Ignition Problem or Carb Problem

[drolston]

Went through ignition hell this winter, caused by spiral wound ignition cables with flimsy brass connectors that broke (invisibly) inside rubber boots to the crab distributor, after a few times removing and replacing. Replaced them with copper core wires from Van Pelt. Perfect fit and they look great with the old-school Raja plug connectors.

In spite of Pertronix good advice that their electronic points would not work with copper, due to radio frequency interference with the circuit, I took the Barn person's word who said Pertronix worked fine with solid copper core wires for years. Didn't work so well for me. I got a weak yellow spark for a while and then it croaked. So, went to the Third Gen points distributor, which I always carried as a backup. Started right up, idled fine for a minute, started to get a little rough, chugged, and died. On cranking, it would chug a little but not start. Replaced the coil with the Bosch Blue; got a nice big blue spark, but still chug with no start. By this time the plugs were looking a little black, so I put in a new set of NGK, gapped to a loose 0.025. Now it will start and run for maybe five seconds, and then stumbles to a stop.

Acts like it is flooding: Smell of gas. Wet plugs.

Pulled the top of of all three 97's expecting to find a sunk float. Nope; they are all shutting flow with the fuel at about 0.5" from the rim. The rear carb bowl seems to evaporate down faster that the other two. Could it be leaking into the manifold? Common with 94 power valve problems, but not so much with the 97's. I raised main jets from .045 to .047 last year. I am maybe too cautious about overtightening the jets. Could one of them have vibrated loose, causing flooding?

Ideas?

As beautiful as those three chrome plated 97's are on that polished Offy tri-power manifold, they may be more trouble than they are worth.

[petehoovie]

Originally Posted by drolston

As beautiful as those three chrome plated 97's are on that polished Offy tri-power manifold, they may be more trouble than they are worth.

Profound ! The Pertronix as well....

[Ken/Alabama]

I’ve had tri-power on my 40 for goin on 25 years and the only problem I’ve had was a couple years ago I experience a small piece of trash inside one of the jets on the primary carburetor.
Feels real good when you stand on it and open up all three. My engine is 3 3/8 bore X 4 1/8 stroke.

[drolston]

Originally Posted by Ken/Alabama

I’ve had tri-power on my 40 for goin on 25 years and the only problem I’ve had was a couple years ago I experience a small piece of trash inside one of the jets on the primary carburetor.
Feels real good when you stand on it and open up all three. My engine is 3 3/8 bore X 4 1/8 stroke.

I agree; when they are working right, they go as good as they look. I am just frustrated that after fighting ignition problems for months, it still won't run right.

Has anybody had main jets unseat themselves and cause a flooding problem?

[flatjack9]

Are you running a 6 or 12v system?

[drolston]

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Originally Posted by flatjack9

Are you running a 6 or 12v system?

12v, negative ground. Pretty darn sure the problem is now carb, not ignition. It ran fine for a minute, so the timing is at least in the ball park. But then it stumbled and died. I still have a blue spark that will jump half an inch at each plug.

If the float settings are good, what could cause 97 carbs to flood?

[frnkeore]

What ohm rating is your coil and do you have a resister in the circuit?

I've found that running a 1.5 ohm coil, with direct 12V, will cause a similar problem.

Unless it's puffing out black smoke, when it runs, I don't think it can be the carb.

[drolston]

Originally Posted by frnkeore

What ohm rating is your coil and do you have a resister in the circuit?

I've found that running a 1.5 ohm coil, with direct 12V, will cause a similar problem.

Unless it's puffing out black smoke, when it runs, I don't think it can be the carb.

You are right. Not the carbs. Took all three carbs apart and found nothing that might cause flooding. All floats set correctly. Main jets all firmly seated. All power valves seated and little pop-ups working freely. Not entirely a waste of time. I did find and fix one leaking main jet plug, and all carb bases with risers really needed tightening.

Again, after the carb check, it ran at fast idle a little roughly, would not wind up with throttle; started hesitating, then after about five minutes just quit. No black smoke, new plugs not black or wet.

I am running a brand new Bosch blue coil which I measured as having very close to 1.5 Ohms. That should not need any other resistor, right?

When I set up the new distributor, I put on a new condenser. Could that cause it to run rough and die.

The spark from the coil wire is blue and will jump almost half and inch when cranking, but it looks a little thin and puny. And it seems erratic when cranking, like it is not sparking every cylinder.

Suggestions?

[40cpe]

You need about 3-3.5 ohms resistance on a points distributor running 12V. Your coil should get hot running a 1.5 ohm coil with no external resistor on 12V. It should run more than 3-4 minutes, though, in my experience.

Pertronix runs on same coil with no resistor.

[drolston]

Originally Posted by 40cpe

You need about 3-3.5 ohms resistance on a points distributor running 12V. Your coil should get hot running a 1.5 ohm coil with no external resistor on 12V. It should run more than 3-4 minutes, though, in my experience.

Pertronix runs on same coil with no resistor.

So the ballast resistor which I bypassed for the Pertronix needs to go back into the circuit?

[HD Rider]

I've run into the same thing with old Harleys. Electronic ignitions use lower resistance coils than breaker point ignitions. Put the ballast back in and try it.

[flatjack9]

The Bosch blue coils I run on a 12v system measure around 3.6 ohms. No resistor needed.

[Bill OH]

I run ,045 mains with #71 PVs in dual 97s on a 221 at 500 feet above sea level. I think .047 is toooo rich. Also connect an ohmmeter to distributor terminal on coil and the other clip to ground and turn engine over by hand with ignition off and see if point resistance goes to zero. Burn points without ballast resistor? I would take a look at the points. Report back.

[41panelmark]

I am having the same problem. I now have the Bosch Blue (internally resisted coil)but will toast points within less than 20 miles. Would like to get this problem solved for sure.

[HD Rider]

That almost sounds like a weak condenser to me.

[scicala]

It sounds like the Chinese condensers may be attacking again.

Sal

[JSeery]

Originally Posted by 41panelmark

I am having the same problem. I now have the Bosch Blue (internally resisted coil)but will toast points within less than 20 miles. Would like to get this problem solved for sure.

Have you ever checked the coil resistance to be sure what it is. I remember something about Bosch knock-offs being out there.

[41panelmark]

Tried a different condenser, this one reads .3 mfd. Difficult to find one that reads 3.5. I have a pile of them and all but 2 read about .26 which I understand is not enough. The 2 odd ones, one reads .4 and the other reads .45 which may be too much.

I installed a 1.5 ohm resister in front of the internally resisted Bosh Blue (which reads about 3.0 ohms resistance). These 2 combined helped bring my voltage to the coil down but it may not be enough.

I am running a 12 volt neg ground system after the coil I am seeing 8 volts is that still too many amps at the points?

[tubman]

The capacitance of the condenser depends on the inductance of the coil. Just about all "modern" coils are best matched to a condenser in the low .20's micro-farads range. I have a piece of Ford literature that lists all of the original Ford condensers and most are rated at less than the .35 micro-farads usually stated. It also says the "under-capacitance will accelerate point wear while over capacitance will hurt performance".

That being said, the actual capacitance of the condenser makes little difference. It is much more important that the condenser maintains a reasonable value under different temperature and transient voltage conditions. Many older condensers will read fine and rapidly deteriorate when they heat up. Testing a condenser without heat-cycling it says very little about it's suitability in service.

[JSeery]

Originally Posted by 41panelmark

Tried a different condenser, this one reads .3 mfd. Difficult to find one that reads 3.5. I have a pile of them and all but 2 read about .26 which I understand is not enough. The 2 odd ones, one reads .4 and the other reads .45 which may be too much.

I installed a 1.5 ohm resister in front of the internally resisted Bosh Blue (which reads about 3.0 ohms resistance). These 2 combined helped bring my voltage to the coil down but it may not be enough.

I am running a 12 volt neg ground system after the coil I am seeing 8 volts is that still too many amps at the points?

Sounds like way to much resistance. You should not need a ballast resistor with a 3.0 ohm coil, something isn't right here. Any idea what the system voltage is at higher rpms?