Popping and back firing from exhaust

[Kenzmad]

Hi guys first post first v-twin so just a quicky really any help would be greatly appreciated.

I had had the firestorm for about 10 month and last month on a run out I developed a rattle presumed it was cct's ( as I read a little bout them) I pulled the bike over straight away switched off and didn't start again till after new cct's were fitted following sirch's instructions. Since fitting them though the bike has developed a pooping from the exhaust when I let off the throttle and sometimes a back fire which it didn't have before, the bike still hits red line and runs good apart from this, is this normal on a v twin?
The timing was spot on, fitted new plugs oil and filter.




sorry if this has already been posted somewhere

[benny hedges]

check you haven't got any airleaks around the exhaust collector under the swing arm, that the carbs are on tight with no leaks at the rubbers, and the carbw will most definately want balancing after being off
hopefully you didn't bend an exhaust valve slightly when it went?
if the cct goes, when you turn it off it Will go Dink and hop a tooth on one cam, without a doubt.
folk say no it didnt, but how do you know unless the cam cover is off when it fails lol!
and if it's slipped a few teeth (like it will) then it will probably have kissed a valve imo.
if you've set it up proper & alls well & good then dont worry - they all pop on the over-run to some degree.

[Jazzscot]

Mine went the other way when my cct went. Before I fitted the manual ones she used to fart and pop on over run. Now she just has a low growl. I know this doesn't help ya but I thought Id share that with ya.

Jazz

[kevg]

There's also a joint in the rear exhaust downpipe next to the rear shock thats a fav for leaks as it's difficult to see.

[sirch345]

Since fitting them though the bike has developed a pooping from the exhaust when I let off the throttle and sometimes a back fire which it didn't have before, the bike still hits red line and runs good apart from this, is this normal on a v twin?
The timing was spot on,

Seeing it only started to pop and bang from the exhaust on the overrun after you replaced the CCT's I would check the valve timing again. From my experience those symptoms sound exactly like the valve timing is one tooth out

I realise it could definitely be a leaky exhaust joint as already been said, so by all means check that first.

If the valve timing is definitely not out and the exhaust is not leaking then I would be inclined to think like Benny, a possible bent valve or two. As a rough guide you can check the valve clearances before removing the cylinder head(s). Bent valves will mean large clearances.

Chris.

[benny hedges]

check the valve timing again. From my experience those symptoms sound exactly like the valve timing is one tooth out

As a rough guide you can check the valve clearances before removing the cylinder head(s). Bent valves will mean large clearances.

Chris.

if the exhaust valves have slipped by a tooth there will be (virtually) no clearance between the bucket & the cam with the engine at the FT_ mark
if you nudge it back (clockwise) a bit & check again, see if the gap opens up before the engine hits FT_
do the same with the rear.
the clearances should be approx 6thou in (.16mm) & 12 thou (.3mm) out.

if you are going to remove the cams to check, it's an idea to mark a line all the way across to make lining up more accurate.
i put tippex on mine then drew a biro line across with a ruler - makes it easier to see, especially the rear exhaust cam, looks like it's bob on but probably isnt/

[sirch345]

Since fitting them though the bike has developed a pooping from the exhaust when I let off the throttle and sometimes a back fire which it didn't have before, the bike still hits red line and runs good apart from this, is this normal on a v twin?
The timing was spot on,

Seeing it only started to pop and bang from the exhaust on the overrun after you replaced the CCT's I would check the valve timing again. From my experience those symptoms sound exactly like the valve timing is one tooth out

I realise it could definitely be a leaky exhaust joint as already been said, so by all means check that first.

If the valve timing is definitely not out and the exhaust is not leaking then I would be inclined to think like Benny, a possible bent valve or two. As a rough guide you can check the valve clearances before removing the cylinder head(s). Bent valves will mean large clearances.

Chris.

Benny Hedges,
By only quoting part of what I posted makes it seem I suggest checking the valve clearances with the valve timing out which I certainly did not. If you look again you'll see I said "If the valve timing is definitely not out " you can then check the valve clearances as a rough guide.

Chris.

[tony.mon]

boys, boys......

Why not just try a compression test?
Easy and quick, & if one cyl's down, then the valves are the main suspect in this case.
If not, check ex system for leak, if not that pop off cam covers and physically check cam timing

[benny hedges]

Benny Hedges,
By only quoting part of what I posted makes it seem I suggest checking the valve clearances with the valve timing out which I certainly did not. If you look again you'll see I said "If the valve timing is definitely not out " you can then check the valve clearances as a rough guide.

Chris.

was just agreeing with you bud, pointing out that if the cam timing has slipped, there probably won't be any valve clearance.
the gear will probably slip until it hits resistance of the valve spring, so there won't be any play.

right what you say about bent valves = big clearance as they won't sit square on the seat or will stick in the guides

hopefully it isn't that like, but even if the valves are bent, it isn't a major major job to put right, and is a good learning exercise for any nooby spannerman imo - sort of like taking your own teeth out for the first time

[sirch345]

Benny Hedges,
By only quoting part of what I posted makes it seem I suggest checking the valve clearances with the valve timing out which I certainly did not. If you look again you'll see I said "If the valve timing is definitely not out " you can then check the valve clearances as a rough guide.

Chris.

was just agreeing with you bud, pointing out that if the cam timing has slipped, there probably won't be any valve clearance.
the gear will probably slip until it hits resistance of the valve spring, so there won't be any play.

right what you say about bent valves = big clearance as they won't sit square on the seat or will stick in the guides

hopefully it isn't that like, but even if the valves are bent, it isn't a major major job to put right, and is a good learning exercise for any nooby spannerman imo - sort of like taking your own teeth out for the first time

OK then Benny I can't argue with that I just didn't think it read like that IMHO. But then anyone who reads it can make up their own mind I guess.

Chris.

[Kenzmad]

Hi guys just letting you know Ive sorted the bike out it was a combination of SMC supplying the wrong plugs and me leaving a pipe off when building back up ooops sorted now though, cheers for all your help

[sirch345]

Hi guys just letting you know Ive sorted the bike out it was a combination of SMC supplying the wrong plugs and me leaving a pipe off when building back up ooops sorted now though, cheers for all your help

I'm pleased too hear you've fixed it Ken Out of interest which pipe did you leave off

Chris.

[Kenzmad]

Yeah I pulled off the air box and there was a little thin pipe some sort of vacum pipe i think down the right hand side of the bike, plugged it back on and it cured it anyway, runs sweet.

[sirch345]

Yeah I pulled off the air box and there was a little thin pipe some sort of vacum pipe i think down the right hand side of the bike, plugged it back on and it cured it anyway, runs sweet.

Ah well at least you find the problem

Chris.