FJ1200 backfire / Wet plug cylinder 3

[callmered]

I am resurrecting the FJ1200, which has been in the shed for a few years. The bike was laid up due to a raft of niggly maintenance issues which I didn't have the cash or time to sort out.

Sorting the fork oil and general maintenance was easy enough, but I am struggling with intermittent firing of cylinder 3.

I replaced all air box side rubbers, as two had perished (3&4). The engine side rubbers are fine. While apart, I cleaned the carbs as best I could. The jets seem fine.

I have performed a leak test, spraying WD40 on the rubbers and air balance caps while the engine was at steady revs. I did not notice any change in revs.

There is definitely spark on the plug, which is of course new. I have swapped plugs between cylinders to ensure it isn't just one dodgy unit.

I have an aftermarket Magnum 4-1 exhaust fitted - has been there since purchase with no previous issues.

As the FJ has 2 ignition coils for the 4 cylinders, I have discounted the coil as an issue. Is this correct?

Could this be a plug lead issue? The leads are the original set, on a 1992 bike.

Oh, and I am just about to check the exhaust header for leaks, (just occurred to me) which could cause backfiring but not a wet plug.

What else should I look for?

[Subike]

You are correct to suspect the leads.
Put new plugs in as well,
Have you done a compression test?
It may be a long shot, but the inlet valve on No3 may not be seating properly after sitting so long.
Have you checked the vacum lines off the carbs?
Being no3 the vacume line cap may be perrished.
Did you clean the tank after cleaning the carbs?

Just some thoughts for you

[SARGE]

I am resurrecting the FJ1200, which has been in the shed for a few years. The bike was laid up due to a raft of niggly maintenance issues which I didn't have the cash or time to sort out.

Sorting the fork oil and general maintenance was easy enough, but I am struggling with intermittent firing of cylinder 3.

I replaced all air box side rubbers, as two had perished (3&4). The engine side rubbers are fine. While apart, I cleaned the carbs as best I could. The jets seem fine.

I have performed a leak test, spraying WD40 on the rubbers and air balance caps while the engine was at steady revs. I did not notice any change in revs.

There is definitely spark on the plug, which is of course new. I have swapped plugs between cylinders to ensure it isn't just one dodgy unit.

I have an aftermarket Magnum 4-1 exhaust fitted - has been there since purchase with no previous issues.

As the FJ has 2 ignition coils for the 4 cylinders, I have discounted the coil as an issue. Is this correct?

Could this be a plug lead issue? The leads are the original set, on a 1992 bike.

Oh, and I am just about to check the exhaust header for leaks, (just occurred to me) which could cause backfiring but not a wet plug.

What else should I look for?

im assuming you've balanced the carbs? .. also the seals on the header may perish ..

post this in the FJ1200 Social group on this forum


welcome to KB man .. nice bikes those FJ's

[martybabe]

Forgive me if this is stupid advice, I am to mechanics what Sundays are to giraffes but.....I have owned five of these bikes an I seem to recall a problem with the float bowls sticking in the carburettors on FJs which required a gentle tap with the handle of a hammer and the use of redex or similar fuel cleaner.

The symptoms you describe seem to fit this , especially as they have been sitting in gunky gluey old fuel.

I do not suggest this as the fault,for I clearly know bugger all but it may be something you wanna look at in the process of elimination. It happened to me twice, both times outside right cylinder and both times cured with a tap and a clean. Good luck and let us know how you get on, in the mean time join the FJ group as suggested above, I'm thinking they may know a thing or two about FJ motors.

[callmered]

You are correct to suspect the leads.
Put new plugs in as well,
Have you done a compression test?
It may be a long shot, but the inlet valve on No3 may not be seating properly after sitting so long.
Have you checked the vacum lines off the carbs?
Being no3 the vacume line cap may be perrished.
Did you clean the tank after cleaning the carbs?

Just some thoughts for you

I'll try another new set of plugs. I was considering iridium plugs anyway.

I have done a compression test and a leak down test. Cylinder #2 needs new rings soon, but #3 seems ok. I did this a couple of weeks ago and have forgotten the actual figures.

The vacuum line caps seem ok. I read somewhere on this forum about holding the bike at a steady throttle and spraying WD40 or similar and checking for a change in revs to indicate a leak here. No indication.

I rinsed the tank, but am not convinced it is clean enough. I will sort that out, too.

At a quick visual inspection, I couldn't find an exhaust leak. The magnum pipe is a little unsociable - I'm trying not to annoy the neighbour too much in one day Don't want him firing up his ring ding for an hour again.

Oh, I spotted some perished insulation on the plug leads. I have wrapped them for now and will grab some new leads.

[callmered]

Forgive me if this is stupid advice, I am to mechanics what Sundays are to giraffes but.....I have owned five of these bikes an I seem to recall a problem with the float bowls sticking in the carburettors on FJs which required a gentle tap with the handle of a hammer and the use of redex or similar fuel cleaner.

The symptoms you describe seem to fit this , especially as they have been sitting in gunky gluey old fuel.

Yep, did that, thanks. The carbs seemed quite clean, considering. I cleaned them anyway.

[callmered]

Sarge, thanks for the link. No, I have not balanced the carbs. To be honest, I don't know why I didn't!

[SARGE]

Sarge, thanks for the link. No, I have not balanced the carbs. To be honest, I don't know why I didn't!

all good advice above too .. ive had one of these bikes since i landed in NZ and once ya get them up and running they are monsters


PS .. i have a bit of FJ info in my Blog also .. im always adding more so if there is anything you need specifically let me know

[CookMySock]

Could this be a plug lead issue? The leads are the original set, on a 1992 bike.

Thats my guess. Swap the lead between cylinders and see if the problem follows you.

Or maybe it just needs a wee cane..

Steve

[martybabe]

If all else fails these guys will have the answer, the DOC is the most knowledgable FJ man on the planet.

http://www.fjfjrbiker.co.uk/index.ph...&action=login2

[SARGE]

If all else fails these guys will have the answer, the DOC is the most knowledgable FJ man on the planet.

http://www.fjfjrbiker.co.uk/index.ph...&action=login2

+1 .. head spanner monkey for the FJCUK

[callmered]

Thats my guess. Swap the lead between cylinders and see if the problem follows you.

Or maybe it just needs a wee cane..

Steve

Believe it or not, the old girl will still hit an indicated 200 km/h. It just takes a little longer... and you have to tuck the toes in a bit.

You know, I am beginning to be convinced it is a lead issue. There is less of a problem at high revs, it seems to be intermittent, possibly temperature related. Sounds like some sort of an impedance issue rather than a short.

Got to experiment a bit more.

[martybabe]

+1 .. head spanner monkey for the FJCUK

Hey hey, someone outside the UK that's heard of him, I believe the little fella's a bit hard to get hold of these days as he runs a full time FJ and FJR service centre and runs one of the biggest clubs In England but despite owning a bunch of FJs, I was always out my depth in his company. The dude will fire off shim sizes, torque settings and alternative fuel pumps when you're just trying to discuss the local pubs .

Ex services too Sarge, you buggers could have a right old chin wag.

Hey callmered, I'll send you some bling, it won't help the FJ but it will say welcome on board.

[callmered]

I feel quite welcome already - what a great community this forum is!

[FJRider]

Believe it or not, the old girl will still hit an indicated 200 km/h. It just takes a little longer... and you have to tuck the toes in a bit.

You know, I am beginning to be convinced it is a lead issue. There is less of a problem at high revs, it seems to be intermittent, possibly temperature related. Sounds like some sort of an impedance issue rather than a short.

Got to experiment a bit more.

Fire the old girl up in the dark. If the leads are shorting out ... you will see where.

and check fuel lines are not kinked ... the fuel will be pumped. A kink may explain intermittent problems.