Hi guys, I'm new to this entire field that is two-strokes. I recently purchased a Grubee Skyhawk GT-5A 66CC engine kit, I currently have approx. 75-125 kms out of it, when I am driving ( when the motor is cold or warmed up ) it makes a loud over-revving kinda noise and you can feel a lack of power, than goes away for 30 seconds and happens again. I've checked the plug and its the brownish color like I was told it was suppose to be, 16:1 fuel mixture for break in, adjusted the carb cable and needle setting so it runs a tad richer, and cleaned the air filter but still seem to be running into this problem a lot. The bike doesn't seem to also get up to top speed, goes maybe 15-20 MPH, and while accelerating up to speed it continually makes that higher pitch/ over revving noise and boggs for a couple of secs, than runs good and starts to pick up speed, than does it again and slows down. I am running the stock plug and have an in-line fuel filter, stock fuel line and fuel tank pet-cock, any advice or help would be greatly appreciated, thanks.
Loss of power/weird noise
- Thread starter Vtech.kicked.in.yo
- Start date
First of all welcome to the forum. You've come to the right place for help and advice.
You really should reduce your oil ratio. 16:1 is too much oil (how many times have I typed that?) 32:1 is a better choice.
My first guess would be that you possibly have the clutch cable too tight and the clutch is slipping causing the over revving. Typically a new clutch doesn't need adjusting but I'll post a link that will give you some advice on how to do it.
http://motorbicycling.com/showthread.php?t=22726
Let us know if this helps.
Tom
You really should reduce your oil ratio. 16:1 is too much oil (how many times have I typed that?) 32:1 is a better choice.
My first guess would be that you possibly have the clutch cable too tight and the clutch is slipping causing the over revving. Typically a new clutch doesn't need adjusting but I'll post a link that will give you some advice on how to do it.
http://motorbicycling.com/showthread.php?t=22726
Let us know if this helps.
Tom
If the noise is a weird high pitched squealing noise, you might have a loose head allowing leakage...is there oil on the cylinder where the head bolts on?
And I fully agree with 2door, 16:1 is FAR too much oil.
And I fully agree with 2door, 16:1 is FAR too much oil.
Thanks for the warm welcome guys, as well as the advice.
I've adjusted the clutch a few times and seem to have it in the perfect spot now, 16:1 is too high? even for break in? everywhere and everyone was telling me it was "needed for proper break in", and yes, there is some small oil spots where the head bolts on, I was kinda wondering what was up with as well, what is the cause and correction for that? Thanks again for the advice guys!
I've adjusted the clutch a few times and seem to have it in the perfect spot now, 16:1 is too high? even for break in? everywhere and everyone was telling me it was "needed for proper break in", and yes, there is some small oil spots where the head bolts on, I was kinda wondering what was up with as well, what is the cause and correction for that? Thanks again for the advice guys!
So I was doing some more research online and throughout this forum, very helpful site I may add, but a lot of people were saying that these china gals seem to have a problem with the head gasket flange on the head isn't evenly milled?? So a fix I've seen is too remove the head, grab a piece of glass, 200 grit or finer sand paper and slowly sand down that flange to even it out? Should I try this to seal that head gasket leak? Thanks guys.
Oh and I did start the bike up at lunch and sprayed some soapy water on the cylinder head ( before it was running ) and while it was running you could see bubbles form where the head is pressed against the motor, hoping this fix will help.
Oh and I did start the bike up at lunch and sprayed some soapy water on the cylinder head ( before it was running ) and while it was running you could see bubbles form where the head is pressed against the motor, hoping this fix will help.
Most all of the members here sand or lap the head to get a even surface, I do it to every engine. I too started with 16/1 but quickly learned it was to much oil, I like to start with 24/1 with good oil. I have used Lucas semi synthetic with good results.
Thank you Greg58,
Ya everyone was telling me 16:1, including the manual that came with it, I will drain out the fuel and go and get me some premium and mix it 24:1 and try that than, not very many kms on it yet so I just want to make sure I break it in the best way possible, and ya I've been reading a lot about how they have that head issue, so tonight I will sand that down evenly and give that a shot, should I repalce the head gasket at the same time or do you think the original would still be ok? Thanks again for the help guys.
Rob
Ya everyone was telling me 16:1, including the manual that came with it, I will drain out the fuel and go and get me some premium and mix it 24:1 and try that than, not very many kms on it yet so I just want to make sure I break it in the best way possible, and ya I've been reading a lot about how they have that head issue, so tonight I will sand that down evenly and give that a shot, should I repalce the head gasket at the same time or do you think the original would still be ok? Thanks again for the help guys.
Rob
I have reused head gaskets since they are aluminum, just make sure it is not burnt anywhere. The 16/1 mixture recommendation is believed to apply to regular motor oil that does not lube well hence the high ratio, 24/1 or 32/1 is plenty of oil.
Lapping the cylinder is a very good, if not essential idea. But, proper torque of the head fasteners is just as important. If you don't own one, buy or borrow an inch-pound torque wrench. Set it for 120 to 140 inch pounds, (don't know what that is in Newton Meters), and make sure you don't exceed 150 inch pounds.
Run the engine and after a couple of heat/cool cycles 'check' the torque again. Don't try to tighten more than the recommended 120 to 140 inch pounds. If the nuts are below that value, tighten them but if they haven't loosened, DO NOT try to get a turn on them.
This is where folks get into trouble by overtightening the fasteners.
Tom
Run the engine and after a couple of heat/cool cycles 'check' the torque again. Don't try to tighten more than the recommended 120 to 140 inch pounds. If the nuts are below that value, tighten them but if they haven't loosened, DO NOT try to get a turn on them.
This is where folks get into trouble by overtightening the fasteners.
Tom
torquing the head won't do any good if the head nuts are bottoming in the acorn
if you don't want to break the tops off the acorn nuts so they'll go all the way down or get open nuts that will go all the way down, you can add flat washers under the nuts till they have more room
if you don't want to break the tops off the acorn nuts so they'll go all the way down or get open nuts that will go all the way down, you can add flat washers under the nuts till they have more room
Which is why we always suggest to get rid of those chrome acorn nuts in favor of shouldered or flanged hex nuts.
One vendor I know of is offering extended length acorn nuts with his engines and they seem to work well. The original kit acorn nuts have been responsible for a lot of problems, head gasket leaks is just one of them.
Tom
Thank you Greg58 and 2door,
So last night I took the cylinder head off, grabbed a sheet of glass, 200 grit sand paper and taped the sandpaper down and started doing circular motions turning the head every so often to ensure even sanding. I may add, that the stock cylinder head had some weird "ring" or raised lip just on the inside of that square flange ( will post before and after pictures later ) so reading up on that, I've seen guys just sand that right off, so I did, put a new aluminum head gasket on and properly torqued the head nuts ( which were replaced with proper nuts rather than those crappy chrome acorn style ) and she still seems to have a tad leak, not nearly as bad as it was before, seems to have A LOT more get up and go! But still is making that weird "thwapping" kinda noise, almost like its over sparking or not igniting fuel properly or something weird, maybe I will grab the ol' Go-Pro and try and get that sound on audio for you guys, thanks again for all the suggestions guys, muchly appreciated!
Rob
So last night I took the cylinder head off, grabbed a sheet of glass, 200 grit sand paper and taped the sandpaper down and started doing circular motions turning the head every so often to ensure even sanding. I may add, that the stock cylinder head had some weird "ring" or raised lip just on the inside of that square flange ( will post before and after pictures later ) so reading up on that, I've seen guys just sand that right off, so I did, put a new aluminum head gasket on and properly torqued the head nuts ( which were replaced with proper nuts rather than those crappy chrome acorn style ) and she still seems to have a tad leak, not nearly as bad as it was before, seems to have A LOT more get up and go! But still is making that weird "thwapping" kinda noise, almost like its over sparking or not igniting fuel properly or something weird, maybe I will grab the ol' Go-Pro and try and get that sound on audio for you guys, thanks again for all the suggestions guys, muchly appreciated!
Rob
That ring is to concentrate the force of the head bolts to give more pounds per square inch by having fewer square inches of contact - if a person wants to sand something, I always recommend sanding the top of the cylinder instead of the head.
UPDATE:
Hey guys, after reading some more forums and watching some wonderful youtube videos, I have determined my bike is "4-stroking" at 3/4 - WOT, now reading on this a lot of guys said to lean the carb and to check air filter blockage, is there anything else I should be aware of or try? Thanks in advance guys.
Hey guys, after reading some more forums and watching some wonderful youtube videos, I have determined my bike is "4-stroking" at 3/4 - WOT, now reading on this a lot of guys said to lean the carb and to check air filter blockage, is there anything else I should be aware of or try? Thanks in advance guys.
Couple other items to note:
I have the stock NT style carb, pin is set on the 3rd notch from the top of the needle ( towards the Rich mixture ) and I am just noticing now that there is an excessive amount of gas in my air filter, any suggestions guys? Thanks again.
I have the stock NT style carb, pin is set on the 3rd notch from the top of the needle ( towards the Rich mixture ) and I am just noticing now that there is an excessive amount of gas in my air filter, any suggestions guys? Thanks again.
Most of my HT's like the needle in the second slot from the top. (almost fully leaned)
If you find it runs great from idle to 3/4 then four-strokes, a smaller main is in order.
I recently soldered up some jets for tuning and found the best one for MY engine was FOUR sizes smaller than the stock jet!
But be careful and tune in small increments since a lean mixture can kill the engine in short order.
UPDATE!!
Thanks maniac57
I have FINALLY found the problem!! after reading some amazing posts about the correct float position I have determined my float was 10mm to low!! Causing way to much fuel to flow in and allowing fuel to drain out the air filter and causing the 4 stroking, so I bent the float arms upwards and to the measurement of 21mm from the base where the gasket normally sits ( removed the gasket for proper measurement ) to the edge of the float, now it runs like a frigen crotch rocket haha. No more four stroking and amazing throttle response, as well as a new record for speed!! 84 km/h so I am more than pleased, thank you so much guys for all the advice and helpful tips, makes a newb like me feel a bit more at ease when there are other people helping with similar problems, so thanks again and happy riding!!
Thanks maniac57
I have FINALLY found the problem!! after reading some amazing posts about the correct float position I have determined my float was 10mm to low!! Causing way to much fuel to flow in and allowing fuel to drain out the air filter and causing the 4 stroking, so I bent the float arms upwards and to the measurement of 21mm from the base where the gasket normally sits ( removed the gasket for proper measurement ) to the edge of the float, now it runs like a frigen crotch rocket haha. No more four stroking and amazing throttle response, as well as a new record for speed!! 84 km/h so I am more than pleased, thank you so much guys for all the advice and helpful tips, makes a newb like me feel a bit more at ease when there are other people helping with similar problems, so thanks again and happy riding!!
Glad you got it sorted out. There are time it seems you just go in circles beating your head against the wall trying to track down the problem.
84 km/h? Yikes... I've flirted with 70 km/h, but that where a speed wobble starts happening on my beast. After a run like that, I'd be looking at repacking my wheel bearings just to be on the safe side.
84 km/h? Yikes... I've flirted with 70 km/h, but that where a speed wobble starts happening on my beast. After a run like that, I'd be looking at repacking my wheel bearings just to be on the safe side.
glad you got it sorted. That is a very impressive top speed. I would need a seat with a hole in it.UPDATE!!
Thanks maniac57
I have FINALLY found the problem!! after reading some amazing posts about the correct float position I have determined my float was 10mm to low!! Causing way to much fuel to flow in and allowing fuel to drain out the air filter and causing the 4 stroking, so I bent the float arms upwards and to the measurement of 21mm from the base where the gasket normally sits ( removed the gasket for proper measurement ) to the edge of the float, now it runs like a frigen crotch rocket haha. No more four stroking and amazing throttle response, as well as a new record for speed!! 84 km/h so I am more than pleased, thank you so much guys for all the advice and helpful tips, makes a newb like me feel a bit more at ease when there are other people helping with similar problems, so thanks again and happy riding!!
x2 on bearings getting good grease. Hope you have good brakes, and a helmet too!
