Howdy Folks,
I recently purchased my first gas bike kit - a Grubee Skyhawk GT-5A 66cc bike kit, preinstalled on a rusty but solid OLD mountain bike. Got it all "as-is" for $150 Canadian, which seemed fair. It appears to have 180PSI! Is this bad? Looks like I should have seen 100-120 PSI, maybe 130, with all these stock parts.
After spending hours learning, researching, cleaning up the old engine, and troubleshooting (it would not start at first), I found out the stock exhaust was SOO CLOGGED UP, it was spewing gas mist out the air filter...
Ran it BRIEFLY (<5 seconds) with no exhaust and it ran like a champ, albeit loud AF.
Once I determined the exhaust was indeed faulty, I ordered a cheap banana pipe with generic-tuned expansion chamber from China (up to 2 months shipping tho), and drilled some holes into my current bastard stock exhaust, before the catalytic converter but well beyond the exhaust port. Runs well enough now and has been my daily driver for approx. a week. I get up to 30km/hr, with much 4-stroking. I can kinda feel it switch BRIEFLY back to 2-stroking on relatively flat ground, but it mostly 4-strokes.
Still learning lots.
Drained the gross old gas (this bike was sitting all winter), put in some fresh "silver" grade gas (89 octane), mixed properly 32:1 ratio for now, with synthetic 2-stroke oil. Also added a newer-style metal-filter fuel filter.
Adjusting carb needle for our colder temperatures in the winter, getting LOTS of 4-stroking going on, trying to find the sweet spot and thinking about trying different jet sizes, although I only have the stock jet, which I understand is a bit wide / rich.
Although my spark plug has maybe an hour of ride time on it, it looks to be a nice caramel colour with needle on the "highest" (richest) setting, but I get MUCH 4-stroke action. Have yet to try the leaner end for more than 1 ride, but I'm worried about overheating my engine with this high PSI, if it is not getting enough oil. I did try lean for 1 ride, and it immediately has more power and less 4-stroking.
Sadly, as I write this, we are actually getting about 10cm of snow where I live, which is unusual. Does make starting the bike much more difficult with a slippery road, and also more dangerous to ride, so I left my bike at home today. Wanted to try it today on the leanest carb setting, but I'll have to wait. I also widened the hole I created in the stock exhaust slightly, and cleaned the air filter which AGAIN had some gas/oil in it (which leads me to believe the exhaust was still a bit restricted). Tried it all BRIEFLY last night and it seemed great.
Also I taped the gaps on the prongs of the stock carb, as they were letting in SOME unfiltered air. Had to remove the carb clamp, took the carb off, and taped outside of the carb "prongs" - taped on outside of carb, but under where the clamp sits. No more air leak now
but I'll have to replace this duct tape with something that will play nice with gasoline.
Lightly cleaned and greased up the main drive sprocket (inside the clutch case), and the chain sprocket (sorry for lack of terminology). JUST got my gear puller from ebay, so I will also grease up the crank arm bearing soonish, to be safe. I've also added locktite to the crappy stock bolts on most of the covers.
Double-checked OHMs of my older-style magneto coil, and it reads 320 OHMs - perfect. Will probably solder connections when the bike is running great, and completely finish the cable management, as the cables and wires are only "half-managed" right now lol. Just swapped back to the original CDI last night, as it was my EXHAUST and not CDI that was initially faulty.
After all this, I finally bought a compression test kit, along with lithium grease, WD-40, NGK "BR5HS" spark plugs, etc., expecting to see low compression on this stock kit. I even ordered piston rings for $5 prematurely, and Zoom Bikes nearby in Canada here hooked me up with a couple surprise free parts like a spare piston, wrist pin bearings, and other things the fella thought I might need for rebuilding a used engine.
Wayyy better experience with them (Zoom Bikes), than with Gasbikes.net. I ordered 3 things with expedited shipping from Gasbikes, and they took over a week to even SEND ONE of the items to USPS - they were not able to send the other 2 items I ordered (gloves and a speedometer), but at least they sent the CDI which I thought I needed. They did provide refund (only after I phoned several times) for the items they could not send, but I still payed extra for expedited shipping on 3 items - ofc this was not even partially refunded.
Took over 13 phone calls from 4 phone #s (my phone, my gf phone, and 2 different VOIP phones) to talk to a live agent more than once (as they were actively avoiding my calls), and nobody knew what was going on, or why the package was not shipped. It seems they did send it that day, after numerous hours of a) initial calling, b) waiting a few hours, then c) trying to call again before they closed for the weekend. It took them over a week after I placed an order. What a joke!!
After all that, my new CDI arrived some time later, but does not match the magneto components (see here: http://www.grubeeinc.com/Magneto Mystery.html). I have SD parts and they sent TZ CDI... They didn't bother to ask, and I was not educated enough to ask. As a secondary question, is it ok to use this TZ CDI with the SD parts? I've slapped on my old "SD" CDI for now, to be safe.
Fast forward to a couple days ago. I did NOT warm the engine up fully (it was only at room temperature) when I hooked up Compression Test Kit. Took it outside BRIEFLY, biked between 5-10km/hr, released my clutch, and was astonished to see 180psi!...
From what I understand now, this seems concerning. I only use it for going to work and back, approx. 10-15 minutes of riding and approx. 3km, mostly flat ground, to get from home to work and vice versa.
Should I be concerned with this high compression reading? If so, what would you folks recommend to avoid this, or to lower compression? I also ordered a set of gaskets from Zoom Bikes, and my old gasket seems good enough; i can MAYBE slap on a 2nd gasket to immediately reduce compression if needed.
Alternatively, if I can run this safely with higher compression and stock parts (with NGK BR5HS spark plug or some other variance of this, maybe a cooler spark plug), I am open for suggestions on how to NOT destroy this engine
To Summarize, I had 4 questions / points:
1) Is 180psi reading "bad"? If so, what would you recommend to avoid piston detonation / deterioration?
2) Any idea why this bike is 4 stroking? It appears to stop and I feel much more power when going uphill (15 gradient or more).
3) Gasbikes is a joke, and Zoom Bikes has been beyond amazing so far.
4) I raised the needle beyond "lowest" setting by filing my own notch, approx. 2 notches below "lowest" notch, and the bike fires riiight up (instantly after releasing clutch handle) at room temperature, but does a lot of 4-stroking (maybe even 6-8 stroking when idle). I tried lowering the needle to the opposite end, and then it takes quite a long time to start firing (approx. 15-30 seconds pedalling at 10km/hr) but seems to have a bit more horsepower and seemingly LESS 4-stroking. Any suggestions? I suspect this is due to larger spark plug gap, and high compression shown in my engine.
Sorry for the rambling, thank you for reading lol
I recently purchased my first gas bike kit - a Grubee Skyhawk GT-5A 66cc bike kit, preinstalled on a rusty but solid OLD mountain bike. Got it all "as-is" for $150 Canadian, which seemed fair. It appears to have 180PSI! Is this bad? Looks like I should have seen 100-120 PSI, maybe 130, with all these stock parts.
After spending hours learning, researching, cleaning up the old engine, and troubleshooting (it would not start at first), I found out the stock exhaust was SOO CLOGGED UP, it was spewing gas mist out the air filter...
Ran it BRIEFLY (<5 seconds) with no exhaust and it ran like a champ, albeit loud AF.
Once I determined the exhaust was indeed faulty, I ordered a cheap banana pipe with generic-tuned expansion chamber from China (up to 2 months shipping tho), and drilled some holes into my current bastard stock exhaust, before the catalytic converter but well beyond the exhaust port. Runs well enough now and has been my daily driver for approx. a week. I get up to 30km/hr, with much 4-stroking. I can kinda feel it switch BRIEFLY back to 2-stroking on relatively flat ground, but it mostly 4-strokes.
Still learning lots.
Drained the gross old gas (this bike was sitting all winter), put in some fresh "silver" grade gas (89 octane), mixed properly 32:1 ratio for now, with synthetic 2-stroke oil. Also added a newer-style metal-filter fuel filter.
Adjusting carb needle for our colder temperatures in the winter, getting LOTS of 4-stroking going on, trying to find the sweet spot and thinking about trying different jet sizes, although I only have the stock jet, which I understand is a bit wide / rich.
Although my spark plug has maybe an hour of ride time on it, it looks to be a nice caramel colour with needle on the "highest" (richest) setting, but I get MUCH 4-stroke action. Have yet to try the leaner end for more than 1 ride, but I'm worried about overheating my engine with this high PSI, if it is not getting enough oil. I did try lean for 1 ride, and it immediately has more power and less 4-stroking.
Sadly, as I write this, we are actually getting about 10cm of snow where I live, which is unusual. Does make starting the bike much more difficult with a slippery road, and also more dangerous to ride, so I left my bike at home today. Wanted to try it today on the leanest carb setting, but I'll have to wait. I also widened the hole I created in the stock exhaust slightly, and cleaned the air filter which AGAIN had some gas/oil in it (which leads me to believe the exhaust was still a bit restricted). Tried it all BRIEFLY last night and it seemed great.
Also I taped the gaps on the prongs of the stock carb, as they were letting in SOME unfiltered air. Had to remove the carb clamp, took the carb off, and taped outside of the carb "prongs" - taped on outside of carb, but under where the clamp sits. No more air leak now
but I'll have to replace this duct tape with something that will play nice with gasoline.Lightly cleaned and greased up the main drive sprocket (inside the clutch case), and the chain sprocket (sorry for lack of terminology). JUST got my gear puller from ebay, so I will also grease up the crank arm bearing soonish, to be safe. I've also added locktite to the crappy stock bolts on most of the covers.
Double-checked OHMs of my older-style magneto coil, and it reads 320 OHMs - perfect. Will probably solder connections when the bike is running great, and completely finish the cable management, as the cables and wires are only "half-managed" right now lol. Just swapped back to the original CDI last night, as it was my EXHAUST and not CDI that was initially faulty.
After all this, I finally bought a compression test kit, along with lithium grease, WD-40, NGK "BR5HS" spark plugs, etc., expecting to see low compression on this stock kit. I even ordered piston rings for $5 prematurely, and Zoom Bikes nearby in Canada here hooked me up with a couple surprise free parts like a spare piston, wrist pin bearings, and other things the fella thought I might need for rebuilding a used engine.
Wayyy better experience with them (Zoom Bikes), than with Gasbikes.net. I ordered 3 things with expedited shipping from Gasbikes, and they took over a week to even SEND ONE of the items to USPS - they were not able to send the other 2 items I ordered (gloves and a speedometer), but at least they sent the CDI which I thought I needed. They did provide refund (only after I phoned several times) for the items they could not send, but I still payed extra for expedited shipping on 3 items - ofc this was not even partially refunded.
Took over 13 phone calls from 4 phone #s (my phone, my gf phone, and 2 different VOIP phones) to talk to a live agent more than once (as they were actively avoiding my calls), and nobody knew what was going on, or why the package was not shipped. It seems they did send it that day, after numerous hours of a) initial calling, b) waiting a few hours, then c) trying to call again before they closed for the weekend. It took them over a week after I placed an order. What a joke!!
After all that, my new CDI arrived some time later, but does not match the magneto components (see here: http://www.grubeeinc.com/Magneto Mystery.html). I have SD parts and they sent TZ CDI... They didn't bother to ask, and I was not educated enough to ask. As a secondary question, is it ok to use this TZ CDI with the SD parts? I've slapped on my old "SD" CDI for now, to be safe.
Fast forward to a couple days ago. I did NOT warm the engine up fully (it was only at room temperature) when I hooked up Compression Test Kit. Took it outside BRIEFLY, biked between 5-10km/hr, released my clutch, and was astonished to see 180psi!...
From what I understand now, this seems concerning. I only use it for going to work and back, approx. 10-15 minutes of riding and approx. 3km, mostly flat ground, to get from home to work and vice versa.
Should I be concerned with this high compression reading? If so, what would you folks recommend to avoid this, or to lower compression? I also ordered a set of gaskets from Zoom Bikes, and my old gasket seems good enough; i can MAYBE slap on a 2nd gasket to immediately reduce compression if needed.
Alternatively, if I can run this safely with higher compression and stock parts (with NGK BR5HS spark plug or some other variance of this, maybe a cooler spark plug), I am open for suggestions on how to NOT destroy this engine
To Summarize, I had 4 questions / points:
1) Is 180psi reading "bad"? If so, what would you recommend to avoid piston detonation / deterioration?
2) Any idea why this bike is 4 stroking? It appears to stop and I feel much more power when going uphill (15 gradient or more).
3) Gasbikes is a joke, and Zoom Bikes has been beyond amazing so far.
4) I raised the needle beyond "lowest" setting by filing my own notch, approx. 2 notches below "lowest" notch, and the bike fires riiight up (instantly after releasing clutch handle) at room temperature, but does a lot of 4-stroking (maybe even 6-8 stroking when idle). I tried lowering the needle to the opposite end, and then it takes quite a long time to start firing (approx. 15-30 seconds pedalling at 10km/hr) but seems to have a bit more horsepower and seemingly LESS 4-stroking. Any suggestions? I suspect this is due to larger spark plug gap, and high compression shown in my engine.
Sorry for the rambling, thank you for reading lol
