Getting stumped with a fuel issue

Started by 94touring, June 15, 2021, 08:35:14 AM

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94touring

Maybe one of you have experienced this before or have some suggestions as I'm running out of ideas.  The mini and hif44 suddenly developed a very lean condition that required choke to keep the car running.  I moved it in and out of the shop like this for a week or so then finally took the carb off to replace o rings in the choke assembly thinking maybe that was the cause.  That didn't resolve it so I took the carb back off and replaced all gaskets, including the manifold gasket, double and triple checked vacuum lines and caps, inspected the float and needle, checked the jet for blockages and so on.  Oh also rebushed the butterfly shaft and put a new shaft in. Basically went through everything.  Got it mostly stable, I'd say 95% of the time idling just fine, showing 14:1 air fuel vs the pegged out lean can't run. However occasionally pulling out of the shop and once on the downhill slope it goes lean and dies. Fires right back up and drives mostly normal.  Mostly normal being my cruise air fuel is as it was before but now I'm pig rich in mid range WOT pulls.  Fuel pump, filter, and pressure check good.  Sticky float perhaps?

BruceK

I see don't know.  Needle seated properly? 
1988 Austin Mini
2002 MINI Cooper S
1992 Toyota LiteAce (JDM)
1997 Jeep Wrangler Sahara

MPlayle


94touring

Yes and yes.  I just adjusted the float, put a different float needle in, and went ahead and put a different o ring set in the choke.  Letting ot warm up and then seeing what it does.

Willie_B

Do you have a hose on the vent opening on the side of the carb. Could it be blocked? It's the time of the year insects are looking for dark holes to nest in.

94touring

All vents correct and no blockages.  I made sure to blow through every orifice.  It runs just fine but for whatever reason wants to go lean occasionally pulling down the slope. I wonder if maybe the piston is just sticking somewhat high at idle and at an angle.  It drives fine now, level or up grades.  So I dunno.  8.gif. The only kicker is my air fuel ratio at WOT mid range is really rich now.  I didn't half the shaft when I put the new throttle shaft in.  Don't know if that really makes that much difference or if with the new bushings less air is getting by. 

MiniDave

#6
I'm still not sure what was going on with mine, but it's working fine now so I'm just whistling while I drive!  ;D

No idea what my air fuel ratio is but my plugs look good, so I'm leaving that alone too.

Does your choke mechanism have two o-rings or one o-ring and a paper gasket?

I have one of each design, the carb on the car (original one) has two o-rings, the test stand carb had on e and a gasket.
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

Willie_B

I was just thinking, could it be wet gas? The water would be on the bottom close to the intake pipe. If it stays running/moving for a bit it gets remixed back in so no more problem till it sits again.

94touring

Quote from: Willie_B on June 15, 2021, 07:30:47 PM
I was just thinking, could it be wet gas? The water would be on the bottom close to the intake pipe. If it stays running/moving for a bit it gets remixed back in so no more problem till it sits again.

Hmm, that's a good guess!  I did have it sitting outside in all these torrential downpours last month not driving it.

Jimini II

A few years ago I had a HIF that had lean/rich issues.
I replaced the jet after being advised that the bi metal strip on the jet may be bad, I had no more issues.
It ran the same as a bad waxstat equipped HS4 would run.

94touring

Quote from: MiniDave on June 15, 2021, 02:32:34 PM
I'm still not sure what was going on with mine, but it's working fine now so I'm just whistling while I drive!  ;D

No idea what my air fuel ratio is but my plugs look good, so I'm leaving that alone too.

Does your choke mechanism have two o-rings or one o-ring and a paper gasket?

I have one of each design, the carb on the car (original one) has two o-rings, the test stand carb had on e and a gasket.

It's the 2 O rings. 

John Gervais

I'm interested in hearing what y'all figure out - this is similar to the lean condition that I had (and still have) which was compounded by a misfiring of said lean mixture.  I cured the misfire by testing various vacuum advance units and installing one onto the distributor.

I've replaced the bi-metalic jet holder with a proper mono-metalic unit that Keith Calver gifted me - it's not a modified bi-metalic unit, it's solid mono-metalic, made from stainless steel, if you know what I mean.

Mine is also 'pig rich' at mid-range WOT (reading typically 10.5:1(ish) freshly calibrated, dash-mounted Innovate Motorsports MTX-L gauge - (cruise at 65 - 70 mph is 14.5 - 15.5:1(ish) )). 

When cruising, if I suddenly lift off of the throttle, it'll richen up to 12(ish), then slowly lean out again - I figure that this is normal from the increased manifold vacuum drawing fuel from the jet.  Soon after, if I haven't 'feathered' the throttle, if I simply lift off and let the car slow down on it's own, coasting on the 'engine brake' to a stop light, the mixture will lean out to 18, 19, or 20:1, stumble and then return to normal idle after around 10-15 seconds. 

I'm debating whether or not to cut a turn or two from the red spring to help hold the piston down - I suspect that the dashpot/suction chamber piston may be 'fluttering'.

And - mine is essentially a brand spanking new HIF38 carb - I've owned it for a few years, but it's done very few miles.
- Pave the Bay -

94touring

Yep I went from a richer than a like 11.8 at 4k rpms to 10.0ish.  It's always had a rich dip there. I have enough spark it doesn't stumble.  If I was motivated I'd pull the carb off for the 4th time and half shaft it and see if that changes it back to normal.  Instead I bought some more needles to tweak to suit whatever changes that the carb and gasket overhaul had.  In any case the lean condition has gone away and I think Brad's water in the fuel tank theory was probably it.  Where I had it parked was just outside the shop, with 3/4th of the car under the roof overhang, the back half exposed.  Which means when it rains, it boy did it rain for awhile here, the overhang flows water like a river.  Most likely right onto my gas cap.

cstudep

It doesn't take much these days, the fuel quality is questionable to begin with and the Ethanol soaks up water like a sponge.

I try to use non-ethanol fuel in all my old stuff, 2 stroke motors, lawn mowers, etc.. but finding it around here is not easy and even the "non-ethanol" stuff seems suspect at times.

MiniDave

Don's Pup had trouble on a run back from a Texas event - the car would even stall at times, but always re-start. I finally convinced him to stop at a gas station and put a bottle of Heet in - problem cured.

I think it's a good idea to add a bottle once or twice a year if for no other reason than to get rid of any condensation that might be in the tank.

I also try to only run ethanol free gas - it sure runs better on 100% gas vs 10% ethanol.
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

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