problem 750L, total headf*k

[richyrich]

Im having a nightmare trying to get my bike started, ive written a few things in diff posts and had some helpful feedback.  Today ive run out of ideas so im starting this thread and putting all the details together in the hope you guys can help.

back in 2004 i had trouble starting a 750L so i put in new piston rings, that raised compression from 100 odd to 120 plus, but it still wouldnt start, i tried new plugs wih it then moved on and put it away.  Later on i got a gs550 with a b6 enigne andn running gear, worked lovely for years.  Last year i put the 750 in, it worked once, i cant remember what if aythign was different that time.   Ive just come back to it.

im using a 100 amp hour car battery to spin it over.  Starting with compression of 120, 100, 50, 120. i got nothing turning it over, so i swapped the old green dyna coils for the bandit ones.  It coughed and spluttered trying to fire.  so i took out the motor, removed the head and lapped in the exhaust valves. Put it all back together and it doesnt even try and fire.  I had both cams 1 tooth out with the arrows pointing horizontal and not at the gasket , so sorted that out and moved a couple shims. 

COMPRESSION:  now it turns over and compression of 135, 140, 150, 135. valve clearances in spec.  If the valve timing was wrong it would not have these numbers, the valves are opening and closing fully in the right order.   With the way these engines work that has to be right ? I got it wrong once now its right.  If id eg mixed up the cams or was tripping looking at the arrow marks or whatever, it wouldnt turn over or have compression im pretty sure

SPark:  Ive tried two pairs of coils, both have reistsance within spec as far as i can tell.  Ive put new 5kohm plug caps on the bandit leads to replace the original 11kohm ones thinking it might give a better spark.  Bar the old, but barely used plugs ( ive got eight cr9 eks so far) , what can be wrong with the HT system ?  It sparks away happily, something should go bang, it should at least try and fire surely...

FUEL:  The bst 38 has a bad reputation in my research for running wthout its airbox, some people get them working.  Today i put on the b6 keihin 32mm carbs that used to run quite happily with pod filters.  The tank petcock  is flowing well also.   Still no attempt to fire

its not fucking magic, its an engine, its science, its got good fuel, good compression, its got a spark, hard to say if its a good one its not orange its bright bluey white.  Perhaps its not happening at the right time ? so what controls that ? i thought with this engine theres no control over the ignition timing with stock parts.

So to my tiny mind, theres three things. 1 the intake valves somehow.  2, the loom ive puled about to fit it in, but it wouldnt even spark or turn over or have lights if id shorted and fucked it somehow.  3. the spark is at the wrong time!

Thats the spinny thing on the right, how can that be wrong,  its the original 750 one, with the original 750 Loom, and a replacement 750 cdi. theres no witness mark of it being filed down i can see. Maybe its mounted wrong, i havent checked, is that possible ?

what the effing hell is going on

 

 

[matt]

Hi, sounds like one of those very frustrating problems.

The ignition rotor on the end of the crank should locate on a pin, so there is only one way it can be fitted.

As long as you rotate the crank so that the marks on the rotor line up with the pickups and then check the camshaft positions, the timing will be correct.

if you are getting a spark at the plugs and fuel into the engine, have you double checked that you have the HT leads going to the correct cylinders? Or if the leads are correct, that the coils are connected up to the right wires? If not then you may have the plugs sparking 180 degrees out on all cylinders. I've done that, not much happens:)

Hope that helps.

Matt.

[richyrich]

I double check that every time i look at the damned thing.

I remembered its not the original loom,  i think its an american b12 one cos it has a pink wire which i saw somewhere is for a fuel gauge. 

If it is that one and ive plugged the 750l ignition into it, is there the hotwire resistor thingy fucking it up?

Maybe i should just change out the loom, wtf.

Its also got a koso speedo-tacho wired up to the remains of the old instrument loom. Not using the supplied scotxhlocks. Its all gotta come out again, thinking out loud

[Captain Chaos]

B12 loom with the 750L ignition lock doesn't work, or you have to put a resistor somewhere (don't know exactly where).

 

[fatblokeonbandit]

there is an anti theft resistor in the base of the bandit ignition barell, it wont go without it, I have one here you can borrow to try if you are stuck,

[Solcambs]

21 hours ago, fatblokeonbandit said:

there is an anti theft resistor in the base of the bandit ignition barell, it wont go without it, I have one here you can borrow to try if you are stuck,

I was going to say the same thing ... IIRC (from the recess of my mind) the CDI expects to see a certain voltage across a wire - otherwise it won't fire. Then again I'm getting old and often confuse different  bikes and projects from the past!

 

This may be of use

http://www.customfighters.com/forums/showthread.php?t=10718

http://www.svrider.com/forum/showthread.php?t=101738

I'd suspect that you need to stick a resistor into the circuit to get 100 Ohm measurement across the wires going to the CDI.

Edited December 16, 2016 by Solcambs

[richyrich]

thanks for the replies guys.  I really appreciate the offer fatblokeinbandit, its been a bit low round here with this mystery going on.  You and capnchaos both agree that 750L ignition key unit pluged into b12 loom wont work,  i wil look into this and try to figure out how that is.  Meantime ive found a workshop that  seems keen and has pic of a gsx1100 streetfighter on the webpage cover, they do mots and welding etc.  Ive got faith they know these bikes and won try and sell me a new one.    So with any luck it'll puzzle them and then i can step in to solve the problem hehe

[richyrich]

good one solcambs that is a mindfeckin inspiration.  Im just gonna ditch the goddam key now. Hell im gonna start work on a wireless loom.  Bloody resistors. thief proof chldproof bkes goddam owner proof grumbl grumble

[fatblokeonbandit]

Why not just plug a bandit switch into the bandit loom and try it, would take 10 seconds..then you would know that the ignition circuit is correct??

[Swiss Toni]

It can't be the ignition switch that's at fault, surely? It's a Bandit loom with a non- Bandit  switch.  And you're getting a spark! Proves the switch isn't the culprit?

Edited December 16, 2016 by Swiss Toni

[richyrich]

well Toni that was  my initial thinking so thanks for the input and your totally right FBOBandit but ive given the sodding thing to a bikeshop now.  In fact the dude from the new bikeshop just called and he was like "started right up wassa problm"  !!!!

So credit were credit is due; CAPNCHAOS said " just put new plugs in" and sure enough all new bike shop said it'd done is put in new plugs.  G*d*m M8th(u*RS   eretceterea and so on and so forth...

i am hanging head in shame ein the moments betwen dancing manically and necking stellas.  So sorry for getting everyone excited i have been banging head ont wall over this for tiiiiime,  i appreciate the ideas guys

people who've looked at it before have said get new plugs but ive got 8 friggin plugs with zero miles on em and i just cant believe it wouldnt even pop and bag and try to fire, i cant find a good explanation of why zero miles plugs can be fecked by cranking ot over ????    

still here we are the man said it runs. i might even relax and start to believe...

mot next week, gs back on the road woohoo

[fatblokeonbandit]

NGK's in oily engines are notorious, get them soaked in petrol and they just give up

 

glad its sorted shipmate

[Madb]

A problem shared = bike on the the road. Yippee! Pleased for ya. Have a good Christmas.  

Edited December 16, 2016 by Madb
Missed words

[Swiss Toni]

That's why it's called...Electrickery! Life's a bitch..,and sometimes you marry one! 

[richyrich]

The conclusion to that chapter was actually a little more nuanced than just the plugs.  Id noticed it was constantly overfueling, which i puzzled over alot, Turns out the float valves werent sealing, the needles were not long enough to sit in the valve seats.  i dont want to mention how i managed to mix up two different old and new sets of float valve parts to achieve this mismatch