My friends coupe - we just finished a pretty big tune up. Replaced cap and rotor, spark plugs, adjusted the valve lash, and examined the points. Cylinder 5 misses occasionally and seems to be intermittent. It has the crappy zenith carbs. I figured it could not be a sticky valve or bad coil since the problem has been intermittent. I did notice that the metal fuel line under the car looks like someone had put their jack on it and was smushed a bit. I would appreciate input.
2800cs intermittent cylinder 5
- Thread starter charofire
- Start date
does the car have points or electronic ignition?
swap plug wires with another cylinder
swap plugs with another cylinder
check plug gap - I believe with a stock engine and igniton, .024 works best based on my scope readings recently
try the old dist cap
bad coil would affect more than the same cylinder so it's downstream of that
did you set mixtures on the carbs? Cylinders 2 & 5 have the shortest runner length so maybe #5 is too lean or rich. Adjust for best idle and see if miss goes away.
still could be a valve and if the above doesn't help then recheck valve lash.
I would think the squished fuel line would affect more than one cylinder.
swap plug wires with another cylinder
swap plugs with another cylinder
check plug gap - I believe with a stock engine and igniton, .024 works best based on my scope readings recently
try the old dist cap
bad coil would affect more than the same cylinder so it's downstream of that
did you set mixtures on the carbs? Cylinders 2 & 5 have the shortest runner length so maybe #5 is too lean or rich. Adjust for best idle and see if miss goes away.
still could be a valve and if the above doesn't help then recheck valve lash.
I would think the squished fuel line would affect more than one cylinder.
It does have points ignition. The cap is almost brand new. I did fiddle with the car as best as I could thus far - we had it idling around 650rpm pretty steady.
And Zeniths aren't crappy.
:-?
I agree with Steve and would swap plug wires or plugs.
:-?
I agree with Steve and would swap plug wires or plugs.
Zeniths
shouldn't remain at 650 idle. When new, and every thing in spec, the adjustment was 750-800.
On the top plate of each carb , next to the primary is an air hole. This hole is a direct port to the idle circuit.
Cover that hole to see if the idle gets better meaning you're lean OR idle gets rough which means your rich.
Get that far and then there's more.
shouldn't remain at 650 idle. When new, and every thing in spec, the adjustment was 750-800.
On the top plate of each carb , next to the primary is an air hole. This hole is a direct port to the idle circuit.
Cover that hole to see if the idle gets better meaning you're lean OR idle gets rough which means your rich.
Get that far and then there's more.
Thanks Chris, was just about to defend the Zeniths!
My bet is it's spark related- not fuel.
My bet is it's spark related- not fuel.
My friend removed his gas tank. Has some rust in it. He is having it boiled and then coated. I told him that he would never get to the bottom of his poor running if rust was working its way into the gas.
We hooked his gas line up to a can of gas with the tank out. Idle did not change when we covered each of the holes as recommended.
no change
when covering the idle air bleeds means you are very lean beyond what the carb was designed to compensate normally.
Open up the idle mixture screws beginning at the rear carb. And check for air leaks around that screw and the idle solenoid. ( Piece of tubing to your ear or a mechanic's stethescope. If you just look at the screw and it's position, then carb to carb, you should be able to guage if the rear is farther in meaning less fuel and the misfire. Concentrate on the reaqr carb first.
Then see if the throttle plates are open by the adjustment screw. They should be just barely.( Being open more than they should be allows more air than the idle circuit can handle causing the lean condition. There is a hole in the barrel where the throttle plate causes a venturi effect that allows fuel flw; so if the plate is past that hole- no idle circuit, no idle fuel, no change when the bleed hole is covered.)
when covering the idle air bleeds means you are very lean beyond what the carb was designed to compensate normally.
Open up the idle mixture screws beginning at the rear carb. And check for air leaks around that screw and the idle solenoid. ( Piece of tubing to your ear or a mechanic's stethescope. If you just look at the screw and it's position, then carb to carb, you should be able to guage if the rear is farther in meaning less fuel and the misfire. Concentrate on the reaqr carb first.
Then see if the throttle plates are open by the adjustment screw. They should be just barely.( Being open more than they should be allows more air than the idle circuit can handle causing the lean condition. There is a hole in the barrel where the throttle plate causes a venturi effect that allows fuel flw; so if the plate is past that hole- no idle circuit, no idle fuel, no change when the bleed hole is covered.)
Similar problem with my zeniths- warped bases leading to vacuum leak. Need to pull them and hone them flat.
Finally an update:
We swapped in the gas tank and the misfire disappeared with good gas.
Car warmed up nicely. But at about 1800rpm, a knocking noise started coming from what I think is cylinder 1. Sounds like a rod end knocking, but I don't know. The accelerator pump(s) in both carbs appear to be not functional, particularly the rear carb. when giving it gas, misses, stalls, 'chuffs' all the usual symptoms of fuel starvation. once you coax it up to higher rpm, it runs pretty smooth
Also, the new oil is completely black already (1 hour of run time).
We swapped in the gas tank and the misfire disappeared with good gas.
Car warmed up nicely. But at about 1800rpm, a knocking noise started coming from what I think is cylinder 1. Sounds like a rod end knocking, but I don't know. The accelerator pump(s) in both carbs appear to be not functional, particularly the rear carb. when giving it gas, misses, stalls, 'chuffs' all the usual symptoms of fuel starvation. once you coax it up to higher rpm, it runs pretty smooth
Also, the new oil is completely black already (1 hour of run time).
Pull the cam chain tensioner piston and ensure that it is not stuck in place:
http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/11310900.html#refertoc
Note correct bleeding technique when reinstalling. Can all be done with just the valve cover off.
Sounds like the carbs could use a rebuild or at least a good look-through.
http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/11310900.html#refertoc
Note correct bleeding technique when reinstalling. Can all be done with just the valve cover off.
Sounds like the carbs could use a rebuild or at least a good look-through.