engine and drivetrain Car Bogging Troubleshooting (Stumped!)

[Utah02]

Hey guys,

 

I'm in need of your knowledge. I have a 1972 carbed 2002. Last week, pinkey and I spent an entire afternoon/night trying to pinpoint and fix my bogging problem. If you dont know, my car wont accelerate past 4000 rpms in ANY gear if I'm pedal to the metal. In other words, if ive eased of the pedal about a centimeter, I can accelerate as much as the car will. If I'm pedal to the floor, anywhere from about 3,500 to 4,000 rpms the car will just cut power. It will hit those rpms and then drop down 500 or so rpms then wont accelerate. It makes a backfiring/bogging noise too. So here is the list of our ideas and attempts to fix it:

 

1. Changed the spark plugs, no fix.

2.  Simple timing issue. Timed the car, no fix.

3. 38/38 carb was too much. switched to weber 32/36 carb, no fix.

4. Tune carb. No fix

5. Pertronix was bad? switched back to points, no fix.

6. Bad distributor all together? Switched to a good one, no fix.

 

 After a little break and some deep thought, we took the car for one more drive. In first gear it went up to 6000 rpms and then the car made a loud POP. The fuel pump just shut off, car died, and we rolled it back to the garage. We were confident then that my upgraded fuel pump was either bad, or pumping in too much fuel and causing the car to choke. We switched out for a fuel pump we knew worked with the car, very confident this was it, and still... no fix.

 

So,

 

7. Downgrade to good fuel pump, no fix.

 

And after hours of practically overhauling the car, we were stumped. I'll add this, when I say "we" I'm pretty much refering to pinkey. He was the one with all the ideas and knowledge to help me narrow things down. So big thanks to Pinkey for helping me out! Even though we came out of this one without fixing it, we narrowed down a lot. 

 

I few more things, I purchased the car in this condition. It did not start when I upgraded something or just randomly started one day. 

 

So tell me what you guys think it can be! 

 

Thanks in advance for the input!

 

Utah02 and pinkey

Edited May 13, 2015 by Utah02

[73tiiguy]

It could be your timing components are worn, timing chain and guides.

[PaulTWinterton]

Every time I read that the engine bogs at 3500 to 4000 rpms it reminds me of my clogged fuel filter in the tank.  Seems to come up a lot on this board. 

 

You don't specify what car you have, and I only know the tii, so take it FWIW.

 

The electric fuel pump starts to labor when the tank filter is clogged.  The first symptom (bogging) happens in the high rpm range when the pump can't move enough fuel.

 

Whether it's a tii or carb car, check your filters.

[73tiiguy]

Every time I read that the engine bogs at 3500 to 4000 rpms it reminds me of my clogged fuel filter in the tank.  Seems to come up a lot on this board. 

 

You don't specify what car you have, and I only know the tii, so take it FWIW.

 

The electric fuel pump starts to labor when the tank filter is clogged.  The first symptom (bogging) happens in the high rpm range when the pump can't move enough fuel.

 

Whether it's a tii or carb car, check your filters.

 

Good point Paul - much easier then a timing chain job!

[TobyB]

Sounds like fuel delivery, still, I agree.  I swear by a real time fuel pressure gauge at the carb, and a check of the inlet screen (if your carb has one- some don't)

 

Or it could be 2 carbs with non- functional power valves.

 

COULD be piston slap- but that usually makes enough noise that you start looking for it, and the 2002 piston's not very prone to it, either.

 

Also could be weak ignition- at WOT at high rpms, your spark needs to be at its best and brightest.  I had trouble with Jenn's car with

a blue coil, resistance wires, resistance rotor and resistor plugs.  Remove one level of resistance, and the misfire under heavy load disappeared.

 

fwiw,,

t

[Utah02]

Sounds like fuel delivery, still, I agree.  I swear by a real time fuel pressure gauge at the carb, and a check of the inlet screen (if your carb has one- some don't)

 

Or it could be 2 carbs with non- functional power valves.

 

COULD be piston slap- but that usually makes enough noise that you start looking for it, and the 2002 piston's not very prone to it, either.

 

Also could be weak ignition- at WOT at high rpms, your spark needs to be at its best and brightest.  I had trouble with Jenn's car with

a blue coil, resistance wires, resistance rotor and resistor plugs.  Remove one level of resistance, and the misfire under heavy load disappeared.

 

fwiw,,

t

pinkey noticed with the pertronix wiring on his car, the wiring bypasses the ceramic ballast resistor. My wiring goes through the resistor. Ill check into that.

 

Thanks!

 

Utah02

[Utah02]

Every time I read that the engine bogs at 3500 to 4000 rpms it reminds me of my clogged fuel filter in the tank.  Seems to come up a lot on this board. 

 

You don't specify what car you have, and I only know the tii, so take it FWIW.

 

The electric fuel pump starts to labor when the tank filter is clogged.  The first symptom (bogging) happens in the high rpm range when the pump can't move enough fuel.

 

Whether it's a tii or carb car, check your filters.

This seems very likely. Ill look into it!

 

Thanks

[Mark92131]

Are you running a fuel filter anywhere in the fuel delivery system?  These also get clogged and starve the fuel delivery to the carb which will produce the symptoms described.  I had a car that would run great on flat ground, but on hills, the junk in the filter would move and block the fuel delivery.  Also check your float height for the Weber to eliminate that possibility and that the linkage will produce full throttle when the gas pedal is floored.

 

Good Luck,

 

 

Mark92131

[732002Malaga]

You're engine is bogging down because your idle mixture screw adjustment is out of adjustment. Correct setting is 1.5 to 2.5 turns. Go to http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm

Edited May 13, 2015 by 732002Malaga

[TobyB]

um.  no.

 

t

[hchueh]

Agree, I'd bet first on a fuel delivery problem, and second on an ignition problem. The fact that everything is fine and then you get a sudden dropoff is why I'd suspect the fuel first. But if that doesn't pan out, one thing that can be incredibly insidious is bad ignition *wires* -- from the coil to the dizzy and out to the plugs. The wires can look fine on the outside but have high resistance on the inside due to age and oxidation. I had similar problems that were completely solved by a new set.

[Simeon]

Will the engine rev under no load to beyond 4000?

I assume that you don't have a rev limiting ignition rotor (you swapped out the whole distributor including cap, wires?)

Off the wall suggestion: could there be a blockage in your exhaust somewhere?

[Utah02]

Will the engine rev under no load to beyond 4000?

I assume that you don't have a rev limiting ignition rotor (you swapped out the whole distributor including cap, wires?)

Off the wall suggestion: could there be a blockage in your exhaust somewhere?

Yes. If I down shift and PPP the clutch it will go beyond 4000 and then slowly die down to 4000 then bog

Thanks

Utah02

[AustrianVespaGuy]

Also could be weak ignition- at WOT at high rpms, your spark needs to be at its best and brightest.  I had trouble with Jenn's car with a blue coil, resistance wires, resistance rotor and resistor plugs.  Remove one level of resistance, and the misfire under heavy load disappeared.

 

I think Toby might be on to something here; which coil do you have and how is it's condition? 

[TobyB]

...and I was liking the rev- limiting rotor theory...

 

heh

 

t