YF on a 200

[mugsy]

Anybody running a 70's YF on their 200? I've tried to run two different ones (a '77 and '73) and can't seem to get the thing to idle :thumbdown: . I've taken them for test drives and at speed they work great . But I can't seem to get the idle speed below 1200 rpms or so. And even at that speed the engine stalls if it idles for a minute or so. It seems to me that something is wrong with the idle circuit but I don't know if its too much air or too much fuel

OBTW, the engine was recently rebuilt and has a D7 250 head on it. And I've checked for vac leaks and there aren't any.....

 

[Explorer]

What distributor are you using? From your post count I would assume you know not to use the Load-a Matic. But figured I'd ask.

 

[mugsy]

Exp,

Good question. I did upgrade to a DS-II. All the parts are new from the parts store, except the wiring harness.

As for the YF's. the first one ('77 model) didn't have an adjustable idle mixture screw. It was sealed. The second one did have a mixture screw but I still couldn't get it to idle at 900 in "park" and then in gear.

 

[Explorer]

Next stupid question, manifold or ported vac to dizzy? I know some use manifold vac, but I've never had any luck using it. Disconnect and plug carb vac port and see if lowers your idle.

 

[mugsy]

Ported.

I can barely get the engine to idle at 900. But when I put it in gear the engine stalls immediately. If I bump up the idle to 1100-1200 and put it in gear the engine runs rougher than a corn cob (huge vibrations) and then stalls out about 30 seconds to a minute later. At the higher idle speed the engine just purrs like a kitten (in park). It's when I shift it into gear (it's an auto tranny) that it runs very rough and stalls. I'm assuming it's either too much gas (running over rich) or too lean. I haven't noticed any black smoke coming out of the tail pipe. So I'm assuming that it's not too rich.

The cam is a Comp Cam with 260 duration for both intake and exhaust and a 110 lobe separation. Right now it pulls about 15 in Hg vacuum. I've adjusted the idle mixture screw to highest rpm and vacuum (both are at the same point).

 

[Lazy JW]

.... It's when I shift it into gear (it's an auto tranny) that it runs very rough and stalls......

Probably won't help but try unhooking the vacuum line to the trans just in case something weird is happening. (Plug the hose)

When that fails to help, back the timing down to 0º initial; this will require that you open the throttle plate a bit more to keep it running and probably a tweak of the mixture. This isn't a long term fix, just an experiment to see if it will idle properly. If it does, then the carb you have may have the idle slots calibrated for an emissions setup; dunno if it can be fixed or not.
Joe

 

[Russ]

I have had a YF on my 66 coupe with a 200 for 6 years. Works great, is smooth and has been trouble free to date. I have my idle set at 700 and is steady [T-5 trans].

 

[RacinNdrummin]

I have a YF(or YFA) from an 83 mustang 2.3 on my 200 right now, and it runs great, I just carb cleaned it out and bolted it on.

 

[mugsy]

Probably won't help but try unhooking the vacuum line to the trans just in case something weird is happening. (Plug the hose)

Good suggestion... I've already tried that.

The initial timing is 12*. But because I have to open the throttle plate there is a slight amount of ported vacuum getting to the dizzy. So at "idle" its about 14* or so.

When that fails to help, back the timing down to 0º initial; this will require that you open the throttle plate a bit more to keep it running and probably a tweak of the mixture. This isn't a long term fix, just an experiment to see if it will idle properly. If it does, then the carb you have may have the idle slots calibrated for an emissions setup; dunno if it can be fixed or not.

Ooooooooo I like that. Good idea. I'll play around with the initial timing and see what I can find. I have verified that the balancer is dead nuts on with my degree wheel when I rebuilt the engine. And it only has less than 100 since the rebuild.


Racin-N-Russ, Do yous guys have the carb number off your respective carbs?

tanx!!

 

[yodabiri]

I have had similar problems with yf's on my mustang. After swapping to a 250, i tried 2 yf carbs and could not get good idle on either of them. Both would idle above 900 and I tried everything to get the idle down to 700 or so. (I have a t-5 manual) Eventually I gave up and machined a carb adapter for my old autolit 1100, and slapped that on there. It purred like a kitten and has much more low end torque than the YF for some reason. So i kept it on there for now. I dont know if that helps, but hopefully it does.

 

[Lazy JW]

Back in the 1970's a whole bunch of vehicles were set up to run at 0º initial timing, and then when the throttle was opened slightly they jumped right up to a "normal" advance curve. Remember those dreaded dual advance distributors?

30+ years later it is difficult to know just exactly which carburetor needs what advance curve etc. then throw in some throttle shaft wear and it becomes a crap shoot. Play with the timing stuff and then you can decide which direction to go.
Joe

 

[Russ]

Mugsy,
My YF has YF4785S stamped into the base.. the usual metal tag is missing or never there. Hope it helps.
Russ

 

[mugsy]

Thanks for the carb info. I'll go check my carbs and see what's out in the garage.

 

[mugsy]

Well I have a brief update.

I decided to remove the '73 YF and install a carb for a '69 Mustang 200 (looks like a YF but slightly smaller). I bought the '69 carb to be the center carb of my Offy Tri-power. But I've put the tri-power on the shelf for now.

I also ended up advancing the static timing until I got highest idle speed. I didn't want to go too far because I've done that (when I bought my junk Pony carb) and the darn thing barely ran. The compression is 9:1 so I *hope* not to have any spark knock issues later, but will have to wait for the warm weather to arrive here in Detroit.

While I was getting the '69 Carb to run all of a sudden gas started pouring out the top. I took the top section off and as I expected some of the teflon tape I used on the filter threads had come loose and got stuck in the needle and seat. While it was apart I measured the idle jet and found it to be a Drill size #51 (0.067"). I then took the '73 YF apart and that idle jet was a #56 (0.052"). Hmmmmm. I also looked at the jet's tip that is located in the bottom of the idle well and both were smaller in diameter than the drills I have, but they are less than 0.040". Maybe the Idle jet is the problem and is why the later carb (with the smaller opening) can't support the engine with only 15" Hg vac at idle.

But the car seems to idle but it's not as smooth as I want. I'll call it "roadworthy" (for now) but I'll be playing with it until I get it solved/fixed.

Thanks for the help/suggestion and moral support.