Topic: Tillotson HR Questions

[more4les]

Well I remember from my youth having snowmobiles with these carbs on them. Not the best carb but easy to tune and repair. I'm running one now on my OHV single and I have a few questions. 1. Why are all the carbs I see used on mowers mounted upside down compared to snowmobiles? 2. The carb I have has an external pulse (3 plate). I've been told to lose the pump and feed it with an external pulse pump. any truth? (using intake pulse - know how to do that correctly) 3. I have rebuilt the carb and it seems to work ok usually. It doesn't tune like it did when we would tune 2 strokes with them. I guess I need a lesson on tuning these things. I'll take all the help I can get.

Lester

[BoNewCo]

 Good info on EC website under Tips & Trix.

[Huffy044]

Lester, I ran them on my Pro-X with a 31 ohv, it is extremely finicky, if it clouded up, I had to adjust the high speed. The low speed pretty much stayed where it ran best at low speed and my secret to the high speed jet was to use an external adjuster located near my steering wheel. It was amazing what a 1/4 of turn did and doing it on the track under load is in my opinion the only way to do it.

[more4les]

I agree with the under load tuning. I remember it was the only way to adjust them on a snowmobile was to ride them down a good straight away and tune to the highest rpm then 1/8 turn rich to keep from burning the piston. Now on the question of a remote fuel pump, should I use one and what modifications would I do to the carb? Do I unhook the pulse from the carb to use on the remote pump or do I run both pumps?

Lester

[Cromwell C4]

I always run both pumps. Run the pulse on the bottom plate to a fitting on the intake, just as you would for the remote pump. You can also cap the bottom plate fitting or use a sealed bottom plate, and then you would use the hole on the carb flange (shutter side) and angle drill the intake flange to where it goes down into the intake port. The factory gaskets and some racing intakes already come pre-drilled for this. And some snowmobile carbs dont have the hole in the carb flange drilled all the way through so you may have to drill it. For general tuning, set the fulcrum arm and pop off pressure for the fuel you are using and engine needs. If using alky, E85, or a highly oxygenated race fuel, you may have to do numerous other mods. When done correctly, they work great with little issue.

[George Herrin]

Call me lesterat home if ya dont have it pm me. I am not gonna get into a long typing deal trying to explain it all. Too lengthy. And yes you need an external pump. And the pulse on the carb plate is more for a two cycle setup.

[willenglish]

Long years ago when I raced open class two stroke karts...the happiest day of my racing career was when I retired my dual hl series carbs for a single hr series tillotson. The dual carbs were difficult to tune..and stay tuned. That hr would stay way more consistant. And still turn nearly 20,000 rpms!  Ahhh those were the days!