My Desmog Thread (2 Viewers)

[BreckenridgeCruiser]

Yeah... If you run the ports open and don't adjust the carb again, it will be running lean. Since you live at altitude, the more air is always better soni would open them up and hook them to a filtered source and then run an AFR or lean drop idle adjustment to set the carb for the extra air.

 

[runnerfan]

Since I need to play with the lean drop anyway I can try both option, ports open/filtered or ports capped. I'll post results, could be interesting. If I experiment with those two scenarios would there be any reason to play with the dizzy again and timing? I have it all tuned to a place that i really like, I think it's about 18* (might be a hair more due to my base altitude) and of course no HAC, just primary advance direct to dizzy.

 

[BreckenridgeCruiser]

I don't think the advance would really need to be adjusted... Essentially with the ports open, you'd be allowing a little more air into the intake and therefore could adjust the carb for a slightly higher amount of fuel to correspond...

The AFR should be the same for the right tune, you're just allowing a bit more in when air is the limiting factor on how much fuel you want for efficient combustion.

I'm not super strong on my advancing knowledge, but the above is what I understand to be true.

 

[runnerfan]

Update - overall running great. Haven't touched dizzy, still at ~18*. Ran with the two carb ports open and closed near the house at 7000 ft and I couldn't notice a difference. I'll be up in the mountains this afternoon at about 9000 ft so I'll do another test run.

Question - adjusting idle mixture screw and idle speed screw with lean drop write ups and OTRAMM's youtube video. The strange thing is I start with mixture screw and bring idle up pretty high, like 1300, but the speed screw is already backed off the plate so i can't flip over to the speed screw and bring the idle back down. I can of course tighten the speed screw down and bring the idle up higher but for the lean drop i want to bring the idle back down with the speed screw. Maybe i'm completely missing something here, which is probably the case. Any thoughts?

For now since I can't seem to tune with the speed screw i've got it set with the mixture screw with the rpms at about 900, remember i'm at 7000 ft, desmogged, HAC delete, and timing at 18*. I think my mixture screw is about 4 to 4.5 turns out.

 

[BreckenridgeCruiser]

Make sure you are adjusting the speed screw... It's been a long time, but you can mistake the speed screw for the choke speed setting which would do what you are describing...

 

[runnerfan]

Yes, adjusting the speed screw. I had just previously adjusted the choke speed screw to 1800

 

[4runner2FJ60]

Is it typical to make carb tune adjustments with the change in seasons? Just checking, with the cooler temps I have noticed a little change in idle speed, and I am wondering if I am running a tad rich now? I am at sea level and adjusted/tuned my rebuild carb in super hot July here, been running great ever since, maybe I am smelling the exhaust more now that it is cold? She has started hesitating when warming up (no heat riser.) My mix screw is set at 3 1/4 turns out. Carb and dizzy were done by Jim C.

 

[BreckenridgeCruiser]

You are probably a little lean... Cold air is denser by volume than hot air so once the engine is up to temp (and this is important) the truck is taking in more oxygen per cycle. This may be slight, but scientifically accurate. Not sure if it would be super noticable.

That said, you may seem rich since the fuel will not vaporize correctly when cold so you may smell fuel as well as idle oddly with fuel condensate that eventually gets into the engine when it is warming up.

Key here is always do adjustments when the engine is at operating temps.

 

[runnerfan]

Figured out my issue! Somebody, and I think I know who, tuned up the idle with the AC idle up screw which essentially overrode the actual idle speed screw because the idle could not come back down. AD idle up switch is deactivated and the vac line capped. I must have locked at every linkage on that carb 100 times before I finally realized what was going on. Backed out the AC idle screw and everything fell into place, redid the lean drop and the truck feels amazing. Great thread, thank you to all who have contributed.

 

[runnerfan]

Update on front of carb HAC ports running open or capped after HAC delete at high altitude. Drum roll... I can't tell a difference. I was up at around 9000 feet and did a few road tests going up steep hills with the ports open and then closed. Not very scientific but I couldn't tell any difference in power or idle when trying to keep the same variables between tests.

 

[BreckenridgeCruiser]

Yeah at that altitude, the extra bit of air probably didn't do much...

 

[duchamp]

Does anyone know of a Desmog kit that’s available for purchase (right now) ? Man-a-desmog is back ordered. I would ideally not pull the pulley off my other truck to survey/ replicate. TIA

 

[brian az]

Does anyone know of a Desmog kit that’s available for purchase (right now) ? Man-a-desmog is back ordered. I would ideally not pull the pulley off my other truck to survey/ replicate. TIA

I used the Jim C stuff …

Products

 

[reddog90]

Maybe this has been hashed out but I searched the thread and didn't find a definitive answer. Which direction should the green end of the choke breaker VTV face? The FSM shows it facing the CB diaphragm. But I have seen multiple pictures of JimC rebuilt carbs (including in the how to desmog PDF) that show the green end pointing towards port (b).

 

[OSS]

Maybe this has been hashed out but I searched the thread and didn't find a definitive answer. Which direction should the green end of the choke breaker VTV face? The FSM shows it facing the CB diaphragm. But I have seen multiple pictures of JimC rebuilt carbs (including in the how to desmog PDF) that show the green end pointing towards port (b).

The emissions manual shows how it’s hooked up.

 

[reddog90]

Yep, that's the exact picture I was looking at last night in the FSM. I guess the pictures of JimC carbs I've seen with it flipped are wrong.

 

[FishTacos]

Yep, that's the exact picture I was looking at last night in the FSM. I guess the pictures of JimC carbs I've seen with it flipped are wrong.

Maybe, but probably not. That thing just restricts in one direction to delay the choke breaker. If you put it in the other way it just overcomes the choke sooner. Only a problem if it's cold out and even then not a big deal. One can eliminate it and have a good tune anyway.

 

[runnerfan]

I had a little extra $ so I went for it and just got the full holly sniper kit from Mosley. I won't hijack the thread with the updates, but damn, that is a game changer! Header + H55 + Sniper = lots of fun. Going from the full desmog that's all beautifully explained in this forum to the Sniper was easy, most everything was already removed and deleted that needed to go. Now I have one vac line from the Sniper to the dizzy advance (and the dizzy vent line if I'm being honest).

 

[FJ40Jim]

Maybe this has been hashed out but I searched the thread and didn't find a definitive answer. Which direction should the green end of the choke breaker VTV face? The FSM shows it facing the CB diaphragm. But I have seen multiple pictures of JimC rebuilt carbs (including in the how to desmog PDF) that show the green end pointing towards port (b).

If it is installed "normal" per the FSM, it delays the CB action.
If installed 'reversed', the CB works immediately on startup. Also it maintains the CB action even during drops in manifold vacuum.

 

[reddog90]

If it is installed "normal" per the FSM, it delays the CB action.
If installed 'reversed', the CB works immediately on startup. Also it maintains the CB action even during drops in manifold vacuum.

Well I cracked one nipple off mine trying to flip it back then so I just removed it from the line. So I guess I am super reversed now.