6 Cyl, weber carb tuning question Options

[Cfletch]

Hey there, some of you guys may remember my issues I was having with my weber carbs that ultimately ended up being a distributor problem. I have sorted all of that out and the car is ready to go to a shop to get an alignment, shifter adjustment, and carb tune. I called them up and they are about 3 months out, so I might get pretty bored and want to attempt more tuning on my end.

Engine is a 2.7L stock CIS engine with Weber 40IDA3C carbs. 123 distributor and an MSD box.

Current problem: Car when stone cold after a week of not running is slightly hard to start, but once its running it idles just fine and does not need any throttle aid to keep the engine alive. Once it is warm enough, I give it some gas to get it to rev up and it really hates going past say 2k RPM. I can baby it to get it past that limit and then it revs up just fine from past 2k or so all the way up to ~6k. I am doing some digging and trying to see what is causing this stumble from idle. Based on my loose reading on other forums, it seems as though the car is on the lead end and could use larger idle jets. Anyone been through this before?

Carb Jet specs are as follows- suggested from Paul Abbott.

Mains: 135
Idle:55
Air Correction: 180
Emulsion Tubes: F26
Venturis: 32

I have even gone as fast as asking AI- which is not something I rely on but wanted maybe some validation and it agreed that 55 idles were too small, also suggested F26 tubes were too lean and I should do something like F16 instead.

Any suggestions are welcome as I have about 3 months to mess around with this till it goes to the shop.

Thank you!

[Tdskip]

Get lots of other opinions, but sounds like the transition from idle to the secondary is not having

[slivel]

If you have verified that the ignition system/timing is correct, then I recommend that you check your carbs in the following order:

1. Pull all jets and ensure they are not clogged
2. Check accelerator pump circuits are delivering suitable stream of fuel
3. Check float bowl fuel levels

[Steve]

I had an intermittent issue with my 2.7 off the line or getting to the mid range. Going from 55 to 60 idling jets fixed the problem. It was also a stock CIS engine.

[930cabman]

Spark timing?

Popping through intakes when revving?

Fuel pressure?

[slivel]

For comparison, my 3.4 has this:

Weber 46's, chokes: 40, main jets: 185, idle jets: 60, air correctors: 155, emulsion tubes: F7. Paul Abbot also did my carbs so if those were the recommended jets, ac's, and et's, I would guess that you are in the ballpark. If you have the jets removed also blow compressed air through the jet passages.

I would highly suspect the accelerator pump circuits are not functioning properly and delivering the volume of fuel necessary to make the transition from idle circuit to main.

[Cfletch]

I had an intermittent issue with my 2.7 off the line or getting to the mid range. Going from 55 to 60 idling jets fixed the problem. It was also a stock CIS engine.

This is the confirmation bias I was looking for, seems easy enough for some success

[Cfletch]

Spark timing?

Popping through intakes when revving?

Fuel pressure?

Pressures at 3.5 lbs, some popping through intakes which to me says lean more than timing. 123 distributor is installed, was set to Z1 on crank cyl #1 tdc and the curve was given to me from Perry. I don't suspect any weird ignition issues.

[gereed75]

The idle jets dominate fuel delivery up into the 4000 rpm range. I like the suggestion of going larger. It is unlikely that you are running so rich through the transition range that the engine is “flooding”, so larger seems prudent. If that is wrong you’ll know quickly as it will get worse

Could be the accel pumps and jets. look down into the throats ( engine not running) and look to see fuel squirting in when you pump the throttles. It probably either is squirting or isn’t. It’s a pretty coarse fuel add. Working or not working.

My carbed 2.4S runs pretty good and idle is pretty solid - but it still spits/chuffs occasionally pretty much all the time when running at partial throttle. I always assume it comes with the territory

[gereed75]

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