22 replies to this topic

[miniGTS]

Twin Su inlet leaking fuel at the manifold, only slightly. And I only see it when I turn the engine off and a few drops run along the gap between the head and block on the driver's side. I've narrowed it down to the exhaust manifold and inlet manifold shoulders being slightly different heights. I've created a step in the thick washer but maybe not enough.

I'm wondering if there's something else I can do? I'm thinking to try 1mm copper wire between the washer and inlet or is that a bad idea?

I'm thinking the copper will compress and push against the inlet shoulder or since the inlet is alloy, will it likely dent the alloy...

Any suggestions?

[nicklouse]

Never been a fan of the step as it can clamp one side better than the other. I tend to put a big grove down the center which allows equal pressure on both sides.

 

of just get one of the manifolds machined.

[miniGTS]

It'll be a bit of a mission to get the exhaust manifold machined because it doesn't go in or out with the engine in. So I'll give it a go with a groove down the centre and see if that does it. I assume the groove should be on the inside, so facing the manifold and when tightened up it'll bend that small amount to provide the necessary pressure?

[Spider]

If it's leaking fuel that you can see, then I don't think there's a manifold leak (which usually shows up as a vacuum leak / high idle speed) but rather the float bowl level is set too high or the needle and seat in the float bowls are not sealing off for what ever reason.

[miniGTS]

I'll check the float bowls as well. It was overflowing previously even though the carbs were rebuilt with a full kit by someone who comes highly recommended.

[Spider]

Check the fuel pressure, if that's too high, they'll do the same.

[miniGTS]

It's a mechanical SU fuel pump. I assume that shouldn't be too much fuel pressure

[Spider]

It's a mechanical SU fuel pump. I assume that shouldn't be too much fuel pressure

 

I've actually had the most trouble with them over-pressurising, in particular, as they age. I haven't bothered to pull them down to see why, but I've had a few do this.

[mini-mad-mark]

It'll be a bit of a mission to get the exhaust manifold machined because it doesn't go in or out with the engine in. So I'll give it a go with a groove down the centre and see if that does it. I assume the groove should be on the inside, so facing the manifold and when tightened up it'll bend that small amount to provide the necessary pressure?

Obviously I don't know your exact parts and there is no pic but from most things I have read/seen its usually the inlet that is thicker than the exhaust manifold?

 

Mainly I wanted to ask what sort of exhaust manifold you were using that couldn't be fitted/removed with the engine in situ? 

I thought there were only two main types, LCB (easy to fit/remove with engine in) or freeflow (slightly more tricky but still do-able especially if the engine stabiliser(s) are removed to allow the engine to rock forward)

 

There is a third, a race 3-1  - never seen one fitted but I assume they would be similar to an LCB to fit as they appear to use a 3 branch connector similar to the Y-piece of an LCB

[miniGTS]

 

It'll be a bit of a mission to get the exhaust manifold machined because it doesn't go in or out with the engine in. So I'll give it a go with a groove down the centre and see if that does it. I assume the groove should be on the inside, so facing the manifold and when tightened up it'll bend that small amount to provide the necessary pressure?

Obviously I don't know your exact parts and there is no pic but from most things I have read/seen its usually the inlet that is thicker than the exhaust manifold?

 

Mainly I wanted to ask what sort of exhaust manifold you were using that couldn't be fitted/removed with the engine in situ? 

I thought there were only two main types, LCB (easy to fit/remove with engine in) or freeflow (slightly more tricky but still do-able especially if the engine stabiliser(s) are removed to allow the engine to rock forward)

 

There is a third, a race 3-1  - never seen one fitted but I assume they would be similar to an LCB to fit as they appear to use a 3 branch connector similar to the Y-piece of an LCB

 

The exhaust in my case is slightly thicker than the inlet. It's a LCB style exhaust manifold that a company here in South Africa used to make for the mini many years ago. The Y-piece is bonded to 2 pipes (center one and 2 end ones into 1) from the manifold. The Y-piece fits over those 2 pipes and it never used clamps but bonded on with gun-gum or something plus years of rust it's near impossible to seperate. Then the Y-piece was welded to the 1st section of pipe where they fitted a flexible type union that the rear part of the exhaust attaches to. I'll be getting the exhaust changed to a smaller diameter pipe and will ask them to make it so that it can be seperated more easily at the Y-piece.

[miniGTS]

After making the step in the thick washer a bit bigger it seems to have solved the fuel leak that I noticed.

[sonscar]

There shouldn't be fuel there to leak.Steve..

[miniGTS]

There shouldn't be fuel there to leak.Steve..

At the inlet and head?

[68+86auto]

After making the step in the thick washer a bit bigger it seems to have solved the fuel leak that I noticed.

 

You've fixed the symptom but not the cause. There should never be fuel sitting there as a liquid, it could've now contaminated your oil too. When the engine is running, the fuel passes thru as a vapour. Your issue is one of the ones that Spider listed.

[miniGTS]

Ohhh, right. I had the float bowl open yesterday as well and I'd say it was a bit over half full on the side where I noticed the leak. It's also possible that I freed up a stuck needle valve when I opened up the float bowl.

Some other symptoms that may or may not confirm an issue with either the float heights or fuel pump are, black plugs, when I push the carb lift pin it sounds like it's about the choke off and if I keep it up then it does choke off..though I thought that suggests too lean? Turning the jets in also makes it run worse and it started to 'pop' like little mini backfires.

The 2 air feeds that would be connected to the engine breathers are connected to each other because it seems to idle better that way. Connecting to a breather has a similar effect to turning the jets in. So, again suggesting too lean?

Just some other info about the engine, it's a SA big bore 1100 on 40thou oversized pistons, lightened and balanced flywheel. The head has the standard 1275 valves with double springs and is gasflowed and slightly ported. Carbs are twin hs2 that's been rebuilt with new butterflies, spindles, springs, jets and currently has a 3in1 oil in the dashpots.