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Title: 179 running rough under wide open throttle Post by: Dave_EH on November 22, 2007, 08:48:47 PM I have a 179 that is quite well sorted.
All ignition equipment has done less than 1000miles (Bsoch HEI with correct advance curve). It has been sitting around for some months. It runs beautifully under light throttle and very smoothly, and also nicely up until around 3000rpm under moderate throttle but bogs down idle open throttle/high revs. It has fresh fuel, and is a correctly jetted Holley 350. Plugs look good - nice coffee colour (NGK BP5ES 40thou). Cam profile is unknown but probably around 28/68 but not much lift. A quick check has revealed all spark leads read approx. 5-6 Ohms. The High Tension lead (coil to dizzy) which I replaced not long ago (it needed a slightly longer one due to new coil design) reads 1.5 Ohms. Have I found the problem - should they all be reading under 2? Leads are Champion from memory 8mm hi temp silicone red in colour. Replacement coil lead is a Bosch super induction Title: Re: 179 running rough under wide open throttle Post by: reddo on November 23, 2007, 05:52:04 AM Maybe you need a bigger main jet... not enough fuel up high??
Reddo Title: Re: 179 running rough under wide open throttle Post by: Ed on November 23, 2007, 08:18:52 AM Dave,
I dunno about tuning Holleys but with bike carbs (mikunis) I always tune the main jet first then subsequently down through the range. what sort of bog down? like a soggy feel and sputtery or it just wont rev harder? if it feels soggy it may be over jetted and if it just wont rev then its under jetted. when did you do your plug chop? at WOT or did you let it settle down to a nice idle again? I would drive it and when it start to cut out, kill the ignition, stop immediately then pull the plug. Again this is how i was diagnosing the bike until I built a sniffer.. these are handy but at WOT you should be below the stoich ratio of 14.7:1 (ie running rich), it gives you an indication of which way to go with your jetting. on leads... I found the ones with least resistance were Top Gun Max 300 (around 450 - 500 ohms per meter). 5- 6 ohm is 5 to 600 or 5 to 6000? you wouldnt get down around 5 - 6 ohm unless it were solid copper I suspect. interestingly i tested an off the rack top gun lead and it was 5-6,000 ohms. HTH Cheers Ed |