TheSamba.com :: View topic - bog-backfire

Thu Feb 20, 2003 9:57 pm

OK. Heres my problem. I installed a weber progressive carb setup on my 1641 the other day, and I also installed a set of headers/muffler while I was at it. I cant seem to get it setup right. It runs like sluggish until you open up the secondary and then it hauls ass. Most times after backing out of a full throttle stint, it backfires, and I mean backfire. We are talking wake the neighbors up 3 blocks away. Anyone know. Could it be timing? I set to where the Bentley recommends. Any help is greatly appreciated. Thanks

Fri Feb 21, 2003 2:04 pm

Anyone?

Fri Feb 21, 2003 3:06 pm

Backfires are usually caused by a rich carb. mixture and an exhaust leak. When you let off the gas at high throttle it creates the rich mixture and the exhast leak gives it the oxygen for ignition. This will put out a real cool flame at night with a stinger. The sluggishness could be timing or tune-up parts related. If you are running a 009 dist. you may want to set the timing at 30 deg. @ about 2000 rpm. Good luck

Fri Feb 21, 2003 8:50 pm

I didnt use a timing light to set the timing. I did it manually and set it @ 7 degrees. I will get a timing light and set it as you recommend. Also, I believe I do have an exhuast leak, I think I need to use some high temp silicone on the leaky areas, as I thought it seemed odd that the paper suggests using no sealant of any sort. The carb is said to be "jetted well for 0-3000 ft altitudes" I think to have proper jetting for a 3000 ft variance in altitude isn't possible, especially considering other factors must be looked at, such as humidity, barometer, temperature, and other factors. What jetting do you suggest I goto? I am in So-Cal, with 60-70 degree weather, at about 70 ft altitude, and usually around 60% humidity. Anyone have an Idea? I looked today and there is two jets visible when looking down the barrels of the carb. one is a 155 and one is a 170 I believe. Thanks again.

Sat Feb 22, 2003 8:02 am

if i remeber correctly the two jets you can see from the top are the air correction jets for the two barrels.under those are the emulsion tubes with the main jet fitted to the bottom of the em tube.
if not there then the main jets are in the bottom of the float bowl.
i think the idle jet is behind a brass screw on the side of the carb.
u definately need to time the engine properly b4 u think of messing with the carb jets etc.