High Compression (180psi!) but Low Power on Stock Grubee Kit

Discussion in 'Motorized Bicycle General Discussion' started by Eagle420, Feb 10, 2019.

  1. Eagle420

    Eagle420 New Member

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    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 :p

    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
     
    Tom from Rubicon likes this.
  2. Greg58

    Greg58 Well-Known Member

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    You may be thinking wrong, to lean the mixture you make the needle longer or move the clip higher on the needle. If your exhaust is restricted that will cause it to sound like 4 stroking, a new pipe will help there. Most of the time the main jet is too large which will cause 4 stroking. A lot of people have changed to smaller jets to correct it, I ordered a set of orifice drill bits and solder up mine and drill them as needed.
     
  3. Greg58

    Greg58 Well-Known Member

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    I'm wondering if you have a faulty compression gauge, 180 psi would slide the tire when you release the clutch. Only highly modified engines get close to 180 psi.
     
  4. Eagle420

    Eagle420 New Member

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    Thank you for your quick responses!

    @Greg58, terminology is maybe what I am getting mixed up. Same deal with "clutch engaged" vs "clutch disengaged". While I am still a noob in general, raising the C clip to the top of the needle, makes the needle sit lower in the jet, hence making the overall gas-air ratio leaner.

    I was running quite rich, and raised the needle (lowered the clip) beyond the pre-filed settings, by filing my own notch a little lower on the needle. This does cause the engine to fire up IMMEDIATELY at room temperature (bike was stored inside my house) WITHOUT having to play with the choke in approx 0 degrees Celcius weather (choke is wide open), BUT I get MUCH 4-stroking when riding in general (in all of the "richer" settings on the needle / C clip), at all speeds, including WOT and 20-30km/hr (my top speeds so far).

    I have tried only ONE ride with the needle dropped quite low (C clip is on 2nd notch from the top, so quite raised) and it takes MUCH longer to get the engine firing on it's own accord, BUT there seems to be more power across the board, and generally less 4-stroking.

    I'm not too sure what you mean when you say "180 psi would slide the tire when you release the clutch". My tire does slide, if I am not on dry concrete, when releasing the clutch and trying to start up the engine.. This is mainly why I had to leave my bike at home, due to all the fresh snow today :p

    i CAN push my bike with the clutch handle released (hence activating the clutch and connecting to the engine), BUT i have to use ALL my body weight (I'm about 200lbs) and I can JUST get it to rotate the piston around once at a time - is this normal? lol

    Regarding the pressure gauge, I tried 2 sets of readings. 1st reading with the new gauge (fresh out of the package) said approx. 180psi. 2nd reading gave 150psi. To do the reading, I attached the gauge, got up to approx. 10km/hr, and released the clutch - same way I'd start up the bike. I did not continue pedalling for more than 2 or 3 seconds, as I often will have to do, to get the engine running with the choke wide open (which btw, I do not usually have to fiddle with). Both readings are quite higher that I feel they should be.

    I will see if I can get a 2nd opinion and borrow a friends' pressure gauge; I also happen to work next door to a "Honda Powersports" dealership. While I haven't made any friends there yet, they may allow me to use a pressure gauge for just a moment. I expect this to take a couple days to get a response back to you on here tho, as it is suddenly HELLA snowy where I live - I suspect I'll be leaving my new (used / rebuilt) gas bike home tomorrow as well.

    Furthermore, I'll give my pressure gauge a 3rd try on approx. the same day as I can use a second pressure gauge.

    The auto parts store had 2 pressure gauges for sale - I chose the cheaper of the 2, as I figured it wouldn't get much use. Certainly possible it's faulty, so I'll double-check and respond again in 2 or 3 days :) TY for your input!
     
  5. Greg58

    Greg58 Well-Known Member

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    Are you opening the throttle when doing the compression test? You get a more accurate reading that way. Yes a leaner tune is harder to start but leaner if faster, cold weather is always a problem for mine, one bike will not start below 35F. Maybe one of the guys that race and modify theirs way beyond normal will have more to tell.
     
  6. Eagle420

    Eagle420 New Member

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    Hahaha ofc more accurate psi reading with WOT. No, I did not open the throttle at all ;) TYVM, I will test again when we don't have nearly 30cm of snow
     
  7. Larry Trotter

    Larry Trotter Member

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    Get some place you can run WOT for a minute, get up to wide open and shut off the fuel. If it starts to 2 stroke again and accelerates just before it dies you are running too rich and need to lower the needle. I would just not worry about the compression, put some premium gas in it to keep it from detonating and life will be good. Larry

    PS: Yes do the compression test with the throttle held wide open, you may hit 200PSI! haha..
     
  8. Eagle420

    Eagle420 New Member

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    TY again. We have had an abnormal amount of snow where I live, and I have not checked compression with WOT yet. Haven't forgotten about my thread here. Still hoping to get this engine running like a top.

    2 small updates:

    1) I've tried some leaner settings on my carb. 2nd to highest notch on the clip, and now the highest notch. I definately notice more power and less four-stroking.

    2) After my last ride home, I a) opened up my "custom exhaust" hole just a LITTLE larger, b) set E-clip on carb needle to highest setting, and c) tried switching back to my old "SD" CDI.

    Today I rode it after these tweaks, and it fired up fine after some pedalling (not nearly as quick compared to when I was running it too rich), and I definately noticed more power. I hit 30km/hr easy... then BAM engine just stops and will not start, even going downhill. I can hear it turning over, I'm going 10-15km/hr, but no iginition whatsoever.

    Turned it around, put on my "new" CDI I had ordered (which I was using on my last ride home) and I still had the same issue. It would run for about 1 minute and then completely stop firing. Had to drag the damned thing all the way to work.

    Checked:

    1- Fuel line flow (it's fine, and basically pisses out fuel)
    3- Fuel flow when connected to the carb. The "fuel in" connection seems a little old / dirty but is also not impeding fuel flow.
    2- Dirt on jet / needle (they were clean)

    My factory float did seem to be "stuck" or sitting on the bottom of the bowl. I've taken most of the stock carb apart, drained it, reassembled it all, and before locking my bike up, I turned the petcock "On" to let the carb/float bowl fill up, and it seems that the bowl filled up fine. I did notice a small bubble rise up from carb, through my in-line fuel filter, and eventually into my tank. Unfortunately, I'll have to wait until after work to ride it.

    I'm still not sure if I fixed the problem, or what exactly the problem was. Do these floats normally tend to stick to the bowl? And also, if the float was sticking to the bottom, wouldn't that result in exsessive fuel?
     
  9. Greg58

    Greg58 Well-Known Member

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    It sounds like you've lost ignition, the cdi is sealed but the magnito coil can get wet and fail or lose the ground connection. Pull the mag cover and check for water, clean the eyelet of the black wire where it grounds. The rubber grommet that the wires pass through will leak sometimes.
     
  10. Eagle420

    Eagle420 New Member

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    I may or may not have connected the old CDI properly or securely to the spark plug... Quickly swapped to my new CDI (which was and is working ok) and it fired up as usual.

    Still not sure if old CDI is toast, but I had to get to my job today, and knew the new one was working, even though it technically does not match my magnet or coil, according to Grubee Magneto Mystery.

    Will check compression again with WOT in a day or two :) snow is still hampering my desire and often ability to test things.

    TY for all your input!!
     
  11. Eagle420

    Eagle420 New Member

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    Also, I have pretty decent power with the small upgrades I did recently (larger drilled hole in exhaust, and leaner setting on carb needle). Not 100% sure how to tell when I am at full power, but I did 30km/hr coming home and only went up to about half-throttle on flat ground!
     
  12. Eagle420

    Eagle420 New Member

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    Probably Thursday I will check PSI again, and also check my spark plug for colour with the new setting. Should be approx 10km total with this leanest setting, so I'll see what my spark plug says. FEELS great tho!
     
  13. Eagle420

    Eagle420 New Member

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    Well, it is snowing AGAIN. Still no PSI test. I do have good news though. I am usong the leanest setting on stock carb with stock jet (and 89 octane gas with approx. 32:1 ratio), and spark plug colour looks gorgeous! I am not a professional, but I seem to ONLY be getting 4-stroking when cruising or lowering my throttle; no or VERY minimal 4-stroking occurs when I accelerate, go uphill, or put any noticeable load on the engine.
     

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  14. Eagle420

    Eagle420 New Member

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    Ok, I finally got my lazy arse out into all this snow and managed to do a couple PSI readings with my gauge. I got 155psi, with WOT the entire time my clutch handle was released, doing about 10km/hr (my typical engine-starting speed).

    I did buy this engine second-hand, installed on a [email protected]$$ mountain bike, BUT it SEEMS that the engine was hardly used. Nearly zero piston colour, zero visible burned carbons, etc.

    Now that I am on a leaner setting, with a new CDI, and my muffler isn't all bunged up, I get pretty good overall power, and hit 30km/hr flatground with about half-throttle. Will go full speed soon and report here.
     
  15. Eagle420

    Eagle420 New Member

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    Do you guys have any preventative maintenance tips or suggestions for this higher compression Grubee engine? Last thing I wanna do is abuse her or burn her out :)
     
  16. Greg58

    Greg58 Well-Known Member

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    If the engine is fairly new it will get better, now that you have it running pretty good I would put some miles on it. As for preventative maintenance check the right side gears for grease every once in awhile and keep an eye on all nuts and bolts. Don't run it too hard and it should last a while.
     
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  17. Eagle420

    Eagle420 New Member

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    TY again Greg. I have put just enough white lithium grease on the clutch and chain pinions, and added lock-tite to most of the stock hardware. I already stripped my exhaust manifolt bolt (lol) trying to get my plugged exhaust sorted out, so when I get around to replacing that bolt / stud, I will likely replace the other stock nuts and bolts as well ;) my new banana muffler should arrive soonish, so I will do these things on that day.

    I do plan on going WOT on flatground for maybe 1 min to check max speed - other than that I will baby the heck outta this Grubee. She is my first 66cc engine and I am already lovin her, now that she is working as expected.

    The bike is a sight for sore eyes hahaha but overall it works great. Function over form, right? Next 66cc will go on a much nicer bike methinks
     
  18. Eagle420

    Eagle420 New Member

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    (forgot to attach a pic)
     

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  19. Greg58

    Greg58 Well-Known Member

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    Keep a close eye on the fenders, the constant vibration will cause cracks near the mounts. Some have had bad crashes when the fender falls on the tire.
     
  20. Eagle420

    Eagle420 New Member

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    TY also man, she does shake a bit in idle. I will add this check to my weekly maintenance / checks ;) I do have the front one mounted x2 to the forks, and x1 to the front (near the brakes), but the back one is just one main quick-release mount on the frame, with another "snake" joint along the fender for adjusting up/down angle.

    I guess it is overall good advice to check ALL screws and bolts on the whole bike occasionally lol, as these bikes are shakey little buggers
     

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