1986 plymouth horizon bad gas mileage
I am getting about 17 mpg driving 30 miles round trip to work. This car has a new weber 32/36 dfev carb, complete tune up, new coolant temp sensor, all vacuum lines removed except for the vacuum advance, heater controls and brake booster. The timing is set at 10 degrees with the coolant temp sensor unplugged. I know this is how you set it on fuel injection but not sure on carbureted. The carburetor was set following the direction from weber and the plugs checked for color. They were a golden brown. I did notice that the rpms will drop while the car is idling after is has warmed up with the choke disengaged for no reason. The car does not smell rich and runs pretty well. I did read these are suppose to get 23-26mpg with a 2.2L 3 speed auto. Any ideas are greatly appreciated.
Cars & Trucks - Plymouth - Horizon - 1986 Plymouth Horizon
Answers & Comments
I really can't give much advice. Since you have modified the original configuration, you're really on your own. If you had a 4 gas analyzer you could monitor the exhaust gas and figure out if the carb is adjusted as lean as possible, and if the timing is correct for what you are trying to do.
Do you know if the vac advance is working on the engine computer ?
And the air intake heater on the air cleaner ?
Well i have done some digging and figured out that the ecm puts out a start up advance which explaines that. So i started digging a little deeper. I bought a vacuum gauge today and hooked it up to the port the brake booster goes to. My vacuum is very erratic. The needle violently goes between 10hg and 18hg. From the research i have done this may indicate a valve spring issue. I also did a compression test which was 140 135 145 145 that looks pretty decent to me. Any thoughts on that?
Sounds like you are on the right track. The swing in the vac gauge can be a weak valve or cam too. I'm surprised the compression test did not vary more than it did, but a weak spring or sticking valve could show up in one test and not the other. You should have some puffing in the intake or tail pipe if it is a valve.