anti-backfire valve (620 1978')

[dirtydatsun78]

I'm new to the datsun scene, and i have a backfiring problem.  I was told there was a port somewhere on the valve setup that could be welded and could prevent this problem.  but i would much rather get second, third, and fourth opinions from people thet know a hell of alot more about them than my non mechanic brother in law:D

[IMH]

I sounds like you brother in law is talking about eliminating the EGR valve.  Bad idea if your state requires emission testing.  I believe Oregon does.  I would troubleshoot the problem rather than removing components. 

[dirtydatsun78]

It could be the EGR but I have seen the unit I'm referring to called the anti backfire valve.  It's located near the brake master cylindar on the firewall.  There are D.E.Q. regs in oregon, but lucky me, I'm out of their range   Anyway, A standard tune up has been done on the little guy, but still got the flame show out the exhaust occasionally.

[LilDat]

I'm with Stephen on this one, you've got something out of whack that is causing this, either a carb that is too rich, or timing issue. I drove my 620 with a busted valve for a couple of years and never had a back fire. The 620 is pretty much bullet proof but does have a temp sensor that allows the secondary barrel of the carb to kick in and  a sensor that tells the second set of points it is time to kick in. Both can be bypassed and the vehicle can be perfectly functional. I always used one set of points on mine. Let's hope your problem is simple with timing or carb adjustment and not timing chain issues. Ken

[dirtydatsun78]

well I just found out there was an air pump filter in this thing. and it was beyond horrible looking,  possibly an original part from the looks of it;) anyway as soon as i removed it, my backfiring problems went away.  like i said i'm unfamiliar with these things but does the air pump in any way cool the exhaust manifold?  it kinda looks that way.  well thank you guys for the info its greatly appreciated

[IMH]

The air pump doesn't cool the exhaust.  It injects unburned fuel into the exhaust stream.  That's how they work although I never understood how that reduces emissions.  The 'filter' you removed is probably the check valve which was bad and causing the backfire.

[dirtydatsun78]

No, it was definiteley an air filter:) not a check valve.  It's right at the end of the air pump inlet tube.  I'm just new to datsuns, I've been a mechanic for 15 years , so I do know a little about what I'm doing ;)