250 trouble

[bigblue91]

rescued an old 77' maverick with a 250. had about 21/2 quarts in it :nono: (and the owner drove it daily) and the trans was shot. i rebuilt the c4 and still need to adjust my kickdown cable though. heres the problem.

-takes gas fine in park, takes gas fine in gear until about half throttle. after half throttle its as though you let off the gas entirely. i need to swap on a spare yf to test it but im pretty sure i tried that a few weeks back with similar results. drives fine though other that the throttle issue. i dont think the transmission is any of the problem,as i can shift manually and the throttle. provides same results.

any help would be appreciated.

 

[bubba22349]

I have a 77 Maverick 250 and C4 too . On the kick down first make sure that it is all the way up with a good spring. Than adjust the screw on lever to down shift (for passing) this would be to personal taste fromm about 40 to 50 MPH when you step down on the gas ped. Did you add an ajustable modulator when you rebuilt the trans? If not this is an easy to do and then you can dial in the shift firmness too.

 

[bigblue91]

i did a stock rebuild, no shift kits or nothing. green stripe modulator (no adjustments)
i will say this i reused the original modulator line the rubber hose used is a little rough.
i might have the kickdown actually kicking too early i will see.

does this sound like the carbs fault at all or should i look more towards the transmission?

thanks

 

[woodbutcher]

Had that problem with my 300 CI six.Plugged fuel filter.Have you replaced yours?
Leo

 

[bubba22349]

does this sound like the carbs fault at all or should i look more towards the transmission?

Yeah sorry about that read it fast and though you were setting the kick down linkage. Since it is just to control the downshift to second and the up shift timing to drive it would not be the trouble. Think your on the right track looking at the fuel system. Before you change carbs though is the fuel filter good? Dose the fuel pump pass the volume test? Will the Fuel cap hold pressure? Are the fuel lines (rubber hoses) in good condistion? IE not cracked or spongy where they might suck shut. Then there is the pick up sock in the fuel tank can be bad too. Good Luck

 

[bigblue91]

yea i out on a new fuel filter during swap, did see a piece in the fuel line (under car) that looked suspicious might need changing, ill look into that.
is there a way to test the fuel pump?

its a strange symptom, as soon as i back the throttle down 1/2 way it picks right back up.

thanks for the suggestions guys

 

[CZLN6]

Howdy blue:

I had a '74 Comet, 250, C4 that did the same thing. Ran fine when cold, and most of the time around town, but any sustained driving and it could barely get past an idle. Checked out everything from the tank to the fuel bowl. Finally determined that it was the fuel pump. After two different fuel pumps, with little improvement we decided it was the eccentric on the cam that pumped the pump had gone flat. The problem was solved with an electric fuel pump.

I'd sure go through Bubba's check list first, to rule out the easy stuff. Oh, and dumping a bucket of cold water on the fuel pump seemed to help for a short while. It sure made a mess too.

Adios, David

 

[bubba22349]

Be careful and pull coil wire and use a coffee can or glass jar your looking for it to have about two pints or so volume in a couple cranks. If it passes then also check the pressure too 4 to 6 psi. The old vacume gauges also had a fuel presure test scale on them. Here is a site link for more info on testing fuel pumps. Good luck

http://www.73-87.com/7387garage/drivetrain/fuelpump.htm

 

[bigblue91]

-replaced all rubber hoses involved in my fuel line. undid fuel line and turned engine over to check the fuel pump. i got 2 spoonfuls in 30 seconds of cranking

-i took it for a ride, died down the road, i was out of gas :rolflmao:

---filled it up and it drove the same, didnt get to check fuel pump today but thats the only thing left i haven't checked as far as fuel system goes.

ill report back as soon as i check some more of the suggestions

@ CZLN6

if it was my cam i would have the same problem in park (past 1/2 throttle) as i would in gear (past 1/2 throttle), correct?

 

[echo1955]

-replaced all rubber hoses involved in my fuel line. undid fuel line and turned engine over to check the fuel pump. i got 2 spoonfuls in 30 seconds of cranking

-i took it for a ride, died down the road, i was out of gas :rolflmao:

---filled it up and it drove the same, didnt get to check fuel pump today but thats the only thing left i haven't checked as far as fuel system goes.

ill report back as soon as i check some more of the suggestions

@ CZLN6

if it was my cam i would have the same problem in park (past 1/2 throttle) as i would in gear (past 1/2 throttle), correct?

Affirmative

bigblue91 it will be a good idea to do these test as well.
1: Start engine and let it warm up to normal temperature:
2: Shut engine off:
3: Remove breather. Your choke should be full open. While looking down the carburetor throat by hand open the accelerator to just below 1/2 throttle. You should see fuel being pumped into the throat. Now open the throttle to full open. You should see plenty of fuel being pumped into the throat.

It all of the above works out fine and you are getting plenty of fuel at 1/2 and WOT, then move to the fallowing:

1: Start engine
2: With engine running and working at the carburetor look down the carburetor throat, by hand open the throttle to just below 1/2 and observe the fuel flow. Then quickly open to WOT and observe fuel flow.

If the choke closes when WOT then you have a mechanical issue with the carb.
If the fuel drops off at WOT then you have a fuel delivery issue.
The carb is not getting enough fuel volume to supply the demand of WOT.

This should help guide you in the right direction…

ps: check and confirm fuel reserve in fuel tank.... :mrgreen:
Good Luck..

 

[echo1955]

I forgot to say, if you are getting sufficient fuel pressure and volume then you have a carb rebuild starring up at you..

 

[bigblue91]

thanks for the advice, ill go through this today.

i rebuilt the carb maybe 30 miles ago, i will test one of my other carters off my other maverick to see if the problem continues.

 

[bigblue91]

---checked carburetor, checked out fine. runs wide open in park fine
-used an old carter rbs (that i know works) on the engine, same results when driving
---swapped carburetor mounting plates with my spare 250, just to see if i was catching air through the old one, same results

after going back and forth from my spare 250 to the mavericks i see the previous owner has plugged some ports.

1. metal tube running to carburetor base to exhaust manifold is plugged off from the manifold.
2. intake manifold is plugged where it should have a tube where a series of vacuum lines can connect to.,


right now im running my lines based upon my 4 doors setup.

should i be getting vacuum from the exhaust manifold, if so i am not?

other than the vacuum mismatch i cant find a problem within the fuel system.

 

[bigblue91]

and the fuel filter was still as clean as a whistle :mrgreen:

 

[MPGmustang]

1. metal tube running to carburetor base to exhaust manifold is plugged off from the manifold.

+

should i be getting vacuum from the exhaust manifold, if so i am not?

No, you should never get vacuum from the exhaust, it exhausts air out, not intakes air in.

the metal tube should not be plugged into ANY kind of vacuum port from manifold or ported from carb, it belongs with the carburator choke spring (usually a black plastic round object on the carb) that controls the choke when it sucks air from the exhaust hole (this hole goes straight through the manifold, air heats up as it passes through),

If you have a working I6 next to it to compare, by all means route away.

vacuum lines that you might/will find
1) manifold vacuum to PCV (positive crank (case) vacuum)
2) manifold OR ported vacuum to distributor canister (for advancing/retarding timeing, this helps in mpg)
3) manifold vacuum line going to automatic transmission
4) optional manifold vacuum to dashboard vacuum gage for mpg vacuum driving

I would check to see if your tranny fluids are full, or see if your kickdown is working... usually when you WOT you down shift to use the higher RPM (HP)

check your distributor canister, mabye no vacuum advance is working (I would blow to check cause if it's broken you'll get a mouth full of fumes if you suck)

well that's my $0.02

Good Luck!
Richard

 

[CZLN6]

Howdy:

Big Blue asked, "if it was my cam i would have the same problem in park (past 1/2 throttle) as i would in gear (past 1/2 throttle), correct?"

Not necessarily. A weak or dying pump or pumper can work with no load, and it can act up intermittently. They very seldon die completely, all at once.

You are ruling out many possibilities. At some point fuel delivery will need to be assessed. The simplest test would be to borrow a pressure switched ful pump from a friend, hook it into the line and see what happens. It the symptom goes away, the next step will be to determine if a new fuel pump will work or if the eccentric drive is the culpert.

You're getting closer.

Adios, David

 

[bigblue91]

the metal tube should not be plugged into ANY kind of vacuum port from manifold or ported from carb, it belongs with the carburator choke spring (usually a black plastic round object on the carb) that controls the choke when it sucks air from the exhaust hole (this hole goes straight through the manifold, air heats up as it passes through),

If you have a working I6 next to it to compare, by all means route away.

vacuum lines that you might/will find
1) manifold vacuum to PCV (positive crank (case) vacuum)
2) manifold OR ported vacuum to distributor canister (for advancing/retarding timeing, this helps in mpg)
3) manifold vacuum line going to automatic transmission
4) optional manifold vacuum to dashboard vacuum gage for mpg vacuum driving

I would check to see if your tranny fluids are full, or see if your kickdown is working... usually when you WOT you down shift to use the higher RPM (HP)

check your distributor canister, mabye no vacuum advance is working (I would blow to check cause if it's broken you'll get a mouth full of fumes if you suck)

---yes, the choke heat shutoff tube (on exhaust manifold) i have ran to my choke and is working as it should

i don't know what its called, it's towards the back of the exhaust manifold (threaded in the manifold) and attaches to the base of the carb mounting plate (which has a vacuum amplifier on it)

it seems as though it would equalize the vacuum pressure some how unfortunately i couldn't remove the threaded tube off my maverick so i could swap on my spare 250's carb mount. so i will have to do without this line.

i do have all the lines you mentioned it should have

2morow i will check trans fluid/kickdown rod and the distributor canister.

thanks for the reply's and advice guys, hopefully i will find the problem down the road

 

[bigblue91]

@CZLN6

i have another mechanical fuel pump i could try on the engine, and see if the problem resides in the pump itself.
i sure hope the eccentric as you mentioned isn't the culprit

 

[woodbutcher]

Hi BigBlue91.There is one saving grace if the CAM eccentric is toast,but the cam is otherwise OK.Remove the mechanical pump,use a blockoff plate for the pump mount hole
and use an electric pump.The block off plate is simple to make.
I used 3/16"plate and used a pump gasket for the pattern.Took about 20 to 30 minutes.
Don`t do what I did.Forgot the gasket the first time.
Veryyyyyyyyyyyyyyyyyyyyyyyyy messy .
Leo

 

[echo1955]

well I put my 0.02 cents in with MPG’s…
check your distributor canister, mabye no vacuum advance is working (I would blow to check cause if it's broken you'll get a mouth full of fumes if you suck)

No vacuum advance will cause engine to stall. You could verify advance with a timing light as well.. and you could T a vacuum gauge at the vacuum canister. This will confirm you are getting vacuum to the canister..