Carburation issue

EstuaryBoy · Mar 23, 2022

I used chromed brass from Surrey Cycles with good results many moons ago, though current consensus appears to suggest variable quality control across different suppliers...

Tom P · Mar 23, 2022

Has anyone had any experience with the current crop of chrome plated brass slides from RGM?

Fast Eddie · Mar 23, 2022

Chromed brass definitely have a nicer feel, maybe cos they’re more slippery or maybe cos they’re heavier, either way they seem to snap shut nicer IMHO.

A ring in your cold start seal isn’t an issue per se, but it is indicative of being old and of the rubber perhaps being hardened, so definitely worth changing.

acotrel · Mar 23, 2022

baz said:
A cable controlled enricher makes quite a difference to the on off type levers
Although it shouldn't!!

Old British motorcycles often do not have nylon-lined operating cables, I always use Japanese cables. If you pick up a cable by its outer, you should be able to hold it up vertical and the inner should just drop freely. The old type of cables were metal on metal - too much friction, and not enough clearance.

baz · Mar 23, 2022

acotrel said:
Old British motorcycles often do not have nylon-lined operating cables, I always use Japanese cables. If you pick up a cable by its outer, you should be able to hold it up vertical and the inner should just drop freely. The old type of cables were metal on metal - too much friction, and not enough clearance.

It's the conversion from an on off enricher lever to a cable conversion on an Amal MK2 we are talking about here Al

acotrel · Mar 23, 2022

baz said:
It's the conversion from an on off enricher lever to a cable conversion on an Amal MK2 we are talking about here Al

So the conversion has modern cables ? Or is it an old bike and the Mk2 s were fitted later and used existing cables. I use Mk2s but I get my finger under the tank and to also flick the right hand lever off when the motor is warm

concours · Mar 23, 2022

acotrel said:
Old British motorcycles often do not have nylon-lined operating cables, I always use Japanese cables. If you pick up a cable by its outer, you should be able to hold it up vertical and the inner should just drop freely. The old type of cables were metal on metal - too much friction, and not enough clearance.

....and, if never OILED regularly, the spiral wound sleeve would RUST from rain water, and create lotsa drag.

baz · Mar 24, 2022

acotrel said:
So the conversion has modern cables ? Or is it an old bike and the Mk2 s were fitted later and used existing cables. I use Mk2s but I get my finger under the tank and to also flick the right hand lever off when the motor is warm

The bike in question has a single MK2 carb
It has a cable operated enricher
I assume with a friction type lever
The point I was making is with the on off lever the enricher is either full on or full off
With the cable type you can start with it on full IE engine revving
Then you can back it off a little to give a reasonable idle from cold
Then fully turn it off when the engine is warm
Well you can with twin mk 2s anyway

Fast Eddie · Mar 24, 2022

Yes, the carb mounted lever is a super crude on / off affair with a massive difference in mixture between on and off.

The cable set up relies on a friction lever and the spring on the plunger, so it can be graduated with a careful hand. It’s still very crude, just somewhat less crude than the simple on / off lever.

cash · Mar 24, 2022

Tom P said:
New enrichener now on order from RGM, close inspection of the old one showed a distinct ring indented into the rubber. On a different note what are peoples thoughts on throttle slides, Alloy vs Hard anodised vs chromed brass?

The distinct ring should not be a problem.
Make could your own replacement pad. Using a small screwdriver the rubber pad will flick out. (you could just turn it over) Take the dimensions off the pad, because I can't remember them it's that long ago, punch a couple out of the sheet of Vition. However, Viton is getting expensive so it might be cheaper to buy the enrichers.
The chromed brass is probably best for a single carb, while hard anodised work well in my twin 34 setup.

robs ss · Mar 24, 2022

Fast Eddie said:
Yes, the carb mounted lever is a super crude on / off affair with a massive difference in mixture between on and off.

The cable set up relies on a friction lever and the spring on the plunger, so it can be graduated with a careful hand. It’s still very crude, just somewhat less crude than the simple on / off lever.

On/Off is good
At least off is off (if the rubber internals are good)!

Fast Eddie · Mar 24, 2022

robs ss said:
On/Off is good
At least off is off (if the rubber internals are good)!

It is good. But some bikes have a rough time between being too cold and just warm enough.

I find it helps with my T140 (twin Amal mk2s) to be able to adjust the lever when cold as it allows me to ride off straight away. If I couldn’t do that I’d have to wait, stationary, keeping the revs up with the throttle.

It has Norton peashooters fitted… the neighbours wouldn’t appreciate that too much…

Then again, I have a bike with twin Mikunis, with lever enricheners, and that’s fine when I turn the enricheners off almost straight away.

Seems different bikes respond differently.

baz · Mar 24, 2022

robs ss said:
On/Off is good
At least off is off (if the rubber internals are good)!

My t140 with lever type enrichment would start and run at over 3500 rpm immediately
If you flipped it off it'd stop
There was nothing in between you couldn't keep it going on the throttle
I changed to cables and it was perfect

marshg246 · Mar 24, 2022

baz said:
My t140 with lever type enrichment would start and run at over 3500 rpm immediately
If you flipped it off it'd stop
There was nothing in between you couldn't keep it going on the throttle
I changed to cables and it was perfect

How is that possible? The hole is covered/uncovered no matter how it gets that way? Not disputing you - just asking how that's possible.

Fast Eddie · Mar 24, 2022

marshg246 said:
How is that possible? The hole is covered/uncovered no matter how it gets that way? Not disputing you - just asking how that's possible.

The hole is flowing fuel, not air, keep the plunger close to the hole and it’ll reduce the flow.

I assume…

baz · Mar 24, 2022

marshg246 said:
How is that possible? The hole is covered/uncovered no matter how it gets that way? Not disputing you - just asking how that's possible.

I can only assume the friction type lever gives you the control
As I said it shouldn't work but does

marshg246 · Mar 24, 2022

OK - understood.

In my experience, even a slight leak there causes be trouble. Really bad when one side leaks more than the other in a dual setup. You start adjusting the air screws and throttle stops to compensate all while trying to figure out why you're fouling plugs and can't get an acceptable cold and warm idle.

chaztuna · Mar 24, 2022

cash said:
It should when the enricher is operated. It might eight stroke like hell and run at 1500 to 2000rpm though.

I had this same issue. My Amal Mk IIs came with #50 enrichener [choke] jets, which are great, if you live in Antarctica! Once I changed the enrichener jets to #35s, I could leave the enrichener levers on for a few blocks, without loading up my spark plugs. By that time, the engine had warmed up enough to idle without the enrichener circuit.

outawack · Mar 24, 2022

WOW what i thread man, i never thought there could be so many reason why a bike wouldn't idle when cold. I just thought it was because it was well cold. More modern bikes have a thing called a choke gentleman i wonder what that's for?.
let it warm up till you out of your street and then ride it like ya stole it and all will be right again.

Tom P · Mar 24, 2022

Well, New enrichener fitted along with new chromed brass slide and for good measure I replaced the standard float with a new stay up one. Glad to say that after a bit of tinkering with the airscrew it runs better than ever. I will reserve judgement on the cold idling for the moment as it idled fine when I fired it up, but the airscrew was set on the rich side. In addition I had a lovely ride down to the coast for a bag of chips in the sun. Thanks for all your help and advice.

Carburation issue

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