200ci runs great! then runs rough.

[Dsteenwyk]

Well title says it all.

Started it up, today ,ran great, idles smoothly, take off start stop all is good!

Got to where I was going, car sat for 20 min, I got back in, started it up, hard to keep it going, wanted to stall all the time, ran rough like it was missing, idled down and died at the light a couple of times. Started it up, it just ran rough, so rough I didn't know if I would make it home or not.

checked the timing and the dwell it's fine, point and wires and plugs look good.

any first suggestions?

 

[bubba22349]

Look at the Carb if it has the correct Float Level setting, also check for Vacuum leaks, as well as Vapor Lock if your having hot air temps were you are. Good luck

 

[Frank]

Yes- hot gas and/or carb. Summer-heat blues. Gas boils at 155* or less. When gas this hot or close leaves the needle and is released to atmospheric pressure, it vaporizes, and the carb goes lean. "Vapor lock".
If the exhaust manifold has a heat riser valve in it (?) if it's stuck shut, will overheat the manifold.
Helpful tid-bits: insulate the gas line from the pump to the carb. Use a thick insulating gasket between the carb and intake. Add a hose to the air filter snorkel routed to pull cool air into the carb. Place a thin sheet of steel between the carb and valve cover along the top of the intake runners to block direct radiant heat of the exhaust manifold reaching the carb body. Add a return line to bleed a small % of gas back into the system to keep enough flow to keep gas moving and cool. Verify that the engine is not running too hot.

Usually vapor lock is worse when first restarted after a hot-soak, lasts a few seconds to a minute or two then as cool gas gets into the system , it clears up. The duration of it can be shortened by heavy acceleration, which moves cool gas into the carb quicker. Next time it has these symptoms on hot restart, if conditions allow, accelerate hard up to speed. If it clears up after doing that, it's vapor lock.

 

[StarDiero75]

Sounds like vapor lock to me. I ended up plumbing a return line to the tank and adding a heat shield to block exhaust heat to the carb. It did an amazing job. The return line helped prevent flooding after shutting off the engine as well. A phenolic spacer between the carb and intake helps as well. If you choose to try the return line route, look for a 75 AMC Matador fuel filter, should ahve 1 input, 2 outputs. if you don't want to drill your tank or whatever, tie it back in as far back as possible to get the most cooling effect

 

[Dsteenwyk]

thanks guys, I'll give it a look and see what I see. and let you know.

 

[78_200_C4]

Most old cars preheat the fuel in a mechanical fuel pump.
Under hood heat is like an oven.
Fuel lines including return lines will get very hot.
Even with a tank mounted elec fuel pump the under hood fuel lines will get very hot and supply very hot fuel to the carb.
A return line will return hot fuel.
But not on my Falcon.
My carb runs cool to the touch.
My under hood fuel line from my tank lip mounted elec. fuel pump is covered with 5/16 ID Heat Shielded Fire Thermo Armor Fire Sleeve Silicone Coated Fiberglass.
The carb sits on a 1/2" Red Oak insulator which is 2 pieces of 1/4" Home Depot red oak fiberglassed together.
I have a 1/4" return line which comes off a brass tee with .045 restriction which is a brass 10-24 screw that I drilled thru then 10-24 tapped the tee.
My air cleaner draws air thru 2" aircraft ducting connected at the radiator support to a 2" aircraft duct flange.
My HEI module is mounted to a CPU cooler on the outside of my radiator support. The HEI module runs cooler than the radiator support.
My return line goes to the inlet of the tank lip mounted elec. fuel pump which is fed by siphon.

 

[Dsteenwyk]

ok, did few things to the mustang today, to try to get it running.

saw an old fuel rubber hose line, replaced it , it was the rubber line before the fuel pump. was thinking it was old and was getting collapsed from the fuel pump. $3 later have new fuel line.

Pulled the valve cover off to see if anything looked bad, you know, bent push rod, something loose or not oily ect... all looked good.

next pulled off the top of the carburetor, made sure the plunger thingy in the middle works up an down easy enough. Checked the float for correct measurement height, realized I did not replace the needle under the float, so replaced the rubber gasket the screw in thing, and the needle. double checked the float height again.

checked to make sure the balls (4 of them) were in the proper place and the check cylinder was in correctly. all looked good, pulled out the balls, cleaned their home, then replaced. checked the fuel filter, its good, and put back together.

pulled the spark plugs, all look the same and good, they are new.

checked the vacuum, it' pulls what it's suppose to checked the vacuum attachment, no leaks.

all of this in hopes I could find out what is not working correctly on my car.

when it starts up, long before it gets hot with the potential of vapor lock, as suggested above, it just runs rough, so rough I cannot keep it idling. and it sounds like it's missing but randomly, when I rev it up, it's just more of the same but faster.

I'm tempted to try to make a video of what it sounds like so maybe that will help me diagnose it.

I am running out of things to try.

any suggests are welcome.

 

[bubba22349]

Did you check the Throttle Shaft (The Arm / Linkage Side) for Looseness and or a Vacuum Leak? This is a common Problem on old Carbs.

 

[78_200_C4]

When it's running rough spray some carb cleaner into the carb or put your hand partially over the carb to richen the mixture to see if it smooths out.
If it smooths out you will know its running lean which could be the carb or a vacuum leak.
You may want to take the idle mixture screw out then blow some air and or carb cleaner in the hole the idle mixture screw came out of.

 

[Frank]

ok, did few things to the mustang today, to try to get it running.

saw an old fuel rubber hose line, replaced it , it was the rubber line before the fuel pump. was thinking it was old and was getting collapsed from the fuel pump. $3 later have new fuel line.

Pulled the valve cover off to see if anything looked bad, you know, bent push rod, something loose or not oily ect... all looked good.

next pulled off the top of the carburetor, made sure the plunger thingy in the middle works up an down easy enough. Checked the float for correct measurement height, realized I did not replace the needle under the float, so replaced the rubber gasket the screw in thing, and the needle. double checked the float height again.

checked to make sure the balls (4 of them) were in the proper place and the check cylinder was in correctly. all looked good, pulled out the balls, cleaned their home, then replaced. checked the fuel filter, its good, and put back together.

pulled the spark plugs, all look the same and good, they are new.

checked the vacuum, it' pulls what it's suppose to checked the vacuum attachment, no leaks.

all of this in hopes I could find out what is not working correctly on my car.

when it starts up, long before it gets hot with the potential of vapor lock, as suggested above, it just runs rough, so rough I cannot keep it idling. and it sounds like it's missing but randomly, when I rev it up, it's just more of the same but faster.

I'm tempted to try to make a video of what it sounds like so maybe that will help me diagnose it.

I am running out of things to try.

any suggests are welcome.

Time to verify fully firing ignition. Your description is beginning to sound like ignition, especially after checking all fuel circuits.
I've suggested this easy spark verification test before and never really gotten any response, may sound corny but it's effective. Put your timing light pickup on the coil-to-distributor wire (not #1), start up and shine it at a good reflective surface. In a dark area helps. Race the engine and observe the light. ANY flickering, that's a misfire.

 

[Frank]

Also, after running it a few minutes, feel the coil. If it's way hot, there's your issue.

 

[Dsteenwyk]

Did you check the Throttle Shaft (The Arm / Linkage Side) for Looseness and or a Vacuum Leak? This is a common Problem on old Carbs.

checked it, it's not loose and no vacuum leak best I can tell

got it running, had to hold the throttle open a little, covered the intake gradually with my hand, still same issue of running rough, just slowed down and died.

did the timing light thing on the coil plug, nice dark surface, sorta dark in the garage with out the overhead light on, NO flickering at all.

Also, after running it a few minutes, feel the coil. If it's way hot, there's your issue. not hot at all nice an cool still.

now that I've run it some, I'll wait until it cools and pull out the idle air screw and clean it out, have a new screw ordered, so when it arrives I'll make sure it's working properly.

right now, cannot get it to idle without dying.

just noticed my carb bowl cover gasket is leaking, it just started since i took it apart, have a new one coming with a few other misc parts.

 

[Frank]

Thanks for checking the spark. the carb is not lean, since you covered it and the engine dropped down in speed. This eliminates vacuum leaks including the throttle shaft. "carb bowl cover gasket leaking" . Check your float height adjustment again. If it's right, then excessive fuel pressure is now a suspect. The gasket leak may be an indicator of an overfilling bowl. It should not leak solid fuel from there regardless of gasket condition.
"cannot get it to idle without dying"- turn the mixture screw all the way in against the seat. If it still runs, this also points to over-filling from pressure or misadjustment of float setting, or a needle that's not seating. If you get it running again, look down in the bore and see if you see fuel spilling out of the main discharge, or anywhere else. Fuel should not be discharging above the throttle blade at idle. The timing light set up as the last test shined down into the carb can help see any fuel discharging from the main venturi or accelerator pump discharge. If there is fuel coming out at idle the bowl is over-full.

 

[Dsteenwyk]

thanks, I'll look into most of that when I have a chance, the bowl was leaking fuel because I took it apart and the gasket is probably not in good enough shape...

since I have a new gasket now, I'll recheck the float height, and double check my new thingy under the float (got the new pin and stuff and put it in earlier names escape me now....)

 

[78_200_C4]

Put trans fluid on the bowl gasket so it doesn't stick and tear. This way you can use it multiple times.