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Carb Problems

Engine not running...much

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cymaz18/10/2018 20:01:13
8670 forum posts
1177 photos

Just tried to start my RCGF 30cc single gas engine. Great spark and the timing is at 28* before TDC. The carb is a HLIC 10Z, my best estimate going by the id numbers and logo on the carb body.

The engine will run on the prime but then go dry. There is plenty of fuel in the carb as I've checked it with the top off. There is a reed block after the carb. There is signs of fuel on all four petals (?).

I've also tried a different ignition box and battery with the same results. Fires then goes dry.

I'm thinking that it could be the reed block playing up or it has a small crack or something like that. I've managed to order a new one with the manifold block. I will also get a carb service kit.

What are views of the engineers out there?? I would love to know your opinions and you spin on it.

jeff2wings18/10/2018 20:42:05
789 forum posts
1872 photos

Cymaz,is this a new or used pre-owned engine ? if it's sat around for a time the diaphragm may be a bit stiff/sticky?

fuel on the reeds will be from the prime  ?dont know

Edited By jeff2wings on 18/10/2018 20:42:36

cymaz18/10/2018 21:11:27
8670 forum posts
1177 photos

Pre owned engine. I also just ordered a carb service kit. I will completely strip and clean the carb and add the new reed block. Thanks for the interest yes

cymaz08/11/2018 08:23:29
8670 forum posts
1177 photos

Managed to get a new carb with gaskets and an engine gasket set. I can’t think of anything else to do.

Denis Watkins08/11/2018 08:59:59
3884 forum posts
60 photos

These carbs should be stored "wet" Cymaz

As they dry out easily, as you found

cymaz08/11/2018 09:10:48
8670 forum posts
1177 photos

I’ve always stored my petrol engines “wet”. Helps the tubing to. The engine was second hand. With hind sight....should have bought newindecision

Jon - Laser Engines08/11/2018 10:43:01
4802 forum posts
179 photos

if there is oil in the pressure pulse opening for the fuel pump this could upset it. It could have congealed and cause a blockage

Petrol Pete08/11/2018 10:47:28
15 forum posts

Hi Boys, I think the needle on the diaphram side of the carb is stuck, probably with dried up fuel, whip the cover and lift out the diaphram, press the arm down gently watching the needle lift off its seat and reassemble, start it with a splash of fuel down the carb or keep flicking with full choke and half throttle to draw fuel through. this often happens when they have been left for a while, i think the petrol evaporates and leaves the sticky oil behind Pete

Engine Doctor08/11/2018 10:54:21
2302 forum posts
27 photos

Hi cymaz . Has the carb been taken off before you had it ? If you suspect it has then check the carb gasket and that the carb pressure pulse passage hole in the reed block , gasket and carb line up . Its a hole on the carb face that fits to the reed just outside the main venturi hole. With this hole blocked the carb will not get a pressure pulse from the crankcase to pump any fuel and run dry as you describe . Its a simple thing to overlook. As also said if the diaphragm drys out then they can get brittle and hard and wont pump any fuel.

cymaz08/11/2018 10:54:50
8670 forum posts
1177 photos

I’ve changed the float needle valve and the diaphragm and reed block after it wouldn’t run - just started on the prime.

It then began to run but wouldn’t slow to idle, only running at over about 3000rpm or so. I thought it also could be a front bearing leaking.

I am going to change the bearings as well....all that will be original is the crankcase, head and piston !

cymaz08/11/2018 10:55:50
8670 forum posts
1177 photos

Just beat me to it ED. Just waiting for the carb to arrive and then all the new parts will go in.

Edited By cymaz on 08/11/2018 10:56:56

Engine Doctor08/11/2018 11:07:37
2302 forum posts
27 photos

Hi Cymaz has the spring been removed from the carb butterfly valve ? this can cause wear resulting in a fast idle. The bearings if suspect could have worn the oils seals This can result in hard starting and poor idle The seals I believe are fitted in the bearings as opposed to separate oil seals but not sure . The crank case compression is more important than cylinder compression as thats the only way fuel can get to the cylinder , That would be my next check if it still runs fast .

cymaz09/12/2018 17:51:15
8670 forum posts
1177 photos

Just ran up the engine again. It’s had new bearings, Walbro  carb swapped from the old Hi-Lo, reed block, gaskets. It started but ran really rough and wouldn’t pick up at all.

What to do? Just as well I bought a new ignition box from Just Engines. Swapped out the old one and wired in the Rcexl unit........different engine altogether! Smooth idle, clean acceleration from idle to WOT.


So the conclusion is that it was the ignition box all along. Although the rest of the work done and new parts put on the engine will not do any harm and may stop any potential problems for a while yet.

Time to fit it into the Dragon Lady.......clock

Edited By cymaz on 09/12/2018 17:52:15

cymaz11/12/2018 05:15:24
8670 forum posts
1177 photos

Ran the engine again on Monday evening after work. I have turned the carb 180* to where the final position would be for fitting into the airframe and added an inlet extension. So I was keen to see if the engine would still run, and it still does!

Leaned out the carb a little more. As a result it’s running smoother and the throttle response is very good......the Walbro carb doing its duty.

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