MTA4 s50 - arrgh won't run

[dazzercx]

Hi All,

Newbie to this forum and a returner after 15 years to RC.

I have a "new to me" Thunder Tiger S50 (uk if that makes a difference) which is next to new and still needs to finish breaking in but I cannot get it to run at all under it's own steam.

Story so far (apologies for going to much into it).

Will run at first prime then dies after fuel runs out in carb (i'm assuming).

Removed fuel primer bulb from the circuit. Attached new line and spun motor over with finger over exhaust - she primes just fine.

Started it and runs then dies after after a few seconds as with the primer bulb installed. You can see bubbles going backwards if that helps but may be just where it just died?

When I put the primer bulb back in she will carry running if I squeeze the primer bulb bit by bit (almost like a fuel pump.

I would assume a vacuum issue but it primes fine with finger over exhaust.

I have bought a new carb and reset to factory settings thinking it could be the carb. Exact same thing.

Loads of compression. Sounds great when manually priming once running?

Confusing the hell out of me.

Any help more than appreciated.

Pic of how it is put back to factory as i got it!

 

[Rolex]

Probably not a pressure leak since it will prime by plugging the muffler. Not a gummed carb since you have the same issues with the new one. That takes us to the next step of possibly being way too rich since the break-in wasn't completed and the new carb is the same. Just for a starting point, lean the HSN about half a turn and let us know what it does, then we'll take it from there.
Also, have you run it with the glo igniter still attached after it starts?

 

[Heisenburg]

Welcome to RC Talk

 

[dazzercx]

Probably not a pressure leak since it will prime by plugging the muffler. Not a gummed carb since you have the same issues with the new one. That takes us to the next step of possibly being way too rich since the break-in wasn't completed and the new carb is the same. Just for a starting point, lean the HSN about half a turn and let us know what it does, then we'll take it from there.
Also, have you run it with the glo igniter still attached after it starts?

Thanks - tried running with the glow still on - no difference. Leaned in the HSN half a turn and no difference!!

Has me stumped for sure!

 

[dazzercx]

Welcome to RC Talk

Thanks - good to be here!

 

[R/C Ambassador]

Assuming all the peripherals are in good working order, i.e. glow plug, air filter, clean fuel, glow ignitor etc. Let's evaluate the primer bulb. Primer bulbs (as I'm sure you know) are essentially designed to get fuel to the carb without having to rotate the engine while placing your finger over the exhaust stinger, or the way we used to to do it, by pulling the pressurization line off the exhaust and blowing into it, yuck. Anyway, the bulb is not necessary and can be removed if you do not want it there. They can easily be the cause of small leaks, because over time, nitro fuel degredates the silicone material (even if the model has been used very little, the residual fuel in the line has the same effect). Remember, nitro engines have a vacuum just like automobile engines and can be tuned for good performance without a pressure line. Ok. Now let's assume the bulb is removed, lines replaced (just couple of bucks), and that still does not work. Here are some good ballpark settings that should get you back to jump street.
1. High speed needle= 3 1/2 turns from closed
2. Low speed needle= 1 3/4 to 2 turns from closed, or flush with barrel body, check the spec.
3. Idle speed screw= look into carb barrell at the slide. At idle, the gap between the slide and the inner diameter of the carb barrell should be about the width of 1 credit card.

Hope this helps.

 

[Rolex]

Just to do a quick check, drop some fuel down the carb throat. Don't put the filter back on but start it immediately. With fuel inside it should start instantly if the glow plug and igniter are both good. It will run full throttle for 2 to 3 seconds and then quit. Let us know what happened.

 

[Tunedfrog]

I use a paper clip for the gap in the carb, quick and easy and keep one or two in my field box.

 

[dazzercx]

Assuming all the peripherals are in good working order, i.e. glow plug, air filter, clean fuel, glow ignitor etc. Let's evaluate the primer bulb. Primer bulbs (as I'm sure you know) are essentially designed to get fuel to the carb without having to rotate the engine while placing your finger over the exhaust stinger, or the way we used to to do it, by pulling the pressurization line off the exhaust and blowing into it, yuck. Anyway, the bulb is not necessary and can be removed if you do not want it there. They can easily be the cause of small leaks, because over time, nitro fuel degredates the silicone material (even if the model has been used very little, the residual fuel in the line has the same effect). Remember, nitro engines have a vacuum just like automobile engines and can be tuned for good performance without a pressure line. Ok. Now let's assume the bulb is removed, lines replaced (just couple of bucks), and that still does not work. Here are some good ballpark settings that should get you back to jump street.
1. High speed needle= 3 1/2 turns from closed
2. Low speed needle= 1 3/4 to 2 turns from closed, or flush with barrel body, check the spec.
3. Idle speed screw= look into carb barrell at the slide. At idle, the gap between the slide and the inner diameter of the carb barrell should be about the width of 1 credit card.

Hope this helps.

Thanks All,

I have tried without the primer bulb and no difference.

I'll go back the basics and try again.

She does run with fuel straight in the carb throat.

Will let you know what happens!!

 

[cbaker65]

Hi All,

Newbie to this forum and a returner after 15 years to RC.

I have a "new to me" Thunder Tiger S50 (uk if that makes a difference) which is next to new and still needs to finish breaking in but I cannot get it to run at all under it's own steam.

Story so far (apologies for going to much into it).

Will run at first prime then dies after fuel runs out in carb (i'm assuming).

Removed fuel primer bulb from the circuit. Attached new line and spun motor over with finger over exhaust - she primes just fine.

Started it and runs then dies after after a few seconds as with the primer bulb installed. You can see bubbles going backwards if that helps but may be just where it just died?

When I put the primer bulb back in she will carry running if I squeeze the primer bulb bit by bit (almost like a fuel pump.

I would assume a vacuum issue but it primes fine with finger over exhaust.

I have bought a new carb and reset to factory settings thinking it could be the carb. Exact same thing.

Loads of compression. Sounds great when manually priming once running?

Confusing the hell out of me.

Any help more than appreciated.

Pic of how it is put back to factory as i got it!

If that has a Mix meter setting ,which is the brass looking screw on the side of the carb. ,make sure that it is set at flush
with in the outer housing of the carb casing ,if that is closed off too much ,you wont get enough fuel flow for that pig!

Also .the fuel line that goes into that style muffler ,pull it out ,an cut the tip off in an angle so that it doesn't bottom out
an close off the pressure to the fuel tank.
Make sure that the tank lid seals good an not losing the pressure ,also ,make sure that the tank filter is not clogged .
that engine is a fuel pig!

The truck looks new ,so it will be a little hard to break it in!

 

[D3MON]

Thanks All,

I have tried without the primer bulb and no difference.

I'll go back the basics and try again.

She does run with fuel straight in the carb throat.

Will let you know what happens!!

given it ran with fuel direct in carb, I'm assuming the engine is not getting prime, follow @cbaker65 advice and try to track down leaks, or plugs in tank.
might try removing the carb and cleaning that out with either some denatured alcohol or soaking it in nitro fuel.
best bet may be to remove needles so its easier to clean out the internals.
also when you are priming the truck with the primer bulb, after a few pumps of the bulb you should feel resistance when the fuel gets to the carb, you should squeeze the bulb half to a quarter more. to get enough fuel in the engine.
double check make sure the primer bulb arrow is going the right way, I've installed it backwards on accident before lol.
to check your tank for leaks, remove the tank, plug one of the lines going out of the tank and blow into the other going in. if it wont pressurize well or releases pressure slowly you know you have a leak.