Author Topic: Maico 490 1981 Mega 2 - starting issues  (Read 6861 times)

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Offline ajcmbrown

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #30 on: August 09, 2017, 01:22:47 PM »
Have you done a leak down test? Air leaks on Maicos are very common, I've even seen one with a porous crankcase casting.
The only other thing I can think of that hasn't been mentioned is a crankcase with fuel laying in the bottom end due to a failed float needle.
Tony.

Offline peely_14

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #31 on: August 09, 2017, 06:33:55 PM »
Hi Tony, that's very interesting!

What should a freshly rebuilt 490 be producing in comp test? 110/115?

Whilst I am away in Vietenam at the moment the old man has kindly been working on the bike. Today he swapped over his CDI unit onto my bike and it's the most life he has seen in her. 1 kick back and 3 misfires. He now has a sore leg and will kick later today haha. He found fuel in exhaust which I assume is from when my carby was fitted and floats were not working.

If some one can indicate a ballpark comp figure he can test that and if all is good there my money is on CDI unit.

Cheers,

JOSH.

Offline ajcmbrown

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #32 on: August 09, 2017, 07:13:52 PM »
Hi Josh, a leak down test is different to a compression test. A compression test will indicate the condition of the top end only.
A leak down test is performed to determine if there are any leaks in the bottom end or crankcase area, it can be leaking crank seals, more likely the ignition side although the primary drive seal can also have a poor seal, and they will suck gearbox oil in and burn it, you'll know if it's that by the amount of smoke if you can start it. It can also be the centre case gasket or sealing area, or as mentioned, a porous casing.
Basically you need to seal the intake and exhaust ports, attach a pressure guage and apply around 10psi, then watch how long it can hold that pressure, and over what period of time it loses pressure.
If it does not hold air, you need to determine where it's leaking from and rectify the leak.
This is important in any two stroke engine as without the correct crankcase compression, your engine can be hard to start, run badly, or not run at all.
I hope I've explained this clearly but I'm sure Youtube will show what I mean. Have a look at this: https://www.youtube.com/watch?v=zdq7NRcUIp8
Tony.

Offline ajcmbrown

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #33 on: August 09, 2017, 07:31:13 PM »
I should have mentioned, if as you say, you have fuel in your exhaust, this will prevent most two strokes from starting almost every time.
Before doing anything else, disconnect your ignition, remove the spark plug, put it in 3rd gear and push it as fast as you can, if you see plenty of fuel mist (the reason for disabling the ignition) being pumped out the plug hole then you may have found your problem.
Put it back together, turn the fuel on only long enough to fill the float bowl, turn the fuel off and try starting again, this has worked for me quite a few times over the years and has saved many hours of looking for other problems.
Good luck, Tony.

Offline peely_14

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #34 on: August 09, 2017, 08:56:57 PM »
Thanks again Tony, all understood. Will let you know how we go!

Offline Nebo

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #35 on: August 27, 2017, 12:21:04 PM »
  peely-14.   No hear from you.

   Have you got the MAICO running yet?.

   We are all dieing to know.

Offline peely_14

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #36 on: August 28, 2017, 11:46:10 PM »
Nebo, thanks for the msg. My emotions have been up and down over the 490.

The latest is, despite using the CDI unit and carby off the old mans bike she would still not fire but was showing signs of life. We then adjusted the timing so that it was identical to the old mans and booomm she fired, hooooorayyyyyy. We kicked her over prob 3 times at home  and decided it was time to take her out and run her in.

I wheeled her off the trailer, first kick and she was alive. With the worlds biggest smile I clicked her into gear for the first time and took off. I completed all of half a lap before stalling her nooooooooo!!!! I kicked and kicked and kicked. Changed the plugs. Tried push starting (I assume too much compression as rear wheel kept locking up). Got tired of kicking, loaded up and went home even more puzzled.

Tomorrow we will also swap over the stator and see whether that helps.

Offline Nebo

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #37 on: August 30, 2017, 06:27:39 PM »
peely-14.   Glad your getting some were.

  Good idea to check the decompresser .

  They block up with carbon. Make sure it is opening fully. Adjust the cable.

  Getting back to the Problem. Sounds like faulty Stator Coil or Pickup/Trigger coil.

  Keep us posted.

Offline peely_14

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #38 on: September 02, 2017, 05:57:01 PM »
Hi guys, i did a leak down test today and discovered a leak at the barrel base gasket (front and back).

I couldn't find any other leaks. leak down results were a rate of 10% per 2mins 50seconds. Does this sound excessive? I'm thinking I will pull engine back out and fit a new base gasket. Then try leak test once again? I understand no engine is 100% leak proof.

What are your thoughts?

Cheers Peely.

Offline Momus

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #39 on: September 02, 2017, 06:13:18 PM »
Front and rear base leak may mean that the case halves are not aligned.

Offline sleepy

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #40 on: September 04, 2017, 10:59:01 AM »
Probably worth changing the gasket and using a smear of 3 bond on the case joints front and back but I doubt if that is causing your starting issue.
Very hard to work out why it won't start without seeing in person, an example is a customers with a YZ465 who couldn't kick start it. After looking at the bike here I could start it but it took 100% effort to kick it, so when the owner turned up I got him to show me how he kicks it. Despite him being over 100kgs he kicked it like a girl just sitting in the seat and prodding at the lever and it was never going to start. After a bit of a lesson on how to kick a bigbore bike and put all his weight into it he has never had to push it since.
Assuming you know how to kick it properly the only thing I can think is the carb maybe flooding a little making it to rich to start. You have said in a previous post that there was fuel in the exhaust, and I would guess it must have had a case full of fuel as well.
When you had it running and stalled it did you fall over? Did you have a suitable place to kick it? I need to stand on a drum beside the bike and use my right leg to kick. I've never been able to start a bigbore Maico with my left leg sitting on the bike. 

Offline peely_14

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #41 on: September 05, 2017, 09:37:42 PM »
Hi guys, so im more stumped than ever.

Today; I tried reversing everything and installed electrical components on old mans bike.

1) I installed my CDI unit and my stator to the old mans bike = would fire on every kick, but not run.
- I removed exhaust to check to see if fuel was sitting in there, nothing! Cleaned plug.

2) I installed his CDI unit and my stator - No fire (lifeless)

3) I installed his CDI unit and his stator - No fire (lifeless)

So now we have two maicos not running,  :-\

I did find that I was able to deliver a stronger kick through his bike prob partly due to lower compression and sounded like his decomp valve releases more air than mine. Im not sure whether I need to pull apart my kick mechanism. Sometimes mine locks up on me at the top. If im not delivering a strong enough kick, could mean Im not generating quite enough spark. Having said his I have kicked the shit out of mine and still been dead as a dodo.

Good point Momus! Sleepy - Yes I would assume it should still start, which it had the other week. Nah I didn't fall off when i stalled it, was just My old man has owned his 490 since it was 6months old, so he has a few years experience kicking the old girls and even he cant kick it over. We are like you, stand on a crate and kick with our right leg. Anyway I can check if CDI is the problem out of bike?
« Last Edit: September 05, 2017, 09:42:37 PM by peely_14 »

Offline sleepy

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #42 on: September 06, 2017, 09:06:37 AM »
Be careful mixing Motoplat components. One 490 I sorted a few years back had a mismatched Motoplat (they should have matching numbers stamped on stator and rotor) which made the timing about 10 degrees advanced. The owner turned up with the bike he had bought recently walking with crutches for his badly damaged ankle after attempting to start it with the advanced timing. The timing marks are only good if the numbers match. I worked out with a timing light where the timing should be and it started quite well afterwards.
Another 490 was starting ok until I bored it 2mm oversize for the owner and after that he couldn't kick start it due to the extra compression. Ended up fitting an 18mm decomp valve and 2 head gaskets.

Offline paul

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #43 on: September 06, 2017, 02:10:05 PM »
Your really chaseing your tail,I've watching this thread for ages waiting for that 490 too start ,my advice to you would be send bike to Paul stacker and get him to go through it ,if you want a reliable bike ( as far as Maicos go ) that's what I'd do ,Geoff Ballard does it ,I've had Maicos I've bought apparently running condition that were pigs. Especialy a square barrell I got from qld ,that was rooted.i sent it to Paul and he sorted it no problem ,food for thought hey

Offline ralph311

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Re: Maico 490 1981 Mega 2 - starting issues
« Reply #44 on: September 06, 2017, 03:46:44 PM »
Well you may as well have my 2c worth to go along with everyone else's  ;)

The short.... it seems you are pretty confident its ignition related. If it were mine I'd get an HPI/Electrex replacement and go from there. Life is too short and 490's are too much fun to be stuffing about with 35 year old ignition systems.

Longer.... now two dead maicos implies you're doing something wrong with your installation (hard to imagine what), both ignitions are marginal (see above) or you've damaged them (haven't been cranking them without an earthed plug I hope?). My clutching at straws suggestions: run an earth wire from the stator to the coil, disconnect the kill switch, use a fine wire electrode plug, reduce the gap to 20 thou and make sure you have only one resistor in the system (either plug or cap).

ps When it fires but won't start, does it kick back? If so try retarding the timing a bit (to say 1mm btdc) to get it running then put a timing light on it to see what its up to.
« Last Edit: September 06, 2017, 03:55:42 PM by ralph311 »