Topic: jetting- popping on let off

[kart74]

I have a CB400F with jardine headers on it. I am running 78 mains with stock pilots. The needle position is in the middle (tried second from bottom but didnt run well). The bike runs great. Seems to have good power through the band, but pops pretty good on let off. Does this mean i need larger pilots as well?

[DJ_AX]

It may simply mean you need new exhaust gaskets. The copper crush gaskets.

[lucky]

Try adjusting your mixture screw and that could get rid of the popping.

How is the throttle response from idle?

CB400F.
Jardine headers.
#78mm main jets. stock is #75
Idle jets? Stock should be #40's Are they?
Slide needle middle position. (stock)

Since you said it loads up at stop signs I would want to make sure the float bowls are not too full.  Stock float setting is 21 mm. Do they overflow at all?
Is your oil level normal? Wondering if gas is getting into the oil.

How do the spark plugs look now?

[kart74]

the only time that throttle response isnt good is when i come to a stop sign. When i go to take off from the stop sign the initial "crack" of the throttle is often not good. Seems loaded up. If i crack it a couple times before taking off it is fine.

[lucky]

the only time that throttle response isnt good is when i come to a stop sign. When i go to take off from the stop sign the initial "crack" of the throttle is often not good. Seems loaded up. If i crack it a couple times before taking off it is fine.

So if the bike is parked and warmed up is the throttle response perfect? No hesitation?

[kart74]

Yes it has stock idle jets. The floats were set by "eyeball" just made sure they were level when the needle closed. Is there a better way to do this? They are not overflowing at all. Oil level is constant as well.

When the bike is warm and just parked i can get it to hesitate there as well. Just not as consistant, but after reving a bit and then cracking it, i get the hesitation loaded up sound right off idle.

[lucky]

You really need to et the floats the proper way. all it takes i a small ruler.
I t may never run properly if the floats are out of adjustment.

21mm or .826 thousandths. That is 1/32 inch more than 3/4 of an inch

[DJ_AX]

You really need to set the floats the proper way....

+1
It can make a significant difference!

[kart74]

so are you measuring to the top of the float... well the top in that picture?

[Doctorlumen]

Gasket surface of the main carb body and actually the true bottom of the float....You measure the float height with the carbs upside down, and the float tang just touching the float needle.


I don't know anyone with a 400/four that doesn't have off-idle/takeoff hesitation. If you find a solution, please scream it from the rooftops!

[TwoTired]

You measure the float height with the carbs upside down, and the float tang just touching the float needle.

This described method is doomed to failure when the float valves have those spring pins in them.  The weight of the float will depress the springs causing measurement error.
Adjust the floats with carbs on their sides.  Float position is easily measured without putting tension on the spring pins, but still making contact, while the float valve is seated.

Cheers,

[lucky]

You measure the float height with the carbs upside down, and the float tang just touching the float needle.

This described method is doomed to failure when the float valves have those spring pins in them.  The weight of the float will depress the springs causing measurement error.
Adjust the floats with carbs on their sides.  Float position is easily measured without putting tension on the spring pins, but still making contact, while the float valve is seated.

Cheers,

The plastic floats are so light it will NOT depress the spring load pin.
You would have to press down on it with your fingers for the float to depress the pin.

The brass ones are a different story, They WILL depress the pin because they are heavier.

[TwoTired]

You measure the float height with the carbs upside down, and the float tang just touching the float needle.

This described method is doomed to failure when the float valves have those spring pins in them.  The weight of the float will depress the springs causing measurement error.
Adjust the floats with carbs on their sides.  Float position is easily measured without putting tension on the spring pins, but still making contact, while the float valve is seated.

Cheers,

The plastic floats are so light it will NOT depress the spring load pin.
You would have to press down on it with your fingers for the float to depress the pin.

The brass ones are a different story, They WILL depress the pin because they are heavier.

I have plastic floats in the both the CB550s and the CB750's I have.  They WILL depress the stock float needle spring pins from their own weight.  The issue is avoided completely if you simply measure float height with the carbs on their sides.

[Doctorlumen]

Yeah....what TT said. What I should have said is that you can't measure float height with the carbs in their vertical position, i.e. how they sit on the bike.

Maybe a better phrasing would have been "upside down"...no. Nevermind. Sorry for the brain fart. 

[lucky]

You measure the float height with the carbs upside down, and the float tang just touching the float needle.

This described method is doomed to failure when the float valves have those spring pins in them.  The weight of the float will depress the springs causing measurement error.
Adjust the floats with carbs on their sides.  Float position is easily measured without putting tension on the spring pins, but still making contact, while the float valve is seated.

Cheers,

The plastic floats are so light it will NOT depress the spring load pin.
You would have to press down on it with your fingers for the float to depress the pin.

The brass ones are a different story, They WILL depress the pin because they are heavier.

I have plastic floats in the both the CB550s and the CB750's I have.  They WILL depress the stock float needle spring pins from their own weight.  The issue is avoided completely if you simply measure float height with the carbs on their sides.

Yes... if the carb is on its side there will be no problem. I agree.

It seems that some float pins are slightly stronger?

[lucky]

Here we go.

BTW in this photo from the internet you can see there is some kind of problem with the posts holding the float pin. Some kind of corrosion or something. Did anybody else notice that?