rotaeng

1980 Engine completely overhauled. 1981 rotor housings 1981 exhaust manifold and exhaust system. 1981 distributor. 1980 carburetor(rebuilt). New NGk spark plugs, wires, rotor and cap. Adjusted mixture and idle screws to the best of my ability. Idles fine with no misfire. See no vacuum leaks.
Problem: Misfiring with much loss of power when shifting in 3rd, 4th, 5th gear at high rpm especially on an uphill grade. As soon as slow down to 2nd gear and push at high RPM there is no misfire.
Any ideas or suggestions on what to check or look for?

gerald m

It sounds like you may have a lean condition at higher rpm when under load , Check fuel pump pressure and filter and float setting . Also check for any loose or corroded wiring under the hood if everything checks out you may want to take the jet sizes up 3 or 4 sizes . if the problem goes away then you can go up or down with jet sizes until you find it;s sweet spot . just because the carb is rebuilt doesn't mean it;s ok . Gerald m.

rotaeng

Thanks Gerald! I will work on your recommendation.

13x

interested in the results

Kn0CKzillA

My 85 does the same thing. if i romp on it from a dead stop once it hits something that feels like fuel cut at about 6k in second gear and ill shift into third and ill have no power. and actually the car will start acting up then die flat out. then it takes forever to get it started again and even then it dosent act right unless i let it sit over night.

OldMazdaProfessional

Define 'misfire'.
Are you saying the engine misses erratically at these conditions or that it's a power loss like you took your foot off the accelerator?
The first condition would be ignition related, the second would be fuel (lack of flow) or possiblya clogged catalytic converter resulting in power loss from high backflow pressure.


Now THIS symptom definitely sounds like a fuel flow problem, specifically a badly clogged fuel filter.

Kentetsu

Both of you: Change your fuel filter.




.

charlie321

+1 on fuel filter. Sometimes the sock on the actual pump may be bad.

rotaeng

Thank you all for your suggestions and thoughts. It does feel like misfiring as there is this power(acceleration) switching from no power, then a little power surge on and off seconds apart. I had already changed the fuel filter and pump. I have wondered about the catalytic converter. thanks for that suggestions.

rotaeng

Sorry it has taken so long to give you an update although I only recently had time to finish working on this. I had to send the carburetor for flow bench testing and exam. He replaced the floats which I am not sure was a lot of the problem. He did find a major problem with the pump check valve and had to change out the steel ball because he said it was the wrong size. Carburetor and car are running great.