Severe Pressure Problems (Cracked tank, pipe, carb???) PLEASE HELP

[TheSweeney]

I am still a total noob at this game but i think i get the general idea of how a nitro engine (And its fuel system) works. But for the life of me I just can't narrow this problem down, please help me.

Engine : SMT .15 CXPro
Carb : Unknown Cheapo Crap!
Fuel: Blue thunder 20%
Glow Plug: Generic crap (But is longer and hotter than the original supplied plug.....How much does this matter?)
Fuel and pressure lines: returned to original length (with fuel filter removed too) for testing..... it didnt help.

Now.... this problem could have been caused during a 'high' speed crash after a runaway, but its hard to say for certain as I ended my run after the crash without testing to ensure the car was 100% OK.
The engine ran, servos responded, And every part of the car appeared physically undamaged. So i packed the car away and came home. The only testing I did was to remove the fuel tank/lines and test the system for leaks underwater. There was a SLIGHT leak and I fixed that (Seems to be fixed using the same underwater test) using some builders silicone.

I didnt get a chance to run the car for weeks after that so thats where the ambiguity comes in, know what I mean?

Since then, I've never been able to get the car to run properly......
Its starts up no probs.... but once it warms up it wont let me get past about half throttle without the engine struggling/choking/chugging and then dying unless i release the throttle.
Before the crash this car/engine had barely been broken in and it was still running fairly rich so i assumed it wasn't that. I leaned the HSN in a bit and the symptoms got worse. so i richened it up a fair bit and it got slightly better. richened it up some more and it got slightly better. in the end I got the HSN so far out that i thought it was gonna spring out the carb and hit me, and the damn car still wasn't running quite right.

By this time i thought i had some major problems, and I assumed it was all down to lack of fuel at high speed and i put this down to lack of pressure (I knew the engine was getting air as it was a new filter and the carb opening was clear. It was getting heat or a source of ignition because the plug was new and burning HOT under a fully charged ignitor, And I knew the engine had decent compression 'cos it was/IS new and pretty stiff to turn over for a small mill).

Also, just for kicks, i removed the pressure line from the exhaust while the engine was running, and not only did the engine idle for just about ever but it also gave me the same ammount of range in how much throttle i could use. REMOVING THE PRESSURE LINE MADE NO DIFFERENCE!

Now... I AM a noob, so forgive me if this is mad, but ....
I thought that a good test to see if the problems where due to a lack of pressure, would be to remove the pressure line from the exhaust while the engine was running. Then I gave it about 50% throttle and it started to struggle so I started to blow into the pressure line! The revs went back up!
I then slowly increased the throttle while increasing the ammount of air i was blowing into the tank. The mill gradually increased in speed untill it was at 101% and it was screaming like it had never done before.

Does that prove its a pressure problem???

I've made pretty sure the leak in the tank is sealed, and I've tried all sorts of madcap ways to increase pressure but nothing seems to work.

What should I do next? This thing is driving me mad.
On the very rare occasion i get the chance to chill out and run the car, i just end up sitting in the back garden fiddling with the car for an hour before giving up.

I have only put about a third of a gallon through this car in THREE MONTHS!!!
PLEASE HELP ME GET MY MONEYS WORTH OUT OF THIS PIECE OF poop SMARTECH!!! Yes you heard me. I own a smartech! I realise now that these things suck. But I'm damn sure that I should be able to get more than a fecking 1/3 gallon out of it!!!

Please help me fix this until I can afford to buy a REAL nitro RC car.
Sorry to any Smartech owners...........Really Sorry


Rant over!

I need to go and chill for a while.

Cheers
TheSweeney.



Final thought: :idea:
How about an in-line one way valve for the pressure feed???

How about a really tiny water pump to push my fuel into the carb? Am I Cracking up? :help:

 

[CJ-FOREVER]

Is the primer leaking air?

 

[TheSweeney]

It was blowing a few bubbles when i tested my botched crack repair, but I had to blow like a mofo to get it to leak.
PLUS the primer button does sometimes stick at 15-20% depressed, if i dont manually pull it back up. Could that be it? I didnt even think of checking that. What a numbnutz!
I'll make sure that the plunger is fully up next time i try it out.

Thanks for the reply.
So... could a leaking or stuck primer cause such a severe lean condition?


Cheers,
TheSweeney

 

[CJ-FOREVER]

I know that motor does not build up a lot of pressure (@ least mine doesn't) I would go and get a primeless tank. I also changed my fuel lines to 8" both carb and pressure. (It made mine easier to tune) Also check you exhaust for leaks. After the crash it might have moved something. Also make sure the head is on tight and the pullstart to. There might be leaks there too.

 

[TheSweeney]

Thanks for the advice CJ. Much appreciated.
And you know what ? After the crash I partly stripped the car, and I removed the pullstart to clean the one-way( It was slipping, due to running waaay wich) . So maybe the leak IS there. I didnt even realise that the pullstart COULD leak. So I havnt even checked/sealed it. I gotta lot to learn
I'll check it out along with the exhaust and the head.
If that dont do it then I'll get the primerless tank. And As I'll probably end up buying one anyway, even if i do sort out my problems....... Any idea what tank would fit a Winner sport?



Thanks a lot for ya help :thumbsup:

 

[CJ-FOREVER]

I will have to get back to you on that one. I have to look and see what tank I bought. Is the sport the buggy? I have the onroad.

 

[TheSweeney]

Yeah, the winner is the 1/10 buggy, the stock tank is a 80cc with the pressure line feeding into the top-corner of the tank rather than the center of the filling cap/lid.

Cheers man,
TheSweeney

 

[olds97_lss]

More than likely, this early in the life of the engine, it's not your pull start leaking, but it may be the backplate. The plate the starter houseing is screwed too.

Also, check your manifold. I don't know the engine, so I don't know if it's a rear exhaust with a round port and springs or not. Or if the muffler is plastic vs aluminum.

With the pressure hose off the tank but on the exhaust, you should get a pretty solid stream of smoke coming out of it when the engines running. I would check the manifold gasket. If it's the kind I described, the gasket is just a silicone ring that keeps the manifold sealed to the engine. If your missing the manifold spring, or the gasket has a big tear in it (from the crash), you could be losing your pressure at the exhaust port on the engine. Or if it's not like I described, I'd check it anyway just to be certain.

Putting a one-way valve on the pressure line has caused more problems than it fixed IME. I tried it a couple times on a couple different engines on my maxx and didn't have good results.

 

[TheSweeney]

Thanks for the info olds97_lss.
I havnt had a chance to check anything yet hopefully at the weekend

The engine has a side mounted exhaust with a plastic muffler. I'm assuming that the gasket is the very thin black 'bit' between the engine and the manifold???? I'll check that as soon as i can. I hate to sound like a dummy but how DO i check the seal of the gasket/manifold and also how do i check the p/s and backplate? and if i do find leak(s) on either of these parts how do i seal them i.e. is there a product I should use to seal them anyway, just as a matter of good maintenance?

Also the muffler is joined to the manifold with a sort of rubber/silicone tube and a couple of zip-ties, is that normal on nitro engines? or should i replace that with something?

Thanks a lot for all ya help fellas.

 

[CJ-FOREVER]

The rubber tube and zip ties is normal nitro engine. I put a duratrax tank in mine due to limited space.

 

[olds97_lss]

Thanks for the info olds97_lss.
I'm assuming that the gasket is the very thin black 'bit' between the engine and the manifold????

Yes, it is. On a rear mounted/round port exaust, it's a soft plyable gasket that can easily get torn if the manifold takes a direct hit. Over time, the vibration actually wears holes in it. You don't have this kind, so I couldn't see it being that.

how DO i check the seal of the gasket/manifold and also how do i check the p/s and backplate? and if i do find leak(s) on either of these parts how do i seal them i.e. is there a product I should use to seal them anyway, just as a matter of good maintenance?

The checking for a leak is more of a phrase than it is an acual action. I believe you can check for a backplate leak by spraying nitro cleaner around the seam while it's running. But to avoid that mess, I just seal it up with sensor safe automotive high temp silicone and let it cure overnight. I take the backplate off, clean it with alchohol and the part of the crank case that touches it. I then apply a small bead of the automotive silicone around the perimiter of where the backplate and crank case meet, put it back together and wait until the next day to give it a run. I also do the same kind of thing with the carb neck to avoid leaks there as well.

As for the manifold, if it was the round port/silicone, (which it isn't), you just check for wear and holes like you would fuel line.

Also the muffler is joined to the manifold with a sort of rubber/silicone tube and a couple of zip-ties, is that normal on nitro engines? or should i replace that with something?

This is how a lot of them are connected. I recently had a tear in the silicone coupler on mine that caused a bad air leak and made for bad tunability. I'd pull the coupler off and inspect for a hole or tear in it. Mine was on the bottom back side so I could see it, but I had a puddle of oil under the coupler after running it.

 

[TheSweeney]

Thanks for getting back to me on the tank issue CJ, I'll start checking out what duratrax primerless tanks are available around here.


olds97 Thanks for clearing all that up for me,
I'll give all the possible leak points a thorough check at the weekend and tomorrow I'll try and pick up some of that auto silicone so that I can seal all the 'joins' when i rebuild.

Thanks for all your advice fellas, you've really helped me out.

Cheers

TheSweeney