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Fluctuating rpm on decel

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Hey guys, I was out riding my rm250 today and I noticed the rpms would sometimes fluctuate if the bike engine brakes. It only happens on deceleration. Any idea what it could be? I did lean the jetting a little bit but I'm still getting spooge.

Edited by Jay762

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Start with the easy things first.  Proper gas/oil mix, proper heat range of the spark plug.  You mentioned that you did make a carb adjustment to lean it out, BUT to get your bike to absolutely run spot on in every condition (temp. altitude, humidity) you should adjust your airscrew before every ride which only takes less than a minute to do.  Start your bike, let it warm up to proper riding temp (radiator cap warm), then hold throttle at 1/4 turn, while doing that turn out (counter clockwise) your airscrew.  This will raise the rpms of the bike, DO NOT ADJUST THE THROTTLE TO COMPENSATE FOR ENGINE SPEED WHILE THIS IS HAPPENING.  Continue to turn out your airscrew until the engine rpms stop accelerating.  when it stops accelerating rpms, your bike is adjusting properly for that days conditions.  If the rpms continue to increase after 2 1/2 turns out from all the way in, you need to adjust your jetting.  Another thing I would check is to see if you have proper fuel flow, because if you've ever run your bike out of gas, the engine will rapidly fluctuate in rpms.  You could also check to see if you have cracked reeds.  Its sometimes a process of elimination.  Hope this helped.

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Sounds like you went too lean on your main jet.  FYI:  You could still be too rich on the pilot and needle but be lean on the main.  Consider going fatter on the main (from what you have) and leaning out the pilot for starters.

This is why I normally just go with a JD Jet kit, they've got the entire range nailed, but that's me. 

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Thanks for the tips guys. The bike ran great before, lots of power but at the end of riding I had a line of spooge down the exhaust and some on the swingarm. When I changed my jetting I only moved the clip one position higher on the needle but it's in the highest position now. It sounds like I should start with the air screw. Is surging on deceleration typically a lean condition then? I don't mind cleaning spooge; I'd rather run rich than lean.

Edited by Jay762
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On 29/08/2017 at 5:44 AM, mike4414 said:

Start with the easy things first.  Proper gas/oil mix, proper heat range of the spark plug.  You mentioned that you did make a carb adjustment to lean it out, BUT to get your bike to absolutely run spot on in every condition (temp. altitude, humidity) you should adjust your airscrew before every ride which only takes less than a minute to do.  Start your bike, let it warm up to proper riding temp (radiator cap warm), then hold throttle at 1/4 turn, while doing that turn out (counter clockwise) your airscrew.  This will raise the rpms of the bike, DO NOT ADJUST THE THROTTLE TO COMPENSATE FOR ENGINE SPEED WHILE THIS IS HAPPENING.  Continue to turn out your airscrew until the engine rpms stop accelerating.  when it stops accelerating rpms, your bike is adjusting properly for that days conditions.  If the rpms continue to increase after 2 1/2 turns out from all the way in, you need to adjust your jetting.  Another thing I would check is to see if you have proper fuel flow, because if you've ever run your bike out of gas, the engine will rapidly fluctuate in rpms.  You could also check to see if you have cracked reeds.  Its sometimes a process of elimination.  Hope this helped.

Few things I don't agree with in this post 

1: if temp and elevation doesn't change drastically then you don't need to set airscrew every ride 

2: if you hold the throttle open at 1/4 turn you will be bypassing the pilot circuit and be running on the needle circuit and the air screw will not do anything 

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Few things I don't agree with in this post 
1: if temp and elevation doesn't change drastically then you don't need to set airscrew every ride 
2: if you hold the throttle open at 1/4 turn you will be bypassing the pilot circuit and be running on the needle circuit and the air screw will not do anything 


You can disagree as much as you'd like, the way o explained to him to adjust his air screw is absolutely correct by Suzuki.

Something I have to say about the people viewing this site. I have only been on here for a few days and all I see is people "disagreeing" with everyone's ADVICE, I thought that this site was designed to help others with ideas on how to fix issues. All I see is people wanting to disagree and argue.

That's all...
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57 minutes ago, mike4414 said:

You can disagree as much as you'd like, the way o explained to him to adjust his air screw is absolutely correct by Suzuki.

Something I have to say about the people viewing this site. I have only been on here for a few days and all I see is people "disagreeing" with everyone's ADVICE, I thought that this site was designed to help others with ideas on how to fix issues. All I see is people wanting to disagree and argue.

That's all...

 

First off, let me extend a belated welcome to ThumperTalk.  Then let me point out that because there's no way of knowing if someone is laughing or yelling when they post a reply to you or about something that you just said then it's nearly impossible to say if they are trying to dis you or just expressing a different point of view.

I advise that you just stick with your stated position and see how a topic unfolds.  Being right or wrong here really doesn't matter because in the end "we" are all in this together trying to help out a fellow rider get back on the track (or trail).

So all's good, and hopefully Jay762 gets it figured out and is able to ride this weekend ~ spoogee free!   :thumbsup:

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23 hours ago, Jay762 said:

Thanks for the tips guys. The bike ran great before, lots of power but at the end of riding I had a line of spooge down the exhaust and some on the swingarm. When I changed my jetting I only moved the clip one position higher on the needle but it's in the highest position now. It sounds like I should start with the air screw. Is surging on deceleration typically a lean condition then? I don't mind cleaning spooge; I'd rather run rich than lean.

When you say it is surging on deceleration is this on flat, smooth, level ground or is this deceleration across the braking chop normally encountered entering a turn on an MX track?

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It's on smooth level ground. I noticed it riding through the neighbourhood. Today I checked my air screw and the rpms seemed to increase past 3 turns out. Perhaps the pilot is causing the spooge and I'm a little too lean on the needle.

Edited by Jay762

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55 minutes ago, Jay762 said:

It's on smooth level ground. I noticed it riding through the neighbourhood. Today I checked my air screw and the rpms seemed to increase past 3 turns out. Perhaps the pilot is causing the spooge and I'm a little too lean on the needle.

So this is more of a diagnostic inquiry?

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If it previously ran fine with the same jetting and conditions then install new crank seals. Lean on decel is usually because air sucks past the seals.

Your spooge could be rich jetting or it might be transmission oil from a leaky right crank seal.

$13 for Tusk seals. Tap a screw in the old seals and pull them out.

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On 8/30/2017 at 7:33 PM, Jay762 said:

It's on smooth level ground. I noticed it riding through the neighbourhood. Today I checked my air screw and the rpms seemed to increase past 3 turns out. Perhaps the pilot is causing the spooge and I'm a little too lean on the needle.

Be sure to evaluate jetting once bike is up to operating temperature. Neighborhood riding typically doesn't allow for this. 

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