Tuned 1.9 8Vmissfire!

[edbar 6]

Hi all, Ive been plagued with a missfire for about 7 months now and cant trace it! It has 11.5-1 compression, newman 300 deg cam, twin 45dcoes alpha management etc.

Cleaned carbs, they work fine, checked all coil etc, has compression. Stripped carbs off again tonight to have another look, pump jets work fine which is what i suspected to be the problem. Symptoms are:

1. cylinder 2 inlet manifold has carbon dust coating it

2. missfire at low rpm

3. sometimes loss of power at all rpm, sometimes clears with alot of spluttering, sometimes take a long time. Lots of backfires out of carbs and exhaust when this happens. Can take days to clear.

4. Can run well at high rpm, turn it off and it runs as above.

I have thoroughly cleaned the carbs and ther is no debris inside, all galleries clear so am inclined to think its not the carbs. Dont want to send the carbs off for a second opinion/rebuild for £200 if its not the problem.

I am starting to think maybe it is a sticking valve as I have tried everything and nothing fuel or ignition makes any differance.

Any help as always greatly appreciated.

Edd

[DamirGTI 342]

.. might sound silly but , tried new spark plugs !

 

Had something similar on my 11.1 CR engine as well (annoying intermittent misfire ..) - did tear it down apart started doing copious amount of testing diagnosis checking replacing , burning my brain , then ... was bloody f*** up spark plug , and just one .. though it seemed perfectly good visually and on spark testing - it was bad ..

 

Also , tried measuring compression ?

One very useful "old fashion" diagnostic tool is - vacuum meter/tester ... it can tell you loads of stuff with regards to various engine problems .

 

Damir

[edbar 6]

Plugs are fine, changed them lots of times, current ones are about 150 miles old.

Done compression test and that came back fine.

Edd

[ORB 227 1 Cars]

HT's? Coil? Ignition Amp?

[edbar 6]

All check out fine, even replaced them with new ones, coil,leads,plugs,crank sensor. Still no different.

[Daz_C 8 1 Cars]

Are the Venturi's screwed in and in the right position ? A screw fell out of one of mine a while back and if i recall correctly had similar issue. Worth a check.

[edbar 6]

That did happen, that is when the trouble started. Put new screws in, was alot better but still had a misfire when trying to accelerate from low rpm, and like i said sometime no power anywhere. Checked those venturies last night they were spot on!

[edbar 6]

Another symptom is the carb for cylinders 1 and 2 spit back very slightly on idle makes an intermitant pffft noise.