poor running!?

[noidea]

Hey,
After doing some work to my engine and putting it back together its not quite running right, it seems to have intermittant power...?
Its just rideable, but when riding it is lacking alot of power. Intermitantly how ever it will running 'right' and be powerful and run well, but only for a short period of time. For instant had it pinned in 2nd and was just thinking, what can be wrong. All of a sudden it started running 'right' and lifted the front wheel, i kicked it into 3rd and it just died again.

Its still got small flames coming out the exhaust if i work the throttle for it, which leads me to think the charge is not combusting properly, leaving the head then the next cycle and charge will ignite, which then ignited the unignited charge from the previous cycle that has now entered the exhaust pipe.

I have cleaned the carby.
Cam timing IS spot on.
Do have spark, but i cant tell if its intermittant.
Im pretty sure valve clearances are right.
Have tried a spare CDI, no change.

This list leaves me mainly focusing on the ignition system, possible a problem with the magneto, coil, or wiring. Yet intermittant power does not seem to be the result of a loose or bare wire as it is not bump related etc.

I have got a spare coil, i will try that next.

This has got me puzzled, any assistance, ideas, possibilities or experiences would be very useful!

Edward

 

[Mack]

If your still getting flames I am inclined to think the exhaust valve is not seating correctly. I have had this happen before. If the valve job was not performed correctly or the valve guide has burs or a piece of metal up inside the guide, the valve can stick when setting the clearance, fooling you into thinking it is right because you have clearance, when in actual fact it is being held very slightly open. It will not hurt to set a very excessive clearance on the exhaust to see if under compression it is forced into its seat and runs better. I know I have harped on this possibility but I have had problems of this nature before. The springs are very weak in these motors and wont force the spring to its seat correctly for setting clearance if things arent exact.

 

[noidea]

Alright ill try and open up the gap to say 6 or 7 thou, exhaust valve is in a shitty place tho lol.

Thing with the valve is that it wouldnt really explain the intermittance, unless its sticking and every now and then sealing properly. Or spining and not sealing at one angle, but it is at another.

I didnt get a fresh valve cut on this head coz i was careful not to touch the seats ($80 quote for seat cut and do wonders for dremel precision lol).

Do you think it might be spark related or am i flying off on a unrelated tangent?

Ill get another vid now that its runing a little better.

Keep the relpys coming, im almost all out of ideas!

Edward

 

[noidea]

Ok,

tried spare coil - no difference
did a compression test - 100psi (dont think i was getting full seal either) so i guess that rules out a sticking/ not sealing exhaust valve?

Ive taken another vid, ill get it hosted and hot link it later tonite.

Edward

 

[Mack]

Thats a very low compression figure.

 

[noidea]

I dont think the seal i was getting was good. Hard holding a press type tester while kicking it over. Ill get a helper tomoro..

what sort of figure should i be expecting? (ive 'relieved' the valves a little, remember)

 

[Stellerlicious]

the compression shuld be geting at least 130 - 150 psi
(i think)

 

[noidea]

ok, vids up http://www.youtube.com/watch?v=eDDR6098ZQk (cheers cruzen)... sound and image arent in sync... mainly listen to it (it sucks you cant see throttle position but you get the jist of what it sounds like)

At full throttle and max revs you can hear the intermittance thru the revs fluctuating.

any ideas guyz?

 

[noidea]

update:

got new plug today. Ran semi good for a while (more frequent power). Pulled the plug and its real black.

Its running super rich.

Carby issues i think.

 

[Cruzen]

ooo so u did do what i said ay... lol

 

[noidea]

which was?

 

[Cruzen]

eh dw, i said get a new spark plug ..

 

[noidea]

good advice, but didnt solve my prob.

Tried a spare carby today, ran exactly the same!

I did notice it was firing out the carby tho, which suggests a timing issue either spark (wasnt very powerful blow out so i guess this) or valve timing, which i have spot on unless the flywheel is one rotation out, but it shouldnt matter... should it?


I guess what ive got left to try is take the timing gear off, spin the flywheel one rotation and bolt it all back together.

I can hear a bit of a ticking noise, sounds to me like valve lash... so hopefully nothing serious.

any ideas? Am i heading the in the right direction?

 

[younggun]

you sure by elimanating possible things u will eventullay find out what it is lol

 

[RD RACING]

this will give you some lessons in modifying 4 stroke engines, reliable when stock and a pain when modded. your ignition timing / coil ect is the fault.

 

[noidea]

yea, just spent 30 mins ruling out valve timing.

Must have damaged the magneto or something like that. Ive got a spare so ill whip it off tomoro and see how its goes.

so much for chinese simplicity lol.


Few more things to cross off the list,

Valve gap, both have clearance over the TDC period and both valves open and close as they shud (no sticking etc)

valve timing, spot on, tried it in 3 diff positions, no change at all to the running...


This f* up has gotten personal now lol, my sanity is at stake now.

either i get it running soon, or its going off a headland in flames! (d/w will have vid cam if its the latter)

 

[mjc85]

Could be you didn't put the carby back together properly, double check.
Could be a bad spark plug, dodgy connection in wiring harness, magneto could be shot and on the way out.

Start with the simplest ie. spark plug, wiring harness or coil as you already have a spare then keep eliminating things its not hard to figure as the bikes are relatively simple with only a few parts

 

[noidea]

Have tried 3 different spark plugs, its not them.

Have tried a spare coil, no change (diff coil means diff ignition lead also)

Its not the carby, i borrowed a friends and put it on mine. His bike was running 5 mins before i put it on with that carb so def not that.


Ive only really got wiring and magneto to go. Ive wiggled most of the connections for no change so im leaning towards magneto or pickup as the failure.

any1 know if a magneto from a ducar will fit a loncin?

keep the ideas coming, im almost all out!

Edward

 

[noidea]

Im all out now.

Tried a new stator today... no change at all!!!

to date i have ruled out the whole electrical system (bar wiring... but its not bump related intermittance so wiring is unlikely)

Compression

Carby/fuel system

Ive checked the valve timing at least 5 times. But ill have another look tomoro....


any ideas guyz? Its almost time to take the engine, sum beers and a jerry can to the nearest cliff...

 

[Linc]

It sounds like an inlet manifold or exhaust leak. Maybe even head gasket.

When you changed over the carbies did you change the manifold as well?. Do it up bookoo tight against the head. Same goes for the exhaust. Check there is not a hair line fracture.....especially check around the exhaust manifold.

Other than that I'm stuped. Hope it helps.