Starting problems with a Little Wonder

[rik672001]

Hi to all
I have just finished building a Little Wonder from Engineers Emporium.
Trying to get it to run I am having problems and hope someone might be able to point me in the right direction
It fires but will not continue to run. I have moved the timing to before tdc and past tdc with no luck.
I am rope starting it and it will only fire with the rope pulled fast.
This seems that the fuel needs to be sucked up hard.
It may fire twice on a pull but no more.
The mixer seems to let it fire when I have it a 1/4 turn open, anymore or less it will not fire.
Could I have an air leak or something like that, If so how would I find it.
The inlet valve is light on the spring and the exhaust is closed just before tdc.
Any help would be appreciated as I am starting to wear out my starter cords at an alarming rate
Thankyou:wall:

 

[Steve J]

to start with try to set up a starter using a fast electric drill. mine is 3000 rpm. then pull off the head and make up a test plate to bolt on the head that you can pressurize with a compressor to check the seal on the valves. relap the valves as much as you have to to get them to seal. a narrow contact on the valve face is ideal. if the whole valve face is contacting the valve seat it will be very hard to get a good seal. good luck and stick with it. the valves have to seal to develop good compression.

 

[rik672001]

Thanks Steve
I will try to start with a drill.
Do you use a belt attached to the drill and flywheel.
I ground the valves with grinding paste and they sit slightly out of the seat so only some of the back of the valve seals on the seat. I didn't grind for too long as I was worried I might wear the seat down

 

[Cogsy]

rik - if you used automotive valve grinding paste then it's probably far too coarse for a model engine. People use various stuff but I only ever use toothpaste and it works for me. Bear mind that's for new valves, not scored ones.

Also, when you say 'grinding' the valves, were you using an electric drill or similar (it's how I do full sized valves)? For models the procedure is to rotate the valves 90-120 degrees, back and forth, by hand, then occasionally rotate them a further 90-120 degrees and rotate back and forth again. Keep doing that for a few minutes and they should seal OK. They will seal a lot better after the engine has fired a few hundred times.

From the sounds of it though, your valves are probably sealing good enough for now if it's firing at all. Make sure your fuel tank is at the right height (just below the carby level) and has a vent in it to allow the fuel to flow without developing a vacuum. Then connect your drill and spin it while you play with the carb settings.

As for using a drill, mostly you can make a hub to engage it direct to the crank, unless it's a large model that your drill doesn't have the power to turn over directly.

 

[rik672001]

Hi Al
Yes I have used automotive grinding paste on the new valves.
I think I will take the head off and redo the valves with toothpaste.
I did do the original grind by hand but on such small valves the paste did feel rough.
I wouldn't have thought toothpaste would be enough to grind valves.
Thanks
Erik

 

[rik672001]

Hi Al

The fuel is in the base and has a lift if about an inch. Do I need a non return valve

View attachment lwe.bmp

 

[rik672001]

This is a picture of it before I finished it

View attachment lwe.bmp

 

[rik672001]

Here is some pics of the engine as it is now

 

[Jasonb]

Looks like you have one with the aluminium flywheels I think they now do them with iron ones ( the Junior certainly has them) as the alloy were just too light to keep the thing turning over on its own.

I would rig it up with a temporary fuel container that is level with teh carb needle to see if that makes any difference before adding a non return valve.

Be wary of trying to start it with something that will turn it faster than the intended running speed, a 3000rpm drill will just throw the governor weights out and you will be trying to start it when all it will be doing is missing as the exhaust valve will be open. A starting handle that engages against the side of an extended flywheel key is a better option as you can keep cranking it for longer unlike the string which runs out of length

I use 1000g silicon carbide powder and a drop of oil to grind small valves, as said the car paste is too rough at about 100g

Is that an Rcxell ignition, looks like it judging by the heavy braided plug lead, if so they have auto advance that is based on crankshaft speed which gets mucked up if you have the sensor on the timing gear as its going round at a different speed



J

 

[rik672001]

Thanks Jason
Yes it is rcxel ignition but I made a small brass wheel and it fires every rotation.
Will this cause any problems with the timing
I will try lifting the fuel from a tin and see how it goes after I sort out the valves

 

[Brian Rupnow]

Your problem definitely sounds like leaking valves. A trick I often use, if the engine is firing at all, is to hook it up to an electric motor to drive it at about 600 rpm. Take the lockout arm off the governors so it isn't functional, hook up the fuel and ignition, and let the electric motor drive it for half an hour, with the engine firing. I use brass or bronze valve seats and steel valves, and the force created when the engine fires will seat the valves and give a perfect seal after half an hours run time. Then the engine should start and run on its own.---Brian

 

[tornitore45]

My engine was doing the same, and of course, I suspected everything from rings to valves but what really fixed it was to increase the spark gap.
I installed a Rimfire without giving any thought but after inspection it just looked to thin a gap, I raised to about 1mm and it started working steadily with intermittent misfiring. I did not have spark plug boots and noticed a spark jumping from plug to push rod.
Your tank seems to be too low, for starters.

 

[Jasonb]

If the disc is on the crankshaft then its not such a problem with the auto advance but you may need to move the position of the sensor a bit further round than you think.

One other thing I find that the suggested needle settings on most hit & miss engines tend to give too much fuel, just try with about 1/8th of a turn of the needle.

J

 

[Swifty]

I used that same brand of ignition in my last engine, it needs to be set for 27 degrees before TDC to suit my engine, it then advances the spark even more as the revs get higher. Yours will be a slower reving engine, so I'm not sure how much advance it needs. You mentioned that you tried setting the spark before and after TDC, I think that you haven't got it advanced enough.

Paul.

 

[rik672001]

Thanks Fellas

I will try a few of the suggestions tonight and let you know how I go

Erik

 

[rik672001]

Hi All
Thanks for the answers. I just wound back the timing to about 25 deg before tdc and it started to try to run on.
After trying for a while my cam gear came loose. So I will repair and do the valves at the same time.
A big difference bringing back the timing ,so anyone using rcxecl ignition be aware that it really needs to be set way before tdc.
I think my valves are another issue and have learnt heaps from you guys. Thanks a lot and will let you how I go in the next few days
Erik

 

[Swifty]

Isn't this site great Eric, your first post was yesterday afternoon and already you are getting results from suggestions by other members.

Paul.

 

[rik672001]

Hi Paul

Yes ,the people here are all too happy to assist with newbies like me. Some of the trail and error these guys have but in over the years is invaluable to someone starting out

 

[canadianhorsepower]

Hi All
I just wound back the timing to about 25 deg before tdc and it started to try to run on.
Erik

Hi Eric
nice to know that you are getting good result result
The problem with that Hall Effect ignition system is the grey
Area about the magnet setting. Not one dealer will commit himself to the set up
because they don’t know the size, type and gap you will have between the sensor
and the magnet. One thing to remember is you will have a spark AFTER your sensor
pass about 2/3rd of your magnet diameter. The best practice before making any degree
for your timing. Assemble your flywheel, hall sensor with ignition kit. Mechanically find your engine TDC, mark your flywheel with a marker at that specific place. Now manually turn your motor till you get a spark at that same place and now you will know where TDC and 0 degree timing meet.
Good luck

 

[Cogsy]

That procedure doesn't always work Luc. The Chinese rxcel copy I used on the Rupnow engine also has 'auto advance'. Manually turning the engine produced a spark and I set the timing accordingly, but when spinning the engine on the starter the unit advanced the spark around 30 degrees.

In the end I just had to keep retarding the timing until it began to fire.