Tillotson HR Carburetor

Sliquifire · Post by **Sliquifire** » Tue Feb 05, 2008 2:34 am

Besides a JD I also own a '72 Merc Lightning. This sled has a 398cc CCW fan with a single Tillotson HR Carb - stock. I have a good idea on what the stock High Speed, Low Speed and Idle mixture screw settings should be at. What I'm not sure of is how to properly adjust these screws for fine tuning. I'm told that the High and Low speed screws adjust air mixture type settings rather than fuel mixture settings - is this correct? I'm trying to figure out what direction to turn the screws to get my desired setting without burning up my sled! Does turning the High and / or Low speed screw in - lean or richen each respective end? Does anyone have or know where I can find fine tuning information on this type of carburetor? I've already checked the Merc site and did other serches with no luck. Any help would be appreciated! I'm trying to get a better idle and get rid of some low end bogging.

PS: I've got more engine info if it's needed.

Thanks,

Slick

JDFanPa · Post by **JDFanPa** » Tue Feb 05, 2008 3:02 am

Start the sled and let it warm up and idle now adjust the low speed this 1 requires a screwdriver the high speed has the tabs on it so you can use your fingers. Turn the low speed in until sled starts to drop rpms then slowly back it out until you get your highest rpm once you get that you may need to back off the idle set screw if the rpms are to high. The high side is best set while riding the sled start with the screw out 1 and 1/4- 1 1/2 turns now hopefully you can have a nice spot to open the sled up while running wot turn the screw either way until it runs the best once you find this spot just back it around 1/8 of a turn. If you get a bog after finding this sweet spot turn the screw in a small amount at a time until it clears up. Just remember these high speed settings are not permanent they may require adjusting with temperature changes.

Sliquifire · Post by **Sliquifire** » Tue Feb 05, 2008 12:23 pm

OK - got it, thanks. But I'm still confused on which dirction to turn the low & high speed screws i.e... if I check the plugs and see that I need to lean out the high end or Low end screw, do I turn it clockwise or counter clockwise to lean? Also, how does an Idle Mixture screw adjustment come into play?

Sliquifire · Post by **Sliquifire** » Wed Feb 06, 2008 2:19 pm

Wow, it looks like I may have stumped this site on this one? First Time - LOL.
Looks like the old Merc will be getting a Mikuni carb replacement kit!

Again, thanks for your help. This site does indeed rock!

Slick

Liquifire 4/6 · Post by **Liquifire 4/6** » Wed Feb 06, 2008 4:22 pm

On a Tillotsen carb, you turn the needles in to lean them, and trun them out to richen them. This applies to both the high speed and low speed needles. They're really not that bad of a carb, but you usually need to dismantle them at the start of every season and install new diaphrams.....the nice part is that carb kits for them are dirt cheap and they're real simple to work on.

Sliquifire · Post by **Sliquifire** » Wed Feb 06, 2008 7:06 pm

Excellent, thanks for your help. Looks like I spoke too soon about the stumping thing!

JDFanPa · Post by **JDFanPa** » Thu Feb 07, 2008 2:55 am

I wasnt stumped just didnt get back to reply. Pete is dead on about putting the kits in every year but yes they are cheap and take about 5 minutes to install. I actually prefer a tillitson over the walbro just for the simplicity alone. I have them on 2 of my deeres but theres no easy way to hook up the choke cable in the big downfall.