Hard starting Mach 1

[machten]

Over 6 months old can cause starting problems. I'm told they make it not so volatile now, for safety, and because modern ignitions are powerful enough to handle it.

I've done a lot of work over the last 20 years for oil majors on the refining end that produce fuels. I'm not an employee, but I consult around the information technology edges.The important thing about fuel is how it is stored. Petrol, mogas, whatever you want to call it contains many of what are referred to as volatile organic compounds (VOC's). VOC's are compounds that evaporate easily from liquid and can escape into the atmosphere. Any loss of VOC's for refineries is bad thing. It repesents a potential environmental exposure and what is referred to as a "quality give-away". ie we've made this stuff to this spec, and now we're letting it spoil to below spec.

If you've ever seen a picture of a "tank farm" at a refinery, you will see some tanks that have fixed lids, and some where you can't see the lids. That's because they are floating lids that float with as near as possible to the stored liquid with air tight seals on top of the product - petrol, avgas, or intermediate feed stock. This is to minimise loss of VOC's by saturating the surrounding air by minimising the surrounding air.

Over 6 months old can cause starting problems

Leave it in your tank for that long, quite possibly, although that will depend on the compression ratio. Put it in low compression tractor - no problem. Governments all over the world store mogas and jet spirit for military purposes for very long periods...just need isolation from the atmosphere.

I'm told they make it not so volatile now, for safety, and because modern ignitions are powerful enough to handle it

Depends on your definition of volatile. There is a common confusion between volatile (easily evapourate into air) and flammable (low ignition point). It is true that premium fuels have a greater "octance density" (so for example, in a ducati twin with a PHF pumper carb, for a 98 octane fuel you will want to reduce the number of CC's per pump to keep your fuel/air mixture optimal). Regardless, it ain't for safety. The key change is more around the ability to control fuel mixture using computer controlled fuel injection. Oil companies would love to make fuel less "volatile", but to my knowledge that ain't what's happening for fuels other than diesel.

Kev

[Bevel bob]

My understanding is that todays fuel burns faster ,and needs less ignition advance, carbs seem to need weaker settings. When i put my bikes away I seal the tank cap vent with a little masking tape to reduce evaporation of volatile elements and ingress of moisture.

[Jordan]

There is a common confusion between volatile (easily evapourate into air) and flammable (low ignition point).
Kev

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Good to hear that sealed storage can preserve the fuel.
I guess that, as well as making it easier to mix with air, easier starting is also a benefit of volatile substances?

Jordan

[Rick]

I think ticklers are just a practical joke- the carburetor should suck the same amount of fuel out of a bowl at float level than a bowl gushing over with excess fuel. Using the tickler gives a visual clue that fuel is available, but also poses a small safety concern. A real 'choke' will choke off some air and make the fuel/air mixture richer with fuel- the tickler doesn't change the mixture.
I've never noticed any better starting after tickling a carburetor, but wouldn't pretend to be an expert.
Rick

[JimF]

An Iridium plug seems to have improved things greatly.

Of course not leaving well enough alone, I had a Unifilter foam "sock" that I had long ago adapted to the velocity stack. It seems to me that it is very free flowing in terms of air volume, but when I install if after the bike is running the RPMs climb.

If I install it before I go to start the bike it does not seem to want to start.

Should I change the idle jet size? If so which direction should I go?

I tried playing a little with idle-air adjustment screw (figuring I was getting less air witth the sock in place so I should adjust it to lean it out, that is to say rotate the screw coutner-clockwise.) I could not seem to make thing better, only different.

Jim

[Bevel bob]

Hi Rick, The Mach 1 and Mark3 have the ssi 29d and a hot cam, this means that at kickstart speed there is not enough venturi effect to pick up fuel, hence the crude richening needed by tickler flooding ,my M3 would not start at all without a tickle although the mixture settings are generally a bit rich.Jim ,the sock on the carb is impeeding the already useless air flow at kickstart speed and is richenning the mixture once you do get it going. For general use on the road the SSi is no good unless its in perfect health and tune and even then its a pain,thats why so many give up on it and fit an Amal.Not me though as i love a challenge!.

[Rick]

BevelBob,
I won't argue with success, and I have read many times that the float level affects the mixture, but I can't make any sense out of it. The jets are submerged in fuel and the air flow over the top of the jet passage draws fuel up into the mixing chamber- what affect does adding a fraction of an inch of extra fuel have? Won't the air flow over the jet passage draw the same amount of fuel regardless of the fuel level? Can a thimble full of fuel create enough pressure to force or inject fuel up the passage? I'm sure the engineers who designed these carburetors didn't add a way to overfill the float chamber without a reason, but I've never understood it.
The extra height of fuel would raise the initial fuel level in the passage, so the fuel may get into the mixing chamber sooner, but it seems almost insignificant to me. I have the Dellorto technical manual, read it again, but still can't see the cause/effect relationship.
I've always thought of the float as a valve to a fuel resevoir(the float bowl) to make sure fuel is always available without having an uncontrolled line to the tank.
The Dellorto manual clearly says the float height affects the mixture, so I'm not arguing, just trying to understand.
Rick

[Bevel bob]

Imagine Rick sipping coffee from a full cup, then sip again with the coffee at a lower level without tilting the cup ,all you get is air --and the burps!!, a bit like my M3 without a tickle.

[JimF]

I'm going to go out on a limb here and make a guess...

Because liquid seeks its own level, the level of fuel in the float bowl is directly affecting the level of the fuel in the jet's barrel across the banjo joint and in the carb. If the level in the float bowl was consistently higher that the top of the jet the fuel at the carb would burble over the tip of the jet constantly.

If the float bowl level was too low the fuel level in the jet would also be low, and I am guessing it would take much more vacuum from the cylinder to draw fuel in, or with the same amount of vacuum less fuel would be drawn in.

To my thinking then the carb designer establishes the float level such that fuel won't just burble over the top of the jet constantly but perhaps at the fluid's quiescent state (given atmospheric pressure as the float bowl isolates the elevated fuel tank's effect) is just under the top of the jet where it can be easily drawn off (atomized) with minimal vacuum.

OK, flame resistant suit is on... fire away!

[MotoMike]

On my amal, it seems to me that the weep hole in the tickler is a good bit above the floor of the venturi and the top of the main jet. so when there is a bit of wetting of the hole on the tickler, there should be raw gas in the throat of the carb. isn't that the case with the ssi?