Glow to petrol conversion, 0.S 120

[martin collins 1]

I have just bought an O.S 120 which has been converted or partially converted to petrol, it was fitted in an airframe so it may or may not have been run in this configuration. The Morris Mini Motors full kit includes a Walbro carb with fittings to mount it but this one looks to have still got the original carb on it, the plug fitted is a petrol one. I have not mounted this or tried running it as i only picked it up yesterday, do i need to fit a MMM Walbro to it to make it run reliably? Converting it back to glow is not an option for me.

[Paul De Tourtoulon]

YES, it won't run on a methanol carburettor, I just got my Saito 150 running on petrol and fitted a cheap 15€ zama carb, why didn't you get the carb from Morris mini ?.

[martin collins 1]

I didn't buy it from them, it was bought from an ad on one of the used model sites 

21 minutes ago, Paul De Tourtoulon said:

YES, it won't run on a methanol carburettor, I just got my Saito 150 running on petrol and fitted a cheap 15€ zama carb, why didn't you get the carb from Morris mini ?.

 

[jeff2wings]

Put it in a test stand and try it then you will know for definite, you can run methanol with with ignition to advantage but as this is probably about cost reduction try it on petrol as this is the pre-surpas model without the pumped carburettor 

[martin collins 1]

Yeah didn't want to run it on glow fuel, looking to run it as a petro motor. 

[Paul De Tourtoulon]

If it was mine, I would run it as a glow and sell the ignition kit.

[martin collins 1]

1 minute ago, Paul De Tourtoulon said:

If it was mine, I would run it as a glow and sell the ignition kit.

Won't fly glow, cant stand the oily mess. For what i paid for the engine i coukd convert it back to glow and more than recoup my money. If i have problems running it as a petrol maybe i will do that and buy a different petrol engine, i wanted a 4 stroke due to noise restrictions at one of my clubs. 

[jeff2wings]

The main issue is needle taper it should be less with petrol by upto possibly 50% I know when running methanol in  my race bikes you would increase the mainjet almost double and different needles to the standard size, obviously a m/c carburettor operates slightly differently than of our model ones,a fine taper will allow a more accurate control of fuel flow necessary with petrol 

[Jon H]

45 minutes ago, martin collins 1 said:

Won't fly glow, cant stand the oily mess

 

4 stroke glows tuned nicely and on the right fuel should be pretty clean. I fly my enya, os,  saito and ASP 4 strokes on 15% synthetic and while they arent spotless they arent dripping either. Things have changed, its not the 20% castor days any more and if the engine is tuned properly they are pretty clean. a quick wipe down with a rag is hardly a big deal. And that is ignoring the low oil content i now recommend for Lasers. Its only about .5% more oil than saito recommend for their petrols. 

 

No idea when you last tried one, but if its a historic mindset of 'glow messy' it might be worth looking at it again as i doubt that engine will make much mess on 5% nitro 15% oil fuel. 

[Paul De Tourtoulon]

You will regret it when you have driven 50 miles, smelling the petrol in your car.

 

 

Ok you can always, but that gold-plated ready mixed fuel but with your OS you will have to add at least 2% of 2 stroke oil.

[martin collins 1]

Flting petrol already Paul, did a fly in on friday an hour and a half away, smell not a problem. Not using ready mixed, i mix my own at the required percentage. 

[Engine Doctor]

Thats an early mk1 OS 120 and not very powerful so will be well down on power if run on petrol. Use the spark ignition by all means and run on methanol ( normal glow fuel)  That old engine suffers with camshaft wear and needs decent bottom end lubrication . Remove cam cover and give it a regular shot of oil an cam will / should last ok.

[Anthony Scott 2]

I have an OS 120AX which has been converted to run on petrol using a MMM kit.  It has the a standard OS carb, is very powerful, idles & accelerates as well as anyone would wish & is remarkably economical.  I use a synthetic oil at 20:1.

[martin collins 1]

Interesting Anthony, i guess i will just have to put it in a stand and try it to see how well it does run.

[Anthony Scott 2]

The 120AX is a 2 stroke!

 

[Engine Doctor]

2 hours ago, Anthony Scott 2 said:

The 120AX is a 2 stroke!

 

And a tottally different animal to the early 120 fs. Design, materials have also developed and modern engin3s like the AX can run on lower oil content the main moviny parts on the 120 fs might cope with lower oil but the camshaft wont. If it fails you just might be able to fit a cam shaft from a later model but check dimensiobs first. Better lobe profile etc gives much better performance. I fitted a camshaft from an OS52 surpass into an early OS40 fs recently and the increase in performance is really noticeable.

[Jon H]

If you want a petrol 4 stroke, buy a petrol 4 stroke. As ED points out, glow engines do not always convert well to petrol for a variety of reasons. This is why there is still no Laser petrol in production. Its just not that simple, at least not if you want it to run well and not give up the ghost after a short time. 

 

At the end of the day you have the wrong engine for your use case and its never going to work. All you are likely to do is break it and destroy its residual value. I am sure you will find a willing buyer for it configured for glow. You can then keep the sparky bits for stock, and move on to something more suitable. Or, just enjoy the simple life and run it as a glow.