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mis-fire over 3000rpm - vx + carbs
Hi, this is related to my Westfield but hope some of you may have ideas.
The car was spluttering and misfiring at low revs, keeps trying to stall etc. We diagnosed this as loose mounting of the carb due to missing stud/bolt and loose thackery washer/plate. It now idles perfectly. However, over 2.5k revs under load, there's little power and it keeps misfiring, spluttering, popping etc. When not under load, it revs fast and clear to red line. It does, however pop a little at constant revs over 3000rpm. Anyone any ideas? Before we did this, the car produced power under load no problems despite the spluttering at low revs. This is Steve's (mechanic) comments as he helped out. When I first saw the car it was running extremely badly,it was misfiring n idle and was very hesitant to pick up. I had a quick look and could see that one of the studs on the manifold that holds the carb on was missing completely and that the rubber washers/thackery's were perished and in generally poor condition. Paul picked up some new misabs and washers from SBD today and I fitted them for him.I followed him home from my place and I had to spank the car I was in too keep up with him lol so it was going alright http://boardroom.wscc.co.uk/iB_html/...ns/biggrin.gif . We replaced the missing stud,washers and misabs and then started the car.It ran really well on idle and just giving it a rev whilst stationary.On the road it was missing its bollox off under load. It felt to me like it was electic related,ie leads or plugs but as previously said the plugs are in good nick also a lovely brown colour and the leads look ok(I left my fluke in the garage) so couldnt check them properly http://boardroom.wscc.co.uk/iB_html/.../bangshead.gif . The washers were set using the penny trick to get the clearance and the backplates were fitted the right way up(the k&n on the filter would be the wrong way up if they were wrong I think?). I removed the filters again and then loosenend the carb mountings just in case I had tightened them again too much which proved to be a waste of time. My gut feeling is that it is a electrical fault and more than likely to be the leads as it will occaisonally clear and the car will pull very well,but having messed around with the carbs admittedly only removing them I cant help but think it might be fuel related. Also, new leads on, new rotor arm. dizzy cap new last year. mechanical dizzy. Answers on a postcard please lol |
what is the history of it?
ie. is this an out of the factory set up car or just been built etc.. pull the plugs now what do they look like? Has it ever run spot on all the time? Was it set up at some point - rejetted for example and the fault now fixed was there when it was jetted? Simon |
Amateur (although professionally done - it was on the westfield stands as a show car when it was built!!!) built back in '97. Been running fine for the last two years that I've had it. Low rev thing getting worse hence the fix to stop unmetered air getting in. Now idles perfectly but problems as above.
Plugs look fine, nice and light brown. Maybe taking carbs off has dislodged some crap that'd blocking the jets? I'll try cleaning them nonetheless. |
quite possibly a jet problem yes.. really need a sniffer up the exhaust to see what the fuelling is doing.. or something similar..
Sounds nice car, hope you sort it. |
A sniffer up the exhaust??? :D wassat then?
Ultimately, it's either electrical or fueling I guess. It's sparking (will double check that all plugs are this weekend) so must be fuel? Most people I've spoken to suggest electrical but I can't see what it is. Once I've elimitated everything then I'll rolling road it with a decent tuning professional as it never harms to do this every coupla years. |
Setting up up DCOE carbs blind?? Good luck to ya! LOL. :p
As JGM.. use an exhaust gas analyser for starters. It's the best way to set them up, along with hooking up the HT leads to ian gnition system analyser to confirm fueling and balance on each cylinder (also rules out ignition faults at the same time). :) |
spluttering
Check the bob weights and the vac advance in the dissy, These can seize up and cause the car to be flat and spluttery..check ignition advance with a strobe/timing light..also check idle jet and main sizes are large enough in the carbs.
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