Choke adjustment

[raleighstang65]

I've been having some problems recently with it wanting to die after it warms up. Here what's been going on:

I recently adjusted the valves/rocker arms after I put about 150 miles on the new cam and installed a shift kit at the same time. Took it out for a drive after this and it ran fine.

Now, it will start right up, sounds great, idles fine until it starts warming up, then the RPM's drop and it dies. I can get it to start right back up but dies after a few seconds unless I keep the RPM's up.

So yesterday I double checked the timing and checked for vac. leaks. None found, initial timing set to 14 deg. with vac. advance unhooked and plugged. Pulled the spark plugs and they all are consistently light brown. Vac. gauge reads a steady 15" at idle. The gas is fresh, fuel filter isn't clogged. I had some problems with vapor lock over the summer, now the fuel line is pretty far from touching anything remotely warm. Fuel pressure is about 7 psi until it warms up, then drops to around 3-4 psi.

I'm running an Edelbrock carb with electronic choke. I discovered that if I kept the choke closed or at least kept it from opening all the way, I could keep it running. I know that as the weather gets colder you may have to adjust the choke to stay closed longer, but here in North Carolina it hasn't gotten that cold yet, it was in the low 60's yesterday. I let it run for about 20 minutes this way and everytime I would let the choke open all the way it would die.

What do you guys think?

 

[bnickel]

sounds to me like you have a fuel pressure problem when the engine warms up. may be time for a new fuel pump

 

[raleighstang65]

Fuel pump is pretty new, only about 6 months old. What should be the normal range for fuel psi when the engine is warm?

 

[bnickel]

Fuel pump is pretty new, only about 6 months old. What should be the normal range for fuel psi when the engine is warm?

around 5-6 psi, generally speaking. not saying that's all your problem but i think that may be a big chunk of it. you may also have a rubber fuel line that is cracked and doesn't open up until the engine (or exhaust) is warm and has warme up the engine bay (or undercarriage) but once the crack does open it starts sucking air instead of fuel. check or replace ALL of the rubber lines first and then the look at the fuel pump if the fuel pressure is still low after that. the fuel pump could be having this exact same issue with the rubber diaphragm too. when it's cold the diaphragm may not be leaking but does when it's warmed up.

 

[raleighstang65]

Would the choke tie into a fuel pump issue at all? It seems like it will run all day long if I keep the choke from opening all the way, which is a recent problem. I will check out the rubber sections of fuel line. I'm pretty sure I replaced all of them within the last year. I am running a braided line from the pump to a filter, then a fitting for the fuel pressure gauge, then a metal line to the carb. I noticed tonight that the small heater hose is touching the metal line just under the carb. I don't think that hose gets hot enough to cause vapor lock but is it possible?

 

[bnickel]

not directly, however if the lack of fuel pressure is causing a lean condition (likely) by keeping the choke partially closed you're creating what would normally be a slightly rich condition but in this case it could be compensating for the lean condition.

 

[ForceFed70]

I think Bnickle is on the right path... you're running lean once up to temp.

However, I kinda doubt it's a fuel pressure thing. You mentioned a new cam... you probably need to adjust the idle mixture as a result. Not sure how that's done on an edelbrock carb, but on a holley there's an asjustmetn screw.

 

[bnickel]

I think Bnickle is on the right path... you're running lean once up to temp.

However, I kinda doubt it's a fuel pressure thing. You mentioned a new cam... you probably need to adjust the idle mixture as a result. Not sure how that's done on an edelbrock carb, but on a holley there's an asjustmetn screw.

there's no reason he should have 7 psi cold and then the pressure falls to 3-4 psi once warmed up. that indicates to me that there is a leak in the system somewhere and the pump is cavitating or sucking air resulting in the loss of pressure. the carter/e'brock carb likes to have 5-6 psi.

i'm not saying that there isn't a choke problem, but i do think there is another underlying issue that is either acting like a choke problem or is being further exaggerated by a choke problem. in any case i think the fuel pressure needs to be examined further to either correct it or rule it out.

 

[raleighstang65]

Should the fuel pressure remain the same when I start it up to say 30 minutes later?

 

[bbatch]

Im not for sure but may be as simple as adjusting the floats in your carb. Your car may require a little more fuel with the recent upgrade of the cam, sounds a little odd but sometimes it is just that simple. When you have the choke on you are letting very little air in so the air fuel mix is fine. However when you open the choke you get all the air in there and your running lean. On he floats there is a tab near the back end that controls how much fuel is allowed in those chambers. if you bend it up slightly so the float will rise more you will give a richer fuel air mixture. I hope i could be of help. Keep me posted on how it is going for you. I am also from NC, I just got stationed in Las Vegas, NV. Completely the opposite of NC lol. Well take care and I hope you can resolve your problem without too much work.

 

[bnickel]

Should the fuel pressure remain the same when I start it up to say 30 minutes later?

fuel pressure should always pretty constant....period, if it's not you have a fuel system problem. another thing it could be is that the fuel sending unit filter sock is clogged and not allowing fuel out of the tank, but that would normally stay that way all the time. i'm still betting on a bad fuel pump personally

 

[raleighstang65]

I'm running a filter after the fuel pump, could there be crap in the pump? If so where would I look if I feel ambitious enough to take it apart and have a look? I hate to throw money at a new pump if I can fix the relatively new one I already have but this might be getting out of my skill set.

 

[raleighstang65]

*Update*

I had some time this morning to try and figure this problem out... still not solved but here's what I saw today.

I am still trying to learn the in's and out's of carbs so excuse me if I don't get the terminology correct. When the engine is running I can see what appears to be a good stream flowing out of both front jets but the passenger side also seems to have a little drip every now and then. And when I let it die or shut it off it will continue to drip for a short time out of that jet. This is a relatively new carb, only on the car for a year and maybe 400 total miles on it. I drained the gas tank several months ago when I replaced the sending unit (for the second time) and there is a new fuel filter between the pump and carb. Could this be a float adjustment problem? Trash in the carb? Needle valve issue?

 

[bnickel]

yes it does sound like you have some trash in the needle and seat. this won't cause a lean condition though, quite the opposite in fact, it would cause a rich condition. what's happening when you are closing the choke butterfly is that taking air away from the motor in effect causing a rich condition, which you are already getting from the dripping fuel which is caused by trash between the needle and seat, thus allowing more fuel through. so basically, it sounds like you have a very lean condition, not just a slightly lean condition. in any case the carb needs a rebuild now to get all the trash out and hopefully once it's all cleaned out and re-adjusted that could very well fix the problem.

you do, however, need be prepared to find other problems too. if you have trash in the carb you could very well have trash in the pump and in the lines as well so be prepared to replace the pump and at the very least clean the metal fuel lines by blowing compressed air through them and definitely change all the rubber lines if you haven't already done so. also, if there is still signifcant trash in the system it's likely that there is rust and sediment in the tank as well, so it would be a good idea to also have the tank flushed to clean out any sediment and if there is rust in the tank you will either need to have the tank sealed or just replace it all together. if there is rust in the tank, though, i would suggest just replacing it as well as the metal lines, new tanks are pretty cheap, generally under $150, and the lines are less than $100 unless you want stainless lines and then they are slightly more than $100.

 

[raleighstang65]

bnickel Thanks for all the help. I took the carb off last night and I plan on taking it to a local shop to have it checked out.

 

[bnickel]

bnickel Thanks for all the help. I took the carb off last night and I plan on taking it to a local shop to have it checked out.

that's good but like i said earlier do yourself a favor and pull the tank and insect it really well to make sure ther is no rust or other crap in it, if there is even a little then either seal it or a buy a new one and at least blow out the lines or you'll likely end up repeating the process.

i have firmly decided that i will no longer re-use a stock original tank without at least inspecting it and preferably just replacing it.

on a related note, i just found out that Scott Drake is now making stainless steel replacement tanks which is a huge step in the right direction especially if you ever plan on converting the car to E-85.

 

[raleighstang65]

I'm thinking I might be better off just going ahead and replacing the fuel system (tank, lines, pump, etc.). I hate to throw money at it but I have drained the tank a couple times now and there was a little bit of debris/crud that came out each time. Thanks again bnickel!

 

[bnickel]

i hate throwing monay at a problem too, but sometimes just having the piece of mind that comes from knowing that something is new and not 40 years old is worth every cent you threw at it, whether it fixes the problem or not. while you're replacing that tank anyway now would be the time to upgrade to the 70 model 22 gallon tank too, both tanks are the same price anyway so that extra 2 gallons is a nice cushion if you're ever out in the middle of nowhere.

i installed a 70 tank and sending unit in my 69 mustang and will most likely install one in my 69 cougar as well. i do plan on running my cougar on E-85 once it becomes available here so i'll probably spring for the stainless steel tank and lines when i do change the tank on it