Gripper timing

[tztwofifty]

Anyone know the timing setting for a 1984 250 gripper tr80? (** edit 1984 doh **)

Found this for older models, is it near enough?

Thanks guys..

Edited July 14, 2018 by tztwofifty
oops

[section swept]

Setting at 3mm btdc would not do any harm as a starting point, but the manufacturers specs must be around some where! Not too sure if your Gripper may have electronic ign. Fairly convinced it’ll be on contacts breakers so go with 2.8mm btdc for zappy pick up or 3.25mm btdc for a bit less go and a softer engine??‍??

Edited July 15, 2018 by section swept

[tztwofifty]

Thanks for that, didn't imagine it would be far out... it's electronic ignition on this one. 

[cleanorbust]

6 hours ago, section swept said:

Setting at 3mm btdc would not do any harm as a starting point, but the manufacturers specs must be around some where! Not too sure if your Gripper may have electronic ign. Fairly convinced it’ll be on contacts breakers so go with 2.8mm btdc for zappy pick up or 3.25mm btdc for a bit less go and a softer engine??‍??

T'other way round. Advance the timing for more pep.

[section swept]

1 hour ago, cleanorbust said:

T'other way round. Advance the timing for more pep.

Fraid not, advance means to spark earlier ie 3.00mm btdc as opposed to 2mm btdc and retard spark later...closer to tdc?

[cleanorbust]

4 hours ago, section swept said:

Fraid not, advance means to spark earlier ie 3.00mm btdc as opposed to 2mm btdc and retard spark later...closer to tdc?

I know. Your earlier message suggested the advanced setting (3.25mm. btdc) would give a softer response. It's the retarded setting which would do that. Hence, t'other way round.

Edited July 15, 2018 by cleanorbust

[section swept]

23 hours ago, cleanorbust said:

I know. Your earlier message suggested the advanced setting (3.25mm. btdc) would give a softer response. It's the retarded setting which would do that. Hence, t'other way round.

I’ll mention a famous name... Miller, he told me that setting the timing at 3.25mm btdc would soften the engine performance and reduce any tendency to start up and run backwards...very embarrassing! Having spent a very long time on ‘t’ shop floor on the tools and then ended up teaching others about the suck,squeeze, bang, blow process et al. I have to say that with a two stroke that has no advance or retard map, mechanism, or vacuum device to alter timing as stated should produce a slightly softer engine as opposed to one set at 2.8 mm btdc. I used this setting on my 325 Sherpa and it was indeed softer or docile if you will, compared with another 325 that was very peppy and much easier to loft the front wheel....and it would start and run backwards...usually into a tree, with rider cursing vociferously! Timing on that beast was 2.8mm and I use these examples to help our man with his 250 Ossa Gripper. That timing was easy to remember ‘325’. I dare say our man with the Gripper will go with 2.7mm or there about. This concludes today’s sermon, ?‍??

[tztwofifty]

Have set it at 3.0mm will see how it goes..

Thanks for the input guys

Cheers, John

[cleanorbust]

5 hours ago, section swept said:

I’ll mention a famous name... Miller, he told me that setting the timing at 3.25mm btdc would soften the engine performance and reduce any tendency to start up and run backwards...very embarrassing! Having spent a very long time on ‘t’ shop floor on the tools and then ended up teaching others about the suck,squeeze, bang, blow process et al. I have to say that with a two stroke that has no advance or retard map, mechanism, or vacuum device to alter timing as stated should produce a slightly softer engine as opposed to one set at 2.8 mm btdc. I used this setting on my 325 Sherpa and it was indeed softer or docile if you will, compared with another 325 that was very peppy and much easier to loft the front wheel....and it would start and run backwards...usually into a tree, with rider cursing vociferously! Timing on that beast was 2.8mm and I use these examples to help our man with his 250 Ossa Gripper. That timing was easy to remember ‘325’. I dare say our man with the Gripper will go with 2.7mm or there about. This concludes today’s sermon, ?‍??

...but it's over-advance which induces a motor to run backwards, n'est-ce pas? So how come advancing it reduced such occurrences?

Fantics were the most common in catching out their unwary riders in my personal experience. You'd reach the head of a queue, release the clutch and cause mayhem behind.

 

 

[section swept]

19 minutes ago, cleanorbust said:

...but it's over-advance which induces a motor to run backwards, n'est-ce pas? So how come advancing it reduced such occurrences?

Fantics were the most common in catching out their unwary riders in my personal experience. You'd reach the head of a queue, release the clutch and cause mayhem behind.

 

 

Advance means the spark occurs earlier, retard means it happens closer to tdc. So advancing the spark in terms of crank rotation means it happens at for example 10 degrees btdc, advancing further the spark could occur at 20 degrees btdc....retard the spark and you move back closer to tbc.

[copemech]

guys, retarding, or setting timing closer to tdc, will allow a motor to rev out higher and mitigates kick back on starting, yet there is a reduction in response at low revs yielding smoother power application.

[cleanorbust]

7 hours ago, section swept said:

Advance means the spark occurs earlier, retard means it happens closer to tdc. So advancing the spark in terms of crank rotation means it happens at for example 10 degrees btdc, advancing further the spark could occur at 20 degrees btdc....retard the spark and you move back closer to tbc.

Yes, I know. 3.25 is advanced relative to 2.8. We covered that. My question was how advancing the timing would reduce running backwards, when it's over advance that causes it.

Advance timing for more pep, retard it for softer response, as copemech says.

Edited July 17, 2018 by cleanorbust

[section swept]

2 hours ago, cleanorbust said:

Yes, I know. 3.25 is advanced relative to 2.8. We covered that. My question was how advancing the timing would reduce running backwards, when it's over advance that causes it.

Advance timing for more pep, retard it for softer response, as copemech says.

The closer the timing to top dead centre the more likely the engine is to start and run backwards. Advancing the ignition point to say 4mm before top dead centre ( occurring earlier) reduces or eliminated this. Retard ( move ignition point closer to top dead centre and there is a more noticeable kick back and a likelihood of the engine running in reverse. Petrol burns at the same rate irrespective of piston and crankshaft speed/ revolutions so starting the burning ( ignition ) sooner before the piston reaches top dead centre allows the engine to make better use of the fuel. Retard the ignition point ( move it nearer to top dead centre ) and the piston may  have gone over top dead centre before complete burning has started. That’s why with a mechanical advance the ignition moves away from top dead centre or the original timing point so then at say 5000 rpm the ignition might be occurring at 15+ degrees btdc. So on a relatively slow running two stroke with fixed timing ( no means of advance or retardation) the closer to top dead centre the ignition the more  initial throttle response the harsher or peppier the engine responds. The closer to the tdc position that the ignition is set means that although the Kickstarter spins the engine in the correct direction of rotation any tardiness in the operators kick may just allow the engine to start in reverse. I can see the point that you are making and was aware of that at the start, ignition advance potentially causing reverse running. Let’s face it we are talking about some really old engine design with very basic ignitions...just large lawn mower engines...even they now have a simple advance and retard map in their electronic ignition systems. Let’s just let our man with the Gripper which has leccy ignition experiment for himself, not sure if that has an ignition curve map. Hey it’s been interesting discussing with you this topic, just out of interest I run a Sherpa 250 with the ignition set at the manufacturers spec of 2.8 mm btdc, but with the vagueness of the contact breakers wear with the heel rubbing against the flywheel ignition cam ( felt pad oiled...high melting point grease on inside of heel....polished cam) after a few hours running the timing will possibly have gone off due to wear and the points closing up a little. More maintenance/ tuning but easier to fix if a fault develops. Your Sherco 200 will be running leccy ignition? ??

[cleanorbust]

Yes, the Sherco has electronic ignition but since owning that I moved on to a 280 Scorpa, where it's possible to tweak the timing by moving the backplate. I run it a bit retarded for that soft, sloggy feel to suit old fashioned riding style.

I also ride a 247 Cota, the very one I bought new in the 70s. Interestingly the recommended timing figure for that model changed from 4.0 to 2.5 mm btdc at some point in the 1970s, though there were no apparent changes to the bike/motor itself.

I've always liked the adjustability and cheap repair options of points systems.

Edited July 17, 2018 by cleanorbust

[section swept]

7 hours ago, cleanorbust said:

Yes, the Sherco has electronic ignition but since owning that I moved on to a 280 Scorpa, where it's possible to tweak the timing by moving the backplate. I run it a bit retarded for that soft, sloggy feel to suit old fashioned riding style.

I also ride a 247 Cota, the very one I bought new in the 70s. Interestingly the recommended timing figure for that model changed from 4.0 to 2.5 mm btdc at some point in the 1970s, though there were no apparent changes to the bike/motor itself.

I've always liked the adjustability and cheap repair options of points systems.

Me to as I said, miles from any where and a dead ignition is not funny but with CB ignition at least you stand a chance of sorting it....until it starts to get dark and you haven’t got a torch??