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Post by bullgod on Mar 22, 2024 2:08:11 GMT -5
Any and all ideas or theories welcome. I recently put a 155cc kit on my bike. I ordered the kit and it was supposed to be a cylinder,head,piston,rings and A12 cam. I received it and it was all that plus a rocker assembly. I installed it with the rocker assembly but it wouldn't work because I couldn't loosen the tappets far enough to set valve lash so I used my old rocker assembly. Bike cranks on the first try but wouldn't idle. I turned idle screw in/up to where it's almost in as far as it will go and finally got bike to idle and sounded ok until I took off to ride and the bike sounds really weird once it gets going it surges and lunges forward while driving like the bike really wants to take off and about every 10 seconds or so it takes off and runs almost normal for about 5 to 10 seconds and then back to weird sounding and lunging. I've cleaned and changed carbs,intake,coil,cdi box, drained gas and put in new. Put on new vacuum and fuel lines and checked timing and readjusted valves to .003/.005 and tried again .004/.005. Nothing has helped. I'm at a loss, can someone help?
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Post by jjoshua20215 on Mar 24, 2024 1:39:08 GMT -5
It take 4 things for an engine to run
1.Gas
2.Air
3.Compression
4. Spark
Gas:
You stated you put a kit on. Did you change the jets? Might take some playing around. Also make sure you adjust the needle jet. I've have the same issue. Moved the c-clip 1 notch and it was like a new bike.
Pull the spark plug and read it for running condition.
Air:
You stated that you changed the lines, but have you confirmed there are no leaks? Have you changes/ modified the air box?
Compression:
Turning the engine by hand does there seem to be hard to turn or does it get hard the pressure quickly bleeds out?
You could've gotten bad parts and are chasing your tail as I've done in the past. There were a LOT of bad cylinder heads going around. I thought the problem was me until I found a good vendor.
Spark:
Take your spark plug out and put it in the boot. Hold the end close to the frame and try to electric start, there should be a strong visible spark trying to jump to the frame.
How did the bike run prior to the kit?
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Post by bullgod on Mar 25, 2024 0:00:44 GMT -5
jjoshua20215 ty for your response and I'll try to answer a couple of the questions u asked at the same time letting u and anyone else know I found the solution and would like to hear from everyone as to if they've ever heard of or come across a similar situation. Anyway I always read my plugs for clues and in this situation it was telling me "LEAN", it was white as snow so that kept pointing me to vacuum leak or carb so I redid the intake spacer by making my own and making sure the intake was sealed and took carb apart and went up in size with jets as well as give a thorough cleaning and still same thing and the engine ran great before except it smoked and slung oil which is why I decided to rebuild top end and up it a little while I was at it. But I kept going back to the rockers in my head because they just didn't seem right. I adjusted the valves at .004 & .005 and when I would grab the rocker at the adjuster nut and tried to wiggle it, I would get practically no movement but yet my lash was set right. This kept popping in my head so finally I said there should be more movement than what was getting so only solution I could come up with was to open the lash a little more because the cam I got had a visually noticeable lift difference so I doubled the lash at .008 & .010. That did the trick, it runs beautifully now. Sounds good, runs good so I'm gonna leave it right where it's at until its broken in and then I might play around with the lash some more. So there was my problem, the valves were staying open all the time even though I was setting the lash where they should be.Has anyone else ever heard of having to do this? Id like to hear from u guys and tell me if this is common or unheard of or what? Thanks in advance.
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Post by jjoshua20215 on Mar 25, 2024 19:02:19 GMT -5
bullgod Sounds like the head and rocker arm assembly you received could've been the culprit. Not sure how, but I have had similar issues with a kits on a GY6 139QMB. I ended up changing to a different rocker arm assembly like you did. I think these cheap parts vendors are mixing up what they send out. Parts should fit with no mods. lol I've done plenty of cheap kits and on almost all of them the heads were piss poor cheap. I mean unexplained compression loss within 150miles. I finally found out that the valves constantly needed resurfacing. Found a decent vendor and never had that problem again. Apparently, a lot of places "refurbish" parts, shine them up and sell them to us poor unsuspecting souls. For the longest I assumed I was too incompetent to tune a carb. Always had a flat spot on accel, and some simply wouldn't tune at all. I used to think I just didn't know what I was doing. Turns out I just didn't know where to get parts from. The exhaust valve likes to close up on new builds for some reason so recheck after break in. And if you ever consistently run lean, they will close due to excess heat. I'm assuming you have the GY6 157QMJ?
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