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SU carb cutting out

Gertofius

Gertofius

New member
Joined
Nov 24, 2023
Hello everyone.

My issue:
It will run indefinitely at slow idle but it will suddenly cut out at anything higher after roughly 5 seconds. It does not sputter or backfire. Its as if I have turned the car off. It feels like it has full power until it suddenly shuts off.

Backstory:
I recently bought it (1982 245 with a 2.1L and a single SU carb). It is a US market car but has a Canadian fuel system installed. I followed a very knowledgeable builder when I rebuilt the carb and everything was running great for several months. I tried to take it around the block last week but halfway through the car lost power and died. I can turn it back on but cannot apply power without it dying. I am familiar with carbs but not SU carbs.

Things I have tried:
I installed a plastic fuel filter to check the fuel going to the carb. The filter has plenty of fuel in it. I detached the fuel line and ran the car right after it died and it idled normally, so there is still fuel left in the bowl. I checked the timing and it is still at 14 degrees and goes up with revs. There isn't fuel coming out into the intake either, I think it is safe to say that it isn't flooding. The SU piston is free moving and the oil is full.

I would be grateful for any advice, thanks!
 
Float bowl level, fuel pressure. How much pressure and volume ?. What is the fuel pump? elect or mechanical.
 
If it dies just free reving it you can take the air filter off and watch the carb as you rev it. You should be able to see fuel getting picked up from the jet and mixing with the air rushing into the intake. Confirm that up until the point it stalls you've got fuel then look elsewhere. Unless it's got some fuel shutoff solenoid or something this doesn't sound anything like a fueling problem.

Tldr- I bet it's not the carb.
 
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Float seems like the logical culprit. Pop off the float cover and check that the valve and float level are in good order. From there… it’s easy enough to start at 0…


Raise the jet to the throat. Center the jet, drop the jet to “0” for your specific carb… hs6 are something like 12 flats or 2 turns out. Hif are something like 3… but I may be wrong on those… been a while. Once that has been done, set the idle, start closed, and go 1.5 turns in. See if it starts. Get warm idle to spec, then return to setting the fuel mix. There should be a lift pin to raise the piston 1/8”. The correct mix should have the idle just slightly raise then resume. Lean will fall, rich will raise and hold.
 
I made some progress today but have another issue. The brass float needle guide had loosened while driving, which pushed the float down and added too much fuel. I tightened the guide and reset the float. To my dismay the carb is now leaking fuel from the air vent on the side of the carb.
 
Gertofius said:
I made some progress today but have another issue. The brass float needle guide had loosened while driving, which pushed the float down and added too much fuel. I tightened the guide and reset the float. To my dismay the carb is now leaking fuel from the air vent on the side of the carb.
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Either your float level or fuel pressure is too high. An engine running badly and bucking hard can also do this.
 
And given the sequence of events here (it wasn't leaking, until they changed the float situation) I'm guessing the float level is the issue.

What model of SU is this? I'm assuming an HIF? It's a bit fiddlier to mess with the float levels on those, compared to the simpler, older HS version.

PS: It's also possible you got a tiny bit of grit in the fuel inlet when working on it. It only take a tiny bit of grit to hold a float valve open, and when that happens, the grit is held securely in place by the float valve pressing the needle closed.
 
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JohnMc said:
And given the sequence of events here (it wasn't leaking, until they changed the float situation) I'm guessing the float level is the issue.

What model of SU is this? I'm assuming an HIF? It's a bit fiddlier to mess with the float levels on those, compared to the simpler, older HS version.

PS: It's also possible you got a tiny bit of grit in the fuel inlet when working on it. It only take a tiny bit of grit to hold a float valve open, and when that happens, the grit is held securely in place by the float valve pressing the needle closed.
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I've had this happen a couple times. Now I blow some compressed air at low pressure through fittings to make sure I don't have any grit in the system before I button up the fuel lines.
 
JohnMc said:
And given the sequence of events here (it wasn't leaking, until they changed the float situation) I'm guessing the float level is the issue.

What model of SU is this? I'm assuming an HIF? It's a bit fiddlier to mess with the float levels on those, compared to the simpler, older HS version.

PS: It's also possible you got a tiny bit of grit in the fuel inlet when working on it. It only take a tiny bit of grit to hold a float valve open, and when that happens, the grit is held securely in place by the float valve pressing the needle closed.
Click to expand...
Its a HIF. I have the float set to 1mm below the rim level. I have sprayed cleaner in every hole and it has come out the other side. The float is the older, discontinued style, but it doesn't slosh or look like its taking any fuel in. I think there is either a clog somewhere I can't see or the float needle has failed in some way. Im leaning towards a clog since I drove it 4 miles without a issue and then it suddenly bogged down while driving. I wish I could upload the picture of where the fuel is coming out, but it keeps saying the image is too large to upload. Its coming from the vent hole on the intake side that goes down into the float chamber. I rechecked the pressure again while its leaking and its still at 2-3 psi.
 
I thought HIF's were supposed to vent flooded fuel (from overfilled float bowls) into the carb throat, making the engine run bad. This was considered an improvement over the HS strategy of dumping it out a vent and down onto the generator/alternator and exhaust manifold.

Try a free account on IMGUR to host your pics?
 
The problem ended up being an embarrassing mistake on my part. When the needle guide loosened itself and I tightened it down, I had put the needle in upside down. Switching that back made it run fine again. It was the 4th time that I had it apart to look at the float that I saw the needle was the wrong way.
 
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