Volvo RWD 140-160 Forum

Th front carb on my '71 144 is giving me problems. Kyle came over and diagnosed what I recall to be a sticking jet. My knowledge of carbs is pretty limited, so please forgive if I am off on my description. From what he said, it is the jet that you can raise or lower the position of with the adjustment screw. I would presume it to be the main jet from the diagrams tha I've looked at. Only mine gets stuck in an upward position, causing it to run on two cylinders. Does my translation make any sense and is it indicative of a rebuild being needed? I have a Royze SU-23 carb tune kit that includes a main jet, metering needle, needle, as well as misc. gaskets and plastic bits. Since the car is already not operational I'm considering taking it apart and replacing any bits that I have replacements for. Any thoughts, suggestions, or words of discouragement?

Took the carb apart completely, replaced the jet and needle, replaced all the gaskets. Once the alternator is back from being rebuilt I'll see if I fixed it...

From my understanding of the HIF6, the jet is fixed (doesn't move in operation). It is the tapered needle that raises and lowers in the jet hole to give the required fuel flow. The jet is initially adjusted (raised or lowered) to set the base idle/fuel flow after which the needle does the fuel control.

So if the needle is sticking, I'd look for free movement of the piston that is holding the needle.

Remove the bell cover, clean the piston. Check spring, and damper oil.

Also, from what I recall, the needle sits in the piston at a bit of an angle.

If you need additional info, I have rebuild instructions that came with a kit from Burlen (may also be online).
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1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

On a HIF carb, the jet is attached to a bi-metal spring that moves slightly to compensate for ambient temperatures.

It results in more consistent performance over wide ambient temperature ranges.
That's why you are not likely to have to make seasonal adjustments (assuming you live in the 0 - 100 annual degree range) to the HIF carb. It runs well all year round.
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'60 PV544, '68 220, '70 145, '86 745T

HIF jets compensate for ambient temperature by sliding up an down on their own.
My experience is that they work quite well. I prefer them over HS6 carbs.

You may be able to get away with simply cleaning the ones you have now.
In any event, pull the carbs apart and give them a good cleaning and since you have a repair kit, change the parts while you're in there. It is not difficult.

Do make sure however, that after you replace the parts that the adjustment screw will raise the jet just above the bridge and moves smoothly - both the screw adjustment and the jet itself. If you cannont get the jet to raise above the bridge, you may have to bend the tab that the bi-metal piece is attached to.

It will make more sense after the thing is apart and you can see how things work in there. The beauty of SU carbs is that they are very simple and easy to work on.
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'60 PV544, '68 220, '70 145, '86 745T

Took it apart somewhat today. From what I can tell, there is a jet directly below the metering needle. That is the part that seems to be sticking up. I can't really tell from the diagram that I have, but would that be the main jet that is sticking? If so, would replacing that part likely solve the issue or is it more likely a jet bearing assembly problem?

There is no "main" jet, because there is only one jet per carb.

I have no idea what may be sticking, but it wouldn't surprise me that the jet has just become stuck with time.

You really need to pull the carb. apart and clean, clean, clean.
The only way to access the jet to clean it is by removing the bottom cover of the carb. You will not be able to clean the bearing surface from the top side of the car. My first guess would be that it is only a problem of gum and varnish on the outside surface of the jet and the bearing it rides in.
Just replacing the jet without cleaning the bearing would be a waste of time in my opinion. I mean you would have it all apart at that point.

It is easiest to do this with the carb off the car since you need to access the bottom.
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'60 PV544, '68 220, '70 145, '86 745T

As I understand it, the jet is raised or lowered with the adjustment screw. We lowered it when tuning it but found that it raised back up while driving. Sorry if I sound ignorant about this, but I am...

You've got to take this thing apart.

The jet is held in place with a lever that is fastened to the carb body within the fuel bowl. Perhaps the screw that holds that lever is loose.

Is the mixture adjustment screw turning in on it's own as well as the jet moving up? That would be really weird. Very strange that it is rising up that much on it's own. I suspect the fastener inside the fuel bowl with what you're describing.
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Lubricate your distributer!