No Sweet Spot

[bbelk]

I have a 1979 R76 with flat top Bing carburetors. There does not seem to be a sweet spot in the float adjustment between flooding and starving. If I get it tight enough not to drip, it won’t run at speed.

Do I need to replace anything other than the rubber tip on the needle valve?

[Ken in Oklahoma]

I have a 1979 R76 with flat top Bing carburetors. There does not seem to be a sweet spot in the float adjustment between flooding and starving. If I get it tight enough not to drip, it won’t run at speed.

Do I need to replace anything other than the rubber tip on the needle valve?

Brad, have you been posting about your flat top carbs and I've missed it (or forgotten about it)? I'm curious for some additional information such as what has been done with the carbs to solve the problem, and whether you've tried new floats.

Notwithstanding what I'd like to know, your problem on the surface sounds like the problems I've had on other bikes, particularly with my '77 R100/7 (the carbs with the pointy tops). I had spent a lot of time with the carbs, adjusting the float level just right, swapping float needles, inspecting and cleaning the seats, and adjusting the floats. And every time the only fix that kept working was to put in new carb floats.

In short, heavy (gas soaked) floats seem to have been my problem. My success in finally 'fixing' my carbs led me to keep a new set of floats in stock. Additionally, having purchased a cheap set of digital scales, I've recorded the new float weights and noted the weights of the old floats in my records.

Unfortunately, I'm not sure I remember where those records are. Are they penciled in one of my repair manuals, or on my logbook (Yes, I started one, despite Duane telling me that's what I needed to do), or is the info somewhere on my hard drive?

If you haven't done so already, buy some new floats. You're going to need them sooner or later. If it turns out that heavy floats weren't your problem, you will still have the warm feeling of knowing that you have a nice new light set of floats right at your fingertips (unless you forgot which box you put them in).



Ken

[Garnet]

+1 on the new floats.

Ken,you need to start a log book to track where you have looged all the info on your bikes.

[bbelk]

Brad, have you been posting about your flat top carbs and I've missed it (or forgotten about it)? I'm curious for some additional information such as what has been done with the carbs to solve the problem, and whether you've tried new floats.

Ken

This is the first post on this issue. I have never ventured very far into any of my carburators so this is new to me. Depending on how proud the parts guy is of them, I will probably go ahead and heed your advice regarding the floats themselves.

[bbelk]

Ken,you need to start a log book to track where you have looged all the info on your bikes.

Being unable to remember what day it is most of the time, I keep logs on everything starting with the first time I have to do something to it. Cars, Boats, Hot Water Heaters, Scuba stuff, Motorcycles, Airconditioners, Me, and the list goes on.

I have everything in Microsoft Word files which lives nicely syncronized between my Smart Phone, my work and my home computers. Some of this nice infrustructure is going away as I leave regular imployment, and I have I-phone envy, so I may have to convert 20 years worth of this stuff to something like Google Docs. Then I could get at it from anywhere.

[Deleted User 61]

Unfortunately, I'm not sure I remember where those records are.

Well, new floats should weigh nearly the same, every time. And depending on the weight of the old floats, they will probably go to a landfill never to be heard from, again.

Or you could keep those particular records with your scale.

[bbelk]

What is the exchange rate to Merican?


Part No. Part Description Quantity Unit Price Net
60060 CARB REBUILD KIT R80/7. R45/65 1978-79 (FLAT TOPS) FOR 2 CARBS, DOES NOT INCLUDE...) 1 9.50 9.50

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60120 FLOAT BOWL GASKET ALL 1970 ON*...) 2 1.50 3.00

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60420 FLOAT ASSEMBLY...) 2 14.00 28.00

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60422 FLOAT ASSEMBLY RETAINING PIN...) 2 0.50 1.00

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60432 FLOAT NEEDLE ALL 1978 ON & ALL 1000cc 40mm...) 2 7.85 15.70

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60438 FLOAT NEEDLE RETAINING CLIP...) 2 0.75 1.50

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Carriage (May vary and be charged extra) 0.00 0.00

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Amount Rate VAT Due
£58.70 15% £0.00
Total Goods £58.70
Total VAT £0.00
Total Due £58.70

[Garnet]

Takes bout $1.62 US to buy a Britsh Pound.

[Ken in Oklahoma]

What is the exchange rate to Merican? . . . Total Due £58.70

Hmmm, how about just going down to Lone Star BMW and ordering a couple floats, and then trying them. The float pin you can wiggle out and put back in. You don't have to worry about it backing out because the float bowl won't let it. You can examine the float needles for anything that might look wrong. Similarly you can inspect the seats. As for the carb kits, do you have reason to suspect that the carbs need them?

I recognize that you're coming from a different place than I am. You believe in treating your airheads right, including preventative maintenance to forestall problems that might inevitably come up. My concern is that you're changing several things at the same time. I would be inclined to change the floats and see how the carbs act. It's easy to do. You don't even have to remove the carbs from the bike.

Then, if that doesn't fix the problem, that would be the time to "overhaul" the carbs.

I might order all the same stuff you are, but I would be inclined to put everything but the floats in my spares stock. In fact I think I pretty much have.

Just a thought. I think my approach won't work for you, but I thought I'd throw it out there.

By the way, I think the concensus has been to buy the stock floats as opposed to the two piece ones which were purportedly developed for using airhead engines to power aircraft.



Ken

[bbelk]

What is the exchange rate to Merican? . . . Total Due £58.70

Hmmm, how about just going down to Lone Star BMW and ordering a couple floats, and then trying them. The float pin you can wiggle out and put back in. You don't have to worry about it backing out because the float bowl won't let it. You can examine the float needles for anything that might look wrong. Similarly you can inspect the seats. As for the carb kits, do you have reason to suspect that the carbs need them?

I recognize that you're coming from a different place than I am. You believe in treating your airheads right, including preventative maintenance to forestall problems that might inevitably come up. My concern is that you're changing several things at the same time. I would be inclined to change the floats and see how the carbs act. It's easy to do. You don't even have to remove the carbs from the bike.

Then, if that doesn't fix the problem, that would be the time to "overhaul" the carbs.

I did order all that stuff. That float was the only one they had, so if its wrong, I am screwed. I do tend to do things all all once and will replace the all the rubber in the carburator. It is simple enought that I may do it one step at a time and test run between steps.

As for buying from Lonestar. Its in North Austin, I am in south Austin. You may be closer.

I might order all the same stuff you are, but I would be inclined to put everything but the floats in my spares stock. In fact I think I pretty much have.

Just a thought. I think my approach won't work for you, but I thought I'd throw it out there.

By the way, I think the concensus has been to buy the stock floats as opposed to the two piece ones which were purportedly developed for using airhead engines to power aircraft.



Ken