i've just re-read this whole thread and i'm still none the wiser?
i'm also intrigued as to an approximate timing setting on a 102.
done the test with a strobe light as suggested and was horrified to find nearer 55 degrees of advance. (i'm using a wipac magneto, points set to 0'50mm or 20 thou)
this particular 102 i'm working on is definitely not one for the purists among us (if you get my meaning, its more "experimental" shall we say)
anyhow, charles suggests that most if not all seagulls should fire at somewhere around 23.5 degrees of advance.
i've done the same test on my FV, SJM, SJP,LLS, LS,SD,SDP and pretty much all of them are between 40-50 degrees. ( i can borrow more accurate measuring devices if it helps)
JEREMY suggested that there may have been some difference with leaded fuels compared to modern unleaded fuels, with regards to flame speed or what we are trying to understand as "timing".
i would very much like to talk with our irish seaguller to see if there is anything in this "adjustable baseplate". he seems to be a bit of a "racer" on the quiet to me.
i wonder if these questions would be better directed at the racers on this forum?
my initial findings of 50 degrees (probably closer to 45 degrees) would seem to tally with JEREMY'S . was there something in older fuel that enabled engines to run more advance (and possibly cooler temperatures in the cylinder). when using modern unleaded fuel i've noticed that most of my motors seem to take 3-4 pulls from cold after being stood idle for a few months, is this the affect of unleaded fuel and HUGE ignition advance. as already mentioned, seagulls are relatively low compression engines so dont really need high quality fuel or high octane ratings, or high compression.
i'm sure that JEREMY will concur that when the baseplate is moved closer to tdc, then initial starting of the engine is so much easier at aound 30 degrees (ish)
surely, this is closer to what BS designed in the first place? so why then, when we do this simple ignition test, do we find nearly twice these figures at around 50 degrees of advance, and carrying out basic checks to see if the screw is correctly located in the dimple,(which they are on my motors) then 50 odd degrees seems massive by comparison? i dont get it!
i've had a bit of experience at racing 2 stroke minimotos in the past. usually 46cc water cooled engines, that rev to around 16-18000 rpm.
ignition timing on these is around 14-16 degrees btdc, which would roughly tally with a lot of scooter engines that have been previously mentioned earlier in this post.
i appreciate that a scooter/minimoto engine have considerably higher compression, but even so, both types of engine are still running on un leaded fuel and were originally designed with leaded fuel in mind.
so with that in mind, i'm wondering if we should be talking to some old 2 stroke bikers and ask what modifications they've made to timing and the use of unleaded fuel.
there may be something in this after all? think back to when leaded fuel was being phased out and unleaded fuel was brought in. i can remember there was a big uproar with classic car owners saying their cars would never be able to run on the stuff. 6 months to a year later and we begin to see the arrival of "lead substitute" on the shop shelves in all its guises.
whether or not you believe in the properties of these products, there might just be something that we're not noticing yet.
if any of you guys run classic cars these days then i think its fair to assume that the timing has been retarded slightly to cope with modern fuel, or the cylinder head has been reworked with harder valves.
so, why not "re-adjust" the timing on a seagull, its easy to do.(just like a classic car)
the only slightly difficult thing is making a different dimple position, very carefully drill the crankcase with a small drill bit to mark it first, then remove the baseplate completely to finish the drilling process being careful not to go through to the crank bush, so that you now have 2 positions to put the screw into. why not join up the 2 holes effectively making a slot so you can have fully adjustable timing from tdc to 50 degrees (similar to those funky marston jobbies)
i am now going to try and run some tests on this "experimental" 102 i have and see if there is any real difference between the suggested normal setting of 23.5` and what i think is fairly typical on a lot of other seagulls as nearer 40-50`.
i'm going out on my boat later this month so i will report back.
remember this 102 aint your average 102 if you know what i mean
i'd like to know what some of you "secret racers" do with regards to timing. share the info for the rest of us. i mean, it can't be THAT secret, or can it?
jon