22 replies to this topic

[sam138]

I’ve just replaced my cylinder head with a new stage 3 unit and installed a new bk450 gasket. I’ve correctly torqued the head down in order and adjusted tappets. Upon starting it seemed ok then when I drove it I could not get past 40mph and it got worst. When I got it back home it was running rough and would cut out if no gas was applied.

As per below videos it shows rough running and a quick video of applying some vacuum back up exhaust system which highlighted possible leak on y piece manifold join. Do you think from the video that it’s just simply that exhaust leak ?

I’m aware of the leak from the thermostat housing in video.

https://m.youtube.co...h?v=Uu9zYML72-c

https://m.youtube.co...h?v=Ks3mciAFrkc

[sam138]

Just to add I have NGK BP6ES spark plugs running. Should these be changed on a 1275 cooper with stage 1 kit and upgraded head ? Maybe to BP7ES as a colder spark plug ?

[Fast Ivan]

You’re going to need to get this set up right with regards to needle, fuelling and timing

[unburntfuelinthemorning]

Have you just upgraded from standard?  Is it just the head you've changed or have you added the stage 1 kit too?

 

Have you changed the carburettor needle?  What needle is it?

 

Have you adjusted the idle mixture?

 

Has the ignition timing been touched?

 

Have you checked for air leaks between the carb and the head?

 

It won't be the exhaust leak.

 

The BP6ES will be fine.

[sam138]

Hi,

It’s just a cylinder head change I’ve not touched anything else. The car had a stage 1 kit already and changed needle which was set up by Peter Baldwin.

Edited by sam138, 29 May 2019 - 07:19 AM.

[RooBoonix]

You've fitted a head that flows alot better than before and not adjusted the fueling and timing to suit, as Fastivan said above it will all need setting up again

[sam138]

Thanks for the reply, I understand it needs setting up but I can’t keep it running and it sounds like it’s running on 3 cylinders and will cut out without gas applied.

When I applied a stage 1 kit I could have the car started and drive to the rolling road no problem.

[johnv]

Next thing to do then is a compression test? I think you're right, it should run OK with the old settings, you just won't be getting the best out of it

[Its a min]

Sounds similar to when I fitted a stock 295 head to mine. It turned out that the compression ration was completely out due to larger chambers in the head and not being skimmed to match.

 

Was your stage 3 a stock head and did you work out the chamber volumes/compression ratio?

[johnv]

Sounds similar to when I fitted a stock 295 head to mine. It turned out that the compression ration was completely out due to larger chambers in the head and not being skimmed to match.

 

Was your stage 3 a stock head and did you work out the chamber volumes/compression ratio?

 

I don't think that the symptoms would be that extreme, realistically there wouldn't be more than 1 or 2 cc difference, and that wouldn't make such a difference in the CR to warrant those problems 

[sam138]

Worked out chambers at 19.5cc in the head
The block has been skimmed once
Pistons are 21963 standard believe 8.3cc
Standard bore 1275
Working it out I’m coming out at 10.5.1

[sam138]

I’ve put a new set of spark plugs in and fixed the thermostat housing leak. Thinking maybe the coolant leak has got into the plug on the right hand side when I started it first time.

Will give it a start tomorrow and see how it fairs.

Failing this will try a compression test.

[cal844]

Compression test and also check the plugs, sounds like you need a needle change to give better fuelling

[nicklouse]

What the was going on in the first video!
Second vid sounds like a bit of a knock going on there.

Have you checked and set the idle mixture? I would also see what the timing is. I presume you have not moved the dizzy.

Have you looked at the plugs?

I would also check the compression.

[Fast Ivan]

Thanks for the reply, I understand it needs setting up but I can’t keep it running and it sounds like it’s running on 3 cylinders and will cut out without gas applied.

When I applied a stage 1 kit I could have the car started and drive to the rolling road no problem.

Have you tried pulling each lead off in turn to establish which cylinder is firing?