took off air box

F

fredwatson

New member
i have a 1995 vmax 4 with light porting,clutch kit,stock pipes, aftermarket can,foam air filters, gear change,burned it down 2 times on the same cylinder ,put new cylinder and piston with ring in it, cleaned the carbs a million times , have a 155 main,47.3 pilot,1 1/2 turns out on air screw ,it says nothing about the clip height .i live in michigan and the temp now is 19 .stock main is 143.8 so i went up to comonsate for air filters .it just doesnt have the snap on the throtle and i wondered if the new air filters were the cause and a mistake. plugs are wet and dark . havent had any runs this year yet. wanted to get it squared away before running it again . the burndowns are not cheap . average compression is 150 lbs an all cyls.any advise is accepted. thanks fred
 

What fuel are you running, 150 compression is 30lbs more than stock, is this sled for racing check to see is your carb boot is cracked or torn
 
Foam filters? Did you remove the stock air boxes? Are you burning the cylinder at 19 above? Can you post pics of the burnt pistons? Is it taking the cylinder down at mid range or wide open?
Sorry for all the questions, but we need more information in order to be much help.
 
I have always heard that the stock air boxes are the way to go unless your are building a strictly race sled.
 
i would think that foam filters would suck warm engine air on a trail sled making it pig rich as opposed to stock air box pulling cold air to run leaner
 
no.2 piston burn down at mid range . high octane pump gas picked track threw old piston away but the edge was burned away stock air boxes removed burn down at 20 degrees f whats up with the clip height is the air fuel screw adjusting the air or fuel? is in leaner or fatter?
 
Air leak base gasket, carb to reed cage boot, seemes unlikely usually it's a dirty/partially clogged pilot or main jet thou, What about float height? float bowl shutting off fuel i.e leaning it out due to wrong float height setting? have you measured that to see if it matches the other Floats on rack?
 
It's a fuel screw. Turning it out more makes it richer. Clip height is in the 3rd position on needle for stock setting. 47.5 pilots are stock. I've upped my pilots to 50's on my sleds.
 
Last edited:
going to check float hgt. should I put air box back on with stock mains? why did you up the pilots? what do you have the fuel screw set at ? and what mains are you running?do you still have air boxes on? thanks for the info. guys Fred
 
Usually on carbs if the screw is on the motor side of the body (slide) it is a fuel screw, if it is on the air box side it is an air screw.
 
I was also told to run airboxes, easier to tune. I was also told by an experienced racer to up pilots because they can cause burndowns if too lean. Fuel screws I run at 1-1/2. But from your compression numbers being so high, like Turch said, I would assume you have a race sled. With 150psi you should run race fuel. My mains are 142.5 but I have different pipes and 120psi. 155 sounds safe on the mains to me.
What I have learned from this site is that most burnt pistons are from lean out and that is usually
From dirty carbs. Make sure carbs are spotless, replace all the oring's especially one on the needle and seat, make sure the little screen isn't plugged under the needle and seat.
If its not the carbs then it is probably vacuum leak, with the engine running you can spray carb cleaner around the boots and other gaskets. If there is a leak the rpm will change.
I would also change the fuel lines, my originals were hard and brittle. And pull the gas tank off and clean and get rid of any old fuel.
 
Years ago I wanted pods as it took longer to replace the airboxes than a cylinder. Before I did I mounted a remote thermometer probe in the carburetor area and noted that the temperature easily reached well over 120* at -40* outside temperatures. Hot air is detonation prone and can cause unexpained burndowns with rich mixtures.
 
You must log in or register to reply here.


Back
Top