High RPM Miss

[nasty51ford]

I finally got to drive my B67 a couple days ago ( I still have the grin on my face!) It runs and drives much better than I had anticipated, and I believe the guy I got it from was wrong about the 55 MPH top speed. I got it up to 40-45 MPH, dropped the main box into 5th overdrive (against the dash) and pulled the back box into high range, she dropped down to 12 RPM, in all the years I have been driving, overdrive transmissions do about 3-4 MPH per hundred RPM, this truck is governed to 2100, so that's another 900 RPM, so roughly, another 30 MPH? I'm thinking it will run at least 70! If the little END 673 will pull the gear. Well, onto the engine problem, it has a medium miss when it gets up in the higher RPM's, like over 1500 or so, it doesn't do it idling, and I can't detect it when accelerating till it gets up to around 1500 or so, and higher. This truck had sat for two years, and the guy I got it from got it fired up, and drove it 100 miles to me, over a two hour drive, does this sound like it needs the overhead run? I am new to working on these old Macks, so any help or advice would be great! I have been wanting one for about 20 years though, and now I finally have one! lol. PS, there is NO blue smoke, and very little black smoke from the stack, and I have over 60 lbs oil pressure warmed up. The engine sounds very healthy, other than the miss!

Keith

[thomastractorsvc]

might be a broken valve spring there is an inner and outer spring maybe it is broken and it is floating at higher rpm listen to my youtube video I was driving along when it broke, took the valve cover off and the outer spring was broken and when I replaced it the inner was broken too lucky never dropped was able to rotate the engine to top dead center and replaced them with out pulling the heads.

https://www.youtube.com/watch?v=9fZxTCGHioo

1959 B 61 with 673END, out for a ride with my youngest son, at about 4:54 broke an exhaust valve spring about a mile from home.

[nasty51ford]

Thanks, doesn't sound like that, it's a real slight miss compared to that, but I will be pulling the valve cover off and checking everything.

Thanks

Keith

[rsb502]

Might be running out of fuel, new filters? Any leaks or wet spots in the fuel system?

[nasty51ford]

Not sure about the filters yet, I just got the truck a couple weeks ago, and I have to park it about 10 miles away, so haven't got to play with it as much as I want. Haven't seen any wet areas though, but the truck did sit for two years without running

Keith

[rsb502]

if it sat that long im sure there is algae growing in the fuel system somewhere, get some algicide for the tanks and swap the filters befpre you get too carried away it could just be a fuel supply issue.

[41chevy]

Aside from the fuel filters i would also take a good look the the neoprene fuel lines. Could have cracks, collapsing under high fuel demand or even the inside closing up partially. Probably as old as the truck.

[nasty51ford]

Yeah, I'm going to have to go through the system and check it all out thoroughly before I do anything else.