cylinder three wont run

[Timt794]

Rebuilt carbs according to carbs 101. Number three cyclinder wont fire. I have 170lbs psi, plug sparks, swapped plugs run for about 30 seconds then cut out. Checked sync and spot on. plug gets black and super sooty. Swapped out number three carb body. Ensured floats are at 14mm. Any Ideas.

[HS2020]

You check to make sure everything is in place on the top side of the carb. Could have the spring just out of place a little. That can cause some issues.

[Timt794]

will check the top set up
thank you
does number three on the pre run a smaller main jet

[HemiKat]

Did you check compression on the other cylinders? I wanna say my 750 with more like 225 psi. Its been awhile though.

[bobthebiker]

sounds like a rich running issue, have you checked that you're getting STRONG spark on #3? if not, do that, it may be part of your issue. as may be a leaking float allowing too much fuel to flow.

[Timt794]

Compression qith motor warm throttle wide open is 170#[+-] 2 psi. Spark is good can switch plug caps from 2 and 3 and number three is still dead but number two is running good. Does anyone know what the exhaust header temp should be? Also does anyone here at Katriders sell the correct o-rings for the floats?

[MickM]

Interesting problem.

You have spark, and compression, and LOTS of fuel.

The plug is fouling because of the unburned fuel,
Is the plug wet?

Have you looked at the exhaust pipe?
I once had a Spitfire that ran badly, when it ran at all.
No power, no acceleration.

Someone had jacked the car up by the exhaust pipe under the car.
It was folded into a big 'C", almost completely closed off.

So check out the exhaust path for bent or flat pipes.

The car would start and run for about a minute.

I believe that number 3 carb uses a smaller main jet.

Is your carb diaphragm OK? and O-ring?
(see carbs 101)

Does the choke move and work for that cylinder?

Mick M

[kevin2502000]

I'm going with the super rich theory also. If you idle up it won't kick in either? You are Positive all of the air jets and passages are clean and have been blown out with compressed air? CHeck the blow test on the needle/seat to make sure it doesn't leak. You can buy those o-rings at a harware store, match up with the same. I can't remember but I think I used bith standard and metric sizes. You are correct about #3 using the smaller main.

[md86]

No , #3 on the pre 750 uses a 110 , and the other 3 use 105's .
Could be MANY things . MY problem was an improper pilot jet . Takes a REALLY close look sometimes to figger out these things ....

[Timt794]

friend put in a dyno jet ket so know I am back tracking to figure out what the cause is. Bike hade problem before the kit. All four carbs had 112.5s in them. Will look at the pilots again they didnt appear deformed but will look to make sure they are the correct ones.

Check shop manual 112.5 in all four carbs on the 600 and 110 in number three then 105 in the other three on the 750. Am going to check the hardware store. Was wondering if hte o-rings would handle the gas

[kevin2502000]

No , #3 on the pre 750 uses a 110 , and the other 3 use 105's .
Could be MANY things . MY problem was an improper pilot jet . Takes a REALLY close look sometimes to figger out these things ....

You are correct, let me rephrase that saying #3 is the odd duck.

[Shipster]

You check to make sure everything is in place on the top side of the carb. Could have the spring just out of place a little. That can cause some issues.

Spring just out of place a little? What if it's not even in there, say for the #1 carb? Not that I'd know anything about that, huh Jimmy? Definitely good advice, again, not that I'd know anything about that or need it!

[steves]

Take apart, and re-clean the carbs.

You either missed something, or the inside of your tank is messed up.

[Timt794]

pulling them down and starting over will advise on what turns up. checking needles and o-rings plus the rest of it.

[steves]

What condition is your gas tank in?