Exhaust burble on 22R with a carby

[antiussentiment]

I've rebuilt the 22R in my !994 Hilux. As there was a pinhole in the exhaust manifold, I bought some 50mm extractors to replace it. I had an exhaust bloke make me a new middle pipe and rear pipe. I did not specify I wanted the thing 50mm all the way though, so he gave me a standard 40mm pipe for the rear.

When I lift off the accelerator (slowing down or coasting). I get a bunch of exhaust burble and I wonder if the pipe reduction is causing this.

I bought a re-manufactured carby and an air fuel ratio gauge as part of the rebuild. At 100km/h cruise the AFR is a whisker over 15 and at idle it's about 13.5. When I decelerate or coast it goes almost full scale lean (about 17).

So the question is. Exhaust pipe or too lean or both?

Any advice from the carby tuning lords etc would be great..

Cheers Andrew

 

[CONROD]

You don't specify if it's running the standard size bore or is it oversize ? 

40mm exhaust is heaps big enough for a standard 22r 84kw engine.

When you say exhaust burble, do you mean backfiring.

AFR is always going to lean off on a closed throttle, because you have come off the main jet and back onto the idle jet, with the new carby you bought did the guarantee you it had the correct size jets in it, also does it idle nice and smooth, might need the mixture adjusted, just my two bobs worth mate, Cheers

This might interest you 

Correct Air Fuel Ratio For 22r? (marlincrawler.com)

Edited December 30, 2022 by CONROD

[antiussentiment]

Hey thanks for the response @CONROD , apologies for not noticing your reply sooner.

The engine is as standard as can be. Though if I recall the bloke who did the machining for me took it to 1st oversize. I did the build in 2019, so I've forgotten. But it was about freshening a 500 000km engine, not a performance build.

No back firing. Just a burbling bubbling sound when I decelerate. I just wondered whether the decrease in exhaust pipe volume half way along my have something to do with it?

After reading the crawler post I think I'll add a whisker of fuel to the idle circuit and see what that does. It idles fine, but as I read over and over again, a little too rich at idle does not hurt. I think the carby is jetted pretty well as part throttle cruise is close to perfect (or what's been suggested in other forum posts I've read)?

The AFR Gauge is an AEM. Nice kit, but it came with the standard 10 second USA warranty. So when the Bosh wide band died after only 8 months they would not replace it.

[antiussentiment]

I thought I'd report back.

I made the idle a little richer and (mostly) it seems to have cured the problem. Very occasionally it's super lean on deceleration. But that's rare. I'm guessing there's a dashpot somewhere that's sticky? It is getting on a bit now so that's to be expected I guess.