L20B backfiring out of the carb

[LeviGideon]

My brother bought a 78 620 a few days ago and, like most everything, it has a few small problems that need to be taken care of.

 

For the most part it runs great. But it backfires out of the carb shortly after shifting. It happens in 1st and 2nd for the most part. I already looks for vacuum leaks and found one leak and took care of it, but it didn't help with the backfiring at all. My thoughts are that it may be running lean, but the float level looks right. What else might it be?

[MicroMachinery]

Timing.

[metalmonkey47]

Have you checked timing? Running ignition too retarded (don't laugh!) will cause some pretty wicked backfires. 13btdc is where I get the most power.

 

 

 

edit: damn you micro, you beat me LOL

[LeviGideon]

That was my next guess. Have any tips on adjusting the timing or a link to a howto for the l-series? I'm used to tinkering with my A15. haha The L20b is a whole new setup to play with.

[Laecaon]

Turn the distributor, 10mm screw where the Dizzy attaches. 8mm upside down if you need more adjustment. I have a tendency to just adjust by ear, and always going for more advance, but making sure it never pings.

[metalmonkey47]

Like Lacaon said.

 

 

L20B is quite different from the A15. I found most power made from my A15 at about 5 degrees, and it hated advance however my L20B @ 13 degrees runs great on 87 octane.

 

If you don't have a timing light, you can try it by ear. I think I recall DatzenMike at one point mentioning just to advance it until pinging under light throttle and then retard it a few degrees.

[banzai510(hainz)]

Have you tried the tech link on Olddatsuns.com.

save it!!!!!!

[datzenmike]

But it backfires out of the carb shortly after shifting. It happens in 1st and 2nd for the most part.

 

If you're driving it how do you know it's out the carb? Could it just be popping in the exhaust manifold? That would be normal.

[Laecaon]

If you're driving it how do you know it's out the carb? Could it just be popping in the exhaust manifold? That would be normal.

 

Mine was doing both when the ignition condenser was going out. Loud shotgun bangs out the exhuast, but more commonly I was backfiring to the intake. Exhaust backfire, well still indicates some sort of problem, but not necessarily timing.

 

FYI, backfire technically is what its name implies and fires backwards, to the intake. Afterfire is after the combustion chamber firing, and goes out the exhaust. Then again, loud bangs are alarming and it all just becomes backfiring.

[banzai510(hainz)]

I assume 78 is EI ignition otherwise yes a Condesor could and will BANG a muffler.

 

I assume to a valve lash ck and timming. should get most of it.

 

One can always do a cam timming ck to ck for chain stretch

 

ck the dizzy shaft for looseness also

[Laecaon]

I assume 78 is EI ignition otherwise yes a Condesor could and will BANG a muffler.

 

Silly me, I wasnt even implying that he had points, just more or less what can happen with bad timing.

[LeviGideon]

If you're driving it how do you know it's out the carb? Could it just be popping in the exhaust manifold? That would be normal.

It backfired a little when I was doing some carb adjustmments trying to get the air/fuel ratio right.

 

So, after adjusting the timing on the distributor with no luck on fixing anything, I decided to double check the firing order on the wires. I guess the PO replaced the wires and he put them on in 1-2-3-4 order... Fail. Runs great now, it's a little sports truck.

[banzai510(hainz)]

I bet thats why he sold it