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Weird sync issue..

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srankin
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Location: Spencerport, NY USA
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Re: Weird sync issue..

Post by srankin »

Did you ever compare or examine the slides on your original carbs to see if they were worn or damaged compared to the replacement carbs?

Not knowing the shape of the originals when you got the bike, I can't guess how much damage time, maintained or lack of, riding and storage, or mileage did.

I guess, I just can't wrap my head around your not being able to fix the original carbs. I say this without knowledge of their condition.

One of my high mile carbs finally met the recycle bin when it started a vacuum leak in the butterfly shaft. The cost and trying to find someone to repair was more than the carb. Now if it had been a Brough Superior original carb, well, money and time is a different story, LOL.

Hopefully you have solved your problem and can get on with riding. Cheers, St.
Owner of a 84, R80RT and 78, R100RS

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schrader7032
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Re: Weird sync issue..

Post by schrader7032 »

A question about the "1-hole" situation... Did both of the original carbs have only the one hole? If so, then why did one carb seem to work OK while the other one did not?

Snowbum has a lengthy article on problems with the early carbs. I didn't read where he mentions the differences in these holes, but he has some specifics about how to get the carbs stable.

https://bmwmotorcycletech.info/earlybingR75CV.htm
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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skyler.robbins
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Joined: Sat Sep 22, 2018 4:14 pm

Re: Weird sync issue..

Post by skyler.robbins »

Hey Hey Kurt..
I feel like the right carb was working correctly.. one thing that had me puzzled on it was that I had to have the idle/mix screw out 1.25 turns.. at that amount, the whole bike felt rich when giving throttle and having slight pops under load.. but perhaps the left carb was contributing to the bad response.
The slides of both carbs are perfect with no scuffing and nice movement. I should have swapped those out from the good working carbs just to see if that was a factor.

I did another thorough examination of the bad carb.. It looks like I "might" have a hairline fracture at the bottom of the pilot jet tower.. hard to get a close up picture, but with the eye, it looks slightly cracked. This part connects to the channel that goes to the single hole.

The only other possible issue is that the butterfly valve area needs rebuilding.. which I very well may do after I get the bike running great with my other carbs that I'll pick up this weekend.

Thanks again!
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srankin
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Re: Weird sync issue..

Post by srankin »

So, your crack could mess with mixture. If you have a crack in the needle area, toss em.

I don't remember you mentioning if you compared sliders from one set of carbs to the other?

Are the butterflies messed up? What gives you the impression they need rebuilt? Are the shafts leaking like one of my old carbs was?

Unless they are in terrible shape with corrosion, or some kind of damage or there is a vacuum leak at the shaft bushing, I wouldn't bother messing with them. St.
Owner of a 84, R80RT and 78, R100RS

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skyler.robbins
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Re: Weird sync issue..

Post by skyler.robbins »

srankin wrote:
Tue Aug 17, 2021 1:13 pm
So, your crack could mess with mixture. If you have a crack in the needle area, toss em.

I don't remember you mentioning if you compared sliders from one set of carbs to the other?

Are the butterflies messed up? What gives you the impression they need rebuilt? Are the shafts leaking like one of my old carbs was?

Unless they are in terrible shape with corrosion, or some kind of damage or there is a vacuum leak at the shaft bushing, I wouldn't bother messing with them. St.
Yeah the butterflies seemed fine.. nice movement, clean, no air leaks so I didn't mess with them.

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skyler.robbins
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Re: Weird sync issue..

Post by skyler.robbins »

Just a final update all..
Got the "new to me" 64/32/11 and 64/32/12 carbs all cleaned up.
Took it out for a good long ride today.. rides like a dream!
Hooked it up to both sync tools.. got it dialed in to perfection.

All is well!

Thanks again for the suggestions along the way of diagnosing this.

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srankin
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Re: Weird sync issue..

Post by srankin »

Thanks for the follow up, St.
Owner of a 84, R80RT and 78, R100RS

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