Carb Tuning

[Spyglass]

For you carb guys out there, I've been through the following on a 97 that has been sitting since 19.

About a month ago:
-Shotgun clean
-New Idle screws => #1- 2.5, #2- 2.75, #3- 1.75, #4- 2.75
-Fuel filter
-New gas
-New plugs
-Replaced Cobra slip-ons with factory exhaust
-Don't know which carb jets are there
-Synch 4 X gauges to carb #2
-Synch carbs (can't recall the inHg)
-No driving due to snow

Today:
-Warmup (it's 27F/-3C)=> occasional cough/rpm drop during warmup
-set idle to 1000rpm as it was stalling with no choke.
-Check carb synch => not synch'd but close, and low at < 5 (should aim for 8-9inHg?)
-Idle screws => no perceptible impact from the initial setting to the stop turning right. Set them back to the initial
-Blip on the throttle has rpm lagging high for 1-2 seconds before dropping again.
-Carbs all synch'd to 4-5 inHg as per picture below.



After 30ish minutes of frigging, I put stuff away and then thought about cylinder temperature. I took the temp 5 mins after shutdown in the plug valley and 1 & 2 were approx 71C/160F, while 3 & 4 were approx 78C/172F.

There might have been a tad more visible exhaust from the right side on the initial cold start, but it may have just been the lighting. No black smoke. No antifreeze smell.

I assume with no change from the idle screws and low vac reading, I have a consistently bad vac leak from something on all cylinders.

Is that a fair assumption?

How about the difference in temp from the left side to the right side?

Thanks for the help.

 

[Radioguylogs]

The idea that all cylinders would have similar bad vacuum leak seems improbable.

I think most of us would expect the carbs need to come apart for a thorough cleaning.....and you can check the jet sizes while you are in there.

 

[MaxMidnight]

When balancing the carbs you are interested in the relative values of the reading and not trying to achieve a specific number. Your photo shows that they are synchronised.
From what you have written the key issue you need to address is the rpm lagging high for 1-2 seconds before dropping again.
This is indicative of a lean idle mixture. Suggest setting idle screws to 2 1/2 turns out. The idle mixture screws not having much of an effect would tend to suggest that there is still a blockage in some or all of the idle circuits.

As Mr Radioguylogs suggests further cleaning is required. If you can't get the crud out by conventional carb cleaner and air blasting you may need to resort to ultrasonics.

 

[3-Max]

Condition of carb boots top (in air box) & bottom is?

 

[Spyglass]

Condition of carb boots top (in air box) & bottom is?

I had the air box off for the shotgun clean, and they all looked sound.

When I get back from the road next month, I plan to pull the carbs to try and learn how they work, see what I'm dealing with, and likely a full rebuilt kit.

 

[Zeus36]

My bet is it's your pilot jets inside the carb jet block. Try the Shotgun again with just compressed air, no carb cleaner, but this time REMOVE each pilot air jet #1 (PAJ1 is #2 in the diagram below) to get maximum compressed air flow to the pilot fuel jet. (When I say compressed air, I'm talking about shop air at around 90 PSI and a blowgun tip.)

The diagram shows pilot air jet number 1 inline with the pilot fuel jet (Item #15). Direct compressed air into every orifice with the carb drains open, you want to try to get an air stream through the pilot jet and out to atmosphere. You could even try air into the drain lines with the drain screws open. When mine was dying at idle when the choke was turned off and stalling with any throttle, I did this modified Shotgun and it fixed what ever was in the pilot jet(s). If this doesn't work, you will need to open the carbs and clean the pilot fuel jet manually with a super fine wire.