11 replies to this topic

[Moon_cookie]

Hi
 
 
So my mini was running poorly and wouldn`t star when it was cold so i decided to do a carb rebuild on my HS4.
Found out the jet was seized and the needle was bent.
Straightened the needle, changed the jet and refitted the carb to the car. but i can`t get it running
 
 
 
Feels like i have checked everything; there is fuel pressure, fuel to the bowl, no fuel leaks, fuel thru the jet, spark, the needle is adjusted and moving freely, the piston is moving as it should, there is oil for the piston and the choke is working. Did the "rough mixture tuning" as the manual says. Also tried starting it without a air filter, with the old filter and with a K&N filter. No luck...
 
 
I got it running a couple of times using starting gas, it would either slowly choke itself out or begin to gain and gain Rpm until i turned it off. Got it running rough one time with the help of starting gas, began adjusting the mixture and it died again.
 
 
Haven`t found anything wrong searching the forums and manuals for tips. the only thing i found was that the needle is supposed to be able to move a little bit inside the cylinder. Mine is stiff and won't budge.
 
 
Its a old aftermarket 1275 and even older HS4, when comparing to photos online my carburetor is missing the crankcase ventilator(?) could that mean i have a knock off carburetor that doesn`t fit the jet kit i bought? 
Before the rebuild the car was running with a homemade air filter and original exhaust.

 

UPDATE

 

Thanks for all the help!

 

I am pretty sure i figured it out;

Between the carburetor and the manifold there is a 2cm plastic spacer,  i only changed the gasket on the carburetor side, and noticed moisture between the spacer and the metal bracket holding the throttle. I removed the spacer; its very uneven with lots of scratches. 

 

Ordered new gaskets and bought some gasket-glue.

Going to try and save the spacer, if not i will just make one. 

Update when it arrives. 

Edited by Moon_cookie, 20 September 2023 - 02:55 PM.

[68+86auto]

It seems the pictures haven't worked. Can you try again so we can see if there is anything obvious. Make sure any of the vacuum ports are blocked off or connected.

I am not sure what tube you are talking about, it might be the overflow which does not matter. It was only fitted minis from sometime in the 80s?

[Moon_cookie]

It seems the pictures haven't worked. Can you try again so we can see if there is anything obvious. Make sure any of the vacuum ports are blocked off or connected.

I am not sure what tube you are talking about, it might be the overflow which does not matter. It was only fitted minis from sometime in the 80s?

after cocking about with the pictures for a while i found out what its called;

its missing the crankcase ventilator and the lifting pin 

[Steam]

The jet tube fitting into the fuel bowl can be PITA, the pipe can twist blocking fuel delvery or the o ring can become displaced and block the outlet

[sonscar]

Check for air leaks around where you have been working.You may have fixed the original fault and inadvertantly caused another.Steve..

[68+86auto]

It seems the pictures haven't worked. Can you try again so we can see if there is anything obvious. Make sure any of the vacuum ports are blocked off or connected.

I am not sure what tube you are talking about, it might be the overflow which does not matter. It was only fitted minis from sometime in the 80s?

after cocking about with the pictures for a while i found out what its called;
its missing the crankcase ventilator and the lifting pin

Not all of them have the lift pin or crankcase vent port. If yours has these or the holes for them but nothing is connected then that is an issue.

If you do not have the crankcase ventilation port then a PCV should be fitted between the crankcase breathers and a manifold vacuum port.

The lift pin is unimportant as long as there is no hole for it.

[gazza82]

Straightened the needle

That may not work .. you probably need a new one ..

[Icey]

Straightened the needle

That may not work .. you probably need a new one ..

I’d agree with this. The needle dimensions are incredibly precise, the chances of getting it back into the right shape is highly unlikely. For all of £10-15, it’s far easier to change it (assuming it’s not been fettled).

[Ethel]

 

Straightened the needle

That may not work .. you probably need a new one ..

 

If it was actually bent to begin with. HS4 would likely be a swing needle.

[Lplus]

 

 

Straightened the needle

That may not work .. you probably need a new one ..

 

If it was actually bent to begin with. HS4 would likely be a swing needle.

 

The OP stated it was fixed in the carb and  not moving a bit as he expected.  Sounds like a fixed needle carb, and as long as the needle is straight enough to stay within the jet hole without binding it should be adequate to get the engine going.   The needle diameter is precise, but the location of that diameter in the jet hole is not so important.  After all the swing jet needles are always biased to one side.

[tarnofsky]

I just sortet a non-starter I recently bought. There were a number of issues that also might affect your car:

Vacuum pipe from distributor to carb not airtight (check for cracks in rubber connectors),
carb seals against maniflow, sandwich plate, throttle spring plate leaking,
worn carb spindle allowing side air draft (move spindle with spring disengaged - any play an it needs an overhaul or change of the carb),
inside the carb bell housing:

check for any soot blocking the free movement of the piston - minor stains on the wall can block - use non abrasive cleaning material only

Check the slot in the piston with your tumbnail - if you slide along the slot with your thumbnail and you feel any dips, that might be where the piston sticks. Can be smoothened with a very fine file or exchanged together with the bell.

Exchange the spring for a correct (in most cases red) spring.

Use 20W50 engine oil in the damper and top up to correct level

 

In any case: throw away the old needle and use a new one. You can't correct any bends in a way that would fully correct it.

 

Or the easy way if your budget allows: buy a refurbished HS4. I recommend Andrew Turner Carbs (www.su-carbs.co.uk). I have bought 3 carbs from them and they all work very well.

 

Always clean any mating surfaces perfectly and ALWAYS use new gaskets.

[coopertaz]

is breather pipe connected to carb? if so try brake cleaner around inlet manifold and carb mounting flanges sounds like you have introduced a leak there while doing other work