I have a 1948 Mercury. Motor is mostly stock with the exception of a pertronix ignition, wires, and coil. Still 6 volt *positive ground. Holly 94 carburetor equipped with the adjustable main jet kit from speedway. Oil bath filter. Electric fuel pump running through original mechanical fuel pump. The mechanical fuel pump is new. I can get to 50 and second and the motor goes through the entire power band. But when I switch to third I can't get past 60. Not trying to set some land speed record. But at 60 I'm uncomfortable on the freeway. I do live in Denver, Colorado, So I'm thinking elevation is probably playing some factor here. But if it's going all the way through the power band in second I'm confused as to why it doesn't do it in third. Hoping someone can help me out here a little bit. Thank you for taking the time and any help you can give.
Well, they were not fast when they were brand new. I’d say elevation definitely plays a role. Also it would be interesting to know what gear ratio is in the rear end. If you crawl under there, should be two numbers stamped on the spine of the rear end. for example, 11-39 is a 3.54:1 ratio. 9-34 is the common 3.78 ratio.
You stated the car is still 6v negative ground. They were positive ground. If the battery is in wrong or the system has been changed, make sure the coil is wired correctly or spark will be weak. And yes, you definitely lose power with your altitude. Not likely that the engine will pull as much rpm in 3rd as it will in second. The load is too great.
My apologies. It's positive ground. I've also been moving my 41 Olds to an alternator and wasn't thinking straight. Been working on these all day.
If it pulls through the rev range in lower gears its down on power, or your brakes are dragging. Find someone with a tailpipe O2 gauge and see what the carb is doing. If thats ok look at the advance curve with a strobe light
I know someone who had a similar problem and after changing everything from spark plugs to fuel filters looking the problem he said I am finished after a months of trying to figure why the car would not go over about 50 mph. The answer to the problem was a stretched throttle cable from many years of use. Make sure the carburetor is opening fully when you press down all the way on the gas petal. I think it is such a simple fix that most people don't even think about it. One time I had an intermittent miss in an engine and it only happened every once in a while. I changed the plugs, wires, distributor, and a few other parts before an 85 year old friend who was a life time mechanic said to me have you tried putting in a can of Marvel Mystery Oil in it and I asked him why and he told me I think you have a sticky lifter and sure enough I never had the problem again. The lesson for me was I thought I had an electrical problem so that is what I was looking for and I never once thought that it could be a lifter hanging up. Jimbo
Via vacuum. Though, the advance is maxed out. I have the crab style distributor and I am wondering if it could be something to do with the vacuum brake? I've read different things and am wondering for this altitude, how I should be using/setting it? I'll check the throttle cable. It feels like it accelerating dine up the the point it starts balking.
I only bring up the vacuum brake because my gut tells me that this feels like a timing thing as the field delivery should be fine. And then if it hasn't it to give it a try but if it is fuel related I have this tattersfield intake with a couple of Strombergs on it. Maybe to swap out the whole intake and carb set up and see if it makes a difference. Not so much concerned about the amount of fuel the car is getting but more concerned about how much air it's getting at this altitude.
The more blanks you fill in, the more we can help you. When you got it "to 85 in the past", was that in Denver like you are now? Can you give us a list of everything you have touched between when it ran 85 to now when it only gets to 50? .......and when on that timeline did it seem to exhibit the power loss?
Getting to 85 was in Denver. It was when I first got the car. Since then I have changed out the cap and rotor converted from points to the pertronix ignition replace the spark plug wires and the coil. All of that work was done after it started to not be able to hit that speed anymore. Nothing that I can recall was really done between when it was hitting 85 and when it would not. I wouldn't have done anything if it was hitting that speed as I'm not really trying to make this a merformace machine. I just want to drive and enjoy it. The higher altitude I get the worst it runs.
Like said above........check carb linkage check choke linkage exhaust system for clog last resort...switch back to stock ignition 6sally6
I remove the oil bath air filter and the accelerates through fine. The habit of thinking it's either fuel or spark, looks like this time is was air that was the issue.
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