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Discussion Starter · #1 ·
I just installed an engine that was recently built and tuned by chris at benchmark, It is a 686 with cams and valves and minor other mods and a Mikuni flat slide carb. It is running a dynatech cdi. Under load it cuts out as if it had a rev limiter. After the RPMs increase it runs great... it doesnt seem like a carb issue... it feels to consistant and acts like an electrical or ignition problem. Does it more as it warms up. when I tried to ride it as it got hot I had to be on flat to get it to go, or even a little down hill.
Any Ideas???
 

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Discussion Starter · #4 ·
CDI is my thought too! I am going to install the stock one to test it... If not calling chris will be on my list of things to do tomorrow

Thanks!
 

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Check the connection on the shift indicator. ( located on top of the engine, under oem airbox) I had the same thing happen to me 2 weeks ago. Turned out to be a bad connection on the terminal. I thought my cdi was going bad also. You can ground the wire to see if the miss goes away, if it does you have a bad switch.
 

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Discussion Starter · #6 · (Edited)
What wire do I ground? I keep thinking its something simple like that. Thanks Dave

Is it the single wire with a push on clip... I just looked at it and will try grounding it


Check the connection on the shift indicator. ( located on top of the engine, under oem airbox) I had the same thing happen to me 2 weeks ago. Turned out to be a bad connection on the terminal. I thought my cdi was going bad also. You can ground the wire to see if the miss goes away, if it does you have a bad switch.
 

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What wire do I ground? I keep thinking its something simple like that. Thanks Dave

Check the connection on the shift indicator. ( located on top of the engine, under oem airbox) I had the same thing happen to me 2 weeks ago. Turned out to be a bad connection on the terminal. I thought my cdi was going bad also. You can ground the wire to see if the miss goes away, if it does you have a bad switch.
Their is only 1 wire going to the sender, I think it is green and has a 90 degree terminal on it.
 

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Try disabling the accelerator pump and see what it does...

If it is the reverse rev limiter it will cut out hard at 20mph...run fine up to there...

James is basically right about it being too rich not sure about the main jet being it tho...more likely the accelerator pump or pilot jet or needle...

Do you have a complete tuners kit for it and who set it up...

If Chris sold you that carb and set it up for you it shouldn't need too much attention with regard to sizes of nozzles/jets/needles but night need adjustments and fine tuning of all elements...
 

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Discussion Starter · #10 ·
checked wire and it appeared to be good connection, so I started it let it run for a minute a so, test drove it and it run great. but as it warmed up it started doing it again. the warmer it gets the worse it is. does it in all gears including neutral and it is very RPM specific. I tried grounding the Reverse sensor wire as suggested and it makes no difference.

I have worked on a lot of bikes with Jetting issues and never had one act like this, but I have also never done much with this style Mikuni carb. does it still sound like it could be something that simple.

I am running stock exhaust for the moment as Mine come up missing after being torn apart for a year. It has only 30 hrs on it and I dont really think it would cause the low speed studder that this has if it was restricted to much... but again... bigger CC and carb... I dont know
 

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Discussion Starter · #11 ·
I bought Engine from Fellow member and He assures me it ran great in his rhino, and Paperwork shows Chris did tune it for him. It only has low hours since it was done last fall. the CDI is the one used on this engine as well...
 

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YES...it could definitely be the exhaust...that motor needs lots of air flow...

What intake do you have...

disable the accelerator pump and see what it does...

The put the leanest needle you have at lowest setting...

Smallest pilot jet...

Remove tip on exhaust can...

If you have an air box remove the lid..

See if those things help or not...

If they all help a little and together help a lot you need a high flow exhaust/intake and correct carb setting/jetting/adjustments....

All of the above...

Not saying that it it...but this is how you fine out...

Also... I see there is a Ron Woods exhaust for sale on the forum today for $350...in case you are interested...that is a great exhaust for that motor and carb...
 

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Discussion Starter · #15 ·
YES...it could definitely be the exhaust...that motor needs lots of air flow...

What intake do you have...

disable the accelerator pump and see what it does...

The put the leanest needle you have at lowest setting...

Smallest pilot jet...

Remove tip on exhaust can...

If you have an air box remove the lid..

See if those things help or not...

If they all help a little and together help a lot you need a high flow exhaust/intake and correct carb setting/jetting/adjustments....

All of the above...

Not saying that it it...but this is how you fine out...

Also... I see there is a Ron Woods exhaust for sale on the forum today for $350...in case you are interested...that is a great exhaust for that motor and carb...
Thanks! I need to get a tuner kit for the carb. I just got the carb with the engine te way it was set up before. It is the stock intake with no porting from what I see, and I dont have an airbox, its just a k&n with outerwear mounted right on carb. I will check the accelerator pump thing asap and find exhaust too! I know I need to change it anyway.

Thanks for all the help. we will find it the problem, and I can learn a lot from everyone in the process!

lol
 

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I don;t think it is the main if it is cutting out right after idle. Try moving the accelerator pump start set screw up some. You want it to activate at about 1/4 throttle. It still sounds like a CDI to me. Did you try the stock CDI yet?
 

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YES...it could definitely be the exhaust...that motor needs lots of air flow...

What intake do you have...

disable the accelerator pump and see what it does...

The put the leanest needle you have at lowest setting...

Smallest pilot jet...

Remove tip on exhaust can...

If you have an air box remove the lid..

See if those things help or not...

If they all help a little and together help a lot you need a high flow exhaust/intake and correct carb setting/jetting/adjustments....

All of the above...

Not saying that it it...but this is how you fine out...

Also... I see there is a Ron Woods exhaust for sale on the forum today for $350...in case you are interested...that is a great exhaust for that motor and carb...
Thanks! I need to get a tuner kit for the carb. I just got the carb with the engine te way it was set up before. It is the stock intake with no porting from what I see, and I dont have an airbox, its just a k&n with outerwear mounted right on carb. I will check the accelerator pump thing asap and find exhaust too! I know I need to change it anyway.

Thanks for all the help. we will find it the problem, and I can learn a lot from everyone in the process!

lol
Sticking the filter right on the carb does not work well I am sure that is part of the problem too...

Start by doing the things I suggested and let me know if you want me to order you a tuner's kit for that carb and/or make you a custom intake for it that works great...and our fuel delivery kit would be a good idea too...

I assumed that if it was a benchmark motor set up by Chis with "valves" that it would have a ported head...

A lot people revert back to stock carbs for simplicity and user friendly operation and still get very good performance and I make a similar intake for it and sell the correct jet kit too...

My last 686 did 0-300' in 6.3 seconds with the stock carb, wet clutch...there are faster ones for sure...but that is quick...
 

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drop one on the main jet and see if it fixes it... its doing it worse as it warms up is because it needs more fuel when its cold...Im betting 1 size to big on main..
 

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Discussion Starter · #19 ·
Havent had much time to work on it, but I did try the CDI and no change, so I pulled the the end of the pipe off and drilled a few holes in the muffler insides... It runs better and has a stumble here and there but The main problem is gone, So I need to change the exhaust first and Then Im sure work on some jetting.

Thanks Everyone for the input! I have some parts to buy so I will be contacting a few of you very soon!
 
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