Carburetor Installation Angle - Airhead

BrokenR80RT · 03-26-2011, 09:02 AM

My carbs have been sitting in my basement for a few weeks after my rebuild, while I do other things on my bike. It's time for an install.

Anyone have any idea what angle they should be installed at relative to horizontal (or vertcal)? I do the fluid mechanics in my head and some tilt angle would definitely benefit the mixture motion. Anyone know what is optimum or the "standard" install angle? It's an R80RT.

Thanks!

jimbee · 03-26-2011, 09:11 AM

don't know if it is optimum or standard, but i place a short bullet level on the bottom of the float bowls and then set them level.

happy to learn if there is a better way....

Quote:

Originally Posted by BrokenR80RT

My carbs have been sitting in my basement for a few weeks after my rebuild, while I do other things on my bike. It's time for an install.

Anyone have any idea what angle they should be installed at relative to horizontal (or vertcal)? I do the fluid mechanics in my head and some tilt angle would definitely benefit the mixture motion. Anyone know what is optimum or the "standard" install angle? It's an R80RT.

Thanks!

Grider Pirate · 03-26-2011, 09:13 AM

Quote:

Originally Posted by jimbee

don't know if it is optimum or standard, but i place a short bullet level on the bottom of the float bowls and then set them level.

happy to learn if there is a better way....

There is nothing you can do about the front to back level. They should be as close as you can get them to level left to right. A Few degrees either way won't hurt anything. I find that Mark I eyeballs work just fine.

supershaft · 03-26-2011, 10:08 AM

They almost always came from the factory slightly tilted in. I think the biggest advantage of doing this is keeping the cables straighter and I think cable routing is crucial.

I friend said that when he worked for BMW AG in the early '70s they told him to get back by the end of the mufflers and visually line up the edge of a float bowl with a cylinder fin and that gets the perfect lean. I do think that does it.

Wirespokes · 03-26-2011, 10:57 AM

I also set them up with a small level. It's tough finding a reference to set them by otherwise - like SS says, eyeball them from the rear against a fin. But I doubt it makes a whole lot of difference if they're off a little bit. The only thing it might affect is the throttle cable adjustment if they don't return to the same spot.

supershaft · 03-26-2011, 11:08 AM

I think it effects the looks because they did come with the carbs slightly leaned in. Most importantly it's for the cables. Not so much the adjustment but relieving them of stress right there at the cable end. Right where the cable end is apt to come loose from the sheath if the cable is cocked to the side just a bit there. If you have been around bikes much, we have all seen this play out over and over. Well, cocking them slightly in largely alleviates that issue.

Tosh Togo · 03-26-2011, 11:18 AM

Quote:

Originally Posted by Wirespokes

I also set them up with a small level. It's tough finding a reference to set them by otherwise - like SS says, eyeball them from the rear against a fin. But I doubt it makes a whole lot of difference if they're off a little bit. The only thing it might affect is the throttle cable adjustment if they don't return to the same spot.

Using a level is only useful if the bike itself is verified to be level first...and most garage floors ain't perfectly level.

A few degrees off dead-plumb won't matter to the carbs one bit, and the aforementioned slight inward tilt to keep the cables happy is a good idea...cables are happiest when the housings are as straight as you can make them for the situation.

Like this-

supershaft · 03-26-2011, 11:29 AM

Thanks TT. I got to thinking about all the cables I have seen separated there at the end. The biggest culprit of that is cables that are too long. It almost always cocks the cable end and F's up the cable. It is a job ordering the right cable but it really matters in the long run as far as keeping your bike working at its best.

I couldn't tell you how many choke and throttle cables I have seen F'ed up by people taking them off the carbs without first taking the adjuster out of the carb top. It kinks the cable badly and ruins the sink from then on.

fishkens · 03-26-2011, 11:54 AM

Quote:

Originally Posted by supershaft

I couldn't tell you how many choke and throttle cables I have seen F'ed up by people taking them off the carbs without first taking the adjuster out of the carb top. It kinks the cable badly and ruins the sink from then on.

SS, excuse my brainfart currently in progress, but how can one remove the cables from the carbs w/out removing the adjuster?

The adjuster is part of the cable, right? My later model cables don't have a slice on the adjuster allowing the cable to be separated from the adjuster.

Are you saying removing the top of the carb w/out removing the adjuster?

Just curious.

supershaft · 03-26-2011, 12:04 PM

By taking the carb tops off. Then they think they don't have to re-sync the cables but what they don't know is that they just F'ed up the sink for good as long as they use those cables.

fishkens · 03-26-2011, 12:22 PM

Quote:

Originally Posted by supershaft

By taking the carb tops off. Then they think they don't have to re-sync the cables but what they don't know is that they just F'ed up the sink for good as long as they use those cables.

Ahh, take the carb top off, wrestle with the cables at the throttle and choke to remove the cables, remove the carbs and try to put it all back together w/out balancing the carbs. Check.

Yes, sometimes it takes just half the time to do it right.

matteo · 03-26-2011, 01:36 PM

Quote:

Originally Posted by Tosh Togo

Like this-

Dude. No way. You need to show more pictures. Or start a new thread. 1954 r51/3?

matteo · 03-26-2011, 01:40 PM

Quote:

Originally Posted by matteo

Dude. No way. You need to show more pictures. Or start a new thread. 1954 r51/3?

Ok, I saw the other thread for this bike.

Wirespokes · 03-26-2011, 07:11 PM

Are you guys hauling around the kitchen sink with you??? What sink are you talking about?

And what does that have to do with synching the carbs?

(all in jest - it takes more than a mis-spelling to throw me off track, but sometimes I just can't help myself. Like all the times I see 'brake' (the Brembo kind) spelled 'break' (something broke or busted). Stuff like that.)

BrokenR80RT · 03-27-2011, 07:17 AM

I'll go with the fin method......just have to figure out which eye to align it with......

.

03-26-2011, 09:02 AM	#1
BrokenR80RT ^OP But I'll fix it. Joined: Oct 2010 Location: Michitucky Oddometer: 157	Carburetor Installation Angle - Airhead My carbs have been sitting in my basement for a few weeks after my rebuild, while I do other things on my bike. It's time for an install. Anyone have any idea what angle they should be installed at relative to horizontal (or vertcal)? I do the fluid mechanics in my head and some tilt angle would definitely benefit the mixture motion. Anyone know what is optimum or the "standard" install angle? It's an R80RT. Thanks!

03-26-2011, 10:57 AM	#5
Wirespokes Beemerholics Anonymous Joined: Jul 2002 Location: Jackson's Bottom Oregon Oddometer: 7,391	I also set them up with a small level. It's tough finding a reference to set them by otherwise - like SS says, eyeball them from the rear against a fin. But I doubt it makes a whole lot of difference if they're off a little bit. The only thing it might affect is the throttle cable adjustment if they don't return to the same spot. __________________ Wanted: Dead, smashed, crashed or trashed gauges BMW GAUGE REPAIRS - TACHSPEEDOCLOCKVOLT METER PODs & LIGHT BOARD*

03-26-2011, 07:11 PM	#14
Wirespokes Beemerholics Anonymous Joined: Jul 2002 Location: Jackson's Bottom Oregon Oddometer: 7,391	Are you guys hauling around the kitchen sink with you??? What sink are you talking about? And what does that have to do with synching the carbs? (all in jest - it takes more than a mis-spelling to throw me off track, but sometimes I just can't help myself. Like all the times I see 'brake' (the Brembo kind) spelled 'break' (something broke or busted). Stuff like that.) __________________ Wanted: Dead, smashed, crashed or trashed gauges BMW GAUGE REPAIRS - TACHSPEEDOCLOCKVOLT METER PODs & LIGHT BOARD*

03-27-2011, 07:17 AM	#15
BrokenR80RT ^OP But I'll fix it. Joined: Oct 2010 Location: Michitucky Oddometer: 157	Thanks.... I'll go with the fin method......just have to figure out which eye to align it with.......

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03-26-2011, 10:08 AM	#4
supershaft because I can Joined: Sep 2010 Location: San Francisco Bay area Oddometer: 6,200	They almost always came from the factory slightly tilted in. I think the biggest advantage of doing this is keeping the cables straighter and I think cable routing is crucial. I friend said that when he worked for BMW AG in the early '70s they told him to get back by the end of the mufflers and visually line up the edge of a float bowl with a cylinder fin and that gets the perfect lean. I do think that does it.

03-26-2011, 11:08 AM	#6
supershaft because I can Joined: Sep 2010 Location: San Francisco Bay area Oddometer: 6,200	I think it effects the looks because they did come with the carbs slightly leaned in. Most importantly it's for the cables. Not so much the adjustment but relieving them of stress right there at the cable end. Right where the cable end is apt to come loose from the sheath if the cable is cocked to the side just a bit there. If you have been around bikes much, we have all seen this play out over and over. Well, cocking them slightly in largely alleviates that issue.

03-26-2011, 11:29 AM	#8
supershaft because I can Joined: Sep 2010 Location: San Francisco Bay area Oddometer: 6,200	Thanks TT. I got to thinking about all the cables I have seen separated there at the end. The biggest culprit of that is cables that are too long. It almost always cocks the cable end and F's up the cable. It is a job ordering the right cable but it really matters in the long run as far as keeping your bike working at its best. I couldn't tell you how many choke and throttle cables I have seen F'ed up by people taking them off the carbs without first taking the adjuster out of the carb top. It kinks the cable badly and ruins the sink from then on.

03-26-2011, 12:04 PM	#10
supershaft because I can Joined: Sep 2010 Location: San Francisco Bay area Oddometer: 6,200	By taking the carb tops off. Then they think they don't have to re-sync the cables but what they don't know is that they just F'ed up the sink for good as long as they use those cables.