New owner... doing a little troubleshooting.

Hi folks... brand new MV owner. Picked up a nice '77 M880 from a member on here. Love the truck... engine feels strong and plan to hang onto it for years.

One issue came up though during the 180 mile drive home. First hour to hour and a half the truck was doing fine on the freeway travelling between 60-65mph. No problems, shifted fine, no strange rattles or shakes... nothing unusual I'd say. I followed behind in another car but the person driving said she felt a large thump on the floor under her feet, then the truck started surging in higher speed. She couldn't get the truck to maintain speeds over 45mph. Limped the rest of the way home and let it sit overnight.

Took a look at it and first thing I noticed the muffler had blown along the top seam and the thump she felt was a HUGE backfire. Pulled the muffle and pipe off and ran the truck with a straightpipe and still same thing.

So far I've also checked the fuel filter (good and clean), tranny fluid level, and then looked the exhaust over... any suggestions.

I drove it and it feels like it's getting too much fuel at higher speeds - it runs like a champ up to about 35-40 then starts surging but never dies.

The previous owner put in a brand new carb, but I'm wondering if my extended 65mph driving could have had an effect on the carb?

Thanks for any help... again, truck runs great up to about 40mph and really I don't plan to be doing much dirving over that but still..



rollin

The fuel lines near the fuel tank rust all the time. I would check for holes that are sucking air and depriving the carb of fuel. Also check the sending unit as they rust at the top also. I have had a backfire split the muffler on one in a similar situation.

Don't rule out the choke or engine timing

Sounds like fuel starvation, with the 4.10 gears, 65 mph is winding that little 318 up.
Sure the muffler would indicate extra was fuel in the exhaust but that little Carter 2 barrel really isn't capable of dumping more fuel than it needs at those RPMS.
I have had floats stick after long 60 mph + runs & flood it out when you back off the gas peddle.

I'd be looking for fuel line damage near the muffler.

I agree with Bob and 319 100%... and in the same mindset also suggest checking the fuel pump pressure.

also, don't forget that there is a pickup screen in the tank, It could also be part of a fuel delivery problem. you can diagnose this by strapping a small gas can to the right fender well and running a hose down to the pump, then take the truck out for a test drive at 60mph. this would prevent you from dropping the tank for nothing.