Engine Trouble A80 2stroke overheating carb boiling spark plug lead burning

Discussion in '2-Stroke Engines' started by Westie, Sep 4, 2013.

  1. Westie

    Westie New Member

    Please help me I just bought me a brand new motorized bike I was running it in not for more than 15mins at a time was going great in till the other day it started running out of power and the motor was hot as so hot the spark plug lead was melting to the plug and the fuel out of the carb was boiling I have only had the bike for two weeks I've got the best 2 stroke oil I could buy 16:1 run in mix (what the Manuel states) what should I do have I cooked it? The motor still runs just gets real hot again after 10mins so I have stopped riding it before it dose to much damage thanks for any help you may give me

  2. Fabian

    Fabian Well-Known Member

    If there is a blockage in the main fuel jet, then the engine will run lean. Otherwise you may have a blockage in either the fuel filter or the fuel petcock valve.

    If it's none of these things then you have an air leak.

    Either way, you may have cooked your engine good and proper. When first firing up your engine, you need to check all of these things to ensure long and happy engine life.
    Last edited: Sep 4, 2013
    Westie likes this.
  3. Westie

    Westie New Member

    Thanks will check it out when the motor is running there's no smoke or loud noises so I'll check the carby failing that time to buy a recondion kit
  4. Fabian

    Fabian Well-Known Member

    One of the reasons i like having an EGT gauge on my bike is to eliminate inconsistencies that come with air leaks and the potential to cook the engine. When an Exhaust Gas Temperature gauge is installed it can be set to display a warning colour if EGT jumps outside of a preset temperature setting, thereby alerting you that something is wrong, before you cook the engine.

    The Koso Rapid Response EGT gauge is so sensitive that it can detect intermittent spark plug problems as EGT drops 3 degrees Celsius every time the spark plug misfires, alerting you that something is wrong with either the spark plug or the ignition system, giving you a warning to fix the problem before things fail completely; leaving you stranded in the middle of nowhere.
    Westie likes this.
  5. jaguar

    jaguar Well-Known Member

    my bike would develop too much suction in the gas tank because the cap sealed too good. It would stop delivering gasoline to the carb because of the suction. I had to drill a small hole in the cap.
    I don't know if it's possible to develop just enough suction to limit the gasoline going to the carb.

    Maybe you have a faulty CDI that is greatly advancing the ignition timing. To know that you'd have to check it with a timing light.
    Westie likes this.
  6. HeadSmess

    HeadSmess Well-Known Member

    hmmmm. to be so lean that things start melting...it shouldnt be able to run at all. or starting is so hard you would have given up and whinged that it wont start... :jester: you really have to baby the throttle when theyre lean, else they cough and splutter and die. you cant just give them full throttle when taking off.

    a blocked jet will do this.

    an air leak can behave rather differently, with it only really being an issue at idle. the throttle slide is closed at this point, so maximum "suction" is placed on the seal. and, at idle, the excess air is a large proportion of the total airflow, making what does pass through the carb leaner. it idles high, theres even more suck, even more air, even leaner, even faster, even more suck again, etc... pretty easy to pop the intake off and give the gasket some sealant. and make sure the carb is pushed completely onto the intake. the slots that let it "clamp" sometimes dont quite cover the end of the intake tube...check!

    crank seals...make for hard starting, and really erratic mixtures...usually on the lean side. the mess under the magneto cover is a dead giveaway.

    if you hit the killswitch does it try to keep running when its hot?

    notice any strange "cracking" noises when its under load? runaway detonation. quality! (not really but is amusing)

    well, it could be a sign that you got lucky and its got a really hi compression head...

    which leads to...

    im suspicious about the plug. get an ngkb(6or7)hs. try it. ive found some china plugs go into self destruct mode. the first thing is to get rid of that china plug! (yeah, i also got one thats 10 years old and going strong!)

    post a pic. have a look at the electrode. if its brown, its not the mixture being lean, or the plug.

    if its all white and blistered looking...we have an issue somewhere. start with the sparkplug and airleaks.

    checking the thing with a timing light is simple, but has a few issues. you need to mark the magneto, so you know where TDC is, and you need marks for 5, 10, and 15 degree advance. you need to put these on yourself. so you may be doing some research first to figure out how...

    with no definite physical guide for when its triggered, unlike a pitbike CDI or a points ignition, these engines pose some challenges to the uneducated mechanics to figure out when its firing when turned slowly by hand... :(

    ie, you need to have it running to time it. so, it needs the marks...and a timing light.

    and then, the biggest question of all is, whats the STANDARD idle advance in degrees anyway? NOONE seems to have ever said what it is ,exactly. how peculiar... :jester: they just say that its wrong wrong wrong.

    8 bdtc is a standard norm at idle on most engines... but the exact value depends on...compression ratio, rpm, cylinder design, head design, octane of fuel, what pipe you running, blah blah blah. some are 2. some are 12.

    but as a basic guide...if you did time it and found 35 degrees advance at idle... somethings not right.

    could be a faulty magneto, badly keyed. that key position is critical. could be a bad CDI.

    and finally...dont bother wasting money on super expensive 2stroke oil, just buy whatever you grab. the engines cheap. run it on 50:1 if the oil is useable in 50:1 (100:1 is a lil too low), forget the 16:1 BS thats based on super high quality pig fat or recycled sump oil for lube.

    it will also be slightly richer if you use less oil, and should run slightly cooler.

    in fact, it might just be the 16:1 causing the issue. cus maybe you miscalculated on the last mix and its way too much oil, and suddenly way too lean?
    Last edited: Sep 6, 2013
    Westie likes this.
  7. Westie

    Westie New Member

    Wow thanks for all that information that's a great help going to pull it apart this weekend and have look I will mix up a new batch of 2 stroke at 50:1 the oil I got is fully synthetic I have a measuring surege to so shouldn't be the fuel..

    (notice any strange "cracking" noises when its under load? runaway detonation. quality! (not really but is amusing)

    well, it could be a sign that you got lucky and its got a really hi compression head...) that dose happen when I was on hills I run a standed muffler and the plug that came with the bike I will up load some photos tomorrow thanks for it comment it all helps
  8. Westie

    Westie New Member

  9. Fabian

    Fabian Well-Known Member

    I am sure synthetic oil @ 50:1 will solve all of your problems. You could also try using synthetic oil @ 50:1 as a social lubricant :devilish:
  10. HeadSmess

    HeadSmess Well-Known Member

    no, no, no! thats 50% ETHANOL BLEND for society!
  11. Westie

    Westie New Member

    So I pulled the carby apart blew it all out put it back together and put a new fuel filter on went to start it up and could feel air coming out the block when I cranked it over so I checked the nuts on the head and they were a little lose so i tightened them up and it's running much better will take it for a big ride tomoro and see how it go's thanks for all your help
  12. HeadSmess

    HeadSmess Well-Known Member

    ooooh, loose head gasket. could do it too.

    that one will usually make a squeaking popping sound when you first start up, and clears up as it gets warmer. unless the nuts were really loose.

    anyways. hope it goes better now ;)
    Westie likes this.
  13. Easyrider

    Easyrider New Member

    Hello Westie,

    I'm a new builder trying to fine tune my engine - A80 high compression 2013 motor. I was fooled for a long time looking for bad running solutions. I'm now making progress, but the bad engineering on the intake manifold was so poor the carbie would not slide fully on and no matter how hard I tightened it on, there was still an air leak, I discovered. If the air leak is big enough it will make the engine run so lean it will overheat. My solution was to grind down the over-weld which stopped the carbie sliding fully on to the manifold, and then using an o-ring ($2 from $2 shop) to inset into the carby so that an air seal was made. Then the engine ran too rich (but cooler). I've just put a smaller jet in (from a wrecked scooter - a .65), and wow, what a difference. I've just ordered some Dellorto jets online at www.gpsimports.com.au (only $3.50 each! but postage too!). I'll look forward to getting it running really smoothly, with the help of this forum. It has been quite a lot of work, but testing for the air leak was the initial key - I used the propane gas method. But the basics must be right first before other modifications and trials are made otherwise money can be unnecessarily spent . Good luck