only fuel screws on tm carbs-wtf?

[stumpy2000]

ok i pulled a bit of a boner today while cleaning the carbs (mikuni tm40's) on an '03 800 HO with rage cages on it...i didn't check the settings on the fuel screws before i popped them out..on the older mikuni carbs (vm's etc) with the separate air & fuel screws i could dial it in from the 1 1/2 turn base setting etc...does anyone know the base setting or the absolute minimum ("safest" lean setting) for the fuel screws on these carbs?i'd hate to have to yank my guts out or melt some chit before getting it dialed in...i assume that the idle speed adjustment controls the air setting for these carbs- so i shouldn't have to worry about that (cause i left it alone) any suggestions would be great cause once the carbs are on the machine it's next to impossible to fug with the mag side screw for adjustment...

 

[Summit8]

Start with 1.5 turns out on the fuel screws, if motor doesn't want to idle down till you hit the choke, give them a half turn out until idle drops down. I've gotta do this after dropping the needle height on notch.

Remember, air screws are on the airbox side of the carbs, fuel screws are on the reed valve side of the slide housing.

 

[stumpy2000]

thanks but- i've only got the fuel screws on these carbs (they're the flat slide type-they don't even have the removable needle jet tubes)...i tried @ 1 1/2 turns to start but it sounds kinda "blubbery" & only seems to get worse as the sled warms up.can a guy just keep tweeking them in and adjusting the idle speed down to establish a safe "minimum" setting (like with the air screws etc on the round slides) or is this gonna cause a " FATAL "lean condition of some sort?it'd be nice to know what to expect or just be aware of...

 

[FNG]

I have an 06 Adrenalin 800 with TM 40 carbs, I also have an 01 Summit 700 with the same carbs, the manual reads "CARBURETOR ADJUSTMENTS: Adjustments should be made in the following sequence:
-Pilot screw adjustment.
-Carburetor synchronization and throttle slide height (preliminary idle speed adjustment).
-Throttle cable adjustment.
-TPS reset (Power Tech engine)
-Idle speed adjustment (engine warmed up, all components installed)."

Then it states
"PILOT SCREW ADJUSTMENT: Completely close the pilot screw (until a slight seating resistance is felt) then back off as specified (1 1/2 turns all engines)."

Turning the screw clockwise leans mixture, and counterclockwise enrichens the mixture.

 

[stumpy2000]

does it list a maximum +/- tolerance for that setting or? i'm thinking that the rage cages on this thing are causing it to run rich in the "bottom end". mostly i'm concerned about leaning 'er out too much and creating a lean condition in the mid range transition by cranking the fuel screws in too far (SQUEAK!...) if it wasn't such a royal pain to re-adjust them while it's running i'd feel better about experimenting....thx again

 

[FNG]

In general if you have to go more than 1/2 turn in or out from the starting 1 1/2 turns out from full in and snug then you need to re-jet.

You actually can get at that little bugger of a screw on the MAG side but it takes a very long and very thin flat blade screwdriver and you are more poking at the cogs on the side of it to get it to turn. I bought a set of 4 or 5 of them for maybe $6.00 at Harbor freight but any long fairly stiff metal rod may get it, heck a bicycle spoke may work and any good bike shop in town will sell you one for a dollar or two. You do need to push a few things out of the way but it is doable for just a slight adjustment. Again, if you have to change the air/fuel screw by more than 1/2 turn just do it right and change your jetting. BTW, when I put Rage Cages on my 01 Summit 700 recently I had to go down 2 sizes in the main jet and turn the air/fuel screw in (clockwise) 1/8 turn. I had to go from a 520 to a 490 (which is actually just 2 jet sizes as Mikuni did something funky when they went to jets larger than 500, the jet sizes don't actually correspond directly to the jets under 500, it is not a linear progression as you would think it should be (got this information by calling Mikuni) so going from a 520 jet to a 500 jet I saw no real difference, dropping to a 490 caused a noticeable difference and ended up being just right for my carbs.

 

[stumpy2000]

this thing used to have a high compression head + etc on it- but it's all back to stock now (except the carbs and cages...) i dropped the mains back to the 430's (it came with 460's) for a "safe" starting point but they're still a little rich...the pilot's are still the 17.5's but i was unsure of the adjustability of the fuel screws on these carbs - you can't just get your hands on the air AND the fuel like the old ones...it seems really fat on the bottom- but it could also be the 0 degree celsius weather we're having too
it's not too often that ya can poke around under the hood in a t shirt outside this time of year!

 

[Summit8]

Do you have adj. needles so you can drop your needles one notch?

 

[stumpy2000]

think i cured my issues... went for a rip this weekend and snapped off the choke lever...running clean n crisp now-lol!musta been hanging up some how - cause it was adjusted as "loose" as ya could get it on the rack....thx for your help everybody!