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TOPIC: Video of "rev pulsing" after letting off throttle.

Video of "rev pulsing" after letting off throttle. 10 May 2018 22:12 #1

  • Cobra
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Got the bike back together after alot of help form all of you. Thank you!!! I have noticed that the bike pulses after i let off the throttle all the way while at speed. In the video you can hear my clutch slip as I hit the top RPMs then I let off the throttle completely the bike rev pulses and is jerky. You can really hear it downhill in the video. Any thoughts on this pulsing? Ill address the clutch slip in another thread.

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Video of "rev pulsing" after letting off throttle. 11 May 2018 06:24 #2

  • THEarmpit
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Same thing happens on the bike I just got running, it's my first old two stroke so I just assumed it was how they were.
Following this thread to see what anyone says about this if it's not normal.
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Video of "rev pulsing" after letting off throttle. 11 May 2018 07:01 #3

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It's hard to tell from the video but it sounds like it's "4 stroking" a little at steady throttle and on decal. Make sure your idle mix isn't too rich. If that's OK try moving the needle clip one notch towards lean and see what happens.
Also, if it only does it in gear with the clutch out, make sure your chain isn't too loose or your sprockets don't have uneven wear.

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Last Edit: by jradnich.

Video of "rev pulsing" after letting off throttle. 11 May 2018 09:20 #4

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Its not 4 stroking, and the chain is smooth from takeoff so that leads me to believe it is ok.

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Video of "rev pulsing" after letting off throttle. 11 May 2018 09:43 #5

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Whatch video at 0:22-0:26 and 1:11-1:20

This is just where I can hear it the most although the issue happens throughout the vid, any time i turn off the throttle all the way at speed. But this should narrow the sound and you are trying to hear.

Each little rev powers the bike for a sec and slightly jerks the bike, I can see the tach bumping up 300-400 rpm with each rev.

This seems like it would be the idle circuit as the throttle is all the way closed but it idles perfect at a stand still and starts easily which tells me that the circuit should be good.

It did seem to get worse when I got gas and added some 2 stroke oil but I only put in 1.2 gallons and mixed in a little less then 4oz of 2 stroke oil. I see people saying lean it out so that is why i mention this.

Could the gears of the bike do this or a slipping clutch assembly? What does your bike sound like going down hill whith the throttle off doing 30mph or similar on flat ground? Is it a smooth deceleration or is it all revy like this?

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Video of "rev pulsing" after letting off throttle. 12 May 2018 20:41 #6

  • Enduronut
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It's not running rich, it's running lean !!
Running it that way could burn a hole in your piston and/or seize it up in a hurry.
Can you post a picture of your spark plug after a ride like the one in your video . . . . so we can see how it's burning?

1. First thing I'd do is to clean the carb, tank, and petcock . . . also make sure the gas cap vent is working.
2. Next, turn the air mixture screw in one turn and see how it responds
3. Then, try lowering the needle clip one groove (which raises the needle) . . . this enriches the mid range and should help the surging/pulsing problem while cruising at steady throttle.
4. Lastly, check for air leaks around the intake and at both crank seals.

.

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Last Edit: by Enduronut.

Video of "rev pulsing" after letting off throttle. 13 May 2018 03:46 #7

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Yes absolutely agree with Eduronut above, it's just super lean on more than just the pilot so yeah raise the needle [drop the clip down] & i say go bigger on the pilot until the pilot screw responds as it should. Hell it's a wonder its not nipped up the piston or holed it but 250 's are a bit less stressed than a 360. Unusual to be so far out if the carburetor & settings are stock, or there's an air leak somewhere. Piston not in back to front?, don't laugh i've seen it done & went super lean & gaspy but a bit different to yours which goes too well for that. I've lost what we're talking but thinking reed inlet DT2? so reed holes in piston & if at the front then --well you get the idea.

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Video of "rev pulsing" after letting off throttle. 13 May 2018 10:58 #8

  • Cobra
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Yikes!! Is this lean?. My Clymer says that its normal but I have black and white photos, I did think that I heard a pinging at high rpm though.
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Last Edit: by Cobra.

Video of "rev pulsing" after letting off throttle. 13 May 2018 16:29 #9

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looks good on the plug but low & mid range at least it terribly lean listening to it. Almost [imagining what would happen] if the choke jet in the bowl cavity was blocked [little drilling down the hole] then if the choke lever was on rather than off then all ya doing is opening an airway & 'could' have 'that' affect. Sorry, just plucking random ideas outa the blue.

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Video of "rev pulsing" after letting off throttle. 13 May 2018 21:05 #10

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I moved the needle clip down a notch down (lifting the needle higher) Feels good with 1/4 - 1/2 throttle. Seems to run best with air mixture screw 2 turns out. Idle drops with air mixture screw turned in further clockwise (fatter).

I still here a rattling if Im cruzing along any speed 15-40 mph and I totally shut off throttle. So it seems that everything is great if the throttle is cracked(more fuel) so how can I get more fuel with the throttle off. I worded that poorly. But I feel that the rattling sound is maybe it running lean. On yamaha nopeds they have a pilot jet that can be changed is there something like that for these carbs. I just want it to run smooth and not be rattling at any rpm...is this realistic or is there some rattling no matter what? I also hear it at 7-8k rpm usually when I switch gears (maybe because I turn off the throttle to shift creating a lean condition) . Thanks again for all the help guys!

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