Drop in Idle while raining

X

Xargon321

Well-known member
like the title says i have a drop in idle while its raining out and here in vancouver, wa when is it not raining!! ;) i have a 200 6 78 block 80 head and a carter yfa carb it has been rebuilt re-bushed and there are no vacuum leak that i can find. it only happens when its raining or just got done raining. no difference when driving. have idle in gear set at 600 when raining it will go to 525-500 some times lower its really weird. thanks for any help.
 
and the problem is?
No, just jokin. But 75 - 100 RPM aint alot (cept @ that low a rev...).

IDK but is the choke OK? Does it get colder when it rains? There may B a connection w/the 2?
I like the vacuum idea cuz w/rain is a low pressure atmosphere - does it have ac (that kicks on to dehumidify?). Hummmm :hmmm: .....
How could it fit in w/fuel or spark...
We'll C what the more experienced have as ideas...
 
No a/c and running a Duraspark II with msd box and coil. ya its not a lot but its just weird never noticed that before tho tha might be because there where vacuum leaks all over the place (carb plate, egr port, etc.) it runs and drives great mpg is a little meh at 15 but that's in stop and go mixed driving. Choke is fine it will do this after it is warmed up as well.

oops guess i should say its a 65 mustang.
 
I have seen similar heppenings, IMO I think it's realated to the air presure that the rain brings, there is extra water in the air, and that lowers idle.

For me as I'm in AZ I see 2 seasons, Eastern summer and summer... (our winters are as cold as NY's summer) ... and what I have noticed is during winter the idle is nice and healthy around 700rpm, but without changing anything when a hot day comes along the idle is now up to 900rpm, air temp and presure play a part on carb'd engines. you don't see the changes on TBI or MPFI as they compensate all the time. that is thier main advantage over carbs, consitency.

it's the same on road trips, if you drive somewhere that changes elevation then you'll notice that the car runs differently.

This is why an old car is so loved, you constantly get to tinker adjust and tune the engine year round. This is also why I'm going for a TBI setup, not the adjusting as I enjoy that, but because it changes and I don't have time right away to pop the hood, espesially on a 12hr road trip, where I have seen a road side adjustment gain 2mpg but lost 45mins' changing jets.
 
i am using the 78 air cleaner but i dont have the exhaust manifold bracket that it uses to hook the air breather up to it. and i dont have a diagram for the vacuum motor on the air cleaner so it just sits open all the time.
 
Is there a 'door' on the tube that sticks outta the a/c housing (kinda like a snorkel). It's not attached to anything else. I seem to remember them in late 70s. I wonder if that were flipped closed if it would help him?

Also back then there was a crinkely (kinda like the ducts for heat from the plenum to the dash outlets) black hose up to the a/c housing. Don't know what these were for but seem related to this?

Lastly, back to the choke: is yer lill tube down to the exh. manifold still there? (very sm alu tube often wraped in asbestos fibers, snuck inta the back of a YF - to drift up hot air).
(Can U tell I'm reachin?)
 
Its a fully electric choke i dont have a heater tube anymore lost that when i replace what had been the Original autolite 1100 after it collapsed a vacuum passage in it, replaced the stock distrib with the duraspark and been that way from then on.

yes on my air cleaner there is a door that is suppose to be closed i assume during warmup and it pulls the air from around the exhaust but i do not have the bracket the attaches to the exhaust to hook this up nor do i have the stuff or the knowledge of where it hooks to to make the air cleaner door work. i dont think its a simple as hooking it up to the carb with a vacuum line. i have looked at 78 fairmonts vacuum diagrams but its like trying to disarm a bomb its not just red or blue like in the movies ;)
 
Xargon321":3m48udaf said:
i dont think its a simple as hooking it up to the carb with a vacuum line. i have looked at 78 fairmonts vacuum diagrams but its like trying to disarm a bomb its not just red or blue like in the movies
Click to expand...

:lol: Yeah some were definitely more complicated than that with differing vacuum signals working the door IIRC. I do think it would be possible to fashion a simple hookup off the exhaust manifold or pipe and maybe just wire or vacuum the snorkel door open full time, duct them together and see if it makes a difference.
EDIT: it would at least see some addtl pre-heated air intake

This stock model is far more elaborate than the one on my old '77 Explorer P/U, that was just a muffler shop fabricated collar clamped to the exhaust pipe.
http://www.allfordmustangs.com/forums/a ... a603-b.jpg

Also IIRC there is a thermostatic controlled variation of the snorkel valve for the 'pre-heater' sytem (there is also an inline version of a riser tube/duct valve) if you find it's something the car performs better with...Good luck :thumbup:
 
well i started dissecting the diagram and its not as complicated as first thought. looks like i just need the exaust tube bracket and some vacuum line as the air cleaner has all the stuff on it to operate the door on it built in. it looks like a simple bi- metal switch that controls the vacuum to the door. and its got to be hooked up to manifold vacuum
 
Right :thumbup: my Maverick setup is a single vacuum line down to the carb, hose to exhaust stove, and a flex hose on air cleaner snorkel to duck cooler outside air. :nod:
 
U guys R goin a lill too fast for me. Can U say what is on the end of each line (sorry) & if it's a tiny vac line or the other types thay connects. Thanks, I'm still wrkin on the PVC from last wk...
:oops:

BTW: hope this gets yer idle prob, X
 
Hey Xargon321 your not by chance the blue mustang i always see parked at Clark College?

Back to the topic at hand what about making the vavle manual like a manual choke? That way you know its opening and closing?
 
my mustang is blue but i dont go to clark just yet tho i do get around in it you might have seen me i live in orchards area so im very close to battleground i am thinking of doing a potluck type of get together for local fordsix members might have to start a thread on that to see who is interested

and on topic i found the manifold bracket i need just need wait till friday to get the money and paint it once it arrives
 
i found the manifold bracket
Congrats!

we have a "prts 4 sale" forum here,
just in case (can't promise anything, worth a try 4 other stuff?).
Do U have an a/c housing or what ever is needed to finish up?
 
sorry, I take 2 many short cuts - meant to say <air cleaner>
It's got several (2 me) odd inlets and outlets, a snout like tube etc...
 
oh yes i do have that has the door and all the doodads that control it just need to get the hose but thats easy. as to weather it works like it should or not i dont know at worst i might have to replace the vacuum motor but we shall see!
 
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