L28 not firing on all cylinders

[M240Z]

Hey everyone, I was wondering if you all can help me diagnose the problems I'm having with my Z. I recently installed triple webers on my L28, but I'm still running the stock pump. As of late the car has been idling and accelerating a little rough. I was thinking maybe I have a stuck valve because I didn't change the oil for a while (changed now), and the carbs were a little rich. It is also making a little noise in the head. 

 

I pulled all plug wires, but when I pulled the wires off of 4&6, nothing happened to the idle as all the others did. The plug wires are getting spark, and I also switch the spark plugs. Why wouldn't those cylinders be firing? I also found that only cylinder 5 was rich, but cylinder 5 was still firing.

 

I changed the distributer cap and rotor, but it is still doing the same thing. I'm going to spray the intake manifold down tomorrow to see if it is sealed correctly, but what else could all this be?

[datzenmike]

Set/chesk the valve lash. A tight exhaust may not seal properly and the compression just pushes out and the cylinder does not fire.

 

Triple webers means every cylinder has it's own carb. It's possible # 4 and 6 are not getting fuel.

 

To be sure you are getting spark, pull each wire one at a time, put an old plug in the end. Lay on a grounded surface and crank the motor over, Gut spark??

 

Check that # 4 and 6 wires are not swapped around..

[M240Z]

Set/chesk the valve lash. A tight exhaust may not seal properly and the compression just pushes out and the cylinder does not fire.

 

Triple webers means every cylinder has it's own carb. It's possible # 4 and 6 are not getting fuel.

 

To be sure you are getting spark, pull each wire one at a time, put an old plug in the end. Lay on a grounded surface and crank the motor over, Gut spark??

 

Check that # 4 and 6 wires are not swapped around..

Thanks Mike for the advise! I'll check the lash and fuel. 

 

Everything is getting spark and I'm pretty sure the wires aren't swapped but I'll double check that too!

[Driftease]

check your main jets they may be plugged. If you believe that it is suffering from a rich misfire then look at the main air bleeds to see if there is debris in there. Last question was the setup ever tuned to your car? These carbs get a bad name because they are not one size fits all and they are difficult to tune if you don't know how they work. A infrared thermometer is a real handy tuning tool check ex temp on all cyl to see if they are all the way dead or firing weak.  

[M240Z]

check your main jets they may be plugged. If you believe that it is suffering from a rich misfire then look at the main air bleeds to see if there is debris in there. Last question was the setup ever tuned to your car? These carbs get a bad name because they are not one size fits all and they are difficult to tune if you don't know how they work. A infrared thermometer is a real handy tuning tool check ex temp on all cyl to see if they are all the way dead or firing weak.

I had them tuned a couple months ago, and the car ran pretty good. When the tuner messed with a couple of the fuel screws he found that nothing was happening. I forgot what cylinders those were on. I dont think the down cylinders are getting fuel.

[Driftease]

Start at the inlet screen of the carbs and if they are clear go to your main jets, of coarse check for other basics on the bad cylinders first. Rent a leakdown tester to test valves and ring seal testing will be done at TDC comp stroke on the cyl you are testing. can you post pics of your plugs too, that would help. try new plugs if you haven't yet I had a 260 here that just had a tune up at another shop and one of the plugs was bad, then the dumbasses screwed around with the carbs costing the customer much more money than it should have.

[Driftease]

I had them tuned a couple months ago, and the car ran pretty good. When the tuner messed with a couple of the fuel screws he found that nothing was happening. I forgot what cylinders those were on. I dont think the down cylinders are getting fuel.

The screws are for idle circuit and only affect idle and tip in

[M240Z]

Today my buddy came over and helped me adjust the valves which were super tight, then I cleaned out the jets on the carbs. The car runs a little better but still a little rough. I'm going to check the screens, but I think my carbs might need rebuilds.

[Driftease]

Go get the book Weber Carburetors by Pat Braden and read the section on DCOE starting on page 85 it will help you. Read and understand before attempting to rebuild them yourself there are a lot of parts to keep track of in there.