Hi again everyone! As it seems to go with this '71, I've encountered another hiccup. This one plagued me for a while then sort of dropped away, well it's back and this time I'm resolved to sort it out for good. The car is a 71, it has a 302 from a 92 Mustang in it, C4 transmission. There is more info HERE detailing what work was done before I bought it from Zach. Since I've had it I've sorted out steering and recently had the harmonic balancer replaced among a few various and sundry things. My problem now is that once the car warms up to full running temp (190-200 depending on the air temp here in GA) it'll start idling rough when I'm stopped, sputtering kinda. When I start it's sluggish for a second or few and makes these sounds that are sorta like muffle pops. Once it's up to speed it's fine for the most part (sometimes you might here a muffled pop or two) and if it's in neutral it seems fine. Thoughts?
Is the sluggish start and initial throttle responses after the car is warm? If so I would think its getting heat soaked and causing the fuel pressure to build and causing a real rich situation. My maverick does the same thing without a phenolic spacer between the intake and carb. Mine will actually run like crap for the first minute or two and show some black smoke......only did this without a phenolic spacer and when the car was nice and hot and sat for a while after getting hot. Also not sure, could be wrong, but 190-200 sounds a little on the hot side especially in the summer. I prefer to stay around 170-180 max if I can help it.
The issue only seems to crop up when the car is fully warmed. It drives fine as you'd like for the first 15 to 20 minutes. The problem isn't universal, it comes and goes, usually a few weeks at a time making it difficult to diagnose. Any ideas on how to keep it cooler?
id bet you are boiling the carb over as mentioned. you can try to lower the ful level abit in the carb, or use spacers to isolate it. One thing, the large air filters can hold heat on the carb. this will cause the carb to get real hot too. MY 62 falcon had a similar issue, as did my old 69. both 6 cyl cars. but the similarity was they both had large air (stock) filters and would allow the carbs to get pretty hot. they would both boil over at full temp, got worse when i would park the car and try to restart hot. the fix was to put a smaller air filter on it and that problem went away (the 6's are known for this, particularly the small ones). I think the ethanol in the fuel allows this to happen easier too. by putting a phenolic spacer under the carb you are keeping the heat soak from the manifold down AND allowing more room for air to flow around the carb. worth a try.
Both of these are great suggestions, thanks much! With the heat though, it bugs me because last week she ran fine when it was way hotter out but then the ugly little problem pops up this week while it's cooler and she's running closer to 190 than 200. EDIT - Here's a pic I took of the carb. I think I may already have a spacer on there?
Yup appears to be a small phenolic spacer. If u have the hood clearance I'd run a 1" phenolic spacer......get that carb away from the hot manifold. If that's not an option u might try the smaller filter idea but I have no experience with that.
The float level was indeed set way to high, I adjusted it down on the primary. Now I have gas leaking out of the adjustment nut, regardless of how tight I tighten the locking screw down. I'm afraid to mess with the secondary float until I straighten this leak out. EDIT- It appears that the "grime" I wiped off was all that was left of the gaskets. Gotta replace those.
Yeah those gaskets for the nuts are pretty cheesy imo. I always seem to be replacing them. I didn't even think about float level........*Duh* lol.
So, one trip down to Summit racing later and I've got the fuel leak issue solved. I'm still having some idle issues but after driving to work I see that I may have been a little over zealous on lowering the float level as it's sitting at about a quarter rather than half. Mustangnut, you were right about those gaskets, they seem pretty lame. I went ahead and bought a few extra kits just to be safe due to how flimsy they seem. I'm going to be fiddling with it over the weekend, see if I can't get it sorted out. Question, should the choke plate be in the full open position at all times? Anytime I've ever had the air filter off, it's always been open, I'm never seen it move when revving or idling with the filter off. I appreciate everyone's help and patience with my ignorance on the subject.
Honestly I never use a choke. I get decent weather all year here in nc and remove all mine. If u don't mind feathering the gas a few minutes in the cold weather I'd just remove it. In the end even fully open its a restriction of air flow. But yes it should stay open except when cold or off.
Thanks! I ended up having to use Other Sources this weekend while the form was down, that was panic inducing. So far I've gotten the float set up right, replaced those dumb little seals and then adjusted the carb mixture and curb idle. She runs better, but I'm still feeling some of that roughness and those pops. I get low RPMs on a cold crank, near to the point of a stall but one or two good revs clears it up, the first of which is usually flat, like a stall. I think my fast idle might need tweaking, but after that I'm mostly back to square one. This weekend I realized that I left off what might be an important piece of info about the car, which is that I have an electric fuel pump (annoying hum/buzz all the time). This thing sucks a lot of juice to the point that I can't get turn signals when I have headlights and wipers going. Might this be related?
Additionally, what's the target PSI when testing the carb? I managed to get it steady around 15 when I was tuning the carb, but that was as high as I could get it to go.
The fuel pump shouldn't kill the turn signals etc etc etc. Something else is going on there. Most electric fuel pumps hum and are quite noisy. Are you talking HG of Vacuum or are you talking fuel pressure.......... Vac should be as high as you can get it. If you don't have a large aftermarket cam Id say 15 is a little on the low side and you are leaving something on the table as far as performance goes. Make sure you have verified timing and then verify it again...... timing also plays a huge part in the tuning process......you will never get good vac readings with timing issues.
Forgot to really comment on your power issue........ either you have a super weak alternator and it cant supply enough juice to power everything. If your fuel pump isn't on its own power source ( circuit ) i highly recommend you make it that way. You don't want to power your fuel pump off of an existing circuit that might be close to its amp capacity.
