very interesting observation (fuel inlet screens)

T

TJ500

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May 17, 2003
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661
Location
Lockport, Manitoba. Canada
My sled (02 700 MM redhead) was giving me a slight burble/misfire just above idle, so I just finished tearing through the carbs... Recent posts have suggested to check closely the fuel screens just under the float needles.... I did this and was lucky that they were pristine and void of any contamination.... HOWEVER...

I did notice that the inlet hole machined into the brass fittings that these screens fit onto, was actually SMALLER diameter than the machined holes in my main jets? (I'm running 145 mains for our cold northern Manitoba climates)....

I did carefully examine and compare diameters of the machined holes, and my mains are definitely metering more fuel (larger diameter) than the inlet orifices allowing fuel into the carbs...

I do understand that there is some overlap on the fuel circuits and that the pilots jets can allow some fuel to the engine at full throttle too... It just seems odd that main jets are metering with a larger diameter hole than the inlet hole allowing fuel into the carbs....

Could and would this be a reason why modded sleds requiring large main jets are burning down?... Could the inlet orifice on these carbs be the actual limiting factor when metering fuel at long WOT runs across lakes etc?...

Just figured I'd bring this up for those who have racing experience and or rebuilding experience.... Any comments are welcome...

TJ..
 
It doesn't matter if the fuel inlet hole is smaller then the MJ because the bowel is and always stays full(constant storage)with a constant flow of fuel.

it's like having a hole in your gas tank wile putting fuel in at the pump,you'll never run it out.


by the way so people know these are the screens under the needle and seat that should be checked and cleaned with any carb maintenance,easily over looked.










Picture019.jpg


Picture020.jpg


Picture021.jpg
 
Yes,with the screw removed(top pic)it will just pull out you may need to gently use a pair of needle nose pliers to pull with because of the O ring making it snug in there...
 
gas is being sucked from the bowls thru the main via vacuum... negative pressure, but still "pressure"...... just seemed odd that this hole wasn't larger than it was....


daman, but the gas pump nozzle is smaller than the hole in the tank!... :)
 
TJ500 said:
gas is being sucked from the bowls thru the main via vacuum... negative pressure, but still "pressure"...... just seemed odd that this hole wasn't larger than it was....


daman, but the gas pump nozzle is smaller than the hole in the tank!... :)
Click to expand...


Don't forget the needle and nozzle.

and... how does one determine if the straw they're sipping thier slurpy from has a hole in it?

A half a mouth full?
 
Dang, wish I would have read up on Viper fuel issues yesterday before "cleaning" my carbs. I had them off and everything looked really good, but I didn't check these float screens before reassembly last night.
I guess if nothing is getting past the screens the rest should look good. I am hoping that the dirty screens are the issue with the intermitent cutting out I experienced last year.
Thanks for the pics daman!
I will be taking it apart and checking those screens before trying to fire it up.

Thanks again guys.
 
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