550 breaking down intermitant

[duzatun]

hey lads
   need help with  a problem had for long time when riding every now n then engine seems to start breaking down usually when give her a bit of throttle might happen twice on one ride might not happen for a few rides if i give it a fair bitt of throttle it will cough and splutter but comes out of it seems to be happening more regular.
bike has 4 into one ex
pod filters
jetted up to 105 or 110 if i remember correctly dont seem to have a problem winding her out to high rpm,s normally
I have checked and cleaned out tank
replaced fuel line
tried spare set of carbs
tried spare set of coils
put in new regulator and rectifier
new batt
new condensors and points
 checked earth
looking at replacing wire loom
but this one has got me baffled any ideas

[z1100r]

 Errm .. explain a bit more about what is happening. More detail please.
Which of these For example:-
1) your cruising along at 50-60mph and open the throttle and it coughs and splutters and doesn't want to go
2) You've been flat out accelerating no problem but when you slow down its erratic
3) Cruising along just fine for 10 mins then for no reason at all it reverts to missing and rough running.
4) Ticks over fine but as soon as you touch the throttle it falters.
5) Lots of popping and banging in exhaust on overrun.

Which carbs have you got..push in or screw in mainjets...?? Both are drastically affected by removing the airbox but the screw in ones more so. Those airboxes are very resrictive and the carbs need richening up alot - over the entire rev range -  when it is removed.  Changing the main jet only affects thrash mode. I would say you are too lean on needles, primary, and air screw. I couldn't fix mine perfectly without a lambda sensor in the exhaust.

From what you said its an erratic breakdown of something....its fine for ages and then plays up and wont go back to normal without you give it a good thrashing.....just like my missus.

[K2-K6]

Have you swapped the plugs to see if it's the same and what colour do they run when it's warmed up on a runout?

[duzatun]

well the missing is completely intermittant it might do it warm or when i first get on it sometimes and then doesnt do it at all for a few  rides when its not playing up the motor seems good through all the rev range. seems to be happening more often over the last couple of months. Normally happens when im just cruising then give it a bit of throttle and it acts like its running out of fuel and if i dont give it a good throttle on it won't come out of it for a long time. When i 1st  put the pods on i jetted it up then a had to lift the main needle one notch and adjust the pilots, synced the carbs took a while tinkering to get it running good. ive rebuilt a few sohc,s over the years but never had this prob before have tried new plugs number three has always been a little darker on the plug that could be a number of things nothing major i hope . ive pretty much eliminated fuel delivery problem i think and been inclined to think maybe electrical eg  have tried another set of coils with the same result. so maybe power to one of the coils. electrical can be hard to diagnose with out correct equipment, as you said (just like our women) chuckle
the carbs are screw in main jets

[z1100r]

 Well it sounds like you know what you are doing and have tried all the obvious things.

     Dodgy kill switch or ignition switch...? or something else that may interupt the 12v supply to the ignition system....??

[K2-K6]

As Z110r says you seem to have covered the obvious and know what to look for, you could do some simple tests along his suggested topics of kill switch etc by when it happens again stop and switch it off with the kill switch then operate the switch a few times, restart and see if it has any effect, then do the same with the ignition barrel swicth if no change.

You can run with a wire direct from battery pos to coil to elimniate loom faults but you'll have no emergency switch-off while doing it so make a join you can pull out if you do.

Old trick but useful, take off tank and run motor in pitch darkness (tarp over you and bike can be useful) you'll be able to see any HT leaks that could be there and crossing to earth.

Check cylinder psi to make sure that's eliminated.

[andy_c101]

K2-K6 could be on the right track.
I had a previous bike, and only when i was working in the last few minutes of daylight did I notice blue sparks jumping from plug cap to cylinderhead. It turned out to be the plug cap; the internal spring clip, that clips onto the plug, was badly corroded and cracked.

[duzatun]

thanks for all the feedback lads
 as i did try another set of coils with their own caps didnt think it could be caps but im goint to check this out anyway you never know the remote possabilities that the other set being second hand could have a faulty cap stranger things have happened.
 and will check out the kill switch and a direct pos wire to coil never thought of that.
If the problem was their all the time it would be easier to find but as it does it intermitant makes it harder
 some times when its happened ive gone straight home so i can check it out but by the time i get home has stopped playing up.
One of those problems when i find it i will never forget these symptoms in the future.
 I will report back on tests i do
cheers

[K2-K6]

Sporadic problems are always difficult to find out as you don't really know what you've done to make them stop so can't absolutely pin it down straight away.

It's just possible if the HT leads are leaking at all then if the same age it could be on both sets, more than possible with the overall age of these things I guess.

I was unable to diagnose an RD250 that didn't run and we went through most things with no success so someone else had a look at it and changed the fuel as a last resort, bingo straight away it started then the owner told me he'd put something like 50p of diesel into the tank wrongly before then adding petrol, it started and drove home but when cold it just wouldn't fire, you have to try and cover off almost everything to get there sometmes!!

It'll be interesting when you get it sorted to see what it was.

[metalcatfish]

This might seem a bit weird but here goes anyway. In running similar setup but with 130 main jets. Fuelling is spot on. However do get horrid misfire in a cross wind.
I spoke to an old british bike expert and he reckons I was right thinking a cross wind would affect the fuelling. I know its weird, but I can run straight on a road with high hedges either side in the fens hit a patch of road with a break in the hedges or open motorway, add in some good cross wind and hey presto, runs like sh*t!

[z1100r]

Thats not weird at all.... I could be cruising down the motorway freezing and wet with my water prrof trousers on and the bike would run shit. I put it down to the rain for ages.....one day on long trip I opend my legs wide and dangled one down for a stretch and the bike surged forward. I thought funnnnny ..what happened then, i eperimented a bit..I could sit there and open my legs and the bike would pick up. My baggy wet trousers were somehow reducing airflow under the seat is all I could put it down to...!!!

[HondaFour]

Ho!Ho! Someones pulling the proverbial