Help - 67 Datsun 1600 Jekyll/Hyde Engine

[VA67.5]

I need some help on my 67 1600 engine issues. The engine goes between running smooth with a good idle to running rough/misfiring/backfiring and not being able to idle. I keep going through the "air-fire-fuel" investigation but can't figure out the problem. The fuel filter is new and the fuel pump was rebuilt and appears to be working ok. I did open up the both carb float chambers and did find one float with a small amount of fuel inside of it. Float was repaired and...now floating. This morning the car fired up very easy and idled great. Probably the best it's every run. I drove it about 3 miles to a local coffee shop and the engine ran perfect. Got into the parking lot then the car started misfiring and would not idle at all. The misfire got worse and finally I had to have the car towed home.

Any ideas on what would cause the car to go from perfect operation to undriveable?

thanks,
Pete S.

[Bwk2000]

I think you can rule out a fuel or air flow problems for now if it ran great (again) for three miles. Focus on the spark …

Not sure what setup you have, but generally speaking you should start by testing your coil, points & condenser, ballast resistor, regulator and alternator. I’m betting it’s one or more of those failing as it heats up.

Also, if you have an EI, that can produce intermittent drivability problems if damaged … rare, but excessive current can cause issues other than complete failure. Only real way to test that is with a replacement EI or by temporarily reinstalling the original points to see if the problem persists.

[VA67.5]

Kai,

Thanks for the advice and a list of key components to test. My car still has the good old fashion points and condenser and hasn't been upgraded to an EI. However, on a brief inspection around the coil and distributor I can see plenty of suspect connectors that were added/changed over the life of the car. By testing piece by piece it will give me the opportunity improve any/all connectors in the chain. Not sure if there are key grounding points that I could also inspect and cleanup as well. Just part of owning a classic Datsun.

[Bwk2000]

Absolutely. Especially all your grounds (see linked thread below). Also, if you can’t remember the last time you replaced the points & condenser, I recommend you start with that.

viewtopic.php?t=9100

[Gregs672000]

The condenser can cause that exact problem. Try replacing that. They go bad and start pulling all the spark from the points I think.

[VA67.5]

Greg,

Thanks. I just ordered a new minor tune up kit including a condenser.

[cbez]

Could be overheating coil. I wanted to be a cool hipster with points ignition but quickly switched to pertronix which has been good for a few thousand miles. I've used it on my last 3 cars and will stick with points on my motorcycle

[redroadster]

Many things possible
Fuel flowing to the pump OK? Best to test it towing is $$$
high compression pistons ? Fuel good ?
Distrib new points, / condenser, centrifugal vac advance OK, timed right but sounds close
Distrib wiring test .carb slides free ?

[VA67.5]

Thanks to everyone that responded on suggestions and potential items to check on the car. It's appreciated.

[Tap]

Hello, I've been lurking around here for a while without posting... I've owned several roadsters. I had one that did what you are describing and it turned out that the points had worked loose, although once loose the car would run at all. Another roadster that was doing this had a bad timing chain. it would run fine that run really rough then fine... really frustrating. Good luck with the hunt.