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a few jetting questions about hesitation and sputtering

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Yet another question from me, i know. Im sorry.

Ride: 08 400sm

elevation: 1000ft

temp: 25 to 50 farenheight

Mods: 3x3, full MRD/SSW, adjustable fuel screw on the stock mikuni 36mm carb.

Current jetting: 25 pilot, 160 main, 3rd clip on dynojet needle, not sure what the fuel screw is at, i play with it constantly as the temperature changes.

Symptom 1: at about half throttle (happens exactly at 60mph in 5th gear using stock gearing) the bike likes to hesitate and not have as much power as other rpm ranges. Its very noticable to the point that i will cruise at 65 or higher to avoid it constantly sputtering. Sometimes its worse than others, but i havent been able to correlate it to temperature or humidity, so im not sure if its a lean or rich condition thats causing this.

Symptom 2: after a full throttle or a hard run up to about 50 or 60 the bike will fall flat on its face with the exact same symptoms as when you need to switch to reserve as you run out of fuel. It lasts no more than 1 or 2 seconds of sputtering until it regains power and will cruise as normal. Im assuming this is because im running the carb bowl dry, but im not exactly sure why. Its aggrivating when i want to go fast >.<

Float hieght is PERFECT, im sure of this. No jets are clogged. Ive checked.

I think i created a topic a while back about this, but i didnt know my jetting then because i had never had the carb off. Now i have the MRD as well. I've even tried 2 separate BSR36 carbs on the bike and the same symptoms occur.

Any ideas on either symptom? Thank you for any help or insight to these problems.

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Check the vacumn hose for the petcock both ends as well as for cracking of the hose. You're in Mo. so you shouldn't have the charcoal cannister the Ca. model has but you never know. the Ca. model has silver gas cap and a vent at the underside rear of the tank, otherwise the tank vents thru the black gas cap. The tank vent must be clear in order to deliver fuel right. If it's not fuel then it must be air or spark. Do the air box removal test and check to see if it runs better without it or not. Your jetting sounds like mine and I'm at sea level with stock exhaust. You might be lean on the main with the MRD but the elevation may make the difference between yours and mine. Have you ever had the stator side case off?

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i dont have the CA version, but how would i check to make sure my black gas cap is clear and vents properly?

I have had the stator cover off, but what would i be looking for?

I've left the airbox cover off at some point and if i recall, it ran much worse. Maybe I'll richen up the main and the needle and see how it runs.

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Run it with the cap off? I'm not sure off hand how to check if it is clear. I would check the stator wires coming out of the case to make sure they are in the right exit location and not frayed or damaged. Then there's something beside the stator inside the case, (pulse something) that causes intermittant trouble as it goes bad. If it ran worse with the airbox off then getting more air (for rich circumstances) is probably not the solution to the problem. Again it sounds lean, the MRD flows a lot of air so maybe you are lean. The surging on a stock bike is defintely lean. Sorry I am about out of suggestions but there are many knowledgeable people that will post up

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Sounds like a fuel supply issue...Have you tried running it on prime?.

What main jet is installed?..When you ran it with the side cover off did it run worse all through the rev range?

Edited by craigodrz400sm

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i cant remember about what ranges it ran badly in. It was a while ago when i had it off and i didnt even know it was off, i had left it off by accident haha

i will try running it on prime next time i ride and doing some full throttle runs.

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