Datsun Roadster Forum-311s.org

Not nearly as good as the soup du jour.

Anyway, I took the Roadster out for a spin tonight and two things happened: the idle kept creeping up, and when I stopped (after an 8 mile drive) the ceramic coated exhaust header was glowing red hot!

I turned the idle set screw before I left the house (it was around 2000 this afternoon) and it was happy at around 900 rpm. By the time I got to my destination, it was idling at 3000 rpm. Might be too rich, not sure. I got the carbs were from Z-Therapy about 8 years ago, but they only have about 50 miles on em.

Do ceramic coated exhaust headers glow like that normally? I've never run the car at night, so I don't know if this is normal.

Any thoughts?

-MD

Just a thought, but I would check the linkages.. My car did this when one of the linkages got longer..

I had this problem with my MG...retarded timing and a lean mixture can cause higher exh. gas temp

Thanks guys! I made some adjustments before I left my parents' place, and it behaved fine on the 8 miles home. (Half were highway).

RCMike -- I actually just replaced the choke cable today, and the throttle cable was replaced a few months ago, both were pretty janky before, but they seem fine now. Good call to check 'em out, though!

Alvin -- I haven't checked the timing yet, but that may be the main culprit. That will be my project for tomorrow! I took my distributor apart yesterday and, lo and behold, it's the non-smog dizzy! I just hope the previous owner knew that and set the timing accordingly.

What ended up fixing tonight's immediate problem, at least temporarily, was taking the idle set screw totally out of the picture (which i found out from the tech wiki is supposed to not make contact with the manifold except when setting the carbs) and I also leaned out the mixture on both carbs by turning the knurled knob on the bottom of the carbs to the right (which I would be counter-clockwise if you were looking at the carbs from the top, or clockwise from the bottom.) It is easier for me to think of it as screwing in a screw -- righty-tighty makes the assembly go up, which keeps gas from pooling in the carbs.

Someone please correct me if my carb therory is incorrect! I'm learning a lot, but I haven't studied up on the engine yet. After rebuilding my suspension and front end, my mind is swimming in car parts and theory!

Cheers,

Carb theory is correct but be careful going too lean if the exhaust header is too hot.
Should go rich.

One thing to check is the taughtness of the accelerator cable. It tends to pull a little when the linkage (bell crank) gets hot. Make sure you have a little slack in the cable as it sits In the bell crank. A about 1mm of slop.

Also check that the cable is properly seated in the accelerator pedal bracket. I have had the cable end ball come out of the "socket" in the bracket and effectively pull the idle up. Ther is a clip the holds the cable end ball in the socket...that I don't have...

Fast idel screw is only used to set the carb balance. It should have a spring on it to keep it tight. I have had to use loctite to keep mine from backing out and getting caught on the manifold and locking the throttle up at high revs - even with the spring in place.

Glowing header was most likely unburnt fuel (rich) being exhausted and burned in the header.