200 inline six makes funky noise

[Anonymous]

When I run my '65 coupe in town everything is perfect, but when it's going on the Interstate, I get this backfire or miss type of noise when I'm around 70 mph and going up hill. Down hill is fine. I though I may need to down shift to 4th, but it still does it. I have no idea what it could be, I've already checked all fluids and carb. Any ideas?

 

[Anonymous]

If it is equipped with a points type distributor, the points may be set too close, and the points are "floating" at higher rpms - thus causing a miss.

 

[MustangSix]

Check your vacuum advance too.

 

[Anonymous]

You might also check for a vacuum leak.
Doug

 

[Junk-Falcon]

sounds

 

[Anonymous]

Now I'm not even close to the expert that some of the fellas above are but doesn't that sound like maybe a lean mixture under load?

I of course could be as wrong as rain, but just a though.

 

[Anonymous]

I'm with 63DropTop - Sounds like it's running out of gas at heavy load. Could be a an obstructed main and/or power circuit in the carb, incorrect jetting (which carb are you running?), or a clogged line or filter.

 

[Anonymous]

I'm running a 1b Carter YF. The car did sit for a while while we repaired some damage, but we put that gas seafoam stuff in the tank, which is supposed to make sure the gas doesn't gel up. Could that have caused a clog in my fuel line?

 

[Anonymous]

WooHoo!

sorry, just excited at the thought of being right for a change!

 

[Lazy JW]

Kinda sounds like a lean miss alright, but I like to start by checking out the ignition first simply because it is easy to do and it causes so many "carburetor" problems. It's amazing how many times I have fixed a carburetor problem with a good ignition tuneup. When you KNOW the ignition is right it makes troubleshooting much easier.
Joe

 

[Anonymous]

He said he already checked the carb, and didn't find anything wrong, so I would start by checking the point setting. Put a timing light on it and check the timing. If that checks out, then check the fuel supply - filter, float setting, power valve, etc...

 

[Anonymous]

I've checked everything mentioned and it all seems fine. The part that bothers me the most is that the jumping or missing doesn't happen in town and doesn't always happen on the interstate. The only constant in this situation is uphill at 70mph. And sometimes it doesn't happen then. I did just replace the starter solinoid and the unviersal joints. If the oil in the rear has not been changed since I got the car (8 years ago), would that cause this problem?

 

[Asa]

if the rear has never been under water, your oil is prolly good, but replacing could be good for longevity
look for fully synthetic stuff, you might pick up a few MPG

i don't think that would cause this noise though, you should poke around when you pull the cover off the rear though (if it's a 7.25") to see if there's anything obvious about it


does the noise happen when you're cruising at 70, or when you're accelerating to 70 and past it?

 

[Anonymous]

Without cruise control it's hard to say if it happens when moving steadily. When going uphill deceleration occurs and I have to compensate to keep it at 70mph. Agian, it doesn't happen every time I'm at a hill, but uphill is the only time it does happen. Almost feels like a loss of power for a second.

 

[MercuryMarc]

I have a similar problem- backfiring and missing only on a very steep hill near my house, 1/2 way up the hilll, over 35 MPH. Goes away if I slow down. Happened even after I rebuilt my carb, adjusted the float, replaced carb with another, replaced fuel filter, and replaced fuel pump. I did find a corroded coil contact from the distributer to the coil- replaced it and it helped at first but I still have the problem.
I cannot determine if it is lack of fuel under extreme load (and angle) or a load related timing issue (advance, vacuum, etc). I have heard before the statement "90% of carb problems are timing problems!" and I can't help thinking that that is your (and my) problem. I just do not know how to test for it. I have wondered if advancing or retarding the timing might help, even though it would just compensate for some dynamic timing issue (currently running at 12 degrees with no pinging).
If you figure out the problem please let us know!
Marc in SF
63 Ragtop
Current 69 200
Rebuilding 78 200 for transplant soon...
http://mercurycomet.net

 

[Anonymous]

WooHoo!

sorry, just excited at the thought of being right for a change!

I do the same thing Bryce... LOL
Chaz

 

[Anonymous]

Let's go back to the first statement
"I get this backfire or miss type of noise when I'm around 70 mph and going up hill" Sounds like timing to me, the motor's getting more gas and the timing is not keeping up with the change.

More than likely at the bottom of the hill at 70 MPH the motor is running at high RPM's, let's say around 2800 RPM's, Mechanical advance is fully in, vac Advance is at midrange (part throttle). You start up the hill and the vacuum drops becouse the throttle plates are opened retarding the timing. I'd guess a week or stiff vac advance diaghram or possibly a miss adjusted (if possible) diaphram or timing.

Just a thought,

Steve

 

[mikeyo]

Hi,
All good ideas posted. Here is one more. Sounds too simple but what shape are the plug wires in? If this happens Only uphill, and not under other hard load conditions (try a short bout of putting power to it with the brakes applied) then the plug wires couldn't be it. The idea is that under hard load you can get a crossfire from one plug wire to another from induction. You can test this out by firing the engine after dark, hold a screwdriver by its plastic handle and run it up and down the lenghts of the wires, look for sparking or glowing along the shaft of the screwdriver. Don't know if its brave or stupid but doing the same test I learned that I can use my fingertips along the wires (after a positive test with the screwdriver) and if the wires are breaking down the tips of your fingers will "glow" in the dark. Be careful not to get burned or caught up in moving parts. Over all sounds like some kind of ignition problem. Just my 2 pennies..lol