Hi I have a 1970's motorcycle that is running too rich. All carbs/airfilter are clean etc. The book says run it on premium. I've heard that modern premium will be alot richer than 1970's premium and that could be the cause of the richness? If so I should maybe drop to 91 rather? Does anyone know if normal fuel has become richer over the years?
clark20,
Mar 12, 9:41am
How do you know it is too rich?
skin1235,
Mar 12, 9:46am
no the octane ratings have remained the same it that 95 octane from the 70's is the same as 95 octane today
running rich is not related to the fuel octane though, its related to the actual amount of fuel remaining unburnt, changing to a lessor octane will not fix this
lack of compression will make it run richer, worn jets in carbs will make it run richer, worn carb linkages and bushes will upset the mixture ( but usually leaner than richer)
Yes much more likely worn jets or the like, or plain poor tuning. Only did with gas is no lead so unless head is rebuilt with hardened valve seats you may want to add additive, but plenty don't bother so ask others with same bike. Assuming it's four stroke.
glyn4,
Mar 13, 6:06pm
Ta for that. Yes I add, additive. I think the jets may need leaning out a littlle. Plugs are very dark but it doesn't blow black smoke out the back so is only marginally rich. Engine in very good shape and tuned well. Cheers.
differentthings,
Mar 13, 6:45pm
Wasn't the old fuel 96 and not 95 octane. They use to put lead in it to boast the octane rating, so the fuel nowdays might be of better quality.(?)
mm12345,
Mar 13, 6:51pm
Composition of lead-free high octane petrol is different to the old leaded fuel - the tetraethyl lead is removed, but to boost octane they added / increased the aromatic content (BTX) and/or other ingredients. So the fuel may be more aggressive on seals/gaskets, making them swell up more or crack and fail. So I guess it's possible that there's an issue with the carb(s) as opposed to tuning of the carbs. Do not run it on regular. The late 70s bike I last had (Guzzi Lemans) had IIRC >11:1 compression (high for it's time) and would pink sometimes when running on NZ leaded super - which seemed to vary from tank fill. Regular would have killed the engine. The need to run additive to prevent valve seat recession in engines without hardened valve seats may have been vastly exaggerated, but it won't hurt anything except your pocket perhaps to add some.
skin1235,
Mar 13, 6:53pm
whatever the octane rate of yesteryear, the same octane rate today will have the same properties
OP the plugs do run darker with the unleaded fuels of today, same as exhaust pipes, gone are the light grey indication of proper burn that used to be, proper burn is now dark brown to black - but not sooty, sooty is still an indication of unburnt fuel ie running too rich
intrade,
Mar 13, 6:53pm
x1
quailty depends on the raw product. remember its dinosaurs and old forrests fermented in to oil. so there is not all the same good stuff. This is where problems with cleaning it comes from loads of sulfur in diesel needs a lot of hydrogen cracking and that makes the diesel dry and insufficient lubricating diesel batches are created then mixed with other fuels and then sold for you to burn and blow up your diesel if your out of luck, its why you always add a diesel fuel additive for any diesel similar variations will be on petrol fuels as its the same raw product.
mrfxit,
Mar 13, 7:29pm
If I remember correctly, in the 70's we had 83 & 86 octane with diesel pumps around the back corner of the stations. I was paying around 85 cents PER gallon back then. $5 got me from Hawera to Paeroa at a fast pace in my hotted up 105E Anglia.
Pretty common to get 20 or 50 cents worth of gas just to keep me going for another couple of days
mrfxit,
Mar 13, 7:58pm
Or was that 81 & 86 octane Leaded of course
We always knew when the car was running right by the color of the exhaust pipe. A very light grey to white was brilliant
elect70,
Mar 14, 6:33am
It could be the toluene instead of tetra ethly lead they use today as a cheap means of boosting octane in todays petrol , old carb seals O rings etc dont like it & may be perished .
daves01,
Mar 14, 7:08am
Gone are the days when as soon as you have stopped after a good ride you all jump off and run to the back to check the inside colour of your exhaust pipe(s).
gmphil,
Mar 14, 7:13am
I sein my mate paint in side of his exhaust white ! when I asked why he told me that he selling and when u mix black and white u get ? cheeky buger I thought never brought car from him lol
sr2,
Mar 14, 7:21am
To the best of my knowledge there is no toluene in NZ pump gas (it's very, very carcinogenic). We used to run 20% Toluene with Number One in our old Holbay Cosworth race engine but that was some years back.
headcat,
Mar 16, 4:19am
No it hasn't. Only the people selling it have.
mm12345,
Mar 16, 4:50am
Toluene (and xylene) in "BTX", aren't the problem, it's the benzene which is carcinogenic (causes leukemia). There will be toluene in NZ petrol, as well as some benzene - but they've been reducing that in NZ and most western countries, using MTBE to boost octane instead. When they first switched to lead-free high octane, benzene levels were high - several %. Now IIRC, it should be <1%. When I was using benzene in a lab - 30 years ago - the bottle would be put in a fume cabinet before opening, door closed, then carefully decanted while wearing gloves etc. Even though there's no lead in pump petrol any more, it's a dumb idea to inhale it, wash your hands in it, use it for cleaning parts etc.
mm12345,
Apr 28, 1:42pm
Also gone are the days where replacing corroded mufflers, exhausts etc was a routine job you'd expect to have to do a few times over the lifetime of a car.
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