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Performance Question

  • Thread starter Thread starter mrquadriga
  • Start date Start date
M

mrquadriga

Guest
First off, thanks for all the advice and help all of you do for this site....

The only motorcycle I've ever driven is the '80 1100L I purchased a little over a year ago, hence, I know very little about the "feel" of a bike. Another post somewhere on this site was talking about power band and RPM's and roll on power so last night I found some lonely roads and tried to put the old gal through the paces. Usually, I'm shifting to the next gear around 4000 or less RPM's. (maybe that's why I get 50mpg! :D ) This may seem silly to you, but I noticed when I got her up to 4000+ RPM's, there was quite a vibration in the area where my body came in contact with the seat. (i.e.-Big Jim and the Twins) Regardless of the fact that it's the best action I've had in a while :lol: , I'm just wondering if that is a normal type area for vibration at higher RPM's? The tires are new this spring and have been balanced and the seat is stock. You people tend to ride a little more aggressively than I do so perhaps you could shed some light on the "feel"? Many thanks, -Pete
 
Re: Performance Question

I think the most probable cause is your carb synch. I have found that a carb synch can be predominantly "tuned" for a specific rpm. With any carb synch, there will be rpm ranges/points where vibration will increase or decrease slightly because due to variables in the induction system, all four carbs will not respond at exactly the same rate and maintain precisely the same relationship to others all the time. The difference at various points may only be 1/2 cm hg, but it can make a big difference in vibration level felt. My 1150 is set to come into "perfect" balance at 70-75 mph.
At that point, it turns to silk. :-) The trade off is that its a little rough in the 30-40 mph range.

Earl


mrquadriga said:
First off, thanks for all the advice and help all of you do for this site....

The only motorcycle I've ever driven is the '80 1100L I purchased a little over a year ago, hence, I know very little about the "feel" of a bike. Another post somewhere on this site was talking about power band and RPM's and roll on power so last night I found some lonely roads and tried to put the old gal through the paces. Usually, I'm shifting to the next gear around 4000 or less RPM's. (maybe that's why I get 50mpg! :D ) This may seem silly to you, but I noticed when I got her up to 4000+ RPM's, there was quite a vibration in the area where my body came in contact with the seat.
Click to expand...
 
GS 1150 carbs sync

GS 1150 carbs sync

Hey Earl, I'm fixin to take my 1150 to a guy that's known to be very good with bike carbs. He should know these tricks, but could you give me a brief description of how you sync carbs for 70 mph as opposed to 35 mph. I have a lot to learn, Thanks for any help.
 
Re: GS 1150 carbs sync

Re: GS 1150 carbs sync

Its pretty simple and not any secret. :-) :-)

Be sure the engine is at normal operating temp before synching.

All you have to do is your normal synch. Once that is even across the board, you need to know the rpm for the speed you want it to be smooth at. For my 1150, 70-75 mph is 4200 rpm. Increase the throttle uniformly and quickly to 4200 rpm and hold it a couple seconds to let it stabalize.
Hold the throttle absolutely still at 4200.

Note the new differences in vacuum balance. Let the rpm return to normal idle and make vacuum adjustments. (at this stage, after already synching at low rpm, vacuum adjustments are 1/16th turn or less, usually a lot less. :-) )


I dont keep it at 4200 rpm because heat build up with the bike sitting still is too rapid. The cylinder head will overheat before the engine's volume of oil will change temp. The oil temp guage is useless in this process....too much lag.

Repeat the process, remembering the new differences and make small adjustments at low rpm.

It isnt as difficult as it might sound. :-)

Starting the process with the engine already at normal operating temp, I figure I have about 30 seconds running time at the 4200 rpm synch point before head temps will either be too high for continued running or the intake tract will become heated enough to alter the synch characteristics.
That part is only my guess though. :-) Usually, I dont need anywhere near 30 seconds running time.

Earl


rphillips said:
Hey Earl, I'm fixin to take my 1150 to a guy that's known to be very good with bike carbs. He should know these tricks, but could you give me a brief description of how you sync carbs for 70 mph as opposed to 35 mph. I have a lot to learn, Thanks for any help.
Click to expand...
 
I'm following you Earl. So if a rider wanted to, he/she could synch the carbs for nothing but in town/commuter driving? I don't wish to start a Hoomgar type thread here, is there something already posted that could help me read up on this? Thanks-Pete '80 1100L
 
Sure, you can set up the synch to be optimum for any rpm you wish. I dont remember there being any thread on this variant. :-) Its a conclusion I have come to through observation and practice. With this approach, my 1150 is very smooth up to about 40 mph, then vibration increases to worst around 50 mph, then decreases until at 70, and is almost non-existant. After 75, it starts to increase slightly, becoming worst around 90 and then decreases again, until at 105, it again turns to glass smooth. At that speed, the image in my mirrors is still. :-)

Earl



mrquadriga said:
I'm following you Earl. So if a rider wanted to, he/she could synch the carbs for nothing but in town/commuter driving? I don't wish to start a Hoomgar type thread here, is there something already posted that could help me read up on this? Thanks-Pete '80 1100L
Click to expand...
 
I've been synching carbs at around 3,500 rpm's always. It's always made more sense to me to synch them at something closer to where you spend time riding, not at idle. Synching at idle can be almost impossible anyway.
If the motor is mechanically sound and the carbs are operating smoothly, they SHOULD hold their synchs fairly close over the entire powerband. But on our older bikes, fluctuating vacuum/slides/throttle plates is part of life.
 
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