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What am I doing wrong?

Submitted by pete_sykes on Wed, 30/03/2022
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Heavy Twins

The engine is rebuilt, The reason is long and complex and starts with bits of piston ring in the sump,  found when investigating why so much oil was coming out the breather. The ring was obviously broken on assembly as the bores were fine. I got away with new rings and a hone, and new shells and a polish. 

It won't start, if I hold the throttle wide open it'll cough a bit and give up after  few revs. 

So far, I've checked my timing. The cam chain marks have 10 roller spacings, the timing marks are aligned as thay should be. With the engine rotated backwards 32deg the magneto is set to just open as it rotates forwards (where forwards means the direction it rotates when runing although that is "backwards" compared to engine rotation). The carb is cleaned ( carb cleaner not a bath) and the jets look clear, the float bowl is filling and the float valve behaves.  The throttle and choke slides go up and down and the pilot air screw is 1.5 turns out. The plugs are new B6ES

But, all I can get is a wuff - wuff- wuff die.

Where do I go next?

Thanks

 

Pete Sykes

 

 

 

Submitted by paul_standeven on Wed, 30/03/2022

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First, do you have sparks at all?  Remove the plugs, insert in the HT caps and place them on the motor for earth. Kick the bike - do the plugs light up?

It may be grandmother-and-eggs department, but did you set the timing on full advance?  Do the plugs fire on compression?  It is rather easy to have the plugs fire on the wrong TDC.  If you are confident that the timing is in fact correct, try swapping the HT leads over. 

It is also possible that your plugs have fouled, due to fuel going in and not being ignited.  Bear it in mind that modern plugs are designed for computer-controlled fuel injected systems, and are no longer glazed to a standard we used to expect. They are much more prone to fouling with an over-rich mixture.  BTW the pilot mixtures are probably a bit rich at 1.5 turns out on the screw.

Also check the kill button lead.  It is possible that it has a short somewhere, leaving your magneto permanently earthed.  Take the wire off the points cap and see if that makes a difference. 

I am running NGK B6ES in my '55 Dominator, and have no issues with them - but they are NOS mid '80s plugs, and therefore MUCH better than current ones.

Paul

Thanks for the quick reply

I have sparks. I have fitted an oil tap, with a magneto cut out cap attached and a kill button My multimeter tells me all works, and kicking with plugs out and oil off has no spark. ( Oil on, I get sparks) but tomorrow I'll put back the old cap with the kill button to check.

I had the timing full advanced on setting, and I took out the wedge to hold it there.  I've also tried swapping the leads, but I was  careful to make sure as I timed it that I followed the instructions to have the cam timing marks at the top and the heel of the  points  follower at the bottom. Plugs are new, but the old ones don't work either. 

Pete

 

Submitted by neil_wyatt on Wed, 30/03/2022

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There are a lot of duff N*K plugs about and have been for years.

Never had a bad Champion yet. (N5 for 88 and 99's and N4 for a 650) you didn't say which.

Mag end cap is a possible cause as are the pick ups, there are some dodgy ones about.

Is fuel getting to the plugs?

Good luck.

Submitted by robert_tuck on Thu, 31/03/2022

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Just really repeating what the guys have said,  N5 would be a good choice  , are the plugs getting wet  ( shows fuel is being delivered) ? . If not try a teaspoon of fuel in each plug hole, or a squirt in the carb .If that gets it firing up then the issue is fuel. Much easier to sort once you have eliminated something.

Submitted by philip_hannam1 on Thu, 31/03/2022

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Woof Woof die ........is generally a sign that the ignition has been set too retarded. The engine fires but then as the rotation speed increases, the Advance /Retard mechanism pushes the sparking point past  even TDC.  This is a common problem among the electronic ignition owners who have set their Dominator engines to a Commando Ignition Point by mistake.

Check your ignition firing point when the A/R is fully open. make sure that all the chunks are turning clockwise when viewed from the points end of the Magneto.

Also re-check the Timing Sprocket positions as well as the Crankshaft to Intermediate Gear Timing marks.

Submitted by harry_atkinson on Thu, 31/03/2022

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Hi All

I had a similar issue with my 99. Sparks but engine would not run. It finally traced back to some duff pick-up brushes that were too soft and 'smeared' carbon residue right round the slip ring. They are easy to identify as they have a flat bottom and look dullish. The 'good' ones have a radiused bottom and are shinier.

To get rid of the 'smear' pull off the top pick-up and insert a petrol soaked rag wrapped round a pencil into the hole so the rag is in firm contact with the slipring. Rotate the engine and keep going until the rag looks clean(ish).

Submitted by pete_sykes on Thu, 31/03/2022

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I checked the timing last night  and I also checked I took out the wedge for the A/R and yes, I took it clockwise looking at the points end to just where the contacts open with the motor on a degree disk saying 32deg. 

So far tonight, I've checked I really did remove that wedge (yes)  and the A/R does move, a bit sluggish not exactly snapping back but it goes back. 

I've  put the old push button points cap back on  instead of the one linked to the oil tap - no effect

I do see a fair bit of blow back through the carb  but I double checked the cam timing  last night too and tonight  I looked at the tappets  again which are fine and valves open and close as I'd expect. 

I'll give it a day or so to clear the memory of how I did it, then restart  with both veloce press and haynes books wide open 

Thanks

 

Pete

 

Submitted by ian_hay on Tue, 19/04/2022

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Phillip,  I'm puzzled as to how an AR unit can further retard an incorrectly timed engine. Surely an AR unit can only advance the ignition.

Yes, it advances the ignition normally  - but remember its wedged open  to full advance as you time the engine so remove the wedge and you've retarded it.

The wuff wuff die symptom fits this - kick it quick enough and you may get the advance to twitch enough to get  a spark that isn't quite late enought to be useless (wuff)  which gives just enough to get it round again (wuff)  before it gives up (die). 

Anyhow it ran in the  garage before I went on holiday and now I'm back it needs to be out on the road

 

 

Submitted by pete_sykes on Sun, 03/04/2022

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Its a runner

I'd better admit it -  timing is beforeTDC.  How many times did I convince myself to get it wrong. The  key is to leave it a while  then go back and go Doh!

 

Submitted by stephen_hampson on Mon, 04/04/2022

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Hi 

Can any one tell me if the fork sprigs on my dominator should be the same length as the stantions

Thanks 

Steve

 

 



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