Carb problems

[Nigel A]

My TR250 has been running on twin SU HS6’s for the last 35,000 miles with no problems. I change the plugs and points every now and then and the plugs have always been a nice colour.

When I removed the plugs this time they were black and sooty even though I hadn't touched the mixture settings for years. Running Rich for some reason was my immediate thought.

Using the lifting pins indicated it was running lean even though the plugs said otherwise. I did try leaning both carbs by one flat but this immediately caused the engine to falter.

i adjusted the carbs by making it run richer and eventually got it running so that using the lifting pins made the revs increase slightly at first and then settle down.

I assume something has worn - jets, needles or both. What do you suggest I do to get the plugs back to a good colour and have the correct mixture settings?

Nigel

[stuart]

Jets and needles for a start and check points.

Stuart.

[jerrytr5]

Float levels? Check the needle valves.

Jerry

[Peter Cobbold]

Sunken float?

[DRD]

Yes I'd check the float chambers aren't flooding first. It could be the floats or the needle valve could be blocked up.

[Nigel Triumph]

Choke mechanism stuck? Or counterfeit plugs?

Try refitting the old plugs.

Nigel

[RobH]

1 hour ago, DRD said:

It could be the floats or the needle valve could be blocked up.

You don't by any chance have Grose valves fitted? 

[Nigel A]

Thanks everyone for the advice
 

Grose valves changed to viton tipped needle valves along with new ethanol proof floats 3 months ago and appear to be working properly . Always buy plugs from Green Spark plug co so sure they are not counterfeit. Choke seems to working properly. Bosch spark plugs used for the first time and they cured my running on but sooted up just like the NGK plugs.

Was hoping there might have been a cheap solution so will follow Stuart’s advice and change jets and needles together with new points on order from DD.

Should I  just buy new jets and needles or is it better to buy a complete rebuild kit.

As it is still drivable I will leave it until the weather deteriorates and then add this to the list of winter jobs.

Nigel

 

Edited September 26, 2023 by Nigel A

[BlueTR3A-5EKT]

Do these HS 6 carbs have thermostat devices on the base of the jet ?   They cause lean mixture as the jets get heated.  There are a couple of ways to replace.  Either completely replace them with regular jets or replace the wax thermo pellet with a piece of solid metal like a new penny or two 

 

Kit is TT1559 from Moss

https://www.moss-europe.co.uk/su-jet-conversion-kits.html

 

Image of wax stat jet below. 

[RobH]

When you replaced the float valves and floats, did you check the height of the fuel in the jets?   It's possible the recommended float gap may not be right. 

 

 

Edited September 26, 2023 by RobH

[DRD]

1 hour ago, RobH said:

When you replaced the float valves and floats, did you check the height of the fuel in the jets?   It's possible the recommended float gap may not be right. 

 

 

Yes indeed, I find the float height needs setting with the needle valve closed otherwise you get flooding.

[Lebro]

I have recently purchased (for my boat engine) some spark plugs from Spark Plugs.co.uk

Very helpful people, & definetely do not obtain their stock from anyone other than the original makers or their distributors.

Would highly recommend.

Bob

Edited September 26, 2023 by Lebro

[Nigel A]

Hi Rob and DRD

Floats purchased from Moss and unlike old ones, these were not adjustable. After fitting I did check with a suitable drill bit and they seemed ok.

Is there something else I should have done?

Nigel

[RobH]

With the float chambers full, take the top off the carbs with the pistons/needles, and look down the jet.  The petrol level should be about 1/8 to 1/4 inch down from the top.  Any higher than that and the fuel can slop out of the jet under cornering/acceleration/braking when the car is on the road, making the mixture rich. 

[Nigel A]

Thanks Rob, 

I will check this properly when I  rebuild the carbs ready for a couple of European trips planned for next year. Reliability is top of my list.

Thanks Peter for the info on waxstats, it looks like I have normal jets so will replace with like for like.

Nigel

[DRD]

18 hours ago, Nigel A said:

Hi Rob and DRD

Floats purchased from Moss and unlike old ones, these were not adjustable. After fitting I did check with a suitable drill bit and they seemed ok.

Is there something else I should have done?

Nigel

The new black floats are adjustable as the metal arm can be bent. But if they are the white plastic ones they aren't and the only way is to put a washer under the valve seat to  raise the float. Also I've found that you need to push the float down so the valve is closed and then check the gap. If I just left it sitting under its own weight it resulted in the fuel level being too high and hence leading to very rich running.

Cheers Darren

[Nigel A]

Thanks Darren

They are the white non adjustable ones and I didn’t think about pushing the float down before measuring the gap.

will have to obtain the correct washers and then check gap again.

Nigel

[MKTR]

On 9/27/2023 at 1:05 PM, DRD said:

The new black floats are adjustable as the metal arm can be bent. But if they are the white plastic ones they aren't and the only way is to put a washer under the valve seat to  raise the float. Also I've found that you need to push the float down so the valve is closed and then check the gap. If I just left it sitting under its own weight it resulted in the fuel level being too high and hence leading to very rich running.

Cheers Darren

That is interesting Darren as I thought the advice was not to press down e.g. https://mossmotors.com/media/instructions/378-470.pdf 

However, it might explain some of my mixture setting issues if I have been doing it wrong.

Mark

[Lebro]

My opinion is that the spring inside the needle should not be compressed when setting float height.

If the viton tip is in good condition it should seal as soon as it touches the jet.

My prefered way of setting float heights is to set the fuel level inside the carb jet to be a couple of mm down from the bridge.

& with HS6 carbs that means a different float setting between the front & rear carbs, as the float chambers are on opposite sides of the carb, & the TR engine is not horizontal !

Bob

Edited September 28, 2023 by Lebro

[DRD]

4 hours ago, MKTR said:

That is interesting Darren as I thought the advice was not to press down e.g. https://mossmotors.com/media/instructions/378-470.pdf 

However, it might explain some of my mixture setting issues if I have been doing it wrong.

Mark

I've tried it that way and still had flooding and fuel leaking through the overflow. If you blow through the inlet you'll see it doesn't close until the float is pushed down.

[harlequin]

4 hours ago, Lebro said:

 

& with HS6 carbs that means a different float setting between the front & rear carbs, as the float chambers are on opposite sides of the carb, & the TR engine is not horizontal !

Bob

When I had HS6s on my TR6 I had trouble getting float heights right. I ended up finding float chambers from a 2500 TC which are unequal depth to allow for the inclined engine and the handed carbs.

George 

[Lebro]

Interesting, I did not know that .

Bob

[harlequin]

9 hours ago, Lebro said:

Interesting, I did not know that .

Bob

At the time I did work out what the difference was and was quite surprised by how much it was.

Since then I have swapped back to Strombergs and the SUs are relegated to a box in the back of the shed.

George 

[BlueTR3A-5EKT]

10 hours ago, Lebro said:

Interesting, I did not know that .

Bob

Nor did I.

 

[Peter Cobbold]

Nor did I.  However  the depression at the jet is enought to lift a column of fuel about 8 cm so the fuel level is not critical -providing it does not slop out up or downhill or in turns, or under braking. Peter