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XR70 slight Pop on decellaration

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I was cleaning up my 10 Y.O.'s 70 last night and adjusting the chain, and noticed a slight Pop on throttle down or down shifting. I tweaked the mixture screw to find start and end of highest idle, then set 1/2 way between. This setting is about 1 3/4 turns out, and it helped, but still has a little pop. Any ideas?? Only mod was to cut rear 1/3 of air filter ball off.

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Adjust your valves, make sure exause bolts are tight, use higher octane fuel, use lower octane fuel.

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The valves are supposed to be set with the engine completely cold. Honda says to adjust them to 0.003-0.005 mm. Go to BBR for a video to help you.

mms://media.bbrmotorsports.com/How_To/Windows/CRF50_ValveAdj_Win.wmv

I'm sorry it's not a link. Copy and paste it into the address bar.

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Thanks guy, thats exactly what I needed. I was curious about finding TDC on one of these little motors (I've done it several times on my 400), but that explains it well.

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