Suzuki Club UK

donkeychomp wrote: ↑

Mon Nov 23, 2020 9:03 pm

If Carling made switches...

They would be cheap and nasty?

Finally got around to getting her MOT'd last week. Nice to have her back on the road after almost 2 years! :yay

Still a bit of fettling to do. Was running like a bag of spanners when warm (only found out on the way to MOT as without insurance and MOT I had nowhere to get her good and hot) I've now set the timing with a light, it was just a degree or two off. Cleaned the carb and adjusted the fuelling. Tried a different coil (made no difference), replaced the dizzy cap and rotor arm, new plugs (need to check the end cap is correct also)

Running better but plugs are sooty so needs to be leaned off a little. Also has a wandering / weak idle when hot. I'm running a SU carb (hiff44) with the Vitara 1.6 8v. I think the SU needs a good service. I've checked and it has the recommended needle for the 1.6 (BFM) but I don't know if the dashpot spring is the correct one. So I'll strip and measure that. I'll also buy a rebuild kit as apparently the throttle spindle seals can go and cause air leaks down stream of the jet.

Some very helpful tips on the SU carb thread on here.. thanks guys!

Also, the airbox no longer fits due to the SU carb, so I'm running just the snorkel with a foam filter, which isnt great, need to either package a better airbox or relocate the existing one to the passenger side.

Getting there!

Those Bighorns look the business on your machine

Lovely sj that

So I've been having some running issues that I'm struggling to get to the bottom of.

I bought a 1.6 8v with an SU carb attached ages ago and installed it earlier this year. it was running fine at idle and pottering around the yard. It was only last month when I took it out on the road to get MOT'd that i discovered that it was stalling when it gets properly up to temperature. starts to splutter and lurch back and forth and eventually cut out. It will then restart with a bit of effort and throttle blipping but when I try to take up drive it cuts out. If I leave it to cool down a little it will generally start up again and be ok for a few miles.

After the first time it happened I tried a few different things I got it running well and had driven it for about 30 miles without issue, then the next time I drove it it started acting up again. I'm now running out of ideas of what to try next. I'll list what I've tried so far and if you have any suggestions pleas let me know.

Ignition system:
New dizy cap and rotor arm
New spark plugs (end gaps are correct)
I've tried a different, used ignition coil but that makes no difference either.
Checked timing with a light and tachometer and adjusted to make correct, it was only very slightly out.
I've got a set of those little in line spark plug checkers and they all show a consistent bright spark.
I've checked the mechanical advance and it looks to be free and in good condition.
I've tried removing the vacuum line from the carb, doesn't seem to make a difference.

Intake:
I've tried a cone filter fitted directly to the carb and also a snorkel with a foam filter in line.
The gasket between the intake manifold and cylinder head was renewed when the engine was installed
The gasket between the carb and manifold looks good.

Fuel:
I've fitted an electric fuel pump as the 1.6 doesn't have a mechanical pump like the old 1.3 did. the pump is just a cheap ebay job that was labelled as suitable pressure for the SU. I think it was 3psi give or take. The pump appears to work ok but I'm tempted to get a gauge to check the actual pressure.
I've replaced the fuel filter that's fitted to the chassis rail just after the fuel tank
I have an in line fuel filter fitted before the carb, you can see fuel flowing but sometimes its full and sometimes almost empty

SU Carb:
I've stripped and cleaned the carb, checked the needle and measured the force of the dash pot spring, its a BFM needle and the compression force matches a yellow spring, both are the recommended setup for a 1.6.
Topped up the dashpot with 3in1 oil
Stripped the bottom of the carb, cleaned the little filter on the jet and set the float correctly
Replaced the seals on the choke and throttle spindles
I've tried the fuelling at various different values but I've tried keeping it around 2.5 turns out as that was recommended on the SU carb thread. after a bit of fine tuning the plugs looked good after a decent drive.

It feels like its a fuelling issue when it cuts out but the problem definitely is worst when the engine is hot. The fuel line feels cold so I don't think vapour lock could be an issue.

Any ideas on what to try next would be appreciated!

What type of Su conversion does it have? An elbow or a modified manifold? when it cuts out is the dashpot on the carb really cold? You could actually be suffering from carb icing, My SU conversion is a nightmare for it as soon as the temperature drops outside and on damp mornings. I would work out a way to rig up an airbox with a hot air feed or just repipe it so that the air filter is near the exhaust manifold to see if it stops it from cutting out.

Also I find they run loads better with the proper straight sae20w SU oil, 3in1 multi purpose oil is too thin, The 3in1 motor oil is sae20 though.

Its a proper welded manifold.

I had thought that, but I'm pretty sure I ran it on a mild day a week or so back when it was around 10 degC and it still happened. Would carb icing happen when it's that warm? Either way I'm not certain, so I'll deffo route a warm air feed and see if it helps. I'll check the dash pot temperature next time too.

Cheers for the oil tip, I had read that 3in1 worked but getting the proper stuff is another cheap thing to try!

It can, it depends on atmospheric conditions as well as the temperature.

Some people do seem happy with 3in1, it’s not that much thinner than the proper stuff, think it’s sae18? but I just prefer proper SU oil, it also doesn’t seem to need topping up as often.

What’s the timing set to, the book says 8*btdc for the 1.6 but myself and others often run up to 10*

Also 2.5 turns on the SU is more of just a base to get it running, I usually take mine out on a road test to fine tune and find where it runs best under real driving conditions, stopping now and again for a little tweak of the screw until I’m happy with it.

We used to use something like 10w30 in the dashpots years ago for SU carbs.
Carb icing can occur at reasonable temps - as Scottie posted it also depends on humidity etc.
I have not touched an SU for many years but ISTR there was a little pin you could move with a finger as a quick check of mixture (the pin moved the Piston up slightly) - but maybe not fitted to later carbs ?.
Good idea to check fuel pressure from elec pump - even the SU elec pumps could give probs when the points got burnt/dirty.

So i had a bit of a play at the weekend, the timing was set to 10 degrees, I've now changed it to 8. I've ordered some proper SU dashpot oil. In the meantime, I put in some 10w40 that I had spare. Noticeably thicker than the 3in1.
The above hasn't fixed the problem. Bogging down on accels and now getting a bit of back fire when using engine breaking approaching junctions etc. And eventually cutting out and difficult to restart straight away.

One other thing I did notice, with the air intake removed from the SU, when idling you can see the piston rattling around a bit despite the damper being full of oil. I notice that if I put a bit of pressure on the side of the piston to stop the rattle it steadies the idle a bit. this may be normal, or it may be totally unrelated. Just thought I'd put it out there. I'll get a few pictures of the carb but it looks to be in reasonable condition overall, i think!

I haven't managed to hook up a warm air feed yet, I'll try that too. Is it possible to have carb icing and not see any visible signs on the outside, or when looking into the carb when running at idle? The dash pot is cold, but not ice cold!

I've ordered a pressure gauge that can be used for checking fuel pressure and vacuum values. will try that with the proper SU oil and get back to you.