Back Fire on Startup followed by Mechanical Noise!

[Seanextra]

Hi All, This is all i was told by the original one owner of my FJ1200 1988 i have just purchased its been pulled down (top end only) and he cant seem to find any issues. The Bike has done alot of Klms but was very well looked after. Can anyone offer some ideas where to check and what might be the possible causes of this? Im not even in the same country as the bike till next week so im really just after some points to check.

Thanks in advance !

[FJ111200]

Hello there.
One possible cause of the backfire is unspent fuel being pushed out of the exhaust valves and into the downpipes and silencer, then catching fire and exploding with the resultant bang.
As to the mechanical noise, could be anything, without being there to actually hear it.

[Seanextra]

Yes its a wild question i realise but im just wondering if there was any common problem with older FJs that has similar symptoms to this. Would a jumped tooth on the cam chain be a possible cause? Backfire isnt usally somthing too hard to fix for any number of reasons but followed immediatly by mechanical noise is somthing new to me ive been playing with bikes and cars for 30 years and never heard anything like that happening as the backfire is usually carb or timing issues not related to a normally running engine the day before then sudden mechanical noise really leaves me with no idea what it could be other than valve train timing head problem. 

[FJ111200]

I'm running my XJR with all FJ1100 electrics, and every now and then if the battery isn't fully charged, it just won't fire straight away and sometimes i get the backfire. I don't know if this is common to early FJ's or not.
I wouldn't say that a jumped tooth on the cam sprocket would cause a noise as i once re-assembled the top end with it 1 tooth out, and it fired up but ran really strangely.
It could be that the cam chain tensioner has somehow got stuck. As i say, hard to tell without being there.

[SkyFive]

As far as the backfire on start up I would suspect a compression and/or valve issue. How do the valves look, are they seating all the way arouind? Is there alot of carbon build up? Were the intake valves and stems wet with oil?

[Seanextra]

Hi All , Finally reassembled this engine without splitting Cases OEM rings a light HONE and new timing chain tensioners where required all the top end was spot on i de carboned it all and reasembled the top and and fitted the engine to frame before adding carbs i decided to do a wind over after filling with new oil and filter to make sure everything was turning over smoothly and to also try and prime the oil galleries and pump . When i hit the button there was nothing so i took my XJR starter and fittted it as i tested the original that came with the biuke and it was dead. Now when i hit the starter button the engine turns over but there is a VERY LOUD  slapping banging noise comming from the Starter area of the Crank case i presume starter clutch. It sounds like any more than a few turns and its going  to smash thru the case its that loud.  Now is this a common thing with FJs I guess this explains the noise the non mechanical previous owner was talking about. and also is this going to be accesable from the sump at all or is it a Case Split exercise ?

[andyb]

Starter clutch needs the cases apart to access. 

[Seanextra]

I thought so just wishful thinking i didnt need too.