grusvag Posted June 29, 2008 Share Posted June 29, 2008 Ok, I'm working on rebuilding the carbs from my 79 XS400SG, and had to buy a spare set for parts. I'm cleaning both of them thoroughly and will choose the best parts from each to rebuild a "new" pair. Problem is that I've discovered that one carb seems to have a post plugged by the factory while it's duplicate has a jet screwed into that same place. Question: Why is one plugged like this? And is it ok to use this plugged one in place of the one that came off the bike that had a jet screwed in there? (Unfortunately, I can't use the one that came off the bike because part of the housing is broken.) This carb came off the bike: There is normally a jet screwed in this hole. It's off right now being cleaned. This is the carb that I would like to replace it with: Why is this plugged? And can I still use it in place of the one above? Same model stamped on both sets: Link to comment Share on other sites More sharing options...
billa65t Posted June 29, 2008 Share Posted June 29, 2008 Hi there, yes you can use the carb with the plugged post it shouldn't make any difference to the running of your bike . your original carbs must be off a UK or europeon spec bike as the jet is a mixture screw and adjustable ! where as the carbs that you have just aquired are US spec ones and the mixture screw has been blanked off to stop it being tamperd with to comply with federal laws? You could if you really wanted to carefully drill out the plug so that you could adjust the mixture but unless you have altered the carbs,airfilter, or exhaust from standard ther should be no need . Link to comment Share on other sites More sharing options...
grusvag Posted June 29, 2008 Author Share Posted June 29, 2008 Hi there, yes you can use the carb with the plugged post it shouldn't make any difference to the running of your bike . your original carbs must be off a UK or europeon spec bike as the jet is a mixture screw and adjustable ! where as the carbs that you have just aquired are US spec ones and the mixture screw has been blanked off to stop it being tamperd with to comply with federal laws? You could if you really wanted to carefully drill out the plug so that you could adjust the mixture but unless you have altered the carbs,airfilter, or exhaust from standard ther should be no need . Cool. Just the answer I was hoping for! Don't know why this bike would have had euro-spec carbs on it. I'll have to ask the previous owner(s) if they know why. Want to keep my variables to a minimum as I'm not sure this bike has ever run perfectly in my possession. One last thing I have to adjust! Thanks. Link to comment Share on other sites More sharing options...
Snailer Posted June 29, 2008 Share Posted June 29, 2008 While we're on this subject - how do I get the main jet holder out of the carb body? I've drilled out the little brass pin, but it still won't budge - tried heating and (not very gently) tapping it out - should I tap it down or up? Alternatively how do you clean the little holes in the side of the jet holder??? BTW I agree with Billa if you want just drill out the plug but shouldnt be necessary. All input including caveats gratefully received Thnx Link to comment Share on other sites More sharing options...
stoggy Posted June 30, 2008 Share Posted June 30, 2008 I justed cleaned mine out, they had sat for about 20yrs, I couldn't get the main jet holder out until i soaked it in gas/carb cleaner for 24 hours. then they fell out when I turned it over. I used a tooth brush and a air compressor to get the little holes clean. Once i cleaned them off and let dry they now sit back in their holes tight too. My tooth brush tastes like gas now though. Drilled? what are you talking about? No man, no drills. But they come out the top. You probably shouldn't pound on anything either its just dirty and stuck, soak it in gas. If gas is bad for carburator bodies why the hell would they mix gas in them? You probably shouldn't put your seals or diaphram in carb cleaner though. If they are filthy rinse them in gas. Link to comment Share on other sites More sharing options...
Cy Welch Posted June 30, 2008 Share Posted June 30, 2008 Cool. Just the answer I was hoping for! Don't know why this bike would have had euro-spec carbs on it. I'll have to ask the previous owner(s) if they know why. Want to keep my variables to a minimum as I'm not sure this bike has ever run perfectly in my possession. One last thing I have to adjust! Thanks. Actually the 79 model year shouldn't have the plug like that but rather a screw with a limit cap on it. The plugged one would be a 1980 or later US model with the BS34 III rather than the BS34 II on the 79's. I haven't seen one from that age range that didn't need drilled out and adjusted, and you may need to replace the o-rings on the adjuster to get it working well. As for the rubber plug, that covers the idle jet in the model III carb. I would not think you would get good result mixing the two carb models as according to the book they are jetted differently. You should probably make sure you have matching model number carbs. Link to comment Share on other sites More sharing options...
grusvag Posted July 1, 2008 Author Share Posted July 1, 2008 Actually the 79 model year shouldn't have the plug like that but rather a screw with a limit cap on it. The plugged one would be a 1980 or later US model with the BS34 III rather than the BS34 II on the 79's. I haven't seen one from that age range that didn't need drilled out and adjusted, and you may need to replace the o-rings on the adjuster to get it working well. Would it be normal for only one of the MS34III carbs to have this plug in it? It's twin did have the mixture screw in it. So it sounds like you'd recommend I use the original BS34II that came on the bike, is that true?. I'll need to find another rebuildable candidate in that case. My original has a broken body. Anyone want to trade a freshly cleaned and stripped BS34III body for a BS34II body? Link to comment Share on other sites More sharing options...
Cy Welch Posted July 3, 2008 Share Posted July 3, 2008 Would it be normal for only one of the MS34III carbs to have this plug in it? It's twin did have the mixture screw in it. So it sounds like you'd recommend I use the original BS34II that came on the bike, is that true?. I'll need to find another rebuildable candidate in that case. My original has a broken body. Anyone want to trade a freshly cleaned and stripped BS34III body for a BS34II body? Darn!! I just got rid of a pair of BS34 II's I hadn't really worked on them enough to know for sure but the slides were not moving but I think with a little soaking they would have freed up. Unfortunately their gone now. Link to comment Share on other sites More sharing options...
grusvag Posted July 3, 2008 Author Share Posted July 3, 2008 I'm an idiot. The two BS34IIIs are fine. They match and I'm just going to rebuild them. Hopefully they won't be too problematic to get running properly. Thanks for everyone's help. I'll let you know how I make out. Link to comment Share on other sites More sharing options...
Snailer Posted July 3, 2008 Share Posted July 3, 2008 I justed cleaned mine out, they had sat for about 20yrs, I couldn't get the main jet holder out until i soaked it in gas/carb cleaner for 24 hours. then they fell out when I turned it over. I used a tooth brush and a air compressor to get the little holes clean. Once i cleaned them off and let dry they now sit back in their holes tight too. My tooth brush tastes like gas now though. Drilled? what are you talking about? No man, no drills. But they come out the top. You probably shouldn't pound on anything either its just dirty and stuck, soak it in gas. If gas is bad for carburator bodies why the hell would they mix gas in them? You probably shouldn't put your seals or diaphram in carb cleaner though. If they are filthy rinse them in gas. Thanks for that. They did come out the top - I had to unscrew the jet about halfway and tap it down to help it out then I got a bolt with the same thread to screw in which I used to tap it out the rest of the way. I couldnt get the washer out so I just tapped it all the way out with a small screwdriver and left the washer in place. This one was stiff all the way out. The brass pins are to guide the jet holder (or needle jet) into the right place to line up the holes so that the petrol/gas can come through the main jet and also from there into the pilot jet in front which is corked with a rubber bung. You don't need to drill them out - they dont secure the jet holder, just guide it. It was well worth taking the needle jet/main jet holder out to clean it as it has 12 little holes to progressively allow more fuel in as the needle lifts. They are easy to clean with a (sewing) needle or a pin and a bit of air and toothbrush!!! BTW grusvag I would have thought that under the brass plug in your pics is a screw just like the other ones Good luck everyone. Thanks for your help. Tony Link to comment Share on other sites More sharing options...
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