you need a return line whether you like it or not.

How so? It's got HIF carbs...where am I going to put the return line (ie where am I plumbing it from)? Is this going to help with the wee little bit of run on?

Oh and I'll probably take a video today for fun and I'll take some decent photos of the thing for a change.

Don't see why, since the factory didn't have one...

I'm not convinced a return line would keep fuel cooler anyway. It would when the car was running but that's not the problem. The issue is when the car stops running and the line heat soaks. There is not the kind of pressure in the line like in an EFI car to prevent the fuel from vaporizing. It didn't rear its ugly head with the new location of the fuel line although the line was pretty warm when we got back to the garage. I doubt it'll be an issue on the highway with all the air flowing though the engine bay but it may be an issue around town in +30C temps when the fan is blowing +100C air back at the engine. I think some sort of insulating wrap will cure it, if it becomes a problem and we have yet to determine that...


Something like this...

http://cgi.ebay.com/ebaymotors/THERMO-T ... 240%3A1318

Your right that on the highway there will not be any problem, where a return line helps is with the heat soak on a restart. As soon as the fuel pump pressurizes the system, fuel will fill the float bowls and then excess fuel will circulate back to the tank, this bleeds off any vapour lock. Also in a carbed vehicle the flow of fuel is often so small that the fuel sitting in the line of a running engine will heat and start to vapour lock, with a return line there is a constant flow of fuel to aid in cooling.

With all that said Craig you are right that if your fuel tank does not have a return line fitting that makes it very difficult. As an FYI the return line is plumbed off the regulator just like in an EFI car, just the regulator is set for low pressure 3-12 psi. (need to use a 3 port regulator)

Many, many cars with carbs over the years have not used a return fuel system and worked flawlessly, so if yours is working now with the rerouted fuel line, drive and enjoy

This works fine if you're using an electric pump that pressurizes when you turn the key on. With the mechanical pump it only pumps when you crank the engine so it only pressurizes the system as you need the fuel...

It's OK, I'm not too worried about the fuel return, but getting the carbs set is another thing. I'm still convinced that there is something not right with the HIF's. The dieseling is still there to some degree - even with the timing fixed, high test in the tank and all other issues sorted. So I'm back to fiddling with the carbs. They seem to be wet inside, and I'm pretty sure they shouldn't be. I've been trying to set the mixture and that is having little to no effect.

Any thoughts (other than ditching them for EFI)?

got a wideband on that motor yet?

I've got the JAW built and have thought about putting the wideband in place, but at this point, I'd like to just get it going a little better and reserve the wideband for when I can actually get the engine to tune. The problem is that nothing I'm doing seems to have much effect. I'll try it when I can get the carbs to behave.

Double and tripple check the float levels, SUs are a PITA for float settings. I am sure you checked the damper drop and it is smooth and complete. I am guessing your dieseling is too rich an idle mixture and/or too high an idle speed. Also what heat range of plugs are you using? may be a tad too hot. (all just ideas to keep you from going EFI )

I'm thinking about changing to my spare HIF floats. Damper drop is fine and equal (matched) - weird part is if you lift the pins or lift the piston a crack (same effect) the engine stumbles indicating lean - but then it behaves like it is rich when driving. Oh, and the idle adjustment screws are basically there for show at this point.

I could try a cooler plug - can't recall the numbers off the top of my head.

No problem. Anytime.
I hope you can get it running smooth really soon. I sure like how it sounds though!

I never could get HIFs to run right on my high compression, big cammed Mini. The HS carbs seemed to be much more responsive to tuning. I know that's a silly thing for me to be saying, since of course there was more than this at stake (single 1.75" HIF versus dual 1.5" HS, for example, and much more time spent with the duals), but I never did like HIF carbs, even on Volvos. David Vizard loved them, though.

Big cams and high compression requires LOTS of fuel at idle, and the excess fuel requirements drop off quickly just above idle. You may very well be lean at idle but rich everywhere else, even in the transition. My V8 wouldn't idle nicely at all with the wideband showing anything leaner than about 13.5:1, but as soon as it got above about 1000 RPM (idle was 850 or so!) it was comfortable at 14.5:1. Keep in mind that incomplete combustion, misfires, and reversion, all show up on a wideband as lean, and at idle with a big cam this is where you'll see most of these sins.

You might need to get radical with the needles. Remember (if you're going off "spec" needles) that what works at sea level doesn't necessarily work at this altitude, or on our fuel. It's only a starting point. You might need to start filing away at the fat end to get the idle rich enough to let you lean out the midrange.

I've sent an e-mail to the SU guru to see what he says. I'm running a pretty fat needle already (BB). The cam isn't all that big, sure it's bigger than stock - but it isn't a radical cam with lobes shaped like rectangles (I thought it was going to be much more aggressive than it is) - Thanks for the tip about lean at idle rich elsewhere.

I can tune it back to the point I had it on Saturday, but I'm thinking I should just pull them one more time and switch to my other floats - my spare set of floates have the tab attached to the bottom of the float (as seen from the bottom of the bowl) while the ones that are in there now have the tab attached on the other side. I'm thinking that this may have been one of the solutions SU applied over the years to compensate for this sort of problem. With the tab on the other side, the metal sits against the plastic and when it closes has some additional leverage. With the originals, if they are at all weak, the pressure will overcome the float and the carbs will flood.

What I think I have now is carbs that are getting extra fuel from the over flow. This prevents me from adjusting the idle and getting them sorted out.

Ok, I've not started the car - it's too cold in the garage and I can barely feel my fingers or feet - but I think I may have the answer to the carb problem. Given that the carbs were not possible to tune and I felt like they were always too rich, I went back for another look at the floats. As Ian has correctly pointed out, HIF's (in fact all SU's) are very sensitive to float level.

At first, this was mostly just a fishing expedition, as I could achieve the tune that Dale and I had on Saturday (which felt pretty good), but the fact that I couldn't adjust the idle and the mixture was troubling me. So I took apart my spare carbs and found that the tab controlling the needle valve was attached to the opposite side of the float (to the bottom of the float looking at it with the cover off). So the needle valve was pushing against the bottom of the float - exactly the opposite to what was installed.

These floats (on the spares) are also SU stock parts (this may be significant) - they are purple - so lets call them the purple floats.

The floats on the carbs had the tab on the opposite side, so that the advantage would be more towards the needle as the tab had nothing to back it up. This wouldn't have created too much trouble as long as the fuel pressure was low (again, significant). These floats were generic with NO SU markings on them - they are white - ergo the white floats.

So I decided to swap some parts (floats, bi-metalic spring) from the spares to the carbs on the car. Now as I tell the next part - in my own defense, I rebuilt these carbs one at a time, so that parts didn't get swapped and the parts are all sided. I noticed that the shape of the purple floats was not the same as the white floats - the purple floats are larger. So in they go, worth a shot.

As I was putting my spares back together with the white floats from the pile of stuff on the bench (both carbs apart) I noticed that if you flipped the floats over and changed them from one carb to the other (they are sided) - the tab sits in the same orientation as on the purple floats...pin drops. The next part of the story is that the white floats have a scoop on both sides (this is where the float height is measured) - as per the manual the scoop in the middle of the float has to be 1mm above the face of the carb body (measured using a couple of dimes and a straight edge). I had double checked my previous measurement - spot on. The purple floats only have a scoop on one side (thus the additional volume).

So my thinking now is that the white floats were in the wrong carbs and in the wrong way around! . This may be the problem as they are not symmetrical. So I got them to sort of work, but the fuel level (and recall the sensitivity to fuel level) was not right at the "stock" setting as I was measuring the wrong scoop. After our run on Saturday, there was fuel in the carbs (wet) - not something that I would expect even in a rotten old SU.

The story doesn't end there - I've been told a hundred times that the HIF's can handle MORE pressure than the HS's. Well, the car use to have HS's and with the same fuel pump on the engine for both the HS's and the HIF's I had to install a fuel pressure regulator and dial it down to 1.5 psi to get them not to flood. More pins dropping . I could probably pull the FPR off the car now and it would work now that the floats are in the right way around.

Anyway, I polished the carbs again and put them back on the car, filled the dash pots with MTL and let it sit. I'll start it up tomorrow and see if that is the problem. I just didn't feel like doing it tonight, even though I really should. I just have a few more things to hook up (chokes etc).

Mystery solved? Stay tuned.

Let's hope so. I could never make sense out of needing the FPR in the first place. I think there is more powah to be had in that engine. It felt strong, no doubt but I suspect once the carbs are tuned properly, it'll feel more stronger...