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Starter not strong enough to crank the engine over with choke on.

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Hey everyone,

So I have a heavenly modified drz. It's getting cold out now, 4C in the morning. I still want to ride to work because in the afternoon it's beautiful out. As the topic title says my bike won't crank over with the choke on. I have a mikuni tm40-6z carb. 150 mj, 22.5 pj, 3rd richest needle on the 3rd clip. Float is adjusted. 1.1 air jet. I bought gel cell bike master battery because I have no exhaust decompression lever on stage 2 hotcams and the stocker wasnt enough. The motor turns over normally when cold with out the choke, but just sputters. Half choke it will slowly turn over, full choke and it doesn't. If I do a half throttle twist with no choke she starts for about 3 seconds then dies, but if I can pull it to half choke while it's running I'm good to go. When it warms up to 10C it starts without the choke no problem. Again just want to reiterate that the carb is clean, plug is new, float is adjusted fine. My thoughts are, weak starter, oil to thick 10w40, or maybe to much fuel entering with the choke. Any thought?

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When I first started reading your post, I was thinking oil viscosity too thick, but the choke affecting the way your bike cranks over baffles me, are you sure? Good luck!

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What you experience with the choke is perfectly correct.  Choke ON you admit more air to the motor and the force needed to compress the full charge is more.  No choke really restricts air entry to the cylinder and the marginal starter can spin it.  I experienced exactly the same thing.  First thing to check is if the battery is providing enough cold cranking amps.  A bigger battery or jumping from an automotive battery will tell you that.  Next is the starter motor can only deliver so much torque regardless of how much battery is behind it.  Next is a way to reduce the compression such as no choke or a functional auto compression release.  My approach was a bigger battery and aded a Hot Cam with the auto compression release intact.  10W40 should be fine for 0 deg C.  Might try 5W40 Shell Rotella T6.

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