When I let the throttle go on my RE13'd 1275, I get a slight popping backfire It's very soft, not a bang. Also when I stop the engine I get a strage little pop in the exhaust pipe that changes note as unburnt gasses burn off slowly.
My timing is correct, and my mixture seems OK (set with a Gunson Colourtune), can anyone guess as to what might allow this to happen? Obviously something is out.

Mick

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

it's all normal mate.

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FOR SALE MInidlx, 1293, GR head, RE-13, GR worked Redline Manifold, 45 mm DCOE,pulsar dizzy , "S" Disc's, Mk II "S" box, 3.65 diff. Minator 10X6's On the loose

yeah i get that to, specially when i'm going downhill with the clutch out and slowing myself with the gears.

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Sunday Morning Mini Sprint http://www.youtube.com/watch?v=UtGuzqBQ32Q my "rendezvous"

Also check the compression with a compression guage. A burnt exhaust valve will also a pop sound out the exhaust.

You usually have other symtoms as well like a miss but its worth a check

Cool, thanks guys. The compression is tops as I had the head rebuilt recently when the camshaft went in.

taa

Mick

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

No - make sure the compression is still tops now as well
It could also be an exhaust valve not closing properly due to either a sticking valve (valve guide grabbing) or tappet clearance too tight.

If nothing else it eliminates some possibles.

Backfire in the exhaust is also symptomatic on an exhaust leak, usually up near the manifold.
It's burning unburned fuel....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Okey Dokey, I'll check those too.

Mick

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

maybe ur car is 'fully sick'

Yeah like 'Fully hospital sik' bro

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I wouldn't worry, ever since i put the RE-13 in mine does the 'pop' too..call it snap crackle and pop..minus the first two... pop..pop.pop

It's very quiet though..

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Starlet Conversion:
http://www.ausmini.com/forums/viewtopic.php?t=15484

Isn't this just valve overlap - ie both the exhaust and inlet valves are open for a very short duration?
If so, it did this in Stu's LS very "badly" (but i loved it), 286 Megadyne Scatter Pattern Kent cam... fantastic rally/fast road cam

Nah- my RE282 doesn't do it, nor did my RE13... both running 1.58:1 rockers.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I have also got 1.5 to one MS forged rockers. Hmmmm better look aty that manifold again...

I've got a question though, seeing that the exhaust is pressurised by the gasses exiting the engine, what compels the air to get into the exhaust via the gasket when there is a leak?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

At the manifold face there is a pulsating flow from pressure to vacuum in each exhaust port, not constant pressure.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.