1962 650ss Build

You might need x-ray vision to look through the float bowl cover and throttle body casting to determine where it is leaking from.

Did these carburetors ever work on any motorcycle, or are they part of a used bike purchase? Could have been ruined by a previous owner using drill bits or who knows what after getting some interweb tuning advice.

If the float needle seat and float needle are matched, and everything is installed correctly, it looks like the only thing that could prevent the float from forcing the float needle up into the needle seat is the tickler rod not returning all the way up. Tickler spring too weak or a sticky tickler. Of course, there might be fuel dribbling out of the top of the tickler if that were the case. Not sure though. Never played much with a monobloc. The two brit bikes I had with a monobloc never gave me carburetor trouble.

If you can, turn your manifolds over so the balance tube loop is on top. It will tend to end up with a little residual fuel in it if it is on the bottom. Not a cure for your issue at all, just a better arrangement of the balance tube. If it is already on top fuel staying in it is miraculous.

Good point Schwany, who knows how good the carbs are if original/used. I fought with original matched sets of 389’s with chopped bloc and a 389/689 set on the Atlas. I got sick of chasing idles and sticking slides that I just spend the money and buy new Amals focusing on getting it solid and not just good enough to run.

Hi, have been somewhat following this, so forgive me if I am off...

You know the little perspex float bowl covers you can get?


Might this help? Just to see if/why it's flooding?

Love the bike and the build. My own 1961 650 Std now sucks through a 928 concentric, no complaints.

ES2 still on a monbloc tho, cheers

Andy

Finally caved. Purchased new 376's from Hitchcocks. They had 2 sets of these in stock. Ordered Sunday evening and they arrived at my place Wednesday evening.

After replacing every piece on the old carbs, and trying every which combination they just weren't holding the fuel. Either it was flooding through the pilot, or through the jet block, or leaking from the fittings at the bottom.

As was mentioned a post or so ago, I do not know the story with the carbs that came with this bike. I'm guessing they're original, but really have no idea what their story is.

The new ones . . . unreal. Cannot believe how well the slides fit. The sound they make when they close on spring is like a sword being unsheathed in some old Ninja film. Also the tightness of the jet block in the carb body, my christ. Fit is perfect and snug at all the fittings.

Long story short. Hopefully this gets me onto the next phase of dialing this bike in. I've got the same factory jetting for the 650ss. Figured will start there. Also removed the choke slides, and filled with the blanking plug.

These will hopefully be fit on the bike tomorrow morning. Also, I know its been mentioned loads, the new carbs come *with* the fibre washer fit under the float needle seat, and in the event the carbs are of new production that washer should be retained? Or removed?

Can't keep straight which is which.

If anyone needs any spare parts for the 376 let me know. I literally have 2 sets of everything.

Very nice.

Yes, fiber washer under seat.

Don’t get discouraged if they leak a bit. Just tighten a little, no ham fisting, and the seals will come around. Seems they need to heat cycle some.

kernel65 said:

Very nice.

Yes, fiber washer under seat.

Don’t get discouraged if they leak a bit. Just tighten a little, no ham fisting, and the seals will come around. Seems they need to heat cycle some.

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Thanks, and good call. Will post back. Hopefully a video of me cruising at 60mph on a nice country road.

Do the new 376s come with anodized slides like the Premieres have?

Glen

New carbs are NICE things.

I do often think that we expect WAY to much out of 50-60-70 year old instruments like these. Manufacturers and designers would find it hilarious that folk were using them in such ways after such time, and on bikes / set ups they were never designed for, running fuels they were never designed for !

worntorn said:

Do the new 376s come with anodized slides like the Premieres have?

Glen

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No. But they do look like a better quality metal than the originals. That being said, they've not seen fuel yet either.

Fast Eddie said:

New carbs are NICE things.

I do often think that we expect WAY to much out of 50-60-70 year old instruments like these. Manufacturers and designers would find it hilarious that folk were using them in such ways after such time, and on bikes / set ups they were never designed for, running fuels they were never designed for !

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Also well said. Tell tale sign should have been "60yr old motorcycle. Put away in a corner 30yrs ago when someone blew up the motor racing it"

This is true
Phil Irving stayed with a friend in Vancouver in the 1980s. Phil commented that he and Phil Vincent designed the Vincent motorcycle to last ten years.
He was shocked that so many were still in use in 1982, about 30 years from new and at 3x life expectancy.
Now we've used them for another forty years.
I'm planning a 3000 mile trip to California (International Rally) next year on my 76 year old half million mile Vincent next year.
Similar things are done with other old British Marques.
Did the Brits build good products in the 40s-60s?
They sure did!

Glen

Wise decision to cave in and buy the new carburetors. They look fantastico.

Enjoy the ride.

Haha. Of course.

New carbs fitted. Cables run. Fuel on. Small leak on the bottom of the chopped carb, but I think its coming from the banjo and could just be a hair tighter. I'll pull these, as I want to shorten the fuel line between the two banjos anyway.

tickle carbs. many kicks. nada. one pop. tickle again. flooded. gonna let it dry out, and will approach tomorrow. Noticed again a bit of fuel in that balance tube, so, pretty confident its just flooded. Will let it dry out overnight and retry tomorrow.



I've been thinking back other adjustments that I've made between when it was starting easily, and where it is now.

1. I lowered the top yoke approx 1.5". I did this because I felt the front end was a bit too high, and the center stand not really taking on the weight of the bike. Would there be an instance in doing this where the inlet tract of the manifold is now pitched too far forwards? And fuel is rolling into the manifolds and or the balance tubes?

2. I removed the screens that I had fitted onto the velocity stacks. I did this when I was thinking that it was too restricted by the screens. I'm going to experiment tomorrow or the next few days with refitting the screens to see if it makes any difference.

3. Lastly, is there an instance where the clutch plate would be too tight or too loose? Would this have any effect at all on starting? With the bike in gear I cannot roll the bike forwards or backwards. So I'm confident that the clutch plates are of good tightness. As a side, this bike has the Newby belt drive, and I'm setting the springs to the suggested turn level in the "instructions." I've also balanced the plate with dial indicator so that it's run true.

1. The way the carbs are mounted on the down-draught head, excess fuel is going to drain into the inlet track.

2. Don’t think this would be a big factor, but could be missing something?

3. Not familiar with the Newby belt drive. If you can pull the clutch and kick through free and the way you describe not being able to push the bike over compression with belt tension as prescribed I would say you’re good.


Are you setting up the carbs as recommended by Amal (air screw 1.5 turns out, etc.)? Haven’t had a bike fail to start without something else the cause.

I’d be tempted to relook at timing/spark, valve clearance.

How much gas is in the crankcase?

Sounds like the flooding you describe is simply that, ‘normal’ flooding rather than faulty carbs.

As mentioned above, with carbs mounted in a downdraught fashion, and manual float bowl flooding, it is going to lead to fuel making its way into the engine.

Maybe it’s your flooding technique? Maybe flooding too much?

You need to be careful as fuel entering the engine in this way can cause ‘petrol wash’ whereby the pistons and bores get washed clean of oil, leading to obvious issues… I know cuz I dunnit.

Hi
You mentioned you lowered the top fork yokes 1.5" why? If the original stanchions were the correct ones than you have just increased the angle the Monoblocs are set at, increasing flooding issues?
1.5" lower screams out to me that something is wrong or was not right with the original stanchions on the bike?
In lowering the front by 1.5" it would seem to me that riding the bike you would feel like you would be falling over the front wheel?
Get back to the to the original Norton specs, set up as per the manual. I did this with my 1963 650 SS and it is first kick every time, although I have a Pazon CDI ignition system fitted to the crankshaft, rather than run the magneto, just because it was cheaper than rebuilding the magneto, I left the shell of the magneto in place for originality.
Only problem with the Amals was the float levels, no flooding but rich running at idle.
Burgs

Burgs said:

Hi
You mentioned you lowered the top fork yokes 1.5" why? If the original stanchions were the correct ones than you have just increased the angle the Monoblocs are set at, increasing flooding issues?
1.5" lower screams out to me that something is wrong or was not right with the original stanchions on the bike?
In lowering the front by 1.5" it would seem to me that riding the bike you would feel like you would be falling over the front wheel?
Get back to the to the original Norton specs, set up as per the manual. I did this with my 1963 650 SS and it is first kick every time, although I have a Pazon CDI ignition system fitted to the crankshaft, rather than run the magneto, just because it was cheaper than rebuilding the magneto, I left the shell of the magneto in place for originality.
Only problem with the Amals was the float levels, no flooding but rich running at idle.
Burgs

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They're not the original stanchions. They're 35mm Ceriani GP forks with the Minnovation Racing triples.

@FastEddie - I think you're right in that I'm flooding too much with the tickler. Also, well said about washing the bores. Makes sense that this would happen. I'm going to drain the sump today and see how much oil is in there as well. Plugs didn't smell of gas, and or weren't wet last night when I pulled them. And I only had the fuel on for a little bit.

@kernel65 Yes, carbs were checked and set to the recommended spec before fitting. Also blew out all the jets with compressed air, and checked to make sure that everything was correct size wise, and that was sufficiently tight. I've checked the points gap on the mag and looks to be in order. Also
checked to make sure that I have decent spark.

Dropping the yokes down 1.5" on the stanchion tubes won't make any difference with the carburetion. If the floats are set to spec it won't flood anymore than it would riding downhill, which is not at all. Your geometry will change and the handling may be a little bit twitchier.

I would use the Norton stock spec for jetting initially. If using a racer's spec out of a 3rd party book for what should be done for racing, you may end up chasing your tail for a while.

It takes a lot of fuel to wash the cylinders entirely of oil. Fuel has to get past the compression rings and wash out the oil rings. Otherwise, every time the piston rises and falls the oil rings will leave some oil behind in the bore. More than likely all that is happening is you are fuel fouling the plugs. Washing the cylinders to the point of engine destruction is certainly possible just not that common.

I know putting the balance tube on the bottom of the intake manifolds is what Norton did with all the straight up motors. My guess is they did that so that users would have easy access to the intake valve cover, but it is better to put the balance tube on top of the manifolds. Particularly if it is a clear tube and you don't want to see any fuel in it. I also think it performs better on top, because it stays clear of fuel.

Petrol wash doesn’t mean ‘Washing the cylinders entirely of oil’.

See piston below, front face is perfect, rear face looks like it’s seized solid !

Consensus of opinion on this was petrol wash. A hypothesis supported by the fact that I later found the float needle housing leaking on this side only.

So petrol wash can happen, and this is what it can look like:

Fast Eddie said:

So petrol wash can happen, and this is what it can look like:

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Guess I misunderstood. I believe it happens although I had a drastic cylinder wash image in my head when I read that. Fuel in the sump and all that jazz. Looks very unfriendly to the piston.

I've never had it happen on any motor I've built, or if I have had it happen it was not severe enough to tear down a motor. I only tear them down when the bottom end takes a poop or I want to try a different engine configuration. Well, that's not true. I did have an out of round overbore done by some genius and that seized a piston, but that was a 2 stroke and a million years ago.

I was trying to be less gloom and doom about the situation, and I didn't think Sean was having float needle issues with the new carburetors. I suppose I could be wrong about that, but it seems less likely than it was with the older carburetors.

Kind of surprised it did not start right up.