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View Full Version : Popping and hesitation on throttle after putting air box back on


50cc
02-14-2013, 10:48 AM
Hi guys,

After my aftermarket filter broke off it's hose I got tired of experiments and put my old air box back on. I re-jetted to its original jets - the #30 idle and the #85 main (as in my bike's specs (http://www.si-zweirad.de/webseite/upload/fahrzeug-infos/050ccm/REX_RS450/public/Datenblatt_RS450-500.pdf)).

Since then I get this strange hesitation on takeoff with few popping sounds from the exhaust and deep drop in RPMs - bike hesitates for like 1 to 2 seconds, RPMs go really low, but then suddenly it accelerates fast and runs great overall. Sometimes, when I decelerate quickly, I hear a single strong 'POP!' from the exhaust. I thought it's running lean and put a #90, but that was too much and bike ran like crap and didn't fix the problem. Now I am with the #85 again since #80 is too lean (I have #70 #75 #80 #85 #90 #95 sizes only).

Mixture screw is at 2 1/2 turns out, exhaust is only visually modified, air box is not modified at all, all hoses are great, I have no air leaks at neither side of the carb and intake is 2 months old, carb's diaphragm is new as well, needle clip is in the middle slot, chops are tobacco brownish, perhaps a hint lighter.

Any ideas?

Thanks in advance,
Ivan

scootnwinn
02-14-2013, 11:00 AM
Try moving your needle clip to the top position hesitation and popping followed by brisk acceleration make me think its too rich...

50cc
02-14-2013, 11:45 AM
Will do that.

Also, the popping occurs only when waiting long on a traffic light without touching the throttle - if it's a short light or I tinkle from time to time with the throttle it does not happen.

50cc
02-14-2013, 01:40 PM
Also, edfr mentioned in the old forums that the cause could be the ACV valve of the carb, but the last time I changed jets I pressed it and it was squirting ok.

Admin
02-14-2013, 02:43 PM
I agree, sounds like a needle adjustment issue.

50cc
02-14-2013, 02:50 PM
Ok guys, thanks again. Tomorrow morning I'll lower the needle and will report.

inuyasha
02-14-2013, 03:42 PM
Hi
Sounds like she's running lean to me
Check for airleaks, since you just put back the airbox i would start there
Take care and ride safely dear friend
Yours Hank

savy09
02-14-2013, 05:44 PM
Go back to the stock 75 jet first, correct the idle and ride.

millsc
02-14-2013, 10:12 PM
the acv valve is on 24mm carbs the 50's have a fuel pump on the bottom. You don't have an acv valve.

50cc
02-15-2013, 07:29 AM
So guys, problem solved - scoot was running too rich. Played with the clip this morning and tried all positions and it runs like before only with the clip at the very top and that makes me think I can go down to #82, #83 or so, but since I have only #80 I'll just stay with the #85, because it runs great now and just as I like it - a tiny bit on the rich side. The bad thing is in summer I'd have to probably downjet to the #80 mj I have, but summer's still far away.

Thanks again to all of you!!

scootnwinn
02-15-2013, 10:17 AM
Glad you got it going I know how it is when they aren't quite right it can drive you mad...

50cc
02-15-2013, 10:42 AM
Glad you got it going I know how it is when they aren't quite right it can drive you mad...

Yeah, I really care about the machine and want to run it with correct mixture only. My heart breaks when I feel it's out of tune. I guess I'm too rigorous..

scootnwinn
02-15-2013, 10:48 AM
Nah can't happen. 2 wheel vehicles require OCD type of attention to all details. You have the perfect mindset

Admin
02-15-2013, 02:52 PM
Awesome, glad ya got it all worked out! :tup: