Atco Commodore B20 with Mitsubishi G221P with Electric Start - Problems

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Mic2876uk
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Atco Commodore B20 with Mitsubishi G221P with Electric Start - Problems

Hi All First post.

I started looking for a newish second hand petrol mower and ended up with a cylinder mower as a project!

First task is to get it running, it has spark, seems to have compression (large resistance change on recoil starter with spark plug fitted). The electric start works. but so far no signs of life from the engine.

So far I have stripped the carb and liberally used carb cleaner. However I have found thanks to this forum that my particular carb is very hard to clean and ultrasonic cleaning is really the only way.

One thing i have noted is when pulling the recoil starter with air cleaner off it spits out fuel, however does not leak fuel when left with tank valve open.

Could this be down to a blockage or is it more likely the intake valve is not closing properly?

Spark plug looked dry suggesting fuel isn't getting into the cylinder.

I'm also fairly unfamiliar with carbs if someone had a diagram of my carb labelling all the adjustment screws explaining what they do and what I should try to get it running.

Forgot to add carb is stamped with Mikuni Corp

I will post photos later

Much appreciated 

Michael 

wristpin
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Unfortunately that

Unfortunately that cabrurettor was total pain. Ultrasonic cleaning is probably your only hope of ridding it of stale fuel etc. Those little Mitsubishi engines ran at nearly constant revs it it was not unknown for them to carbon up the valve heads and stems so it may be worth giving it a decoke. I think that I've posted most of the specific Mitsu bulletins etc in the past but I'll sort out what I have .

 

Added

https://www.dropbox.com/s/lt7q0uhgvy5s2y2/Mitsubishi%20and%20Mikuni%20ca...

Mic2876uk
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Hi wristpin thanks for your

Hi wristpin thanks for your reply.

I've attached a few photos and video of the carb and the valves (head removed) see link below

https://photos.app.goo.gl/MLhzGDfg5v7QShLc8

The screw / jet visible from the bottom clearly someone has tried to remove in the past and broken half the head off the screw, however the parts diagram I have doesn't show that as a removable part. Is it supposed to be removable or not? If so where could I get a replacement if not I guess I just have to hope ultrasonic cleaning can fix it.

If not where could I get another carb from as I have almost no information about the one I have are there suitable alternatives?

I have also attached a video which shows the intake valve closes almost at tdc is this normal?

Thanks again

Michael

wristpin
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I wouldn’t worry about the

I wouldn’t worry about the valve action as different manufacturers use different methods of achieving some compression release to aid starting.

I’ve got no personal recollection of dismantling one of those carbs but that slot head item that you highlight certainly looks as though it is a screw in emulsion tube or main jet, very similar to that in a Dellorto carb and I’ve seen plenty of those chewed up and generally mistreated.

As you have probably found out, nearly all references to Mikuni carbs seem to relate to either their motor cycle carbs or the later ones used on BS engines . It’s possibly a long shot but it may be worth contacting the Gateshead Mower Centre who bought all the Atco Spares when Bosch disposed of their lawnmower interests. That Mitsubishi engined machine had a fairly limited production run, consequently there’s not a lot of new old stock out there.

Perhaps you can post a scan of your parts diagram to add to the rather meagre information available on this carburettor.

Mic2876uk
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Thanks again Wristpin,

Thanks again Wristpin,

For all the info and manuals I've gathered so far are in the attached shared folder below, I think all of this has come from trawling though this site;

https://drive.google.com/open?id=1NX5mSE3jIMbrWKDFFFGk6vhfxLqfHuW2

I will add to it if I find any more info, I would especially appreciate a workshop manual for this engine.

wristpin
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 I think that those bulletins

 I think that those bulletins etc were posted by me originally but the Atco Commodore one is not the correct one for the Mitsubishi engined machine, and as far as I can see there is no illustrated parts list for the Mikuni carburettor, only the Tillotson carb used on a different model.. I will post the Mitsubishi specific IPL / Operator’s manual when I’m back at the PC later but I’m fairly sure that there’s no breakdown for the carburettor.

 

EDIT

Here is the IPL and Ops manual for the Mitsubishi engined machine but as you will see there is no IPL for the Mikuni carburettor

https://www.dropbox.com/s/1ackso38a0vb1ml/Atco%20Commodore%20Mitsubishi0...

Ive got one other place to look but I don't think that Atco ever published a breakdown of the carb.

SECOND EDIT

Found this

https://www.dropbox.com/s/bkz3qf41xqxr5gh/AStco%20Mitsubishi%20ME1k%20G2...

As you said in your first post there is no sign of a removable emulsion tube or main jet. Seems a bit odd  - if it is a pressed in, non removable component, why the slot suggesting that it unscrews?  

 

Mic2876uk
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Thanks yet again Wristpin,

Thanks yet again Wristpin,

I had not managed to source the electric start manual thanks for that.

I had found the parts diagram for the engine which should be attached to my google drive link in my last post.

I've reassembled everything after giving the carb a good clean with carb cleaner and an airline (not ultrasonic yet) and still no joy.

I'm really starting to question the valve timing as shown in the video in my earlier post as when cranking with no air cleaner you can see an atomised mist of fuel being sent out of the carb the wrong way.

I've no idea why someone might have taken the engine apart and refitted it back together with the timing around 180deg out but i guess anything is possible.

I've also replaced the fuel line and added an inline fuel filter to prevent any further contamination and replaced the spark plug with the correct plug - after cranking spark plug looked dry suggesting its not getting any fuel

Video showing cranking with starter and fuel vapour coming out the carb

https://photos.app.goo.gl/2yj6pg7cEcEQsqyx9

I guess next step is have a look at the valve timing gear and see if there are any markings indicating correct timing

wristpin
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Unfortunately trying to view

Unfortunately trying to view your vid on the iPad caused all sorts of grief.

Take the head off and just go through the four stroke cycle - suck, squeeze , push , blow and see if the valve and piston positions correspond to what would be needed to achieve this.

180 degrees out would be immediately obvious from just viewing the valves. One tooth out, not so obvious . The crank shaft and cam gears will be marked, sometimes matching dots or even a chamfered tooth. 

Does the engine actually show signs of having been pulled apart ?

Mic2876uk
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I'll have to take head off

I'll have to take head off again to record the complete 4 stroke cycle, but the induction / suck part is shown in the video below

turning engine over by hand, no head intake stroke only

https://www.youtube.com/watch?v=IaWKWL2bMdk&feature=youtu.be

cranking engine with starter motor no head

https://www.youtube.com/watch?v=VS5mzz44C74&feature=youtu.be

trying to start - petrol vapour coming out intake

https://www.youtube.com/watch?v=2QTBcTf1YA4&feature=youtu.be

Hopefully youtube will be more ipad friendly :)

its hard to tell if its been apart recently but tbh i have no history of when it last ran

hortimech
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Hard to tell from the short

Hard to tell from the short video, but it looks to me that it is the decompresser causing the slight lift and will not be the cause of your problems. The way it works is that there will be the main lobe on the cam that opens the valve normally, there will also be a slight 'bump' that slightly opens the valve to release compression at startup, once running it has little or no effect.

I would remove the valves and examine, them and if required, regrind them, I would also check the tappets.

wristpin
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Yes, your YouTube clips work

Yes, your YouTube clips work fine. 

Carburettor venting, either external or internal, and the part played by atmospheric pressure.

If we are really pedantic over four stroke operation, strictly speaking,  to say that it sucks in mixture is incorrect. Lowering the piston creates a negative pressure area in the induction tract and the venturi effect of atmospheric pressure passing through the carb draws the fuel from the float bowl through the jets . To allow this to happen the float bowl is vented to atmosphere, either internally, probably via the air cleaner, or on some carbs via a baffled orifice directly through the top of the carb.

Where is all this leading to? Well, for the carb to function it must be vented so that atmospheric pressure may do its job so as well as ensuring that the jets etc are clear, make sure that the carb is venting. I have seen homemade gaskets between the carb and air filter effectively sealing off the vent passage.

 

 

 

Mic2876uk
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Hi Hortimech thanks for your

Hi Hortimech thanks for your help!

I had to google decompresser and i found centrifugal force auto decompresser which my engine definitely doesn't have or are you suggesting the cam as a bump that always lets a bit of compression out? Also the systems tend to be on the exhaust cam as I guess you'd get a back fire through the carb if the intake cam wasn't sealing.

Hi Wristpin,

I'm still confused how a blocked orifice on the carb would allow air flow in the wrong direction if we are assuming the valve timing is correct.

Fuel is getting into the air stream but as far as i can tell from the brand new spark plug its not getting into the combustion chamber

hortimech
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Yes, if there isn't a

Yes, if there isn't a mechanical decompressor, then there may be an extra small 'bump' on one of the cam lobes that slightly opens a valve to release compression at startup. This can be on either of the valves.

 

wristpin
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First task is to get it

First task is to get it running, it has spark, seems to have compression (large resistance change on recoil starter with spark plug fitted). The electric start works. but so far no signs of life from the engine.

Have you checked the flywheel key.? Unlike points ignition,  with electronic ignition the engine will spark regardless of the position of the flywheel trigger in relation to the crank position. so If the flywheel key is sheared or even partially sheared you spark may be occurring at the wrong time in relation to the other parameters required for ignition.