vibration and weird change of speed

B

bassplyr101

New Member
So I just put on a new #41 chain, wire, and ngk spark plug!!! Bikes runnin smooth as glass minus to serious vibration! Also the bike will get up and go pretty quick then kinda hit a certain speed stay there for about ten seconds then accelerate again. Not entirely sure why or what this could be. Its a 66cc with an NT carb. Any suggestions???
 
Doublecheck your engine mounts, some people have had their studs, bolts, mount to loosen or break which caused vibrations translating into poor performance (fuel foaming, etc). Other than that, I know that my engine will not go to it's top speed when cold especially recently (winter) but once it's hit the top speed once (39mph!) it will do it again easily without "hitting the speed limiting wall".
 
Thats a very good point! I shoulda considered that it is cold and hasnt been ran for a week or two prevois to me takin it out with new parts in it haha. But i did go through and tighten the mounts earlier today. :) but the fact that it is cold and wasnt warmed up properly would definitely be the main and most obvious culprit haha
 
The most important consideration is how much fuel you've burned. These little 2 strokers need to see a fully broken in condition before you can accurately determine how they run. As the miles accure they run better. Burn through a couple of gallons then see how it runs. New engines with little to no run time can be deceptive.
Tom
 
None of my engines ran their best until they had about 150-200 miles on them, 4stroking will start to be less and normally they start to smooth up a good bit, at this point, that's when a good carb. tuning along with a better flowing exhaust makes a world of difference.

You might try moving the clip on the carbs metering rod up 1 notch, it is also possible that you're having a rich mixture condition at the lower rpm's and that is causing it to lug down at midrange a bit until it clears up at higher rpm's.

Just a thought.

Peace, map
 
Well just took it out on a good hard hour ling ride or so. Ince it warmes thing is golden through the entire power band :) man that spark plug and wire did a world of good! Im gonna check my spark plugs color once it cool down. What color should i be looking for???
 
A nice medium - lite chocolate brown is where mine run, I use Opti2 mixed at around 80:1 so mine may run a bit lighter color than with a heavier oil mix like 32:1 - 40:1 mix would, but if it looks brown and not gray or white you should be good.

map


bassplyr101 said:
Well just took it out on a good hard hour ling ride or so. Ince it warmes thing is golden through the entire power band :) man that spark plug and wire did a world of good! Im gonna check my spark plugs color once it cool down. What color should i be looking for???
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Awesome :) that exactly what mine looks like! Looks like i just need to rum a consist fuel/oil mix and bike should stay runnin great. Although i think my carb has a bad gasket somewhere cause a small amount of oil is comin out above the bowl lookin thing on the bottom.
 
Good deal, if it's just a slight film around the fuel bowl I wouldn't be real concerned but it could be that the screws just need to be tightened up a bit, if that doesn't do it, a new gasket is pretty easy to make for the fuel bowl, or you could just smear a very thin skim of Seal All Sealer on it and it will be good.

in case you're not familiar with Seal All, here is a pic for ya.

Peace, map




bassplyr101 said:
Awesome :) that exactly what mine looks like! Looks like i just need to rum a consist fuel/oil mix and bike should stay runnin great. Although i think my carb has a bad gasket somewhere cause a small amount of oil is comin out above the bowl lookin thing on the bottom.
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Are you aware that drilling the air filter will change your air/fuel mixture? If you do, then I would go progressively and check the plug after a short ride each time you drill bigger. The mixture might not change much and these engines tend to run rich from the factory but you never know.
 
I personally have found no good reason to drill bigger holes in the air filter housing, these little engine can get plenty of air through the holes that are already there in my experience, just a free flowing exhaust system and a correct jetting on the engine after it is broken in good makes a world of difference all my bikes cruise @ 30+MPH real nice with smaller sprockets, a free flowing exhaust and a good tune on the NT carb.

I did shave some material off of the heads to boost compression a bit, but mainly I just have them tuned pretty good to where they aren't lugging down and 4 stroking from being to rich, with a good flowing exhaust.

these little engine don't really have to be all that fancied up to perform well if they are just set up right in the tuning.

Like I said, I don't see that you would make any gains by drilling the air filter housing, all that will do is let water in if you ride in the rain or run through a bunch of water.

Peace, map (^)


bassplyr101 said:
If i were to drill a couple holes in my air filter how big should i make them???
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One of my engine mounts broke off and i think thats why the vibrating and bubbly fuel is happening! Where can I buy a new mount and the double sided bolts?
 
nathanmd33 said:
One of my engine mounts broke off and i think thats why the vibrating and bubbly fuel is happening! Where can I buy a new mount and the double sided bolts?
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Look over on left side of this page, scroll down to last vendor add which is thatsdax.com click on his parts link on his page and go through the pages until you see what you need.

Or you might also find what you need on jnmotors site which is very top right hand side of forum page.

For the studs you need M6x1.00 studs, if you have a local bolt nut and fastener supplier store you can jist buy some grade 5 or better bolts that are long enough and cyt them with a hacksaw to the length you need and they will be much better than th bolts that come with the engines.

Hope this helps

Map
 
so why dont you just fix the vibration? (titanium wrist pin, less advanced ignition, and/or remove the crank and drill the needed holes in it)
 
48ccbiker said:
so why dont you just fix the vibration? (titanium wrist pin, less advanced ignition, and/or remove the crank and drill the needed holes in it)
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you make good points here if a person has the skills and the tools needed for the job, but I'd guess by the description of " bubbly fuel " and " double sided bolts " that nathanmd33 may not have what he needs to do those mods, if I'm wrong here please excuse me nathanmd33.

only thing I do not agree with is that a less advanced timing will make a badly balanced engine run smoother........ that aint gonna happen...... some people may think it does simply because retarding the timing on the china girls limits the rpms they will turn thus making it seem that at WOT the vibes are less, been down this road and have run they same engine with stock cdi, Jag design cdi and the HD's Lightening cdi with unlimited timing advancement, no change in vibes with any of the ignitions but best performance and best top speed has been with stock cdi and the HD's Lightening CDI, timing retarded is not an improvement in any way on the china girl engines in my experience, you wont see any fast bikes at the track with a Jag cdi period, they work fine on a stock or very slightly modified engine, but when you need to step it up and get all you can get out of it the Jag is detrimental to top speed and power performance.

Map
 
Yes, Its because the engine mounts. I had the exact same thing happen to me. I was curious and the back two mounts had broken off inside. I got a drill and slowly worked them out. Just be carefull when you drill them
 
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