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running crap

  • Thread starter Thread starter mazza
  • Start date Start date
M

mazza

Guest
hello again guys just a quick story .bought a gs750g from work mate, only ran with the choke on so thought i would put carb kit in but read would be better just to put the orings on the old jets and bits .the kits where for an 850g coz every one said when ordering parts for 750g order 850g instead so got 850 kits as i said but just changes the orings and gaskets .refitted the carbs and managed to get it ticking over all lumpy and crap but when reved would stall straight away and only rev to 4000revs .then he tells me they not original carbs as old ones where very pitted so he bought a set of carbs off ebay for a gs500 was i right to stare at him in silence and call him an idiot or can the carbs be salvaged with the complete 850 carb refurb kit ,or should i stick em on ebay and get the right set set for the the right bike ,not sure of the differences .
sorry its a 1980/81 gs750 with the cv mikuni carbs
 
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Owwwww... my eyes!!

Sorry mazza, but I can't offer any help. I'm pretty sure your carbs should be the BS32 CV carbs, but I'm not positive about the European spec bikes.

From your description of the stalling when you give it throttle, it sounds like they need a thorough cleaning instead of just o-rings and gaskets.

Good luck.
 
mazza said:
... bought a gs750g from work mate, only ran with the choke on .....managed to get it ticking over all lumpy and crap but when reved would stall straight away and only rev to 4000 revs....a set of carbs off ebay for a gs500..... not sure of the differences .
sorry its a 1980/81 gs750 with the cv mikuni carbs
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As mentioned, the carbs are most probably BS32 CV type. However, jets will be sized for 500/550 and not 750, resulting in a lean condition all over.

That is why it only runs with the choke on, because the larger engine needs more fuel.

The carb bodies are the same (not sure about spacing on the rack), but you will need jets, needles and needle jets according to 750 specs. Not sure if it will be cheaper to get complete carbs for 750, or just the brass internals.
 
The 550 and the 750 used the same BS32SS carbs, but all the jets were different sized. Even with the differences, it should still be able to rev up better then you're indicating. Does sound to me like you still have some cleaning to do. Doing a half a$$ed job on the cleaning will never yield good results.

Re-jetting the carbs might be more expensive then just getting the correct carbs. If it were me, I would look for a proper set of carbs for your bike and sell the ones you have. Without doing a complete survey of what jets are in your carbs, there's no way to know if they're even 550 carbs to begin with, so that might be a good starting point.
 
If it were me, I'd get the correct carbs and ensure they are jetted as stock and go from there. Otherwise, there is just to much guessing to do. Also, did I read that correctly ?? Do you have a GS750G ? Do you have a shaft drive 750 ?? If so, they are very rare indeed. :)
 
mazza said:
hello again guys just a quick story .bought a gs750g from work mate, only ran with the choke on so thought i would put carb kit in.......
Click to expand...

Cant help you anymore than what has already been said.
Am not any carb expert, although I would think that carbs from smaller engine could work on bigger engine, at lower rpm.
THe fuel & air, total volume, at say 4000 rpm on bigger engine would be about same as needed on smaller engine at, say, 6000 rpm. Weiter that is true or not .....
The fact than need choke to get it to run at all, sounds like general problem with carb needing cleaning; ports plugged.

But, anyway, would like to see pics of 750G.

.
 
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i will post some pictures soon i did take some with my phone but very grainy . yes its a jap gs750g ive put some 850 jets and stuff in at the moment they are pretty close to what came out but i am going to be on the look out for some 750 carbs .ebay show a few sets for about 3/400 dollars plus about 60 dollars shipping to me in the uk seems pretty steep at the moment .will post again tuesday
 
I wouldve ran a compression test first
always do that before you buy a new motorcycle
 
well fitted the carbs with 750/850 bits and managed to get it running and reving but still bit crappy will need to vaccum sync them then check again fitted another regulator now charges as well .think hes fitted a electronic ignition as there is 4 wires coming from the generator .the loom has been murdered theres wires joined plugs cut off. guna be long time trying to resurect this one .IMG_0360.jpgi i take it this is the 8 valve engine

 
really not sure how to upload more photos
 

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Let us know what size jets you have in those carbs currently. Pilot, Main, Pilot Air, needle and needle jet. If you're using the original GS550 carbs then your jet needle is going to be pretty far off and the main air jet (pressed fit) will be of a little as well. Should be able to get her running with that main air jet though.
 
pilot jet is 42.5
air jet 190
needle jet y5 ,are the original in the carb
air screws, are original in the carb with new oring and washer
main jet 112.5

looking at bike cliff carb info the y5 is fitted in the 750 but now reading ,im now 2nd guessing myself and not 100% now if it does have the y5 but rings a bell
the jet needle is from the old 750 carbs
most of the stuff from the old carbs was corroded ans the oaf i bought the bike off had tried to rebuild the old carbs and pretty much broke most bits trying to get the jets out /
the only original 550 parts in the carbs are the floats needle jet /emoulsion tube and the air adjuster needle
hope this makes some sense
to me it smell a bit like its overfueling very strong smell
 
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What process did you use to clean the carbs. Did you do a complete disassembly? Did you dip them for 24 hrs? Did you spray cleaner through all the passages? Did you poke each orifice?
 
Ecklund said:
This is right of course.
But you never just dragged one home before?
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these days its hard to find a trust worthy person, when I was 21 I bought a 81 CB900 that needed "carbs adjusted", turned out it had crap compression on all but one cylinder, 22 I bought a Magna 500 with the same problem. So no, I dont and wont do that anymore, best $40 I invested was on a compression tester
 
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