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Discussion Starter · #1 ·
So this new sled I bought had some running issues. It has compression and spark. So I thought it was a fueling issue. I have the carbs apart, they are of course filled with mystery substance gel clumps. Anyways, I checked the settings of the adjusting screws (some sort of piloting I guess) and wanted to verify the settings.

1994 Thundercat 900cc

Okay, I counted the turns in until it stops...

Carb 1 (PTO leftside):

Big Screw - 3.3 turns
Small Screw - 2 turns

Carb 2 (Middle):

Big Screw - 5.5 turns
Small Screw - 1 turn

Carb 3 (rightside):

Big Screw - 5.7 turns
Small Screw - 1 turn

Does this sound normal? If not, what do you guys recommed a better starting point? I think the engine was flooding out (the trunk was filled with over 20 spark plugs, fouled?).

Thanks in advance!
Ken
 

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The small screw (air mixture screw) should be 1 turn out. The others with the springs I never count. I set them up with carb slide in so that there's one eighth of an inch gap at the bottom of the carb slide when you look through the small side hole of carbs {the side that goes into the engine) (all exactly the same) Then I adjust cables so that all slides start to move at same time by laying carbs side by side and working throttle a bit.
 

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Discussion Starter · #3 ·
<div class='quotetop'>QUOTE (thundercat900 @ Jan 31 2007, 01:26 PM) <{POST_SNAPBACK}></div>
The small screw (air mixture screw) should be 1 turn out. The others with the springs I never count. I set them up with carb slide in so that there's one eighth of an inch gap at the bottom of the carb slide when you look through the small side hole of carbs {the side that goes into the engine) (all exactly the same) Then I adjust cables so that all slides start to move at same time by laying carbs side by side and working throttle a bit.[/b]
I cannot grasp what you are meaning with the larger screw. Attached is a picture: down the small bore

 

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<div class='quotetop'>QUOTE (WhiteHawk @ Jan 31 2007, 05:02 PM) <{POST_SNAPBACK}></div>
<div class='quotetop'>QUOTE (thundercat900 @ Jan 31 2007, 01:26 PM) <{POST_SNAPBACK}>
The small screw (air mixture screw) should be 1 turn out. The others with the springs I never count. I set them up with carb slide in so that there's one eighth of an inch gap at the bottom of the carb slide when you look through the small side hole of carbs {the side that goes into the engine) (all exactly the same) Then I adjust cables so that all slides start to move at same time by laying carbs side by side and working throttle a bit.[/b]
I cannot grasp what you are meaning with the larger screw. Attached is a picture: down the small bore


[/b][/quote]
like thundercat900 said the big screw with spring in the pic is your idle screw... put a 1/8 drill bit in that end that you see in the pic so the slide sits on it and then turn the idle screw in until the slide lifts slightly...


BM...
 

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this was posted on carb syncronizing awhile back on here, I just had it saved as a file....
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This is one area where there is a lot of misinformation on the process, even in workshop manuals. This will outline the simple methodical professional shop steps to synchronize your twin (or triple) 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 a 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.
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BM...
 
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