I noticed that when I downshift in both my 65 tiger and 64 Alfa backfiring seems to occur. I put 91 in both, but I'm wondering if I need to use some sort of additive to the fuel.....anybody else deal with this? Am I on the right track as I'm pretty sure carbs are tuned correctly....thanks
Gas octane question
- Thread starter Growler
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Change in octane rating has more to do with engine detonation on combustion...backfiring is unburned fuel igniting in the exhaust system, although I have seen backfires through the carb. It sounds like you might still be rich in the mixture, although timing could be involved, also.
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When you say backfire on changing down.. are you saying it is missing when you drop a gear and accelerate?.. or when you change down and engine brake, in which case you get the popping through the exhaust as the compression takes up in the motor?
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Throat Clearing
Generally, air needs to infiltrate the exhaust system in order to provide enough oxy for a "backfire". And yes, some unburned fuel needs to be in the system also. Check for rich idle and leaking head pipes/connections. Most of my aging toys do this anyway, which reassures me that they're still running . . . . . . .
Generally, air needs to infiltrate the exhaust system in order to provide enough oxy for a "backfire". And yes, some unburned fuel needs to be in the system also. Check for rich idle and leaking head pipes/connections. Most of my aging toys do this anyway, which reassures me that they're still running . . . . . . .
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If It Ain't Broke . . . . .
As long as it's out the backside and not up thru the carb, yer fine . . . . .
As long as it's out the backside and not up thru the carb, yer fine . . . . .
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if its under engine braking that's normal on any older car.. depending on exhaust system as tune it can be a subdued deeper rumble.. or can be rally car style quite loud popping and banging... if its just that out the exhaust under engine braking I would not worry at all.
Warren
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Plug color
Take out a couple of the easy spark plugs and check the color. I remember your car is rather stock looking. I put regular in mine as it has 289 heads but probably is a 260. Most older exhaust systems can have some little holes or gaps that also help to create the extra noise. Some motorcycles have drain holes built in to the old pipes to free up condensation. The old lowrider trick was to drill holes into the exhaust so it would really sound off after a revving. You are not asking about lead additives as well are you?
It is pretty normal even my old 65 falcon 289 2v with stock exhaust had a blub blub blub blap on deceleration.
Take out a couple of the easy spark plugs and check the color. I remember your car is rather stock looking. I put regular in mine as it has 289 heads but probably is a 260. Most older exhaust systems can have some little holes or gaps that also help to create the extra noise. Some motorcycles have drain holes built in to the old pipes to free up condensation. The old lowrider trick was to drill holes into the exhaust so it would really sound off after a revving. You are not asking about lead additives as well are you?
It is pretty normal even my old 65 falcon 289 2v with stock exhaust had a blub blub blub blap on deceleration.