misfire above 5000 rpm

After breaking in my Commando 850 for 1000 km, it makes troubles. I could rev it with ease up 6500 rpm with 800 km. Suddenly it won't pull above 5000. I have really bad misfires, it pulls strong up to 5, then it get worse. Valve lash is checked, minimal adjustment was required, carbs are cleaned again, fuel level is setted to 2mm below, jets are stock, the whole engine ist stock, except the lower cylinder base gasket ( none ) and a boyer ignition. Carbs are synchronized also the cables so the airblades are parallel.
Is there some trouble with broken valve springs? Ignition is completly new. I have mounted a second pair of spark plugs for safety.

Thanks a lot and have a nice day
Marco

i had a similar issue, sorted removing the air filter... just an idea

Try this idea. Turn on BOTH gas taps then go for a rip.

If it pulled to 6500 prior and nothing changed in carb like jets falling out or float bowl loose or gasket manifold failure, then I'd go directly to electrics and ignition. The 5000 mark is a magic number associated with Boyer and I've had that power wall hit me right at 4900/5000, no more power to pull further unless most the load removed by down hill or lower gearing, still lost its pull at 5000. Boyer wires and cam chain slack combined in my case. Hope that's all yours is too.
Must always change plugs out as once mis-fires begins, as it can be d/t plugs themselves or the once good plugs are now fouled by the mis-fires from other causes, but continue the symptoms even after the first caused solved, but no help mysterisously. We should all by plugs in V8 packs, NKG usually better chance of good ones out the box than Champions. I've had Champions on two occassions be show stoppers on just replacing old still functional plugs, till I put back the old ones to get to store to get non-Champion V8 pack. Always worth while to start at night and tug and poke probe and rev watching for tiny flashes of shorting wires.

After Breaking In my Commanndo FOR 1000 Kilometers . Gees I Hate Metrics . 1000 Km is the dont go past 1/3 throttle for a conservative olde farte .

The old original chrome rings would take 2000 MILES to seat and get ZERO oil consumption . The Faster you run it in , The faster you run it out . :shock: :cry: :evil:

Wheres my . . . . .

O.K. , missfire could be just a less than firm spade connection in the ignition circuits , presumeing the slides dont rattle with a fingertip in the throat .

I THINK YOUR MOTORCYCLE IS TRYING TO TELL YOU SOMETHING . I shouldve murdered the snot I let ride the Comando who came back " I did 80 mph "
AS the cam seating process at that milage meant I HADNT , and wouldnt , on the 23 T sprocket .

With some mechanical marvel of anglo saxon origins , or otherwise , you can ordinarilly feel how free its running .
A Chrysler I had that had been one owner , 70.000 miles , 80 Yr old , baulked at 60 mph as itd never been over it .
Sympathetic light load variation of thoootle and gear speeds loosed it of over six months to a natural 80 mph gait .

Theyre all in a rush these days , take it easy . The old hand on the cylinder to note temperatures and so on .
ASSUMEING the jettings not lean , running in out of town or not sitting at traffic lights , is considered saner .
A race track & progressively upping operational parameters whilst checking / retouqueig ( tappets after ) gets
things done in a more controlled way . :lol:

The olde git who tested Commanndos at MIRA , development bikes against the Honda mule said '' they were found '
to be faster , better handling , and more economical that the 750 four . The disc was developed to counter its only
advantage .

Theyed lap at a ton for a hour & come in and refuel , and a mechanic would CHECK TUNE . The Honda was left rattling on its sidestand for the 5 / 10 minute stops . :lol: :shock: 8)
Opinion was the Honda was a 100.000 mile grenade . ( its shelf life at that type of operation ) .MAINTAINED , the Commando was better . And it didnt rust . Drip drip drip .

IF youre useing it hard ( run in in 1000 k's :? ) keep it all dialed in , to a T . please .

Ha ha ha Matt, keeping a Commando in good tune is sorta like keepping an old wood frame piano in tune or a sail boats trim lines. Rough running though can cause a cascade of faults all the way down to the crank bearings. Break in should be rather abrupt and vigorous to seat rings quick as can and keep oil wedge on vital cam and lifter surfaces. Shut down after first minute of reving to let cool so rings don't smear/burnish the bore texture, then repeat on longer intervals of a few minutes a go over 2000 rpm. Then change oil and ride it varing throttle but trying to keep rpm up for oil wedge, then re-torque, again, all the engine fasteners including the sideways bolts though cases. After about 20-30 min of this should be read to race on with what ever ring sealing left soon done too. BTW its good idea to flush gear box rebuild oil after fairly short time too.

I don't think think my breakin methods are the point of the problem. Fact is, a flat tappet cam need a brake in for 15 minutes with a minimum of 2000 rpm, proper installing with cam lube is recommended! Running at idle is very bad for a flat tappet, the oil flow is less. I opened my Chryler 440 this week, it survived the same brake in method :wink: . I will strenghten the block with a girdle and run now a roller cam. Everthing else stays in place.
http://www.youtube.com/watch?NR=1&featu ... 0CRdmafjHA

After a first break in of two times 15 minutes and cool down, the commando gets a new filter and oil. Checked valve play and carb settings.

The first i have done was to fill up the gas tank, second was the carb settings controlled and plugs replaced. I'll focus on the boyer ( 600 mls ).
Maybe i try the dyno, there is one located near my village.

Greetings
Marco

Yea , just saying ' one ' can go " half throttle @ 1.000 miles & full at 2.000 on a protracted run in , if ' we ' are aiming to get 20 years out of it .

Chrysler 440 mightnt fit in the C'do frame to well , dang . A real car , anyway . Story Time , etc etc . BOYER . ARGH . That Explains it !! ? :shock:
maybe .
Wonder if with the lost spark a spare lead would shoow the spark voltage ( colour ) Mostly here the trobles related to battery state . low battery turns it to mush .

A fe Commandos had 6 Volt coils with ballast resistor . If you dont park it overnight in 6 ft. of snow , Id consider 12 Volt.The differance is about the same as with the lighting .

Still be wary of other than intermittant full throttle operation at low miles , below 1500 . these antiques are of a era beyond the present.Though Spitfires ( R R Merlin )
didnt exactly get treated with kid gloves on the service evaluation requirement test flights ( pre relese ) , the odd one went BANG .Takeing it easy if its alldone right gets a
degree of work hardening / truth / stabilisation that may not necesarilly be achieved gung ho & hard out .

Only on one occasion was he forced to bale out, when the engine of his Spitfire exploded. Henshaw was thrown out of the aircraft by the blast and became entangled in his parachute

Because the Tempest V increases speed so rapidly in the dive, it is not difficult to enter compressibility range at high altitudes (approaching speed of sound). This can only be done in a dive. The maximum permissible airspeeds at various heights are :





I.A.S.

Height



370

30,000



410

25,000



450

20,000



490

15,000



540

10,000

And things of that nature . :lol: Might pay to see the brakes work . No changeing into second at the ton to slow down , it can have similar effects . :? :wink: Wheresaa pictureoff the motorsicle, please .

Hey Marco,
have you checked the Timing,?
If your happy nothing has changed with the Carbs, or fuel lines,
I'd go for the timing light,.. just to be sure it hasn't slipped a bit.
What do the plugs look like at 5,000 revs and 3/4 throttle.
AC.