bob654 Posted June 11, 2020 Share Posted June 11, 2020 Hi, again. I did quite a bit of work on the GS750 today. When I was packing up to come home I thought I would start her. Only ran on three again, cylinder 3 again. So I checked ; coils, plugs ( swapped with old seemed to make a difference to the overall running, I may have bought knock offs on Eblag) . With all the testing and swapping, tank on, tank off, tank on, I lost track a little, anyway, now runs on cylinder three, only not on cylinder four. Also swapped the vacuum hose for the tank, from 2 to 1 carb. When I found out it swapped cylinders ,I checked/ swapped plugs, and leads, to various cylinders, no difference. I can guess, its some fleck of dirt in my spotlessly clean carb 4 ,but I cant think of anything else. If I run it with the plug out on 4, theres no vapour comes out. Would revving hard in neutral bring in the other jet and produce vapour? Also a bit of a coincidence, isint it? 3 then 4 but different reasons? Any ideas? Quote Link to comment
Reinhoud Posted June 11, 2020 Share Posted June 11, 2020 (edited) If the cylinder isn't running at all I would suspect the ignition, if the cylinder runs when you give it more throttle it would be the idle in the carburetor. Do you have a stroboscobe to adjust ignition? If yes, connected to the cilinder what isn't running, if the strobe works you have oignition and the cause would be in the carburetor. Are all screws and needles adjusted in the same postion? Are all floats adjusted equally? IKn other words, is everything adjusted the same in all 4 carburetors? How's the valve clearence? Also, a sparkplug what sparks outside a cylinder, doesn't necessarilly sparks in the cylinder, this could be the case with a sparkplug what had to suffer "testing" and overfuelling (and cleaned after that) Edited June 11, 2020 by Reinhoud 2 Quote Link to comment
BigT Posted June 12, 2020 Share Posted June 12, 2020 Why would you swap the vacuum line from the vacuum port to the float bowl breather? I'm surprised #2 is running 1 Quote Link to comment
Gixer1460 Posted June 12, 2020 Share Posted June 12, 2020 2 hours ago, BigT said: Why would you swap the vacuum line from the vacuum port to the float bowl breather? How did you conclude that? There is a vacuum fuel tap and he swapped the vac. hose from one carb to another - nothing to do with breathers ! 1 Quote Link to comment
bob654 Posted June 12, 2020 Author Share Posted June 12, 2020 (edited) Things is, it was then it wasn't working, and jumping cylinders is just incredible . I will try more throttle today. I do have a stroboscope and I will try that, cheers. All screws and floats, and needles are the same, factory, plus V and H exhaust, recommended settings. I don't know what the valve clearances are. I'm not happy with the plugs, when I tested for spark it seemed keener to arc through the side than spark through the electrode end, and have sent for new, reputable ones, also a fuel bag, to hang up, so I can stop taking the tank on and off after every check or adjustment. Thank you Reinhoud. Edited June 12, 2020 by bob654 add imfo Quote Link to comment
bob654 Posted June 12, 2020 Author Share Posted June 12, 2020 4 hours ago, BigT said: Why would you swap the vacuum line from the vacuum port to the float bowl breather? I'm surprised #2 is running No, I swapped from one out-let one one carb to an other out-let on a different carb. I was sort of thinking ,- Is it getting fuel cos its the two end cylinders that are playing up? I bought this to learn more, and, I am certainly puzzled more. Quote Link to comment
bob654 Posted June 12, 2020 Author Share Posted June 12, 2020 (edited) I want to add. Spark plugs are black sooty I thought this might be because of all the stop start and no riding.What do you people think? I could go one rating down to burn off the deposits? From B8ES ,to, B7ES? Edited June 12, 2020 by bob654 add imfo Quote Link to comment
Reinhoud Posted June 12, 2020 Share Posted June 12, 2020 Oh, something else, the manual says Denso or NGK plugs, my GS1000 doesn't want to run properly on Denso. Something I found out accidently. Bike ran like crap and couldn't figure out what was causing it. What brand do you have? 1 Quote Link to comment
Reinhoud Posted June 12, 2020 Share Posted June 12, 2020 Black and soothy is too much fuel, or ignition timing. Overfueling can cost you sparkplugs. Quote Link to comment
BigT Posted June 12, 2020 Share Posted June 12, 2020 (edited) 8 hours ago, Gixer1460 said: How did you conclude that? There is a vacuum fuel tap and he swapped the vac. hose from one carb to another - nothing to do with breathers ! Because only one carb (#2) is a vacuum tap. The other two taps are vents for the float bowls, to allow the fuel level to rise and fall. How did I conclude that? Knowledge Edited June 12, 2020 by BigT 1 Quote Link to comment
BigT Posted June 12, 2020 Share Posted June 12, 2020 6 hours ago, bob654 said: No, I swapped from one out-let one one carb to an other out-let on a different carb. I was sort of thinking ,- Is it getting fuel cos its the two end cylinders that are playing up? I bought this to learn more, and, I am certainly puzzled more. Well, you need to learn that #2 is a vacuum port, designed to open the fuel tap The other two ports are vents, to allow fuel to rise and fall in the float bowls So, you just created a massive air leak on the #2 cylinder. And that's the reason I stated I was surprised the bike would run on #2. You are numbering from left hand to right? Quote Link to comment
bob654 Posted June 12, 2020 Author Share Posted June 12, 2020 1 minute ago, BigT said: Well, you need to learn that #2 is a vacuum port, designed to open the fuel tap The other two ports are vents, to allow fuel to rise and fall in the float bowls So, you just created a massive air leak on the #2 cylinder. And that's the reason I stated I was surprised the bike would run on #2. You are numbering from left hand to right? Does that mean two is the master. Yes left to right. Quote Link to comment
Gixer1460 Posted June 12, 2020 Share Posted June 12, 2020 45 minutes ago, BigT said: Because only one carb (#2) is a vacuum tap. The other two taps are vents for the float bowls, to allow the fuel level to rise and fall. How did I conclude that? Knowledge How do you balance the carbs then - they all have a vacuum port. Any of which could be used for the tap vac! Quote Link to comment
gs7_11 Posted June 12, 2020 Share Posted June 12, 2020 The vacuum port is in the cylinder head on GS's. This is OSS isn't it? 1 Quote Link to comment
bob654 Posted June 12, 2020 Author Share Posted June 12, 2020 8 minutes ago, gs7_11 said: The vacuum port is in the cylinder head on GS's. This is OSS isn't it? In the cylinder head? oss? Quote Link to comment
gs7_11 Posted June 12, 2020 Share Posted June 12, 2020 (edited) 29 minutes ago, bob654 said: In the cylinder head? oss? Sorry, to clarify, in answer to Gixer1460, the balancing ports are in the inlet tract, not on the carbs. As BigT says, only one of the brass spigots on the carbs is vacuum....the other 2 are float bowl vents. OSS = Old Skool Suzuki! Edited June 12, 2020 by gs7_11 1 Quote Link to comment
BigT Posted June 12, 2020 Share Posted June 12, 2020 4 hours ago, bob654 said: Does that mean two is the master. Yes left to right. No, it means #2 is the vacuum port For syncing carbs, #3 is the master on BS carbs Have you synced the carbs? 1 Quote Link to comment
BigT Posted June 12, 2020 Share Posted June 12, 2020 3 hours ago, Gixer1460 said: How do you balance the carbs then - they all have a vacuum port. Any of which could be used for the tap vac! I balance the carbs (which I just did) by using the sync vacuum ports on the head. We're talking carbs here. There is only one vacuum port on the carbs. We had this discussion like, what, 3 weeks ago? You still haven't figured out what the 3 taps on the carbs are for? Quote Link to comment
bob654 Posted June 12, 2020 Author Share Posted June 12, 2020 (edited) 1 hour ago, BigT said: No, it means #2 is the vacuum port For syncing carbs, #3 is the master on BS carbs Have you synced the carbs? Bench synced I was about to start tuning for the first time when it started missing. Edited June 12, 2020 by bob654 sp Quote Link to comment
BigT Posted June 12, 2020 Share Posted June 12, 2020 The cylinder that's missing may be farther out of sync than you realize Try the sync and see if that cures the problem 1 Quote Link to comment
gs7_11 Posted June 13, 2020 Share Posted June 13, 2020 10 hours ago, bob654 said: Bench synced I was about to start tuning for the first time when it started missing. Have you fixed the carb rubber seating problem yet? I would do that first. 1 Quote Link to comment
bob654 Posted June 13, 2020 Author Share Posted June 13, 2020 Mikuni VM26SS. The pilot fuel screw ( on the bottom) on of these has been over tightened and now can stick up through the bottom of the venturi I saw this when I rebuilt them and considered it to be usable with care, I now have my doubts. I want to wait for the remote fuel tank to arrive so I can have an other go , ignition timing, checking plugs, before pulling the carbs again. I have, however been looking to replace this carb if its the culprit ( I cant remember which one it is, I thought if I didn't know it wouldn't cloud my judgement). Can anyone tell me if the GS1000 had the same carbs? Quote Link to comment
bob654 Posted June 13, 2020 Author Share Posted June 13, 2020 Just now, gs7_11 said: Have you fixed the carb rubber seating problem yet? I would do that first. Yes , a very easy fix, as it went. 1 Quote Link to comment
bob654 Posted June 13, 2020 Author Share Posted June 13, 2020 (edited) the GS1000's look the same certainly and in so cases are called VM26 is this enough? Edited June 13, 2020 by bob654 Quote Link to comment
BigT Posted June 13, 2020 Share Posted June 13, 2020 (edited) The 1000 and the 750 have the same carb bodies. The mounting plate/idle screw are a bit different, but interchangable Naturally, the jetting/slides/needles are likely diffferent. The 750 jetting seems to change every year Just be sure to get the the correct carb body, because 1-4 are all different Wait, you have VM carbs? I thought you had a post 80 bike. On VM carbs, the vacuum port is on #3 Edited June 13, 2020 by BigT 1 Quote Link to comment
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