backfiring

Well....I'm still stuck

My car will not rev all the way up smoothly (bit better after timing)...

once i get to around 4k it backfires and some black smoke comes out.

Carbies also occassionally backfire gas out of throats when this occurs.

have tuned the carbies [although some strange issues still (can do up fully and still run & choke bit stays down when i take choke off) however, they have been kitted.

-I've replaced the fuel pump with a brand new one.

-Checked and corrected the timing

-have spark at all cylinders

Now, when I lean it out...the carby backfire increases but the exhaust one does not change....so i REALLY stuck now.

Tacho also v. inaccurate, often sounds like revving up smoothly @ engine but exhaust popping.....

sorry if this is a very vague description but I v. confused & any help really appreciated as i will be driving it in a week or two.

Huw

Now' date=' when I lean it out...the carby backfire increases but the exhaust one does not change....so i REALLY stuck now.

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'Spit back' through the carbs is a classic indicator of lean mixture. Unless you have an airleak in the intake system (after the carbs or at places like the throttle spindles), then try richening the mixture a small amount using the adjuster at the bottom of the carbs. Another possibility is incorrect needles...if you have 240Z carbs on an L28 you should be using SM needles as the standard 240Z needles will be too lean (and, of course, I'm assuming you have used some sort of fluid - eg ATF - in the piston damper).

 

The exhaust 'backfire' may actually be fuel 'exploding' in the exhaust system, also usually caused by an airleak. Depends on when it's happening....for example if its occurring on overrun, then odds on you have an air leak.