ConchZ

If by blowback you mean that it is backfiring or popping through the carb, the first thing to try is to richen up the mixture on that carb, as that will cure "lean pops" through the carb.

I think you also need to consider the vacuum line for the power brake booster. It's a preformed rubber hose and the routing is slightly different for a 73/74 than an older balance tube. I have a 73 with round tops. My PO kept the original intake and balance tube, but I have a really nice polished set of intakes and matching balance tube that I want to swap on there this winter. However, I'll have to buy a different vacuum line.

The fuel pouring out of the overflow on the float bowl is a big clue that you've got a float valve problem, and it's stuck open now, but it could also stick shut. This worked for me once. Use the back end of the screw driver to whack the float bowl to see if you can jar it loose for at least long enough to get you home, then take off the float bowl covers and clean it up/out. If you're having problems with the float valve, that's the place to start for your drivability issue. I've had mine stick open and stick shut. Either way will cause the car to buck and hiccup. You gotta clean them up and reset the float levels once you are done. You could spray carb cleaner down and around the valve and work it to see if you can loosen it up. Blow through the inlet on the top of the bowl to verify the valve is opening and closing appropriately. Next place to check is the choke cables. Are they still set right, or did one of them come loose,, leaving the nozzle too far down/up. Sounds weird, but it's happened to me. After the above, recheck your timing, then take if for a ride. If you still have problems, go after the ignition components.

Does anyone know where I can get a new set of downpipes for the stock 1973 manifold? Do I have to get them custom made? Has anyone done that, and what did it cost? If I can't get new downpipes for a reasonable cost, my only options are: 1) Headers, or 2) Find an older exhaust manifold and use the MSA exhaust kit (MSA doesn't make it for 1973 manifold). Any other ideas? Thanks!

http://www.thezstore.com/page/TZS/PROD/23-4166 or http://www.zcarsource.com/upper-strut-spacer-rear-70-78-new_8_54060_48618.html There used to be a diagram in the blackdragon catalog, but I can't find it there anymore. Maybe someone can post it for you. Without these little 1/2" spacers, you get a slightly sagging rear end.

You are correct, carb cleaner is flamable. My bad. However, spraying it into the carb of a running car in my experience usually results in a stumble. It isn't flamability, but rather liquidity that is the problem.

I think that if your strut mounts aren't falling apart, then you don't need to replace them. I lived on a small island when I redid my suspension, so I ordered pretty much everything I thought I would need, including strut mounts, just so I would have it. The new strut mounts looked just like my old ones, which were probably original. One thing I didn't order was the spacer that goes between the spring perch and the strut mount. Originally rubber, they disintegrated quick. Go with poly here, just because the part takes a lot of wear. MSA sells them, or you can make some out of a poly bump stop by cutting it down. As for KYBs, I have them, but I also have the Eibach springs and poly bushings. The ride is rather rough, but I don't think its because of the Eibachs.

Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible. As for throttle shaft leakage at highway speeds, you are probably right. The unmetered air getting past the throttle shaft bushings would go down as a percentage of total air flowing through the carb, as compared to its percentage at idle. Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible. As for throttle shaft leakage at highway speeds, you are probably right. The unmetered air getting past the throttle shaft bushings would go down as a percentage of total air flowing through the carb, as compared to its percentage at idle. Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

Ok, I swapped over my other set of SUs. Car fired right up, idled too high...oops, forgot the return springs. Put them on, and it idles just fine. Sprayed a little carb cleaner around the throttle shafts, and got the same effect as with the other carbs. A slowing of the idle speed. Maybe this is normal? I can't imagine throttle shaft bushings being air tight. There must be some leakage. Why am I worried about this in the first place, you may ask? The car runs fine. It all started with diagnosing hot running at highway speeds. After checking everything I could think of, I thought maybe its running lean, so I started looking for air leaks. I may have solved the highway heat problem, it was bad connections in the inline fuse holder on the electric fans. I just need a hot day to test if it's cured. Should I just stop messing with these carbs? BTW, I also solved the vapor lock problem. First, I bent the fuel rail back as far away from the head as I could. This helped a lot, but didn't cure it. Next, my other set of carbs came with insulators that were over twice as thick as the ones with the other carbs. These cured the problem. Matt

Thanks P and J.

I would caution everyone to use Teflon(PTFE) rings, and not plain rubber. Just imagine a ring deteriorating in gas fumes and heat to the point that it breaks and gets sucked into the intake. Where to get some PTFE rings of the appropriate size?

That's awesome. Might have to try it. Wonder if my grandpa's old shopsmith can be used to turn that.

Thanks again Leon. Your explanation about the timing makes sense, and fits with articles I've read. My heater hoses are a few years old, and I think I put them on right. I don't think they would have fit any other way, and the heater works when needed. The thermostat is a 180 Nissan unit that I tested in a pan on the stove. It starts opening around 180, and does open up fully. Out of curiousity, can someone hit their thermostat housing with an infrared thermometer after a long drive and tell me what it reads? I wonder if the outside of the housing reads 200 on everyone's due to the exhaust manifold below it. I may be chasing something that isn't really a problem. As for the carbs...well darn. At least I've got some other ones I will try.

Blue, were you happy with this fix? Did it last? Matt