44 replies to this topic

[timmy850]

I assume this is a 1275 engine? 

 

What's the diff ratio?

 

What is your static compression ratio?

 

Have you checked the throttle cable will open the throttle blade?

 

Has it got a heavy flywheel?

[PACINO]

I'm no expert but after watching the video, I'd say your ignition advance isn't working properly. Has it still got the 123 ignition fitted?
 
If it were a normal distributor I'd guess the advance weights were maybe seized

Hi 84City! Yes, I've still got 123Ignition total electronic dizzy.

[PACINO]

If it were mine I would be to get it out in the country and run it up through the gears the way you did in the last bit.

Cheers Lplus!
Yes, next weeks I'd like to get open roads ... to check really the engine, making more kilometers.

Edited by PACINO, 17 October 2024 - 01:30 AM.

[PACINO]

I assume this is a 1275 engine? 
 
What's the diff ratio?
 
What is your static compression ratio?
 
Have you checked the throttle cable will open the throttle blade?
 
Has it got a heavy flywheel?

Hi Timmy!
-It's a 1310cc engine.
-I don't know the diff ratio. Two weeks ago, I did a compression test, and the result was 150 PSI on the four cilynders.
-I understand that you are asking me if stepping on the accelerator fully opens the carburetor butterflies. Is that so?
-Yes, I've got a heavy flywheel. Is the original.



Luis

[timmy850]

A compression test tells you something different than the compression ratio

The compression ratio is calculated using the engine capacity, head volume and piston dish (and a few other things). Did you calculate it before you assembled the engine?

Engines need to be built as a complete assembly for them to work properly. You need to match:
Camshaft
Compression ratio
Cylinder head
Diff ratio
Distributor advance curve
Carburettor

Sounds to me like yours isn’t working together as a complete unit

[Lplus]

 

If it were mine I would be to get it out in the country and run it up through the gears the way you did in the last bit.

Cheers Lplus!
Yes, next weeks I'd like to get open roads ... to check really the engine, making more kilometers.

 

Further thoughts on the part throttle behaviour, it's possible the mixture is rather weak at part throttle which can lead to a feeling of hesitation even though the engine doesn't actually misfire.  Clearly under acceleration the mixture is rich enough to give plenty of power.  It will be easier to diagnose when the engine is fully run in.

[gazza82]

Which needle are you using in the carb?

[PACINO]

A compression test tells you something different than the compression ratio

The compression ratio is calculated using the engine capacity, head volume and piston dish (and a few other things). Did you calculate it before you assembled the engine?

Engines need to be built as a complete assembly for them to work properly. You need to match:
Camshaft
Compression ratio
Cylinder head
Diff ratio
Distributor advance curve
Carburettor

Sounds to me like yours isn’t working together as a complete unit

Hi Timmy! No, I've never calculated the compression ratio. To do this, they need some value that I don't have. I've the measurements of the new pistons, cylinders, diameter of the intake and exhaust valves, but not of the cylinder head chambers.

[PACINO]

Which needle are you using in the carb?

Hello Gazza! Twin S.u Hs2 carb with GY standard needles.
Regards

[timmy850]

The GY needle was standard for a 998 Cooper twin carb. If you have a 1275 with more aggressive cam and much more displacement then you will likely need a proper tune to get the correct needles

[Lplus]

The GY needle was standard for a 998 Cooper twin carb. If you have a 1275 with more aggressive cam and much more displacement then you will likely need a proper tune to get the correct needles

The 998 cooper also had blue springs whilst all the other coopers had stronger red springs.  Given the OP's engine is a 1310 those needles and springs are too weak especially at larger throttle openings, though under acceleration the autorichening due to the dampers will mask that so it does seem to accelerate well.

 

The 1275 S had M needles as standard which are significantly richer above half throttle. It might be worth the OP getting some richer needles prior to any sustained high speed driving.  I still think it will improve anyway as it gets more run in.

[PACINO]

Thanks guys! It is easy to adapt "M" needles and they are not excessively expensive. A few years ago I fit on "AH2" needles which are a little shorter and thinner, and they were too rich. An engine does not run better by introducing more petrol in it. Another thing is the "M", which possibly, as Lplus says, is more appropriate for this new engine.
I wear blue springs but I've also worn red springs. I've them at home.

The cylinder head has big valves but the chambers were NOT enlarged. It is a delicate job (everything must be cubed at the end to do it correctly) and it is not cheap.

When I have money, I'm going to buy a cylinder head from Calver. Besides being a humble and excellent guy, I have not met anyone who knows more about these British engines.

Luis

[Lplus]

Thanks guys! It is easy to adapt "M" needles and they are not excessively expensive. A few years ago I fit on "AH2" needles which are a little shorter and thinner, and they were too rich. An engine does not run better by introducing more petrol in it. Another thing is the "M", which possibly, as Lplus says, is more appropriate for this new engine.
I wear blue springs but I've also worn red springs. I've them at home.

The cylinder head has big valves but the chambers were NOT enlarged. It is a delicate job (everything must be cubed at the end to do it correctly) and it is not cheap.

When I have money, I'm going to buy a cylinder head from Calver. Besides being a humble and excellent guy, I have not met anyone who knows more about these British engines.

Luis

AH2 are richer than M, so maybe M would be closer to the optimum.

[stuart bowes]

An engine does not run better by introducing more petrol in it.

But it does run better by having the right amount of fuel supplied

I think what they're suggesting is that it's possible you're running lean at higher revs / more open throttle

[PACINO]

An engine does not run better by introducing more petrol in it.

But it does run better by having the right amount of fuel supplied

That's true. Thanks Stuart!