cant go fast for long....help!?, drives around town all day, but not on highway! Options

[rbmorrisiii]

Ok, so i got this car ('73 1.7L) about 2 months ago. single carb - yes i know this isnt the best fuel intake, but i am going to try to make it work. I tried to drive it home - about 90 miles, but it only went about 15 miles before it slowly crapped out. losing speed unitl i had to pull over. it would start again and drive, but couldnt go fast for long.

so, I: changed fuel filter, spark plugs, oil, cleaned oil screen, pulled gas tank and ran all new fuel hoses and clamps (found a kinked line which i thought was the problem - also found the vent in the gas tank to be smashed, so i re-opened that and ran a new hose to underneath the car) the lines looked fine running through the car - and when i blew them out they seemed to be free of any clogs etc.

I reconnected everything, and started her up today. same problem. she ran a little better and could run all day around town, but took her on the highway and she would only stay in 5th gear for like 20 seconds then started tanking in speed - down-shifted to 4th.....3rd...then pulled off the highway...noticed some smoke in the back so i pulled over to let her rest. the smoke was coming from the HE's - both sides on the "opening" closer to the muffler. the PO had screwed in wood screws into the gap i'm assuming to keep them from rattling, and that gap is where the smoke was flying out of. after a 15 minute rest i started up and drove for another 15 minutes with no major problems.

Why wont she go on the highway!

I'm stumped!

I'm new to the mechanical arena so overexplain things if you think you need to.

whats my next step? someone told me the timing may be messed up, 'cause when you switch to carbs you to need to adjust?!?!

help!

Thanks for all the help in advance, so glad to finally join the 914 world!

ill have pics of my bag of bolts soon!

-R.B.

[ericread]

You've only got three areas to look: fuel, spark and mechanical.

I think we can rule out mechanical as it runs well at lower speeds.

As for spark, could be, but no indications yet.

Fuel. OK, you're running a single carb, which you recently rebuilt. We see fuel pump issues pretty apparent in the Fuel Injected engines, as there's either fuel pressure or there isn't fuel pressure. With the carb, you have two main areas; 1. The fuel pump must provide enough fuel to the carb so that your engine doesn't become starved for fuel. 2. Your carb float must be properly adjusted. If the carb float is not properly adjusted, then no matter what fuel pressure you're running, the float may not be allowing fuel into the carb itself.

As fuel pump failures are pretty rare (not that they never ocurr) I would take a look at your carb float adjustment.

Keep in mind, the only difference between running around in town using high rpms adn driving on the highway is merely your transmission gear. Therefore, you should be able to recreate your problem by driving at higher rpms around town.

Eric Read

[Rand]

Keep in mind, the only difference between running around in town using high rpms adn driving on the highway is merely your transmission gear. Therefore, you should be able to recreate your problem by driving at higher rpms around town.

Not really. The motor has to work a hell of a lot harder to pull your car down the freeway at 70 than it does around town at the same rpms.

How are your temperature readings? Do you have a head temp gauge?

[ericread]

Keep in mind, the only difference between running around in town using high rpms adn driving on the highway is merely your transmission gear. Therefore, you should be able to recreate your problem by driving at higher rpms around town.

Not really. The motor has to work a hell of a lot harder to pull your car down the freeway at 70 than it does around town at the same rpms.

I was speaking from a fuel management issue. Granted, the engine will work harder from a stress standpoint getting up to highway speeds, but once the speed has been reached, maintaining the speed is not that stressful on the engine.

Eric