Hello:
Here is my setup. Just looking for some insight on jetting and tuning as my bike is being a little difficult with me at the moment. Here's the specs:
1964 Vespa GL
166cc 2-port kit from scooterworks
20/20 carb-
55/160 idle jet
160
BE3
100 main
2 1/2 turns out on the mix screw
Idle screw is fully turned in
SIP road exhaust
It was running really good when I first got it together but as it has broken in and the weather has warmed up I've had to start tinkering with it to keep her going. She still causing me issues though so I am thinking MV insights might help.
1st issue- Low idle, I bumped the idle jet up from a 38/120 but I still have the idle screw in all the way....seems like it's almost there but not quite. Hesitant to bump up further because of issue number two I read about here.
2nd issue- Seems to lose power with throttle wide open from the middle to the top of the range. I read on here that too rich a mix will cause some sputtering. Plug chop looks fine and chocolaty but maybe the larger idle jet+same BE3+100 main is causing a rich mix at higher throttle ranges? Before tinkering with the idle mix screw, I would rev it up high during adjustment to ensure smooth operation across the range but on the upper end of the range it seems to start missing like there is a rev limiter or something. I read here that this too can be indicative of too rich a mix but it's doesn't seem like it's 4 stroking but more of a rev limiter sound.
Backfiring....used to start in 2-4 kicks...now it takes more and often it will backfire loudly then following that start up after the 1-2 more kicks. This seems to be a rule, backfire, then start right up. It never enjoys having the choke pulled out to start but does like the fuel on unless it's already warmed up then it prefers fuel off.
FYI points and ignition are NEW and bike has strong spark. Points are gapped to .330 mm, anything bigger and it won't start. It ran so well when I first got it together I didn't have to do much tinkering with the carb at all....now that it is broken in though and warming up outside it's being a bit troublesome. Also, I replaced the points due to the screw holding them slipping and closing the gap (talk about power loss) so I went ahead and replaced them while I was in there. Any thoughts on my jetting setup or perhaps should I be looking somewhere else? I didn't mention timing because I simply installed the stator the way I found it (I took pictures during dissassembly) and the motor was running when I bought it but needed to be rebuilt due to a bad selector rod bearing and rear wheel bearing. Thanks in advance everyone.