Blackmax
New member
when I swapped my 540 carbs to my 440 years ago, I changed nothing except for mains... then I went to 40s it made a huge difference, they are still on it actually... I think I still have them, I'll have to find my 540s carbs and see whats in them...
BM...
BM...
tyler440
New member
the needle clips are in the middle, the mains are 290's... sitting on the sled facing forward there are little screws on the right of the carbs slightly behind the slide... these are the ones that are 3 turns out... i am really interested in what your carbs have for jets blackmax...i was originally told to just use the carbs exactly the same as a 540 but that didnt work for me... when i richened it up it made all the difference in the world... also i have my floats lower than what the specs are... and that doesnt seem to make a difference.... im still getting a thick cloud of gas vapor out of the airbox side of the carbs
Blackmax
New member
for shits and giggles, put your 40 pilot back in and turn the pilot 1/2 turn out from seated position.... leave the clips on #3 on the needle and put your float back to spec and give her a whirle... your carbs should have Q0 brass and 6DH4 needle... I will look this weekend for the carbs...
BM..
BM..
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tyler440
New member
been there, tried that... thats where i started... see pervious posts 
Blackmax
New member
but you had the pilot turned out way to far creating a lean... now I'm thinking that your to rich with 50s....
also I reread somewhere that your idle screw is all the way in? if it is I think you should re-sycronize the carbs...
1. Adjust pilot screw to 1 ½ turns out (turn all the way IN till stops then count 1 ½ turns OUT). This assumes that the pilot gas jet has been cleaned as above)
2. Open the throttle to full open and check that each throttle slide is up the maximum amount (i.e. disappears up into the carb body). Adjust the cable adjusters until an equal amount of throttle slide is seen, just peaking through on each carb. It is surprising the number of sleds I have seen with a major difference in the full open position.
3. Once cables are adjusted for full open, fully turn out the throttle adjusting screws (to past were it touches the throttle slide)
4. Insert two 3/16" dia drill bits (or 4" long peice of round bar) into each carb (diameter size should be adjusted to suit the throttle cut away), seating the drill bit under the throttle slide, so that they stick out the end of the carb evenly. Screw in each throttle stop screw until the drill bit "dips" a little, find the happy spot, where the screw just touches the slide. Repeat for the other carb. With a felt pen mark the screw head flat-slot position for reference on each carb body..
5. With the drill bits still in place, perform the fine cable adjustment - by gently opening the throttle and seeing that each drill bit moves at precisely the same moment. Adjust the cable adjusters on the carb or on each cable so that movement is even (should be only ¼ - ½ turn each).
6. Start the sled it will likely idle too high, wait for engine to warm up, then adjust each throttle stop screw down (out) by EXACTLY the same amount, i.e a ¼ turn at a time on each, using the felt pen reference mark to make sure the adjustments are same. The idle should be even and by blipping the throttle the pick-up should also be even.
7. The pilot jet air screw may be adjusted at this time, but by very little, no more than ½ to 3/4 turn in either direction. The effective range of adjustment for the pilot jet is 1 turn to 2 1/2 turns. This is where a bit of skill & experience comes into play. By turning one screw a little at a time with the engine running (on both cylinders) you can gauge any difference in running and find the sweet spot. When you hear the engine revs race, you want to turn it back a 1/8 to ¼ turn - the sweet spot is not at the extreme. The idle may need to be dropped equally again.
If you have to screw it in all the way or out all the way, then the pilot circuit is still clogged, maybe not completely, but enough to affect the running. Go back and clean the jet.
BM...
also I reread somewhere that your idle screw is all the way in? if it is I think you should re-sycronize the carbs...
1. Adjust pilot screw to 1 ½ turns out (turn all the way IN till stops then count 1 ½ turns OUT). This assumes that the pilot gas jet has been cleaned as above)
2. Open the throttle to full open and check that each throttle slide is up the maximum amount (i.e. disappears up into the carb body). Adjust the cable adjusters until an equal amount of throttle slide is seen, just peaking through on each carb. It is surprising the number of sleds I have seen with a major difference in the full open position.
3. Once cables are adjusted for full open, fully turn out the throttle adjusting screws (to past were it touches the throttle slide)
4. Insert two 3/16" dia drill bits (or 4" long peice of round bar) into each carb (diameter size should be adjusted to suit the throttle cut away), seating the drill bit under the throttle slide, so that they stick out the end of the carb evenly. Screw in each throttle stop screw until the drill bit "dips" a little, find the happy spot, where the screw just touches the slide. Repeat for the other carb. With a felt pen mark the screw head flat-slot position for reference on each carb body..
5. With the drill bits still in place, perform the fine cable adjustment - by gently opening the throttle and seeing that each drill bit moves at precisely the same moment. Adjust the cable adjusters on the carb or on each cable so that movement is even (should be only ¼ - ½ turn each).
6. Start the sled it will likely idle too high, wait for engine to warm up, then adjust each throttle stop screw down (out) by EXACTLY the same amount, i.e a ¼ turn at a time on each, using the felt pen reference mark to make sure the adjustments are same. The idle should be even and by blipping the throttle the pick-up should also be even.
7. The pilot jet air screw may be adjusted at this time, but by very little, no more than ½ to 3/4 turn in either direction. The effective range of adjustment for the pilot jet is 1 turn to 2 1/2 turns. This is where a bit of skill & experience comes into play. By turning one screw a little at a time with the engine running (on both cylinders) you can gauge any difference in running and find the sweet spot. When you hear the engine revs race, you want to turn it back a 1/8 to ¼ turn - the sweet spot is not at the extreme. The idle may need to be dropped equally again.
If you have to screw it in all the way or out all the way, then the pilot circuit is still clogged, maybe not completely, but enough to affect the running. Go back and clean the jet.
BM...
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first off, it doesnt matter if you have the air screw at 1/2 turn out or 2 turns out, if thats where it runs good so be it, theres no performance advantage to having the screw in almost all the way, as I said before you need MORE gas in a piston port engine to rev smoothly then a case reed sled. What you may need is a slide with more cut away to tune in the idle. It is a general rule of thumb that once you get past 2 1/2 turns out on the air screw youd need the next size down in a pilot jet, but you may be just fine at 2 1/2 turns out with 50's once you have run the sled and cleaned out the case and pipes good. You can only do so much tuning on a jackstand!
Your going to always see a fuel spitback spray coming from the carbs on a piston port engine as well, no way around it! On the old sleds like rupps and stuff, your clothes would be absolutely soaked with fuel from the carb spitback coming out of the carb, this is perfectly normal on a piston port engine.
This is what I would do as my next step, reset the float level to std setting, I would then wait until the weather is cold out, below 25 degrees and test ride the sled with the floats set, 50 pilots, 3rd clip on needle, and your 290 mains, run the sled for a little stretch cleaning out the case and pipes and then do short burst of 150-200ft from a dead stop, pay attention to how smoothly it revs or any stumbling problems, check your plugs,piston tops.
then do short burst of 300-400ft and never use more then half throttle, do the same plug/piston checks.
then finally do full throttle runs of 500-600ft, and check the plug/piston wash.
you will be able to isolate the rich settings from the lean this way and tune the entire fuel curve in by doing it in steps.
Your going to always see a fuel spitback spray coming from the carbs on a piston port engine as well, no way around it! On the old sleds like rupps and stuff, your clothes would be absolutely soaked with fuel from the carb spitback coming out of the carb, this is perfectly normal on a piston port engine.
This is what I would do as my next step, reset the float level to std setting, I would then wait until the weather is cold out, below 25 degrees and test ride the sled with the floats set, 50 pilots, 3rd clip on needle, and your 290 mains, run the sled for a little stretch cleaning out the case and pipes and then do short burst of 150-200ft from a dead stop, pay attention to how smoothly it revs or any stumbling problems, check your plugs,piston tops.
then do short burst of 300-400ft and never use more then half throttle, do the same plug/piston checks.
then finally do full throttle runs of 500-600ft, and check the plug/piston wash.
you will be able to isolate the rich settings from the lean this way and tune the entire fuel curve in by doing it in steps.
tyler440
New member
wow, now ive got all kinds of things to try but they all kinda rely on cold weather and snow..... neither of which i have right now this winter sucks... its is snowing and blowing here now maybe later this weekend we will have some snow... maybe
but they all kinda rely on cold weather and snow..... neither of which i have right now this winter sucks... its is snowing and blowing here now maybe later this weekend we will have some snow... maybe
daman
New member
I was just wondering..so a STOCK 81 srx is a dog on the bottom,,how's it for trail riding,,should i avoid buying one..
Thinking of picking one up.........Hmmmmm
Thinking of picking one up.........Hmmmmm