Misc: Everything Else Starting Problem - Series 'C' BIG Single

[Jez Nemeth]

Just doing some maths calcs and getting nowhere accurately...trying to second guess Advance and roughly where it might land through the range. If JR was getting 90bhp (67Kw) from the engine, must have been around 8,000 rpm -so trying to work out the curb on that from start, given that we don't have his cams (Will find that Chap Roy) -and with what I have max would I'm guessing 6500 tops with my set up (to be proved either way). And this being much milder running on petrol rather than dope.

Kind of guessing 4/5 degrees be about right starting, but as pace increases may be more than 34/36 + at top revs.. really need a rev counter methinks and the strobe with degrees marked out on the casing or bolt the timing wheel on the primary pulley more accurately...

Another point -Mal you were dead right, belt was too tight, loosened it and feels better generally -thx for that one.

 

[bmetcalf]

The ATD design limits the max advance. A device that replaced the quill and mounted a degree wheel to allow the crank to get oil while dynamically timing the mag used to be available.

 

[Jez Nemeth]

Being a bit dim here, Q? -what advance do the really big bore V-twins use, or the Big TP/Irving racer's on each cylinder?

Equally, a 1600 harley...but likely all electronic at that size.

 

[greg brillus]

Generally around 4 to 6 degrees retarded for good starting, and 26 full advance........we tried 28 on a single and it would ping........even on 26 if you really tried on a hot day it could be made to ping, so we decided to run it on 95 octane fuel. This with twin plugs, Grosset twin spark ignition, 36 mm Dellorto carby........My racer is 665 cc and runs over 30 deg full advance twin plugs, on methanol fuel........but that is a different story.

 

[Chris Launders]

I had a friend 50 years ago with a BSA A10 and one day I noticed while he was working on it with the timing cover off it had an auto advance unit on it as well as manual control, when I questioned him about it he explained that setting the timing "by the book" was ok but with the manual advance on it he could tweak it "on the road" to get it right under real conditions, then he would retime the auto to that and lock up the manual control.
I'm sure you could arrange something similar to be able to rotate the distributor a little while in use for the same reason.

 

[royrobertson]

My Racer on 11.3 compression, 30 thou squish clearance, twin plug ignition, Terry Prince bathtub heads and 50/50 Esso super/Avgas runs on 24 degs full advance. The advance curve is built into the dual (one for each cylinder) twin plug Interspan total loss ignition systems and because it it roller start where it is retarded is really not that important as long as it STARTS. I think when I strobed it last it was 8 degs. Note racer engines run on full advance nearly all the time. However It does "tickover" at 1000 revs when really it shouldn't as there are no throttle stops in my race 40mm Amal mk 2 smooth bore carbs. However the throttle slides have a small hole drilled in the back which allows just enough air to pass to do the trick.

 

[timetraveller]

Just checking Greg's statement above. Four to six degrees retarded for starting. I think that is (say) four degreed BTC fully retarded for starting?

 

[greg brillus]

Pretty much anything before TDC is needed or else starting will be hard.......The only issue with many of the ignition systems that are available is that the advance curve is usually fixed........so if you retart the timing at full advance then the low speed/starting advance will be moved to the more retarded possition and this is not ideal at all.

 

[Jez Nemeth]

So I'm starting at 4 deg BTDC (retarded) -Advance with present set up in distributor gives 24 deg full Advance... That's sounds like it's all within the boundary and ballpark.

Lots of great info -thank you folx. Gotta be half of what a bored twin gets set at or close as dammit. Twin spark seems a complete must to sort next...

My calcs -and these are guestimates mind you, so big pinch of salt, but one of them returned 5.7 deg starting point as being right for capacity...but with soooo many parameters that can't be accurately be measured easily possibly closer to 4 (+ a smidge) for best starting -seems like running might be good for now, maybe not full blast, but good enough to get down the motorway at a 70 evenly...

Well time to go see! Making some adjustments and with a mate whose kindly offered to spot for me as we give it a 'snag' list shake down and run out on the road, if she'll start (for fellow aussies, I'm not referring to sausages... )

Will be using the small coil from the BTH unit for this one -starts much easier with it, a newer Gel one, suspect with built in ballast too -may not last too long though -not what it was designed for, it'll overheat and fail is the common consensus -12v being pumped through it rather than a trickle feed of a few volts (Be interested to find out what a BTH does actually pump out to it's little coil...gonna put a drill on it and find out now) - they're £15 or less to replace and really easy to get hold of ... not made of money, but.

Stand corrected -11.4 output from the Electronic BTH mean average, but never quite 12V...interesting, should work on kick you'd think??!! Hence weak spark, not enough resistance, general problems of rolling kick-over, pick up speed, back to original issue -"you will start!" Kick-itty-kick, kick, kick....ad infinitum

If I can get to this stag-do camping in Pembroke on it this afternoon that be great (mrs sister is getting hitched)...Barfundle bay hmmmm....

 

[vibrac]

We ran twinsparks on our racing Comet for 2 seasons with BTH coils (old version) we run Tri spark system this season with twin coils on the racer (4 plugs) now on the rolling road its easy to see what settings give the best results. Of course we start the plot with a foxley at meetings