Just wondering about something... It's a 1972 R50/5: - Good compression (140+ each side) - Carburetors rebuilt and decently synched by ear - Valves adjusted to spec. and re-checked recently - Valve rockers adjusted (rotate but no up and down movement) - Idles at about 1000 rpm or a bit more So it really runs great. I've just noticed that when the engine is fully hot (like after a 2 hour ride) there seems to be louder valve clatter and also some additional low-frequency engine noise or vibration (sounds more "throaty" on the exhaust). Hard to tell on the vibration if it's just my hands being tired after a long ride, but it does seem to be there. Maybe this is normal, in which case I'll stop worrying about it. I have tried fiddling with the throttle cable stops at the carburetors (raising or lowering a bit) but that doesn't seem to have much effect either way. Is it worth tuning some more, or is this just what the airheads do? Thanks.
My guess (and it is only that) is if all clearances are good the additional noise may be from the loss of damping from the heated oil (cold versus hot)
I have to say, when these bikes are "new" to us, we worry WAY more than they need to be worried about. They're tough old birds, and unless something is horribly wrong, they seem to go on and on and on.... You might need to satisfy your curiosity, but I know that I have worried about non-existent problems, a lot!
The sounds mine makes also change with temp but in subtle ways, there shouldn't be anything too drastic/alarming. About vibration... Try synching your throttle cables again. You want a nice even pull on both of them. I check this JUST off idle. About noise... Are you SURE there is NO up and down movement on the rockers? Even after torquing?
Thanks for the replies. I'm not using synthetic oil -- it is the BMW brand dino oil, 20W50 Also, I'm sure the valve and rocker adjustments are good. I checked them again (after hearing these noises) and they are right. Rockers don't move up and down. So it is probably just some things loosening up with heat. Makes sense, and I'll stop worrying for a while. If I ever run into an experienced /5 mechanic around here I might ask about synching the carbs some more. Seems that I have done all I can on them and random tweaking doesn't have improve things any more. it may be they are as good as they get, and I just don't know it.
I found the best way to tune (at idle and slightly above) the carbs that don't have vacuum ports is to do the "dead spark" method, where you short the spark plug lead on one side, work on the carb on the other, and try to balance them that way. There are a couple of "tools" that help do that, the easiest for me was the one that Northwoods sells, a simple threaded-rod that allows you to lay a screwdriver and short one plug at a time, going back and forth to get them just right. Works well! Old School, for sure!
And the "loud valve noise" might be the usual transmission clatter on a hot engine with poor carb synch... --Bill
Ok, so this is going a bit off the original topic, but what the heck... I understand the carb balancing process and have gone through it more or less (using my hearing rather than the shorting method). What I don't understand is that the adjustments all seem to be for the idle -- turning the mixture and idle screws. My idle is just fine -- seems very even and smooth. IF there is a problem, it's at around 4000 rpm and even that seems variable (depends if the bike is moving or not, and how much load is on the engine). Some carb tuning descriptions also talk about turning the cable stop adjusters that are on the carbs, as this can adjust what the carbs are doing when the throttle is open more. But I guess you don't want to adjust those too much, as then it throws things off at the low end. So is the adjustment of the screws just for idle adjustment? Does adjusting the cable stops make a difference for anyone at higher rpm?
Mixture screws adjust mixture and have an impact on idle speed idle screw adjust idle speed cable free play adjusts when the butterfly's move in relation to each other. Remove the free-play and idle will increase as the butterfly lifts High RPM's? cable free-play would only effect higher RPM running if it was really unequal (AFAIK)