Jeff G 78

Will do. Thanks Blue.

Yep Blue, I was going the right way with the tabs. I tried going both ways and nothing seemed to help. Right now though, the carbs appear to be working okay dynamically even though statically they show low.

Thanks Jim! I did the dynamic level test on the rear carb only so far and it appears to be fine. The level stays pretty close to the proper level with the floats adjusted to the FSM float-to-lid measurement. The fuel pressure stays at 7 psi on my crappy little gauge. I think I'll be okay at least until I get to the track and put it under a load.

Makes sense Jim. While tuning the carbs, when I crack the pistons, both carbs bog indicating a lean condition. Do I open the mix knobs a bit to adjust that? I was watching some MG tuning videos and on real SU's, they have another screw on the side which is how he said to adjust the rich/lean when the pistons are raised slightly. EDIT: After rewatching the video, I see that MG SU's don't have the knob on the bottom, so I guess the mix knob the right place to adjust for rich/lean, right?

Yep. I checked.

Great ideas Jim. I will add a T to the bowl-to-nozzle hose and check the dynamic level as well as try the Q-Tip test. My front and rear float heights are different because it's a '72, but I can still tell what they are doing. The tops of the floats *should* be at the FSM specified heights of 16mm and 12mm from the lid while running, right? I do have bowl drains, but I can't think of a good way to add a fitting without leaking. It's a small metric threaded bolt in the drain so other than drilling the center bore of a stud, I can't think of another good way. That might be tricky to get right in my drill press. T-ing the supply line will work as a quick test. If I am still 5mm low and I can't fix the condition, should I try to compensate by giving the mixture knobs an extra few turns out, or will that just cause other issues?

Yes Steve. I could try that.

Chuck, my pump is a Carter from Summit. It's the one that Bryan Little's website recommends and several other Z racers use the same pump with great results. The carbs I'm borrowing are 4 screws, so at least they won't have the float height differences. I don't know for sure how much the height matters, but from what I read, a low level will cause a lean condition at high RPM like Blue suggested. And that is exactly what I have had happen in previous races. The car runs great in the driveway with no load.

I don't have any pics handy of the fuel site hose, but here are a few pics of my visible bowl. You can see the low level compared to the sharpie line at the right height. The level is the same whether I use the carb bowl with sight hose or plastic test bowl. The float itself is higher than the FSM says it should be when the valve shuts off, but the height is still low. One more bit of info is that the float rises smoothly and then "pops up" when it closes. Similar to how a toilet valve works, I guess. The float doesn't simply rise and stop with a smooth finish. I have no idea if that's normal or not.

Yes, I do have the '72 carbs with the long arms in the front carb. Both carbs have the same issue though. The return does have the orifice in place. I have also pinched off the return with no change. Hey Chuck, thanks for the offer. I do have a set being shipped from a guy in VA. Want to come to the race? Make my car right and I'll give you a 90 minute race stint. The race is at Nelson Ledges this Saturday. We'll be there late Thursday night for a Friday practice.

Exactly Steve. Tony had some questions and thoughts, but nothing that was an "ah ha" thought. I will try some stuff today, but I'll probably have to swap them with the 4 screw carbs I'm borrowing.

Yeah, I will call them tomorrow. I just spent an hour chatting with Tony D and he couldn't come up with any good explanation. Hopefully Steve at ZT can offer some advice. I have a set of rebuilt SU's being Fed-Ex'd to me tomorrow to borrow for the race, so if ZT can't help, I'll do a swap on Thursday before I leave town.

Checking with engine off and electric fuel pump. I can check them in the bowls or in a plastic test bowl with the same result. Both carbs do the same thing. I can watch the float rise and when it stops, the float to lid is way closer than the spec - yet it's still low.

I am at my wit's end on my racecar. I cannot get my SU fluel levels to set right. Both bowls are 5mm low no matter what I do to the floats, valves, or pressure. I've tried everything I can think of, but I am now out of time. I leave for a race on Thursday afternoon and I have no confidence that I will get it to run right. I'm looking to borrow a set of known good SU carbs that I can have overnighted to me right away. I'd have them for about 1 week. After my race, I plan to send mine to ZT if I can't solve the problem, but for now, I need something that works. I just built a 2.8" 9.5:1 motor with a mild cam that should make about 175 RWHP, but it won't do me any good if I can't get the carbs to work right. The first time I will know for sure is on the track as the car is not street legal, so all I can do is tune mine in my driveway and try to compensate for the low fuel levels. I know it's a lot to ask, but I'm out of spit.

Check your head for warpage. If the head was warped an a machine shop milled it flat, the TOP of the head will still be warped. A warped top will force the cam to bind and break. Run a straight edge along the valve cover mating surface and check all along between the straight edge and head with your thinnest feeler gauge. There should be zero gap anywhere front to back. If you don't have feeler gauges, shine a flashlight at the joint and see if light bleeds though anywhere. I would not swap the towers. I leave them alone and just keep the cam, rockers, and lash pads together.

Looking good!

Here is what I did. Keep in mind that I am thrashing to finish my race car, so I didn't take the time to perfect the plastic bowl, but it does work. I like Blue's idea of doing the bowl work first using water. I wasted WAY too much time this weekend trying to get my float heights set. I'm not sure I ever did get then right. I have to get to bed, but I'll explain more later.

OK, today/tonight was a really rough experience, but I might have found an easier method of setting float heights. I was using the sight glass method today for the first time on my new engine to set the floats. The front carb went OK, but the rear carb was giving me fits. I decided to take a different approach and I cut a plastic water bottle in half so that the bottom of the bottle was roughly the same height as the carb bowl. I set the lid on the open container with the float hanging inside and measured down 20mm from the bottom of the gasket (3mm from bottom of gasket to inside of lid) and I put a sharpie mark on the plastic container. I then turned on the pump. With the container setting on top of the SU bowl to get the correct angle, I could now watch the fuel fill the "bowl" and watch the float itself. This is by far easier than messing with the real bowls each time. Within seconds, I could tell what the height was without the need for a sight hose or the hassle of wiggling the lid into place and risking gasket damage. I could make changes to the float in 1/4 the time it took me to put the lid on the carb bowls and it was super easy to see the fuel height directly rather than indirectly through a sight glass. In the end, I decided that I need new float valves ASAP. I have emails out to all Z owners near me. I have to get it ready for a race next weekend. Hopefully I'll have the parts I need tomorrow. If not, I'll be making an emergency plea for help. I'll take pics of the setup tomorrow if I have time.

Wow, thanks guys. I never realized that I needed that much initial with the cam.

Steve, I thought exactly the same thing about pulling the vacuum hose, but the FSM never mentioned it. I reread the instructions several times and it wasn't to be found. It makes me feel better that 17° initial is normal. I can probably get it to run there. The chart shows 8° static, 17° mechanical and 30° vacuum for my '82 distributor. So, I should run the 17° initial, and plug the vacuum advance? I have never studied timing, so I'm at a bit of a loss as to what the vacuum does. I understand the mechanical better, but not the vacuum part of it.

I have a design worked out, but I have been spending every waking minute prepping my 260 for a race next weekend, so I never got around to making them. After the race, I could probably knock a few out. My plan is to use 1" acme thread rod to get maximum wear and pulling power.

Sure is purdy Guy! I fired mine up today. After many stupid problems that appeared out of the blue, it fired up within about 2 seconds and purred immediately. So far, the new MSA exhaust sounds great. I went with four hangers and it really helped the alignment. Other than the muffler hanging lower than I'd like, the rest fits really well. I have an ignition timing question. I *thought* I remembered checking the idle timing with the vacuum hose removed, but the '78 FSM didn't say anything about the vacuum advance when setting timing. When the distributor is at mid-slot, it idled at about 1300 RPM (pulled the carbs from my race L26 and didn't touch them) sounds great, but the timing light shows a ton of advance. It was something like 20° or more. I adjusted the idle screws to get the idle down to ~800 and then turned the distributor and got the initial timing down to about 14°, but it started running rougher and had a delay in throttle response. When I clamped the vac hose, it wanted to stall. With the vacuum advance in place, I checked the total advance at 2800 RPM and it was 46°. I am running the stock '82 NA distributor which, according to the distributor advance curve excel file, that dizzy should be at around 55° total advance. I'm really shooting for a lower number like high 30's with the higher compression. So, my question is, how do I set the initial timing with that distributor? What am I doing wrong?

Here's what I did last night. This was my first solo engine install. I've always at least had a spotter to watch the other side and help guide the engine into position. Here's the flex pipe on the end of the collector. You can see how it helps the alignment between the header and the exhaust pipe. I also added heat shielding to the tunnel to help keep my feet cool. I should have it running later today.

Guy, the indicator goes on the valve spring cap and you need to go through the full lift, so .5" range is just barely enough, but I find myself moving it at least 4 or 5 times until it doesn't over travel at one end or the other. You need a bit of extra travel at both the top and bottom of the stroke, so 0.5" range minus cam lift at zero lash (0.460" in my case) is only 0.04" and then divide that by 2 and you end up with only 0.02" to work with at each end of the indicator stroke. Does that make sense? To find TDC with the head off would be simple with a dial indicator. When it comes time, I'll walk you through it rather than go into the details now. Make sure you take lots of pics and keep us posted on the engine build.

Guy, you can get everything at Grainger or on Amazon (what CAN'T you get on Amazon???). I got my Mitutoyo about 25 years ago. The only regret is that almost all of them read 0 - .5" and the cams have roughly a 0.450" lift, so it takes a lot of fiddling to get both the zero and max lift within the range of the indicator. They sell 0 - 1" range, but the price goes way up. Expect to pay over $200 for a 0 - .5" and quite a bit more for a 0 - 1". Go with 0.0005" resolution. Of course, you can find something WAY cheaper if you don't go with Mitutoyo. I'm sure Harbor Freight has them for $10 I think this is the modern equivalent to mine at Grainger for $226.50. MITUTOYO Digimatic Indicator, Battery - Electronic Digital Indicators - 5C711|543-783B - Grainger Industrial Supply The 0 - 1" jumps to $485.25. MITUTOYO Electronic Indicator, 0-1 In, Flat Back - Electronic Digital Indicators - 4GPY4|543-476B - Grainger Industrial Supply Here is a magnetic base by Mitutoyo for $201.50. MITUTOYO Magnetic Base - Indicator Holders, Bases, and Stands - 22N461|7033B - Grainger Industrial Supply The degree wheels can be found anywhere, but get a large one. The one I made is 16" diameter and it isn't too big. Summit Racing sells every size and brand.