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Unleaded & 'bio' petrol
UNLEADED & BIO FUEL IN 2CVS.
First the good news.
A) All 2cv4, 2cv6 (Dolly, Charleston etc.), Dyane4, Dyane6, Méhari, AK, AZU, Ami8
and Acadianes produced since 1970 have M28, M28/1 or A79/1 engines. All will run
correctly on unleaded fuel, with just a few provisos.
2cv engine in a ‘kit’ car or lightweight special.
B) If the 2cv engine has been fitted into a ‘kit’ car or special body then different
parameters apply, specifically that the car is usually lighter and more aerodynamic
than most original 2cvs, therefore the engine is virtually never laboured so it runs
cooler! It may only run a little hotter in stationary traffic, in general no extra
Most importantly you should be guided by the advice of the kit manufacturer.
Now some reservations.
The main reservation is that the addition of bio-ethanol to 'petrol' is not good for your 2cv in any way, it is corrosive to metals used in older cars and to rubber used in fuel pumps, seals and fuel pipes.
C) Old 2cvs with 375cc or 425cc (A53 or A79/0) engines, or Ami6, AK350, AZAM6
with an M4 engine may not run forever on unleaded or modern leaded fuels. Exhaust
valves may eventually burn on these vehicles as they were made for use with the
older, lower octane (70 to 90) fuels, their problem is the valve timing (camshaft
profile) which was designed for lower compression rating. However, provided these
vehicles are not driven persistently at top speed, problems should not arise.
1) All vehicles in A) above with healthy engines may be run on Premium (95 RON)
unleaded fuel although ideally with a protectant against the effects of ethanol and valve seat recession.
2) All 2cv – type engines have hardened valve seats although even harder seats were introduced only in late 1986.
3) The engine must be properly and regularly maintained.
4) Maximum total ignition advance (dynamic not static) must not exceed 34°.
5) If engine ‘pinks’ (pings) under load, retard the ignition timing to cure it!
6) Tappet (valve rocker) clearance to be set between 0.20mm and 0.25mm cold. This
is wider than manuals state but with good technical reason.
7) The carburettor must be complete, have no air leaks and be correctly fitted.
8) The exhaust (collector) crossbox under the gearbox must be fitted. Sports – type
‘two into one’ systems are not recommended. (See also Para. ‘B’).
9) An original air filter and box should be fitted. (See also Para. ‘B’).
10) Do not drive with grille blind (muff) fitted in summer!
11) Due to higher volatility of modern fuels, change oil each 3000 miles (5000km).
12) A last reminder that this advice is specifically aimed at 2cv engines fitted into
2cvs, See paragraph ‘B’ if fitted to something different!
13) We thoroughly recommend the use of Miller's VSPe fuel treatment, this provides manganese as a protectant against valve seat erosion and just as importantly combats the adverse effects of ethanol (found at up to 5% by volume in UK fuel and up to 10% in French fuel).