Cold start - again

Cold starting is an issue on my 1968 420G. It needs lots of Easystart and a very gentle foot to coax it into life. Once warm it runs well and evenly, mixture and idle are set nicely.

So I have read most of the forum’s posts on the ‘hisser’. I undid the Otter switch and checked the solenoid was working. It was. I then tried to start it without the Hisser connected and that was better, but it still idled at very low rev’s and needed as much coaxing into life as before… gentle foot, if pressed too hard too quickly, it died.

Then I got it running by itself at very low idle and decided to re-connect the Otter switch. Initially nothing happened, no hiss and no engine idle change, but then with a throttle blip, the solenoid clicked, the needle sank all the way down and the engine died immediately.


Plugs are clean, no black smoke at all.

I’m thinking the adjustment on main carb as well as the hisser may be too lean…?

I’m going to take the hisser apart to clean/inspect and see if I can find the blow-back valve to see if that may be sticky, though some on the forum state that would not have been fitted on my car…

Then I think I will try adjusting the carbs from step one. I have the manual.

Any other suggestions very welcome.


a toggle switch under the dash makes a HUGE improvement buy passing the otter switch.
Then turn up the idle screws…start it at 1,300 rpm with the switch on, slowly back it down till your happy
Modern gas is garbage for old cars, filler not gas.
Vapor lock, hard starting and destroying internals is common if it sits in ethanol gas too long.
In the states if you runvr racing ynleaded fuel or PURE FUEL you would think you put a new engine in the car.
good luck

Are you actually getting fuel to the hisser? The fuel passage can sometimes block up with rusted jet spring, so when the solenoid opens the hisser it ends up working as a massive vacuum leak.

How do I check for fuel?

There should be a small triangular Al plate straddling the hisser needle. That plate is above, and partially covers, the air intake of the hisser. Those bores should have a bit of fuel in the bottom of them. Just stick a piece of string down, if it comes up wet, then you’re getting fuel to the hisser.


You can also just jump in with a 12 volt battery , you will here it click.
If its working the idle will go up drastically.
good luck
My markII was frustrating till I put a toggle.
It runs soooo sweet now.
ps if its working do not keep it on for more than a minute, you will load up the plugs

Hi all,

I took a look today and there was no fuel at the bottom of the two side pipes of the hisser. However, I had forgotten my key so could not engage the fuel pump. I take it there is only fuel there when the pump goes as if it stands for a while surely the petrol in there will evaporate?

Or should there be fuel there at any time?

If the fuel passage is blocked with… rusted jet spring (what’s that?), how to I clean that out?

Anyway, I took a piece of tube and blew/sucked into one of the two holes next to the central intake hole and I could not push or pull air through… but not sure if that was supposed to be like that… ? The other was the same. The central one blew back into the hole where the needle was (I had taken that out).

I also cleaned out the float chamber of the carb that the hisser is connected to.

Whilst I had the needle out I saw that the needle adjustment screw was all the way down - tight - so that may just cut the fuel off altogether when the needle drops. I have ‘opened’ it a little, see what happens tomorrow, IF I don’t forget the key again! :woozy_face:

Wish me luck.


If the fuel passage is blocked with… rusted jet spring (what’s that?), how to I clean that out?
No 11

The “slow run” adjusting screw acts on a lever which pushes the jet down, against the jet spring (which will push the jet up if you slacked the screw). This spring is at the bottom of the carb, so any water that collects in the fuel reservoir will cause it to rust. Every now and then I find a carb with this spring rusted away.

The hisser is fed with fuel by a pipe:

If this pipe is blocked, then the hisser won’t get any fuel.

Unfortunately, the banjo bolts holding the pipe tend to be rusted to the bottom of the float chamber, so it’s best to avoid taking these parts apart - check with compressed air that the passage is open.

Thanks, that will be it then as definitely it is not getting any fuel. Bottom of the intakes are bone dry. As soon as the hisser engages (even with a warm engine) the needle drops, hissing starts and the car shuts down immediately… so the hisser effectively just acts as a vacuum leak.

I did try and blow through the bottom of the 1st carb float chamber, but got nowhere as my blowpipe was too large in diameter. I may have to try and take the banjo bolts off, if they are not too rusty… I’ll have a look.

In the meantime, lots of Easystart to get going!


My pic , wrong spring :roll_eyes:

undo the ASC jet spring nut, and take the needle & spring out, see if its ok

adjust the nut & needle about halfway (or as per FSM)

I doubt its blocked or the attached carb will be starved, car wont run

dont drop the spring & valve inside the ASC down into the engine bay (if you take it apart),
have found a few while dismantling cars, that would be an expensive mistake

they can be a fiddly mongrel thing to get right on a tri-carb, but once working, should start the vehicle instantly

The ASC jet spring is fine and I adjusted the needle to about halfway, but no joy, hence my conclusion that the bottom spring must be at fault.

I will have a go at removing the bottom banjo’s to see if the is the case next week.

I did drop the copper top of a spark plug down the cylinder hole once, but fortunately someone had one of those grabber thingy’s on a stick. I bought one myself immediately to have alongside my magnet on a stick. :slight_smile:


Paul take the front carb off complete with ASC. its far easier to undo the banjos etc on the bench. take photos before you strip so you get the correct orientation when you rebuild.

Ha! Result!! :smile::smile::smile:

I decide to leave the carbs in place and attempt to remove the banjo’s from underneath. Not too awkward except for my right forearm now has indents and scratches from the anchor bracket from carb no 1 throttle return spring.

The bolts are 5/8 and no 21, the latter being a standard plug removal socket.

Both have washers between the heads and the ‘bridge’ and the ‘bridge’ and the carb/hisser respectively. Make sure you don’t lose them!

This is what they look like when they come out. One washer was stuck underneath the carb so is not in the picture.


After cleaning the bolts were unplugged again. Then the bridge. It was totally stuck, completely blocked. It took 30-45 minutes and the tools in this pic to finally get it unblocked. I nearly drilled out the end plug to put a small drill bit through the bridge, but a few bent nails and a thick piece of metal wire cut off at an angle did the trick.


Once I had the banjo’s back in, car started up first turn and hisser works perfectly!

Well worth the effort.