Fuel screw setting

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Larry Bryzelak

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Sep 11, 2014
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Wyandotte, Michigan, United States
I have a 99 srx 600. I just rebuilt the motor last year and maybe but on 100 miles of riding. I had a low end bog so I cleaned the carbs including the fuel screens and it does the same thing. So then tried to adjust the fuel screws from 1 1/8 to 1 1/2. It did the same low end bog once again. Keep in mind I bought this sled with a blown crank. So I was reading on here that when you adjust the fuel screws you turn them in until there snug. Then set your turns. Well my question is what happens if someone turned them in more then snug. I say this because I noticed when I set the screws to my spec I can see the needle part of the fuel screw sticking up in the carb intake. And they don't look the same height. Could this be from an over tighten of the fuel screws? I hope to get some feedback back on this because I have not seen a post about this issue. Thanks.
 
larry when you seat the air screw, do they tight,en. i would think if somehow they were striped it would just continue to turn. the low end bog can be a hundred different things. 3:16x (yammie tony)
 
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Well I bought a new fuel screw and put it in and you can barely see the needle now looking through the carb. That's kinda why I'm stumped here. I bought bigger Pilot jets but haven't tried it yet because I want to figure out the fuel screws first to make sure that's not causing the problem
 
Looking at the fuel screw you just bought and the other ones do they look the same in size? Try swapping the screw to another carb. See if you see the same difference. Make sure the seal and spacer are the same distance in the jet from tip to o ring. It could be the springs are shorter then the other new one.
 
Ok I'll check it out. I was thinking the previous owner tightened the fuel screw too much and maybe put a groove in the fuel screw stem? I don't know what it is made out of tho. I would guess it would be a softer metal. Sorry I'm just thinking out loud.
 
^^^^That may be the issue. You only need to "lightly" seat the fuel screws and then adjust out to proper setting. Perhaps remove all 3 and compare to see if someone strong armed them!
 
YAMMIEGOD3:16 said:
larry when you seat the air screw, do they tight,en. 3:16x (yammie tony)
Click to expand...

That's just it IDK why Yamaha along with most other manufacturers call them fuel screws. They are an air screw. Turn in to enrichen, out to lean.
When you went to the larger pilot this cured some of the lean condition. Turn the screw in a bit to eliminate the idle hang...............SRXtreme
 
Correct me if I'm wrong but, I believe if the screw is downstream of the slide (engine side) it is a fuel screw. If it is upstream of the slide it"s a air screw. Turn out to richen idle.
 
SRXtreme said:
That's just it IDK why Yamaha along with most other manufacturers call them fuel screws. They are an air screw. Turn in to enrichen, out to lean.
When you went to the larger pilot this cured some of the lean condition. Turn the screw in a bit to eliminate the idle hang...............SRXtreme
Click to expand...

sorry but your mistaken, the screws are "fuel screws" as they are before the slide in the carb(engine side of carb), they meter fuel not air. If the screws are located behind the sled(airbox side of carb) then they are air screws. This is like this on all brands of snowmobiles.

so on a yamaha snowmobile you turn the screws out from lightly seated to make the idle and low speed operation richer!
 
a srx600 should be using 47.5 pilots and 1.5 turns out on the screws from lightly seated. As to your original question you can over tighten them and usually it will either strip them out or it will smash the seat slightly, but just tighten till you feel it snug then turn out 360 degrees which is 1 turn then a half turn 180 degrees, repeat for all 3.

usually 1.5 out on srx is a good point to start they like being a little richer then leaner. if you find you need to be at 2 or more turns out you would want to go to the next size pilot jet after 2 turns out as the fuel screws will not have alot of thread left to hang onto,and usually youd need a 50 pilot at that point.
 
What about if the air box was gutted? Whoever had it before me gutted it and looks like they drilled some holes in the bottom of the air box. What can happen if I leave it that way? Could this be part of the bog that I had and maybe the idle hang too?
 
Larry Bryzelak said:
What about if the air box was gutted? Whoever had it before me gutted it and looks like they drilled some holes in the bottom of the air box. What can happen if I leave it that way? Could this be part of the bog that I had and maybe the idle hang too?
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I've played with this before and never had good luck with gutted airbox but this is only my personal experience. I've got adjustable inlets on my sled now and by the time I was happy with it they were pretty much closed haha. I think this could definitely be the source of your problem.

Sent from my E6560C using Tapatalk
 
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