149 replies to this topic

[Marc13]

Quick update.

I've changed the wires that I needed to and the coil +ve is now wired to the top left of the fuse box. It starts much better, doesnt cough at all whilst trying to start and revs fairly well.

Took it on a 10 minute drive today and it does get very stuttery. Just seems to lose a bit of power and stutters, then revs more cleanly again. Happened quite frequently. If i dip the clutch when it happens, its seems to rev nicely. Its a bit disconcerting as it makes you think its about to die.....but it hasn't yet.

 

Any thoughts?

And considering the above - should I go through the process of checking the things on the carb, that Graeme suggested a few pages back?

[Ethel]

If you have access to a timing strobe check that first. Then I'd look at the air filter, if only because it's so easy to eliminate.

[sonscar]

If the plugs have ever been wet these symptoms often occur,drying them does not cure it.I personally find NGK do not like being flooded.Others may have different opinions.I find modern plugs do not like the use of choke and soon fail,again others may disagree.Steve..

[Marc13]

If you have access to a timing strobe check that first. Then I'd look at the air filter, if only because it's so easy to eliminate.

Thanks Ethel. Unfortunately I dont have access to a timing strobe. But I will check the air filter.

Could it be a fuel pump issue? Or is that likely to be a case of when it fails, it fails permanently?

[Ethel]

The carb holds enough juice to damp out the pump affecting throttle response.

 

You could remove the hose at the carb then crank the engine to see what it'll pump in to a jar. Just a teaspoon's worth per spurt would do  

[Marc13]

The carb holds enough juice to damp out the pump affecting throttle response.

 

You could remove the hose at the carb then crank the engine to see what it'll pump in to a jar. Just a teaspoon's worth per spurt would do  

I assume the its the hose that goes to the fuel inlet port that I need to dosconnect?

Should I pump the throttle when i start it  - or just turn the key?

[Marc13]

Just a couple of question on the hose/connections from the carb:

1) The hose that got chewed up by the fan is the one running left to right (just in front of the carb pot) in the 1st photo. The link for the replacement that a couple of you guys kindly posted for me shows a hose that changes in section at the ends, where it connects to something. If you look at the hose in question on the 1st photo, you can see that to the left it joins a branch, and not directly the carb. Its doesn't change section size there. If you look at the 2nd photo, which is where the hose goes to the right and down near to the fan and radiator, you can see the connection at the bottom and this too does not change section size. Therefore am I better just ordering a length of  standard rubber hose - but will I need 1/2 inch or 5/16ths?

2) What does this hose actually do? And what is it connecting to A) at the right hand end? B) at the left hand end after you follow the branch further left...see last photo for where it finishes (has the clamp around it at the bottom)?

3) I read somewhere that it is not necessary to connect a hose to the Crank Case Breather Pipe Connection at all.....you can just block it off! Is this true and what are the pro's and con's?

[Ethel]

Yes the carb fuel inlet hose. I doubt the pump is faulty, but it's quick & free to eliminate  before you start chasing other possibilities. The throttle on an SU has no direct effect on fuelling. It only controls the airflow as a means of limiting the engine speed. The air/fuel ratio is entirely down to the venturi created by the piston over the jet & how much the needle is obstructing it. (ignoring the choke if talking about a Hif).

 

If you're still unsure about the holey PCV hose just block it off where it enters the Y piece. 

[sonscar]

Crankcase breather and transfer case breather?Disconnecting them and plugging up the carb hole is possible but you will suffer oil fumes in the cabin and possible oil leaks.Steve..

[Marc13]

I dont fancy the oil fumes or leaks! So i will replace the pipe. Do you think its a 1/2 inch or a 5/16th?

Ethel- you have followed much of this problem. Regarding the choke / no choke. It still wont start (at all) without choke. And when starting from cold, once it has started with choke, if you push the choke back in, it doesnt like it even when pressing the accelorator. It only wants to run with choke (certainly when cold).
The juttery/stuttery thing i described whilst on the move, happens either with or without choke.

Ill test the pump - so I'm just looking for about a teaspoons worth of fuel with each crank?
I'll look at the air filter - am i just checking that its free of gunk?

[GraemeC]

You can’t just push the choke straight back in - if it needs it to start then it’ll take a good couple of minutes until the engine is warm enough to run without it.

[Marc13]

I'd start with 3 in 1 oil in the dashpot, if that doesn't give a clean throttle response try 20w50 engine oil (which is what was specified in the manuals).

Id remove the carb top and piston to check that the jet is clear, do the same for the float valve

Just started to look at the carb.

So I have took the dash pot off and the piston came away with it. See photos below.

1) Where is the jet....what am I looking for?

2) If you look at the photos you can see that 'needle' coming out of the bottom of the piston is slightly bent. Will this be causing an issue?

3) Is there something specific I need to check with the piston?

4) Does everything look ok with the carb - now that the top is removed?

5) How do I get to the float valve to check that is ok....remember I'm a newbie, so basic instructions please :)

6) Is there anything else I should check, while I am looking at this stuff?

Edited by Marc13, 18 October 2020 - 03:21 PM.

[Ethel]

First off, it's handy to prepare a spot where you can sit the piston down upright. Poke a hole in an upturned can or cardboard box to stick the needle through.

 

The jet's where the needle goes, right in the middle. Go down the ramp from the jet towards the engine and the hole at the bottom is the choke jet.

 

The needle's what's known as a bias needle. There's a little spring behind where it's secured in the piston that pushes it off centre. The idea is it sits consistently in the jet without a need to centre it & less risk of if sticking, even if it does actually get bent.

 

It does look a little dirty. Unscrew the black top to remove the damper piston, keep it upright to avoid getting covered in the oil. Lift the piston and damper tube will poke out the top so you can remove the retainer circlip (if present). then you can lift the dashpot off to reveal the piston & spring. Try not to drop anything or stretch/ kink the spring. Go careful with the cleaning, don't use anything abrasive, particularly on the inside of the dashpot and the machined face of the piston that runs over it.

 

If you stick a bit of hose on the overflow pipe & blow down it you should force petrol out of the jet, and choke if you pull out the control. You might have to stick your finger on the main jet to divert the pressure out the choke. It won't tell you anything particularly conclusive, but it will give you a bit of an idea of what's what.

 

Youtube has some great videos. There's a really good explanation of SU's from University Motors.

[Marc13]

First off, it's handy to prepare a spot where you can sit the piston down upright. Poke a hole in an upturned can or cardboard box to stick the needle through.

 

The jet's where the needle goes, right in the middle. Go down the ramp from the jet towards the engine and the hole at the bottom is the choke jet.

 

The needle's what's known as a bias needle. There's a little spring behind where it's secured in the piston that pushes it off centre. The idea is it sits consistently in the jet without a need to centre it & less risk of if sticking, even if it does actually get bent.

 

It does look a little dirty. Unscrew the black top to remove the damper piston, keep it upright to avoid getting covered in the oil. Lift the piston and damper tube will poke out the top so you can remove the retainer circlip (if present). then you can lift the dashpot off to reveal the piston & spring. Try not to drop anything or stretch/ kink the spring. Go careful with the cleaning, don't use anything abrasive, particularly on the inside of the dashpot and the machined face of the piston that runs over it.

 

If you stick a bit of hose on the overflow pipe & blow down it you should force petrol out of the jet, and choke if you pull out the control. You might have to stick your finger on the main jet to divert the pressure out the choke. It won't tell you anything particularly conclusive, but it will give you a bit of an idea of what's what.

 

Youtube has some great videos. There's a really good explanation of SU's from University Motors.

I have the pot sitting on a box and have unscrewed and removed the black top with the damper tube. The decorative chrome casing then cam away. Leaving the dashpot and the piston inside it. The dashpot will only lift to the top of the piston, but wont come away. There is something at the top of the piston that prevents the dashpot lifting entirely away....how do I get around this?

[Marc13]

 

First off, it's handy to prepare a spot where you can sit the piston down upright. Poke a hole in an upturned can or cardboard box to stick the needle through.

 

The jet's where the needle goes, right in the middle. Go down the ramp from the jet towards the engine and the hole at the bottom is the choke jet.

 

The needle's what's known as a bias needle. There's a little spring behind where it's secured in the piston that pushes it off centre. The idea is it sits consistently in the jet without a need to centre it & less risk of if sticking, even if it does actually get bent.

 

It does look a little dirty. Unscrew the black top to remove the damper piston, keep it upright to avoid getting covered in the oil. Lift the piston and damper tube will poke out the top so you can remove the retainer circlip (if present). then you can lift the dashpot off to reveal the piston & spring. Try not to drop anything or stretch/ kink the spring. Go careful with the cleaning, don't use anything abrasive, particularly on the inside of the dashpot and the machined face of the piston that runs over it.

 

If you stick a bit of hose on the overflow pipe & blow down it you should force petrol out of the jet, and choke if you pull out the control. You might have to stick your finger on the main jet to divert the pressure out the choke. It won't tell you anything particularly conclusive, but it will give you a bit of an idea of what's what.

 

Youtube has some great videos. There's a really good explanation of SU's from University Motors.

I have the pot sitting on a box and have unscrewed and removed the black top with the damper tube. The decorative chrome casing then cam away. Leaving the dashpot and the piston inside it. The dashpot will only lift to the top of the piston, but wont come away. There is something at the top of the piston that prevents the dashpot lifting entirely away....how do I get around this?

 

i've sorted it - the tiniest of retaining clips. Its a bit gunky in there. I'll give it a gentle wipe down