Hi guys, I don't have much carburetor experience, and I'm a little out of my element. I'll try and explain everything that has happened up to this point so far. The car is a 66 merc colony park with the 410. It was driving fine when it stopped idling. It would run at speedsome up to 90 mph. I haven't pushed it past that yet. I had the carb rebuilt by professionals. Paid 180. Ouch! While it was out, I replaced the plugs and wires, gapped to 45. Got the carb back and it now won't go past 45mph without sputtering out. Thought it was a spark problem, Tried re gapping to 35 Setting timing, was at 15, now at 10 Tuned screws for idle to ???rpm by ear Filled the tank since we were getting low. Wanted to eliminate the duh, you ran it out of gas reply. No changes other than improved drivability under 45. I took the carb out and back to carb guy. He checked everything and was nice enough to show me how it all works. His theory is the bowl is emptying and pump isn't keeping up. To check this we ran it up to 45 till it stumbled, put it in neutral with my foot still on the floor, turned the key off. We opened up the car on the side of the road. Primary side was a little less than half full, secondary was all the way full. Maybe the bowl was empty and the cam bumped the pump over a few more times before I could shut it down???? Took it back home and tested pump pressure. It's at 8psi. The pump also looks new and shiny Next is to put a tank on the roof and run a line under hood to eliminate the possibility of it being a tank or main line problem. I have worked on cars long enough to not believe in coincidence. It ran good at speed before the carb guy touched it, why not now? I don't know enough about carbs to answer that question. Wtf happens at 45mph on a carb that I don't know about? Car revs freely and high in neutral and park. Even tried a burnout, but this pig seems too heavy. No sputtering there either. Also revs high under acceleration load. No sputtering. Down hill, we can get to 55 without a sputter. Thoughts? Greatly appreciated. Casey
What type of carburetor? Autolite, Holley, or? Also, have you visually checked if you are getting true full throttle opening when the pedal is floored?
If the rear bowl had the right amount of fuel in it, and the front did not, then it probably is starving for fuel when it's under load. This suggests that there's some kind of restriction in the fuel system somewhere. What does it have for a fuel filter? Could the fuel line be clogged somewhere? or leaking (sucking air between the tank and pump)? What about the pickup screen inside the tank?
Try blowing through the fuel line from the fuel pump back to the tank; it may have something stuck on the "sock", or these's other trash in the tank, and do it with a compressor, not your mouth/lungs (don't need to ingest/inhale gas)! Clear fuel filter or all metal you can't see through? I blame a lot of tank/fuel line/carburetor troubles on the alcohol infused gas out there; the alcohol loosens stuff in the tank up gasoline does't, and puts it in suspension, then it plugs up the sock, lines, and filter. By all means, try the separate temporary fuel tank just to see. It does't have to be mounted "up high" as long as you use your fuel pump. An outboard motor fuel tank on the floor would work with the hose out the wing window (yeah, I've done that!). I am Butch/56sedandelivery.
Check for vacuum leaks, when is the last time the condensor was replace(if you're running points) I had a buddy who's 351 would fall flat on its face on the freeway, I had a huge vacuum leak from a broken rubber cap. I have had bad luck with condensors the last few years.
Wow, thanks for the quick replies gents. It's a stock four barrel carb. It has a protronics unit (I think that's what it's called), no mo points. Yes, we get full throttle. It revs high and pulls well up to 45. It has a plastic clear filter under hood. No sediment is apparent. I'll try blowing through the lines as well in the next few days. Good suggestion on the boat motor tank. I've got an old evinrude tank. I'll also search for vac. leaks. Here she is. It's in the classifieds too. Kind of embarrassing to have a fat girl with short legs on a test drive. Need to get her fixed before she sells.
Will it go past 45 if you ease up to it instead of full throttle? Have you pulled the cap and rotor and checked the contacts to see if they are burnt?
Try your same route with the fuel cap loose or off entirely. If your cap is vented and the vent has plugged, it will act like that.
Had a Holley on my O/T 68 F-250 with a 410 in it with a similar problem after a carb rebuild. The problem turned out to be the wrong needle & seat, (too small).... Fixed that and the problem went away....... Lynn W
I suggest you check that the float level in the front bowl is adjusted correctly. The video below shows how to set the float level. The carb featured is a 2100 but the adjustment for your 4100 will be the same. The distance measured in the video, 3/16 inches, matches what I remember of Autolite carbs.
just as well bite the bullet and take off the gas tank and really clean it out. then reinstall using new hoses and lines. put a good filter between the fuel pump and gas tank.
A young guy I knew (Tom somebody) had a '57 Pontiac that he and friends lowered, (very low) and suddenly it had a top speed of 40 MPH. Ran good up to that...then fell on its face. Didn't do it 'til after he dropped it. I raised the "short" (car) up on the hoist, and right there was the fuel line, (metal) flattened out for about 14", where Tom had bottomed the frame on an incline. (probably 'showing class' entering John's Drive In, 'Class' could be shown by dragging your front bumper, scraping noisily across the steep apron...everybody would turn to see who's 'real low', (and therefore, real cool) Low cars could scrape the right frame rail. California thing. Anyhoo, I replaced (and relocated) the steel fuel line, clipping it along the inside of the frame. Good fix.
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