Trouble running hot

[sparkydave]

I've got a new problem that has cropped up recently, and I'm a little stumped. My '77 Midget has the original Zenith-Stromberg carb, but I have bypassed the mechanical fuel pump with an electric pump because it had lots of trouble with vapor lock a while back where I could hear the fuel boiling inside the fuel pump.

The wife and I went to the A&W Friday, and before we got there, the engine was stalling out at idle. At every red light, idle would drop way down, it would cough and die. Once we got there I popped the hood and tried tweaking the idle speed up a little to see if it would stay running. On the way home, it was stumbling at speed, and a couple times felt like it was stalling. Going up a steep hill however, it seemed to have the usual amount of power. The stumbling at speed almost felt like when it did when I had the vapor locking issues. Temperature gauge was reading normal. Once I got back home I tried holding the throttle at 1000 RPM, and noticed it running very unevenly, like it was running very rich.

Today I went to see if I could figure out what was going on, and even after running for a while in the garage at 2500 RPM to get it good and hot, it's running perfectly normal, and has no trouble idling. Only thing I did notice was that thermostatic flapper in the air intake that's supposed to vent the hot air into the intake when cold seemed to be somewhere in between, whereas I kind of expect it to be closing off the hot side and leaving the cold side fully open. I've got a good mind to wire that thing so the hot side is always blocked.

Any ideas? Ignition timing is good, although I haven't checked the valves in a while. They are making their usual happy ticking.

 

[Stan Kowznofski]

Try different fuel and replace the fuel filter?

 

[sparkydave]

Ugh, it came back. Fuel filter would not be the issue, it would be stalling under load if it was clogged. It seems to be heat related. It was running fine until we got on a little stretch of highway and was cruising at 55. Stopped at the red light, and noticed the alternator light was glaring at me and the tach was reading zero. After our ice cream, it was being very temperamental to restart without giving it throttle. Once we got moving it started getting back to normal after a mile or so.

I'm thinking it's related to its tendency to not wanting to idle when it's hot. Any ideas? Fuel is fresh, carb is in tune, doesn't seem to be running hotter than normal.

 

[zabond]

When you got to a red light, did it stall for the alt light to come on or was it still running? if it stalled did it restart easily or did you have to wait awhile? is the coil getting hot to touch when the problem arises?

Russ

 

[sparkydave]

The alternator light was on because the engine stopped. It restarts if I give it gas, but I have to keep giving it gas to keep it running. I haven't felt the coil yet, but it is the original. Someone on another forum indicated the stock coils were known to fail when they got hot. Not ruling it out, it just seems odd that it runs at speed, it just won't stay idling.

 

[sparkydave]

Found it! Cracked elbow on the EGR valve. A colleague had suggested checking the EGR valve, he postulated it might have been sticking open when hot. It occurred to me I had never "de-carboned" the EGR valve as the routine maintenance calls for. Took the valve out, cleaned it, and just for yucks I put the hand vacuum pump on to make sure the EGR and the dizzy advance would hold a vacuum, and whoa, I can hear it leaking from the EGR elbow. Runs much better now with a new elbow.

 

[NutmegCT]

Feels good when things finally come together, eh?

 

[sparkydave]

You betcha! Was close to pulling the trigger on a rebuild kit for the carb.

 

[sparkydave]

Trouble running hot, part deux. Seems like once we've been on the road for a while, it will get to where it's running below normal idle, and close to stalling. Have to keep feathering the gas to keep it from stalling, though I'm not always successful. Now tonight it did something strange. I've been leaning toward it gets hot, the carb gets hot, and it becomes unhappy when the carb is good and hot. I've ruled out it doesn't have another vacuum leak as before.

After the wife and I went for our A&W fix before they close for the season, it stalled once at a light on the way there. On the way home, I was sitting at a light, it was idling slowly and bucking a little for several seconds as we waited for the light to change, then suddenly, without touching the gas, it idled normally. Now I'm starting to wonder if I have a flaky ignition. It did it again in my driveway as I was letting the wife get out. It was pocketa-pocketa, shudder, shudder for several seconds, and then suddenly it's back at normal idle like flipping a switch. While it's got this nearly stalling idle I can get whiff of the exhaust and it smelling richer than normal.

The strange thing is it runs fine along the road, it just has trouble idling when it gets hot. In light of this new quirk, does it sound like the coil? Coil is original, it has a Pertronix ignition, the cap and rotor are relatively new, and the wires were replaced a while back.

 

[JPSmit]

unlikely to be the ignition.

I would start with coil. I got this for Ms Triss - > Porsche and Volkswagen Ignition Coil Bosch 9-220-081-083 0 221 119 027 4047024817180 9.220.081.083 0221119027 9220081083 0.221.119.027 0-221-119-027 9 220 081 083 | Pelican Parts < - transformed the car. You will need to bypass the ballast as it has an internal ballast. (I kept mine just in case I need to put an old coil back in)

In terms of idle - did you set the idle with the engine hot or cold? It took me years to realize I needed to do it with a hot engine.

 

[sparkydave]

Thanks, JP. I got a new coil from Moss, and the initial test drive seems positive. Started up easily, and at least driving it around until it was good and hot it wasn't stalling at stop signs. I suppose putting the old coil back in and seeing if it comes back would be a worthwhile test.

I checked the air piston on the carb after it was good and hot, wondering if it could be getting stuck near the idle position. Seemed to move freely, but since I've seen it get carboned up, I'm thinking maybe cleaning the gunk off it would be worthwhile.