Carb' Issue - ATD's - Ignition timing

[Martyn Goodwin]

Not sure what happened then with my last post so will try again.

I do exactly as what Martyn does except I have set my piston stop which is made from an old spark plug to the actual timing figure I use. That way it can sit in the bikes toolbox and if I need to retime when away from home, you can put the stop in the cylinder, bring the piston up to the stop on the compression stroke and then rotate the mag until the points just open without rotating the engine. You need to lock the atd at full advance ( I use a piece of wood made to fit in the atd). Then tighten the atd nut.
That way you can reset the timing when out on the road without carrying a timing disc. In fact it's the way I do it in the garage as well.

Cheers
Simon

Hey Simon,

Have you been looking in my tool tray? I have a couple of piston stops both made from old spark plugs. And the one in my tool tray is set up for 33 BTDC so I can do "on the road" work, just like you.

Martyn

 

[Howard]

Too much retard !!, so i'll beef up the idling mixture or add a wee bit more weld to the ATD ears?

Sorry, It's my poor English, I meant "retarded too much" not "too much retard" - ie the overall timing needs to be advanced, not the amount of movement in the ATD. Another symptom, when my twin runs retarded the engine gets noticeably much hotter after a short run.
The plug will usually show how the fuel mixture was just before the engine was stopped - probably the pilot jet - that's why you need to do a plug chop at full throttle to check the main jet, but as I said, I'm not confident modern UK fuel gives the same results as good old fashioned leaded petrol.
I'm not sure what carbs you're using, but there are lots of websites explaining how to tune Amals. If adjusting the timing doesn't work check pilot jet, needle position, slide cutaway, fuel level etc. Unless you're on a race track or an Autobahn they're more likely to be the problem than the main jet.

H

 

[bmetcalf]

I have trimmed a short piece of fuel hose to wedge my ATD at full advance. If rebuilding your original unit is needed, an alternative is a new Roy Price one from the Spares Co. They seem to be available again.

 

[nkt267]

This is what overadvancing and a slightly weak mixture can do

 

[cinquecento]

nkt267 , there must have been some indication of that horror coming about, even only if it was only appreciated with hindsight; i hope?

I've followed MartynG's posts withinterst on timing matters. However I think my first step will be to reset points + 2 thou' (from 12) which I believe had been suggested by Sid B' as a quick fix to ascertain if lack of fulladvance wasa problem.

 

[Martyn Goodwin]

nkt267 , there must have been some indication of that horror coming about, even only if it was only appreciated with hindsight; i hope?

I've followed MartynG's posts withinterst on timing matters. However I think my first step will be to reset points + 2 thou' (from 12) which I believe had been suggested by Sid B' as a quick fix to ascertain if lack of fulladvance wasa problem.

Remember, changing the point gap from the recommended 0.012" will have a detrimental effect on magneto efficiency

 

[nkt267]

nkt267 , there must have been some indication of that horror coming about, even only if it was only appreciated with hindsight; i hope?

I had run the bike for about 3000 miles without making any adjustments.The only thing that I know of was Ethanol being added to the fuel.
Also I was running at 70Mph+ 2 up on the dual carriageway and thinking'Who needs a twin'..John

 

[cinquecento]

ouch!

there are rogue mixes that some outlets seem to use, had one where I filled a jerry can which went into a fibreglass tank an 'melted' it where I had no trouble previously and also a unit Triumph where the air slide stuck open when I eventualy managed to strip and clean the carb' it was as if the innards were covered in an acid that were disoving the moving parts.

Back on topic, I credited Big Sid B' with thedea of increasing full advance by opening points gap 2 thou', reading trough Tuning for Speed, Irving actually states this as an option to locate ideal full advance setting.

 

[Howard]

Never credit anyone else, until you've checked with the great man.

When Honda released their oval piston racer PEI wrote in MCN all the technical reasons why it would never win a race. The next week, someone from Honda UK wrote to MCN effectively saying that the old duffer knew nothing and the great god Honda knew what they were doing. I hope he's still choking on his words!

H

 

[Jim Richardson]

A couple of years back I holed a piston, it was a foul day on the motorway, all you could hear was rain and wind. during the rebuild I stripped the carbs and found that the carb on the failed cylinder had blocked, it had only been cleaned out 2 weeks before.
At a rally on the Isle of Wight, 3 of us filled up at a local petrol station, one of us overfilled and the petrol washed the paint from the tank, it didn't react, it was washed away like kiddy poster paint. it set on the chrome panels, back home local fuel wouldn't shift it.
JimR