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Bad stumble / stutter from nowhere

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My drz sm has developed a very bad stutter/ stumble , at steady throttle it feels like it almost dies then comes back it sometimes back fires a little too this happens in all gears at about 1inch from the closed position, it has run fine for over 5k , I removed the air box cover & it improves the throttle response but the stutter/ stumble is still there . The only 2 things that changed were the rear sprocket from a 39 t to a41 & the weather here droped about 20 f this week but it's still in the low 70s any input is greatly apricated Specs are. Cw 440 bb , stg 1hot cams , full yoshimora exhaust , drz e carb 155 main jet , 45 pilot jet , ocemp needle clip 3 , 2.25 turns on the fs , 65 starter jet , 60 pilot air jet , 200 main air jet bike has been ok for the last 5k then this came out of nowhere

In advance thanks for taking the time to help me out

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Sound like fuel starvation. Still running stock vacuum petcock? Could be some build up somewhere in the carb.

Bikes been running ok for 5 k has a raptorpetcock

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So today I filled up my tank & put some sea foam in it , swapped out my air filter for a K&n and turned in my fuel screw 3/4 of a turn to lean out my pilot jetting & went for a ride , bike was the same at first , after about 50 mile it was way better ( I kept going back to were the stutter was 50 to 60 in 5th gear , each time it got a little better ) filled up my tank again & headed home on the way I put my fuel screw back to 2 1/4 turns out by the time I got home ( about 200 miles ) all was good again so I swapped my air filter back & it stayed ok , so Im thinking I must have had some sort of blockade in the pilot jet ?

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Lean & lean.

Bike is running ok again now , when I was trying to sort out the low end stutter I removed the air box cover , definitely had better throttle response ? So was thinking of raising the clip from 4 to 3 (lowering the needle) to lean out the mid range what do you think ,? I'm Usually around 1000 - 4000 ft asl thanks for your input ( my first post states the needle clip is 3 , it's not its 4 ) sorry for the misstake Edited by peter
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Bike is running ok again now , when I was trying to sort out the low end stutter I removed the air box cover , definitely had better throttle response ? So was thinking of raising the clip from 4 to 3 (lowering the needle) to lean out the mid range what do you think ,? I'm Usually around 1000 - 4000 ft asl thanks for your input ( my first post states the needle clip is 3 , it's not its 4 ) sorry for the misstake

Yeah, try clip 3.  And 2 turns out on fuel screw.

Edited by Throttle5
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Yeah, try clip 3.  And 2 turns out on fuel screw.

Took the top off the carb tis morning & it was on clip 3 ( sorry ) put it on 2 & the bike runs a lot better epically when I'm up between 3000 - 5000 asl I live at 1000 ft asl the bike definitely runs better on clip 2 all round

Again thanks for your input mate

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Took the top off the carb tis morning & it was on clip 3 ( sorry ) put it on 2 & the bike runs a lot better epically when I'm up between 3000 - 5000 asl I live at 1000 ft asl the bike definitely runs better on clip 2 all round

Again thanks for your input mate

Cool...I've had my share of jetting issues.  :smashpc:  No expert, just gotta try different things till it works.  Glad it's working out. 

BTW my mods are extremely similar to yours, right down to the gearing.  I love the bike !!

Oh and if you haven't done suspension yet...DO IT !   :worthy:  :thumbsup:  :thumbsup:

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Cool...I've had my share of jetting issues.  :smashpc:  No expert, just gotta try different things till it works.  Glad it's working out. 

BTW my mods are extremely similar to yours, right down to the gearing.  I love the bike !!

Oh and if you haven't done suspension yet...DO IT !   :worthy:  :thumbsup:  :thumbsup:

Suspension is all stock , got it set up a while back by Dax , sports bike suspension tuning San diego was the best thing I ever did to my bike , now has 29,500 k on it , also have a vfr 800 but I love my little drz getting the suspension set up was defiantly the best bang for my $ I have spent , night & day difference is a term that's used a lot with drz mods , 3x3 , hot cams , yoshimora exhaust, fcr carb , bb kit , I've done all these but getting my suspension set up was truly night & day
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