briarswood57
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| posted on 19/8/19 at 07:01 PM |
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Crossflow - fouling 3 out of 4 plugs - any ideas
Hi there,
Looking for some help from the collective. Got 1660 Crossflow in the Westfield running on twin 40s. The car had been in hibernation for 15 or so
years before I bought it - work done by me includes carb rebuild, new accuspark distributor, coil and leads. It’s all through an MOT but here is the
problem - it’s consistently sooting 3 out of 4 plugs within 20 miles. I would expect it running a bit rich but can’t fathom out why it soots cylinder
1,2 and 4 but cylinder 3 is ok.
Idle is always a bit lumpy but past 3k revs it runs fine.
Any ideas what to check? Has anyone had a similar issue?
Thanks in advance.
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rusty nuts
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| posted on 19/8/19 at 07:16 PM |
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Excessive fuel pressure ?, incorrect float levels ? jets etc , blockage ? worn pistons, rings ,bores , block breather ? Incorrect valve clearances ?
Have you tried new plugs of the correct heat range? Carb balance?
[Edited on 19/8/19 by rusty nuts]
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briarswood57
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| posted on 19/8/19 at 07:45 PM |
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Hi there. Thanks for the ideas
Tried some of those - float levels checked when carbs rebuilt a few months ago, however I’ll check for blockages.
Carb balance I think is acceptable - I did it by ear so perhaps using a vacuum gauge - I’ll try that
Rings - I did a compression test which was equal across all cylinders and well within range. Worth doing a leak down test?
Plugs are the NGK BP7ES (3rd or 4th set this season) which I think are ok but happy to be corrected.
I’ll have a look at fuel pressure and valve clearances before I take the head off for a more detailed look at the bores etc. That’s a job for bank
holiday weekend:-)
Thanks again for the ideas.
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perksy
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| posted on 19/8/19 at 08:01 PM |
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Get the balance right first and then go from there
Might sound daft, but Have you checked to make sure the jets are all the same size etc?
How did you set the initial mixture strength up after rebuilding the carb's?
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rusty nuts
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| posted on 19/8/19 at 08:06 PM |
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Before taking the head off do a compression test when the engine is hot and throttle fully open the put a few squirts of oil into each cylinder and
recheck compressions . Does the engine reach normal operating temperature?
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AlexXtreme
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| posted on 20/8/19 at 08:23 AM |
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Agree comments above, get the carbs balance right first before trying other options.
I brought a simple flow meter and which made it much easier
[Edited on 20/8/19 by AlexXtreme]
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MikeRJ
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| posted on 20/8/19 at 08:48 AM |
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It's possible they are all jetted the same (but incorrectly) and you have an air leak on one cylinder. If you are using Misab plates and the
compliant rubber or Thackery washers on the bolt, then check this all very carefully since air leaks are pretty common.
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briarswood57
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| posted on 20/8/19 at 10:58 AM |
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Thanks for the suggestions - all good areas to explore - its helpful getting some differing views to help prioritise.
I think the order of priority is:
1) Do a hot compression test as suggested - if that indicates other issues then I might need to think again, howerver assuming compression is Ok then
move onto:
1) Confirm jets are all the same size - apparently the carbs were re-jetted with the original owner, however now I think about it he did mention
something about passing on a box of jets - might be some got switched
2) Double check for leaks - when I rebuilt the carbs I put a new MISAB plate and thackery washers on but worth checking again
3) Balance the carbs so I'll get onto the internet and get myself a carb-balancer (unless anyone here has one going cheap?)
4) Check valve clearances.
I think thats probably a sensible order to start with over the BH weekend and see if that sequence improves things.
On a related note - my understanding of the DCOEs is that the only "dynamic" adjustment is the idle screw which is used to set the idle
and balance the carbs. All the other adjustments would be by replacing jets?
Thanks again for the input.
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rusty nuts
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| posted on 20/8/19 at 11:51 AM |
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Check and adjust the valve clearances before attempting to do anything with the carbs, you won’t be the first to get caught out by tight valves .
Trying to set carbs should only be done after valves, timing etc have been attended to .
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gremlin1234
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| posted on 20/8/19 at 11:54 AM |
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quote:
Originally posted by briarswood57
On a related note - my understanding of the DCOEs is that the only "dynamic" adjustment is the idle screw which is used to set the idle
and balance the carbs. All the other adjustments would be by replacing jets?
don't they also have a choke control?
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briarswood57
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| posted on 20/8/19 at 01:01 PM |
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quote:
Originally posted by gremlin1234
quote:
Originally posted by briarswood57
On a related note - my understanding of the DCOEs is that the only "dynamic" adjustment is the idle screw which is used to set the idle
and balance the carbs. All the other adjustments would be by replacing jets?
don't they also have a choke control?
No choke control on mine - in as much as there is no choke to pull on. I assumed mine had the choke delete kit, however just had a look at the net
and now not so sure....... something else to investigate.
Next stupid question - should I set valve clearance hot or cold.
Thanks again.
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rusty nuts
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| posted on 20/8/19 at 02:04 PM |
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Valveclearances should be set according to the camshaft manufacturers settings ,probably cold though , what cam does it have as the settings may not
be as standard?
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AlexXtreme
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| posted on 20/8/19 at 02:18 PM |
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with these carbs you should not need a choke anyway as you will flood the engine..!
I would have thought the clearances would be as standard as the gap is to take account of the expansion as the components heat up ... that is just my
suggestion though as others might now better
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briarswood57
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| posted on 20/8/19 at 03:00 PM |
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quote:
Originally posted by rusty nuts
Valveclearances should be set according to the camshaft manufacturers settings ,probably cold though , what cam does it have as the settings may not
be as standard?
I believe it’s a 234 Kent “fast road”. I can see the clearance values on the Kent website so
I’ll have a go at that tonight. It didn’t specify hot or cold but I’ll go for cold.
Thanks again.
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rusty nuts
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| posted on 20/8/19 at 05:22 PM |
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While your at it make sure that all the valves open properly, wouldn’t be the first camshaft to have worn lobes.
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briarswood57
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| posted on 23/8/19 at 08:40 AM |
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quote:
Originally posted by rusty nuts
Valveclearances should be set according to the camshaft manufacturers settings ,probably cold though , what cam does it have as the settings may not
be as standard?
I believe it’s a 234 Kent “fast road”. I can see the clearance values on the Kent website so
I’ll have a go at that tonight. It didn’t specify hot or cold but I’ll go for cold.
Thanks again.
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briarswood57
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| posted on 23/8/19 at 06:13 PM |
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Thanks for all the help so far. Quick update - valve clearances seemed a good bit out - fairly tight so have readjusted as per Kent Cams spec, however
just picked up a cheap DTI from Amazon and going to check valve lift etc and reassure myself it is indeed a 234 cam before I go any further.
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AlexXtreme
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| posted on 24/8/19 at 05:06 PM |
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my money is on the carb balance :-)
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