Hot idle problems
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
Hot idle problems
With the hot weather the last month or so I am having problems holding a idle at long hot lights. I have had to kick the idle up to 900 when cold than at long lights in the city it dies down to 500 and wants to stall. I think it is the hot air in the engine compartment choking the air flow. A friend thinks the fuel lines are getting hot causing a vapor lock to the carb. But when I give it a little pedal to get the rpm up to 1000 it still runs but not well. Then when I get moving after the light it runs OK. I do notice the AC air is not as cold when this happens. 
Does anyone have some suggestions?
Does anyone have some suggestions?
Racer
Joined: Apr 2005
Posts: 402
Likes: 4
From: Nassau
The easiest way I can think of to check your theory about a hot under hood condition is to open the hood when its stumbling. If its just hot air it should rev back to normal. I hope you are lucky and thats all the problem is.
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Originally Posted by Bangkok Dean
With the hot weather the last month or so I am having problems holding a idle at long hot lights. I have had to kick the idle up to 900 when cold than at long lights in the city it dies down to 500 and wants to stall. I think it is the hot air in the engine compartment choking the air flow. A friend thinks the fuel lines are getting hot causing a vapor lock to the carb. But when I give it a little pedal to get the rpm up to 1000 it still runs but not well. Then when I get moving after the light it runs OK. I do notice the AC air is not as cold when this happens.
Does anyone have some suggestions?
Does anyone have some suggestions?
If the car runs well in cooler weather. I suggest you get a dual electirc fan. It will help with air circulation.
Jim
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
I think the car would not run at all with vapor lock. It would stall and not start again at all until the car cooled way down.
Isn't there an idle control solenoid on your throttle that kicks in to bump up the idle air inlet when the AC is on? This mechanism might need to be adjusted or lubricated.
The AC air warms up when the engine speed drops because the compressor is turning much more slowly. That's normal.
Isn't there an idle control solenoid on your throttle that kicks in to bump up the idle air inlet when the AC is on? This mechanism might need to be adjusted or lubricated.
The AC air warms up when the engine speed drops because the compressor is turning much more slowly. That's normal.
Drifting
Joined: Jul 2005
Posts: 1,891
Likes: 2
From: Baltimore MD
Originally Posted by jdp6000
It could be a thermostat problem. what are you running? It could be as simple as a rad cap...does your system utilize the overflow??
If the car runs well in cooler weather. I suggest you get a dual electirc fan. It will help with air circulation.
Jim
If the car runs well in cooler weather. I suggest you get a dual electirc fan. It will help with air circulation.
Jim
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
Originally Posted by jdp6000
It could be a thermostat problem. what are you running? It could be as simple as a rad cap...does your system utilize the overflow??
If the car runs well in cooler weather. I suggest you get a dual electirc fan. It will help with air circulation.
Jim
If the car runs well in cooler weather. I suggest you get a dual electirc fan. It will help with air circulation.
Jim
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
Mine (78)was doing that last summer until I cleaned/ tuned carb...including the changing internal inline filter....temps here were 90-100F..idle would drop to 500,engine stall..occasionally...it is not vapor lock..
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Its not a hot engine problem, and the aux fan that came on that car (and mine) is pretty lame. Dean your on the right track I think. There is a little bimetal hot bleed valve on the carb, I can't remember exactly what it does, but it some sort of compensation for the carb getting hot, Lars would be the guy to nail that down. A good Aux fan might help in moving air into the engine compartment.
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Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
I just noticed you have an Edlebrock carb, I don't know how close it is to a rochecter, but check this out
http://www.tocmp.com/manuals/Carbs/R...73_4M_0004.htm
http://www.tocmp.com/manuals/Carbs/R...73_4M_0004.htm
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
Hotter air gives you a leaner air/fuel mixture. Maybe try to richen your carb. Not sure about yours but on the Rochester QJet there are two easy ways to do it. First, you could turn your idle mixture screws counter clockwise (out). Second you could turn the power piston lower stop counter clockwise (up, so the primary rods sit higher in the jets allowing more fuel). Try 1/4 turn at a time to see if you notice a difference. Just a thought.
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
Forget what I said, Lars says outside air won't affect idle.
http://forums.corvetteforum.com/show....php?t=1367477
http://forums.corvetteforum.com/show....php?t=1367477
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
...unless you're so hot under the hood that you're boiling fuel in the carb... The question raised on that other post was whether a slight change in outside air temp will make the idle speed go up and down. Heat soak and hot under-hood conditions can do other things affecting drivability and re-start characteristics.
Drifting
Joined: Jul 2003
Posts: 1,253
Likes: 1
From: East China MI
Maybe this will help. I just experienced the same problem. Ditto on your symptoms. (I get a lot of heat sink when stopped at idle anyway.) I was having the problem and I pulled into a parking lot and opened the hood. To my surprise, gas was spitting out of the vents and the primarys and secondarys had about a half an inch of gas on top of them. (The engine was at normal temp) After waiting for the flood to clear, the car started and ran fine all the way home.
After searching the hollow cavities of my brain, I decided to lower the floats a little (no more than 1/32"-1/16") so the hot gas would not get too high in the bowl. At that point, I still had a very small trickle coming out of the adjustment ports. That seems to have cured the problem as it would not repeat after I did this. Try letting your car get hot and sit at idle, then take a look and see if your getting flooded. Who knows, maybe I stumbled onto something.
After searching the hollow cavities of my brain, I decided to lower the floats a little (no more than 1/32"-1/16") so the hot gas would not get too high in the bowl. At that point, I still had a very small trickle coming out of the adjustment ports. That seems to have cured the problem as it would not repeat after I did this. Try letting your car get hot and sit at idle, then take a look and see if your getting flooded. Who knows, maybe I stumbled onto something.
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
Thanks everyone I will be checking the float levels after the Classic car show going on this weekend. The hight float thing may be something and easy to fix.I see that in the Edelbrock trouble shooting there is a note to make sure the fuel lines are not close to heat source. I will be checking that also.
This is what the engine looks like.
This is what the engine looks like.
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
Originally Posted by jpatrick636
Maybe this will help. I just experienced the same problem. Ditto on your symptoms. (I get a lot of heat sink when stopped at idle anyway.) I was having the problem and I pulled into a parking lot and opened the hood. To my surprise, gas was spitting out of the vents and the primarys and secondarys had about a half an inch of gas on top of them. (The engine was at normal temp) After waiting for the flood to clear, the car started and ran fine all the way home.
After searching the hollow cavities of my brain, I decided to lower the floats a little (no more than 1/32"-1/16") so the hot gas would not get too high in the bowl. At that point, I still had a very small trickle coming out of the adjustment ports. That seems to have cured the problem as it would not repeat after I did this. Try letting your car get hot and sit at idle, then take a look and see if your getting flooded. Who knows, maybe I stumbled onto something.
After searching the hollow cavities of my brain, I decided to lower the floats a little (no more than 1/32"-1/16") so the hot gas would not get too high in the bowl. At that point, I still had a very small trickle coming out of the adjustment ports. That seems to have cured the problem as it would not repeat after I did this. Try letting your car get hot and sit at idle, then take a look and see if your getting flooded. Who knows, maybe I stumbled onto something.
Now i am thinking the problem is the A/C when I turn the A/C off when in stop and go traffic the idel seams to stay the same. 
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
Originally Posted by SIXFOOTER
there should be an AC high idle solenoid on there to kick the idle up a tad when the ac is on, is that working?