RobLyon
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| posted on 30/6/11 at 09:49 PM |
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Misfire under semi hard cornering
Hi,
We've got an ex 750MC Sylva striker that were having issues with. The car runs a 1.8 silvertop zetec on weber dcoe 40's, facet pump with
small inline filter and DTA ignition only ECU.
The car ran great at Cadwell, fine for the morning at Oulton but in the afternoon started playing up. The car would be fine for the outlap, okay for
the 2nd then would start to misfire on the 3rd getting gradually worse until it was completly un-drivable.
We replaced all the plugs and leads and carried out some other service work then at rockingham it wouldnt even complete one lap. It would drive fine
round the compound but once we tried to get on the track it died after semi hard cornering. We've cleaned the inline fuel filter and facet
filter, changed the coil pack and crank sensor and its still playing up. Were convinced its fuel related but dont know much about carbs. I've
ordered a book on service and maintenance of webers but its not arrived and I want to start working on the car tomorrow. Any suggestions or things to
check/rule out? i want to plug the laptop into the ECU and see what the sensors are doing.
Thanks in advance for any help,
Cheers,
Rob
ETA: No black smoke out the exhaust so dont think its overfuelling
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keithometune
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| posted on 30/6/11 at 09:55 PM |
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unless the fact that it occured under cornering is a red herring it could be worth rigging up another fuel supply, in case there is a blockage in the
tank.
keith
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steve m
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| posted on 30/6/11 at 09:58 PM |
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What about a swirl pot ?
it could just be lack of fuel in the tank ?
or a fuel tank blockge not allowing the fuel thru,
ie no vent hole in the filler ?
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bi22le
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| posted on 30/6/11 at 09:59 PM |
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Fuel starvation?
I had splutters in my Striker and the gauge said 1/3 tank. The tanks are wide and shallow allowing plenty of sloshing on long or fast corners.
Obviously try putting more fuel in??
HTH
Biz
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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rgrs
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| posted on 30/6/11 at 10:01 PM |
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Check the tank breather. If it's blocked or not working this will give a fuel starvation issue.
Unfortunately it normally only shows up when driving harder.
Roger
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RichardK
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| posted on 30/6/11 at 10:03 PM |
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Is the fuel tank pressurised when it all goes bad?
Cheers
Rich
Gallery updated 11/01/2011
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RobLyon
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| posted on 30/6/11 at 10:09 PM |
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Cheers for the responses guys.
I forgot to say the tank is vented and was brimmed.
I dont think there is anything wrong with the setup per se, more a component has failed/blocked.
A guy at work who plays with motorbikes has suggested a float could come loose?
How would I tell if the tank is pressurised? If it vents when the cap is undone?
Theres what appears to be a check valve just before the carbs, could this be blocked/damaged?
Thanks again,
Rob
[Edited on 30/6/11 by RobLyon]
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DavidM
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| posted on 30/6/11 at 10:19 PM |
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I had a similar problem, and it was a partially blocked needle valve in the carb float chamber. The car could be driven around slowly, but the faster
it went the worse it got because fuel would be drawn out of the float chamber faster than it could get in.
David
Proportion is Everything
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mikemph
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| posted on 30/6/11 at 10:40 PM |
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sounds float or needle valve related to me.
If the fuel flow into the float bowl is not keeping up with demand the level will be dropping down in the float bowl added with corning force sloshing
the remaing fuel in the bowl to one side, which in turn will lead to very lean or no mixture at all.
This would also explain the misfire as it would be most likely it only one carb so 2 cylinders would be going down while the other 2 are fine.
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cliftyhanger
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| posted on 1/7/11 at 06:15 AM |
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I had a problem with dellortos overfuelling during autosolos (hard cornering) I suspect the fuel in the float chamber was surging, letting the float
go down, lets extra fuel in, and as you come out of the corner it over-richens the carb. It chucked out loads of black smoke and misfired. A real
PITA.
In the des hamill book he shows a mod to remove excess fuel for off-road vehicles. Basically a bit of tube set to the fuel level in the carb float
chamber, and a scavenger pump to return excess fuel to the tank. Sounds like overkill, and my solution is to install EFI 
May be worth considering, check if you are getting black smoke.
Also, do LH or RH corners have a bigger effect?
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mad-butcher
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| posted on 1/7/11 at 08:05 AM |
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don't dcoe's have a small filter in the banjo.
tony
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procomp
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| posted on 1/7/11 at 10:17 AM |
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Hi
I would suspect that the cornering is a red herring. It is however quite common for the coil packs to play up. Hence many racers with silvertops
fitted carry spares. Try a second hand one that is known to be running fine on a road car. Some after market replacement ones are off poor quality and
can also give problems under load.
Cheers Matt
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RobLyon
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| posted on 3/7/11 at 08:49 PM |
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we've spent all weekend tinkering and the only thing we found was the wire from the alty to the starter motor was loose, possibly meaning the
battery wasn't getting charged (the battery is a bit duff) Does the coil pack draw more current than the alty can provide at higher revs? i.e
does the alty only charge say ~2-5krpm? I think its a daihatsu charade alty but some of the pulley ratios seem to have been adjusted.
Cheers,
Rob
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mikemph
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| posted on 4/7/11 at 12:06 PM |
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Sounds like a good suspect.... Misfire caused by low battery.
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