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Off Idle Stumble

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I'm having a bit of difficulty with the slow speed jetting on my '08 230. I've done all the usual uncorking and am running the recommended jetting of 45 pilot, raised needle (a two groove needle with 3 sm washers under the richest groove) and a 125 main. The bike has a little stumble/burble just as I lift the throttle off idle/closed position. It quickly straitens out and everyplace else it runs smooth. I don't know how many turns the idle mix is (it's hard to count with that goofy EPA screw) but it's less than 2. I'm thinking maybe I need to go back to the 43 Pilot? This little bike does pretty good WFO but the slow speed plunking is one of this bike greatest assets.

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Warm up bike, then before it gets too hot from idling too long, adjust Idle mixture screw for fastest idle speed then set base idle where you like it best.

Edited by adnohguy

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Warm up engine and adjust idle seems to be a contradiction in terms, Ha! I made a little "D" shaped tool to adjust the idle mix screw and I'll be damned if I can get in there and adjust it when the engine is hot, but that make sense so I'll figure something out.

The filter is clean and properly oiled

Thanks!

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Warm up engine and adjust idle seems to be a contradiction in terms, Ha! I made a little "D" shaped tool to adjust the idle mix screw and I'll be damned if I can get in there and adjust it when the engine is hot, but that make sense so I'll figure something out.

The filter is clean and properly oiled

Thanks!

As opposed to adjust mixture screw when the engine is first started from dead cold....does that help you?????

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Adno - I understand exactly what you mean. It's just that I haven't yet figured out how to reach in to the bottm ot the carb and adjust the mix screw without burning the daylights out of my hand. It's a tight squeeze to reach arond the exhaust and the starter motor from the other side is no peach either when it's hot.

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They have been making right angle tools for that reason for years and years....

Try adjusting an inline four cylinder if you think your bike is difficult....

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I have the T-screw and it makes it easier, but there's still the risk of burning your hand. Plus the handle interferes with the float bowl and is barely able to scrape by when rotataing it. Maybe that's a good thing--at least you know it will never get more than a half turn out of adjustment. What I do is drape a thick towel over the exhaust pipe and quickly adjust the screw. I've also used one of those fireproof plumber's cloths and wore a glove.

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Use a Dremel tool to cut a slot in the head of the idle mixture screw.  Just 1/2 turn can cause off-idle problems.  A too-lean condition is almost indistinguishable from a too-rich condition.  One way to tell is if it gets better or worse as the bike warms up.  Better when warm means it's too lean.  Another way is to apply just a little bit of choke and see if it gets better or worse.  Better with choke means it's too lean.

Edited by VortecCPI
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ok, so I've made a tool to adjust the idle mixture when the engine running and up to temp, a "D" shaped tool on the end of a flexible shaft much like the idle speed remote knob. When I adjust the mix the fastest and best running setting is fully closed!? This doesn't make sense. I asure you the air filter is clean and properly oiled and no the choke is not on. It seems to run fine but still has just a bit of off idle burble. I'm really puzzled by this fully closed mix setting, it shouldn't be this way but it idles ok?. And just to remind, I'm running a 45 pilot. Any carb gurus got any ideas?
Thanks

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I've been doing some research and am thinking that this problem might be related to the air cut valve. Based on what I've read, maybe if the air cut valve were stuck in the actuated position and causing a too rich condition with the throttle closed, this might cause the need for a very lean idle mixture setting and maybe cause the off idle stumbling too. I'll go take a look at it.

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Unfortunately  you made need to pull the carb and check everything including the air cut and float level.

 

The bike has a little stumble/burble just as I lift the throttle off idle/closed position. It quickly straitens out and everyplace else it runs smooth.

 

 

I've had the same problem on various bikes and the cause was either rich or lean. :banghead:

 

On some of my XRs I've had this problem (XRs also use PD series carbs) and the problem was richness and fixed by dropping the needle and/or main jet size.  On my CRF250X the cause was a lean condition just off idle (as measured by an air fuel ratio meter)  so opposite fix.

Also on my XRs I've had problems with the the two small discharge ports in the floor of the venturi plugging from debris. If the one near the slide plugs the bike is difficult to start cold and the off idle throttle response is rough from the lean mixture. If the one over the mixture screw plugs it is difficult to get a good idle. On decel if the exhaust does anything more than a light burble the low speed circuit is lean, or the air cut is not working, try turning out the mixture screw 1/2 turn as a check.   If the float level is high or low the mixture screw setting for best idle will be different than normal. I can't find my notes to tell you the exact relationship.

 

Not good news for your situation but I think the previous advice in this thread will get you to a solutions.

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