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Might be a red herring.

What tappet clearances are you using?  
The cam in my 3 A requires 0.018” inlet and 0.020” exhaust.  This is very different to the standard and many other sporty cams.  Would incorrect tappet clearances affect fuelling?  We all know about the possible clatter of course.

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On 7/19/2022 at 7:26 PM, Bfg said:

^ I was just writing in reply much the same, you posted first.  B)

"I would have thought that one needs to identify the camshaft first. On a bench a dial-gauge would be used to measure a cam's lift and its ramps, and that would be in reference to tdc. 

With the engine together and in the car I would have thought a dial gauge down onto #1 cam follower would achieve the same. From that data you may be able to identify its spec., and then inquire as to the correct timing "  

However, if the engine is performing that willingly and spinning at 5000 rpm without bending a valve, nor spitting back through the carbs or inciting explosion of un-burnt fuel in the exhaust - I would doubt if its timing might also be the root cause of that much more fuel consumption. 

Pete

 

 

That is also my view on cam timing. If it was out enough to impact on fuel consumption there would be other symptoms as you describe.

 

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On 7/19/2022 at 7:43 PM, BlueTR3A-5EKT said:

Might be a red herring.

What tappet clearances are you using?  
The cam in my 3 A requires 0.018” inlet and 0.020” exhaust.  This is very different to the standard and many other sporty cams.  Would incorrect tappet clearances affect fuelling?  We all know about the possible clatter of course.

Yes, a good point. I have them set at .015". There isn't any significant tappet noise and she performs well.

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On 7/19/2022 at 8:11 PM, Ian Vincent said:

If you have a strobe, what is the ignition advance when the engine is ticking over at 900 rpm?

I have just got my strobe back from a mate and yes, timing could have been an issue. It was set at about 3-4 deg advanced at idle. I have doubled that to about 8-10 deg advanced, similar to my other car. The engine idles better and when the rain stops I'll give it a test drive and adjust from here.

I thought it was set correctly but I must have cocked it up somewhere along the line.

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Re the tappet settings, I have been instructed to set the tappets at 23/25thou on my fast-road cam. I also have 86mm pistons and extractor exhaust.

At first I thought it was a joke but at those settings the valve openings and closings match the prescribed degrees (clock gauge measurements with a calibrated cardboard disc stuck to the pulley)

There is the tappet noise of course. Had I known about that before starting out and buying all the "improvements" I would have settled for standard and the quiet life and the smooth idle!

And she is thirsty.....

 

 

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That timing may still be a bit retarded. You need to set it about 32 degrees when it’s “all in”. With a 10 degree cam in the distributor that will leave you 12 degrees at idle. 

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Did a check on my MPG yesterday when I filled up, about 50% local driving, & 50% on a longer trip returned 32 MPG

Bob

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I too have been suffering from poor fuel consumption about 24MPG in mixed running my TR2 87mm pistons,  a low port head with 1.5 mm SU carbs which I have recently rebuilt.

It was about the same before I rebuilt the carbs and replaced all the rubber and seals for ones that should be Ok with E10 fuel. It was a rather disappointing result.

I then made further investigations, replaced a failed vacuum advance unit and reset the timing a bit more advanced. the result was 31 MPG over similar mixed running including the heat wave which was very hot for the east coast of Scotland.

The timing and advance curve must have a more significant affect on the MPG than I believed. 

I have now filled up with E10 and will see how it goes over the next couple of tanks of fuel.

 

Ewan 

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On 7/22/2022 at 6:28 AM, Drewmotty said:

That timing may still be a bit retarded. You need to set it about 32 degrees when it’s “all in”. With a 10 degree cam in the distributor that will leave you 12 degrees at idle. 

That sounds a lot. Manual says 4 degrees BTDC to set, with maximum advance being 15 degrees. I suppose modern fuels allow for more advance than when the cars were originally made though.

Ralph

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23 minutes ago, Ralph Whitaker said:

That sounds a lot. Manual says 4 degrees BTDC to set, with maximum advance being 15 degrees. I suppose modern fuels allow for more advance than when the cars were originally made though.

Ralph

Exactly. 

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1 hour ago, Drewmotty said:

Exactly. 

Problem with the manual is that it does not state crankshaft or distributor degrees.

15 max at the distributor is 30 at the crank.   That makes sense as the yard stick is 32 degrees max on petrol engines without any special gubbins.

I have often wondered if the manual stated 4 degrees should be distributor not crank.

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          I have a TR2 instruction book which recommends 80 octane fuel so perhaps the workshop manual has this figure in mind when setting up the engine.

          Cheers

          Richard

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Posted (edited)

Most of us here use BP 98. A rule of thumb as a starting point is to have the ignition about 8-10 deg advanced on the crank pulley mark. Depending on the engine adjust it to just ping, then back it off a few degrees.

We are currently on a 4-day tour through western NSW, I'm in my daily driver TR2. I'm getting 30mpg which I'm happy with. I prefer it a bit rich on long hight speed runs.

I'm yet to get the car with the poor consumption out to see how it goes.

 

 

IMG_1338.jpg

IMG_1339.jpg

Edited by John McCormack
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