My 75 Comet 250 has an idle problem that goes like this...When it is started it idles really high. After a while I can kick it down to a somewhat decent idle, but it takes a few attempts to do it. Then after it calms down enough to put it in gear, I can start driving. As I drive and progress in speed, the idle seems to rise and rise. So if I stop at a stop light the car is ready to launch if I'm not pressing the brake firmly, and it will! If I put it in park the engine idles really super high until I kick it down again. I don't need to drive too far or too fast for this to happen. Approx 30mph and a quarter mile is enough to create the problem. I know I have vacuum leaks that I'm addressing as I find time, but this seems to be a progressive problem based on acceleration. Are we talking tranny issues, not engine? Any ideas?? Thanks!
sounds like a choke problem...take the breather off...press the gas pedal half way down and return slowly. see if the butterfly in the throat of the carb is closed.
Go out after its sat over night, remove the air cleaner, the choke butterfly should be completly open. open the throttle part way, if the butterfly closes with a snap, its set too tight. Look on the black choke cap, it has an arrow that says more or less, loosen the 3 screws and turn the cap in the lesser direction. when cold you want the choke butterfly to just go closed, depending on temp, you can adjust it more or less. You might also want to check on the heat tube comming from the exhaust manifold up to the choke housing, it may be pluged.
Actually I just noticed the heat tube is loose on the choke side and is not connected to anything on the bottom of the line. It's a hardline with insulation around it. It was chopped off or something or rusted away or something. I cant even tell where its supposed to go. So that needs to be replaced, but how does it hook up to the exhaust? Ahh, my next challenge, time to do some research.
Ok, so I found the heat tube input area on the exhaust manifold and the tube is rusted off flush with the manifolds surface. The tube coming from the choke is intact all the way down to the manifold and is short by two inches. I don't have a way to get the tube out of the manifold. So is there a way to rig this to work by somehow bridging the gap? The hardest part is the manifold side of the problem because there is nothing there to work with. At least I could add some more metal tube or some hi temp rubber hose to the existing tube from the choke, but there is no way to attatch it to the manifold. I am open to ideas.
On a lot of those 6 cyl as well as V8s, that heat pipe runs all the way through the exhaust manifold. It sticks through about an inch, your choke housing has a vacum port in it, that sucks hot air through that pipe into the choke housing to heat and weaken the spring, so the little vacum operated piston can pull it open. My uncle used to use a long drill bit and drill that tube out of the manifold and reistall a copper line, and route it to the choke housing. from the factory there was a rubber line attatched to the lower end of that tube, and it ran I think to the air breather, so only clean air was sucked through it.
since it idles fast when cold and after it warms it idles down it would seem to me that the high idle is set too high. If it takes more than 5-6 minutes to idle down then you probably need to adjust the choke setting as well.
Paul, I did adjust the idle screw to a good level but the idle speed went up an up and it came back from my test drive idling high. But since my choke isn't working due to the manifold heat tube and fresh air tube from the air cleaner being broken/missing, I think that may be my main problem. However, I don't know where I will find those parts. I may need to fabricate as suggested by Tomboy, but its not my specialty......
You can get brand new choke tubes from www.RightStuffDetailing.com What was the outside temperature? What part of the country are you located in?
East coast, 50 degrees. Thanks for the link too. I went outside and checked the butterfly, cold engine, and it was 3/4 open. I started the car and got high idle. After a few minutes I kicked it down to a low enough idle to drive. I drove it around for a few.minutes and parked. Super high idle now. The butterfly was all the way open now. I kicked it down hard and the butterfly closed up almost all the way, and I got a super low steady idle. Does that pretty much sound like the heat tube problem still?
I guess I'm asking that if I buy the parts needed to fix this, does it sound like a cure based on how the choke reacted tonight as I just described? If its 50/50, I might consider an electric choke upgrade if its available for the 2150, or a carb swap that has an electric choke option. Obviously I'd like to take the most inexpensive road for now but I'm afraid I'll get the part, install it, and not solve the problem. I just don't know a lot about carbs and chokes yet.
All of my small vac tubes are dry rotted or cracked to one degree or another. I'm pretty sure I need a valve cover gasket too. I've got capped off tubes here and there also, about 6 of them. So I'm guessing that's a good startingng point. Hopefully fixing all of that and the choke heat tube replacement will help a lot.
BINGO!!!! I would also recommend getting a rebuild kit and rebuild the carb. They are cheap (around $20) and easy to rebuild.
