Tecumseh hh100 carb

on my 72 10xl i have rebuilt the carb about four times and it isnt the lme carb its a walbro and now it idles but if you pull the throttle up it just plain dies i dont think its adjustments i am wondering if a hm100 carb will work with the governor if i use my original throttle shaft

Well I don't think that's a carb issue. I had a tractor that idled but when you gave it any gas it died, and it turned out that there was a bolt broken off under the head and it didn't have enough compression to run at high RPMs. I fixed that and it ran fine.
It could also be a bad head gasket, engine being too cold, stuff like that. Is it a flathead or OHV? Have you taken the head off recently, and if so, have you replaced the head gasket?

i dont know it has about 45 lbs compression cold and it used to before we rebuilt the carb only run at full throttle its a flat head

How many PSI?

Kinda hard to check compression accurately since the cam on some engines are made to dump compression starting up, easier on starter or pull starting it. Unless you know you overheated real bad, it would be safe to assume the rings are good. I would bet that the carb needs more adjusting. The engine idling and engine running at speed are considered 2 separate circuits (pathways) inside the carb, even though the 2 needs each other. You are getting gas to the carb and to the circuits. The idle circuit is after the main jet and branches off to the idle mixture screw, then to the barrel of the carb. The main jet (ofcourse) feeds fuel for running off idle which is where you are having the problem, so it sounds like this is where the problem is. Jets are certain size holes for certain engine sizes. If the carb came off a smaller engine or bigger engine then you get too little or too much gas.  Or maybe this is where the clog is.

A tattle tale sign that the carb is too small or too big is when you turn the screw for the idle mixture screw. Usually 2 turns is perfect. Less then 2 turns, then carb is too big. More then 2 turns, then carb is too small. Plus or minus 1/2 turn for fine tuning is normal.

Wrong jet size. Not too familiar with a walbro carb. Parts might not interchange on these 2. Techumsa carbs usually have an adjustment screw for the main jet on the screw that holds the fuel bowl on. Walbro, I have no idea if the main jet is adjustable or is a set hole diameter for the main jet, you can either adjust the main jet screw or drill out the main jet hole bigger. These carbs might have vacuum ports, plug those ports, they are vacuum leaks.

Techumsa motors have pressure lube oil systems. The oil pressure works the easy start on the cam. If low or no oil then the easy start won't disengage and engine will only idle if it even runs, plus will backfire trying to start engine through exhaust. And when it does run, will run and sound funny or weird at idle. Check oil level to make sure the level is full.

That's all I got, Hope it helps.

45 psi which it starts fine and runs good at idle but anything more it just falls on its face

It's the main jet or venturi tube plugged? I'm thinking that as the throttle valve opens it's not getting enough gas with the increased volume of air.

It should have 70 psi.

I have had the same issues on my kholer command that has a walbro carb on it . it would run for about 15-20 min fine then would die , taking the jet out wasn't an option because the jet screw was stripped out,putting a new carb on it fixed it but the 'new ' carb has some sediment that i am still cleaning out , the main jet has about 6 or 8 holes along the brass insert that clog pretty easily and just cleaning the bottom hole without taking out the jet does not clean the small holes which causes issues with how much fuel it can pull into the carb . also the needle valve can clog .

When you close the choke and throttle up it works? then its not getting enough gas through the jet or it has something impeding the vacuum system like one of the holes on the jet insert. when you take off the carb bowl does it have any oil in it ? the pcp could be blowing oil through and coating the internal parts of the carb and be causing it to blow some blue smoke from the burning oil . That would cause a reacuring problem of not running well .

which adjustment is idle the bottom screw or the side

the needle valve is kinda at an angle in the side of the carb close to the end that bolts up against the engine . the idle screw just hold the throttle plate at a point to set minimum closing so the engine doesn't die. the needle valve helps with fuel flow

oops i talking about something else . the idle mixture screw is by the engine side of the carb, it should be clean and 1.5 turns out from being all the way in

it will have a little spring under the screw part , and if this is a newer carb it will have a plastic knob on top of the screw that is very annoying

so the bottom is the high idle or the one that allows wide open

bottom of what ? the bowl ? i meant bottom of where the screw goes in , it needs to be screwed all the way in then back it out 1.5 turns . its located on one side of the carb and is closer to the engine block than the air filter . it can look like a regular screw with a little spring on it or it can have a plastic cap that looks like a little black triangle with a screw inside

I dont have too much experience with Tecumseh engines, but the ones I've seen the high throttle mixture screw in on the bottom of the bowl sticking out at an angle. Although judging by your initial post it sounds like the main jet is clogged, so as you rev it up and when it goes to switch from the idle circuit to the main circuit it cuts off fuel and kills the engine.

That's what i thought, but he said its a walbro and i have not seen a walbro with a side screw on the bowl, if its a model i am not familiar with then i am not being very helpful

is the motor a ten hp ? i googled the make hh100 and its the same carb as i have on my 10 hp Tecumseh but this is an old model and not sure the numbers are .

I googled the carbs and the 2 carbs mentioned should be interchangeable. What matters is the mounting holes on carb (ofcourse). You can google yourself and look for mounting specs. Ask questions to the seller of these carbs for the size of engine they are meant for (HP rating).

Here is a pic with the adjustment screws numbered and with a vacuum port.


1- idle speed, screw in to raise idle speed and screw out to lower idle speed

2- vacuum port, some carbs have them and some don't. If the carb you choose has these ports, you need to plug them off if not used because they are a vacuum leak if you don't. They also can be in different spots too.

3- idle mixture screw. Screw all the way in till it stops without forcing, then count the turns screwing out. Good place to start is all the way in, then 2 complete turns out to get motor running, then adjust accordingly. Newer original carbs do not have this adjusting screw and is preset at factory for a specific engine and engine size, will be difficult to use these carbs on other engines of different size or different HP ratings.

4- This is your main jet mixture screw, is the screw at the bottom and in the center of fuel bowl. 2 complete turns out is a good place to start to get engine running and adjust accordingly. OK, newer, original carbs won't have this screw, it will have just a brass bolt in it's place which means the main jet is NONadjustable, to adjust mixture on these carbs you need to remove this bolt, then remove the jet (some carbs, the jet and the bolt are one peice) and drill the jet hole bigger yourself, if drilled too big then engine will run rich on main jet because it is getting too much gas through hole.

5- Drain screw, used to drain fuel bowl for maintenance and storage of engine. Some carbs have this and some don't. This drain screw is off to the side on the bottom of bowl.



As mentioned in some of the descriptions, the newer carbs from original engines do not have the adjustable mixture screws on them They are made without them and the holes are drilled to sizes needed at the factory for a specific engine size, usually are a pain to put on different motors and usually don't run right. These carbs are for EPA specs to reduce emissions. You should stay away from these carbs.

I'm known to think outside the box sometimes. What happens if you loosen your gas cap? I've had an engine starve out on throttle up due to the cap being clogged.

mightyraze wrote:

I'm known to think outside the box sometimes.  What happens if you loosen your gas cap?  I've had an engine starve out on throttle up due to the cap being clogged.  

that is a real possibility i ran it without the hood for a while because one pin on the hood busted off and dirt off the hood itself


Mod Edit: Fixed your post, message in the title box    - Mightyraze

or your fuel filter is partially clogged . I had an old steel fuel tank on one of my mowers and it had an old fashioned screw in fuel shut off . the engine would run good for about 3 min, then die . I cleaned the carb like 3 times and took apart the fuel pump only to later find out the fuel shut off had broken and the lead tip of the valve had broken off and clogged my fuel line . What is this troublesome engine on anyway ?