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Hi all Im back again for more advice pls  about gs 850 gt carb jets , ive had hell of time getting it to run properly starts fine 1st 2nd gear fine after that holds back runs like crap  . however ive sussed out whats wrong by putting tape round the cone type air filters and leaving a small gap engine runs great now , so ive checked the main jets they are  size 130  and manual says should be size 155  a previous owner must of fitted them. my question is , ive got them cone type air filters no doubt giving more air than a standard air box , so im thinking instead of buying size 155 standard mains but getting 160 mains  . can anyone with a bit of carb jetting experience advise on this please carbs are the cv type  many thanks for any help   

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Have you got the 'good' cones or the 'bad' cones?...............LOL They all flow more air but some more than others.

I'd stab at around 170-175 if std is 155 but that still be lean'ish. Are the carbs original to the bike as thats a possibility - someone has swopped carbs that don't have the same internals as the 850 types? If so - bigger jets is hit or miss - but you've nothing to lose by trying?

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A 155 main jet for standard sounds very big to me, I think I was running 136 or 144 on my old 850 with pod filters and open pipe.

Just had a look in the manual and it says 102 for slide carbs and 115 for CV standard.

Also as it's running OK at first and then plays up its not a lack of constant fuel check the breather hole in the tank cap is not blocked as this will let some fuel through but then air lock the tank and stopping more fuel coming out.

Edited by wraith
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Are you talking about full throttle, high RPM here? Cos if not, you might find it's needles, float heights, or another fault, other than main jets.

Like Wraith says, something around 130-140 should run well enough. I think 115 sounds right, not 155, for standard Airbox.

Have you still got the stock air filter?

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15 minutes ago, wraith said:

A 155 main jet for standard sounds very big to me, I think I was running 136 or 144 on my old 850 with pod filters and open pipe.

Just had a look in the manual and it says 102 for slide carbs and 115 for CV standard.

Also as it's running OK at first and then plays up its not a lack of constant fuel check the breather hole in the tank cap is not blocked as this will let some fuel through but then air lock the tank and stopping more fuel coming out.

sorry my mistake  it is 115 not 155 standard   but it has 130's fitted and ran terrible but now ive tapped round the air filters blocking of probably 2/3ds air it runs ok so cant be vacuum in tank  i will check anyway  im thinking up the size of main jets to 160  and taking tape off air filters , was looking for input on possible jetting sizes on those filters  

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No dont have stock filters , I have cleaned carbs fitted new idle jets and new needle valves with their filters adjusted floats with vernier gauge they are spot on , a friend gave me the idea to put tape around filters to determine if the mains were big enough  checked them and seems their not . so thought id ask you chaps it has two 2 into one exhaust pipes with two reverse cone megga's on the end they do have baffles but are straight through i suppose the exhaust is not helping either     

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41 minutes ago, Gixer1460 said:

Have you got the 'good' cones or the 'bad' cones?...............LOL They all flow more air but some more than others.

I'd stab at around 170-175 if std is 155 but that still be lean'ish. Are the carbs original to the bike as thats a possibility - someone has swopped carbs that don't have the same internals as the 850 types? If so - bigger jets is hit or miss - but you've nothing to lose by trying?

no idea what the cones are like good or bad they was on the carbs when i got them 

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I think a 160 main will be too big, if you think jet sizes go up in 2.5 or 5 depending on the jets xD so even going to a 144 or a 150 will be a big jump from a 130.

I'd start by going to say 144 /146 main jet as that's a good 5 or 6 jet sizes up.

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 according to the manual its supposed to be 115 as standard as far as i know these are the original carbs  so 130 is far to small . as ive got non stock air filers that work better with lots of the are blocked off i was wondering if slightly over sized mains  mains would work . the do make 158 jets for cv carbs  144 /6 are smaller than standard . I may be wrong but by taping the air filters would suggest to me that its getting to much air to fuel , seems to me at least that it needs more fuel to cope with the air filters  i was wondering if anyone here had a gs 850 with these non stock filters on and had to rejet the carbs 

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wow big money  could be quicker  but bit risky with the quids have to be a bit frugal with my pension these days after all its just for a summer toy , my biking only days were over may years ago lol  

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A 144 main jet is much bigger the standard 115 main jet and is bigger than the 130 main you have, the bigger the number on the jet the more fuel it will let through basically (very basically ;))

So I'd put say a 144 ish size jet in and remove the tape off the filters.

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25 minutes ago, Wolf said:

mauvdw@gmail.com

iv got a jeting chart and some carb maintanance manuals i can mail thru if you want 

FB_IMG_1526062207990.jpg

jetting chart might be handy  think ill get larger jets not sure to go with the 144 as been suggested by Wraith as these are bigger than whats fitted now or to go to standard  115 and adjust needle if need be   jest costing £20 a set from Eblag not bad but cant afford to keep buying sets  so im looking for the best option with a little bit of tweaking of needle air screws etc  

Edited by ron
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1 minute ago, ron said:

jetting chart might be handy  think ill get lager jets not sure to go with the 144 as been suggested by Wraith as these are bigger than whats fitted now or to go to standard  115 and adjust needle if need be   jest costing £20 a set from Eblag not bad but cant afford to keep buying sets  so im looking for the best option with a little bit of tweaking of needle air screws etc  

Thing is with cone filters as speed increases the pasing wind runs carbs lean my vm26 slides also had 115 s oe and it almost cost me burnt valves from a runing lean . Try the shoping site 'wish' or 'ali x' for jets . Ithink dyna jet is also a good option 

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5 minutes ago, Wolf said:

Thing is with cone filters as speed increases the pasing wind runs carbs lean my vm26 slides also had 115 s oe and it almost cost me burnt valves from a runing lean . Try the shoping site 'wish' or 'ali x' for jets . Ithink dyna jet is also a good option 

cheers ill look them up , I did notice before i put tape round cones  my plugs were completely white and as you say i dont want burnt valves or worse a holed piston 

23 minutes ago, Wolf said:

mauvdw@gmail.com

iv got a jeting chart and some carb maintanance manuals i can mail thru if you want 

FB_IMG_1526062207990.jpg

jetting chart might be handy  think ill get lager jets not sure to go with the 144 as been suggested by Wraith as these are bigger than whats fitted now or to go to standard  115 and adjust needle if need be   jest costing £20 a set from Eblag not bad but cant afford to keep buying sets  so im looking for the best option with a little bit of tweaking of needle air screws etc  

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If your not running a big bore or running say 750 carbs on a 1000 etc, you should not need to alter the air screws, not with your set up anyway.

First thing you need to do is the main jet and get it running right with that, then alter the needle height to get it smooth. If you go to your local bike shop they will most of the time swop jets once you have bort the first 4 jets ;)

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Hi to all thats answered my original post yesterday , I think i must of been having some kind of senior moment or im just getting senile, i can imagine some of you thinking what is this bloke on . Anyway  , I somehow was thinking jet size 115 was 155 and that my jets of 130 were smaller than 115  . DOH  sorry if i confused any of you , OK Start again jets fitted are 130 so they are BIGGER than the standard jets but i need to choke in effect the carbs by taping round the cone air filters  to get it to run without to much fuss, a kneeler  racing friend suggests the main jets are still to small. I think Wraith come up with a good idea to try size about 144 ish  so think ill try these .Thanks again all who have helped and i do apologize for being a dumbass and confusing the issue , Its an age thing lol        

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I've got part of a Dynojet kit I would sell you for a few quid. It's what's left from mine for a GS1000G with BS34 carbs, so should be about right. I only used the needles and the smaller mains for use with an Airbox.

There's 2 sizes of main jet, which are going to be about right for cones and an open 4:1. There's also a new main air jet which is important.

I can copy the instructions and tuning guide. Let me know if you're interested.

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3 hours ago, gs7_11 said:

I've got part of a Dynojet kit I would sell you for a few quid. It's what's left from mine for a GS1000G with BS34 carbs, so should be about right. I only used the needles and the smaller mains for use with an Airbox.

There's 2 sizes of main jet, which are going to be about right for cones and an open 4:1. There's also a new main air jet which is important.

I can copy the instructions and tuning guide. Let me know if you're interested.

thanks for the offer but ive ordered new 4  jets this morning  from Koolinquiet on Eblag £12.76 free delivery  bargain I thought they have dispatched them already hopefully they will do the job Many thanks  

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