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gs750 carbs

  • Thread starter Thread starter chazz
  • Start date Start date
C

chazz

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hi i have a 77 gs 750,i am having problems with the carbs,number three wasnt working properly it would come in when it wanted,now three and four have the same problem,i just cant get it to run on all four,3&4 spark plugs are always soaked,yet when you dry them off,and put them in the ht caps turn it over there is a brilliant spark,but once replaced nothing,its only started to do this recently,any ideas cheers :cry:
 
Could be due to multiple reasons
1) interchange your spark plugs and see if the problems still persists. if not buy new plugs and check.
2) You may be flooding the engine - check the carb heights - needles may be sticking hence more fuel and drowning the plugs
 
Need more info. Could be a lot of things.
Did you get the bike with these problems or did it run fine and just start doing this? Has it been stored for some time?
Anything else you notice that's not right? Fuel dripping anywhere? Blue/white smoking?
Is the bike stock or have intake/exhaust, etc, mod's?
 
when i put the bike together,i cleaned the carbs as they had been stood for a while,at the time i was using my old engine.i put the carbs back on and fired the bike up it was running eratic,so i sorted the timing out,when i started it again it was still on three,a friend and i tried balancing the carbs but couldnt get them spot on,the dancing rods on the gauges were all over the place,i then got my new engine and fitted the same carbs to that,only to get the same response still only on three, with number three only coming in intermittently,again tried balancing without much luck,so ive been running the bike on three [not good] then the other day number 4 decided its not working,so now its only on 2,ive swapped the leads over and new plugs but still wont work, im begining to get fed up now,so any help will be grateful :cry:
 
I'm guessing it's fuel related because you say with either engine, the spark is good to all 4 cylinders if you wipe the plugs dry. As soon as you install the plugs, you lose a cylinder, and now two. 3 and 4 are the problem, so this wouldn't be caused by one weak coil. You could have two weak coils of course.
You should have cleaned and gapped the points if you still have them and check timing. Pitted points may mean the condensors are bad. Also inspect the plug caps for clean/solid connections and check the terminals at each coil for clean/tight. Be sure the plug leads are in good condition and not cracked, causing arcing. Be sure the plugs are NGK B8ES or same and gapped correctly.
If too much fuel is entering those cylinders, the plugs will get wet and the spark will track to ground instead of jumping the gap.
With #3 cylinder, there's the added chance of the vacuum line leaking fuel into the cylinder. Check petcock for leaking.
If the petcock is good then too much fuel at 3 and 4 could be jet size related, dirty carbs, float level related, float valves not seating (any fuel dripping/overflowing?), fuel/air screws adjusted incorrectly, etc.
I would first check the pilot fuel screws (underneath) setting and the side air screw settings. If adjusting these fails to help then I'd check the float levels and possibly re-clean the carbs with high pressure.
If someone has adjusted the screws wrong, those cylinders can run rich.
There's no exact setting for the pilot fuel screws (underneath) but if you do not have problems at 1 and 2, then use their settings as a starting point. Seat the screws at 1 and 2 LIGHTLY and count their setting points. Depending on if the bike is stock or modified, the settings should be between 3/4 and 1 3/4 out, roughly. If the screws at 3 and 4 are out more (richer), try adjusting them to match 1 and 2. I would like to know where they're set too and if the intake/exhaust is stock.
As for the side air screws, setting them for highest rpm isn't possible if the bike is running/idling poorly. So try setting them to 1 3/4 turns out from lightly seated as a starting point. USE A GOOD FITTING TOOL. If the bike runs better, then adjust the side air screws using the highest rpm method. If your problems are screw related, this should get the bike running better and you can then fine tune the screws as they are very sensitive to adjustments.
You could also have intake leaks. Impossible to set the vacuum levels if you have leaks. Intake leaks are most commonly caused by poor o-rings in the manifold or the manifiolds themselves.
 
cheers,just bought an overhaul kit,for all four carbs so i,ll get stuck into it on sunday while i,m off work
 
chazz said:
cheers,just bought an overhaul kit,for all four carbs so i,ll get stuck into it on sunday while i,m off work
Click to expand...
Not sure what the kits will do for you.
If you have any fuel leaking out the bowl dump lines, you could have poor sealing float valves, or just dirty. If no leaks, the valves are probably fine.
If any brass jets come in the kit, I wouldn't use them because they may not be the same precision as the Mikuni jets. Always just clean the stock jets. They'll be fine.
Any o-rings that come in the kit may be OK to use and of course, the gaskets. I'd get Robert Barrs o-ring kits for your VM carbs. You get every o-ring needed.
Rebuild kits offer different parts. Not sure what your kits include.
Not trying to be negative but many kit parts, float valves for example, are of poor quality. Their jets may be incorrectly drilled/sized. No good reason to not re-use the Mikuni jets. Be aware.
 
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