must prime carb to start engine
#1
Junior Member
Thread Starter
Join Date: May 2014
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
must prime carb to start engine
I am not sure why this is happening, but in order to start my tower hobbies trainer I have to put a couple of drops of fuel directly into the carb for the engine to start. Even after running the engine for a couple of minutes and shutting it off, I must re prime the carb in order to start the engine. can someone please let me know as to what may be happening and how to resolve this issue. Thanks in advance.
#2
My Feedback: (1)
Most trainers have the tank mounted too low. Got to make it look like a Cessna with a windshield, so with a vertically mounted engine this can happen. Also you may have too much fuel line for ease of use, but shorter is always better.
You can open the throttle and choke it by pulling the prop through while holding your thumb over the carb. Some are easier to start if you just put your finger over the exhaust when you first spin the prop with a starter. Lots of techniques,
You can open the throttle and choke it by pulling the prop through while holding your thumb over the carb. Some are easier to start if you just put your finger over the exhaust when you first spin the prop with a starter. Lots of techniques,
#4
Junior Member
Thread Starter
Join Date: May 2014
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
I actually tried a method of both of your answers. I put my finger over the exhaust opening and the carb at the same time and spin the prop to bring fuel into the carb. What I noticed when I do this is after I remove my fingers, the fuel sucks back out of the carb.
#5
My Feedback: (3)
The real question here is, does the engine keep running and pull the plane around okay?
If the engine needs primed, via eyedropper or pulling the prop around with fingers on the carb, that's okay. If it runs okay and pulls the plane around reliably, it's all okay. When you stop the engine, there's no need for the fuel to stay in the fuel line. There's probably stil a few drops left in the carburetor.
So... does it keep running on the ground? Does it keep running at high RPM when you lift the plane and point the nose up? If so, you have no problem.
How's the plane otherwise?
Best wishes,
Dave Olson
If the engine needs primed, via eyedropper or pulling the prop around with fingers on the carb, that's okay. If it runs okay and pulls the plane around reliably, it's all okay. When you stop the engine, there's no need for the fuel to stay in the fuel line. There's probably stil a few drops left in the carburetor.
So... does it keep running on the ground? Does it keep running at high RPM when you lift the plane and point the nose up? If so, you have no problem.
How's the plane otherwise?
Best wishes,
Dave Olson
#6
Moderator
My Feedback: (1)
+1 for Dave (Scar's) answer. assuming the engine runs well and has no other major issue, there's no need to fix anything.
if on the other hand the engine does NOT run well, the other symptoms (priming required for EVERY start, fuel runs quickly back to the tank)
indicates the tank may be too low.
if on the other hand the engine does NOT run well, the other symptoms (priming required for EVERY start, fuel runs quickly back to the tank)
indicates the tank may be too low.
#7
Moderator
Every engine I've had that had the fuel run back down the line after priming had an air leak in it. Change the fuel line going to the carb first, then the needle valve o ring. An engine that won't prime by coving the carb inlet but will by blocking the exhaust is a dead giveaway of a leak, since the former works be creating a vacuum and the latter works by creating pressure.
#9
Junior Member
Thread Starter
Join Date: May 2014
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
ok guys, I followed through on all your suggestions. I pulled out the fuel tank. changed all fuel lines, checked o rings, shortened fuel lines and now the engine won't even start by priming the carb. As I see it either I need a new engine but at this time, I am seriously considering going to an all electric air fleet. I have had it with the unending things that go wrong with gas engines.
#13
Moderator
When I've had an ornery engine before, I have taken it off the plane and pressurized the engine to see where it leaked air. Screw the HSN mostly out and hold your finger over the carb and exhaust. You can dunk it in water if you want to pinpoint the leak.
#16
could be dealing with multiple issues. Is this a new engine? How is the compression in general? Are you getting good ignition/glow from the plug since it does not start at all? Tried priming the cylinder directly? Sorry if this is a very dumb question but the carb and exhaust lines are not crossed mismatched right?