still misfireing

[tattoo]

after fitting new camchain tensioners,checking and rechechecking the timing,fitting new coils,leads,caps,plugs,checking the fuel pipes for twists,cracks,the breathers to make sure their fitted and sealed ok and balancing the carbs the thing is still misfireing on the rear cylinder...i thought all these things would cure it but on taking it for a test run the rear cylinder went off once again....am i missing something coz it's driving me mad.

andi

[warby221]

If you’ve done all the usual tests fuel compression and spark unfortunately you’re in to mechanical problems like sticking valves, blown head gasket, worn rings and worn carb’s especially if it’s only happening on one cylinder.
First thing to do is a compression test and let us know the readings
Hint if the compression is down on the rear put a small amount of heavy gear oil down the bores and retest if the compression go’s up the rings are worn if it stays the same it’s probably something to do with the valves or head gasket. The oil seals the bores for a short time while you do the test

[sirch345]

Hi Andi,
I've just been going through your original post on the valve timing, ( http://www.vtr1000.org/phpBB3/viewtopic ... 70#p146870 ) If it had been missing at around 6,000rpms and above I'd have said it was 180 degrees out, but seeing as you followed the link in your original post that shouldn't be the case.

Seeing as you know it's the rear cylinder that's mis-firing, even though you've tried different coils you could swap over the HT coils (front to rear and vice-versa) and see if the mis-fire transfers to the front cylinder.

If still no joy, if you've not already, check valve clearances and may be a compression check. If still no luck by then it's more than likely to be fuel related IMHO.

Chris.

[tattoo]

hi chris

i'll try swapping them round first thing and do a compression check while i'm under there..i was thinking of changing all the fuel pipes and vacuum pipes for new ones this year to eliminate any fueling or vacuum probs that i may of missed.

are the figures for compression in the workshop manual reliable???

[tony.mon]

Might just be a carb problem.
Could you buy or borrow another set to put on to try?


Re comp readings, yes, the Haynes ones are usually about right, but I find typically that the front cyl gets lower before the rear one. May be due to oil surge under acceleration and wheelies.

[benny hedges]

have you looked at the condition of the carb diaphragms also????
a mate had the same symptoms - bike would tick over ok, but under power would splutter like mad and die on the rear cyl, turned out the diaphragm was split and was hardly lifting the slide...

[sirch345]

hi chris

i'll try swapping them round first thing and do a compression check while i'm under there..i was thinking of changing all the fuel pipes and vacuum pipes for new ones this year to eliminate any fueling or vacuum probs that i may of missed.

are the figures for compression in the workshop manual reliable???

Andi,
I wouldn't worry too much about what the manual says (although as Tony says the Haynes manual figures are pretty good), what's more important is that the readings for each cylinder are both fairly similar to each other.

Can you give us a bit more info on the mis-fire, like when exactly does it happen, or is it there all the time, and at what rev's etc etc

Chris.

[tattoo]

tbh benny i never thort of checking the diaphragms but will do....thanks for that..

if i wheelied the bike i'd be looking for a new bed to sleep in tony as it's the only bike in my collection the misses will get on...a quick call to a mate in morning should get me some spare carbs to try.

thanks for all the advice lads n i'll keep posted on what i find....now the nightshift becons

andi

[tattoo]

Hiya

changed the coils round this morning and the mis-fire moved so fitted the old front coil and the new lead,cap and took it for a quick run round the estate and everythings great...no mis-fire or rear cylinder dieing...it did however feel alittle vibraitey on acceleration,not hesatateing tho just alittle bit of vibration but i'm going thro everything from front to back and top to bottom again to make sure everythings good before i do another carb balance.

i'd like to thank chris,tony.mon,benny and warby221 for all their help and advice...top lads..

andi.

[tony.mon]

No worries, it's easier diagnosing problems over t'internet that working out in the bloody cold.......

You might want to balance carbs again as the misfiring cylinder could have given you a false reading.

[sirch345]

Aw it's nice to be appreciated

Good to know Andi you're making progress in the right direction

As for the extra vibes, as Tony says the carbs will most likely need re-balancing now that it's firing on both cylinders. I would do that first and see if the extra vibes are still there after that,

Chris.