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surging issues

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Hey everyone I'm having issues with my1990 xr600r I recently rebuilt the motor and when I cruise down the street it has a surging at anyconstant speed I put a big gun evo exhaust pipe on it and I tried playing around with the jetting with no luck. Right now the jetting is stock with a starting point 65 slow and 165 main tried bumping up the main to a 170 and same results also tried moving the clipdown as well as up and got same results....also when at idle and you wot it bogs way down and kills the motor im not much of a carb guy just wondering what your guys input is thanks

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I'll try doing that however what gets me is that it ran perfect with those jets before why the sudden change? Only thing that really changed was the exhaust system its bigger in diameter than the stock.... Would moving the clip on the needle tell me if I need the smaller jet also?

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Update**** put the bigger main back in with the needle clip on the second from top making it leaner and screwed the fuel mixture screw out 3-3 1/2 turns and seems to do a little better mid range is not popping so much but lower rpm seems to remain similar not as bad though ...... Might go back to middle clip and see what that does. Will post my findings

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Well moved the clip down and didn't help at all made it worst I think your right on going down with the mains but just doesn't add up to me since now I'm running a bigger exhaust system.... When I moved the clip down had to practically close the fuel mixture screw all the way.... Might get a 168 main or 162 which I think is the next step down from 165

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At a total lost so I tried moving the clip to the top making it the most lean and bike barely runs and slowly giving it throttle kills it too it has to be that it's to lean I hate carbs haha getting ready to break down and take it to a shop. I just dont want to after so many issues with shops around here

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You sure you have good fuel flow from petcock? usually a surge is caused by lack of fuel then refill & deplete, over & over , causing surging. Off jetting usually causes consistent poor performance, loading up stumbling or flatspots etc. Your venting of tank good? What about Mastera210 idea of air cut off valve diaphram? Or put old pipe back on & see if clears up?

Edited by bork

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Ya definitely good flow from tank but I'm getting the loading up stumbling effect. Sometimes worst than not. I have not checked the side diaphragm yet but maybe that could be my issue since everything else I do really makes minimal changes

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165 is a really big jet, i dont think that is stock as you said. Try a way smaller main like a 155. The fuel screw only affects idle, not mid range or top end. With that said, this sounds more like a float issue. Have you inspected the float condition and height?

Get a 155 main and a 158 main and try one of those on the second clip and report back.

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your stock jets should be 165 main / 62 pilot

 

Main:   '88 to '90  #165; after '90  #152

Pilot:    Up to '88  #62; after '88  #60

 

I have an '89 with stock exhaust, baffle removed, airbox uncorked and I am running a 168 main, 68 pilot, screw is at 2.5. 

With these jets I am a little rich, but I prefer a little rich over lean.

It isnt perfect yet, but Im still tweaking.

 

I think you typically adjust the needle clip last. (I would leave it int the middle slot)

Mine will bog/kill the engine with a quick off idle twist of the throttle, especially if it isnt totally warmed up. (the 68 pilot really helped with this)

Edited by markc522
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Ok reviving this thread so I tried playing with the jets suggested and getting same results surging while at a constant speed. Had a buddy check it out he thought maybe an ignition issue so opened up shop manual and did diagnostics on the wiring. Everything seems to be fine we are suspecting either cdi unit is bad or regulator I have a Ricky stator wired up for 200 straight watts bought the regulator from them as well the HD one should that have an ohm reading when touching both leads?..... Basically this is what's happening idle is fine and wot is fine but when it's at a constant speed it feels like the motor is cutting in and out also when your at a stand still and wot it it bogs down and kills the motor I don't remember it doing that but I could be wrong. Any ideas what I should check and not check?

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Now according to the book it says the the plug that goes from the cdi box the black/yellow wire to the high tension cord which I'm guessing is the spark plug wire without the cap on? It should read 7.4 to 11k but I'm getting 4.5k which is in spec when testing the ignition coil to the spark plug wire without the cap I'm lost completely

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