wont stay runnin, real boggy

Discussion in '2-Stroke Engines' started by sphynx.0029, Oct 22, 2009.

  1. sphynx.0029

    sphynx.0029 Member

    ok i doubt there is anything anyone here can tell me that i have not tried but who knows.

    extremely hard to start(clutch is catching fine)
    once started it will not stay running, boggs down, have to keep pedaling to make teh engine continue to turn over. holding thrott full while pedaling to make the motor catch while clutched. and have to keep pouring teh thrott to keep the engine barely running.(have tried every carb adjustment known to man).
    as far as the carb goes we (al.fisherman and myself) have changed teh intake back to a non-ported(for boost) manni, tried 3 of 5 needle positions, changed and replaced the gasket, checked the float positioning, CHANGED CARBS COMPLETELY, nothing is working from that end and teh issue still persists.
    no power when the engine is running, will not carry itself.
    and tone sounds too deep to me like it is trying to bogg just running while pedaling. will not stay running on its own.

    this is an 80cc HT kit, the very same that Al.Fisherman and myself made the taredown tutorial out of. so we know that everything inside the engine is correctly installed. one note of interest tho.

    during the taredown, we could not save and did not replace the lower jug/cylinder gasket (base gasket). we have made our own but i fear that it is not thick enough. could be part of the issue but im not a mechanic so i would not know.

    i originally had a tick/rattle in the engine, (thus the reason for the taredown) come to find out that the ticking was teh SBP Head gasket.
    when matched with SEVERAL other head gaskets both original and more SBP gaskets, some of them, the inner cut was not matching to the piston stroke, not perfectly circular, stacked together we found that not only were a couple from SBP uneven, but other originals were too. the piston was hitting the uneven part of the gasket.

    it ran fine thru the whole break in and now it is nothing but junk(or at least i am starting to think so, again not a mechanic). i would just like it to run. i can get teh rest. or does it just need to R.I.P?
    Last edited: Oct 22, 2009

  2. andynogo

    andynogo New Member

    Does it have resonable compression when you pedal start it?

    Also turn the fuel tap off and try starting. If it suddenly takes off after a while it may be your main jet is somehow now too big?

    I've had to close my main jet up (solder & redrill) as the standard jet was way too rich and it four stroked constantly.

    Got good spark? Could be that as well.

    Good luck!
  3. mattysids

    mattysids Member

    Also remember that if you see a spark, it may not be sufficient for proper combustion

    I live up in the cold, and thing absolutely will not start because my CDI loses 90% of power in cold

    Ordering a new one soon
  4. Al.Fisherman

    Al.Fisherman Active Member

    Tried to pull start with my bike. Would start, but not for long
    Compression 150psi. Compression tester installed and pulling with my bike
    Changed out CDI with new one
    Installed my carburetor on his bike
    Installed his carburetor on my bike...Ran fine
    Changed to a NEW NGK plug. Gap at both .025 and .030

    Going to change coil and install my plug next.

    I've worked on hundreds on engines and have never been stumped as this one has me.

    it has intake..fuel
    good compression
    no muffler so has exhaust
    to me it has to be electrical.

    Some of the things we did to it. Shaved head and cylinder, piston hitting head and made base gaskets. Used folder files (not from PC but the ole fashion ones...lol)..we have three on all sealed with Indian Head sealer. We have 2 head gaskets both copper coated. Installed a boost bottle but since made inoperable to eliminate possible problem. Disconnected kill switch.

    Before the base gaskets were installed the engine was running ok, but the problem we had was that the piston was hitting the head gasket. This was the engine I tore apart and made photos of. I'm wondering if the base gaskets are screwing up the intake/exhaust cycle????
  5. sphynx.0029

    sphynx.0029 Member

    just a note of interest, Al.fisherman is my dad and we rork on this together, so, to eliminate any confusion, any posts that he makes on this subject are not suggestions. they are things we have done to try to repair the issue.

  6. andynogo

    andynogo New Member

    The only way the base gaskets could stuff it up is if they block the transfer ports but you seem to know what you're doing so scrub that one!

    Tricky! I think you're right- you've replaced most of the components so it must be coil or winding?

    I'm guessing you've checked/swapped the plug wire and cap?
  7. Al.Fisherman

    Al.Fisherman Active Member

    Done, when we installed the NEW CDI I keep in stock.

    Friday 2pm
    Think I figured out WTF was going on. We pulled the bike (towed) to do a compression test yesterday. Seems that at any speed above a fast idle the compression is good. BUT at a idle the compression is too low to accommodate the engine.
    Last edited: Oct 23, 2009
  8. sphynx.0029

    sphynx.0029 Member

    Ok here is another part of the puzzle.
    my engine gets good compression at high RPM. but not enough at low RPM to get fuel from the crankcase to the top of the piston for combustion.

    i am thinking we will next change out the piston and check inside the cylinder to make sure that there is nothing of note there to find.
    any other suggestions would be welcome. thanks to all for teh assistance.
  9. zaviii

    zaviii Member

    It may not be getting enough fuel or running to lean. I would try moving the needle up one position. Take a look at this video which will tell you what the 4 adjustments do to the air/fuel mixture. What is your oil fuel mixture ratio?

  10. sphynx.0029

    sphynx.0029 Member

    tried 3 of 5 needle positions as stated in orginal message, even changed carb from non running bike and put it on another bike, works fine, took carb off good bike put on non running bike only to find...guess what, still not working, i am thinking it is in teh motor.. thanks tho
  11. zaviii

    zaviii Member

    Bike not running.

    Sometimes you just get a bad motor. I have built a couple that had bad motors for whatever reason. Swap the motor out and it ran fine.
  12. sphynx.0029

    sphynx.0029 Member

    didnt want to have to spend another 100 bux, but it is looking like that is what it is going to entail
  13. andynogo

    andynogo New Member

    Another thing to consider is poor sealing in the bottom end- base gasket, crankcase half gasket, main crankshaft seals or it may just be that your rings are stuffed. Does adding oil make a very large difference in compression at low revs? That would indicate stuffed rings. Good luck.
  14. sphynx.0029

    sphynx.0029 Member

    well during the taredown we lost the crankcase gasket and did not replace it but pops says its ok. im not the mechanic, but i understand how it works, kinda. as far as the base gasket, we made one out of 3 layers of manilla folder file cut to match and indian head on the base, in between each layer of manilla and on the bottom of the jug for a good seal. dont think that is the issue as we cant get the dern thingy off now...IT'S ON THERE!!
    and tried a few different fuel mixtures first thing to eliminate that issue. also moved the needle in the carb to several positions to see if that would do it too but no good. Even took the carb off and put it on another MB and tuned it just fine, took it to work 3 nights since and not 1 problem other than cold start...that sux BTW...
  15. sphynx.0029

    sphynx.0029 Member

    oh and we just decided to build another so look forward to the pix, will be a blue titan trail blazer
  16. GearNut

    GearNut Active Member

    A very good way to test if the case gaskets and/ or seals are leaking is to fabricate block-off plates for the intake and exhaust mounts on the cylinder. Use the gaskets as a template for making them. Attach the block off plates to the cylinder, not forgetting the gaskets to seal them. Rotate the crankshaft untill the piston is at botton dead center.
    Apply no more that 2 to 3 psi steady air pressure to the engine through the sparkplug hole.
    Harbour freight sells small in-line pressure regulators with gauges to assist in this. I recommend modifying an automotive no foul sparkplug adapter (available at any parts store) to connect the air line to the sparkplug hole.
    Check all seals and gaskets for leaks with windex. look for bubbles. Leak found, fix it.
    No leak found, your problems are elsewhere.
  17. eastwoodo4

    eastwoodo4 Member

    good info gearnut.

    just so you guys know,the fuel mixture in the crankcase gets compressed when the piston goes down.thats what makes the fuel mixture shoot into the cylinder when the piston gets below the intake port in the cylinder wall.so if you have a leak in the crank case you lose that compression.
  18. GearNut

    GearNut Active Member

    Which can also lead to a lean mixture (due to intake leak), and fighting the carburetor adjustments to fix it right will have you pulling out your hair. The carb is not the problem at all. You will also get a pathetic transfer from the crank cavity through the tranfer ports. Poor off the line power and flat high speed power.
    Last edited: Oct 26, 2009