Learn me troubleshooting SUs

So, my Mini has to be up and happy in a bit over a week. It's been getting grouchy, preferring to be on the choke most of the time and not happy about idling. It's never liked idling below 2000 due to a fairly rowdy cam, but it's getting out of hand. The carb is a single HIF 44.

I'm thinking there's an air leak. I did have the engine out a while back so the manifold was off. The car was down for a while at that time so I don't recall if this behavior started right then or not, but I don't think so. I do have a fresh set of gaskets for the manifold.

I've been through setup a few times, setting idle etc but can't come up with a happy setup. So - what should I be looking for? How to troubleshoot? Hose it down with carb cleaner to find a leak?

I'm not good with carbies. Please help!

Got oil in it?

Check for air leaks, especially with your "runs on choke" comments.

Check the float level, check that there is no junk in the float bowl, and that the floats don't sink.

The throttle shaft bushings can leak air which is pretty common I think.

Oh, and you're 100% sure it's not a spark issue?

I've been through the ignition in the past, I think we're good there. The car does like to foul plugs if you don't run it hard occasionally - it's a fairly horny little engine.

 I've checked the float, but I'll get in there and do it again to be sure. I even replaced the needle just in case it was worn. Definitely has oil. I've been through the SU setup guides multiple times, which makes me think it's something wrong and not a setup problem. I'm going to go through the whole thing again as it's been a while since I was under the hood, and not make any assumptions. But if the settings are all right and there's nothing visibly wrong, what else should I be looking at?

If it's the throttle shaft bushings, that should show up on a carb cleaner test - yes?

HIF's are easy!

Go ahead and order a kit with a new jet and seals. 7ent.com is my recommendation. When you take the float lid off it will never seal again without a new o ring.

Anyhow. Tip the carb upside down and the with a straight edge across the sealing surface the center of the float should be 1mm below the straight edge.

Pull the damper and needle out. Adjuat the jet up til it is level with the bottom of the throat.  Then dial it back down two revolutions of the screw.

Replace the seals on the butterfly shaft. 

Clean the damper assembly and pour out the oil.  Reassemble and pour some atf in the tube. 

That really is all there is. 

Do you know your cam specs? I could run your setup through winsu and see if it recommends a different needle and spring.

What is the engine size? To me that seems like a fairly large carb for a small engine but that may be normal. Theoretically if the CV slide is working properly that shouldn't really matter though. But why carry around a larger carb if it's not needed? 

Thanks Jumper, I was hoping you'd chime in. I've already ordered a rebuild kit - i figured it wouldn't hurt to have one just in case. I don't have your access to tools - if I have to ream out the body to fit new seals on the butterfly, any idea what size so I can get my hands on a reamer? Or do I misunderstand the procedure of replacing the seals?

Cam is a Piper HR270 on a big valve 10:1 1293 built by Rob Walker Engineering (I have full specs if needed). Needle is a BBA. Oil is 3-in-1. I am not planning on changing the carb at this time.

Which header? LCB?

The seals are just rubber cups. Actually even the shaft bushings are serviceable on an HIF

Yup, LCB.

The rebuild kit on 7ent mentions reaming, which is why I asked.

Disclaimer:

I don't do HIF carbs. HS4  or walk.. 

With the HS series carbs what I have learned the hard way is that the method described in the manual for setting the fuel level in the bowls does not work; Too many chinesium parts on the market that never read the manual.  Whatever combination of drill bits or chicken bones they tell you to use  as a gauge, seldom results in a proper fuel level in the jet. So just rip those pages out of the manual.

If I recall, the manual for the HIF calls for a blood sacrifice when setting the float level, but I suspect that it can be checked the same as the HS4. Remove the bell. Turn the key until the pump shuts off indicating the bowl is full. Then take a piece of hose about the size of aquarium hose. Using said small diameter hose, blow a small but sharp puff of air directly down the jet .

What you have done is to push the column of fuel down into the jet. If the floats are set right, you will get a slight flood of fuel over the bridge. If it does not come over the top of the bridge, then the jet is too low. If it floods the carb, it is too high. You want a nice film of fuel  over the top, not a flood.

The other way to check is to pull the choke all the way open. The while looking down from the top ( bell removed) make sure that the fuel is just over the top of the retracted jet. 

Note that these test are done with the jet moved down the recommended 2.5 turns from flush with the bridge.

HIF carbs seldom have worn throttle shafts, so that is probably not the issue.

Another thing I find on SU cars is warped flanges on the induction system. Either carbs or manifolds. This is an intake from a Healey that would have given me fits had I gone and used "as is". I painted the surface with a marker and ran it over a flat abrasive surface. You can see the warp.

As it turns out, it gave me fits anyway because the chinesium float needle/seat assembly did not work. Was only able ot figure it out using the method described above. Note how with the float lever all the way down, the needle still wont let fuel in. Tip is probably made of rubber rather than Viton. These were SU parts. Supposedly.

WinSU recommends an BBF needle with a yellow spring. Not sure how that compares with the setup you have though

I'll check the spring color, I'm pretty sure it's yellow from memory. I'm assuming the basic setup is correct, as this is a behavior that has changed over time. Thanks for running the numbers, now it's off to learn what the codes mean because it's interesting to know.

Thanks for the tips, Nohome. I've set the float level using a caliper in the past, but I'll check the whole thing for flatness and make sure I don't have any leaks. I'll probably tear into the car tonight or tomorrow, then there will be more questions 

What you have done is to push the column of fuel down into the jet. If the floats are set right, you will get a slight flood of fuel over the bridge. If it does not come over the top of the bridge, then the jet is too low. If it floods the carb, it is too high. You want a nice film of fuel  over the top, not a flood.

Should read...then the FLOAT is too low. 

NOHOME said:

If I recall, the manual for the HIF calls for a blood sacrifice when setting the float level, but I suspect that it can be checked the same as the HS4. Remove the bell. Turn the key until the pump shuts off indicating the bowl is full. Then take a piece of hose about the size of aquarium hose. Using said small diameter hose, blow a small but sharp puff of air directly down the jet .

What you have done is to push the column of fuel down into the jet. If the floats are set right, you will get a slight flood of fuel over the bridge. If it does not come over the top of the bridge, then the jet is too low. If it floods the carb, it is too high. You want a nice film of fuel  over the top, not a flood.

I don't doubt you, and I don't doubt that once you've learned to do this that it's easy and reliable. But boy does it sound like learning to read tea leaves or chicken bones, especially when you get to the part where you're identifying "correct" by the type of flood you see... How much calibration does the "sharp puff" need?

I'm reminded of the Peter Egan column on the topic of "Should You Buy a British Motorcycle?":

• Fifty points if your clutch adjustment procedure is so arcane and complex that only a taciturn hermit machinist and former RAF Gloster Gladiator mechanic named Alistair who lives on a farm in Vermont is able to make it work correctly.
• Twenty more points if Alistair requires a "gift" of strong Stilton cheese and Isle of Islay single-malt Scotch before he will even consider working on your bike.
• Ten more if Alistair is said to have murdered a man who brought the wrong kind of cheese.

In addition to what's been said, here's some other things to think about:

If you haven't checked it in awhile, check the compression just to be sure.  With that cam and CR, you're probably in the 175ish range, but it's more important that it's consistent.  If it's off, re-torque the head and then check it again (we see a lot of people change head gaskets when they just needed to re-torque the head and adjust the valves).  Then go through a valve adjustment.  Given that you've got a big cam, you might be having some issues as those things have big ramps and wear happens fast, even with good oil.  Part of your idle issue may be the valve lash--I don't know the specs for that cam, but big cams usually like loose valves (maybe .018-.020") and loose valves really help idle quality even though they clatter a bit more.

Regarding timing, if you've got points, make sure you've got 60 degrees of dwell.  Then check the timing and curve with the vacuum disconnected.  With that CR and cam, I'd want about 20 degrees BTDC at about 1000RPM and 32 degrees all in around 3000-3500RPM.  If you can't get it to idle down to 1000, maybe 22-25 at 2000.  If it's got a bad curve, 32 all in is the most important part of the timing.   Then reconnect your vac advance (if you have one).  It's controversial, but I prefer manifold vacuum to ported vacuum because it improves idle quality.  Try it and see if you agree.

I've learned not to touch the carb unless I've done/checked the stuff above.  

Then go to your carb.  Spray all around with carb clean with the engine running looking for vacuum leaks.  As mentioned, HIF throttle shafts usually are okay.  Nohome and Jumper have given you great advice about the rest of the carb setup.  All I can add is that there is a bi-metallic compensator in HIFs that sometimes causes troubles and other times the enrichment (aka choke) O-ring will be bad.  Either will make erratic performance.  We also see more sunk floats in HIFs than HSs or HDs.  If the jet isn't close to the bridge (within 2ish turns), that's also an issue--either it's set wrong or the needle is way wrong.   

Regarding having to use the choke:  The first 2/3 of the choke should only change the idle and the last 1/3 richens the mixture.  If you can figure out if the choke is just opening the throttle more or actually richening the mixture, that will help your troubleshooting.   I usually set the chokes to raise the idle to about 1800 RPM in that first 2/3.  Once you get to the last 1/3, the idle speed usually goes down a bit unless the engine is dead cold.

I'd think with that cam and CR, if all is good, you should be able to get it to idle around 1000-1200RPM.  Of course, I'm in Michigan and you're at a higher elevation, so my advice may not work very well at your altitude.

Any advice or guides for base lining a pair of hs2's?  Rebuilt mine when restoring the car and no way are they set up right. Got it to run, but the throttle does nothing and I have to play with choke.  I need to set timing, but having trouble getting to marks.  (Bugeye sprite with stock 73 1275, stock exhaust manifold)

Here is a link to tuning the SU carbs that is pretty hard to mess up. 

https://www.mgexp.com/phile/1/492119/SU_idiot_guide.PDF

The puff of air down the jet might sound subjective, but for me it was a breakthrough in getting SU carbs to work; the book method of adjusting the float level seldom works and can cause no end of frustration. 

The air puff is just a way to confirm the level quickly. The real non-subjective test is for float adjustment  (with the jet set 2.5 turns down from the bridge) is to  pull the choke all the way down ( i use the linkage on the carb cause lord knows if the cable is set right) and look down the jet holder. Fuel must cover the retracted jet but  just barely.  1/8" would be max.

Wish they had made the SU float bowls with a hole in the side so that you could adjust like a holey where you raise the level until it comes out of the sight hole.

Pete

I have zero useful to add.  I was going to mention the shaft bushing, but that's been covered.  I'm just here to say, that when Keith comes asking for help it's either the end of days.  Either that or the GRM forum is evolving into it's own  AI fountain of all knowledge and Google will have to buy out the whole empire or GRM will surpass Google as the go to place for any and all questions in the known universe.

Hey, there's a lot I don't know! And I'll take GRM experts over random and unvetted information dredged up by Google any day.  

Thanks for the additional tips. My carb parts will be here Monday, so I'll spend the weekend checking the setup (again) and looking at the other aspects that Carl suggested. This is great stuff.

So, I’m no carb expert. But the jet didn’t seem to want to adjust. I flipped the carb over, pulled off the bottom of the float bowl and found this. It seems...less than perfect. The jet was jammed in place, surprise surprise.

Yes, this car has sat for a while as I rebuilt a trans and then moved to a needy house. I suspect that I may be able to improve the situation. 

FYI, the valves were also quite tight so I’ve opened them up on Carl’s suggestion. Once the rebuild kit is here tomorrow, the carb will go back together with less crust. 

I think you found the problem!

Much better. Everything moves smoothly. 

it wasn’t the only problem, though. I found a cracked vacuum cap that would have been an intake leak (I’m guessing it would be the vacuum source for the dizzy if it had vacuum advance, which it doesn’t) and I replaced a bunch of gaskets on the manifold that may have leaky. Timing check will have to wait for the car to run :)

Keith,

I'd set the valves to the recommended setting from Piper (if you've got the cam card)--my .018-.020 was a bit of a generalization.  I did check Piper's website and it looks like their bigger cams are more in the .016 range, although some are as tight as .010-.012, which is very tight in my mind.  Nonetheless, looser is usually safer than tighter and usually helps idle.

Looks like most of your problem is the sludge in the carb, though.  Sometimes carb problems aren't ignition!  (I'd still check the ignition, though.)

Carl   

Question for you, Carl. When you’re giving valve clearances, should I be adding in the rocker ratio? I don’t know what it is on this car - I’ll dive into the paperwork - but am I reaching for a 0.016” feeler gauge or something else if we’re looking for 0.016”?