Tillotson TFB Carb Won't Start

#1
I have a stock predator hemi that I have installed an electric start, stage 1 filter and jet from GPS and a 1 inch exhaust with a silencer on it. So far I had the stock carb with the larger jet on it and it runs and starts ok, but since the stock carb doesnt have a fuel mix screw, I bought a $15 replacement off of Amazon to get some adjustment to get it to work a little better. With the Amazon carb and the jet it came with it barely ran or idled when I put the big jet in it the thing ran poorly and smoked like it was too rich. So I put the stock carb with the big jet back in and its back as it was before, but I want it to start better and idle better.
So I purchased a TFB carb and got a chance to get it installed today. It wont even start now. After reading about it a little bit I learned it has an accelerator pump that squirts some fuel in it. With that knowledge I tried again by twisting the throttle body 10-15 times and it starts and turns over 3-5 times and dies. So it seems like its just not getting fuel. Does this carb need a pulse pump to operate correctly? Is there something else I need to do with this to make it operate?
 
#2
Pull the spark plug, if it’s wet you’re obviously flooding it. You normally shouldn’t have to pump it that much ( for the lack of a better term ) If wet, dry it and the cylinder out and try again without twisting the throttle.
New guy jumping in.
Often times people think bigger carb means more power. Well yeah if your turning high rpm’s, bigger valves etc…
On that motor I would stick with the stock carb and jetting.
That’s assuming you’re still using a governor. If not a slightly larger jet is in order. My suggestion is put stock carb and jet back in and run the piss out of it and check the plug porcelain color when it’s hot…If it’s light brown leave it be.
 
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#3
Thanks River, the "carb" I have on there now is a Tillotson TFB, which is supposed to be a "fuel injection" carb. From what I have read it relies on vacuum pulses from the engine to provide a fuel injection type of thing. There are no jets or anything, and the diameter of the inside of the car is actually a little smaller or almost the same size as the stock carb. So, the whole thing is a little different than the stock carb. Pretty much every example I have seen of these on the net have a pulse pump supplying the fuel.
 
#4
Thanks River, the "carb" I have on there now is a Tillotson TFB, which is supposed to be a "fuel injection" carb. From what I have read it relies on vacuum pulses from the engine to provide a fuel injection type of thing. There are no jets or anything, and the diameter of the inside of the car is actually a little smaller or almost the same size as the stock carb. So, the whole thing is a little different than the stock carb. Pretty much every example I have seen of these on the net have a pulse pump supplying the fuel.
That’s a new one on me. Time to read up on this as it’s an interesting concept. I’m a hot rod guy at heart, these mini bikes have me obsessing. Sorry if I was preaching to the choir with regards to carbs. From what I read this should be a direct replacement for a stock carb, without jetting issues…very cool. It sounds like a no brainer ….hmmm are the galleys, ports on the carb lining up with the gasket / motor ? Pulling a pulse problem ? You’re looking for answers, I’m asking questions….my bad….
 
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toomanytoys

Well-Known Member
#5
I have one of those tillotson carbs on the shelf. Never tried to use it yet. I’ve read some extremely mixed reviews on it.

there is no mixture screw on the stock carbs as you are aware but there is a pilot jet you can change. Stock is .16 I changed it for a .20

this helped the idle and the off idle stumble I had. I’m running .37 main and .20 pilot on a ruixing amazon carb. But jetting numbers are way too subjective for it to be a rule.

https://www.google.com/amp/s/www.bm...o-GX200-Clone-Predator-212cc_p_119.html?amp=1
 
#6
Right, the only galley I saw motor side was that standard little one that has the hole in the top left of the gasket, and opens up under the back of the carb. Thats what I originally thought might be "powering" the carb, so I thought it was odd that it seems like a standard 212 carb. So yes I was careful to get that gasket and the one on the heat shield right. I wonder if I need to remove the heat shield? Like you said everything indicates that you just bolt it on, adjust the mixture/idle and go... or maybe it needs that pump, I have one and may install tomorrow just to see if that makes it happy, unless someone else chimes in.
 
#8
I actually got it to work today, no pulse pump, just turned the mix screw allen head counter clock-wise 3/4 of a turn and opened the idle up 1/2 a turn. At the moment I dont have the chain on it just the torque convertor, and in that configuration it seems to run pretty smoothly. I left it set for about 3 hours to cool down and it started right up with the choke on. Going to see tomorrow morning how it behaves and if it seems ok I am going to get the chain on it and finally ride it tomorrow.
 
#9
Right, the only galley I saw motor side was that standard little one that has the hole in the top left of the gasket, and opens up under the back of the carb. Thats what I originally thought might be "powering" the carb, so I thought it was odd that it seems like a standard 212 carb. So yes I was careful to get that gasket and the one on the heat shield right. I wonder if I need to remove the heat shield? Like you said everything indicates that you just bolt it on, adjust the mixture/idle and go... or maybe it needs that pump, I have one and may install tomorrow just to see if that makes it happy, unless someone else chimes in.
Are there carbs getting a pulse from the block through the gasket/flange? I always wondered what those worm holes were for...
 
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#10
I am not really sure Mike... I dont see where else it would be getting any "energy" from other than that hole at 10 oclock on the gasket.
There is not a whole lot of info about these out there... the TCT version seems to have more info than the TFB version of it, but I think the only difference is the bore size of the carb.
 
#11
I am not really sure Mike... I dont see where else it would be getting any "energy" from other than that hole at 10 oclock on the gasket.
There is not a whole lot of info about these out there... the TCT version seems to have more info than the TFB version of it, but I think the only difference is the bore size of the carb.
So there's no vacuum port, like to power an internal diaphragm? I've heard of power boost or whatever but assumed it was built into the carb itself. I think I also assumed it was a thing of the 2-stroke world, or full blown motorcycles?

And then is there a float in the carb? (I haven't looked it up, I'm being lazy). I'm just thinking here that if a pulse pump is needed to drive the booster, I wouldn't expect a float needle to be restricting flow in the usual way.
 
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