Tillotson 101

korndog

korndog

New Member
#1
#1
There are several models of Tillotson carburetor to choose from and there is a bit of confusion as to what the model numbers mean and what size is best for each application. I asked my friend and mentor EC Birt (THE Tillotson man) to help out the mini bikers and we came up with this little tutorial. The current offerings available from Tillotson that you might be interested in are as follows:

HL-304WX - .875 venturi, 1.00 shutter. This carburetor is spec'd to have a lean drill pattern and to be prepared by the importer or builder to the customer's specifications. One thing for mini bikers to keep in mind is that this carb is really meant to be an alcohol carburetor once it's drilled. It has double volume stacks and a large inlet needle and seat not needed or necessarily desirable for most gasoline clones. Why isn't it good to have more volume? Well, you want the carburetor to be close to your needs in its basic form and only make fine adjustments with the needles. Closer it is to having the correct fuel curve, the easier to tune.

HL348F - .875 venturi, 1.00 shutter. This is a purpose built alcohol carburetor made for kart racing and is ready to go for OHV engines burning methanol.

HL-334WX - .790 venturi, 1.00 shutter. This carburetor isn't talked about much, but might be the best choice for most of the mini bike clones that are being built right now. The carburetor is setup to be a gas carburetor and is very close if not perfect right out of the box for gasoline OHV engines.

945 Special - This is a 304wx where the venturi has been bored to .945 and the throttle bore to 1.06". Drill pattern is optimized for the open class engines. This is the carburetor for the highly built cones with bigger valves and high lift cams.

All of these carburetors are upgradeable with special machine tricks and other blueprinting tasks to make your carburetor even better than out of the box. If you have any questions, you can PM me and I will get you an answer.
 
olajoe808

olajoe808

Banned
#3
#3
Gotta dig EC. That ole timer has to have the best sense of humor on all of 4cycle. Just about every post he ends with a hehe or something of that nature. Not too mention his many write ups. When I got my 380 gasser from Russ I went straight to the wizard for the lowdown on a alchy conversion. He had me on the floor rolling when he told me they only come from the factory built for alchy even though the one in my hand was a gasser straight out of the box. Man that was a hoot. But with as much know how about racing in general it made the most sense to give their operation the go ahead with converting the carb. Three carbs later, and still as much a fan as with the first.

Nice write up, good job...:thumbsup:
 
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korndog

korndog

New Member
#4
#4
olajoe808 said:
Gotta dig EC. That ole timer has to have the best sense of humor on all of 4cycle. Just about every post he ends with a hehe or something of that nature. Not too mention his many write ups. When I got my 380 gasser from Russ I went straight to the wizard for the lowdown on a alchy conversion. He had me on the floor rolling when he told me they only come from the factory built for alchy even though the one in my hand was a gasser straight out of the box. Man that was a hoot. But with as much know how about racing in general it made the most sense to give their operation the go ahead with converting the carb. Three carbs later, and still as much a fan as with the first.

Nice write up, good job...:thumbsup:
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Not sure on the 380 gas. He told me they never made a gas 380 and he designed that carburetor. There may have been some 1.06/1.125 carbs made for other markets, but the 380 is a proprietary number belonging to EC and was made for alcohol. Did you happen to take some pin gauges to the needle holes and discharge ports when you had it?
 
mmisterbungl

mmisterbungl

New Member
#8
#8
korndog said:
HL-304WX - .875 venturi, 1.00 shutter. This carburetor is spec'd to have a lean drill pattern and to be prepared by the importer or builder to the customer's specifications. One thing for mini bikers to keep in mind is that this carb is really meant to be an alcohol carburetor once it's drilled. It has double volume stacks and a large inlet needle and seat not needed or necessarily desirable for most gasoline clones. Why isn't it good to have more volume? Well, you want the carburetor to be close to your needs in its basic form and only make fine adjustments with the needles. Closer it is to having the correct fuel curve, the easier to tune.
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I'm starting to wonder if I'll ever get my 304 tuned with my set up. I can't get out of the lowend rpms without the motor cutting out:shrug: I've tried several combos with the high and low needle to no avail.:censure:
 
minidragbike

minidragbike

Supporting Speed Nut!
#9
#9
mmisterbungl said:
I'm starting to wonder if I'll ever get my 304 tuned with my set up. I can't get out of the lowend rpms without the motor cutting out:shrug: I've tried several combos with the high and low needle to no avail.:censure:
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The low needs to be open up more. It's to lean on the bottom. I bet if you ease into the throttle really slow it might get into the high RPM. But if you instantly hit it it will bog out.
 
korndog

korndog

New Member
#10
#10
minidragbike said:
The low needs to be open up more. It's to lean on the bottom. I bet if you ease into the throttle really slow it might get into the high RPM. But if you instantly hit it it will bog out.
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304WX - Charles is right. It's even possible it will be too lean even if the low side needle is out all the way or cut off at the tip. The low and transition discharge ports (and the needle hole) are too small for even gas if they are stock. If the guy you bought it from didn't set it up right, then you won't have any adjustment from the low side needle.
 
mmisterbungl

mmisterbungl

New Member
#11
#11
minidragbike said:
The low needs to be open up more. It's to lean on the bottom. I bet if you ease into the throttle really slow it might get into the high RPM. But if you instantly hit it it will bog out.
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yes, that's what happens exactly. if i gradually ease into it i can get up higher rpms. but if i slam it, BOG. I was talking with KD the other day and told him that I see there is a little aluminum looking collet in the lowspeed needle hole when I take the needle out and look in there.
 
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