Fuel only goes to engine when I cover exhaust

[corvetteadk]

Pull start RS4 3 ONLY gets fuel to engine when I put my finger partly or fully over exhaust exit hole.
I've checked for obvious air/fuel leaks in fuel lines and exhaust and put pressure on fuel tank top/cap when starting and nothing. Fuel filter is clean. Maybe the pipe I have on here is no good?

SHouldn't I see fuel spitting into the carb when I am pulling starting? Makes sense to me.

 

[Rolex]

Put a few drops of fuel directly into the carb and try to start it. If it starts, your carb is fine. If it starts and stalls in a few seconds, your needles are gummed up. If it doesn't start or even sputter, check your glow plug.

 

[nedlynitro]

He is right, also, make sure your fuel line is set up good, once the fuel line going from the tank to the engine, was set up badly, on my truck when i got it second hand, and the engine would not pull the fuel, cause the hose ws kinda long, it went up and then back down before hooking to the engine, making a hill the fuel needed to climb, i hooked it differently and it worked fine, also will want to check your gaskets, make sure they are good or oil them to ensure, clean clean clean, these aren't car engines, they are model engines that run off a very combustible fuel! Require alot of tuning and cleaning to keep a healthy engine.

 

[jschleer]

Low compression?

 

[corvetteadk]

Low compression?

Oh boy....I hope you are wrong jschleer!

It will start when I drop fuel into carb.....then dies within a few seconds (after all the fuel is burnt up.

Now, if I drop fuel into carb, start it.....and put my finger over the stinger off and on, off and on, off and on.....it will continually run.

Is the more probably thing bad compression or maybe an exhaust leak that I haven't yet seen? Is there any nitro tricks to check and locate exhaust leaks?

Oh boy....I hope you are wrong jschleer!

It will start when I drop fuel into carb.....then dies within a few seconds (after all the fuel is burnt up.

Now, if I drop fuel into carb, start it.....and put my finger over the stinger off and on, off and on, off and on.....it will continually run.

Is the more probably thing bad compression or maybe an exhaust leak that I haven't yet seen? Is there any nitro tricks to check and locate exhaust leaks?

To me, the engine looks GREAT inside??? No visible scores in the sleeve or anything like that that I can see. I took off the exhaust and looked underneath and around piston and it seems to look pretty good. What you guys think?

Put a few drops of fuel directly into the carb and try to start it. If it starts, your carb is fine. If it starts and stalls in a few seconds, your needles are gummed up. If it doesn't start or even sputter, check your glow plug.

Rolex....you seem to be quite a guru on these forums! Thanks for your input! Since I can keep engine semi-running by puttin my finger on exhaust and off....you think it could still be gummed up needles?

 

[Rolex]

It sounds like you need to remove the carb and give it a good cleaning. Probably a clogged needle valve.

Another thing you can do is remove the line from the muffler and blow into it to see if you notice a loss of pressure. If you do, you have a break somewhere in the lines or a leak in the fuel cap.

 

[corvetteadk]

He is right, also, make sure your fuel line is set up good, once the fuel line going from the tank to the engine, was set up badly, on my truck when i got it second hand, and the engine would not pull the fuel, cause the hose ws kinda long, it went up and then back down before hooking to the engine, making a hill the fuel needed to climb, i hooked it differently and it worked fine, also will want to check your gaskets, make sure they are good or oil them to ensure, clean clean clean, these aren't car engines, they are model engines that run off a very combustible fuel! Require alot of tuning and cleaning to keep a healthy engine.

what gaskets are you referring to nedlynitro? Forgive me for not knowing, I'm dumb when it comes to nitro, but learning!

It sounds like you need to remove the carb and give it a good cleaning. Probably a clogged needle valve.

Rolex....from your point of view, what do these pictures tell you about the engine (if anything)?

The problem is not the hoses...and not the tank.....and not the muffler itself......the problem is somewhere between the carb and the connection between the exhaust port and muffler

 

[Rolex]

The gaskets he's referring to would be in the fuel cap and on the neck of the carb. Loosen the locking nut on the carb, press down hard on the neck and tighten it back up. You might need to seal it, but for now just snug it up.

The engine looks good, from what I can see.

You can also try starting it with fuel in the carb, then use your finger as a partial choke on the carb neck. If you can keep it running for a while like that, the needles might clean up just from the fresh fuel running through.
Which also brings up the question, what kind of fuel are you running, and how old is it?

 

[corvetteadk]

The gaskets he's referring to would be in the fuel cap and on the neck of the carb. Loosen the locking nut on the carb, press down hard on the neck and tighten it back up. You might need to seal it, but for now just snug it up.

The engine looks good, from what I can see.

You can also try starting it with fuel in the carb, then use your finger as a partial choke on the carb neck. If you can keep it running for a while like that, the needles might clean up just from the fresh fuel running through.
Which also brings up the question, what kind of fuel are you running, and how old is it?

Blue Thunder 20%........maybe 8 months old.
I don't think I would be able to keep it running like that (finger over choke), as there is not enough pressure to keep fuel running to the carb once started. I am pretty sure that's the major problem.....fuel is simply not getting to the engine when I pull the pull string.....and even once the engine is started, fuel does not get pulled to the carb unless I stick my finger over the stinger/exhaust tip.
If i try that, will it create more pressure to allow fuel to enter carb?

check this pic out....now that i'm thinkin about it, i forgot something. there are two long bolts that secure/hold exhaust elbow onto the exhaust port on engine. The screw on the left in this pic will not torque down, it is semi-loose and free spinning in there, as if maybe it's stripped? u think maybe exhaust leak there and causing de-pressurization for fuel system?

 

[Rolex]

Give it a try. It's like choking a car carb. The intake sucks it in. If it doesn't work, keep using the exhaust to keep the fuel flowing. It MIGHT clear the needles. If not, you'll have to take them out for a cleaning.

 

[corvetteadk]

The gaskets he's referring to would be in the fuel cap and on the neck of the carb. Loosen the locking nut on the carb, press down hard on the neck and tighten it back up. You might need to seal it, but for now just snug it up.

The engine looks good, from what I can see.

You can also try starting it with fuel in the carb, then use your finger as a partial choke on the carb neck. If you can keep it running for a while like that, the needles might clean up just from the fresh fuel running through.
Which also brings up the question, what kind of fuel are you running, and how old is it?

Knoxville eh? I spent 6 years there in Bible college at Crown (right there in Powell)
My wife is from there (met her in college) and we spent Thanksgiving there with family. nice area

Knoxville eh? I spent 6 years there in Bible college at Crown (right there in Powell)
My wife is from there (met her in college) and we spent Thanksgiving there with family. nice area

Though this engine barely has any time on it (just break in time basically), it has sat for quite some time since it has actually ran. Maybe the carb needles are gummed up. I assume you are talking about just backing the high speed and low speed needles all the way out and cleaning them with carb choke cleaner then? I guess I should back out the idle screw too or no?
The LSN seems to look good, looks like a needle to me, nothing gummy on it or nothing...nice and pointy

 

[Rolex]

No kidding! I've been here for 5 years, Clinton for the previous 5. New York before that.

We had an RC track on the corner of Clinton Hwy and Edgemore Rd, right across from Powell Elementary.

 

[corvetteadk]

No kidding! I've been here for 5 years, Clinton for the previous 5. New York before that.

We had an RC track on the corner of Clinton Hwy and Edgemore Rd, right across from Powell Elementary.

Well I'm pretty sure we never crossed paths cuz i would have remember your scary face! (avatar, lol)

 

[Metalhead Matt]

If your header isn't secured tightly, you'll have a leak there and won't be able to build pressure. It looks like there's plenty of room to use a longer bolt and put a nut on it. I bet this will solve your problem.

 

[corvetteadk]

If your header isn't secured tightly, you'll have a leak there and won't be able to build pressure. It looks like there's plenty of room to use a longer bolt and put a nut on it. I bet this will solve your problem.

good idea with the longer bolt. I'll try it.
Hoping to get to this issue today.
QUESTION: is there supposed to be any gasket (metal or rubber) that sits between exhaust port of engine and exhaust???
here is the old bolt with some metal that came out too....guessing that's stripped threading from the old bolt. I hope this works! New one going in.

 

[PaulC]

Just linking up posts.

Check my post where I had similar fuel pull issues causing it to run too lean (I think) or not pull fuel at all.

Mine seems to have solved itself though, for now.

Again, like yours mine was stored for a good 6 months or so.

Your exhaust header sounds like a good thing to fix though. If you can get it running and it's still a son-of-a, just keep working at it, or clean the needles.

Seems these engines do not like being stored for long periods without a strip down and rebuild.... which I'm desperately trying to avoid

Paul

 

[Metalhead Matt]

Not so much a rebuild, but a complete tear down and cleaning. Which requires a seal job as well.

 

[corvetteadk]

didn't work.....still no fuel feeding to carb when I pull the pull string......same symptom....fuel pressurizes only when finger over stinger.

Fuel doesn't pressurize when i put finger over carb hole/neck so i guess next step is to take carb apart and clean needles. bummer.

I have a good question......even if my needles are gummy (which from what i can see they are clean) the fuel should still pressurize when i pull the pull starter, right? So, that said, that wouldn't be the cause here right?
maybe i have an air leak and need to just pull whole engine out and do a soapy water air leak test???? would that be a possible symptom?

 

[Metalhead Matt]

You have to plug the stinger to get fuel to the engine. That's normal. Only when the engine is running should it build enough pressure to keep the tank pressurized.

 

[corvetteadk]

thank you for clearing that up. knowing that will help alot. so...possibly i did fix it when i put the new bolt in the exhaust elbow. stay tuned