jonbill

I never heard of adjusting the pressure of the mechanical pump. I'd start with getting a pressure gauge and inserting it in the fuel supply line to a carb. if it passes that test, then maybe take the top off one, including the valve and check theres a good flow of fuel when the valve is open.

I don't know, my car only has the mechanical pump from the factory, so my pressure is regulated by an Aeromotive FPR.

maybe your float valves are sticking or your fuel pressure is too low. I reckon full float chambers allow you to drive gently for say 3/4 mile. so a couple of full throttle runs might empty them, and then if the valves are blocked or no fuel pressure it could take 15 seconds to fill again at idle. should be easy to prove.

confusing. you don't want to be running it much at 8 and 9, you'll have a sump full of fuel! if you lift off and close the throttle at 4000, its ok for it to go to 22. there's no load and only enough fuel for idle. As the revs come down towards the idle range the AFRs should come back down until its idling as it was at the start. is it staying at 22 when the tevs are back down to idle speeds? I don think it would be sticking float valves. how old is you wbo2 sensor? flipping between super rich and super lean might be a dead or clogged sensor.

I'm not sure I understand what you mean by "after" a pull. Are we talking about high rpm WOT or high rpm on closed throttle? If the former, I'd be looking at the air correctors. they are quite big at 195 so could be making it lean above 6k rpm. if the latter, it really shouldn't matter. could you maybe sketch how the AFRs vary with engine speed and throttle position?

Ed, yes, you're basically right. the main circuit is activated by air flow through the secondary venturi and a number of things affect when that transition from idle to main circuit happens - rpm, throttle opening, choke sizes, emulsion tube selection being the main ones I can think of. when I was running my triple carbs, cruising, at even 3500 (80 mph maybe?) , it was all idle jets. In short, its the combination of some revs *and* some throttle that will make the switch to the main circuit. sorry that probably doesn't help solve the problem though!

when you tested compression, did you do it with the throttle open?

assuming you have an LHD car, the drivers side is the tight side and the passenger side is on a sprung tensioner so you will feel a bit of slack.

as 240260280 said, your air correctors only have an affect at WOT. similarly , your emulsion tubes and main jets have no impact on idle and gentle cruising. if changing things on the main jet stack ruined the idle, it'll be because you inadvertently disturbed something else. check everything. are your jet stacks all screwed down snugly?

at what RPMs do you have those A/F ratios? I'd think your throttles are unbalanced or the linkages are binding a bit to have it slow returing to idle like that.

that doesn't sound good. engine out then.

did you adjust the idle screws? I would expect you'd need to open them a bit to keep the mixture right. the "idle" jets supply both the progression holes and the idle screw. the idle jets alone determine mixture during progression, the idle jet and idle screws together set the fuelling at idle. whe you go full throttle, the fuelling is determined by main jets and emulsion tubes so isnt a good test of your new idles!

It sounds like it is going lean as you say. The fact that it takes 4-6 blocks to come on and another block to recover suggests its fuel supply not jetting (as ZH says). Another test would be to stop on the hill when the problem happens and see if it struggles to idle.

https://www.ebay.com/itm/221709332289

the runners look quite slim, but I couldn't see a diameter given for them. they may be an airflow limitation compared to the Jenvey ITBs.

and the idle jets too? much of the part throttle running is on the idles, not the mains.

I think they're both m8 bolts, 22 nm.

Are the jets stacks all the same then for 5 as for the other cylinders? I don't think the linkage can make #5 alone rich. It has to be something unique to #5. its jets, tubes, air bleed, cylinder rings, valves, throttle plate etc.

I think that says they share a design, not the part though. The body diameter is 2mm different, the choke couldnt fit.

sure, why not? chokes might be harder to come by than 40 or 45s, but I expect thats the only practical difference.

I'd check the numbers on the jets and tubes first, that should be a 10 min job. swapping carbs around can be a fair bit of work, depending how the linkages are done.

obvious guesses are that cylinder 5 unit is different from the others. have you taken the jet stacks out and compared them? is #5 idle screw the same as the others, and screwed out the same amount? its still a dcoe, so I dont think its different from a 40 or 45 in how it works.

I only have two idle holders, .2 and .1, so I work with them.

if you were in the UK I could lend you my box of spares. :)

I tend to compare the L28 to 2.0 Pinto engine. they've got a lot in common and the size per cylinder is close. I wouldn't at this point go for leaner holders. I'd just go for 40 jets and see what difference it makes.