Hey folks.. Great forum.. I am the proud owner of a '76 620 70,000 orig miles.. but... I can't drive it. Here's the skinny.. Bought it about 50 miles from my home it had not been driven very much in many years. The owner said that the gas tank had been removed and cleaned. ok. Filled up the tank started driving it home got about 25 - 35 miles down the road and running great then putt.. putt... blah... died. ok it's not my first old car, so, figured old filter was clogged. managed to get it started runs normal for about a mile or so then dies again. Well this happend all the way home. Got a new filter (it was really dirty) started fine, drove around my neighborhood running good for about a mile or so then putt... putt.. blah... died again. ok fuel pump? checked the output from pump when cranking. hmm no gas, ok. Got a new pump put on, started and runs great.. this time I let it run in the driveway for about 15 - 20 min runs good. took it for a ride same scenario. sit for awahile and starts and runs again..Help!!!!

i had a similar problem but mine was fixed when the pump got replaced... is there some sort of possibility that you're getting vapor lock or something? possibility of the tank not being legitimately clean?

welcome man... hope you figure this out

Thanks for the welcome.. Is there a screen or a filter in the tank that might get clogged when driven .. but when it sits all the sediment goes to the bottom and it starts again? Just a thought..

no idea man... as far as i know there's nothing like that but there is always the possibility

Try driving it with the gas cap off the tank. Maybe your evaporative emmision control is plugged up and causing a vacuum to build up in the tank.

Al

Couldn't hurt to drop the tank and clean it very good. if anything it'll give you peace of mind.

Thanks to all for the ideas and imput!.. Took off the tank and having it cleaned and re-lined! Hopefully this will solve this issue once and for all.. It was pretty nasty on the inside. Will post later with the results and possibly some pics. Thanks again!

I've had a 620 for many years. Twice had symptoms similar to yours. It would run fine for awhile or sometimes, then other times not even at idle (unless I continually pumped accel pedal). Both times, the cause was that the carburetor main jet entrance was blocked. First time by a grain of sand, second time by a glob of what I guessed was dried gasoline gum/residue.

I suspect a blocked main jet might also be the cause of your problem.

Next time it starts choking/dying, start pumping the accelerator pedal. If it runs better, then the cause is not enough gas, very likely a blocked main jet (carburetor accel pump is not supplied thru main jet). If that's the cause, it's easily fixed, you can see blockage of jet. Take off the carb front glass/cover (not carb top) to get to the main jet, may need to unscrew main jet to clean.

I would clean off the front of the carb where the glass is, to see the fuel level in the carb. Then next time it starts choking etc, stop on level ground and look at the fuel level in the carb. Confirm that the carb fuel level is near the indicator mark.

Or don't wait for it to happen again, just run engine at idle then shut off & look thru the carb front glass. If it's only a little low or high, it won't cause very rough running. But if much lower or higher than should be, then it will. Too low level could be due to several things: bad float setting, blocked fuel inlet needle&seat, blocked inlet screen in carb where fuel line enters, plugged fuel filter, bad fuel pump, blocked fuel line. My 620 factory manual shows no fuel screen/filter in the gas tank.

Logic: more likely cause is not enough gas, not too much gas (& exhaust would be black if too much gas). So determine how far gas is getting. Is gas getting all the way into the carb bowl, and with the level high enough? Even if it is, fuel could be blocked at main jet entrance.

If it runs OK at idle and low engine speed, but not OK after sustained high engine speed, then a common cause is a plugged fuel filter. Doubtful the new main fuel filter got plugged up again so quickly, but easy to check. Another thing comes to mind, if it runs OK when engine is cold, but not when engine hot, then one possibility is the distributor condenser. They can be OK when cool but fail short or open when hot, so if testing it, test it both cool and hot.

Hope this helps.

Let us know what you find out, to help others who may get same problem.

Thanks to all for the info and advice! Got the tank back hooked it all up put a new filter on again 5 gal of hi-test, and with a little coaxing of the throttle... I'm back in the saddle again.. well for the first time as I only drove it home from where iI bought it! Drove it around the neighborhood to start building confidence, then, farther and more. Totaled up about 10 miles just around the block. Well we'll see if it continues to be a success! I'll get some pics up soon.. Thanks again all! Hope to keep my 620 for many years to come.