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Hesitation when I blip the throttle

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Not sure if it's just the design of the carb but when I blip the throttle to lift the front wheel over a rock or log, I get a hesitation and no wheel lift. I've done Dave's mod and I suspect I'm running a tad rich because when it's warm out the bike doesn't want the choke on to start. Starts fine with no choke. In gears 3-5 there is no hesitation and 2nd gear is only minor. Any ideas on if and how I can tune this out? When the rpms are high there's no hesitation in any gear.

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You should be able to lift the front in first, at least. This not meant to be a blanket statement, but if you can start the bike cold without the enrichner, I'd say you are rich, which could cause the problem you are describing...

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Well........unfortunately the only way to stop that is either clutch the bike to get over the object,,or toss the CV carb in the trash and put on a pumper carb.start lookin for an FCR MX ,,late model..40mm or 41mm..you need the squirt,,you open the throttle on these carbs and the engine goes lean......with the accelerator pump you squirt bfuel into the intake the moment the throttle is crack,,curing the lean spike..

 

unfortunately,,this is the main issue with the CV barb..

 

Your jetting is rich,,leaning it out may help,,but very little..

 

B

Edited by brianhare

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I can pop wheelies in 1st gear no problem, just can't do it from an idle while putting through a tight trail. That's when I get the hesitation/lag/bog. I'll try turning the screw in a bit to lean it out and then get used to clutching more often if that doesn't work!

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I'm under the impression that it is lean for the 1st micro second , when whacking throttle from idle. Try 1/2 choke & see if there is any change. This is why most go to a pumper style carb. (nature of the beast) You can usually reduce it but it may happen still, ocasionally. You did raise your needle by shimming, right? (daves mod) The needle usually affects most or range except idle & WO. Do you have the idle screw mixure under carb in front? Sometimes richening it will help also. There is a good you tube video of setting that screw.

  Watch it all the way thru, start to finish. I know some of it is basic, but some is very important at same time.

Edited by bork

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With the standard mods tuned correctly in 1st from idle the front wheel will certainly come up.

I ride mine like a trials bike.

 

55/158 is often a bit rich. Sometimes it is fine.

 

How thick a shim under the needle?

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Dave, the shim is the size you recommend in your mods. I'll try leaning it out a bit with the screw. Any guidance on how much I should turn it? It's 2.5 turns out now in accordance with your mods. I don't know how much difference a turn makes. Should I start with 1/4 turn, then try 1/2, then 3/4, etc. or just go straight to a full turn?

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How about float level? Too low can cause different settings.

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The float is, unfortunately, not adjustable. But it is seldom a problem.

 

I always tuned with the screw by turning the screw in while it was idling until it flatered a bit, then back out until smooth again, then back out another half turn.

 

The bad thing about jetting is the only way to know you have it right is to try all other jets and settings and everything you try makes performance and rideability worse.

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The float is, unfortunately, not adjustable. But it is seldom a problem.

 

I always tuned with the screw by turning the screw in while it was idling until it flatered a bit, then back out until smooth again, then back out another half turn.

 

The bad thing about jetting is the only way to know you have it right is to try all other jets and settings and everything you try makes performance and rideability worse.

 

Currently my idle seems a little flatered which points to the screw needing to be backed out a bit, but it starts (on warm days) without a choke which points to rich. Maybe my idle is set too low and the bike is rich? If that's the case I'll try what you suggested. It's definitely rideable and I only noticed the lag in the woods while idling along. Maybe I'll go to a 14 tooth front sprocket and see what happens and not even mess with the carb for now until I learn a bit more carb voodoo.

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gearing lower,,going with a 14 front makes quite a difference in these bikes....running rich is a problem though,,if you crack the throttle and it`s already rich then adding fuel brings it richer and does not create more power..a leaner running engine will jump to life when it gets that additional air and fuel..even more so on a pumper carb that squirts fuel right into the intake before the valves,,it instantly gets the fuel required with no lag..

 

B

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Not sure if it's just the design of the carb but when I blip the throttle to lift the front wheel over a rock or log, I get a hesitation and no wheel lift. I've done Dave's mod and I suspect I'm running a tad rich because when it's warm out the bike doesn't want the choke on to start. Starts fine with no choke. In gears 3-5 there is no hesitation and 2nd gear is only minor. Any ideas on if and how I can tune this out? When the rpms are high there's no hesitation in any gear.

Why would you need the choke when the air temp is warm? I rarely have to use my choke and certainly not when it is warm. I had similar issues as you..a flat spot when wicking the throttle. I went from a 55 to 58 pilot and it eliminated it. Jetting is peculiar with these bikes, it would make some bikes run far too rich but mine likes that 58. I tried the fuel screw adjustment but it did little. My main is 160...have a DJ needle @ #4 clip. Off idle the bike is a rocket..

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I just did my first completely stock 650L ride. A friend handed me his 2007 and a fistful of cash telling me to give it more power or make it lighter. I had to tell him lighter would take a bunch more money but the HP thing is easy. Don't know how anyone could like the stock performance, other than a strong midrange surge the bike was pretty weak. Easy starting hot or cold but horrible stumbling off idle, then the surge if you yank WFO and hit the relatively low rpm peak. Part throttle stumbles thru all range with heavy popping and backfires off throttle. I replaced the CV with a TM40 (no pump) installed a K&N with the mesh cover, desmogged and removed the airbox baffle. Completely different power characteristics now. Still easy starting but the off idle stumble, popping and backfire are gone without a trace. It will lift the frontend easy thru 1st and 2nd and acceleration is stronger. Maybe 3-4 more estimated horsepower but engine function is far better. The XRs ONLY Mikuni flatslide is a bargain and is worth the cost in the way it makes the engine run alone besides the extra HP. My 650L has a pumper and is better than the TM but still this is a good conversion. Going to try several pipes next and the Hotcam and JE are waiting on the shelf. Going to try to be as analytical as possible for using a seat of the pants dyno.

Edited by valvesrule

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OP,  I see a FCR-MX carb in your future. 

Edited by D0T-C0M

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Currently my idle seems a little flatered which points to the screw needing to be backed out a bit, but it starts (on warm days) without a choke which points to rich. Maybe my idle is set too low and the bike is rich? If that's the case I'll try what you suggested. It's definitely rideable and I only noticed the lag in the woods while idling along. Maybe I'll go to a 14 tooth front sprocket and see what happens and not even mess with the carb for now until I learn a bit more carb voodoo.

 

Could be the pilot jet needs to be changed too. Try the screw, then if no joy try the pilot.

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