EME 120 twin problems

[Peter Smedley]

Dear all

I’ve a problem with an EME 120 that has me absolutely stumped.
It’s got a good ignition sub c battery, currently at 8v
It’s got two new cm6 plugs
It’s had a new reed valve block
The timing is spot on
It’s got good spark on each cylinder
It starts well and at is very powerful at full throttle
Draws fuel easily

However, despite the easy starting, it will not run well on the port cylinder. On a long idle a good amount of oily smoke is seen and it doesn’t clear until 3/4 throttle.
Swapping the leads makes no change in running, it still is poor on the port cylinder. It runs consistently colder than the starboard pot.
The port plug when pulled is soaking wet.
I’ve run out of ideas and brain power.....anyone else got a solution?

[Alan Cantwell 1131]

Possibly down on compression on the errant cylinder, New ring, or the pistons picked up, and scored the liner,

[Peter Smedley]

Good and equal compression on both cylinders ! Thanks for the quick reply. The engine has had no more than an hours run and is about 2 years old

[Tony Collins 1073]

Remove the reed valve block and check that all reeds are in good condition and are seating perfectly even if they are new.
Also check the cylinder base gasket on the offending cylinder.
Tony

[Alan Cantwell 1131]

It will have equal firing, one could mask the other, I suggest obtaining a compression tester, doesn’t cost a lot, https://www.ebay.co.uk/i/383288414080?r ... %3D2386202

[Peter Smedley]

I’ve bought a new hall sensor. A few people have had trouble with these on twins on the RCUniverse forum. It’s worth a try. A club mate has a compression tester, that’s in the pipeline.

[Alan Cantwell 1131]

Best of luck with it, keep us informed

[Peter Smedley]

As it’s pouring down outside I thought I’d look at this troubleshoot twin.

I’ve made a short video and there’s does seem to be a problem with the cdi box, as far as I can tell.
It’s appearing to fire on both plugs when the hall sensor is moved quickly over the magnet. However, when moved very very slowly ( just creeping around by hand) only one spark fires.


https://youtu.be/P9StyOulYBM

The spark stays only on one lead. Changing plugs makes no difference. So in practice swapping the ht leads on the engine should swap the fault to the other cylinder but it doesn’t !

[Alan Cantwell 1131]

Changed plugs?

[Peter Smedley]

Alan, changed the plug on the non firing side...made no difference

[Alan Cantwell 1131]

Done the compression test? But it is beginning to look like an ignition module problem,

[Peter Smedley]

New CDI box has arrived. After doing some further reading this is not a problem exclusively to me. Fuel is dripping from the carb at intervals. This could be a bad metering needle and seat. A new carb is on order. Also I have ordered a service kit, I will try this first and then if its the seat then the new carb will go in.

The tank is about 1"above the carb. I've got other gas engines where the tank is above the carb ( noteably my Evo 33gx in a Stampe), they do not drip.

More investigation need while being furloughed.

[Tony Collins 1073]

Using a process of elimination for a logical fault diagnosis.

1. Ignition system outputs are interchangeable therefore as there is no change
after swapping over it rules out ignition fault.

2. Faulty plug, ruled out by fitting new.

3. Good and equal compression on both cylinders precludes them from excessive smoking

4. Gasket faults anywhere would create a weak mixture throughout, hence no smoking.

5. Carburettor fault. This would not be selective of either cylinder. What happens to one
will happen to another.

6. Cylinder running much cooler and smoking. This would indicate excessive fuel input.

7. What controls the fuel input to either cylinder? The reed block and reeds.
There may be a problem with the side of the reed block and reeds that are serving that cylinder.
Maybe stuck open or faulty -loose maybe.

If I think of anything else I'll come back.

Good luck with it and keep well.

Tony.

[Peter Smedley]

Tony, good of you to reply

1. Good spark from original cdi and new one on the old plugs and hall sensor. I’m sure the one spark I saw at very very slow turn over is the problem

2. Correct

3.Correct

4.New gasket fitted and not over tightened to crush and damage

5. Seems likely now

6. Excessive fuel always in the port cylinder ( from the pilots seat)

7.I will double check the seal of the reeds. I remember that there was no gaps and there was nothing broken or cracked. New block installed recently

Cheers, stay safe

[Tony Collins 1073]

Hi peter. You may well have a carburettor fault but remember this one carb serves both cylinders.
You may well have a spark at slow speed a bit behind the other. Their are two ignition systems and very slight
differences in coil efficiency, associated components etc can cause this. but still operate fine at normal speeds.
If changing leads over makes no difference, forget all about the ignition system.
Tony.

[Peter Smedley]

Tony, you’re thinking is sound. As in my previous post a new carb and service pack are on their way. The only thing not changed now is the carb. Thanks

[Tony Collins 1073]

if you can find out why one cylinder is getting more fuel than the other you will have the answer.
Tony

[Peter Smedley]

When I do....there will be a small celebration ,online !

[Tony Collins 1073]

Just had another thought:-
Increased back pressure [exhaust] levels can cause increased emissions, increased fuel consumption, and can negatively affect engine performance.
Tony.

[Glenn Masters]

Hello Peter / Tony,
I think it may be the reeds causing the mischief here . . . Is the reed block of the type that the reeds can be turned over to better press against the block surface ? Its always a good indication if , when the crank is rotated back and forth against compression you may hear a *farting* sound as the mixture tries to pass through to the crankcase ? Check the gasket seals of the reed block assembly . . . .