Hitchcocks Forum

Hi all, Do any of the forum members have any advice about what petrol to use in my 1946 350cc Civvy CO? I've read contradictory advice on using lead replacement, not using some brands, using bog standard unleaded with no addatives, only using super unleaded as it has better qualities etc.

Anyone have a reliable runner that can tell me what they use?

Cheers, Chris.

p.s. It ran for 2 seconds on easy start last night, the first time in at least 42 years.

I am sure you will get advice which is varied and even contradictory on this subject. So let me start the ball rolling. I have a collection of bikes built between 1951 and 2011. They were variously built in England, Italy (despite being called Honda), and France. Last year I sold 2 bikes built in the USA and one actually made in Japan. None of my engines has been modified to run on unleaded fulel. I have petrol tanks made from steel and Fibre glass (original fitting in 1972) and recently sole one with an aluminium tank. My fuel is dispensed via Japanese type carbs, pre-Monobloc, Monobloc, Concentrics, a little fronch thingy and by fuel injectors. Fuel pipes are variously copper, clear and reinforced plastic (polythene) from my local aquatic centre, and black "rubber" looking pipes. None of my carb slides stick, no O-rings have rotted, no floats have sunk and no fuel lines have rotted through. Similarly none of my tanks leak. Then I should add that none of my tanks have been "lined" with tank sealing gloop either.The purpose of this tome is to illustrate that there is much myth spread about modern fuels in my opinion. So I would simply fill up with unleaded and enjoy riding your bike. Isn't it a great feeling when a bike starts for the first time in very many years due to your own efforts. Of course other opinions on modern fuels are available, and will no doubt be made known to you. HTH rather than confuses.

The low comp CO engine is designed to run on very low octane petrol (by today's standards), down to 70 octane or so if I'm remembering correctly, as that was all that was available after WW2. I.e. any petrol you can find today will have sufficient octane number.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

However, this engine does not have hardened valve seats. The valve seats are cut directly into the cast iron head. Because of that I have until now run my 1953 Model G engine, which is exactly the same engine, on standard unleaded 95 octane WITH "a drop" of lead substitute almost every tankfull. To be exact: 1:1000 as pr. the instruction on the bottle. The extra cost is very little. It may or may not be necessary, but I would rather not have the valve seats worn out or burnt because I didn't do this. It is a major job to insert new valve seats in this head..-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

And then there is the question about ethanol in the regular petrol. At least here in Norway, standard 95 octane contains at least 5 %, maybe up to 10 % ethanol, which may or may not be good for parts of the engine. So from this spring on, I always fill up with Super 98 octane, which so far doesn't have ethanol in it. Just to be on the safe side. Again, the extra cost is small as I only ride 1000 - 2000 km a year and use less than 35 - 70 litres of petrol anyway..-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

This is how I see it..-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Regards, Anders F. R.

I just forgot to add that my tank was treated with Bill Hirsch tank sealer 10 years ago. That stuff claimes to withstand ethanol and other additives. I have had no problems with it so far, and are going to use the same stuff in my BMW R51 tank as all the parts of that bike slowly comes together as a whole.-.-.-.-.-.-.-.-.-.-.-

Rgds. afr.

The owners handbook for my 1952 BSA A10 refers to plug fouling and " continued use of leadded petrol. The engines were designed to run on pool petrol, a low grade mix of anything available.........
The only time I've suffered exhaust valve seat recession ( measurable at about 1 mm) was a 1992 Bullet Indian made head with a valve seat made of some sort of monkeymetal..... since replaced with something more durable......My 2 drachma