Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Nourish A65 Motor

Thanks Pete for your observations. Youve hit the nail square on it's head mate.
"If you need to turn it back to 28 degrees full advance,you'd still have 8 degrees at idle.
8 degrees at idle is less than ideal,and the engine will run hotter when you're idling in traffic,as compared to 12 or even 20 degrees."

This is the other side of the coin, and I have experience with this, just retarding a standard A65 unit isn't going to give bottom and top end satisfaction. Perhaps a Norton unit then? All contributions gratefully received..

I ran my A65 big bore for years on a no advance mechanism. special oldham drive with outrigger bearing, it ran and started very well. Your project is fascinating, are you going for a clutch outrigger bearing like Mark Parker's?

I think it needs to be realized even though we are talking about timing in degrees the long stroke and different rod ratio effect where the piston is at in the bore. So I think comparing timing degrees to a 74mm stroke motor is not particularly relevant. Doing a heap of dyno runs showed where the timing was most effective with an 89mm stroke and around 10-1 compression with my motor. It doesn't seem to generate an unusual amount of heat idling. I'd be happier with 5 to 7deg adv at idle, because it may start better, but more than that with my old carbs it may be difficult to keep the idle speed down.
The Pazon altair advance curves for twins all seem the same, just set different. Gavin I'd try the ign you have, at least to begin with.
I'm sure you are going to have a lot of fun when you get the thing going.

It's that Nourish thread again! I have some updates to share: Firstly, the hot cam that came with the motor has been sold and I have purchased a spitfire profile 90 deg. job from SRM. The cylinders have come from Germany and I have left the complete engine at Coltec in Hollesley Suffolk, for compression ratio calculations. From the beginning, it was obvious that if a radical ratio was to be avoided, considerable amounts of material would have to be removed from the pistons. This is being done to hopefully result in a 9:1 / 9 1/2:1 ratio. After that, it's all ready to be assembled, with the crank, rods, head, cases, cylinders all ready. Should be 1-2 weeks now.

Good show Gavin!

Why are you aiming for such low cr ? My A10 is quite happy with the 10.5:1 cr. I wouldn`t be afraid of running high cr.
Espeially with that spitfire cam which isn`t exactly small iirc.

Back again folks. Assembled motor is in the bike. All ready to go now, it's just awaiting the ignition. After much debate with "Knowledgeable types", and furrowed brow stroking; I have acted on a C5 kit from Wisconsin. I have fitted a Thunderbolt head with at the mo, a 28mm MK1 Concentric. In part, because it will be easier for me with limited means/time to set up the fuelling. Just to recap, it is a 90mm stroke, 77mm bore 838 motor. The kit has been posted/ will come with four pre programmed "Curves", 30, 32, 34 and 38 full advance figures. What do the panel suggest I start with?

Regards

28deg max is what I'd set it to.

Hi Mark

Thanks. It's what I thought too, but C5 thought it too low . I didn't buy the optional plug in $70 tuning thingy, perhaps later. I'm going to start with 30. Better advanced than retarded as they say.

Exhaust system is interesting. I won an auction for a pair of used Unity TT pipes, which I may fit, or a kind soul has offered a pair of A10 Spitfire high level pipes. Don't think It'll go well with the rearsets I prefer. Just get it running is my priority, so any combination might be fitted later, including my standard siamese or 2 into 2, but without rearsets. Spoilt for choice. I dialled in the cam with a three keyway wheel, and the original timing marks were irrelevant. The kit looks great, just pinpoint exact TDC, and you pick your curve. Getting close now.

When we talk about timing using the C5 ignition (PowerArc based technology) there are two aspects. First is what advance is used at zero rpm and the second is timing at idle.
We usually set timing in the 10-12 degree area at zero rpm with an idle set around 20-22 degrees.

I recently played with my Ural and increased start timing from 10 to 18 in small increments. The engine did NOT start better with more advance but did have a greater tendency to spit back. I went back to 10 degrees.

Timing at higher rpm is set on most engines to 36-39 total advance for street ridden vehicles using readily available pump gas (petrol). This ignition multiple sparks at all rpm and engines respond well to the timing we've set. The system is rpm based and can be adjusted while riding.

NickL I think you may be right about using a single carb. If one piston is halfway down its induction stroke, is the other piston beginning its induction too? Or is the second piston beginning its exhaust? I'm back from a good 80 mile high speed run, and one cylinder is noticably richer than the other.
I am thinking that the first piston's mixture is compromised by the other as it now has to share the fuel halfway down its stroke.

Me thinks the carb is too small for that big a motor. I would aim for a 30 or a 32 mm Concentric on a single carb head.

Are you sure you are not burning a bit of oil on one side?

I'm with Nickl on this one. Go with the twin carb head and get rid of the balance tube (?) Once you get it running right then try the balance tube. Baby steps.

Hey Nick, do you think a balance tube messes up the carburation on a 90deg? I have a balance tube on mine? And it seems ok. I'd probably have to adjust the carbs if I blocked it off, but it might be interesting to see.

I use the balance tube on my 76% also. Dick

Thanks for the replies everyone. What I have is a 30mm Mikuni set up for a 650 BSA, but with the clip at the bottom and a 280 Main, seems to be ok.
With regard to the cam, as its such a torquey motor, I cant see my personal need for hot cam for my riding style, so a Spit profile will do for me.
I do have a twin carb big valve head I bought from a visitor here, but although I prepped it for use, it has had a hard life, and some gorilla has drilled at an angle through one of the studholes, maybe done at the factory: I dont know. This will need further investigation I think as to suitability. It has also been planed to death, and I dont think the carbs would have anything to mate with on the inlets! Its not a big job for me personally to swap heads, and I have another matching Mik, so I think the best bet is buy an un messsed with TC Head.
I am very pleased with the C5 Optical ignition system, it starts 1st or 2nd kick everytime.

Back here to post updates. It now has a T/C head on it and 2 30mm Miks, balanced to perfection. No balance tube, 240 mains, running at 30 Deg full advance. I think I will order the programming kit from C5, just to see what can be achieved with different dialled in curves. Its proving difficult to find time to ride and test it. Really quick compared to anything stock, its more like a Guzzi, but still retains its BSAness when bimbling through towns here. First off, I'm going to 220 mains, as I nearly emptied a tank yesterday, and I only did 70 miles, WTF? I'm getting different signals regarding timing. With the optical kit, (And three sparks per cycle) higher full advance is claimed by the makers, and I can easily switch from 30 to 32, 34 and 38 without buying the programming kit. Visitors here suggest 28, which is not the be-all-and-end-all, but more importantly, its the way it gets there. Any advice greatly appreciated

Programmable ignitions IMHO are the best dollar per dollar mod you can run. They take up the slack of all the other systems combined. Especially if you can set specific timings to specific rpm-s.
I found for me, the best use is in starting rpm on kick only bikes. Set an initial timing of 5-10* BTDC below 300-400 rpm, and the bike kicks like butter. As soon as the rpm hits 400ish advance it to whatever timing it likes 28*-30* whatever.
Same goes for those "hot spots" where the bike tends to detonate. Just roll off the advance thru that range, and re apply it after.
If you like HI rpm, dial the timing into a straight line down toward 0 advance from say 7k to 10k. It will allow the engine to over-rev without grenade-ing. This helps if you break a chain, miss a gear, blow a clutch, climb a mountain, ect.

Fuel mileage is a whole nuther story. Power, and rpm improvements always equal increased fuel consumption. I've taken 60MPg bikes down to 20MPG, and 100MPg two strokes down to 15MPg. It's just the nature of the beast. I would be careful compensating with jetting to increase mileage. Without an O2 sensor installed or an Exhaust gas Temp. gauge you could lead into trouble.
I'm sure you're on to this...

On the other side of the coin, if you ride like an old lady... you might keep some of those miles in the tank. Maybe...

The fuel consumption issue, I have traced to a leak in the fuel tank, (Its 50 yrs old you know), what a bugger, so Ill be replacing that I think with an Indian made one. I hear they are ok. Nah, I've taken it to Sheldrake and Wells, in Ipswich, about 2 miles down the road from my place for repair.

LOL... Where I live, 2 miles gets you to a phone where you can start calling to find a shop.

One issue down... ???to go?

C5 tell me they are waiting for another batch of programming kits, and I am to reserve a place in the queue for a unit $75, plus duty no doubt. Tank should be back tomorrow, so it's off to Cawston, (A 50 mile trip) [Wow}, to have it professionally lined. I have a good painter contact, and the paint code I use is,{For anyone interested} Renault (B12) No 1 Beige Metallic, K1 Aquabase) This will mean more to a paint man I'm sure. Suffice to say, that it is a wonderful old gold, good enough for my UK&General Export 1965 requirement. He did my sidepanels already, and they are exquisite.

Having a blast programming the C5 kit, got a Guzzi curve emailed from Wisconsin, but I will try my own 29 deg. one first.

Here is a Guzzi curve for reference:-