Major Backfire... Damage?

F134 engine

After installing a new Solex carbureator with good results I then replaced my old IAY (?) style distributor with a new OMID-ADA "electronic" distributor. The new distributou and carbureator ran well but then the O-A failed in about 20 miles. To prove to O-A their part failed, I reinstalled my stock distributor but made an installation mistake that caused a single but tremendous backfire through the exhaust. After quickly correcting my distributor install error and setting the timing, it started easily, idles well. O-A is sending me a new module for the distributor.

But I have new issues. I can high rev and rapid release the throttle without any issues. As I increase the RPM, I can watch the centrifugal timing advance smoothly with my timing light. But under any sort of load, in any gear, it stumbles and very mildly backfires and has no power. It did not do this before.

The coil is new, resistance is in spec.
External resistor is new, resistance is in spec.
I checked the point gap. Good.
At idle, timing is 5deg advanced (using stock indicator on timing belt cover and camshaft pulley notch).
(A tachometer is on order so I can check my idle speed.)
A Holly fuel pressure regulator is installed at its minimum setting (2 psi per Solex spec) (gage is on order to actually check fuel pressure)
The 0.010" fuel pump shim is installed.
The fuel filter is new.

The only changes between running well and now:

One loud backfire in exhaust system (I suspect I now have an exhaust leak)
Idle screw adjustment on Solex
Volume screw adjustment on Solex.
I don't know absolutely where the timing was set originally, but I think it was 5deg advanced like now)

 

Just thinking, when you had the electronic distributor did you open up the spark gap ? Now with points did you re gap plugs? you need to check your timing.

 

Intake (vacuum) leak. Damage to the carb or a gasket?

Try testing with a vacuum guage.

 

Hey, Rusty; 'Sorry.. I failed to say the plugs were also installed brand new with the new Solex. Spark plugs are J8C and gapped to spec and torqued tight per the FSM. I did not change the spark plug gap when I later installed the O-A electronic points.

I also inspected the cap and rotor.. no obvious issues. Both appear to have only a few hundred miles on them but I cleaned them up anyway.

The last thing I did before driving it was recheck the timing. It is spot on 5deg advance. Hmmm... 5deg advance is the left side of the metal tab indicator (attached to the timing gear cover) correct? That makes sense since crankshaft rotation is clockwise and the left side of the tab is BTDC (advanced).

If I slightly advance the timing, shouldn't that increase power in a situation when it bogs down under any load? Remember, I don't know where the timing was when it was running well...

Thanks.

 

The condenser is new, but I have the old one. I'll try that. I'll have to see if my meter reads capacitance.

Do you mind giving me a little education about condenser effects? I thought it only reduced arcing at the points (to reduce metal transfer). Thanks.

 

I have a dual pressure/vacuum gage permanantly installed in the engine compartment reading intake manifold suction. The vacuum scale is only about a 5/8" arc, but per the gage I'm drawing about 18 to 20" of vacuum at idle. Vacuum dropps off as I raise the RPM.

I've read on line to start the engine and use a propane bottle with the (unlit) nozzle aimed at all the joints and see if the propane gets sucked into the any unwanted gap in the intake path and increases the RPM. I'll give it a try. Thanks

 

I put a voltmeter on the resister (between the ingition switch and coil) and watched the voltage with my digital voltmeter. Yikes... It bounces all over the place and gets really low sometimes. It reminded me of the output of the voltage regulator inside the fuel gage. I guess that makes sense after looking at the construction of the stock (pre electronic) voltage regulator, but one has to wonder about the effects of that noisy power feeding into electronic points circuitry.

 

The metal transfer is a secondary function of the capacitor. Primary is to boost the power of the coil.

 

When we were kids we used to manipulate the ignition on-and-off to make huge backfire explosions.

I dramatically ruined a number of mufflers, but also was told that it could 'lift' a valve and bend it. Just a thought.

 

? isn't timing supposed to be 5 btdc ? Or am I backwards on 134.

 

I've heard that

I followed Howard's suggestion and found the Feb 2017 conversation about condenser issues, and followed several of the reference links. (Thanks, Howard).

It included a way to test the condenser/capacitor.

 

I had that happen to me the carter pen fell out of the throttle linkage at the carburetor and the engine went to full throttle while driving one day. When I went to shut it off it back fired and blew the guts out of the muffler.

 

Yep. 5 deg BTDC (i.e. advanced

Hmmmm...

 

I tried to start the Jeep today and had no spark. I checked the coil input voltage and it was only 2.5 VDC. So, I bypassed the ignition wiring and added a jumper from the battery to the ballast resistor inlet and cranked it again... BINGO... spark.

No matter what else is going on, it appears I also have an ignition wiring or voltage regulator issue.

An old Jeep is certainly a great and continuous source of retirement projects...

 

I don't see how the voltage regulator would affect this. Possibly the ignition switch.

 

I will disassemble the ignition circuit tomorrow, but could a stock voltage regulator fail by delivering too low a voltage? And if it does fail that way, couldn't that prevent the coil ftom making a spark?

Is it common for an ignition switch to fail and create a large voltage drop?

Thanks.

 

The voltage available in the wiring harness will reflect the battery voltage. The regulator controls the charge returning to the battery, from the generator.

A regulator failure would eventually drain the battery, but you said direct battery power gave a good spark.

 

No. You can remove the voltage regulator and still start and drive your car as long as the battery holds up.