S1 Etype Fuel problem

ChrisC · Post by **ChrisC** » Wed May 21, 2014 1:54 pm

My learned friends...

For some reason my Etype has just started to have performance issues. On checking the carburettors I found one dash pot damper that was not doing any damping (so was replaced) but more worryingly there was a lot of dark coloured fuel sitting in the carb body and manifold...

Initially I suspected flooding but the carburettor floats are set to have the fuel level somewhere around 5-8mm below the jets and they dont flood when the fuel pump is turned on. *** In the picture the jet has just been set at the top of the bridge ready for re-setting - I merely took the picture before removing the fuel....

The fluid is very definitely petrol and logically the only way it can get that colour is to be running BACK from the inlet manifold picking up carbon on its way. So why on earth is that happening.

Performance wise - the engine continually 'jerks' in a minor way and the power curve drops off at 3000rpm... this problem happened suddenly and I can't for the life of me get the engine running correctly now.

Any ideas? I'm running an SU electronic fuel pump (if that matters)

vacbag · Post by **vacbag** » Wed May 21, 2014 3:43 pm

Chris.
Have you checked whether the choke has stuck closed or part closed.

Steve.

ChrisC · Post by **ChrisC** » Wed May 21, 2014 4:13 pm

Yuh, the choke is fully released but I should have said that the issue is on all 3 carburettors...

MarekH · Post by **MarekH** » Wed May 21, 2014 5:12 pm

Are you sure it isn't picking up rubber, rather than carbon?
Are you using premium grade fuel - is there any ethanol in it?

Take a sample of the fuel from the tank and see whether immersing the rubber parts in the fuel path gives you the same result.

kind regards
Marek

ChrisC · Post by **ChrisC** » Wed May 21, 2014 5:43 pm

An interesting thought Marek but the fuel in all the carburetor float chambers is clear so it is become 'dirty' after it has been sucked through the carburettor body.

Its not so much the colour I am worried about it is why there is so much petrol sitting there in the first place...

ChrisC · Post by **ChrisC** » Wed May 21, 2014 6:41 pm

interim update...

I have no idea why I tried this.... but I have just opened up the spark plug gaps from 25 to 40 and the engine is a LOT smoother now. I had forgotten that I reset the gaps to factory standard a little while back. Perhaps my high output electronic ignition didn't like the small gap

Now I have a smooth tick over and 'almost' no fuel sitting in the carb body. The engine also pulls better but is still falling off at 4000 revs so I suspect I still have some tuning to do...

one step forward... :D

abowie · Post by **abowie** » Wed May 21, 2014 10:12 pm

Dashpot oil?
FWIW, in that photo, the jet looks pretty high.

KingRichard · Post by **KingRichard** » Thu May 22, 2014 6:23 am

I have gapped my plugs at 30 thou using electronic ignition and Lucas DLB105 coil. Works fine.

Also think the jet is too high.

Richard

ChrisC wrote:interim update...

I have no idea why I tried this.... but I have just opened up the spark plug gaps from 25 to 40 and the engine is a LOT smoother now. I had forgotten that I reset the gaps to factory standard a little while back. Perhaps my high output electronic ignition didn't like the small gap

Now I have a smooth tick over and 'almost' no fuel sitting in the carb body. The engine also pulls better but is still falling off at 4000 revs so I suspect I still have some tuning to do...

one step forward... :D

ChrisC · Post by **ChrisC** » Thu May 22, 2014 6:59 am

Thanks Richard...

And yes the jet is too high - i took the photo before it was moved from the start position.

stef · Post by **stef** » Thu May 22, 2014 7:45 am

Could it be a blocked overflow pipe that does not release the pressure as you pump fuel in, therefore stopping the float to rise and close the valve.

malcolm · Post by **malcolm** » Thu May 22, 2014 9:36 am

I'd have thought it loks more like oil contamination in the petrol than carbon.
Could a damaged inlet valve allow fuel back into the manifol and thus carb during compression stroke? Any oil from worn bores could then be mixed? Sorry if that's nonsense, just a thought! Or just dashpot oil as abowie said?

ChrisC · Post by **ChrisC** » Thu May 22, 2014 12:42 pm

Guys, sorry, for clarity...none of the jets are flooding when the pump is powered up and the problem is on ALL THREE carburettors...

Is almost as if suddenly the engine was not sucking in the fuel. However as mentioned changing the spark plug gap HAS improved things and the puddle of petrol is much less now...

christopher storey · Post by **christopher storey** » Thu May 22, 2014 1:41 pm

I still do not understand why the jets are so high. I normally set mine, as a datum, about 65 thou down from the bridge and then tune from there, usually ending up with them between 65 and 70 thou down. I do not understand what was meant about " moved from the start position " . This looks to me as though there is a fundamental weak mixture problem

ChrisC · Post by **ChrisC** » Thu May 22, 2014 2:52 pm

why do you do that Chris? the manual says unscrew the mixture screw until the jet is level with the bridge... thats my 'start to tune' position

christopher storey · Post by **christopher storey** » Fri May 23, 2014 6:14 am

Levelling them with the bridge is merely to achieve a common position. The vital sentence in the instructions is the one at the end of that paragraph : "Turn down the mixture adjusting screws 2.5 turns " . In fact, because the pitch of the screws is rather coarse, variable and therefore inaccurate, I always use a depth gauge , digital in my case

abowie · Post by **abowie** » Fri May 23, 2014 6:15 am

ChrisC wrote:why do you do that Chris? the manual says unscrew the mixture screw until the jet is level with the bridge... thats my 'start to tune' position

Once level with the bridge you then screw them down 2 1/2 turns; that's the start position.

ChrisC · Post by **ChrisC** » Fri May 23, 2014 6:51 am

ah okay merely semantics then Chris as the true start of the process is in reality setting the jet at the bridge level

PeterCrespin · Post by **PeterCrespin** » Fri May 23, 2014 8:32 am

The E-type manifold runs down from the ports so back flow of condensed fuel on stopping is common if the engine has not been totally heated up or is misfiring, you just don't normally expose that area.

I'm not at all convinced that your engine suddenly went from fine to rough because of a points gap that didn't change between good and bad running conditions. Yes, changing it may now have helped but logic dictates you are at best covering for whatever the issue originally was.

Pete

ralphr1780 · Post by **ralphr1780** » Fri May 23, 2014 10:15 am

I would rather place my bet on simply oil brought by the breather pipe, condensing mixed with petrol.

ChrisC · Post by **ChrisC** » Fri May 23, 2014 11:57 am

Thanks Chris - Fair point on the manifold running down and you are right you would never normally see if there is a back-flow post engine turn off.

Points gap? no i never mentioned points (I have an electronic distributor)... its the Spark PLUG gaps I changed from 35 to the workshop manual setting of 25 because I *thought* I had set them wrong.

Closing story:

I have just taken my time to clean the plugs and set all the spark plug gaps at 35. I then set all the jets at 2.5 turns from the top of the bridge and I am pleased to say the engine now pulls freely all the way to the red line so I am happy again.

So for me - the factory setting of 25thou for a plug doesn't work and 35 thou is significantly better.

Perhaps my electronic distributor, high output coil, high lift cams etc need this tweak, I dont know but its definitely better now. But it does show you how important plug gaps are

Case closed. thanks for replies.

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