dasintex

My Feedback: (10)

I have a brand new DLE35RA mounted on a plane about a 1 1/5 yrs ago; started the engine then, started right up, ran great, broke the engine in, never maiden flew the plane yet; now engine won't start, fuel does not get to the carb; all fuel lines, tank and connections good, no gas or air leaks, changed the carb thinking it was plugged up with old fuel from 1 1/5 yrs ago, still no fuel getting to carb, would bad reed valves be a possible problem preventing proper Engine Pressure pulsing?

ahicks

My Feedback: (2)

Though reeds could cause something like that, it is SUPER unlikely on a new/low time engine. They'd have to be missing pretty much - unless something were dropped in there when you had the carb off. That's happened before, where the debris was holding a reed petal open. If you want to check that (remote) possibility, there's a few things you can do when you have the carb off.

If the carb is dry internally, it's not going to pull fuel/pump worth a darn. Easy to cure by removing the plate held in place by one screw, and soaking the carb internals with a few drops of fuel. This is actually the most frequent issue with a new/low time engine

Another thought while you have the carb off, there's a gasket between it and the reed block. There's a small hole in it that gasket that needs to line up on a hole in the same place in the reed block and the carb. That small hole supplies the vacuum signal that the carb uses to pump fuel.

You say all lines are good. Have you had the tank apart to inspect the clunk line? If so, what happens when you put a piece of fuel line on the tank that's long enough to allow you to suck on it?

dasintex

My Feedback: (10)

I like the idea of soaking the carb internals with some fuel, makes sense; I don't believe the tank is the issue, had the tank off, plugged all the lines except one, blew air into and out of tank all checked out, tested all three lines this way; I will double check the gasket to ensure the vacuum hole lines up, appreciate the suggestions.

flyinwalenda

My Feedback: (5)

What kind of gasoline were you running..........pump gas?
If so, I'll bet the fuel pump diaphragm has stiffened-up ....probably in both carbs.
Try to prime the engine with some fuel straight down the carb at full throttle with a squeeze bulb, full choke, and try to get the engine running. After a few times the carb may start to draw fuel.

dasintex

My Feedback: (10)

Instead of taking the Carb apart, could I not just pump a bit of fuel into the supply line into the carb?

ahicks

My Feedback: (2)

If only it were that easy! You can try, but rarely is that possible. That's one of the things that makes this so difficult for so many people (getting the carb to prime). Been at this a long time, and pulling the cover with the single screw is the easiest reliable option I've run across.

kmeyers

Hand flipping can ruin your shoulder, and yields one pulse per flip.
Try this:
Turn the plane off.
Turn the ignition off.
Have the choke off.
Pull the spark plug out and turn the engine over with any electric starter (any starter will turn it over with the plug out and no compression).

With the plug out it should turn easy and fast. You should be able to watch the fuel move to the carb.
With the choke off you can not flood the engine if it is closely tuned at all (you just get a proper mixture).

After this return the plug and start normally.

karolh

Dasintex, did you eventually get your engine going ??

dasintex

My Feedback: (10)

Not Yet, took a break from the plane for the Holidays, I plan on removing the carb and remove the one cover and wet the carb with some fuel, I have a feeling that the last time I ran the engine, I did so until the tank emptied which may have dried the carb out, can't remember for sure it was some time ago, I sometimes do this with my Glow Engines, out of habit I may have done it with this gas engine, probably not the thing to do.

karolh

I store my models with the gas fuel tanks partially filled which helps to keep all the plumbing lines and carb diaphragms flexible.

dasintex

My Feedback: (10)

A quick question; to access the single screw cover I would have to remove the engine to remove the carb because there is only about a 1/2" clearance to the firewall; however, my engine is inverted and the 4 screw cover on the other side of the carb is easily accessed without having to remove the engine or carb, could I not just remove this cover, lift off the diaphragm and gasket and prime the carb?

flyinwalenda

My Feedback: (5)

The cover with a single bolt is where the fuel diaphragm is as well as the sediment screen. The cover with the (4) bolts is where the metering diaphragm is as well as the float.
The float may be stuck so if you remove the 4-bolt cover and gently push down on the tang that lifts the float that may help to get fuel into the carb.

ahicks

My Feedback: (2)

Yes, the cover w/4 screws will work just as well if the single screw side is difficult to access. Anything to get some fuel on those little flapper valves inside the carb. Pay careful attention to the order the components (gasket and diaphragm) are removed and reassemble in the same order!

R.J. Rose Ocala FL

This problem is common with new carbs also. One way I have found to resolve is to choke engine and place a thumb over the choke plate bleed hole and then prop it (with ignition OFF). Do this until you feel fuel dripping from carb, usually only requires a few flips. May require a helper if the carb is difficult to reach.

karolh

On the early Zenoah engines that came fitted with carbs without choke plates that was the standard way of starting them as most Zen engines like to be really wet for starting.

dasintex

My Feedback: (10)

What does the hole in the choke plate do? I have read or heard that some people close this hole, a previous poster suggested placing his thumb over the choke bleed hole to help get fuel to the carb, thinking that closing this hole is something I should look at?

flyinwalenda

My Feedback: (5)

Yes folks have closed the air bleed hole in the plate usually with solder to help a weak carb. You could try it. If you are going to solder it make sure to remove the plate and clean it well.

ahicks

My Feedback: (2)

The hole is not necessary for our application. It's a left over used on bigger engines and other applications. I solder all of mine closed for quick, easy choking when they come out of the box. I would caution that those considering this move not get too creative with other ideas, as if they don't work out, it's a pretty sure thing the engine will be sucking it in. A sheet metal screw or nut and bolt for instance, would be examples of plans that could cause internal disasters if that were to happen.

TexasFlash

For those who don't care to remove the engine/carb, a trick is to fill a syringe with gas and pressure up the fuel inlet line from the tank to the carb. A bit of pressure will overcome the popoff pressure and prime the carb by only pulling the line from the tank. It's easy to flood it this way but it will get gas to the reeds inside the carb and loosen up a possible sticking needle at the same time. You can aim the carb down and watch for gas to run out as an option.

karolh

I use hi- temp silicone to seal the hole so that just it case it gets dislodged and is ingested it won't do any damage.

dasintex

My Feedback: (10)

Success;

Got the engine started; soldered the airbleed hole shut on the choke plate, removed the cover on the carb and wet the inside of carb with some fuel; cranked the prop a bunch of times till I saw fuel arrive at the carb, turned on ignition, a few flips later and it started, ran for awhile on low throttle because I didn't have the wing on, shut it off before it came close to running dry; plan now is to start again in a few weeks before I put the cowl back on just to be sure I got it fixed, post analysis, last summer or spring when I first ever started the engine to break it in I believe I ran the engine till it ran dry.

Appreciated all the help!

karolh

Good show.

Eulboyington

Hello,

I'm very surprized that not one speak about the pop-off pressure of our RC carburetors ..... The main reason because fuel don't go to the carburetor is that the pop-off pressure is outstanding high often more than 36 psi !!!!!!..... 95 % of the RC gas carburetors are not correctly setted to the adequate po-off pressure for our RC hobby, even on brand new engines. With a correct pop-off pressure, the fuel move from the tank to the carburetor with several propeller flips ( without ignition); it's a essential thing for our RC gas engine.
From my own professional experience on Model Engines Maintenance in France ( search "MODELISME MICROMOTEURS SERVICE" on Google and FaceBook) above listed best pressures for WALBRO / TILLOTSON and clones :
> 40 cc engines : 0,8 Bar / 11 psi
50 - 70 cc engines : 0,9 Bar
80 - 100cc engines : 1,0 Bar
110 - 120cc engines : 1,1 Bar
120 - 150cc engines : 1,2 Bar
> 150 cc engines : 1,3 Bar
The pop-off pressure setting and technical explainations could be easy found on YouTube ( I also made a video in French)

karolh

Wonderful that you made a video and it would be great if you shared it here but remember most of us speak English and not French.

Truckracer

My Feedback: (19)

Hmmm, going to have to disagree with part of this. First, pop off pressure has almost zero to do with how well a carb pulls fuel during starting. A tight choke plate is far more important in this case.

I have noted and published the higher pop off pressures on many of the newer carbs supplied on our engines. I feel this is a result of too many carbs having a too low pop off that causes far more problems for our use than a too high pop off. Our engines run just fine with a wide range of pressures. There is no "right pressure" though certainly engines will run slightly different through varying throttle settings with different pressures. Those in the know can use pop off to their advantage to tune a carb for their specific needs. Most users will be happy with the carb just the way it is supplied.

A too low pop off can cause varying mixtures with different airplane attitudes and "G" loads. At an extremely low pressure, flooding can occur and mid-range response gets sluggish from a too rich mixture. A too high pressure can result in strange, unexplained out of range needle valve settings (as can a too low setting but in reverse). There are other issues I won't go into.

Summary, many of our carbs are now supplied with a pop off pressure somewhere between 26 and 30+ pounds. They use to be in the range of 20 - 28 or so pounds. The carbs start and run just fine at this now standard higher pressure. Unless you know what you are doing regarding pop off pressure ..... don't worry about it! For the most part, this is a non issue!