I had the opportunity to spend a few hours driving the T-bird yesterday, and noticed what appears to be throttle-induced knocking.
<preamble to question>
I've got a hobby car (the T-bird is my Mom's, believe it or not!), and I just replaced its 650dp main body with a main body from Proform. When I tried to start the car, I got an impressive fireball spouting out of the carb, so I promptly called Proform tech before I burned the house or the car down.
What I found out from him was that when a mix gets excessively lean it tends to ignite without the help of a spark. In the case of my hobby car, there was a *lot* of extra air coming in with the new main body, leading to the carb backfire on a very cold engine.
<end preamble>
Thinking about this when driving the Thunderbird, I noticed that there was a break-over point with the throttle that changed as RPM increased. If I floored it from a stop, I'd get horrific knocking, but if I rolled on the throttle I could keep opening it up without causing any knock.
This makes me think that the root of the knocking is maybe a carb problem and that I could maybe address it with richening the mix. Of course, I'll have to research that one - the carb came with the motor and car (4bbl Autolite?).
And a quick BS-meter question. The car's been worked on by a mechanic who specializes in old Fords, and while he's done great work, he's said a couple of things that don't sound right. First, he said that the motor couldn't handle conversion from downdraft to PCV, although later relented and did the conversion (my Mom has trouble breathing, and the fumes from the downdraft were overwhelming).
So for the "real or BS" question - he also told her that this motor couldn't handle modern 93 octane gas (apparently due to all the modern additives), but that strikes me as wrong since I'm guessing the additives are mostly the same across the octane spectrum, and the only difference is the relative willingness to combust. Anyone here care to corroborate or debunk this? I'm guessing that switching to "hi test" would also help the knocking.
Thanks,
JLW
<preamble to question>
I've got a hobby car (the T-bird is my Mom's, believe it or not!), and I just replaced its 650dp main body with a main body from Proform. When I tried to start the car, I got an impressive fireball spouting out of the carb, so I promptly called Proform tech before I burned the house or the car down.
What I found out from him was that when a mix gets excessively lean it tends to ignite without the help of a spark. In the case of my hobby car, there was a *lot* of extra air coming in with the new main body, leading to the carb backfire on a very cold engine.
<end preamble>
Thinking about this when driving the Thunderbird, I noticed that there was a break-over point with the throttle that changed as RPM increased. If I floored it from a stop, I'd get horrific knocking, but if I rolled on the throttle I could keep opening it up without causing any knock.
This makes me think that the root of the knocking is maybe a carb problem and that I could maybe address it with richening the mix. Of course, I'll have to research that one - the carb came with the motor and car (4bbl Autolite?).
And a quick BS-meter question. The car's been worked on by a mechanic who specializes in old Fords, and while he's done great work, he's said a couple of things that don't sound right. First, he said that the motor couldn't handle conversion from downdraft to PCV, although later relented and did the conversion (my Mom has trouble breathing, and the fumes from the downdraft were overwhelming).
So for the "real or BS" question - he also told her that this motor couldn't handle modern 93 octane gas (apparently due to all the modern additives), but that strikes me as wrong since I'm guessing the additives are mostly the same across the octane spectrum, and the only difference is the relative willingness to combust. Anyone here care to corroborate or debunk this? I'm guessing that switching to "hi test" would also help the knocking.
Thanks,
JLW
Comment