Bogging issue resolved but curious now

Discussion in '2-Stroke Engines' started by jsw5620, Feb 23, 2010.

  1. jsw5620

    jsw5620 New Member

    Guys, I have the 80 Skyhawk engine (or I guess the 66cc) on my bike and I have been going thru the break in procedure. I have almost ran 2 gallons thru it (about 4 tanks). I followed the break in procedure by varying the throttle and not going over 15 mph. Here recently I have been opening the throttle a little more and found that it had a terrible bog condition and was a turd. I pulled the carb apart yesterday and found the needle seat and main jet were laying in the bowl. Had I not got a little impatient with the throttle during break in, I would have never known there was an issue the way it ran.

    My question now is, how on earth was this thing running that way? It idled fine and seemed to have decent power until I opened the throttle more here recently. It didnt seem to smoke really at all and didn't 4 stroke as far as I could tell. I have read also that during break in, these things could get as low as 60-80mpg, but checking the odometer, I have only gone about 40 miles on two gallons of gas. Does that seem normal? The original plug did indicate it was running rich before I took the carb apart, so I moved the eclip to the second from the top notch and installed a new plug. I took it out for a ride and it was still bogging and thats when I took it apart and found the problem in the bowl. I have that fixed and managed to get 28mph out of it in a short burst and it is running great now. Just curious as to how this this was able to run with the needle seat and jet laying in the bowl. Is 40 miles out of 2 gallons normal during break in?

  2. AussieSteve

    AussieSteve Active Member

    When you say 'needle seat', I guess that you mean the slide needle valve/jet and not the float needle seat, or it would have been a bit more than rich.

    It amazes me that it still ran. Sort of running on fumes from the float bowl, without the slide needle valve and main jet to act as a venturi. I would have thought that it would run lean under those conditions. Possibly rich down low then lean at higher revs.

    No, 20mpg is not normal, during run-in or otherwise. See how it does now.

  3. jsw5620

    jsw5620 New Member

    Yes it was the valve/jet and not the float needle. My only thought is it may have fallen out the day before yesterday when I decided to give it a little more throttle than I had been. But still, that doesn't explain the 20mpg. I know the accuracy of the odometer may not be spot on (Bell wireless), but I know I have not been over 40 miles as I have only ridden around my neighborhood and my thought was "This thing is drinking the gas!". It is running a lot better now, so I will keep look closer at the MPG now. Since the break in procedure said 4 tanks, I am guessing it is no where near being broke in at 40 miles then.
  4. professor

    professor Active Member

    Probably there is an orfice the tapered needle fits into ( I don't have an HT) and this fit (up nearer the air flow), gives you the low speed and idle settings.
    As the needle is pulled up by your throttle increase, you also pull the needle beyond the place where it is controling the mixture via that orfice, into the transition to the main jet. THEN, it went beyond merely rich to Niagara Falls rich.
    Amazing to me it didn't drown.
  5. jsw5620

    jsw5620 New Member

    It's amazing to me it didn't drown either. The reason I feel it was like that the whole time is because of the 20mpg. It baffles me that it ran like it did or even at all. Here is a pic of it.

    Attached Files:

  6. AussieSteve

    AussieSteve Active Member

    Yeah, it might have only just come loose.
    It might have been loose in the bowl from the factory, too.
    I've heard that story a number of times now.
    I'm tempted to pull my needle jet out in the morning to see if I can make mine run like that. See what happens, I might.

    Mine sucked a lot of fuel at first, before I got it tuned properly, but not as much as your's. (Mine's also a 66cc.)
    I found that I had to go down from the stock 0.76mm main jet to 0.72mm and set my slide needle at it's leanest to get decent performance. The fuel consumption improved dramatically then.

    Regarding your odometer, if you set the valve stem of the front wheel at the bottom, mark the spot with chalk, then sit your weight on the bike distributed as it would be when riding, then roll forward one turn and mark the (valve-stem) spot, then you can measure the distance and enter it into your speedo/computer as the wheel circumference, or divide by pi for diameter if needed.
    That will give you very accurate results with the speedo and odometer.
    (My 26" front wheel, with 50psi and my 50kg bodyweight, weighs in at 25.57" diameter.)
    If you use JPilot's 'GearRatio.exe' to calculate speed vs rpm, the measured exact loaded diameter figure will ensure that you get accurate results.
    I take an observed speed reading from my (Cateye VELO) speedo, then enter that along with wheel diameter and the other ratios and I get an accurate rpm figure as a result. Handy.
    I hope I didn't go too far off topic.

    ... Steve
  7. AussieSteve

    AussieSteve Active Member

    Sorry, you both got in new posts before I finished my reply. Getting slow in my old age. (The 6 beers don't help, either.)

    professor, once the slide needle jet and main jet are gone, there is nothing extending down into the float bowl to suck up fuel, so as the revs get higher it's likely to get more and more lean. I don't know how it stayed rich at lower revs, but it sounds like it must have been.

    If I'm seeing things wrongly, someone please correct me.

    ... Steve
  8. jsw5620

    jsw5620 New Member

    I see what you are saying Steve. I am just scratching my head as to the crappy MPG. As it had been, I would have been lucky to get 10-15miles before I ran out.

    On a side note, what kind of fuel ratio are you running on your 66? I am running the recommended 20:1 like the place I purchased it from said to. I know everyone has an opinion, but from a quote off their webpage, I am scared to change it. Here is the quote below.

    "We ran 32:1 for a while when we started our biz. But in 1 week we had 4 seized pistons come into the shop. After that we switched to only using 20:1 Motorcycle Synthetic 2 stroke-oil. Since then we have had ZERO problems with piston seizure. This engine is a 2 cycle design, therefore, a gasoline/oil mixture is necessary. During the break-in period (1st 2 gallons of fuel) and after, the ratio is kept at 20 parts gasoline to 1 part oil. Use a good quality MOTORCYCLE SYNTHETIC 2-STROKE OIL. "
  9. AussieSteve

    AussieSteve Active Member

    I ran 16:1 for about 350km, (220 miles), then went down to 20:1, where I plan to stay, for a couple of reasons.

    First, that's the recommended mix after run-in.

    Secondly, my carb tuning would suffer slightly if I reduced the amount of oil. The mixture would be richer all 'round, but already I can't get it lean enough in the ~mid-throttle openings, even with the slide needle at it's lowest.

    Third, these engines have a very poor piston ring to cylinder wall seal, due largely to distortion. The oil helps heaps in terms of compression and probably more than usual with my 16:1 hi-comp head.

    Finally, even with all of that oil, my engine runs cleanly and burns everything off the plug, which is always a dry, light-tan.

    Good quality synthetic oil is definitely best, I use fully-synthetic Castrol racing 2T oil. Organic oils tend to leave a lot of residue on the piston skirt etc. The old organic racing mix was part castor oil, but that leaves blow-by residue as described.

    I also use 'Nulon Pro' octane booster to increase the octane rating a little, (by 7 RON points), to avoid detonation with the high compression.
    I know this is only a 66cc, but you should feel the compression with the RSE billet head.
    I kick-start on my centre-stand, but still sometimes it's like stomping a block of concrete.
    I've ridden almost everything up to 600cc singles in the past, but still this compression surprises me. (My stock centre-fire head measured 115psi and the Rock Sold Engines billet head clocks 142psi.)

    For run-in, my kit's instructions recommended 500km, (300 miles), at 16:1, and no more than 20kph, (12mph), and 30 minutes running in one ride.

    * Now let's wait for the arguments recommending everything from 25:1 to 100:1.
    Been there, done that.

    When all's said and done, if you want absolut minimum oil for some reason, as some do, run it for a while, then remove head and barrel and use a wooden dip-stick, (skewer), to measure the amount of oil in the bottom of the crankcase.
    As long as the crankshaft flywheel is running in the top of the accumulated oil to throw it around, everything's OK. Assuming a good piston-ring to cylinder wall seal, this method is possibly the best for determining ratio.
    * More arguments now?

    ... Steve
    Last edited: Feb 23, 2010
  10. jsw5620

    jsw5620 New Member

    I agree with the 20:1, it's just confusing with all of the arguing about it on here. If the people I purchased it from recommend it too, then I will stick with that.

    As far as the break in, from what I have read I was expecting at least 200 miles out of that 2 gallons instead of the 40. I am including a pic of the original plug (before I found the valve/jet problem. It was a lot wetter than in the photo as it has been removed for a couple of days), and a pic of the new plug after the problem was fixed. Is it better to tune for a tan color now if I am still in break in, or leave it a little on the rich side until after about 200 miles? The new plug to me (about 3 miles on it with varying throttle) still looks a little rich. My slide needle has five notches and from the factory it was in the middle/third slot. The new plug it is in one notch above the middle or second from the top.

    Attached Files:

  11. AussieSteve

    AussieSteve Active Member

    A bit rich during run-in is a good idea. I didn't lean mine out for the first 100 miles or so.
    Having said that, from the look of your plug, the 'after', that's a bit too rich.
    (At least it indicates that you probably don't have air leaks where the carb attaches to the inlet tube.)
    I'd suggest dropping the needle to the lowest notch, (mine's a 5-notch version, too, only the older ones have 4 notches), clean up the plug or fit another, then see how it is. You'll feel the difference in mid-throttle performance.

    Then a 'plug chop' with a new plug at wide-open throttle, (WOT), will help determine if you need a new, smaller main jet. (Then you'll need to re-set the needle height.)
    Dellorto 5mm main/pilot jets fit nicely. DellortoDirect is one source.

    If you're not already using an NGK B6HS plug, grab one.
    Then, after getting the mixture about right, if there's still a little too much oil on the plug, swap to the slightly hotter B5HS to burn off residues rather than reducing the fuel/oil ratio, in my opinion.

    After run-in, I get roughly 150mpg, but that's 'getting up it' a bit, with the odd little mono etc. Also, that's with the shift kit, so it might not be too relevant.

    There's a pic of my plug below, when the fuel/oil ratio was 16:1. It's not quite as white as it looks, that's a combination of the flash and some white ceramic showing through on a near new plug, but since then I've gone slightly richer with the 20:1 mix and the plug is slightly darker.
    No need for a black, oily plug, even at 16:1.

    ... Steve


    Attached Files:

    Last edited: Feb 23, 2010
  12. jsw5620

    jsw5620 New Member

    What kind of plug gap are you running, Steve?
  13. AussieSteve

    AussieSteve Active Member

    0.6mm, (0.024")

    ... Steve
  14. jsw5620

    jsw5620 New Member

    I did a plug chop as you suggested at WOT. Here is a pic of it. Looks like I am on the lean side. Also it seems to have a studder/missfire at WOT also. Not sure if this could be because of the lean condition.

    Attached Files:

  15. AussieSteve

    AussieSteve Active Member

    I replied to your PM earlier without realising this is the same issue. I'm hopeless at remembering usernames.
    There's a bit of repeated info.
    Did you check the 4-stroking video?
    Is that your stutter/misfire?

    A bit hard to see well in a pic, but that doesn't look lean from this angle, only new. A bit longer at WOT might have been better.

    ... Steve
  16. jsw5620

    jsw5620 New Member

    How long does the WOT throttle run usually last doing a plug chop to get an accurate plug reading? I am nervous about running this thing too long WOT and it grenading, especially when "The Boys" are sitting right above it. :grin5:
  17. AussieSteve

    AussieSteve Active Member

    As I mentioned in the answer to your PM, hold it WOT from a low speed, let it build up to flat out and hold it there for another 20 seconds or so. (WOT doesn't necessarily mean peak revs.) That'll total at least 30 seconds.
    If you do it on the flat, it won't 'grenade', it won't have enough power to over-rev and hurt itself, especially for only that long.

    On an aside, regarding the two bikes and their problems, best thing to do is start an easily identifiable thread for each.

    ... Steve