Sunny 50cc reverse trike not starting By jomama0867 (Read 727 times)

[jomama0867]

I'm working on a Sunny DG50TKA reverse trike (2012 with only 300 miles on it). The previous owner put a BBK kit on it (50mm), and it was running but VERY hard to start. He would crank the starter for 20-30 seconds before it would "catch", and finally clipped a valve, which left him with no compression (go figure). So, as I'm swapping heads to get it running I've come across a situation I haven't seen (or heard of), so I am convinced that one of you "gurus" has the answer; here goes:

When I crank it over, the starter bogs down as if the battery was low, but the battery tests fine. Also I noticed the wires from the battery were warm, so I checked the battery grounds, changed coils, even changed starters but no change. When I put a fresh battery in ther was no difference, still bogs down on cranking. So here's where the weird part comes in, I pull the spark plug and screw in my compression tester hose, open the throttle and hit the switch, and it turns over COMPLETELY NORMAL (although it doesn't start of course)! I re-install the plug and wire, and it bogs! I've tried this with the plug wire, without the plug wire, changing spark plugs, WOT, no difference. Checked valves, even changed cams {?!??!), NO DIFFERENCE, but all I have to do is check compression and it cranks normal!! Any ideas??

[cyborg]

You have some seriously high compression,,,it's either that or the plug is firing before tdc,,,put the plug in and don't hook up the coil wire and turn it over,,see if the plug not firing does it,,,and I know it's a stretch but pull the plug and see if there's interference between the plug and piston,,,check the plug and the piston top to see if they're touching slightly

[jomama0867]

Thanx Cyborg, I thought about the plug interference and pulled the head but didn't see any obvious signs of contact on the piston, valves or plug. I usually work on 150's so when I hooked up the compression tester and got a reading of 80 psi, I didn't know if that was good or bad (but I didn't consider it high)!. I put a stock 50cc head on to diagnose, but will have a new BBK head tomorrow (Friday), so I'll wait until then, put the correct head on, and try again!

[jomama0867]

Right again, Cyborg . . .  SERIOUSLY high compression! I put the 50mm head back on and the ignition sounds "normal". Now all I have to do is get replacement valves, etc., etc.

[cyborg]

Great find!! There's a piston right there