19 or 21 degrees conundrum

[grandpa]

Hi Chaps
I have bought a jet 200 it has a sx200 engine with GP crank the cylinder has the SIL "S" symbol, electronic ignition ,dellorto PHBH26 carb and clubman exhaust.
What should I set the timing to?,SX 19 or GP21.I am in the process of converting it to dc.The timing appeared to be set at 25 degrees.I am using the positive stop method of determining the TDC.The engine starts and runs ok but its not ready yet for the road.
Thanks,
Grandpa

[EddieStone]

I'd go for 21 degrees BTDC. It was explained to me that modern petrol contains a high percentage of ethanol these days that burns much slower than petrol back in the day. Retarding your ignition takes account of this. I think I used 23 degrees on my Li.

Also the ethanol petrol burns at a much higher temperature and the retarded timing helps keep your engine cooler.

[coaster]

I'd go for 21 degrees BTDC. It was explained to me that modern petrol contains a high percentage of ethanol these days that burns much slower than petrol back in the day. Retarding your ignition takes account of this. I think I used 23 degrees on my Li.

Also the ethanol petrol burns at a much higher temperature and the retarded timing helps keep your engine cooler.

I'd drop it to 17 degrees for the same reason, 21 degree way to advanced for today's fuels imho

[Warkton Tornado No.1]

Post by grandpa » Wed Nov 23, 2016 12:02 pm

Hi Chaps
I have bought a jet 200 it has a sx200 engine with GP crank the cylinder has the SIL "S" symbol, electronic ignition ,dellorto PHBH26 carb and clubman exhaust.
What should I set the timing to?,SX 19 or GP21.I am in the process of converting it to dc.The timing appeared to be set at 25 degrees.I am using the positive stop method of determining the TDC.The engine starts and runs ok but its not ready yet for the road.
Thanks,
Grandpa

Since our beloved scooters were designed many years ago, the original blueprint hasn’t been moved on accordingly.

However, knowledge gained means there are two main reasons to retard the ignition from the original recommendation.

• All things being equal, two strokes are fundamentally different to four strokes in needing the ignition retarding as the engine increases in speed as the fuel ‘charge’ becomes a much finer mist, down to molecular level. The consequence is a much greater surface area of those molecules & they need less time to burn. Despite not being a ‘fan’ of the electronic ignition on ‘restorations’, I was a convert to retarding electronic ignitions decades ago for performance motors.

• The petrol available no longer has it’s rated Octane boosted with the addition of lead & the fuel currently available is not as capable in terms of anti-knock (pre-ignition)

Personally, I always run my vehicles on the best fuel available whether petrol or diesel. So that equates to Tesco, Shell or BP Super unleaded for road scooters. I also advocate a large bleed (tailpipe) on the exhaust of Ø25 mm on a 200 to help the engine run cooler & contribute toward any desired over-rev.

From what you say your engine should be in a slightly higher state of tune than standard with its SIL barrel (Stage IV) carburettor & exhaust.

Unfortunately, there is the temptation of retarding too far & the engine loses its pick up through the gears.

I’d aim for the higher figure, but guesstimate you want around 17 - 19°. However, you need to try with your ‘seat-of-your-pants’ dyno to be sure.

I hope this helps & you’re not bored to death....

[Phil D]

Personally, I always run my vehicles on the best fuel available whether petrol or diesel. So that equates to Tesco, Shell or BP Super unleaded for road scooters. I also advocate a large bleed (tailpipe) on the exhaust of Ø25 mm on a 200 to help the engine run cooler & contribute toward any desired over-rev.

Not that it really matters for a two stroke but I have given up using supermarket fuel in our family cars as a guy at work had a nearly new Golf Gti engine wrecked the engineer told my colleague not to use the stuff as he had lost count of the engines he inspected where poor quality fuel was to blame .
There was a case in South Wales where supermarket fuel was to blame(Tesco I think) for wrecking engines.
You pays your money you takes your chance!

[johnnyXS]

I'm with Coaster on this

Firstly ..innocenti never intended their scooters to rev to anything like the revs we take for granted today .For example the Li150 series 3 in standard for reaches peak power at approx 5300rpm which is quite bit less than most modern tunes achieve.
The higher an engine revs the further you need to retard the ignition if you want to avoid pinking detonation overheating siezing and holed pistons .

Secondly the originally recommended advance of 23 degrees was for high octane fuels available back in the 60s typically 105 Ron leaded with zero ethanol or additives.
Todays unleaded fuel is 95 RON or 98 RON premium or super unleaded. There is a huge difference . The higher the octane the greater compression the fuel will withstand , the better the performance and the more ignition advance you can apply .

On Standard Lambrettas with a fixed advance and using todays fuels we need to consider what the max advance can be at peak rpm to avoid these problems.

I run my bog standard LiS 150 at 19 degrees without any overheating problems and good performance but you need to bear lots of other things in mind like the fuel , engine clearances , compression ratio, stage of tune and especially type of use like long extended runs at high revs etc

[Warkton Tornado No.1]

Post by Phil D » Wed Nov 23, 2016 2:29 pm

Personally, I always run my vehicles on the best fuel available whether petrol or diesel. So that equates to Tesco, Shell or BP Super unleaded for road scooters. I also advocate a large bleed (tailpipe) on the exhaust of Ø25 mm on a 200 to help the engine run cooler & contribute toward any desired over-rev.

Not that it really matters for a two stroke but I have given up using supermarket fuel in our family cars as a guy at work had a nearly new Golf Gti engine wrecked the engineer told my colleague not to use the stuff as he had lost count of the engines he inspected where poor quality fuel was to blame .
There was a case in South Wales where supermarket fuel was to blame(Tesco I think) for wrecking engines.
You pays your money you takes your chance!

Phil, I don’t want to upset anybody by getting too far OFF Topic , but I actually agree in the case of diesel fuel (as I found to my cost) when a pump was wrecked whilst being a regular user of Supermarket fuel.

Nowadays, I endeavour to use Shell V power diesel exclusively in my eight year old GM 1.9 TiD engined large estate that has topped 200,000, uses no oil yet delivers close to 50 MPG overall. I was cynical of the likely benefits in paying more, but the engine runs smoother with either BP Ultra or the Shell V Power. The only petrol fuelled objects I have are Lambrettas, lawnmowers, chainsaws, a generator, a blowlamp & a camping stove!

However, back to the point I was trying to make, Tesco Super Unleaded was one of the best as far as Octane the last time I looked into the subject of Petrol. As far as I know, that is the only Supermarket fuel that is worth the risk because I believe it is also stable compared to lesser grades.

My understanding is that the reason that fuel can become a greater liability, if purchased from Supermarkets, is due to the inconsistency of supply & mismanagement of it. Morrisons & Tesco have been implicated in fuel problems & I reason that a station tied in to a brand such as Shell or BP is likely to adhere to greater standards than just achieving profits by pulling shoppers into its stores.

[Phil D]

That's the trouble I guess WT1 it's a bit of a postcode lottery I suppose .
I also remember some fuel related problems on route to and from Kelso this year people were saying fuel may have been bad?
I don't think we are too far off topic Fuel /ignition are all related

I admit I am slightly biased against Tesco having spent too many needless hours waiting with containers being very slowly unloaded . Doh wandered off topic!

[grandpa]

Hi chaps
Thanks for all your replies I have seen 17 , 19 and 21 mentioned.Sticky's book seems to lean towards 19 .I have never used supermarket fuel only BP super unleaded in the scoots
Thanks for your advice
Grandpa

[CHRIS in MARGATE]

It was total folly to think there was ever any advantage or performance gain in using 105 octane petrol. Our beloved engines were designed to run on cheap petrol. Sadly that "cheap" petrol equates to what is now our dearest petrol which is available as 97 octane from BP Texaco Shell. Forget Tesco momentum 98 which is overloaded with additives. Lead plays no part in our conundrum and filling the tank with lead pellets is again, another folly. Lead was there to protect the valves and seatings on 4 stroke engines.
19 degrees is as far as I would ever retard on a statically timed standard or lightly tuned engine but I would want to see and record the timing point right through to maximum rpm.
A lot of these figures ( there are exceptions from trusted posters on here) come from people whose mate told them so, without any rationale and that is what they swear by.
Use a good timing disc, good TDC tool and strobe right through the rev range.
For me, 17 degrees is overkill and 6 degrees back from where it once was.
I am always open to change but show me quantifiable evidence first not just guesstimates.

[MickYork]

Personally I would try it at 17. If it runs ok then it's problem solved.......if it doesn't knock it back to 18 and keep going till you feel comfortable. If it's getting too high (19+) maybe start looking at an advance/retard unit.

[Warkton Tornado No.1]

Post by CHRIS in MARGATE » Wed Nov 23, 2016 8:25 pm

It was total folly to think there was ever any advantage or performance gain in using 105 octane petrol. Our beloved engines were designed to run on cheap petrol. Sadly that "cheap" petrol equates to what is now our dearest petrol which is available as 97 octane from BP Texaco Shell. Forget Tesco momentum 98 which is overloaded with additives. Lead plays no part in our conundrum and filling the tank with lead pellets is again, another folly. Lead was there to protect the valves and seatings on 4 stroke engines.
19 degrees is as far as I would ever retard on a statically timed standard or lightly tuned engine but I would want to see and record the timing point right through to maximum rpm.
A lot of these figures ( there are exceptions from trusted posters on here) come from people whose mate told them so, without any rationale and that is what they swear by.
Use a good timing disc, good TDC tool and strobe right through the rev range.
For me, 17 degrees is overkill and 6 degrees back from where it once was.
I am always open to change but show me quantifiable evidence first not just guesstimates.

Chris. All fuels have additives.

How you can seem to be so certain that Tesco's is any worse than others, I do not know.

I mean no offence, but perhaps you have more information to back up your claim.

I remain open-minded & before responding to your comment, I looked on-line to see if there was anything that indicates it might be detrimental to 'our' engines. I couldn't find anything that is relative to two strokes.

However, it was some time ago that I learnt of the Tesco Momentum 99 from Charlie Edmonds & I believe that he is still held with some high regard.

[sunrisemac]

Lead was there to protect the valves and seatings on 4 stroke engines.

I am pretty sure that lead in petrol was primarily to help prevent engine knock and boost octane rating to slow down burn of fuel when ignition occurs, the protection afforded to the valve seats was more of a bonus.

[Dazts1]

I read an interesting article a couple of years back in a ford pulication. Owning an old ford I read with intrest. All high octane petrols were tested by running a car up on the rolling road. Car then drained of fuel , refilled and run up again until all brands of fuel was tested. The fuel that came out on top was indeed Tesco's momentum. At the time I found it hard to believe, but it seems to keep coming out on top.

[Warkton Tornado No.1]

Post by Dazts1 » Wed Nov 23, 2016 10:06 pm

I read an interesting article a couple of years back in a ford pulication. Owning an old ford I read with intrest. All high octane petrols were tested by running a car up on the rolling road. Car then drained of fuel , refilled and run up again until all brands of fuel was tested. The fuel that came out on top was indeed Tesco's momentum. At the time I found it hard to believe, but it seems to keep coming out on top.

There are many aspects to fuel.

For instance, I think you race Group Four, Daz, so undoubtedly use Avgas.

That will be primarily because it enables you to run no fan with some safety margin, as the engine runs cooler. You also run a programmed ignition to keep the engine @ optimum through it’s fuelling/rev range.

However, those with adequate, water cooled engines have the added option of using Super Unleaded that will release more power than Avgas.

So, its ‘horses for courses’ & there is loads to commend Super Unleaded of the available pump fuels. Again, an on-line search will show that there is definitely more power for the taking if the engine is able to take advantage.

Grandpa doesn’t have a bog-standard engine which is why I brought it up.

I think most of us are singing from the same hymn sheet....

[coaster]

Super Unleaded may be the 'preferred' fuel of choice but if you plan to tour on you scooter you need to set the engine up to be comfortable with lesser fuels especially if contemplating trips into Europe. That would be my main reason for setting static at 17.

[CHRIS in MARGATE]

"Tesco Momentum", I read either on a forum or from "my mate down the pub" has given rise to an unusually high level of complaints (now I am one of those who heard it from a mate !!!). I was going to start using it this year but I did indeed read of its additional additives on the internet and this was supported by one of the big motoring organisations; I will try to find it.
Timing, timing, timing. When I do engine work for anybody, I always record a short video clip of the strobing and send it to them. I take photographs of everything so people can see that I am actually inside and can show them worn or broken parts. Why? Satisfaction, pride, ego. Anyway my point being that 19 degrees on standard or lightly tuned engines is what I am comfortable with and stand by. Doesn't mean I'm right and all else are wrong or vice versa but I don't recall personally seeing or ever seeing evidence from any other party that setting ignition to 19 or even 21 has caused a top end failure. Most disasters that I have seen have been caused by poor carburetion rather than timing set beyond 17 degrees.
Evidence is what we need m'lud; evidence.
Kind regards to all posters on this thread.
Chris

[CHRIS in MARGATE]

From one of the Petrol head forums.

You will not notice a performance problem with Tesco's 99 RON unleaded. Badged as 'Tesco Momentum 99. But the fuel itself is a basic 95 RON unleaded fuel laced with bioethanol to a maximum of 5% by mass. Ethanol is very good at inhibiting pre-ignition as it does raise the Research Octane Number of the fuel to which it is added. Tesco's petrol is produced by Greenergy. Or, at least, most of it is.

Read more at: http://www.torquecars.com/forums/thread ... uel.15673/ - © TorqueCars.com

Still just opinions I'm afraid.

[HxPaul]

From one of the Petrol head forums.

You will not notice a performance problem with Tesco's 99 RON unleaded. Badged as 'Tesco Momentum 99. But the fuel itself is a basic 95 RON unleaded fuel laced with bioethanol to a maximum of 5% by mass. Ethanol is very good at inhibiting pre-ignition as it does raise the Research Octane Number of the fuel to which it is added. Tesco's petrol is produced by Greenergy. Or, at least, most of it is.

Read more at: http://www.torquecars.com/forums/thread ... uel.15673/ - © TorqueCars.com

Still just opinions I'm afraid.

I always use Sainsbury's 95 when I fill up,unless I'm away from home,then I use any petrol station I can find but I still fill up with 95,and even then I fill my tank at Sainsbury's before I set off.Someone once said on this forum that they filled up with 95 because very few people use 97 and therefore you dont know how long its been standing in the tanks at the petrol station,so any ethanol added to the petrol has longer to attract moisture.I might add that I've been filling up with 95 for about ten years without any problem.By the way,I have static 12v ignition and I always set the timing at 17 degrees BTDC.

[EddieStone]

I'd go for 21 degrees BTDC. It was explained to me that modern petrol contains a high percentage of ethanol these days that burns much slower than petrol back in the day. Retarding your ignition takes account of this. I think I used 23 degrees on my Li.

Also the ethanol petrol burns at a much higher temperature and the retarded timing helps keep your engine cooler.

What was I thinking,? I meant 19 degrees. Mine's at 19, not 23. It used to be 23 back in the day and it's still my default figure. I'll delete the post to avoid confusion.