DRLA 36s and how to stop my bus backfiring?

So @scrooge95 could feasibly put up with the back firing - until techenders.

Then @mikedjames test her (A) readings with her current jets vent set up etc. That gives a benchmark.

Then Sarah could change the idle and emulsions without *******ing about with her linkage. Hopefully it sorts the backfiring etc. Mike retests the (B) readings. To ensure its safe to drive and not rich or lean etc etc

Then Sarah could decide if, at Techenders, she wants to tackle the vent change, carb linkage readjustment and then take (C) readings or stick with the changed jets and emulsions (B) or go back to how it all is currently (A).

 

Correct.
Main jets are relatively cheap, so all things considered, your best safe halfway house without getting in a tangle with the linkage and balancing is to get the .2 emulsions then go with other's experience of safe jetting to go with those emulsions, 30 vents and 180 airs which would be 135 mains.
And while you're at it change the idles that have 60 scrawled on them but could be anything to either 57 or 60. In reality you could fit 50 idles and it would drive fine but it would be a pig to start in the winter. If you want me to recommend idles for you, go for 60 for easy starting. Dells like big idle jets.
Are you ok with setting idle mix?

When you get to changing the vents for 28 you will need smaller mains but at least they are cheap and the 135s won't hurt anything meanwhile, just be a bit rich. - safe to drive to a rolling road and fine until you got around to that even if it was months after changing the vents.

One last thing - if you were to accidentally put your idle stacks in the main stack hole you will have to take the carb off and shake it back out - ask me how I know.

 

You can change the emulsion tube, air correctors, idle and main jets with just the tops off the carbs. Best you will need to know what impact it makes in terms of rich or lean etc etc.


To change the vents you have to remove the metal air filter holder bases (3413 & 3414) to be able to get to the vents to change them.

Despite what I posted earlier...You may even be able to leave the long cross bar and the two linkage arms (3400) attached, plus leave the helm joints and hex rods attached at the top and just remove the bottom nuts 3399 that connects the helm joints to the carb linkage. Then undo the lock nuts from the swivel ball joints, undo the A/C base and lift it off for access to the vents etc. This causing less disruption to balancing carbs and Linkage. EDIT Prhaps yo could even leave the bottom helm joints connected?

You don't actually need to remove the carbs to get to the vents but may decide it is easier that way.

After the changes you need to know the impact on rich or lean etc
View attachment 136992

 

Experience, not just mine, says 30 vents with the correct .2 emulsion and already correct 180 airs - 135 mains.

And again, common knowledge - smaller vents suck more fuel so it will be richer which is safe, but not so rich it would wash the oil off the barrels and wear the rings. This is the point in time where rolling roading it to fine tune the mains a bit makes sense for both performance and fuel economy - everything else already done in a safe order to known "best" combo.

 

Did someone set them for you at techeneders? You wouldn't have been able to stop me showing you how if I'd been there and then you'd know. It's very easy to do, you could try it right now just for the fun of it and to see if you can stop the idle popping which is a sign at least one is set too lean.
Warm up engine.
Pick a screw at random.
Unscrew half a turn, see if pop stops. Did the engine speed up a tad? Try another half turn. No joy? screw it back in to where it was unless the engine speeded up a bit/sounded better then leave it in new position. You are listening to the exhaust BTW.
Try another and repeat above.
The above is just for you to see if you can easily and quickly stop the idle popping and gain some confidence while you're at it.
So...
The normal check/set is to screw them IN (one at a time) until the exhaust pops/engine falters then unscrew 1/2 turn at a time which will first stop the popping, then increase the idle speed a little and generally sound smoother - do that until unscrewing more doesn't make any difference then back in to where it last helped. Once you've gone around all 4 go around them again because now the engine is more balanced, the first ones you did may prove to be screwed out too far.
Then go for a proper drive to fully warm it up and do it again. This time you'll most likely find they all need screwing in 1/2 turn or so because hot engines don't need so much fuel, but this is when you get it set correctly too.

 

I mean change as per your recommendations.

I suggested earlier that Sarah could just change her emulsion and mains before thinking about changing the vents, but I thought the worry was that it might make her blow her engine up! Hence why I'm saying you need to find out the impact the changes make in terms of rich or lean

 

After a while, you'll find yourself checking the mixture if the engine seems uneven at idle by UNscrewing them one at a time listening for an increase in speed/smoother idle.

 

The only worry I would have would be changing the emulsions but NOT changing the mains which are technically much too small but maybe work as a bodge around for the incorrect emulsion. I would definitely NOT just change the emulsion.

 

So fairly easily:
Sarah could change her emulsions and main jets (to what you recommend).
Plus do her idle mixture adjustments (as per your instructions above, which even i have managed to do thanks).
Then see if she fancys tackling changing the vents - which is far more involved when you have CB performance carb linkage!

 

I'd change the idle jets too, those are someone's drilled out at home jobbies, which could also be true for the mains which may be drilled out bigger than the stamp on them. All well and good when you're tuning your own carbs and saving money but as soon as the next person gets them it's a lottery for them.

 

@Zed is this the correct info in one place then?

@scrooge95 easy jobs
Emulsion: 9164.2
Idle jets: 57
Main Jets: keep the current 122 for now

Adjusting idle mixture as per @Zed s instructions.


Harder job
Vents change to 28s when you have the confidence / time to do it.

 

No, as we were just discussing, changing the emulsions while keeping the mains could be disastrous, not worth the risk. 135 mains for the 30 vents.
60 idles would be easiest winter start. 57 ok too, nothing much in it.
I'd be adjusting the idle mix before any changes, just for the practice and probably stopping the idle popping too which would be satisfying. No harm can be done doing this.

 

I would say 28 vents and a trip to the RR to find out what mains you need unless I missed that recommend earlier?

 

Probably playing with the air bypass screws