Think I have it now I didn't come back and update this tread with the difficulties I was having with the idle but thought some of you might be interested in how it came out. Although the Summit carb fixed 90% of the stumble under light throttle, I never got the idle completely smoothed out. Idled not too bad when it was REALLY warmed up but wasn't smooth most of the time and sometimes would even drop a cylinder on idle. Changed the distributor and carb and it still wasn't right. Just installed an electric radiator fan and was testing it this morning. I set the fan to come on when the thermostat housing got to about 190, the top radiator hose would read about 165, and you could hold your hand on it for 2-3 seconds. HUGE improvement in idle. I think the problem is I need a hotter thermostat. Not sure -- I'll have to recheck it -- but think the thermostat housing was only getting to about 170 when the fan was set to come on at a lower temp. Think I would have picked up on that issue sooner if it had a temp gauge. Gotta get some gauges. Thanks to everyone for your help. :Handshake Jim
Do you have the exhaust crossover passages blocked under the intake ? I block all mine, sure it takes longer for the carb to warm, but I prefer the cooler intake instead of a heated one. And I never run a choke, never found the need to. They're usually nothing but headaches anyway.
That's a good question. I didn't do anything to block them but neither did I check them to see if they were blocked. Manifold is a used Edlebrock Performer and I also wondered if it might have been blocked by the previous owner some how. I guess the intake manifold around the carb ports is normally heated by coolant, right? Summit carb has an electric choke but it comes off really fast. Picked up a 195 degree thermostat today and I'm hoping that solves the problem. Will put it in tomorrow. Thermostat housing is currently only showing 170-172 degrees when the fan is set to come on at low temp. Not sure what thermostat is in there now. Maybe 180 degree that's opening a little early.
Im running a 180 and never have any problem w/ idle after the engines runs 2 or 3 minutes, even when it's below freezing. I have elec. choke. I don't know if the manifold ports are blocked, cuz I have had no reason to remove it. Im glad u were able to get a major improvement in driveability.
Gees you wouldnt get far up here in Oct-Nov. at the end of the season. Its cool to read the posts on here with all the different lifestyles and ways of life. Makes it more enjoyable than it being just a car site.
Whoops, you said EXHAUST passages. Like I said, I didn't do anything to block them but I can't say if they were open. Does the non-emmisions Performer 289 have exhaust passages to heat the maniford?
I can start and idle my vehicles down here in 20*F weather, without a choke. And in the case of the 5.0 in my 89 Ranger, without touching the gas pedal (yea, it's got a carb without a choke too)
You got it. Exhaust cross over passages directly under the carb. Pretty sure that intake has em. As I said, I have no use for that passage but it would help in cold weather until the motor warms up. In warm weather all it does is needlessly heat the carb.
I think I have mentioned this in another thread...BUT make sure the ground under your distributor cap is tight. Mine came loose one time and I was about to think I had a blown head gasket or something because there was condensation(just happened to be at the same time) on my dipstick. Anyway, I go to adjust the points thinking that was the issue and saw that the screw that held down the ground was loose and rolling around. tightened it in and everything was beautiful.
Good call!! While the 195* thermostat helped, its still rough for several minutes till it gets good and warm. Checked the temp of the intake manifold where it should be heated with exhaust and its cooler than the intake runners. Can't be getting any exhaust heat. Like I said, I didn't do anything to block those passages but I didn't check them before I installed the (used) manifold. I expect they are blocked or the gaskets don't have holes there for some reason. Heads are also used but it doesn't seem likely they would be modified to prevent manifold heat. Maybe someday I'll check it but for now I'll live with it. It doesn't sound good when first started so I may get motivated to check it out. Anyway,I'm glad to FINALLY know what the problem is.
