O.S. "F" plug won't keep ignition.

[John Wagg]

I have bought a second hand O.S. 48 FS and fitted a new O.S. "F" plug.

Been playing with it today and discovered that as soon as I detach the glow lead the engine stops.

The engine came with an idle bar plug and on refitting it the engine runs. Got it to run fine with reasonable throttle response but does seem a bit rich going off the exhaust smoke.

The engine is a Surpass but I guess a few years old as it's got an air bleed style carb' instead of a having a slow mixture needle.

 

Any thoughts on being able to use a non-idle bar plug perhaps a different temperature range.? 

Or maybe needs a different fuel too my straight  or  my 5% nitro fuels.?

 

Edited April 23, 2021 by John Wagg

[Martin Harris - Moderator]

Usually a symptom of being far too rich.  Unless there are fake OS F plugs out there you shouldn't have too much trouble from that.  The idle bar protects the element from excessive cooling from a rich mixture which is probably why it runs on that one.  How's the tank level - if it's really high it may be contributing to the problem.

[Jon H]

I would reset the air bleed to half open and start from scratch on the tuning. My Dad's os 48 has used F plugs since i was about 4 years old so it should be a good combo

[John Wagg]

Thank you both. Will check the air bleed and take note of tank level. Engine was on a test stand so level can be altered if needed.

Cheers.

[J D 8]

        Remember air bleed slow running adjusts the opposite to twin needle carbs, turn in for richer and out for leaner.

[Richard Acland]

Just a thought, I recently had a similar problem with a couple of my engines that have the OS F plug. As soon as I disconnected the glow at idle the engine would cut.

No amount of adjustment would get it to idle without glow. After all the usual checks, fiueltank fuel lines etc someone asked how old my fuel was. When I said probably over year he suggested getting some fresh fuel and trying again. Problem solved. They now all run perfectly. So fuel can go off after a time and cause problems.

[John Wagg]

Fuel is about 9 months old. Bought late-ish last year. Kept in the garage all winter. Thanks for advice.

[Engine Doctor]

Check mixture first, sounds like its rich then think fuel . If fuel has been kept in a tightly close can in a cool place it should be fine . Only ever had one lot of fuel go bad  in over 30 + years . 

 

Check air bleed / idle adjust hole is not blocked You should be able to see the air bleed screw as it closes the air bleed inlet . Set if half way as a starting point .

[John Wagg]

Fuel's have been kept in their tightly sealed containers over winter. Have used on another 4 stroke last week. O.K.

So don't expect it is the fuel. ?

Had the carb off to inspect the air bleed and not blocked. (you have to take the carb/inlet off to get a good view of the air bleed).  2 full turns to go from fully open to fully closed. Screw set now half way across open air-hole.  

Thanks for the input. Not had chance to re-try yet but will report back when I can.

 

P.S. I still do have some 25 year old fuel if that's any good to anybody.

Tempted to try it sometime. ?

[Don Fry]

It’s not the age, if sealed from new, it’s the castor oil, disgusting stuff. 
1st WW pilots used to have a ration of whisky, to balance the opening of anal sphincter. Chuck it out, a fair weed killer. 

[Engine Doctor]

14 hours ago, John Wagg said:

 

 

P.S. I still do have some 25 year old fuel if that's any good to anybody.

Tempted to try it sometime. 

If it's 25 years old then probably castor based fuel,not good modern engines inc four-strokes as it varnishes various parts when it get too hot.

Best use it for lighting BBQ or bonfire??

[Phil McCavity]

Keep the ancient castor oil fuel for cleaning engine parts and cases, you know then that you have a solvent that will clean without attacking and degrading anything it shouldn't.

[Don Fry]

1 hour ago, Engine Doctor said:

If it's 25 years old then probably castor based fuel,not good modern engines inc four-strokes as it varnishes various parts when it get too hot.

Best use it for lighting BBQ or bonfire??

Now, I ON ONE OCCASION, AND DEFFO NEVER AGAIN, sprayed some on a patch of weedy ground, to singe it into submission. Tossed a burning taper on, nothing to be seen. Thicko  here had forgotten methanol burns with a virtually invisible pale flame. Walked on the pick up my taper, and did a St Vitus dance off, singing words of praise. (Weeds were harmed in this experiment, as were the hairs on my legs.) Take great care. It also whooshes like petrol if it ignites on hot things

[Bob Cotsford]

I had a pestilence of tiger lilies a few years back and none of the over the counter weed killers would touch them.  They just lapped it up and if anything multiplied even faster.  This was about the time I gave up using IC motors so while clearing out old fuel bottles I tried dosing the lillies with some castor based SM stuff that had been lingering at the back of the shed.  Within days they were dead to the tips of their roots but of course nothing else will grow there now.

Note - methanol in the runoff or drains is not appreciated by the waterboard!

[Martin Harris - Moderator]

I'm not sure that they would be all that bothered by the odd half gallon -

 

"methanol has a half-life of just one to seven days, and given its high rate of biodegradation, methanol spills are not likely to persist. Methanol is used extensively in the nation’s wastewater treatment facilities to reverse the damaging effects of nitrate buildup in sensitive aquifers and waterways by accelerating biodegradation."

[John Wagg]

Thank's again guys for the input, much appreciated.

last year I did a couple of engine runs on our back grass (won't call it a lawn) and now two patches of bare earth. I know it makes good weed killer but at £25 a gallon maybe not.  ?

I have used the old fuel as a de-gunk on engines. Even managed to free up a couple of bearings etc.. Mind I did replace the bearings in my Laser 62 as they were a bit rough after 16 years of just lying around with caster inside them. Now converted to using synthetic based fuel. 

[John Wagg]

Hi'- Done another run with the O.S.48 FS this morning and still no joy with the O.S. "F" plugs. Tried two just in case one was duff.

 Runs fine on the unknown idle-bar plug and also runs on an O.S. No.8 as well. The No.8 doesn't seem as sweet as the idle-bar one but still runs good and reliable to be usable.

Did the test on straight fuel this time instead of the 5% previously. Idle speed is good and picks up well with the No.8.

Fiddled with the idle air bleed screw and rev's increased very slightly on tick-over when opening (weaker) but don't like messing about so close to the prop'. 

Rain and gales stopped any more play for today.

 

 

 

Edited May 3, 2021 by John Wagg

[J D 8]

             It would seem that the previous owner found the answer for you, the idle bar plug.

              All engines [ of the same type ] may be made equal but some may be more equal than others. [ sorry Thomas Jefferson ] Some just prefer a different set up from standard. I had a two stroke strimmer that was a right sod to keep running. After much of the usual messing about a change of spark plug up or down the range [ can't remember which ] and it worked well for years.

[Don Fry]

That’s interesting knowledge, I would have assumed, if an OS 4 stroke won’t go on an OS F plug, it’s the motor, and get shot of it.

[John Wagg]

7 minutes ago, Don Fry said:

That’s interesting knowledge, I would have assumed, if an OS 4 stroke won’t go on an OS F plug, it’s the motor, and get shot of it.

Why is it the motor ? Why get rid ?

Runs on the idle-bar and the No.8 plugs. It's an old-ish engine (Surpass) but has good compression and runs well.

 

Next time I will give the 5% fuel another go but don't expect any changes.

 

 

[Braddock, VC]

Just my £0.02 - check that the valve timing is correct, it's quite easy to do on the 48, two cap screws to take out on the camshaft cover, prior to this set the engine at tdc. When the engine is at tdc there is a punch march (indent) on the end of the camshaft against one of the gear teeth, this should be in line with the pushrod tubes and the centre of the camshaft. It doesn't really matter if the indent is adjacent to the pushrods or 180 degrees opposite, it should be in line with those pushrods.

If it isn't then you should reset it.

FWIW they will run with the camshaft one tooth out of synch, only in one direction out of synch and I can't remember which. 

I did hear a story that if you set them up 90 degrees out of synch you can run the engine in opposite rotation but I can't confirm this. Next time I change bearings I'll give it a try.

[John Wagg]

22 minutes ago, Braddock, VC said:

Just my £0.02 - check that the valve timing is correct, it's quite easy to do on the 48, two cap screws to take out on the camshaft cover, prior to this set the engine at tdc. When the engine is at tdc there is a punch march (indent) on the end of the camshaft against one of the gear teeth, this should be in line with the pushrod tubes and the centre of the camshaft. It doesn't really matter if the indent is adjacent to the pushrods or 180 degrees opposite, it should be in line with those pushrods.

If it isn't then you should reset it.

FWIW they will run with the camshaft one tooth out of synch, only in one direction out of synch and I can't remember which. 

I did hear a story that if you set them up 90 degrees out of synch you can run the engine in opposite rotation but I can't confirm this. Next time I change bearings I'll give it a try.

Thank you for that and will do. Coincidently the engine has run backwards a few times when I first started with it.

It is second hand so will do no harm to check.

Cheers.

[Don Fry]

1 hour ago, John Wagg said:

Why is it the motor ? Why get rid ?

Runs on the idle-bar and the No.8 plugs. It's an old-ish engine (Surpass) but has good compression and runs well.

 

Next time I will give the 5% fuel another go but don't expect any changes.

 

 

Read my post, “I would assume”, you have supplied knowledge, thank you.

[John Wagg]

2 hours ago, John Wagg said:

Thank you for that and will do. Coincidently the engine has run backwards a few times when I first started with it.

It is second hand so will do no harm to check.

Cheers.

Valve timing checked and while I had the engine out of the stand also checked the valve clearances. All O.K. but the timing "dot" wasn't easy to  see.

So now coming back to one of the original suggestions that it maybe the fuel. ?  

Is a No.8 plug hotter than an "F" ? 

[Denis Watkins]

The F plug has a thicker gauge element to stay lit for the fourth stroke

To answer your question

A number 8 is a medium 2 stroke plug

A3 is a Hot 2 stroke plug

The F plug stays lit longer

You do have a problem if the tappets are set ok and the timing marks aligned

It does sound like you are one tooth out On timing

Edited May 3, 2021 by Denis Watkins