QJ off idle lean bog.

[F-BIRD'88]

Now if you had a Baker electric car like Jay Leno
drives yiu eliminate all these issues around cold short trip low miles issues when going to the store.

100 years ago they had the right idea for in town commuting. No warm up required.
https://www.popularmechanics.com/cars/a1609/4215940/

[rfoll]

I would play with the primary metering rods.
The APT adjustment is critical. The APT trims the whole fuel circuit including the idle off idle transition.
If you drill the IFR you are stuck with it.
If you set it up for COLD (extra fuel) it won't be right for when warm. too rich.
The height and shape of the primary metering rods is much easier to adjust and MANIPULATE ±.
When stone cold its all about the choke and fast idle system.. Manual override (driver) control helps. Same with cold spark advance..
Quick heat to the plenum is key reguardless.
Carbed engines need time to "warm up".

Already been there. I even tried a stiffer spring under the power piston. It shouldn't be a surprise that it is difficult to measure the spring rate on something that small. It really changed nothing so I went back because raising the metering rods and opening them sooner relates to fuel milage, and these cars are daily drivers. When the main metering system comes in the car really takes off. But the idle and transition circuits need to be capable of reaching the engine speed where the main system and APT setting matters.

[77cruiser]

Are you using gas with ethanol?

[JCR]

The other thing is that the fuel the carb was designed for, no longer exists. The gasoline formulations now are for the burning of fuel using high pressure injection systems that can easily atomize cold fuel. I was on a forum a few years back discussing gasoline and driveability of carbs, and a petroleum engineer posted, we don't make gas to run in carbs anymore, we formulate fuels for injection. I guess we should just be happy that they will still run on what is being produced and sold? And on most muscle car engines that I work on which mainly get driven in summer, I block the cross over heat, as on a hot summer day the extra heat will boil the fuel causing all kinds of driveability issues.

Excluding the elimination of TEL from fuels in the early 1970s the major change to pump fuels has been the reduction of the aromatics portion and the inclusion of oxygenates in gasolines over the last few decades. In general, old car carbs need to be richened up from the old OEM specs to run better on the modern fuels. Also be advised of summer vs winter blends mandate by the EPA. See the current gasoline requirements in the link.

https://www.gasbuddy.com/go/summer-blen ... d-gasoline

[Geoff2]

I believe later QJs [ emissions ] had smaller idle mixture screw holes in the t/bore. This might explain why the screws are so many turns out. If the engine needs more mixture than the holes can supply, the t/blades would need to be open further to get the extra fuel from the T slots. This, in turn, may leave insufficient T slot for the transition to the main system. So try enlarging the mixture holes 4 or 5 thou.

[F-BIRD'88]

Did you try simply upping the primary main jet one size?

The gas mileage capability of a QJet is only realized because heating the plenum greatly improves fuel vapourization which allows stingy jetting.
You are not going to make it richer yet not make it richer.

[rfoll]

I guess this might have been lost in the previous posts, but the flat spot is always there,even when the outside temps are over 80 degrees. There is lots of 25 mph driving in this town and much of it puts me in that funny spot where the engine is is lazy. When everything is up to temperature I can just drive through it. These carbs have been on many other engine combinations with either stock or low performance Edelbrock manifolds and the problem was not there.

[77cruiser]

Have you ever tried going up 1 jet size? By what you are saying it's lean even when fully warmed up, it's just tolerable then.

[rfoll]

It's only lean at engine speeds below the operation of the main circuit, and only when I try to raise the rpm above a dead idle. I can actually drive along in a continuous state of bog, unable to accelerate. If i manually drop to a lower gear, the rpm will rise to allow the jets to start feeding and the car takes off.

[Papastoy1]

Can you tell us how much of the transfer slot is currently exposed? And have these Qjets ever run correctly on these 2 vehicles in the past in either high or low temperatures?

[Papastoy1]

Something else I just remembered. You do have gaskets on both sides of the squarebore to spreadbore adapter? Make sure the Qjet side gasket matches up correctly to carb as there several different design qjet base gaskets.

[Rick!]

Enlarge the idle tubes by about .003. BTDT at least a few dozen times last century. PM if you want details and tools to do it.

[rfoll]

Finally an answer to the original question!

[gnicholson]

yes the late q jets need the idle feed opened up . like said .003 usually does it. you dont want to go anymore than nec. you either need to carefully remove the tubes or have long than typical wire size drill bits.

[F-BIRD'88]

It is critical when using a QJet that the PCV valve flow rate at idle be correct for the job. Too much idle airflow thru the PCV will make the carb run leaner at idle and low speed. This kind of stuff is critical with a QJET.
Wrong PCV valve can really mess with the calibration and drivability.