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Author Topic: 4 stroke engine starting problems  (Read 3579 times)


  • Joined Jul 2012
  • Angus
4 stroke engine starting problems
« on: July 24, 2012, 02:41:03 pm »
Hi , I aquired an Agria fingerbar mower. I has a 4 stroke MAG petrol engine. The pull cord turns and there is a first ignition with smoke but it does not continue after that. I have replaced the spark plug and changed the petrol for fresh petrol. Any suggestions what other things to look at. i have not been able to find a manual on line. I uded a borrowed one last year and it seems pretty indestructable so hope the problem is easy to fix.
Any help / advice welcome.

« Last Edit: July 24, 2012, 03:17:43 pm by ddangus »
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  • Guest
Re: 4 stroke engine starting problems
« Reply #1 on: July 24, 2012, 04:04:14 pm »
hi ddangus - I am no expert but sounds like a the fuel supply to me.  There must be some kind of spark to get the initial smoke.
When struggling with lawnmowers & rotovators etc in the past it can only be spark / fuel supply / compression. I always go right back to basics and test each one. 
Have you proven the basics - fuel definately flowing and good spark available?
I am not familiar with the engine so not sure if it has a choke or not.
There is always a danger of telling grandma how to suck eggs so apologies if thats the case here.


  • Joined Dec 2011
  • Gascony, France
Re: 4 stroke engine starting problems
« Reply #2 on: July 24, 2012, 08:48:23 pm »
If it runs for a few moments and stops it is probably a blocked main jet in the carb as said. If it only fires once it may be a manifold problem. Our Briggs and Stratton has pressure balancing diaphram built into the carb to block joint. Didn't know they used them on four stoke mowers until a few weeks ago. The mower is 12 years old and the new diaphram was £4. There was nothing visibly wrong with the old one until it was pointed out that the diaphram had simply lost its elasticity. This was due, said the mechanic, to Ethanol in unleaded? He changes dozens every year! So perhaps the MAG engine uses the same system.


  • Joined Jul 2010
Re: 4 stroke engine starting problems
« Reply #3 on: July 26, 2012, 08:00:13 pm »
Hi ddangus,
It sounds to me like the jets in the carburettor have varnished. Unbolt the carburettor from the engine ( including removing the cables, and take photos before you undo anything so you know how it goes back together ) and remove the screws holding the carburettor together. Gently lift the top off, and look inside.
You'll be able to remove the gunge at the bottom of the carburettor bowl, and if you get a can of carb and jet cleaner from your local motor factor, spray everything inside a couple of times, letting the cleaner evaporate off between each time. DO NOT take wire or small drill bits to the brass jets, you'll mess up the carburation if you do.
Put the two halves back together, refit the screws, bolt it back on to the engine, reattach the cables and that should be it!  ;D



  • Joined Jul 2012
  • Angus
Re: 4 stroke engine starting problems
« Reply #4 on: July 30, 2012, 02:40:31 pm »
Thanks for all the advice. I will have a go a cleaning the carburretor jets and will defo take pictures before taking it appart. have been there before wondering how to all fit it back together.




  • Joined Aug 2012
Re: 4 stroke engine starting problems
« Reply #5 on: August 29, 2012, 10:21:31 pm »
Just a little tip as i am used to card jobs on old bikes lol i found the best way was take one jet out at a time soke it in thiners over night use compressed air to blow it clean dont poke the hole with any wire neadle etc hope this helps o also use gasket sealer round the joint as it might suck air in after you have opened it


  • Joined Sep 2009
  • England
Re: 4 stroke engine starting problems
« Reply #6 on: September 02, 2012, 10:36:55 pm »
Nothing to do with the question but ..........
Years ago I was stripping and re building a BSA Bantam, I was reading an enquiry in a magazine from someone who wanted to know how to get the piston rings back in, somebody else had provided the answer which was signed

'yours sincerely, Flatfingers of York'

Always makes me smile when I think of it and this thread brought it back, thanks  ;D
Time flies like an arrow but fruit flies like a banana.


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