Posted: May-05-2008 09:04AM

Okay, I got the carb out yesterday and began exploring:

The float is in excellent condition and does not stick or rub anywhere. So heat should not affect it in any way.

Next, I removed the float, inlet needle and jet for inspection and comparison to older jets I have.

Measurements: 

The inlet needleis identical to another new one I have - even measured it with my brand-new micrometer. The overall diameter (over the ribs) is about 0.2429" . The O.D of the conical metal tip is approx. 0.1243"

An old needle ad an overall diameter of aprox. 0.2330".

The inlet jet however was a different story:

The main bore where the needle goes in is slightly less than 1/4", measured using drill bits (go/no go). Typical for all 3 samples. 1/4" = 0.2500"    6mm =  0.2360mm so it is somewhere in between.

The jet size for both the oldest jet and a replacemet for (another carb I rebuilt) were identical - approx 0.0692" - probable design diameter  of 0.070". (I used an old main jet needle as a tapered feeler to measure the I.D.)

The jet in the newest (current problem child) carb was visibly larger estimated I.D. of 0.1084" for a possible design diameter of 0.100" or 0.110"

Suspicions:

1. The fins on the new needles are visibly wider than the old one, and are much closer to the I.D. of the main bore. It might be that the plastic needle body and/or the jet expand reducing the clearance until it sticks.

2. With the larger jet diameter, the conical tip has a larger circumference to seal. Larger circumference equals larger contact area, resulting in  both a larger surface to seal and reduced sealing pressure per sq. mm of contact area. Since the float is the same, it can only generate so much force - maybe not enough for the larger 'valve'. This doesn't explain the temerature sensitivity, unless we take into account the buoyancy differential of gasolene at different temperatures (beyond me!) However, if we consider that the expansion of the needle fins may just be large enough to push the needle off-centre, then the cone may not be centred in the jet orifice, resulting in leakage.

It could be a combination of the possibilities too. 

So, I took one of the new needles and very carefully filed down the ribs maybe 2 thou or so for an outside width of about 0.239". That's still larger than the oldest needle. I also removed any burrs from the plastic and bevelled the end of the fins slightly to avoid hang-ups.

I reassembled the carb with the new 0.070" jet and the shaved needle. 

Reinstallation maybe tonight. 

"Hang on a minute lads....I've got a great idea."

Posted: May-05-2008 08:01AM Edited:  May-05-2008 09:06AM

Thanks for the sympathy and understanding (and the forearm offer!). I do like a challenge (within reason). I once had to remove and reposition the shift links of a remote type shifter with the engine and transmission in the car! These miserable little pieces sit above the shifter housing and are on splined shafts with pinch bolts. If they are off by even one spline, the shifter pattern goes all wierd. So, I had to do it several times to get it right. My wrists still ache thinking about it.

"Hang on a minute lads....I've got a great idea."

Posted: May-02-2008 05:33AM

Wow Dan, that sucks! All I can say is that if I were closer to you I wouldhave gladly donated my forearm to assist in installing your speedo cable.

I did mine and you know what? I drove it for a week and it stopped again, the problem with mine is the actual box cable thing keeps slipping back because the new cable doesn't have the little holder deal thing inside it like the old one did, so I guess I need to order a new one. I just haven't felt like messing with it.

Posted: May-01-2008 07:18PM

"I don't know much, but what I do know I know little of "

Posted: May-01-2008 05:37AM

Thanks for the ideas guys. I've been down all those roads. It seems to be more a temperature + time problem

Here's the short story:

original (to engine) mechanical pump > rebuilt HIF44 (resetting float numerous times) > brand new HIF 44 (resetting float numerous times > reroute fuel line in engine bay away from heat > add regulator > new mechanical pump > insulate fuel lines in engine bay > Facet fuel pump in boot with regulator moved to boot (away from heat) > sent the whole she-bang to the professional Mini mechanic who was frustrated by it (checked and adjusted the regulator to about 2.5 psi, stripped and rebuilt the carb 3 times before discovering a small piece of brass milling swarf inside the jet screen...) > rip all that out and install a brand new SU electric pump. Always filtered.

Each time it works for awhile - minutes or hours or days or weeks or months (never consistent) then takes a hissy-fit. That's why I said "Last fall, after a relatively successful Mini season..." The old problem of the non-repeatable experiment.

At various points it seemed as if boiling gas was fooling the regulator (why I tried fuel line insulation) moved it to the boot), or boiling fuel getting past the float valve. Although... is happens when the outdoor temperature is not excessive and/or the engine isn't overly hot. 

Now I am suspecting that it has something to do with either tolerances between the float valve seat and needle and/or a thermal expansion issue in those components somewhere. Maybe the body of the carb expands allowing the valve body to loosen or the valve seat or needle expands increasing the side clearance so the needle goes out of alignment or sticks. I have 3 jets and needles to play with. I may invest in a micrometer. (I've always wanted one of those!)

Or maybe the float itself is expanding and sticking on its pivot shaft or against the bottom end of the inlet needle.

"Hang on a minute lads....I've got a great idea."

Posted: Apr-30-2008 07:45PM

"How can anything bigger be mini?"

Posted: Apr-30-2008 07:25PM

"I don't know much, but what I do know I know little of "

Posted: Apr-30-2008 04:00PM

Steve

Life is driving Minis.  Everything else is just waiting.

Posted: Apr-30-2008 09:03AM Edited:  Apr-30-2008 11:08AM

Some of you may recall trhat I have a recurring problem with gas (no not Martin's Chili kind of gas...) leaking from the carb.

Last fall, after a relatively successful Mini season, I was putting Desiree to bed for the winter. All was in readiness and the last thing was to add the stabilizer to the fuel in the full tank. Now.. just run the engine a bit to get the stabilizer up to the carb. Just as I'm finishing, I detect the telltale slowing of rpm and the change in exhaust odour. DANG. I shut her off and rolled her into her resting place. Over the next couple of weeks, the odour of raw fuel was growing stronger in the garage. Below Desiree's engine was a small puddle of gasolene. There was also a small puddle below the heater valve on the clutch housing. I siphoned off the fuel tank to the below-the -carb level and left it for warmer weather (the garage is uninsulated and unheated)

Ah, spring at last! The very first thing I tried was the fuel system with paper towels wrapped around all the fuel lines in search of a pinhole. ("How else would gas get to the front side of the engine", I pondered.) Nothing, nada, niet, rein. Okaaaaay??....maybe just a quirk.

On to other issues.

The plastic cowling for the later 3-clock instrument panel wa lying on the passenger side floor where I'd left it after coming off for the umpteenth time. Lets fix THAT. All the metal clips were loose, requiring the instruments to be removed and the clip screws tightened. Okay, the wires come off easily and with no damage. But the speedo cable was another issue. Try to figure out THAT clip by feel (worse than a young lad's first bra strap!). Allright! instruments out and on the bench. Getting smart in my old age, I realized the quick way to align all those clips was to put them into the plastic cowling first and then fasten the instruments to the. EASY!

(Okay, I'm back)

So, now that I had the instruments out, I decided I should look into changing the speedo cable. I already know my substantial forearm isn't gonna reach down there behind the engine, so I loosen the engine steadies, undo the rad mounts and shift the rad forward. No good. The rad has to come out. This is when I discover the rad is oozing and some of the fins are starting to get flakey.The tips of my fingers can now just reach the bottom end  of the speedo cable, and after an assortment of tool tests, a cheap pair of stamped pliers (Fiat I believe) manages to loosen the knurled ring. Out comes the cable!

Miraculously, the new rad, hoses and cable arrive in 2 days! But that weekend has other commitments.

Now, the old speedo cable has a rubber firewall grommet, but the new one doesn't. The grommet comes off the old cable OK, but when trying to stretch it over the new one, the plastic latch on the instrument end breaks off. DRAT! Being ingenious, I figure I can make a key to fit in the rectangular hole. This takes time to carve out of a block of plastic, but it does work and is held in place by a zip-tie, which provides the springiness. Electrical tape (red, because black is boring...) then covers the zip-tie to keep it from sliding. Back in business!

"Assembly is the reverse of Disassembly" proceeds, except I learn it is easier to reinstall the instrument pack by fastening it to its mounting bracket and then installing the mounting bracket back onto the firewall. Oh, and the pliers I used worked better in removal than assembly because the available space for leverage says so.

Next the rad goes in with the fan on the right way, but only then do I notice how close (2mm) the fan blades are to the crankcase vent. Off it all comes again, and a new fan spacer is made of aluminum to add to the exisitng one.

Haynes is right.. assembly IS the reverse of disassembly - they just don't say how many times one needs to do it to get it perfectly right (and they don't take into acount parts than break in the process). 

So, this past weekend all is together and the rad is filled and it is time to start her up! I turned the key listening for the fuel pump and YESSSSSSS - only one click to pressurize the line - the carb float valve is holding!

 I rolled the car out of the garage before starting a there is 'storage' oil in the cylinders and it will need choke. Smoke is expected. After a short cranking Desiree comes to life with a roar! She continues to warm up and the cooling system warms, the thermostat opens and no apparent leaks! This is looking promising! As she warms, she will run without choke and settles to a proper idle. Gunning the engine produces a bit of a fart, but hey, she's been asleep a long time. At this point, my wife comes around the corner of the house and reports that Desiree is popping flame out the tailpipe. But that goes away as she continues to warm. I have not put the full insurance back on, so a road test is not in the cards.

And then it happens.

The idle starts to falter.

The mixture is richening.

There's sooty smoke coming out the tailpipe. 

And yes, there's raw gas dripping form the carb bowl vent.

I shut her off (Desiree, not my darling wife!)

I pull the fuel pump wire off the fusebox terminal and restart the engine. Idle returns to normal and I burn off the gas in the bowl, then return Desiree to the place in the garage.

I'm beginning to think she likes staying in the garage we built for her (or so she thinks) or riding around on flat-beds at over $100 per ride.

So it is back to mucking with the carb.

and I still don't know if I've solved the speedometer problem.  

"Hang on a minute lads....I've got a great idea."