikes. There is the rubber tipped float needle. Actually a specific rubber called Viton which is hard. The other type of tip is called a hard tip and it is metal. So no extra material added the needle is made from one piece of brass.

Float needles and floats need to be replaced occasionally when they won't seal. Some riders get much more use from them than others. The condition of the seat in the carb is also important but it is more complicated to replace.
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Old 06-10-2012, 09:47 PM   #8
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Quote:
Originally Posted by mykill View Post
Look at the opening of your needle jets. Are they round? They wear out and cause rich running off idle. They are a wear item and should be replaced.

You are talking about the needle jets on the slide, right? Not the float needles. I replaced both the jets and the slide needles. The jets were size 2.68 The bases looked fine.

My only remaining issue is the right cylinder refuses to come down to a reasonable idle. It's stuck at around 2K. I've got the throttle cables slack, the butterfly screw completely backed off, and the enricher is in the fully off position. I double checked for leaks, and am reasonably sure the carb is tight on both sides. I just replaced the float needle on this carb with a new one, and set the fuel level to 24mm. Could it be that I need to lower this to get a nice idle? It's weird because I did the same treatment on the left carb and that cylinder is running fine. I did a valve adjustment, and checked timing. I'm going to try swapping floats to see if that makes any difference.

I did clean up the advance unit the other day, but if that was the cause wouldn't both sides be running too fast?
Should I get new springs for the advance unit just for maintenance? What is the average lifespan of those little guys?
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Old 06-10-2012, 10:00 PM   #9
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The slide needles are the jet needles. The jet needles go into the needle jets. I basically just go by the condition of the jet needles. If they are worn, you can bet the needle jets are too. That's what they wear against.

Check and make sure the right carb's throttle plate closes completely. That might be your problem.

supershaft screwed with this post 06-10-2012 at 10:21 PM
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Old 06-10-2012, 11:17 PM   #10
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Quote:
Originally Posted by supershaft View Post
The slide needles are the jet needles. The jet needles go into the needle jets. I basically just go by the condition of the jet needles. If they are worn, you can bet the needle jets are too. That's what they wear against.

Check and make sure the right carb's throttle plate closes completely. That might be your problem.
Yeah the terminology for those always screws me up. I replaced both jets and needles so I hope that's not the issue.
The little seat for the needle jet seems to just sit very loosely in the carb body. I remember reading somewhere where this can be a problem if they don't sit deep enough or too deep, but I don't remember whether it was ok for them to sit loosely in there. When I take the carb off I'll take some picures if it looks fishy.
(This is the part that just pokes into the main air passage/venturi).
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Old 06-10-2012, 11:56 PM   #11
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That part is called the atomizer. I don't remember for sure right now but I think you can put those in upside down? At any rate, they need to go in the right way and then it should all be in exactly the right place when you tighten down the jet tube. BMW calls that part a venturi but I don't because the carb already has a venturi that actually is a venturi. I don't think you are remembering that right.
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Old 06-11-2012, 07:19 AM   #12
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Some suggestions:

Double check and make sure your throttle cable is not hung up on the right side, where the cable enters the adjuster at the carb.

On the high idle on the right side, pay attention to supershaft's suggestion to double-check how well the butterfly seals to the plenum chamber. If it's not a good seal, slightly loosen the butterfly screws (just enough that the plate can be centered and seat nicely to the sides of the chamber, then while pressing the plate inward, tighten the two screws).

Check that your intake stub (screwed into the head) is not loose (causing a vacuum leak).

Slightly richen the mixture on the right side. Too lean can result in high idle.

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Old 06-11-2012, 02:27 PM   #13
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Thanks for all the good suggestions. I'm still at a loss at the moment, I checked the butterfly, and it is seating perfectly. No light comes through and the dimple is in the correct orientation. The slide seems to move up and down to the stop completely and smoothly. The throttle cables are loose, the enrichers at the bottom stops, fresh gaskets on them and orientation double checked with the dimples pointing down at 4 o'clock or so towards the inlet channels.

I just replaced that carb's idle jet (from 50 to 50 because that's what they sent me- asked for a 45- The old 50 was looking a bit chewed up and the o ring was done even though I had replaced it in March). Is it possible that idle jet isn't sealing properly and I got a bum jet? I'll put the old one back with a new o ring and see what happens. Also wondering whether the float/fuel level can have a dramatic effect on idle speed. I set it dead on at 24mm. The valves are adjusted at .10mm intake and .20 exhaust.

Am I correct in the assumption that the timing/advance would not affect a single carb? When I disconnect the right side, the left can be set to idle right at 1k using the butterfly adjuster. Once out on the open road, the bike is fast, and pulls smoothly through all the gears. (The gearbox is a bit clunky, but I'm learning the tricks to smoother shifting) I feel like I could even pull a wheelie (though I never have tried)! When I slow down though, it's like having cruise control. The bike pulls when in gear with the throttle released obviously.

The one thing I haven't been able to check definitively for is air leaks. I didn't have a can of starter fluid or similar, so I just went over retightening the collars/clamps. I was considering using some teflon tape just as an experiment to help them seal better, and if that does the trick, order new rubber. Bad idea?

GodOmelet screwed with this post 06-11-2012 at 02:37 PM
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Old 06-11-2012, 03:00 PM   #14
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On a side note, anyone know what the standard throttle cable length for the /7 is? Are these the Europa bars? They are Magura I think. Here's a picture (sorry about the dark shot)


I ordered new cables based on what I thought to be stock handlebars, and the ones Mortons sent me were 40" I believe, whereas the old ones which are toast, with exposed bent up outer sheath, and ragged cables were 43". I tried fitting the 40" ones and they just barely fit, with very limited routing options. As you can see in the photo, the throttle cables look very unhappy in their current configuration. I think I may have to rotate the brake/throttle assembly to get a better angle, though for my arms, this is optimal.

While trying to diagnose the high idle I put the old ones back on just to have extra slack. They are very jacked up but work. If I can find the correct size maybe Mortons will exchange the 40" with me.

GodOmelet screwed with this post 06-11-2012 at 03:08 PM
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Old 06-11-2012, 03:08 PM   #15
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I do replace the rubber pieces when they are looking tired. Not every one every year but pretty regular. I've always had idle problems tho. I think my mufflers were drilled by a former owner and my bike seems louder than other Airheads.

I bought a tool for balancing the carbs. It's been a big help but I still have issues. I bought a Harmonizer. Being sold by Grok in the Vender's section. I like it. I think it is cheaper than some other balancing tools. And I can now balance the carbs but since I still have issues I must have an engine problem elsewhere.

My heads are in high mileage state. I will have them fixed sometime this year I hope. Then I should have a balanced engine. Yes?
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