Help Diagnosing Poor Running twin plug 2.7
 

I have had a series of events that i am not sure are related and the cause of my poor running motor. The motor is a twin plug 2.7. With PMOs and twin MSDs. It was torn down to replace some pulled case studs and new bearings a few months ago, resealed and put in the car. The car ran fantastic for several weeks but I noticed a slight backfire at idle and off throttle that got progressively worse over several weeks.

For kicks, I removed the jet stacks and cleaned them out.

As the backfiring issue was happening, I also had a battery drain issue. While removing the alternator to see if it was the problem, I noticed a loose wire and figured that was my problem. But since the alternator was out, I went ahead and had it checked. It came back fine and charges well.

On my my first drive after reinstalling the alternator, the car would not hold idle and was way down on power. When trying to accelerate, it sounded horrible, like it was down a couple of cylinders. My first thought was the progressively worse backfire issue got to the point where it would not run, whatever that problem was.

I also checked all coil wires to make sure I had not loosened them while messing with the alternator.

I checked the fuses and power indictaor lights on the MSD boxes and they are getting power.

The motor has about 1k miles since being reassembled, so I decided to change the oil and adjust the valves thinking that could be the issue. All valves are now adjusted and it still runs like crap.

So, I am going through my head what the issue cold be.

- could I have pinched a wire or something when reinstalling the alternator. Would that even cause my problem?
- is the previous backfiring issue related to the overall poor running condition or are they separate issues?
- could the issue be related to the distributor, rotor, cap, timing? I am new to twin plug dizzied so don't know what I don't know yet.

I think I am going to take the fan housing off to make sure the alternator wires are ok. If that doesn't do it, I will pull the dist and checks its function.

Any thoughts are appreciated.

Fan housing off to check coil wires? you lost me.

I wonder if you have a spark issue with an MSD? Can you put a timing light on all of the coil wires (1 at a time) and see if they are sparking? While your at it check the timing and see if it is close?

Is the backfire out the carbs or the exh?

Oops. Thanks Erik. I meant take fan housing off to check alternator wires. Original post corrected.

Oops I said coil wires I meant all the plug wires.

I knew what you meant. Thanks.

The symtoms you describe point to fuel delivery ..

of fthrotle backfiring is usually indicitive of a lean condition and carbs probably need to be adjusted . Same for throtle on hesitation , also point to fuel delivery.

Since it is not unusual to have carb rebalanced/ adjusted after a break in period i would take it back to who did the work and have them look at the fuel delivery and carb adjustments.

A few suggestions.

1. What is your battery voltage? low voltage will Prevent the MSDs from charging properly. They draw quite a bit of current and without voltage to support you may have problems.

2. Clean carbs. The car sat, you can pick up debris from dried/evaporated gas in the float bowls. This easily clogs idle jets.

3. Check for debris in the gas tank. Pull the sender and look in the bottom with a bright flash light. If you see anything floating clean the tank.

4. Check the tank fuel sieve. The supply line has a mesh sieve to prevent tank crud from getting to the fuel pump.

5. Check the connections to the fuel pump. Is it getting correct voltage. incorrect fuel pressure will cause problems. Check to see if the fuel pump is getting warm - this indicates that it is starting to fail.

FWIW I know the folks at Franz Blam have a lot of experience with PMOs. probably most of the air cooled shops do though.

I have always wondered about that, if its spitting out the carbs though dont you have a situation where the mixture is igniting before the valve is closed so (assuming the spark is igniting the mix) it would be a spark timing issue. That is what makes me think its an MSD thing. I think I heard about MSDs failing slowly or intermittently in the past, I believe it was a very frustrating trying to diagnose (I do believe that MSDs are usually bullet proof).

It was spitting out the pipes, not teh carbs.

Turned outo to be an easy fix. I called Franz (he did the work on the motor) and explained the issue. He said to go clean out the idle jets and call him back. I questioned him becuase I thought the issue would clear up at higher RPMs when the idle jets were not being used. But, he is the master, so I did it anyways. Damn if that didn't; clear up the issue.

The car has a fuel cell and all new fuel lines, so I should not have a recurring issue with sediment going forpward.

Thanks for the feedack all.

man I love this car - twin plugged 2.7 - yummy.

Glad you got it worked out.

If you would consider a trade for my 84 lime green hot rod please let me know. Also keep me in mind if you ever decide to sell :-)

snip

famous last words.

you just jinxed it.

thanks Lewis.

Thanks Erik, but not interested in a trade. That being said, everything I own (wife, kids, house, cars) are for sale for the right price :)

Erik - PM sent