Runs only with choke open

[xshinyax]

My bike starts on cold engine just fine with choke open, but even after several minutes of warming and running, the motor dies when I close the choke. Engine floods when warmed up and doesn't start up until cool down, I guess it's because of choke open.

To be more specific, when I start to close the choke, the rpm starts to go up to like 5-6k. And then the motor dies if I close the choke completely.

What should I look for?

[myol]

Year & make of bike? Sounds like bike is running very lean.

[QKENUF4U]

sounds like carb cleaning time. pilot jet/s are prob. clogged if its been sitting for awhile.
if its just started doing it then could be lean. take some carb cleaner and spray around the carb boots/bodies and see if you notice a difference in rpms (youll have to have someone keep it running)

[xshinyax]

Thanks, I was guessing about running to lean too.

One more question, is replacing jets by myself(n00b) supposed to be hard? I have an aftermarket jet kit that came with the bike, do I have to fine-tune after installing?

The bike's 90 honda. (Yes, I love Kawasaki but had to take the deal)

[hot_shoe_cv]

First of all I think you mean you have to close the choke to keep it running...when the choke is closed the air to the carb is shut off, creating a rich fuel mix. Conversely, opening the choke restores the air/fuel mix. There is no off or on regarding the choke . Just a matter of semantics but makes the mud a little clearer .

You didn't provide any info as to how long the problem has been going on or whether you have done any air flow modifications or how old the bike is ....these little bits can all be factors. I'd first look at a possible air leak before getting into the carb. If it's an older bike the boots may have developed very small fine line cracks which may cause a lean fuel mix. Have you already re-jetted, and is that when the problem started?

[xshinyax]

It's 1990 CBR600f.
I meant that I couldn't get the bike or motor run with choke closed. The engine stops as soon as I close the choke. No mods done to bike. I think the bike's been doing for sometime but previous owner didn't mention the problem. Anything done to carb was carb synchro. No oil leaks from I can see.

So start with spraying around with carb cleaner first and see if air leaks before getting into carburetor?

[hot_shoe_cv]

Yes, I always try to do the easiest possible solutions first and also check the clamps holding the boots to the carb.
And once again, you aren't quite getting the terminology re chokes... a closed choke is what you are referring to as an "on" choke. An open choke is the position normally used when the engine is operating properly. It is easy to understand the difference when you see the inside of the carb. When yo look inside the carb body and operate the choke, you'll see that it closes off the air, thus allowing a full mixture of gas to be introduced into the engine. This is what you are doing to overcome the lean condition that you have now.
I don't mean to be picky but using the right terminalogy in any situation can help prevent receiving the wrong information.

[xshinyax]

Exactly what you stated, I apologize if i confused people, I am fairly new to technical term. I just wanted to state my problem as far as I know.
Thanks for helps.

[hot_shoe_cv]

Not a prob. I hope you get the problem solved and let us know how you did it

[mach1]

Hi

I have the same problem with my 440 ltd, i have to close the choke to keep it running. i don't know what happend to my bike can you help me please
thanks

[hot_shoe_cv]

Originally Posted by mach1

Hi

I have the same problem with my 440 ltd, i have to close the choke to keep it running. i don't know what happend to my bike can you help me please
thanks

When did this problem start? what changes, repairs, modifications, etc have you made just before this started?
Very often the problem indicates an air leak around the carb or air box hose leading to the carb. Check all the hose connectors and the rubber hoses to see whether there are cracks in the hose. A very small crack can allow air to enter the carb leading to a lean condition.

[ledman]

Had problem on my 800 and ended up the cable.Would pull my choke out to start and would run great till warm and the start to back fire,would push choke back in but it did not go all the way back in.

[Alizard]

Originally Posted by hot_shoe_cv

First of all I think you mean you have to close the choke to keep it running...when the choke is closed the air to the carb is shut off, creating a rich fuel mix.

In the old days.... the choke operated that way (reducing air flow through the bore to rich the mixture as the choke was applied)... hence the name 'choke" as it was like strangling the airflow.

Now the choke on Mikunis is just another jet you can activate to dump in more gas. It doesn't actually affect airflow at all, just adds more fuel to rich up the mixture.

[Alizard]

Originally Posted by xshinyax

It's 1990 CBR600f.
I meant that I couldn't get the bike or motor run with choke closed. The engine stops as soon as I close the choke. No mods done to bike. I think the bike's been doing for sometime but previous owner didn't mention the problem. Anything done to carb was carb synchro. No oil leaks from I can see.

So start with spraying around with carb cleaner first and see if air leaks before getting into carburetor?

Drop the float bowls and hose them out with carb cleaner. The pilot jets are easy to remove in most carbs if you want to clean them thoroughly and spray cleaner through the passage way. I would think to get an air leak bad enough to kill the engine like this would be so big you could see it.

[Alizard]

Originally Posted by hot_shoe_cv

And once again, you aren't quite getting the terminology re chokes... a closed choke is what you are referring to as an "on" choke. An open choke is the position normally used when the engine is operating properly.

That's even confusing to me.... the choke jet on mine is "riching up the mix" when the plunger is raised to OPEN it allowing fuel to flow through it, and it goes back to "normal" operation when the plunger is lowered completely closing that jet off.

[mach1]

Hi
ok i just bought this bike for 150 dlls and i just try to turn on the engine, ok i removed the air box and the filters to i will install a cone filters on each carb, do you think the hose connected to the air box is the problem?. the rubber from the carb holder looks good but i put a silicone just to be sure theres aren't a air leak

Thanks

[StarGate]

Originally Posted by bountyhunter

That's even confusing to me.... the choke jet on mine is "riching up the mix" when the plunger is raised to OPEN it allowing fuel to flow through it, and it goes back to "normal" operation when the plunger is lowered completely closing that jet off.

Thats because you have some people trying to use the Open/Closed and others using the On/Off terminologies, and it's hard to mix the two. Then when you throw the two diff types of systems whether it be an en-richening type or true choke into this mix it just creates mass confusion.

If everyone would just use the On (normal cold start position) Off (normal running position) and forget about the type system used on a particular brand carb it would make things a lot easier. I know, FAT chance of that happening but can always hope.

P.S. You referred to the butterfly closing the throat as something used "In the old days". That same system is still used by some manufactures on some carbs.

[Alizard]

Originally Posted by StarGate

P.S. You referred to the butterfly closing the throat as something used "In the old days". That same system is still used by some manufactures on some carbs.

I'd be surprised if there are still manual chokes being put on new designs, mainly because they allow a very easy way for somebody to move a lever and increase the unburned hydrocarbon emissions of the engine by about a million times by making it run really rich.

I thought all the new designs used EFI to take away the possibility of such things..... and make the engine run better with less emissions.

I haven't looked at new bikes in a while, maybe they still do use the old style carburetors on some. Considering what a pain they are, I wouldn't miss them.

[Alizard]

Originally Posted by mach1

Hi
ok i just bought this bike for 150 dlls and i just try to turn on the engine, ok i removed the air box and the filters to i will install a cone filters on each carb, do you think the hose connected to the air box is the problem?.
Thanks

No, that's a crankcase vent line not a vacuum line.

[Alizard]

Originally Posted by StarGate

Thats because you have some people trying to use the Open/Closed and others using the On/Off terminologies, and it's hard to mix the two. Then when you throw the two diff types of systems whether it be an en-richening type or true choke into this mix it just creates mass confusion.

If everyone would just use the On (normal cold start position) Off (normal running position) and forget about the type system used on a particular brand carb it would make things a lot easier.

OK: choke "ON" for rich setting, choke "OFF" for standard setting.

If I wanted to be mean I could point out that the EFI systems create a "choke ON" setting by adjusting the total time the injectors stay open as a function of a control loop that reads the engine temperature.... I think the manual calls it the "cold loop" or some such thing.

At any rate, that's why EFI engines run good right at start up and you never have to fiddle with a choke.