3K Trouble

[mika93]

Hey guys, got a little old 3k in my little old rolla and whenever I go to accelerate it starts missing and backfiring, I've replaced the spark plugs, leads and dizzy cap. What could be the problem and What else should I have a look at replacing?

Thanks

[Banjo]

Sounds like you've tackled the right area, because your description indicates it is possibly a break down of a high voltage component in the ignition system. As you've replaced leads, cap & spark plugs, and the symptoms haven't changed, then it is not one of those.

 

What about the rotor button or the points themselves. If not, then I would be checking that the ignition timing hasn't changed. Other possibility is that the centifugal advance weights in the bottom of the dizzy aren't free, and that the vacumm advance isn't working OK. (lift dizzy cap & suck on rubber line removed from carby, & see if plate rotates slightly)

 

If all else fails, put you head under the bonnet in the pitch dark tonight, with the engine running, and see if you can see any HV breakdowns.

 

There's always the possibility that it is the carby accelerator pump, but your description points clearly towards ignition.

 

Good luck ! Let us know how you go

 

Cheers Banjo

Edited September 25, 2014 by Banjo

[ke70dave]

How about the condenser? The little capacitor on the dizzy. I had one of them go on me once. Would idle fine but would splutter under any load. They are cheap to replace (~$10) so worth doing if you have changed everything else.

[Taz_Rx]

How about the condenser? The little capacitor on the dizzy. I had one of them go on me once. Would idle fine but would splutter under any load. They are cheap to replace (~$10) so worth doing if you have changed everything else.

 

And while you're at that you might as well spend another $10 and chuck a new set of points in it to! If the felt tab had worn down a bit they might not be opening very far which could also cause your miss.

[mika93]

It misses at idle too, will have a look at it tomorrow and let you know, thanks for all the answers!

[altezzaclub]

Carburettor! Accelerator pump may not be working as banjo said, easy to check as you should see fuel squirt down the first throat when you open the throttle quickly.

 

Then either an air leak in a hose/junction that leans it out, so check any vac lines on it & spray something around the gaskets after you've tightened up the manifold bolts-

 

or a blocked fuel jet/drillway which also leans it out. That means stripping the carb and hosing out the jets and drillings with petrol.or a compressor.

 

It would be nice if its points & condensor, that's easiest to fix.

[GJM85]

I've got a 3k dizzy at home where the weight posts have worn out a divot in the guides. If goes full advance and stays there.

[mika93]

Well I'm pretty sure it's just the points but the rotor cam thing (not sure what its called) seems to be worn down aswell, anyone know where I can get new ones? Or should I just get a whole new dizzy?

[altezzaclub]

rotor cam thing (not sure what its called)

 

Grab a photo or find one on the web of what you're referring to. The rotor tip burns away slowly, but faster than the rotor cam wears.

[Banjo]

 

[mika93]

Yeah that thing! What's the best way to set points? It'll idle fine now but super bad under power

[Banjo]

OK ! Get yourself a new set of good quality points & fit. Remove the rotor button. (pull straight up) Set the points so the rubbing block on the points is just touching the "flat section" of the cam on the shaft, & tighten the points adjustment screw.

 

Turn the engine by hand slowly, until the rubbing block is now on the tip of the cam. (max point opening)

 

Measure the gap accurately with feeler guage. If the gap is less than 0.45mm, then the cam on the distributor shaft is too worn, and the dissy should be replaced. If the gap is greater than 0.45mm, then with the rubbing block on the tip of the cam lobe, set the gap to 0.45mm & tighten screw. Turn the engine by hand slowly and measure the points gap accurately on each of the four (4) cam lobe points. If they vary widely in measurement, then the cam is worn, and dizzy should be replaced.

 

Don't forget to smear a fine bit of grease on the cam to prevent the rubbing block & cam lobes wearing during use.

 

The point gap sets the dwell angle, or the period during which the points are closed & current flows through the coil, building up the magnetic flux. If you have a tune-up meter with a dwell measure setting, this is the best way to set the points. The dwell should be about 45 - 50 deg. (good book says 46 deg.)

 

Hope that assists.

 

Cheers Banjo

Edited September 27, 2014 by Banjo

[altezzaclub]

Do you have access to a timing light? You'll need to set the timing at 8deg after you set the points gap, then rev the engine and watch the advance increase. It should climb to about 36deg by 2500rpm. There may be problems with the weights in the dizzy under the points plate, and they control the rate of advance.

 

If you haven't already got them, you might as well buy a dwell meter (which includes a tacho) and a timing light, you will use them all your life..

[megamannz123]

Hard to diagnose without driving the car but also it may be the coil, crapping out at high revs or under load. Does it have a ballast resistor set up? that might be faulty or it may just be a crappy connection somewhere. On the other hand as previously mentioned it may in fact be a fuel issue? blocked/dirty carb, fuel filter or pump. All these things can cause problems too. Good luck!

[mika93]

New points am she's running like a dream! Well it was until the coil cracked and now it's stuck on the side of the road haha. Anyone have a spare coil sitting around on te Sunshine coast?