Potentially a newbie question. I am rebuilding my R80ST carbs for the first time was checking the model IDs as is recommended to get the base setting before reassembly. The sheet I have identifies the R80ST has having IDs 351 and 352, but what I actually have is 323 and 324, which the sheet identifies as the R80 (at least the displacement is the same). Given the base settings are different for these ID sets, which do I follow?
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Bing Carb ID mismatched to model (323&324 on a R80ST)
- Thread starter bmcdonou
- Start date
GTRider
52184
What is the production date on your ST? You can find that by inputting the last 6 digits of VIN at https://realoem.com. I’m guessing you have an ‘83 model, as those 323/324 carbs shipped OEM on the bikes. The 351/352 designation came after jetting changes outlined in SI 2120 dated August of 1984 were applied in production. The changes can be viewed at https://bmwmotorcycletech.info/R80-fuel-mileage-problems.htm
As to which settings to follow, I run the 351/352 settings on my own ST, along with the smaller intake snorkel on one side as discussed in the bulletin. I did not change to the updated slide#; the bike seems to run well without that.
HTH.
Best,
DeVern
As to which settings to follow, I run the 351/352 settings on my own ST, along with the smaller intake snorkel on one side as discussed in the bulletin. I did not change to the updated slide#; the bike seems to run well without that.
HTH.
Best,
DeVern
Correct. It is an '83 (production 12/82). Thank you for connecting the dots and for sharing the bulletins. I had not seen those.
The current carbs have the 150 and 40 jets, so I'll have to update to the 351/2 setting. Main jets are cheap, but darn those needle jets are $50+ for the pair - ouch. I also keep an eye out for the alternative snorkel of mine doesn't have it already (suspect it doesn't but will check). Thanks for the help!
The current carbs have the 150 and 40 jets, so I'll have to update to the 351/2 setting. Main jets are cheap, but darn those needle jets are $50+ for the pair - ouch. I also keep an eye out for the alternative snorkel of mine doesn't have it already (suspect it doesn't but will check). Thanks for the help!
I would set the carbs up based upon the numbers of the carb. Do a proper synch of the idle mixture and speed along with the throttle cable tension. Then evaluate the engine's performance in terms of start off response and how the bike runs at mid throttle range say around 60-65 mph. If you dare, you could see what kind of top end speed you have...do you run out of RPM changes while you still have some throttle to use? What is your gas mileage? What do the plugs look like when you do a throttle chop at cruising speed? You could adjust the jets/settings from there.
Just curious, have you owned this bike from day one?
OM
I wasn't born yet when this bike was new
Lucky you!I wasn't born yet when this bike was new
Older machines have lots of chances to have different parts swapped in as they run through different owners.
OM
While we are on the topic of my carbs, separate but related question - what is supposed to be used to be connected to the vacuum ports?
When I took the carbs off, there were hoses connected to those ports. Thus I thought they were some sort of gas overflow vents with hoses leading away from the heads. However, I now realize they are the vacuum ports and the hoses run into the top engine cover (I have yet to trace them all the way). Does this sound familiar to anyone? I cannot find any examples or diagrams online showing this setup.
I know the at least some of STs had a rebreather system, which mine has been deleted, but I don't believe these ports were part of that system.
My experience is that these usually need to be capped in some manner otherwise risk air leaks. I've included a picture of what my port looks like.
When I took the carbs off, there were hoses connected to those ports. Thus I thought they were some sort of gas overflow vents with hoses leading away from the heads. However, I now realize they are the vacuum ports and the hoses run into the top engine cover (I have yet to trace them all the way). Does this sound familiar to anyone? I cannot find any examples or diagrams online showing this setup.
I know the at least some of STs had a rebreather system, which mine has been deleted, but I don't believe these ports were part of that system.
My experience is that these usually need to be capped in some manner otherwise risk air leaks. I've included a picture of what my port looks like.
Sorry. Please ignore. If there was a way for me to delete this I would. Of course, as soon as I post, I watch Brooks Garage videos on the pulse air rebreather system, and indeed they were part of this. I will plan to follow his tutorial remove these hoses, fill the hole on the air box, and source some sort of plug for the vacuum fitting.
Put a screws into them or cover them with a vac caps; then you can remove them if you use a vacuum balancer. I suspected that there was a hose between the carbs to balance the vacuum signal between them, but that was just a guess. Also possible is the notion they went up into the top cover the pick us the oil mist from the crankcase breather valve. Again, just a guess and will probably be immediately contradicted by one of the experts.
pauls1150
MOA #24991, south of Los Angeles
Cap them; standard vacuum port caps work fine. The "balancing" of vacuum is worthless (and might even be degrading due to extra volume or potential leaks) if the valves and carbs are set up properly.
(The breather just dumps the oil mist into the airbox.)
Snowbum has more info at https://bmwmotorcycletech.info/pulseair.htm
(The breather just dumps the oil mist into the airbox.)
Snowbum has more info at https://bmwmotorcycletech.info/pulseair.htm
I am curious enough to bite - why do you feel balancing via vacuum is worthless? If you control for the extra volume or leaks do you not feel it can result is a more/less balanced system? Prefer the RPM drop or other method?
GTRider
52184
I think the comment referred to leaving the crossover vacuum lines connected once the pulse air system has been removed from the airbox and the relevant holes and ports properly plugged. The vacuum tubes from the carbs ran up to a 3-way “tee” fitting at the airbox, where vacuum was then supplied to the pulse air bits. Some prefer to just cap the vacuum ports at the carbs and remove the vacuum hoses and the tee at the airbox, and plug the hole where the tee lived. Some prefer to cap the tee inside the airbox and let the carbs stay connected via the vacuum lines. On the airheads, I don’t think it makes much difference either way as there are other adjustments/settings at the carbs that have greater influence. But, I once rode a fuel-injected R1100RSL, with injector bodies similarly capped and vacuum tube removed, into the Irv Seaver shop in California for service and the German mechanic there was quite emphatic about needing those vacuum lines in place to get a proper synch on the TBs. And, when I got the bike back with new tubes installed I will say it was the smoothest that bike had run since new so there’s that.
Best,
DeVern
pauls1150
MOA #24991, south of Los Angeles
Obviously I was not clear on this, sorry....
If you have a vacuum balancing gauge (whether it's home-made, a differential gauge [where the center = "0"], a Twin-Max, multiple vertical tubes of liquid, or whatever), yes it is worthwhile to equalize the vacuum pull of the two cylinders. This helps ensure equal loading of the work that each cylinder does.
BUT - when that task is completed, THEN cap them off. Having the cylinders "share" vacuum negates your work of balancing because the Volume of the intake path is now constantly changing: while one cylinder is on its Intake stroke, the other is on Power stroke. You also have no need to increase the volume of the vacuum paths due to the hose itself (and maybe it will develop a pinhole or a tear someday).
I agree that Seaver's usually does excellent work. But... My present 1150RT, and my past 1100RT and past 1150RS all had no vacuum crossover, nor the infamous charcoal canister; I pulled it all off. My bike is smooth enough that a coin sitting on the gas tank at idle will not shake off. "Smooth" is accomplished by being overly anally retentive (something I'm usually pretty good at) when adjusting the valves prior to attempting to sync the injectors AND when doing the cable adjustments plus "idle to 2500 rpm" balancing. (I was taught this by Joe at Marty's when I had the 1100, and it's worked well every time.)
I can only surmise that DeVern's mechanic vanted (or thought it necessary) to return ze bike to faktory specs...
Paul S
If you have a vacuum balancing gauge (whether it's home-made, a differential gauge [where the center = "0"], a Twin-Max, multiple vertical tubes of liquid, or whatever), yes it is worthwhile to equalize the vacuum pull of the two cylinders. This helps ensure equal loading of the work that each cylinder does.
BUT - when that task is completed, THEN cap them off. Having the cylinders "share" vacuum negates your work of balancing because the Volume of the intake path is now constantly changing: while one cylinder is on its Intake stroke, the other is on Power stroke. You also have no need to increase the volume of the vacuum paths due to the hose itself (and maybe it will develop a pinhole or a tear someday).
I agree that Seaver's usually does excellent work. But... My present 1150RT, and my past 1100RT and past 1150RS all had no vacuum crossover, nor the infamous charcoal canister; I pulled it all off. My bike is smooth enough that a coin sitting on the gas tank at idle will not shake off. "Smooth" is accomplished by being overly anally retentive (something I'm usually pretty good at) when adjusting the valves prior to attempting to sync the injectors AND when doing the cable adjustments plus "idle to 2500 rpm" balancing. (I was taught this by Joe at Marty's when I had the 1100, and it's worked well every time.)
I can only surmise that DeVern's mechanic vanted (or thought it necessary) to return ze bike to faktory specs...
Paul S
Thanks both for the clarity and deeper dive. I opted to remove the lines, cap the ports, and plug the t-hole. Good to know that smooth can be accomplished and what I should aim for. Right now, I am far from that so still working on it - have not gotten to the point where I can attempt to balance (chasing a fuel level, float issue).
Speaking of being anal about value adjustments - if I can bother you with another potentially stupid questions - where EXACTLY is TDC (or OT). I see the | OT S | (in a vertical orientation, of course), but I have been unable to find it written EXACTLY how to line that up. I tend to think that they wouldn't bother put a line above the OT is it wasn't there to be used, so I lined up that line with the line on the sidewall of the case. This mean the S is basically below the viewing window, and OT is in the bottom 1/3. I've seen others say to place the "OT" in the middle, and pictures where the OT and S are both in the viewing window (i.e. centered between the top and bottom lines). OR - does this amount of degrees not matter? If this isn't making any sense, I can take a pic tonight as to what I am lining up.
Speaking of being anal about value adjustments - if I can bother you with another potentially stupid questions - where EXACTLY is TDC (or OT). I see the | OT S | (in a vertical orientation, of course), but I have been unable to find it written EXACTLY how to line that up. I tend to think that they wouldn't bother put a line above the OT is it wasn't there to be used, so I lined up that line with the line on the sidewall of the case. This mean the S is basically below the viewing window, and OT is in the bottom 1/3. I've seen others say to place the "OT" in the middle, and pictures where the OT and S are both in the viewing window (i.e. centered between the top and bottom lines). OR - does this amount of degrees not matter? If this isn't making any sense, I can take a pic tonight as to what I am lining up.
pauls1150
MOA #24991, south of Los Angeles
Allow me to introduce you to two very useful libraries:
1) Snowbum (now deceased, unfortunately) has a HUGE site of airhead info, at https://bmwmotorcycletech.info
Go to https://bmwmotorcycletech.info/ignitionsingleplug.htm and about 2/3 of the way down, he explains what should be in the timing window.
2) The Internet BMW Riders also has a very use library of tech info, at https://ibmwr.org/index.php/airhead-tech-articles/
1) Snowbum (now deceased, unfortunately) has a HUGE site of airhead info, at https://bmwmotorcycletech.info
Go to https://bmwmotorcycletech.info/ignitionsingleplug.htm and about 2/3 of the way down, he explains what should be in the timing window.
2) The Internet BMW Riders also has a very use library of tech info, at https://ibmwr.org/index.php/airhead-tech-articles/
Great resources. I have certainly come across Snowbum's site before. It has the unique ability of being both extremely helpful while also eye-crossing.
Embarrassed to admit I am still confused on TDC, however. He initially explains that the line marking are for other purposes (+/- 3 degrees; timing?), and that OT centered in the window is TDC. But then explains further down that for 1981+, the marking above OT is TDC. I guess perhaps both could be true (dual purpose), and given the bike is 1982/3, reasonable to use the line vs centering OT.
"There is an OT marking on the flywheel for top dead center (exactly and fully, both pistons outwards)....Some Airhead motorcycles flywheels (clutch carriers) have some markings with two lines, they are 6° separated. These show the official limits for double images (use a strobe lamp), and thereby show maximum allowable differences between cylinders.....when the OT mark is centered in the timing window, assuming the flywheel is properly installed, both pistons are very precisely fully outwards." but then states further down "1981+: the LINE next to OT is TDC".
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