Air screw adjustment.....again

[Larry D]

First of all, I've searched but couldn't find an answer. Second, I've done all the recommended maintenance that is throughout these forums. Valve adjustment, carb dipping, o-rings, etc....Third, the bike is stock, with the exception of a Mac 4-2 exhaust. And fourth, I've found no air leaks.

So, the bike has been having a hard time settling to an idle and surging also. I've also had some very experienced folks from this site in my garage and they have said that the bike is running rich.

Tonight (it was a beautiful day in Indianapolis today!) I decided to try the highest rpm method. The air screws were at 2.5 turns out from lightly seated. I warmed the bike up by riding around the neighborhood for awhile and parked in my garage and setup my remote tank and a fan for cooling.

After getting idle somewhat stable and at around 1100 with the large carb knob, I set forth....

My goals were to stabilize the idle and lean it up a little. I turned #1 air screw in and it seemed to have no affect. The same with #2. However when I turned #3 in, the idle took off like a scalded dog !! Great !! I turned the large carb knob so the idle went down to 1100 again and turned some more. It still climbed, so repeated the process until it made no percepted effect. Moved to #4 and it had no affect, similiar to #1 and #2.

So, I ended up with #1, #2 and #4, 1.5 turns out and #3 only .5 to .75 turns out.

I'm sure this leaned out the bike and after "dropping" the throttle from 5000 rpm's it settles nicely at 1000-1100 rpm's.

Finally the question for all of you....Is it unheard of for the air screws to be set at different turns out ? Is this common ? I've always thought that they would be somewhat set the same.

The bike now sits in the garage with the remote tank still attached waiting for another nice evening tomorrow. I'll try firing it up and see how it acts then. I know plug chops are in order but it's difficult because, I'm not all legal yet. I'm going this week though.

Thanks Everyone and don't forget to vote tomorrow.

[Dave8338]

Intake o-rings replaced? If the #3 had that much of an effect...I'de suspect a leak somewhere...

[Larry D]

Intake o-rings replaced? If the #3 had that much of an effect...I'de suspect a leak somewhere...

I thought the same..air leak. None found, however and I don't have intake o-rings.

[Nessism]

No intake O-rings? Please explain.

[Larry D]

No intake O-rings? Please explain.

Perhaps, I have my nomenclature confused. I thought the intake o-rings were the rubber intake boots that are bolted to the engine side on some models.

[Nessism]

Perhaps, I have my nomenclature confused. I thought the intake o-rings were the rubber intake boots that are bolted to the engine side on some models.

There is a large O-rings between the rubber boot and the cylinder head. These O-rings flatten out and leak with almost 100% certainty if they are the originals.

[Larry D]

There is a large O-rings between the rubber boot and the cylinder head. These O-rings flatten out and leak with almost 100% certainty if they are the originals.

My bike is an '81 GS750L, 16valve. I do not have these. I have rubber angled cylinder shaped boots that fit over the engine intake ports.

Edit: And they're brand new.

[Nessism]

My bike is an '81 GS750L, 16valve. I do not have these. I have rubber angled cylinder shaped boots that fit over the engine intake ports.

Edit: And they're brand new.

16V engine? Now that you mention it, I don't think you have those O-rings. I'm suffering a little brain fade tonight it seems.

[TheCafeKid]

No, you DONT have those orings, did you check to see that your vaccum gauge port screws are completely tight? And to answer your original question, NO its NOT uncommon for the mixture screws to be set a little differently from one another. I dunno how much differently yours are, ( i didnt read the whole post, sorry) But its quite COMMON for them to be set a little off, as you're supposed to set each for highest idle. And, some would go further to say that when dynamic or vacuum syncing the BS type carbs, its best to set the INNER two cylinders a little lower than the outer two as far as the amount of pull goes. Now, for instance, on my former 1100G, we found that highest idle settings and best running had the screws set completely different across the board. One might have been at 2.25 turns out, Two at 2 flat, Three at 2.50 out and four at maybe 2.75 out. I dont remember the actual number of turns, but they were all different. With the bike running, a temporary tank hooked up and the vac line that goes to the carbs from the petcock PLUGGED (important!) run the bike till at normal opperating temp. Its best to usually have a fan blowing over the motor, somtimes two if its really hot out. When adjusting the carbs, it may take some time, especially if you're syncing, and you dont want the motor overheating, as you have the revs a bit above idle, and no air moving across the aircooled head. So use a fan. Anyway, once the bike is warm, adjust each screw, one at a time, listening carefully for the idle to climb to the highest point. Go slowly, to allow the motor time to catch up to your adjustment, and when the idle reaches a point where it doesnt seem to speed up anymore, stop and turn the screw back a bit to find the exact point that it reached highest idle and stopped. Then move to the next. You may end up close, you may end up drasticly different. If your screws end up more than 3 turns out, you may have a jetting issue, as in they are too small for the intake and exhaust combo you're running. If its a stock set up, you may have a dirty pilot circuit, or someone has messed with the carb jetting prior to your purchase. Let us know what you find, and I hope this helps..

TCK

Oh forgot one tidbit. Once you have the screws set for highest idle, and are satisfied, be sure to turn your idle adjust KNOB back to normal idle of around 900-1200RPM.

TCK

[Jackbob]

Quote; and the vac line that goes to the carbs from the petcock PLUGGED

...Damn i knew i had forgotten to do something when synching recently. This might explain why #3 cylinder is running rich. Thanks.

[TheCafeKid]

Quote; and the vac line that goes to the carbs from the petcock PLUGGED

...Damn i knew i had forgotten to do something when synching recently. This might explain why #3 cylinder is running rich. Thanks.

No problem. Yes, on some of my bikes, it simply refused to idle at all without that vac line plugged. I just use a phillips head screw driver shoved in the line, works well. It likely is the source of your problem, as you had to turn it out so far just to keep it running that once you plugged it, its way rich. Give it another go and let us know if it worked!

TCK

[Larry D]

Thanks All,

No problem, Nessism, my brain shuts down sometimes too.

The air screws are now set to: #1, #2 and #4 are 1.5 turns out and #3 is .75 turns out. The Mac exhaust, although it is a 4-2, and mimicks the the stock exhaust, of course, it is not.
When it was "searching" for idle and I removed the air filter box lid, it seemed to smooth out some. So, it needed more air. The only carb that had any effect was #3. So, I set #1, #2 and #4 as Mr Suzuki did. If I turn #3 any more than 10 degrees either way the bike starts to bog down.
After I get home tonight, I'm taking it for another little ride and see how she acts.

I curious as to why the vacuum line should be plugged while performing the highest rpm method ??

And yes, the carb sync bolts are tight. I'm very confident that there are no air leaks.

[Larry D]

Thanks All,

No problem, Nessism, my brain shuts down sometimes too.

The air screws are now set to: #1, #2 and #4 are 1.5 turns out and #3 is .75 turns out. The Mac exhaust, although it is a 4-2, and mimicks the the stock exhaust, of course, it is not.
When it was "searching" for idle and I removed the air filter box lid, it seemed to smooth out some. So, it needed more air. The only carb that had any effect was #3. So, I set #1, #2 and #4 as Mr Suzuki did. If I turn #3 any more than 10 degrees either way the bike starts to bog down.
After I get home tonight, I'm taking it for another little ride and see how she acts.

I curious as to why the vacuum line should be plugged while performing the highest rpm method ??

And yes, the carb sync bolts are tight. I'm very confident that there are no air leaks.

I guess I should be calling these screws, the idle mixture adjust screws.

[Dave8338]

As far as the difference in settings with #'s 1,2, and 4 being exactly the same...I'de now suspect an air restriction of some measure on the #3. Could even be a casting issue from the factory. Possibly a different sized jet? Nothing is perfect.

Oh and as I only think in 8-valve language...I must apologize for mis- directing the choir and needing the Kid to slap sense back into the masses...

[Larry D]

As far as the difference in settings with #'s 1,2, and 4 being exactly the same...I'de now suspect an air restriction of some measure on the #3. Could even be a casting issue from the factory. Possibly a different sized jet? Nothing is perfect.

Oh and as I only think in 8-valve language...I must apologize for mis- directing the choir and needing the Kid to slap sense back into the masses...

No problem at all Dave. My brain only thinks in 16 valve language.

I've been completely through the carbs when I cleaned and dipped them, they were all intact and stock.

The bike has always run rich. At least in the time I've had it anyway. probably because when I got it, it had a 4-1 exhaust and the PO tried to compensate with the mixture.

I'm thinking that because of the "almost" stock Mac 4-2 exhaust, that it requires a little more air than normal. I've read that these bikes came somewhat lean from the factory and were set 1.5 turns out, give or take.
I believe that this exhaust flows more easily and therefore requires slightly more air coming into the system. More air out, needs more air in.

It was just strange to me that the only carb that made any difference in the idle was #3. And I just thought that they would all be set approximately the same turns out.

It also seems like a very lean setting, but time and plug chops will tell....