WILL RUN WITHOUT #4

[willrcr15]

Don't under estimate the importance of the inlet housing O ring, we have never ending issues with a few bikes of different sizes & the one common issue is that O ring, such a simple fix that is easily overlooked.

[Timbo]

Exhaust system swapped out yet?   
Still beleive you could have a restriction there......

[Jonesy :-)]

Hey Steptoe
Have you done a plug chop at max achievable revs to see if the plug is lean? might support Mal's theory of inlet manifold leaking with velocity and maybe also what rasputin might be hinting at?
oh, I just read your last post again....too late you've already replaced suspect manifold.

[rasputin]

I did one time have a valve timing issue that presented as yours does. It had more to do with the actual cam (timing/clearances) as that was off, but when combined with an intake leak all bets were off. Might have to check for an intake leak.

[steptoe]

top end fixed, ran it , no difference
pulled the carbs, all good, no blocked holes, all 8 floats at EXACTLY 25.7 mm
have replaced number 4 intake manifold just because and removed and resealed all others, {while I had the chance}

haven,t reassembled or run, ran out of time, next days off

Xtian,, our illustrious godfather seems to think all things are beginning to point to tyre pressures, will check next chance I get

[steptoe]

I actually got to spend a couple of hours on her today.
------ started with a stone motherless cold compression test, 180 psi {dry}, no issues there,, valve seats, rings or head gasket
------ bloody cam lobes are perfect,,, was dissapointed, but it,s a good thing I suppose
------ valve clearances checked --- all in or on clearance tolerance except 4 ------ intake was .08 at least half what it should be, have fixed that now
------ I did also notice {and I,ve no idea how I missed this step} but the cam sprokets are 180 degrees arse about face, {you do know there are timing marks on them too right} well I missed it, will have to change that before the top goes back on, there goes the change 1 thing theory
------ might get to it tomorrow but time constraints may not allow but will change pipes next and see

all plug threads are original

[Timbo]

Trying times indeed, my money's on one of these Steppie, the way you say it won't rev past 5K indicates to me perhaps lack of compression (That's OK) or your prefabricated exhaust system/ baffled system could have closed up or simaler. Swap out the system and see what happens.
Or perhaps air box not seated correctly? Ignition timing and vacuum advance correct? While you have the lid off for the valve clearances, check the valve timing, long shot but worth checking.
Keep us posted....

[Jonesy :-)]

Just some more rambling that may or may not be relevant to your situation.
On the posty bike and being very noticeable being a single when carby played up and not having other cylinders to help and half disguise a problem.

Main jet had a little burr or flap that would restrict the mighty 110cc donk from revving out, would idle and run fine at lower revs and partial throttle, but when you opened the throttle fully it would stumble and not rev out
Running oxy tip cleaner through the jet would sort of move the burr/flap out of the way but not remove it, this would cure it for a while until the burr/flap would close over again. Ended up replacing carby, (wasn't much more expensive than buying a jet) and now the sheep cant get away from the mighty 110 posty.
Helpful? probly not, but sounds like similar problem.

[excess.11]

You didn t say if the plug thread in the head had been helicoiled.....or...if the spark observed is with the plug resting on the head....or....via the colourtune plug.........can you watch the spark via the colourtune plug while you rev it in the problem area of revs ?
Can you check you have the correct polarity to the primary connections on the affected coil ....don t assume...........actually test it.

[steptoe]

---Jeff, the plugs are anti sieze free, a drop of oil to stop threads picking up is all
---jonesy, pipes are aftermarket with my baffling system, Mal P did mention pipes so that will also be on the agenda, I do have a very good mates spare pipes in the roof I,ll throw on and see
----carbs were running fine on the shed bike to set up, so I know they,re good
---- did forget to put in that the plug is sparking the same as the others
---- have also discounted advance wiring and canister

[Jonesy :-)]

something blocking or partly #4 header, try another set of pipes, do your pipes still have the double skin original headers, seen it happen in an industrial situation where inner skin of a double skin pipe collapsed, blocked pipe. may or may not be your situation, clutching at straws i know.......
did you try a different set of carbs, or your carbs on another bike
The above seem to be the only things common to that cylinder you haven't mentioned changing.
The electrics on these bikes do some crazy s4it. my old, now new xs wouldnt start when cold until I pulled No:1 spark plug out, would crank all day without firing until I did so. ended up doing a harness transplant to cure it. hopefully you'll stumble on the cause of your problem without going to such extremes.

[excess.11]

Geoff...could the thread in the cylinder head of # 4 be insulated by someone adding antiseize of some sort of threadseal....or has it been helicoiled ?

[steptoe]

This will probably have to be read a couple of times to get the jist of whats going on
since the second wellington rally the red bike {81 RH} hasn,t wanted to rev/run past 5000rpm, pulls like a train up to but won,t go over, it also has a stumble between 2000---2500

over the last few days off I,ve started investimigating and have so far found bugga all,  let me begin by saying it,s not carbs, freshly rebuilt with filters and i can change the colour of flame with colour tune, rules out carb issues
------ pulling the spark plug caps off one at a time I discover #4 is not firing, swap 3 and 4 plug, still number 4
------ change plug cap, still  4
------ change the  coil feed wires and plug leads, still number 4,,, coils ok
------ change tci box, twice, still 4
------ check compression, all reading with in cooee of each other, no riding valve
------ bypassed harness from tci to coils with new wire, still 4
------ replaced coils completely, still 4
----- even added an extra earth straight from the coil mount bolt to battery, no change

so it,s not electrical
------- could be intake manifold sealing but all air fuel mix screws are very close to each other, unless all 4 are leaking a little, highly unlikely
------- have done the airo-start spray without a change, as Mal P said maybe its got to get some velocity behind it to make it leak
------- timing ?? doubt it  because even without 4 cap on it runs sweet over 3000rpm

so my next days on it will include swapping intakes, going inside and checking cam lobe hieghts, generally pulling shit apart I didn,t want to pull apart
partly why I,ve been a bit quiet,, can,t get mine going so how can I offer advice to anyone else