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I realize this is a crude shortcut, but has worked for "in the field" diagnosis. Very crude, but would like to hear the technical thoughts on it. A bike that is to lean can be easily proven as to lean by a slight turn of the choke, restricting the air flow, thus increasing the fuel to air ratio. If it runs better, then it shows the need to increase the jetting size. I see this often in the kid crowd where the kid has talked his parents into buying a new pipe with no regard as to the "system" of things. Thoughts? Is there  a trick for diagnosis of the opposite

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Usually the "Mikuni Roll of Method" will take care of that issue.

So do a search for "Vorteccpi" here on TT as he has posted the method at least a dozen times....

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Chokes don't actually choke anymore. Older carbs had a plate the chokes the intake, carbs now have a circuit for extra fuel.

In case you hadn't noticed, we have 'older' carbs on our 'older' bikes.

 

You BS level is off the scale, once again.... :banghead:

 

 

:ride:

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In case you hadn't noticed, we have 'older' carbs on our 'older' bikes.

 

You BS level is off the scale, once again.... :banghead:

 

 

:ride:

My apologies.  I have an CV30 on my bike(M/L) model. So the crf230f has a plate that 'chokes' the intake?

Just noticed that it had a lever, that's old school, I thought it had a knob for a choke. 

Edited by Yap Yap

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Usually the "Mikuni Roll of Method" will take care of that issue.

So do a search for "Vorteccpi" here on TT as he has posted the method at least a dozen times....

I had seen this. Would you consider this to trump the highest idle at app 2 turns out process or just a crude way of pointing in the direction needed?

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I had seen this. Would you consider this to trump the highest idle at app 2 turns out process or just a crude way of pointing in the direction needed?

 

The Mikuni Roll-Off Method is not crude in any sense of the word.  I quit doing Plug Chops long ago after I started using this method.

 

And yes.  If an engine performs better with partial choke it is too lean.  A fully-warmed engine will perform worse with even any amount of choke applied.

 

Idle mixture has nothing to do with main jet size selection.  Though all the circuits technically play together idle mixture screw position and pilot jet have almost no impact on the main jet during sustained WOT conditions.

 

Back when I was testing the Dial-A-Jet this is what I used to get it right.  You know instantly when your main is right or wrong and if it is too lean or too rich.  This method may not get you to best-power main size but it lets you know for sure what side you are on.

Edited by VortecCPI

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I googled dial a jet. Interesting.... but I can see how it did not take off. 

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The Mikuni Roll-Off Method is not crude in any sense of the word.  I quit doing Plug Chops long ago after I started using this method.

 

And yes.  If an engine performs better with partial choke it is too lean.  A fully-warmed engine will perform worse with even any amount of choke applied.

 

Idle mixture has nothing to do with main jet size selection.  Though all the circuits technically play together idle mixture screw position and pilot jet have almost no impact on the main jet during sustained WOT conditions.

 

Back when I was testing the Dial-A-Jet this is what I used to get it right.  You know instantly when your main is right or wrong and if it is too lean or too rich.  This method may not get you to best-power main size but it lets you know for sure what side you are on.

Hey, believe it or not, I have been looking for your roll off method. I have seen it many times in the archives but I am having no luck finding it now

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Hey, believe it or not, I have been looking for your roll off method. I have seen it many times in the archives but I am having no luck finding it now

 

http://www.mikuni.com/tg_main_jet_size.html

 

"The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.

If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.

If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one."

 

 

Extra thoughts on this...

 

Be sure the engine is fully warmed up and use a high gear such as fifth or, if you ever use it, sixth.  Don't bother testing using low gears as the result will be meaningless.  Testing on a slight incline is a good idea as well.  An engine that is spot-on on a level smooth road may be too lean on road with a slight incline or on a trail with lots of resistance.

 

If you need to get closer than this you must start chopping plugs.

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http://www.mikuni.com/tg_main_jet_size.html

 

"The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.

If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.

If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one."

 

 

Extra thoughts on this...

 

Be sure the engine is fully warmed up and use a high gear such as fifth or, if you ever use it, sixth.  Don't bother testing using low gears as the result will be meaningless.  Testing on a slight incline is a good idea as well.  An engine that is spot-on on a level smooth road may be too lean on road with a slight incline or on a trail with lots of resistance.

 

If you need to get closer than this you must start chopping plugs.

Thanks, I just finished 20 pages of the jetting sticky, gave up, and see your post, thanks. So do you still choose your idle jet size by app 2 turns out, highest idle?

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Thanks, I just finished 20 pages of the jetting sticky, gave up, and see your post, thanks. So do you still choose your idle jet size by app 2 turns out, highest idle?

 

Slow/Pilot jet sizing is usually very easy and almost always ends up a 45 at sea level.  Install a 45 and get the engine up to full operating temperature.  Then adjust the idle mixture screw for fastest idle.

  • If less than 1/2 turn out you need a 42 jet
  • If more than 2-1/2 turns out you need a 48 pilot jet

Most all CRF230s like a 45 but some, like mine, need a 48.  Technically I can use a 45 when it's hot but it is not enough when it is cold.  I am usually at about 1/2 turn when it is very hot and up to 1-1/2 turns when it is very cold.  If the air and engine get super hot and I am crawling it is a bit too rich with 1/2 turn but that straightens out once air gets moving over the engine again.

Edited by VortecCPI

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I found my notes, but will point out that my float level was not verified, my valves I keep checked and motor always warm, after trying about every combination that was reasonable, I finished up with 120 main 45 idle jet and air screw backed out 1 3/4. Stock needle in the 4th position, uni air filter, baffle in stock pipe.   This did not come from recommendations but through trial and error of what worked best on my bike. I did not cut plugs for verification, one reason is that mine seemed to have an obvious sweet spot, revealed by it not liking the other combinations, obvious lack of performance. I wonder if this was the case with others since the power up kit is a larger main. 

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Slow/Pilot jet sizing is usually very easy and almost always ends up a 45 at sea level.  Install a 45 and get the engine up to full operating temperature.  Then adjust the idle mixture screw for fastest idle.

  • If less than 1/2 turn out you need a 42 jet
  • If more than 2-1/2 turns out you need a 48 pilot jet

Most all CRF230s like a 45 but some, like mine, need a 48.  Technically I can use a 45 when it's hot but it is not enough when it is cold.  I am usually at about 1/2 turn when it is very hot and up to 1-1/2 turns when it is very cold.  If the air and engine get super hot and I am crawling it is a bit too rich with 1/2 turn but that straightens out once air gets moving over the engine again.

Hmm, interesting, I might check mine for cold weather.... never thought about that. It was tuned in the summer

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Mike Coe proved long ago a 132 main was way too big:

 

"It was worth more than 1.5 HP!! With the 132 the A/F mixture was @ 11.0:1 and the power would level out at 16HP. After going down to a 125 and then the 120, the engine pulled cleanly all the way to the rev limiter and 17.83HP. This was on a bone stock 230 with "power-up" mods. I could have gone even leaner and picked up a little more power, but decided to stay a little conservative."

 

Your trial and error match Mike's own findings:

 

"This is what I recommend for your bike and all others with stock engine with exhaust baffle and airbox snorkel removed. I ride my stock bike from 0 - 6500+ elevation with no changes in jetting between the desert and mountains.

120 main jet (used to be 132)
45 pilot jet
Stock needle with clip in fourth groove from the top
Accessory needle with clip in fourth groove from the top.

I have found that for low elevation riding, as in the desert, the "power-up" needle adds a touch better performance, but looses that same touch when riding in higher elevations of 4000 and up."

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Works for everything.  At WOT at high RPM a carb is a carb is a carb.

I assumed it so, but had rather ask than assume. LOL, I am an inquisitive person. Now I am looking online to see what the "roll on" method is

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I assumed it so, but had rather ask than assume. LOL, I am an inquisitive person. Now I am looking online to see what the "roll on" method is

 

It usually never hurts to ask.  Jetting an air-cooled engine with a carb is a compromise at best.  Air density is forever changing as is engine temperature, more specifically head/intake temperature.  These are archaic machines by comparison to other bikes that have EFI with sensors and ignition control.  Newer bikes can make a myriad of adjustments as conditions change but ours can not.

 

The good news is with simplicity comes durability and reliability.  The PD carb is incredibly forgiving as is the old two-valve 4T engine.  You can be off a good bit and these engines will manage just fine, unlike some very finicky 2Ts and newer high-tech 4Ts.  I wouldn't trade the simplicity of my CRF230 for anything.

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