72cc bbk from scrappydogs By 07jonway50 (Read 1,714 times)

[07jonway50]

I bought the 47mm bbk kit from Scrappydog. I had a mechanic Rich refered me to install it for me. My scooter is a 07 Jonway 4 stroke with 20mm carb, 88 main jet, super hot perf coil, racing cdi, iridium sparkplug, uni filter, carbon fiber exhuast, and 5gram perf rollers. Before the upgrade I got up 38 mph easily, most of the time 40. After the bbk install I test rode it right after and it topped out at 20 mph. The mechanic said it had to break in for 100 miles. It was running way rich so I down jetted to an 84. Then, same problem so down to a 75. The accel is better but it starts losing power and almost backfiring after 15 mph. Im so fed up, any help is greatly appreciated

[Bashan]

In my opinion that 100 mile wait is a load of crap. I don't think you should have taken a new head out and tried to break a speed record but certainly it should have gone over 20 MPH. OK, you've pretty much ruled out anything electrical with all of your upgrades. The first thing I would check if you had a new head installed is the compression. The new head might have a faulty valve or maybe the gasket is leaking. It's not complicated if you have a tester. I'd rule that out before going any further, here's a link: COMPRESSION TEST Let us know what happens, Rich

[jake aka:ventoscoot]

ditto to Bashan. Harbor Freight has a Compression tester kit for pretty cheap (I think I paid like $30) that has the correct 10mm adapter with it.

[jake aka:ventoscoot]

Also, have you asked the mechanic who installed it to do a compression test? Maybe Rick at Scrappydog has some suggestions. He is always great about answering emails in very quick fashion and has good suggestions.