Richie-Van-GTi 70 2 Cars Posted April 10, 2007 Ive been suffering from intermitent detonation (only noticeable on idle) on pot 1. Im systematically working through everything and so far the only thing I can find wrong is the exhaust valve on that pot has a tight clearance, its .305mm and should be .4 , will this be enough to give the intermittant fault? Dont want to strip the cam out and replace shims if not. Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 a tight clearence on a exhaust is not as bad as on inlet... as they are fairly big anyway it would deffo not give a intermittant fault it would give bad compression on that cylinder when hot... as it could possibly hold the valve open is it det? or pinking? have you checked the basics.. plugs.. injectors..inlet air leaks Share this post Link to post Share on other sites
Richie-Van-GTi 70 2 Cars Posted April 10, 2007 (edited) new plugs, its on carbs so no injectors or wiring issues, new rotor, cap and leads etc and definatley no air leaks. The issue is it 'pops' inside the engine on pot one intermittantly. When it does it blows back out of the carb on pot 1 as well. http://www.pgacnortheast.co.uk/pop.mp4 bad recording from a phone but recorded at exhaustr end and engine end so you can see whats what. Edited April 10, 2007 by Richie-Van-GTi Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 when did you last have the carbs checked? it could be a jetting fault it is possible for i chamber on the carb to be out of sync or a fault with the carb itself has it just started? or has it been like that since fitting Share this post Link to post Share on other sites
Richie-Van-GTi 70 2 Cars Posted April 10, 2007 the carbs were recently stripped down and cleaned out properly then reassembled. The engine did run fine for a while then this started. It was previously over fueling badly (it was blowing fuel back out the inlet http://www.pgacnortheast.co.uk/cough.3gp ) I'm struggling to find the cause of this. A really helpful person over on honest john has converted that first vid to mp3 then expanded it and listned to it and reckons itys down to detonation caused by exhaust valve on pot 1 but as yousaid it doesnt explain it being intermittant and how its getting back out the inlet. The engine has had a leak down and compression test, both come back fine. Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 i dont know mutch about bike carbs... but the principle is the same have you swapped the carbs from side to side? if it is possibe... that would tell you if it is the carb its self can`t see how the tappet close could cause det.. wich is in principe timing overly advanced it would do it all the time vid looks like big overlap on cam or over fueling is it ok at high revs Share this post Link to post Share on other sites
Richie-Van-GTi 70 2 Cars Posted April 10, 2007 seems fine at high revs, caznt swap carbs end to end. Its a standard 1.9 cam so dont know what the overlap is like on them? Could the timing just be totally out and its only noticeable on pot 1 ? I know if you crack the throttle open it 'borks' and takes a while before it will rev like it does in that vid. I have now got smaller main jets in to try and cure the overfueling. Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 can`t see how timing would give a fault on 1 pot and deffo not intermittant standard cam will not have big overlap .. only if it had a big rally cam would that affect it it does sound like it needs a run on the rollers to check carbs i would recomend the rolling road tuner i work at but my boss dont do bike carbs Share this post Link to post Share on other sites
Richie-Van-GTi 70 2 Cars Posted April 10, 2007 As soon as I get it running well enough and fiunish putting it all back together its going down to motoscope for a session there. I know Frodo's is going there on friday so hopefully he will give back some good reports Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 is that the chap from wellbury he was saying it was going to motorscope... must be the guy... i was at his tonight doing some wiring engine looks nice Share this post Link to post Share on other sites
frodo_monkey 0 Posted April 10, 2007 Cheers Jim Looks a lot nicer without all that crappy wiring in the way Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 what a strange coincedence it all came out i take it? i hope it will only take a hour tomorrow should have it running in no time Share this post Link to post Share on other sites
frodo_monkey 0 Posted April 10, 2007 You are the boy! Theres still a bit left, I was a bit of a wimp and didn't want to rip out something wrong - but the snips are right there for tomorrow Share this post Link to post Share on other sites
jimbean 0 Posted April 10, 2007 no problem i will have a look tomorrow but it should be fairly simple... and less wires means less weight to go even faster.. will see you tomorrow at about 5.45 Share this post Link to post Share on other sites
Richie-Van-GTi 70 2 Cars Posted April 11, 2007 Aha, so frodo's is sorted then? I was gonna pop down tomorrow if not to look at the wires but sounds like you got it all in hand now Share this post Link to post Share on other sites
TT205 42 Posted April 12, 2007 Another idea for you If it like an intermittent 'popping' only at idle or on the overun - I've had this with carbs (and tb's) and on each occasion it has been an air leak on the rubber sealing rings to the manifold. They don't seem to last 2 minutes on my car and if the carbs/manifold is disturbed/removed, I've had to replace them every single time as they have always swollen and will not seal Dave Share this post Link to post Share on other sites
Richie-Van-GTi 70 2 Cars Posted April 12, 2007 (edited) Ive had the manifold off yesterday to tap it ready for vac advance take off's so its been refitted now with new gasket and a smear of liquid gasket so should defo not leak there. Im going to also replace the rubber joint on pot 1 between mani and carbs just in case there is a fault there that I cant see. Also while I been at it, Ive redonme the shims so there is no tight clearances anywhere, also retensioned cambelt as it was a touch tight. Fingers crossed all will be well, cant do anything till new cable pulley arrives for the twin cable setup. Edited April 12, 2007 by Richie-Van-GTi Share this post Link to post Share on other sites
