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Misfire - Ignition Or Fuel Problem?


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At throttle my tach jerks 1200-1500 rpms, a misfire, the car stumbles.

 

I believe it´s running rich since the exhaust is always sooty. There´s also a stumble and hesitation when I´m quick on throttle, runs quite fine if I ease in to it and revs fine all the way to 6k on 4th gear. Worse is if I WOT it, let it enginge brake, and the hit it again. Idle is quite fine, but not perfect, it stumbles a bit.

 

But also the breaker plats is bothering me. I can move it just a tad by sucking the vacuum tube, but not all the way. Even moving it with a screwdriver seems a bit heavy. When I do manage do move it by sucking, it stays put when holding vaccum.

 

On attached video, you´ll see the jerk of the tach and notice the hesitation.

 

Very, very thankful of thoughts on where to start. Fiddling with jets or remove and fix up the dizzy?

 

And, hope you´re having a nice weekend!

 

 

misfire.MOV

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measure BATTERY / Charging voltage first.

 

under load as you describe, if the charging system in Kputt

and the battery is low - you will get those sorts of running problems - too

low voltage

 

then check the points for clean, correct gap (0.016"/ dwell 60 degrees)

check the condition of all wiring to the coil and to the distributor.

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Thanks! WIll do. Makes sense as well, I´ve got a bit of sway in the headlights - brighter on throttle. Noticed on garage wall. Also a bit of jumpy gauge needles when turning on light, blinking and so on. WIll check ground. (Again, I did place an extra ground from under dash grounding point to battery ground in engine room, but anyway..)

 

Will also check wiring, although I have a Pertronix Ignitor.

 

And one day I´ll replace the breaker plate anyhow, it seems bad.

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12.2V at 1000 rpm on battery terminals 1000 rpm, tried revving and never got more than 12.7V. 11.8ish at idle (about 850rpm).

 

12.56 at battery with ignition off.

 

Will check whether it´s alternator or regulator.

 

Edit: And now had a quick check at alt. 12.2 at idle. Bummer.

Edited by GreenSwede
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A stuck/sticking point plate will cause the tach to twitch, as will points that have too small a gap.  FYI, the point plate doesn't move very far at all from the vacuum portion of the advance. 

 

Another thing to check:  make sure you carb's accelerator pump is putting out a nice squirt of gas into the primary barrel throat when you work the accelerator linkage--check with the engine off so you can see the spray from the nozzle.  A poorly functioning or dead accelerator pump diaphragm can also cause a hesitation as you transition from the idle circuit to the main jet circuit.

 

cheers

mike

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A stuck/sticking point plate will cause the tach to twitch, as will points that have too small a gap.  FYI, the point plate doesn't move very far at all from the vacuum portion of the advance. 

 

Another thing to check:  make sure you carb's accelerator pump is putting out a nice squirt of gas into the primary barrel throat when you work the accelerator linkage--check with the engine off so you can see the spray from the nozzle.  A poorly functioning or dead accelerator pump diaphragm can also cause a hesitation as you transition from the idle circuit to the main jet circuit.

 

cheers

mike

Thanks! 

It does seem a bit sticky, I recall being able to make it move quite a bit by sucking many years ago. And I´m no smoker, so I think my abilities is somewhat the same..=) 

 

And the weber squirts. Not quite sure about the jetting yet, but I´ll fix the charging first. And maybe go over the ignition again. I do have a new breaker plate laying around, just haven´t worked up the energy to remove the dizzy to replace it yet. And I guess while there I´ll tear the whole thing apart.

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FYI, you can replace the point plate without pulling the distributor.  Just don't lose any of the little retaining screws down into the centrifugal weight area below the point plate; they're the very devil to retrieve.

 

Really? Is the plate held by the screws on the outside of the dizzy alone?

 

And thanks!

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Well, had a better look at the breaker plate and that, the hose actually seemed a bit plugged so I replaced that. Disattached the arm to the  vacuum unit and the plate moves smoothly. Still think it´s heavier to move it by sucking, but it moves.

 

Also adjusted the distance on the pick up for the Pertronix in the dizzy, seemed to improve unloaded throttle response a lot.

 

Replaced alternator, it produced 12.2V and now I have 14V at battery when running at 1000rpm. 

 

But, the hesitation is still there, and the flickery of the tach. Hesitation worst at higher rev, noticeable difference on WOT from 2000 rpm that gives maybe a minor hesitation, while on 3000 rpm it really takes a deep breath before revving away. Revs well after that, up to 6000 rpm and probably past if I´d let it.

And, it seems my idle got worse with more volts.. Misses a bit, and at 1000 rpm noticeable misses every now and then. Same thing deceleration, puffing every now and then on the way down.

 

Too much fuel? On low speed circuit?

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