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79 GS850G carb baseline

  • Thread starter Thread starter Anonymous
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Hi, all, More carb questions, this time re: baseline set-up of my 850 with stock VM26SS's. I found the pilot screws were set at 3.5 turns out, when the book calls for 5/8 of a turn out from bottom. The bike has always had an over-rich condition except at higher power settings but I never checked these because "these are set at the factory - do not touch"!! Anyway, the bike has a MAC 4 into 1 pipe and K & N filter element in the stock airbox, and is otherwise stock. Question is: baseline according to the book, with needles in center position? Or go a little richer with needles and pilot screw settings? (Jet needle # 5DL36-2, main jet #102.5, pilot jet #15) Thanks in advance, folks>
 
Re: 79 GS850G carb baseline

My 79 750E uses 26mm VM's, and with 102.5 mains, stock airbox/filter and exhaust gives a medium brown burn on the plugs with the fuel pilots set to 1 1/4 turns out, pilot airscrews at 1 3/4 turns, floats set to 24 mm, needles in the middle, and carbs synched to 14 in HG at 1200 rpm.
Those settings should work out just fine for your 850.

Earl



dodger1 said:
Hi, all, More carb questions, this time re: baseline set-up of my 850 with stock VM26SS's. I found the pilot screws were set at 3.5 turns out, when the book calls for 5/8 of a turn out from bottom. The bike has always had an over-rich condition except at higher power settings but I never checked these because "these are set at the factory - do not touch"!! Anyway, the bike has a MAC 4 into 1 pipe and K & N filter element in the stock airbox, and is otherwise stock. Question is: baseline according to the book, with needles in center position? Or go a little richer with needles and pilot screw settings? (Jet needle # 5DL36-2, main jet #102.5, pilot jet #15) Thanks in advance, folks>
Click to expand...
 
Re: 79 GS850G carb baseline

dodger1 said:
Hi, all, More carb questions, this time re: baseline set-up of my 850 with stock VM26SS's. I found the pilot screws were set at 3.5 turns out, when the book calls for 5/8 of a turn out from bottom. The bike has always had an over-rich condition except at higher power settings but I never checked these because "these are set at the factory - do not touch"!! Anyway, the bike has a MAC 4 into 1 pipe and K & N filter element in the stock airbox, and is otherwise stock. Question is: baseline according to the book, with needles in center position? Or go a little richer with needles and pilot screw settings? (Jet needle # 5DL36-2, main jet #102.5, pilot jet #15) Thanks in advance, folks>
Click to expand...
3.5 turns is way off on those pilot screws (underneath the bowls). 1 turn out will get you in the ballpark, then test. This may be all you need to do to stop your richness problem at lower throttle positions.
After making the pilot screw adjustments, adjust the side air screws for the highest rpm. Put the bike on the centerstand and warm it up first. Starting on either side of the bike, adjust the two screws facing you in 1/4 to 1/2 turn increments. Turn them until you achieve the highest possible rpm's. When the rpm's stop rising, stop turning. Fine tune them. Now do the other two the same way. When all 4 are set, you can adjust the idle to 1,100 rpm by using the idle adjuster knob. They usually end up about 1 1/2 - 1 3/4 turns out. Like I said, adjusting both these screws may be all you need to do. Test before messing with the needles.
The "-2" at the end of your jet needle # is the factory set e-clip position. That means your clip is in the #2 position from the top. For your mod's, raising the needle is probably not necessary. If you feel the needle should be raised I think 1 position is too much. You can raise the needle a 1/2 position by using a jetting spacer. Putting the clip in #3 position and then placing the jetting spacer on top of the clip is the next richer needle position setting. The jetting spacers for your carbs are about .022" thick. Be sure to put the plastic spacers back in the same order you found them. Thicker spacer on top the e-clip (and jetting spacer if used) and the thinner spacer below the e-clip.
If you disturb the jet needles, you must re-synch the carbs. A vacuum tool synch is much better than a manual synch. But at least do the manual synch if you don't have the tool.
PS: this all assumes you still have the stock air box LID on.
 
Earl and Keith, OK; you've given me a logical start here. Couple of things to add, though. One - I forgot to mention that the side air screw (idle screw as I call it on the car's TQ) on # 1 carb is frozen and the slot is "screwed" so to speak, and #2 yes I'm running the stock air box but with the end covers opened up. This was an attempt to cure the over-rich condition, as was lowering the needles one notch and going to NGK #7 plugs. Any comments re the frozen air screw? The rest I'll put back to stock as you all have suggested.
Paul
 
The airscrew frozen and buggered is a tough one. The only thing I can think of to try that will not damage anything if it doesnt work is to take a dremel tool with a tiny bit and try to recut the slot in the top of the screw. Once that is done, I would put three or 4 drops of penetrating oil on top of the screw and then take a hot air heat gun (type used for stripping paint..similiar a hairdryer but hotter) and heat the aluminum around the screw. The hot air gun will get the aluminum too hot to touch, but cannot get it hot enough to melt. Aluminum expands with heat fairly quickly. There is a good chance it will expand enough to allow the penetrating oil to seep into the frozen threads. Repeat the heating process a couple times and then let it sit overnight for the oil to penetrate. It will at least give you a shot at getting the screw out. If not, nothing harmed.

Earl



dodger1 said:
Earl and Keith, OK; you've given me a logical start here. Couple of things to add, though. One - I forgot to mention that the side air screw (idle screw as I call it on the car's TQ) on # 1 carb is frozen and the slot is "screwed" so to speak, and #2 yes I'm running the stock air box but with the end covers opened up. This was an attempt to cure the over-rich condition, as was lowering the needles one notch and going to NGK #7 plugs. Any comments re the frozen air screw? The rest I'll put back to stock as you all have suggested.
Paul
Click to expand...
 
And to add to Earls logic: the carb body will heat and expand a little more than the brass screw, so that may help. Just use the best fitting tool you got. If you can cut a new slot in the screw, it's best to try turning the screw IN first until LIGHTLY seated, clean out any crud from the threads and then start turning it out. If you can get it close to 1 1/2 turns out and it's really turning hard, you might want to stop because that's very close to where you want the side air screws anyways.
If you don't have a dremel, this idea worked for a member a few weeks back: To cut a new slot, take a small drill bit and drill two holes about the same width apart as the tool you'll be using. Go about 1/8" deep. Then carefully drill out everything in between. If you space the bit just right it will go smoothly and all the material will come out right. Place the screwdriver in and if it feels like a good fit, give it a couple of moderate taps to "jar" things and help the tool set in the new slot. Then try it. Again, turn the screw IN first until seated, clean, and then come out. These screws seem to have more of the factory sealant near the tops of the threads, so if you try to turn them out first there's more sealant fighting you. Turn them in first and clean the threads as best you can and a few drops of lube will help but keep the slot free of lube when turning.
 
I forgot to mention, you said the "air box end covers" are opened up. I'm not familiar with the size of these covers, but any sizeable holes will significantly increase air flow. With this new info, it's possible you may need to raise the jet needles 1 position. I haven't jetted bikes for extra air holes in the stock air box. So this is just a guess.
 
OK, guys, I have baselined the carbs as follows: Pilotscrew 1 1/8 turns out, Needles on the middle clip, and air screws 1 1/2 turns out. Slides are evenly set to 1 mm above the throttle bore at W.O.T. Keith, my ref. to the air box end covers was when I was trying to lean the thing out. Covers are back on so we have a stock air box with a K&N replacement filter inside - LIGHTLY oiled!! No joy with the frozen air screw on #1 carb, hopefully its still at the stock setting. New battery tomorrow so I'll post the results.
 
Unless you are planning on starting the bike at WOT and increasing rpm, that isnt going to work. :-) :-)
Manual synch is set with the slides in the at rest/closedno throttle position.
Set the gap between the slide and carb throat on the #3 carb by turning the idle adjustment knob. This will raise/lower the slide on the #3 carb and also 1,2 and 4. Set the gap between the slide skirt and carb body on the airbox side to 9/64" with the throttle closed. (use a drill bit shank as a guage) Then set 1,2, and 3 slide heights with the adjuster on top of their respective slides (under the top cap) After setting carb 3 with the idle adjustment screw. Do Not use it when setting the slide clearance for 1,2, and 4. When you have all rour carb skirts resting at the same height above the throttle body, then turn the idle adjuster knob in two or three turns.

Earl


dodger1 said:
Slides are evenly set to 1 mm above the throttle bore at W.O.T.
Click to expand...
 
Earl, I believe he's talking about the fully open position. Suzuki calls for the bottom of the throttle valves to be .5 to 1mm above the top of the main bore when looking into the filter side. But he did'nt mention the fully closed position at all.
The fully open position setting is supposed to be done AFTER the fully closed positions are set.
 
ahhh Keith, I had the impression he was going to start set up for wide open. heh heh
Earl :-)


KEITH KRAUSE said:
Earl, I believe he's talking about the fully open position. Suzuki calls for the bottom of the throttle valves to be .5 to 1mm above the top of the main bore when looking into the filter side. But he did'nt mention the fully closed position at all.
The fully open position setting is supposed to be done AFTER the fully closed positions are set.
Click to expand...
 
Well,that woulda been a hoot, trying to start from WOT. Yeah, I refer to the factory setting of 1mm above the bore for the WOT throttle stop - mainly to line up all the slides as best I could on the bench. Earl, thanks for the closed-throttle set-up procedure. That isn't covered that clearly in the manuals. However you both refer to measuring slide - bore dimensions from the airbx side. Are you measuring from the cutaway or the back of the slide? (I measured from the back of the slide) BTW, since I can't adjust the air screw on #1 my thinking is to synch the other three to it using the vacuum carb synch tool.Comments?
 
When doing a manual synch for the fully open position, you have to look up through the filter side. The fully closed position is done looking at the engine side. I do my fully closed position manual synch the way Suzuki says to. Looking in from the engine side, I lower the slides until the little nicks are all the same. If you've got decent eye-sight this works fine. This will make your vacuum synch go quicker.
 
Before synching, be sure your timing is correct and adjust the side air screws for the highest idle. Adjust them after the bike is warmed up. After setting all 3 (in your case), turn the idle down to 1,100 rpm with the idle adjuster knob.
Don't adjust the remaining carbs to match a carb that may have a mixture problem. You don't know where the screw is set. Just treat it as "normal". Adjust the vacuum levels to the other three first, and then make the last carb match them.
In jetting, trying to compensate for a little problem, ALWAYS creates bigger problems.
 
Keith,
Thanks for that, I was pretty much winging it re: initial start-up procedures. Maybe it's just as well the local parts store forgot to order my battery so nothing got done today.
Cheers, and I'll post results.
Paul
 
I would treat all four carbs as being "normal" The adjustment effect of the carb #1 airscrew is very minimal in operation beyond idle range. I wouldnt worry about it. Just do a manual synch on all four, then get #3 set to the base line vacuum value you want, and then match 1,2, 4 to that. 10 in Hg @ 1200 rpm will usually run about a light tan. 12-14 in Hg about a medium to dark tan and 16-18 in Hg burns in the brown range on my bikes.

Earl

dodger1 said:
since I can't adjust the air screw on #1 my thinking is to synch the other three to it using the vacuum carb synch tool.Comments?
Click to expand...
 
Hi, all;
Did the prelim. set-up as discussed and it fired up immediately. Backed the main idle screw off to 1500 and it sounded fine. Went for a 45 min. ride, came home, reset the idle to 1100 or so and looked at the plugs. An even light tan on all four. Bear in mind these were NGK B7ES pieces-one # hotter than the stock #8 plug.They were sooty from the last go-around. I didn't play around any more today as ambient temps are 39C-105F and that's hot enough to cause beers to jump out of the fridge all by themselves. (Ain't retirement great?) Anyway, it ran pretty good except for some intermittent back-firing on the over-run in 4th or 3rd (4-6000 RPM) At this point I'm sort of at the (if it ain't broke-------) stage. Comments?
 
I think you should put the B8ES plugs back in.
What do you mean by "backfiring on the over-run"? Do you mean popping during deceleration? This can be an exhaust leak or a lean condition. It could also be related to those hotter plugs you're using. I would put the 8's back in and see how she runs. If she still pops, check your header bolts. The gaskets may need replacing. If it's the carbs, getting rid of all the popping can be difficult. You can try turning the pilot screws (underneath) out a little (counter-clockwise), maybe a 1/4 turn and re-test. Keep notes so you can set them back to where they are now if needed.
 
Keith, popping under decel is what I mean. I concur on the plug change back to 8s and I'll check the header bolts.And yes I noted the initial set-up in writing. More later and thanks again.
Paul
 
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