steve m
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| posted on 23/4/04 at 07:25 PM |
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twin 40 high emmission problem
Hi
Does any one have any idea's on what is happening to my carb setup
It failed the MOT yesterday on Hydrocarbons of 10000 + when the limit (I believe) is only 1200, this problem appears to be only on no 1 cylinder as
all of the other3 can be wound down to nothing, but no1 the mixture screw does nothing to the mixture
today I have totally rebuilt the carbs and blown thru them with 100 psi, every jet etc has been cleaned with thinners and blown thru, all of this was
only done a month ago !!! so I dont expect any change to happen
for info I am running a 1700 xflow lightened and balanced with a 285 cam and stage 3 head
no 1 cyl (offending cylinder) is down 7 psi on the other 3 cyl
all of the valves are moving the same distance, so in theory the cam is ok,
I have new ignition coil, leads, rotor arn and plugs
what else can I do
hence my other post on the for sale a dcd 28/36 wanted !!!
no MoT means no Stoneleigh so I am well PISSED off !!!
regards
steve
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ady8077
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| posted on 23/4/04 at 07:46 PM |
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Hi steve
What compression is the other 3? and did you add a tea spoon of oil to number one
Is the exhaust as hot on number one?
Adrian
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steve m
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| posted on 23/4/04 at 07:54 PM |
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all comressions were done running (ie the other 3)
no oil was added as the pistons are dished and cut outs for the valves so I would need about 4 spoon fulls !!
No 1 seems cooler than the rest
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Deckman001
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| posted on 23/4/04 at 09:11 PM |
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Steve, I have a carb off of a 1620 x/flow, it was on a grass track racer(runs rich), I'll need it for when i run mine(next year probably) your
welcome to borrow it if it helps any 
Jason
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ady8077
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| posted on 23/4/04 at 09:19 PM |
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Hi steve
Have you tried swapping the carbs over?
No 1's comp might be too low to get good combustion?
Adrian
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britishtrident
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| posted on 23/4/04 at 09:59 PM |
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I suspect either an ignition misfire or burnt/non seating vavle.
Check the valve clearances, check plug, plug lead and dizzie cap, if you have points ignition check the points gap on all 4 lobes of the dizzie cam
--- if you have a Ford/Fomoco/Autolite/Motorcraft distributer with points always set the points to the wide end of the gap tolerance and recheck
after the engines has run for 20 minutes (this type of points close up after initial running)
If none of the above it looks like a valve problem do a compression test properly ie warm up engine remove all plugs crank engine on starter with
throttle held full open this is the only way that give meaningfull results.
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gregf27
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| posted on 23/4/04 at 11:00 PM |
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had same problem with very high emissions,turned out to need the cylinder head bolts re-tightening!
worth a check!
regards,
Greg
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steve m
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| posted on 23/4/04 at 11:05 PM |
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Thanks for responses
Jason I may call you !!
do you know which type of downdraft it is ??
regards
steve
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Deckman001
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| posted on 24/4/04 at 06:59 AM |
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No , not yet, but it is on the engine at the mo, so will have a look this morn and post later
Jason
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Deckman001
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| posted on 24/4/04 at 01:23 PM |
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Hi steve you have u2u
Jason
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steve m
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| posted on 25/4/04 at 06:26 PM |
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Update
i swapped the carbs and the problem was still no 1
a leak down check showed no 1 exhaust was leaking
The head is off again as no 1 compression was well below the others,
new valves in no 1 have dramatacly improved the static leak check. so hopefully by tomorrow nights I should be running again, (on all four !!!)
thanks for all the responses
regards
steve
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Dave Ashurst
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| posted on 25/4/04 at 08:12 PM |
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Steve
Was the exhaust valve bent perhaps? (Look at it rolling along overhanging the edge of a flat table) Any evidence of valve contact on the piston?
How's the cooling system? Have you got a header tank? Has the engine recently overheated due to low coolant level?
The valves can jam open until a piston hits them back if the head gets too hot. Just a thought.
Edit: The point being; if it's got an overheating problem sort the cooling system out before it recurs! 
regards
Dave
[Edited on 26/4/04 by Dave Ashurst]
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