JustDSM

I'm desperately trying to locate the vacuum source for the vacuum diaphram circled in red below? I've stumbled upon a vacuum diagram once that was very blurry that had it listed as "TP" for Throttle Positioner. I'm unsure of it's function but I do know its connected to a actuator arm.

Any tips on how to route this into the vac. system? Currently it's just open on my truck.. I'll post up some pictures in a hour or two with how my trucks vac. system is currently routed if that is of any assistance to you folks.



Thanks a ton,

JustDSM

Here is the only known vacuum diagram I've been able to locate with the "TP" diaphram. I'm unable to follow this vacuum line to determine how I should route the line.

My '83 has very minimal vacuum system, nothing like the mess in this diagram. It's unlike any diagram I've seen posted, so that leads me to belive it's a "custom" job, even though there are no electrical connectors dangling or obvious vacuum hose modifications. Everything looks very stock appearing.

83

I'll try to remember to check my truck this weekend. I've never found a vacuum diagram that matched my setup, either. I think it's just how these trucks are...I don't think mine's been messed with, I think there were just a ton of different setups. Yours looks like mine though, so hopefully if someone else doesn't figure it out for you first, I'll be able to help.

JustDSM

The carb pic above isn't mine, but rather just one I found with the "TP" Diaphram.

Here is my truck's setup as it sits.. If you guys need me to remove the air cleaner I can..

83

Got carried away getting my transmission back in and haven't really looked at my carb yet, but I'm still planning to if you're still looking for help. I'm about to leave town until Friday, but I'll definitely check it out before too long.

JustDSM

That's ok 83. Truck is running well without it, but I would like to get everything running 100%. whenever you have the time, any info you could provide to its proper hook-up would be very helpful.

Thanks!

JustDSM

Stumbled upon this info:

General Description:

1. To reduce HC and CO emissions, this system opens the throttle valve slightly more when decelerating than at idle. This causes the air-fuel mixture to burn more completely. This system was used on some 1979-1981 models only.

2. The system consists of a throttle positioner, a VSV and connecting hoses. It operates in conjunction with the vehicle's speed sensor.

3. The vehicle at speeds above 16mph(26km/h), intake manifold vacuum acts on the TP diaphragm and the TP is set. The throttle valve is in the midium or high speed position. Upon deceleration of the vehicle above 7mph(11km/h), the throttle valve is held in a position that is slightly more open than at idle. Upon deceleration below 7mph, at atmospheric pressure acts on the TP diaphragm to release the TP and the throttle valve is returned to the idle postion.

kj1074

interesting, i never knew how it worked. ran into vacuum lines issues when i rebuilt my engine. I went through so much crapola to get the asian carb to work. I finally broke down and bought a weber.

83

Well, I promise to look again today, but that would explain why, when I quickly checked it out as we were putting my tranny back in, it looked like I didn't have that peice on my carb. I will check again today though, since I didn't remember exactly what your photos looked like when I was checking mine.

trekkerpaul

iTrader: (3)

Funny to have found this thread as I just went throught the same questions about my 1983 truck. I have a definitive answer for you.

Thie part you are wondering about is the idle up device vacuum that is only used if you have AC on your truck. IF you do not have AC then it can sit open or cap it. I have a factory manual and found it in the AC section. Mine is also CA emmisions, so I was freaked out about the extra 3 ports on the side of the carb which are only used on RV and high altitude applications.

Hope this clarifies the issue for everyone

JustDSM

I'll certainly take the FSM description of its operation over the text I found. Thank you very much for that tid-bit of info! My truck also had those 3 ports capped..

83

Sweet. Glad you got an answer. I've been procrastinating...