Backfiring

Cliff · Post by **Cliff** » Sun Jan 27, 2008 9:28 am

I had similar symptoms once (not me personally) and it proved to be the stator.

Trxbadger · Post by **Trxbadger** » Mon Jan 28, 2008 2:03 pm

No i'm not running premix, can't even get the sucker running to check for possible leaks. New battery on trickle charge as i type this post then i'll check the stator etc.

sipaldi · Post by **sipaldi** » Mon Apr 14, 2008 11:52 am

Just a thought, are the two wires that slot onto the coil on the right way around? Worth double checking. Apart from the stator and whats been mentioned I can only think of poor compression in one cylinder? Rings not moved when you fitted the heads? Just built an engine up so I am trying to think what could have gone wrong for you. You have the fuel pipes from the tank to the carbs fitted correctly? I think there are three and a breather?
Keep us up to speed on your problem and i will keep scratching my head!

Trxbadger · Post by **Trxbadger** » Mon Apr 14, 2008 4:21 pm

Hey sipaldi how's it going? Just been trying to get it going, no luck yet. I've switched the coil wires around and as for the fuel tank well i've bypassed using that, got in line fuel filters which i fill with fuel using a syringe. i know the tank and tap are ok just eliminates it. Reset the pickup air gap and cleaned all earths. Today it is sparking simultaniously on both plugs, tommorow could be a different story.
Beginning to wonder if its got a big crankcase leak? Havent got a comp tester but it seems pretty good with the old thumb over the plug hole.

Cheers for your help i'll keep you posted.

KwakOn · Post by **KwakOn** » Tue Apr 15, 2008 11:29 pm

is the fuel igniting in the expansion chambers, (as opposed to actually firing the crank backwards.. )

if so could it be a slight coolant leak which is allowing enough moisture to conduct the spark into the unburnt fuel somehow.

sorry, just a wild untheoretical not very logical guess..

Ex-LC · Post by **Ex-LC** » Wed Apr 16, 2008 1:31 am

Have you checked the stator and coil outputs. They were the guilty parties when mine started playing up (loss of power and backfiring).

Neil

Trxbadger · Post by **Trxbadger** » Wed Apr 16, 2008 3:21 pm

Afternoon Kwakon and Ex- LC, can't be anything to do with water leakage as i haven't got the radiator on or any water in the system, eliminated that. I've checked the stator again yesterday as per the manual and the h.t coil, all within manual specs. Somebody told me they had similar problems as mine on a kmx125, turned out to be the diode so i have even checked that as per the manual. No probs there. Please keep the ideas coming guys no matter how daft you think they may be and i will check them out. Hopefully at some point i can use one of these

instead of this

JanBros · Post by **JanBros** » Wed Apr 16, 2008 10:23 pm

is it just the right cylinder that backfires ? if so : take out that sparkplug and try starting it on the left cylinder.

*When it starts, switch the carbs. if it doesn't start then

carb problem

* If it doesn't : take off carb's, blow air through the crankcase/sparkplughole to make sure there is no more mixture/fuel in the engine. then spray some startpilot/brakecleaner in the cylinders.

if it doesn't start : ignition problem
if it starts : try again spraying startpilot in the cranckcase. i fit doesn't start : cranckcase problem, if it starts : carb problem

Trxbadger · Post by **Trxbadger** » Thu Apr 17, 2008 4:05 am

Morning JanBros, well it was backfiring on the right cylinder but now it's started on the left, don't know why as i've changed nothing around. It's all very random hence my thinking that it's electrical gremlins. However your advice is sound and i'll get some startpilot and see if that sheds any more light on the situation. Will have to wait till the weekend now as i'm working on the Trx tommorow.
Too many bikes and so little time. Cheers for the help, will keep you posted on the outcome.

KwakOn · Post by **KwakOn** » Thu Apr 17, 2008 9:35 am

my second engine had a bad crank seal (centre) when I got it and it was impossible to start without clean/new plugs. the crankcases were filling with fuel (plug fouling) but it didnt backfire as I remember and it went well once running.