I installed a performance kit for the DS650 - a racing pipe, 45mm Mikuni flatside carb, and rev box (no high flow filter yet). I am having trouble getting the carb adjusted correctly. When I installed the carb the plugs were all fouled so I went to a smaller main jet. Now the plugs aren't fouling. The problem I have is that when idling, if you tap the throttle real fast, the motor hesitates before reving up. If you don't tap the throttle as far and/or as fast there is no hesitation. When you are taking off from a stop or near stop (engine idling) and nail the throttle in first gear, there is a delay and then all of the sudden the motor kicks in like crazy with the front end coming off the ground! The hesitation does not occur if you nail the throttle starting from an RPM above idle. I've played with the pilot jet, jet needles, needle position, air screw, etc but can't seem to get rid of the hesitation. I'm wondering if this is common when running a large 45mm flatside carb with a high flowing pipe on a 650cc motor? I don't have this hesitation with the stock CV carb. Can someone explain why this hesitation is ocurring and which circuit I would adjust to reduce it or eliminate it? By the way, the carb has an accelerator pump that squirts gas fumes in the main bore as the throttle is being depressed, but this is disabled on the carb. I'm wondering if I should enable it? I think it can flood the engine.

 

I am gone to take a long shot at this one, but as with anytime you go to a larger opening for air to pass you lose velocity. If you have changed all the adjustments on the carb, then maybe just the air velocity flowing through the carb at that low of an RPM is causing the hesitation. One the RPM and air velocity pick up, you have no problems. Maybe a higher flowing air filter may help this, or raising the idle slightly till the prob goes away.

 

You might try and jet up 1 size on the piolt jet and raise the idle a little bit too. If nothing helps then you could make a custom intake track for the filter that is longer. The longer snorkel will give you higher velocity and this will help the hesitation. It sounds to me like the airflow through the bigger carb isn't "fully developed" this will make it carburate poorly off idle. Then when you rev it up crtical mean flow velocity is achieved and it takes off quickly. I don't know if there is room to make a custom intake track but I know lengthening it will help give you more velocity. If nothing fixes this bore out the stock carb and call up Mr. Wood and tell him you expect your money back.

CT250R

 

I think your problem may be "loading up". Try blipping the throttle and reving the engine really good and see if it still happens. If it doesnt then you may still be too rich on the pilot. Have you tried calling the performance company you bought it from? It could also be a case of to much fuel, i.e. too big a carb. Timing advance could also help you.

 

If the problem is too lean, there is an accelerator pump available for some tm flatslides. The accelerator pump shoots a little gass into the carb when you open the throttle. Call sudco, they would know if one is available and price.
I think I would call the people that sent you the kit first and see what they say.

 

I'm pretty sure that the pilot circuit is not correct. According to Mikuni, the idle RPM should go from low to high to low as you turn the pilot air screw from around 1 1/2 or 2 turns out to around 3 turns out. The pilot screw does not behave this way. Instead, the idle RPM goes from low to high and remains there with more turns beyond 3. According to Mikuni this means that the pilot jet is too big - with the air screw all the way out there is still not enough air. The carb came with a #40 pilot jet in it which is huge. I have tried as low as 30 but that isn't low enough. I think I need a #25 or #20. I'll have to go back to the harley dealership and pick those pilot jets up and try them. Hopefully the off idle hesitation will then be solved. If not the next thing I'll try is the accelerator pump.

 

I went all the way down to a #22.5 from a #40 pilot jet and still have the hesitation. I'm getting stumped on this one.

 

I did some reading on accelerator pumps and I think you guys are correct in your diagnosis - it is a momentary lack of gas (lean condition) as the throttle is suddenly opened. I probably should be running the pilot jet as rich as possible instead of going down in size. I can run the jet needle richer too. I'll set the idle higher. I'll get a high flow air filter. I think I'll try to enable the accelerator pump as well.

 

I am a tech and your problem is definatly lack of accelerator pump enrichment. Four strokes NEED a accelerator pump. Simply put air accelerates faster than fuel, this is why there is a bog when you open up the accelerator, then when the fuel catches up the bog stops. An accelerator pump sprays fuel in ahead of the slide so it can get a head start on the air. I can't believe that anyone even sold a four stroke carb without an accelerator pump. The stock carb is set up diffrent in that it uses a vacuum diaphragm to open up the slide. The slide opens up much slower this way. Kawasaki is fond of this style of carb it makes for an easy riding carb with only as much slide opening as the engine requires. the stock carb has throttle plates which also slow down air flow.

 

I enabled the accelerator pump and it appears to have fixed the hesitation problem off idle. I will further test it out this weekend.