Bogging down/hesitation in a 72 250C
 

Hi,

My car runs fine except when I drive for more than 30 miles highway. Then there is a hesitation and bogging down. If I floor it, it picks up again only to bog down again 5 secs latter. If I stop for a few minutes or slow down to 40mph the car runs okay again. A friend following me noticed a puff of white smoke as this problem occured. I've had the car 2 weeks and that's the only problem I have. I changed the fuel filter just incase but the problem still happened last week. Any ideas?

Thanks

how is
 

the temp when all this is happening?

if the timing were retarded it would gradually get hot and might approximate this behavior.

tom w

White smoke - how white? If it has a grey.blue hue to it, it's oil. If not, it might be coolant (head/gasket) or transmission fluid. The latter happens to me when I let off completely at (quite) high speeds - the manifold vacuum is so great, and my module leaks a bit, and causes tranny fluid to get sucked into the engine and be burned. The larger the leak in the module, the more smoke when you let off at high speeds, or the less vac is required. If your engine is overheating, it will be too lean - huge power loss. If you're getting smoke from oil, it could be rings or valve stem seals. Burning oil can foul plugs, causing power loss - but usually, at highway speeds, plugs become cleaner from oil burning, not dirtier.

And thats the twin carb Zenith model? Sounds like fuel accelerator pumps on the carbs to me, the levered and rubber booted piston looking devices on the side of the carbs. A very common problem with Zeniths thats easy to fix with replacement parts. Otherwise can be distributor advance mechanism, from ignition perspective. Or valve clearance adjust.

Regarding white smoke, dunno, and wouldnt worry about it if the car doesnt burn alot of oil. Meanwhile check the oil while the engine is idling - blown headgasket will show water bubbles on the dipstick.

I would look for a clogged tank strainer. I would also check the two little filters in the carb inlets - where the fuel line enters.

If you have the fuel pump with the removable top (little screw on top), I would pull it and check the screen inside. If you have the really old style with the screws around the diaphragm, there is an filter in the inlet side.

I suspect you are getting rust and scale from your fuel tank clogging the fuel flow.

And speakin of fuel filters, has anybody seen the really old ones lately with wingnut and round glass bowler top lids that lets you see the gasoline inside? I think they were phased out in '63 Fintails or therabouts, had em on Pontoon models too, a really cool retro-upgrade part if you could ever find one. I think originally the glass lid was cap on the pump, then was separate fender wall mounted, deffinitely worth grabbing if you ever see a parts car that old.

Thanks for the responses. I really think that its a carb or fuel starvation issue as everything else is okay. I will fiddle with them over the weekend. I plan the Weber upgrade soon. I hear it improves performance over the dual zeniths. Anybody done this upgrade?