Will not start WITH choke on.

On my M2, BS34 carbs, I can start the bike with the choke off, but it taks quite a bit of cranking. It kind of sputters along for a while, but cannot quite catch and keep running on its own. I have to keep the starter going to keep it sputtering along. After a minute or so, it will run on its own. I can help it along with a little blast of starter fluid in the air intake. With that it will start right up.

Normally, I would start it with the choke on. But on this bike, if I pull the choke on, even halfway, it absolutely will NOT start.

After it is idling on its own, if I pull the choke on, it will rev up for about a half second, then sputter and die.

What might be happening here? I'd like to be able to start it up normally with choke on until it warms up a bit, then turn off the choke.

More info:
Stock airbox, non-stock 4-2 turnout pipes, 1135/10.25 piston kit. BS34 Carbs, 130/40 jets, air screws at 1.5 turns.

You don't have a choke on your bike... you have a set of enrichener circuits. Sounds like they are obstructed (they need a good cleaning).

Has it ever run with the current setup?

KZCSI wrote:

Has it ever run with the current setup?

Yes, it seems to run fine with the current configuration--once I get it started and warmed up.

wiredgeorge wrote:

You don't have a choke on your bike... you have a set of enrichener circuits. Sounds like they are obstructed (they need a good cleaning).

George,

Prior to putting these carbs on, I did do a thorough cleaning--disassembly, carb dip, blew out all passages. But I'm sure it's possible I missed something.

I was originally thinking that maybe the problem is that I was already on the rich side of things, and pulling the choke (enrichener) on was just making it too rich.

However, the plugs don't seem to indicate rich to me (unless I'm reading them wrong). They come out fairly tan/white, but with just a slight tinge of blue. Is that indicative of a rich mixture?

If it is rich as is, where would I start adjusting? Air screws? Pilot jets?

Thanks.

Sounds like the enricher is actually leaning it out. Have you tried starting with the enricher AND starting fluid?

loudhvx wrote:

Sounds like the enricher is actually leaning it out. Have you tried starting with the enricher AND starting fluid?

No,I have not. What would that tell me?

Hi Steve,

The enricher plungers allow additional fuel into the carb throat when they are raised thereby enriching the mixture. As opposed to restricting the air flow like a true choke does to enrich the mixture.

I can't get my head around why the enrichers stop the starting when the plugs do not indicate a too rich running condition.


Sounds like an intake leak to me. Are you sure you've goot all the hoses connected?

kzcsi

Post edited by: KZCSI, at: 2008/01/09 13:53

The enrichener circuit has both gas and air feeds and if the gas is not flowing, extra air presents itself to the start up mixture which wants to see a richer than normal mixture and leans it out. As I said, not everything was cleaned as it should be. I would also take care with continued starting fluid use. That stuff can be dangerous.

Skyman wrote:

loudhvx wrote:

Sounds like the enricher is actually leaning it out. Have you tried starting with the enricher AND starting fluid?

No,I have not. What would that tell me?

Since it would not start at all with just the enricher, if it starts with the enricher and starting fluid, it would support the theory that the enricher is not getting fuel, and only air. This unfortunately means the carbs are probably going to have to be opened again.

I only wonder which carbs, if not all of them.

Post edited by: loudhvx, at: 2008/01/09 13:57

wiredgeorge wrote:

The enrichener circuit has both gas and air feeds and if the gas is not flowing, extra air presents itself to the start up mixture which wants to see a richer than normal mixture and leans it out. As I said, not everything was cleaned as it should be. I would also take care with continued starting fluid use. That stuff can be dangerous.

Thanks George, I was not aware of the air component to the enricher circuit.

Bill

On many carbs, like the VM series, there is a hole in the venturi set back in the venturi about 1/2" that is easy to see. This is the air jet for the enrichener (starter) circuit. On the BS series, the air jet is in a different location. You have to take off the top, pull out the slide diaphragm and under there is a hole about 1/8" diameter leading down to the starter plunger well. This hole passes a significant amount of air to the well so when the plunger is open and no gas, there is a lean condition about the same as if you left a vacuum cap off a vacuum plug by the volume of air. HARD STARTING!