fuel not moving through the tubing when i prime

[sandiegan]

HELP!

Motor will not turn on or run.

Fuel is not moving towards the carb when i prime (pinch exhaust and pull the pull-start)

if i pull the starter very rapidly, the fuel barely moves up like an inch.

I have replaced the fuel tubing and inspected the tank for cracks... nothing.



Is this a sign of a motor with no compression??

Last time the motor ran, it would run for about 10 seconds and die. Then it wouldnt start up at all.



All advice is appreciated.

 

[MotoGod]

Try removing the pressure line from the pipe and blowing in it. I always have issues when I try to prime my Revo pull start by blocking the exhaust. I have MUCH better luck when I blow in the line instead. Revo fuel line is just too damn long. It would take me 3 min just to get fuel moving. lol

 

[RC Addict]

It could be no compression. It could be an exhaust leak. Start looking at the exhaust first.

Try this: Remove the pressure line from the exhaust. Blow into it, forcing fuel up to the carb. Watch the fuel line and blow for about a second after the fuel gets to the carb. Now try to start it.

Also, to check your compression, spin the flywheel by hand with the glow plug in. If there is some resistance at Top Dead Center you are fine. If it spins 360 degrees with no resistance at all then you probably have a toasted mill.

Try removing the pressure line from the pipe and blowing in it. I always have issues when I try to prime my Revo pull start by blocking the exhaust. I have MUCH better luck when I blow in the line instead. Revo fuel line is just too damn long. It would take me 3 min just to get fuel moving. lol

You were faster than I...

 

[sandiegan]

Thanks for the fast reply.


I just tried what you said - the engine fired up first pull and then died immediately (after about 1 second)

I'm assuming i have a leak somewhere....?

 

[RC Addict]

I would check the compression as described. If that checks out ok then check the exhaust gasket and couplers if you have them. Silicon can rot and/or tear.

If both check out check your seal on your fuel tank lid. Then check your fuel lines for cracks or pin holes.

But it really sounds to me like you have no back pressure at all. Did you recently replace the exhaust?

 

[sandiegan]

Also, to check your compression, spin the flywheel by hand with the glow plug in. If there is some resistance at Top Dead Center you are fine. If it spins 360 degrees with no resistance at all then you probably have a toasted mill.

OK just tried this. I can feel a tiny bit of resistance but not a lot. Like i can easily spin it past TDC with one pinky finger.


How much resistance am i supposed to feel?



And no, i did not replace the exhaust, but i did remove and reinstall it (at the silicon coupler) the elbow has never been removed from the engine (its RTR)

 

[RC Addict]

Ok. To rule out the exhaust as the culprit remove the exhaust elbow from the engine. Place a finger over the exhaust port and try spinning the engine by hand again. If you feel resistance now you know it is the exhaust. If there is no resistance still you know it is the engine itself.

The resistance you feel will vary. Like I can not even get the engine in my LST to go past TDC no matter what by hand. It is very tight.

It is very possible you lost the pinch. The sleeve is tapered in at the top to seal the chamber off for compression as the piston moves toward TDC. You can get a re-pinch to restore some of the taper.

 

[sandiegan]

Ok. To rule out the exhaust as the culprit remove the exhaust elbow from the engine. Place a finger over the exhaust port and try spinning the engine by hand again. If you feel resistance now you know it is the exhaust. If there is no resistance still you know it is the engine itself.

just tried this and resistance feels the same (little to no resistance)

i have a brand new AE .15 that i bought on ebay for a good price and it is impossible to go past TDC using all my strength (but then again, it is BRAND NEW)

i will install the new engine and see how it runs.

 

[RC Addict]

Yep, I would say your mill has lost it's pinch. This guy comes highly recommended by olds97-lss for that kind of work, and there is a nice explanation of pinch. Much better than I described it I am sure!

http://www.rayaracing.com/

 

[sandiegan]

Thanks RC addict! The new swap is in, just did the break-in procedure, and its running pretty good!

I can't believe my AE .15 is already dead. It only had 1.5 gallons through it. When i bought my GT2, it came with a cracked fuel tank so it was running very lean and hot as i broke it in. That might be the reason is failed so prematurely.



2 questions:


1. I read somewhere that you can increase compression by removing a spacer from the head. Is this true?

2. My new swap is making a whining noise whenever its moving, and pitch increases with vehicle speed. Could the gears be too close together causing this noise?


Thanks in advance.

 

[olds97_lss]

1. I read somewhere that you can increase compression by removing a spacer from the head. Is this true?

2. My new swap is making a whining noise whenever its moving, and pitch increases with vehicle speed. Could the gears be too close together causing this noise?

1. Yes. They are called head shims. However, the only reason to change shims is to get the compression right for the fuel your running. Higher nitro content (25%+) usually requires more shims than an RTR engine has. Running lower nitro content (0%-15%) may require less shims.

If you raise compression too much, the fuel will detonate. That means it explodes too early in the rotation of the crank, which will rob power, raise heat and damage parts.

If you lower compression too much, the fuel will fire too late, which will waste fuel and waste power by blowing it out the exhaust as the piston is coming down in the stroke.

Most non-high performance engines come from the factory shimmed to run 15%-25% nitro content fuels. Deviation from that range will more than likely result in requiring a shim change.



2. Check your spur/cb mesh and check that your spur is not rubbing on the face of the bell of the clutch bell due to improper shimming of the flywheel pushing the bell out too far. Not all engines are the exact same dimensions and typically require different shims behind the flywheel to get everything to line up properly.

 

[RC Addict]

I can't believe my AE .15 is already dead. It only had 1.5 gallons through it. When i bought my GT2, it came with a cracked fuel tank so it was running very lean and hot as i broke it in. That might be the reason is failed so prematurely.

I can almost guarantee that lean condition cooked that first mill. I am glad I could help you out!

 

[olds97_lss]

+1 on that. A lean engine is usually a good performing engine... just not very good for very long.