R75/6 carbs vs /7

Andey
Posts: 61
Joined: Wed Sep 02, 2020 12:45 am

R75/6 carbs vs /7

Post by Andey »

Basic question, are the differences between the /6 (64/32/9 set) and /7 carbs (64/32/13 set) just the jetting?

I had the /7 carbs installed with stock /7 jetting and it seems to make the bike run bad, but it seemed to run cooler, which for the summer months isnt a bad thing.

But i've rejetted it with the stock /6 jets...

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schrader7032
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Re: R75/6 carbs vs /7

Post by schrader7032 »

Pretty much correct, Andey. Best to use the /6 settings and confirm how the bike runs, what the plugs look like, gas mileage, etc. in order to tweak the end result.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Andey
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Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 carbs vs /7

Post by Andey »

Thanks!

I was wondering if the carb bodies themselves might have been different...

My /6 seems to be a bit of a Frankenstein, with a /7 brake light switch too... the previous owner just seemed to have bobbled the bike together...

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srankin
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Location: Spencerport, NY USA

Re: R75/6 carbs vs /7

Post by srankin »

Beware previous owners!

Being a denizen of an airhead repair shop, I have seen some wild things done to bikes.

The scary thing is work done on a bike by someone who thinks they are a mechanic, know all there is to know about airheads, and haven't got a clue.

Wiring stuff seems to be the biggest thing POs mess up.

I feel for you having myself suffered the wrath of a PO and his "Knowledge". In my case, money and time fixed the problem and my bike is a joy now.

Good luck with your repairs/restoration/riding. St.
Owner of a 84, R80RT and 78, R100RS

Andey
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Re: R75/6 carbs vs /7

Post by Andey »

Thanks, I think I’ll need some luck from time to time..!

Agree with the wiring... the rear harness was zipped tied to the subframe with a plastic sheath and those terrible hard plastic hardware store connectors added... those have no place on a motorbike in my opinion... just rewired everything this weekend to run inside the frame...

Puzzles me how people mistreat the bikes, don’t get me wrong, I’m definitely not a mechanic... but you have to do what’s right for the bike.

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srankin
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Location: Spencerport, NY USA

Re: R75/6 carbs vs /7

Post by srankin »

Some people ARE mechanics or electricians, some are not. Problem is when the ones who aren't think and act as if they are.

It is really sad when a previous owner has screwed a bike up so badly they don't want to or can't deal with it then unload it on some poor soul. I feel really bad for people wanting to buy their first airhead bike and finding it to be a nightmare.

The source of reliable places and people to work on airheads is shrinking. BMW has a kind of fuzzy thing about them. Some dealers won't work on them at all, some do but don't have mechanics that know the bikes. Independent shops exist but like any shop, it can be a gamble dealing with them.

As for individual mechanics, oh boy, I have seen some beauties. I have followed the forums of MOA, Airhead and Vintage for years. There are some people giving advice who shouldn't be.

I will be quite honest, I am a mediocre mechanic, and sometimes I don't give the best advice. I am not afraid to tell people this as well as to apologize for my bad advice or information.

I have spent this season getting my soiled dove into proper condition after buying it and finding out the previous owner did things he shouldn't have done. Now she is a thing of beauty and a joy to ride.

May you have a joy to ride. Cheers, St.
Owner of a 84, R80RT and 78, R100RS

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San Arthur
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Re: R75/6 carbs vs /7

Post by San Arthur »

Andey wrote:
Wed Sep 02, 2020 10:11 am
Thanks!

I was wondering if the carb bodies themselves might have been different...

My /6 seems to be a bit of a Frankenstein, with a /7 brake light switch too... the previous owner just seemed to have bobbled the bike together...
Andy would you post some pictures of your bike?

Thanks
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

Andey
Posts: 61
Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 carbs vs /7

Post by Andey »

Images are the current state (number plate facing camera) and when I first got it...

-Overhauled the cylinders, honed, new rings, new valves.
-Main stand bolts rusted through the main frame, so had to drill through and add a custom nut to the inside
-overhauled the front wheel, new bearings and seals, new disc, and had to hone the master cylinder due to the pitting... new seals on the piston...
-Italy rearsets...
-list goes on...

(Just realised this photo was before I did the wiring...)

long way to go, so much to do, but at least it starts and rides ok...
Attachments
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4FCE16BC-127D-4110-BF52-3319106D5909.jpeg

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srankin
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Location: Spencerport, NY USA

Re: R75/6 carbs vs /7

Post by srankin »

Well, the pictures look very good. I hand it to you that you are taking this in stride and restoring this bike yourself.

As long as you are enjoying or have the right mind set, even bad thing can be turned into good. I call my RS my soiled dove, perhaps lemonade would be a choice for your bike, LOL.

I like the feeling I get when I turn something broken and cobbled up into something sleek and magical. There is no better feeling than to pump up one's chest and say, "Yes, I restored this, you should have seen it when I got it".

Of course I do feel sorry for the people who find their bikes beyond their ability to fix and are left with a sour taste and disappointment.

Thank God we are on the good side of things. St.
Owner of a 84, R80RT and 78, R100RS

Andey
Posts: 61
Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 carbs vs /7

Post by Andey »

It’s a dream of mine to own a classic BMW...

Eventually it will need to be restored, might as well invest the time to learn! It’s definitely a journey doing it... and as you say ST, it’s satisfying...

I’m not a mechanic by trade, but I couldn’t bring myself to take it to the garage to a chump who would know less than me about the bike... so have to get your hands dirty... thank goodness for the community of knowledge online... wouldn’t have be able to do it otherwise

But the lady is tired, just took it out for a late night spin, the clutch definitely needs some attention... the bite point is a little high on the levers (actuates early on the pull)...

Diverging from my initial carb question too, the final drive has 37/11 stamped on it (it’s a r60 final drive if I’m not mistaken...the r75 should have a different ratio...) and My speedo is a w=1.186 green dial (which should’ve only have come from a r80)... is there anyway I can find out if it’s really a 37/11 final drive? No one would just use the housing right?

It’s completely hacked together...

I think I should open a new topic on this...!

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