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Engine dies if revved


andytr6

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I reported this problem some time ago but now have additional data.  Car is GT6 Mk3 with 2500 engine and HS6 carbs.  I've cleaned tank , new fuel pump, lines and fitted replacement overhauled carbs (same type though), new electronic dizzy and coil.  Car starts OK but with quite a lot of cranking, runs Ok then when warm if you bleep the throttle it tries to die.  Also will die as you come up to a junction.  Faster idling helps.   I also tried fitting a more powerful battery which didn't make a difference although it cranked over faster. I now noticed that undoing oil cap also causes it to die or removing pipe from rocker box to carbs has same effect, so is it a breathing problem?  Any ideas?

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I have the same on my GT6 but I found that the rocker cover is not air tight and letting in alot of air (and also some oil out!  :P ). So I disconnect the breather pipe to the carbs and blocked it with an old condensor! I'll get a new rocker gasket and seals for the rocker cover bolts and then try it again.

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Thanks for interest - I am on second set of carbs with same problem and refurbished this set myself and made sure jets move and needles, etc, - so I don't think its carb problem.  Same symptoms with both sets of carbs. Haven't checked fuel pump pressure but there is fuel in the filter and when above 1500 rpm it runs well.  Seems like blocking the breather pipe to carbs is worth a try - maybe a wine cork....  I don't know what the pipework to carb from rocker box is for?  I always assumed its a way of burning vapours from rocker box through the carb.  On my TR6 a garage who did some work to improve running closed off carb connections to rocker box and fed the rocker box tube into a pepsi bottle - its still like that and full of gunge from rocker box vapours...

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As it is presumably okay when cold, have you made sure it isn't just running too rich? The spark plugs should be dry and light tan in colour. If they're wet and oily then it's too rich. There are a few causes of this problem but give us some feedback on the state of the spark plugs before we go down that route.

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I suspect it is caused by excess crank case pressure, my 2.5 hs6 engine had to run with a crank case breather into an oil catch tank otherwise it would just splutter and die. you will also need to ensure that all the joints on the inlet manifolds and adaptors for the hs6 are air tight otherwise you will get a similar effect, a liberal application of clear silicone on all surfaces will help to cure it.

pm if you want more info

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1700 wrote:
I suspect it is caused by excess crank case pressure, my 2.5 hs6 engine had to run with a crank case breather into an oil catch tank otherwise it would just splutter and die. you will also need to ensure that all the joints on the inlet manifolds and adaptors for the hs6 are air tight otherwise you will get a similar effect, a liberal application of clear silicone on all surfaces will help to cure it.

pm if you want more info


...which jolts my memory into action
I had replaced the cyl head gasket, put everything back into place ,come to start and it had the same symptoms
I had not seated the inlet manifold properly and was not tight on the inlet gasket
Reseated,tightened down , and hey presto ...perfect  

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well its possible that that could be the problem - I'll check - although I replaced the carbs with like for like, I didn't touch the inlet manifold which was fitted by the previous owner.... So its air somewhere anyway, whether inlet or crank case breathing fault.  Job for the weekend - rugby permitting.

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Well I tried sealing the carb inlet from rocker box and it made no difference.  I made a visual check of inlet seating and looks OK.  I also checked carbs are working OK and mixture was a bit rich so I adjusted that - nothing so far stops the dying when revved while warm engine problem....

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