DRLA 36s and how to stop my bus backfiring?

Looking the 29's I have TBH I don't think I'd trust that they are the correct profile though there's nothing wrong with an in between size - could be perfect. I might whack them in and try them for fun as I have the AFR whatnot, piles of jets and some experience. I think you're in the do it once and go camping bracket so pukka 28's are what you want.
Specialist smecialist, £400 is outrageous. It's an hour work if he drags it out once you've got your emulsions, 28 vents and known size idles fitted. You've seen yourself how easy it is to change the jets and you have your fuel pressure sorted. All you need at that point is to know your mains are not too lean at WOT.
Looking at your photos, the idle jets have 60 scrawled on them... they could be anything. I'd add a set of 57's to your shopping list.
Pump jets are fine and Eurocarb do not have DRLA pump jets, they sell you DHLA ones that are shorter and cause the fuel to dribble down the inside of the venturi if the vents are smaller the 32's. Eurocarb can be pretty arze if you don't know what you're doing, I gave up on them decades ago, sick of them selling unsuitably jetted carbs and stuff like the pump jets without telling you. They also sold me those 29 vents as DRLA 40 vents. Arze.
TheGreenSparkPlug company are cheaper for carb parts and nice people IME.

 

I guess jetted mine, went to the RR and they didn't need to change anything, you might find the same but I bet having said £400 they would fart about changing stuff for a few hours then put back what you came with to justify the ludicrous charge.
One I went to claimed his jet change had added 20HP but all he actually did was rev it higher. He was supposed to be "the man" but they are all potentially sharks. He also tried to butter me up saying my engine was the smoothest running one he'd seen (he knew I'd built it). At the time it had a hopelessly out of balance flywheel that made me cringe getting past 2,,000 rpm.

 

Maybe your best bet is to start the conversation with the RR people by telling them that you have a mild 1776 in a bus with 28 vents, .2 emulsions, 57 idles, 180 main airs, 2.5psi all of which you know are correct and just want to check your mains at WOT and change just those if they are too lean. That will educate THEM that you know what you're doing and save thinking you're ripe for plucking. It will also limit there "do everything" bill possibilities. If they claim all that is wrong or might be, they're bull pooping - avoid. Carbs are simple things when you get your head round them and some things on Dells (.2 emulsions, 180 airs and 55-60 idles, 2.5psi) are cast in stone as is 28 vents for your engine size. THE ONLY thing to check is the mains at WOT.

 

How about changing the emulsions and idles etc to what zed said, but leave the Venturi at 30 for now?

That means you don't need the carbs/ linkage to be taken off at this stage.

 

Airey tuning?
Cold thing is totally unnecessary.
Hmm, yes changing the vents you need to take the tops off the carbs, remove the pump jets and secondary venturis after loosening their holding bolts/lock nuts and not dropping anything. You'd find it easier to disconnect their fuel supply hoses too and remove the main jet stacks. I never replace the gasket but I'm careful it doesn't get stuck partly to the top and partly to the bottom - it needs to come off with the top as the float won't go through it.
If you still fancy it and have a centre linkage you don't need to disconnect it and the carbs won't need to be rebalanced - that's a big plus for centre linkages.
The smaller vent will make it richer so it won't blow up.
I don't remove the whole carb. I can change the vents in both carbs in 20-30 minutes but i have done this many times and the carbs are infinitely more accessible on a type-4 engine.

Not a bad idea Paul, but no use rolling roading it if the vents will be changed later. It would be a good start and Miss Scrooge might be entirely happy if that alone stops the popping, which I think it will, BUT changing the emulsions WILL change the AFR so no guarantee the engine would be safe.
So, Yeah, I still think the best course is change the lot then RR the mains pronto and don't put foot to the floor meantime..

 

Pretty sure @scrooge95 has the CB performance type linkage which has to come off to be able to change the vents

 

Work of the devil (all hex bar linkages). In that case... maybe this is not a job for Sarah, it just keeps getting harder doesn't it? It wouldn't stop me but I have the confidence and experience to balance after (which might not be needed but probably would need a tweak.

 

Linkage diagram

 

I do so love the simplicity of the centre pull linkage. You can do all the above we've been discussing without touching it. Even taking a carb off is just pinging the connection off the throttle lever.

 

Change the parts Zed says . You don’t have to buy new , shop around or put wanted ads out . It will get you 90 % there . Venturi are £16 each etc then you can play with main jet size which you’ll need around a 135 ish . £400 and two days to RR is crazy all you need is to know is it’s not lean not for them to eek the last bhp and max rpm. Also make sure they are balanced using a snail vacuum meter

 

You're right there, the flat never wants to be in the right place. When I remove them to get the vents out I put one finger on the inside jet end then unscrew until it will just PUSH out enough to remove the vent then leave it like that. I've found it stays straight 9/10 times that way.

 

You could mark the position of both Linkage arms.

Measure both Hex rods before removing them from the linkage arm at the top and from the throttle stops at the bottom. Then they will stay the same length.

Then disconnect the accelerator cable, before removing the entire long hex bar from the filter bases in one go. Put a finger over each end of the big bar so you don't lose your springs.

I've seen it done, they pushed the long bar towards the right hand carb, then removed the left side from the ball with a finger over the left side so the spring stayed in place. Then remove the right side again taking care not to lose the spring. Then drop one side of the bar down and wrestle it out.

Change your vents, jets, emulsions as per recommendations.

When you come to re fit the linkage back together it will hopefully be as close as possible to how it was and won't be massively out of balance or sync.

Then go to the rolling Rd for a fine tune of Linkage and carb balance etc etc

 

I have seen at least one instance of that linkage where to add to the misery, it was hitting one of the carburettor filter bases, and levering against it so the ball joint one end had eaten a huge hole in the cross bar making balancing at idle, and balanced throttle opening a thing of the past. Was that @F_Pantos ?

 

A real test of patience there! You know it must but it won't. lol

I find 135 is right for 30 vents, 145 for 32 but never AFR'd 28's but would have guessed 125-130. I'm guessing the incorrect emulsion is over fuelling and the small mains are compensation. The .3 has a smaller "waist".

 

I have a spare LSU4.9 Wideband sensor lying around so I just bought a driver module so I can finally finish my "mobile" AFR meter - a bit of 40mm dia childs swing leg with a boss on it, a sensor and a small box with an AFR dial on it - this may become available for loan/roving mechanic duties.

It will vanish into the noise of bus related eBay purchases.

 

Told you you could do it . Should've warned you about taking the pump jets out...

What @Zed said above. You're almost there if you go down to 28 vents (a necessity in a van IMHO). You can fiddle with jets endlessly, but there is no ideal solution. Get it ballpark - everyone seems to end up with more or less the same - and then leave it. Your .2s can be turned into .1s by soldering up the top holes (did it on mine, with no ill effects). Can do it for you if you like.

Avoid Mr X, for reasons previously stated. Price is ridiculous, and - believe me - they won't have "a selection of jets". Having the van overnight makes no sense.

Mains - I'd go for 127s as a starting point. They'll work well, and by the time they're fitted you'll be sick of the whole business (I'm still driving on oversized mains, 'cos I can't be arsed to change them ). Life's too short.

Vents you can change yourself, assuming they'll come free, now you've got your courage up. Pity about the cross bar linkage (I hate the things, centremount is soooo much simpler), but you can likely swap them without taking the carbs off.

 

Oops. You've got .3s, and need .2s. I need to look at my pic. Ignore what I said above.