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Popping sound at half throttle

2840 Views 12 Replies 3 Participants Last post by  TWBARR
I am a noobie. I recently serviced my 1998 TDub the other day. Changed front and rear sprocket with new chain. Changed tires to Shinko SR428s. Also changed oil and filter. Noticed a good leak around front of crankcase cover left side (order new one for $5.90). Drove it before I noticed the leak and at half throttle there is a popping sound which seems to come from the engine side of the carb. Unsure if this means that the valves need adjusted or it is loosing compression from the leak.

Is the crankcase under compression? Could this be the cause?

Another question, I also changed the sparkplug and pulled it after ran a couple of miles to test everything, the sparkplug is white on end of tip?

Any suggestion from the vast wisdom on this forum is greatly appreciated.

PS all the work I did cost around $100. Local shop wanted $410 for parts and service. This forum saved me a lot of money. THANKS TO ALL!!!
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Was it popping before you messed with it? If so, considering the white plug, I'd guess too lean. If not, I'd guess a pinched wire when the stator cover was replaced.

It was not popping before and it only pops once, its not a loud pop just a small pop almost puff. Have not messed with the carb at all, just cleaned air filter, took crankcase off to replace front sprocket and the other above mentioned. Before though it had a champion cpark plug and replaced with a DR8EA. Could the resistor be the cause, should I replace with a D8EA?
Cleaning a dirty filter will lean the mixture.

I run the Champion plug from Walmart. No problem. The resistor plug should make no difference.

Should I tune the carb?
Does the engine tell you the carb needs tuning?

If it is running too lean, I would think that the carb would need tuning. Again I am a noob to the doityourself maintenance. I have worked on more cars than motorcycles. Also is the crankcase under compression therefore losing power do to the leak when I first test rode it? The gasket is on its way...
Crankcase alternates compression and vacuum depending on if the piston is going up or down.

Cars exhibit the same driveability problems as motorcycles when jetting is not right. See the carb tuning sticky in Tech. It lists symptoms of too lean and symptoms of too rich. If you have symptoms, make a small adjustment to rectify the symptoms. If the symptoms get worse, adjust the other way. If the symptoms get better, make another small adjustment. Keep making small adjustments until the symptoms go away.

Thank you Qwerty for all your help and wisdom. I will work on the carb this weekend and replace crankcase gasket. Also hope to adjust valves, they do seem a little off.
For an update I changed the crankcase gasket, no more popping!!! I also had to adjust the idler due too to low of idle and engine shuting off at idle. Runs great now.
Great sticky put on this forum by Qwerty on the techincal help.

Carb Tuning
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