Paulwhite Posted January 11, 2011 Share Posted January 11, 2011 hi all need some help and i have tried the search but couldnt get a good result. and looking through google just got me confused. anyway my exhaust keeps spitting out flames or "afterfire" i think the technical term is. iv got a free flow air filter (just search butterfly valve) and an aftermarket exhaust, the plug is reading rich ??? , the timing is spot on (did it yesterday) and every time i let go of the throttle BANG! no matter what rev range it is. i cant make the mixture any leaner as its a keihen (or keihin?, kiehen?) carb and cant adjust it without getting new needles and jets (which i dont really want to do) iv tried re-setting the mixture screw and its helped a little. any suggestions? oh and forgot to mention i cant ride the bike as its not fully built so the best i can do is get the engine running in neutral and rev it. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted January 11, 2011 Moderator Share Posted January 11, 2011 hi all need some help and i have tried the search but couldnt get a good result. and looking through google just got me confused. anyway my exhaust keeps spitting out flames or "afterfire" i think the technical term is. iv got a free flow air filter (just search butterfly valve) and an aftermarket exhaust, the plug is reading rich ??? , the timing is spot on (did it yesterday) and every time i let go of the throttle BANG! no matter what rev range it is. i cant make the mixture any leaner as its a keihen (or keihin?, kiehen?) carb and cant adjust it without getting new needles and jets (which i dont really want to do) iv tried re-setting the mixture screw and its helped a little. any suggestions? oh and forgot to mention i cant ride the bike as its not fully built so the best i can do is get the engine running in neutral and rev it. This may sound silly but is it in the exhaust or the engine. My old GSX600, tuned by TTS (google em) at Silverstone would pop and bang on the over run esp from high revs. Well actually it shot fkin great flames out if you did it at night. All to do with fuel, valve overlap and ig. It went like f with well over 90hp at the rear wheel and is still doing it at nearly 30Kmiles (fk off R6 owners thats a lot on a gsx they go less than 70 stock). Has it started since the ignition was put right, maybe it needs to be a little wrong to work now you have the pipe and carb. TTS moved the suzuki's 4-5 deg to work with the vernier valve gear and setting the valve overlap. Link to comment Share on other sites More sharing options...
Ttaskmaster Posted January 11, 2011 Share Posted January 11, 2011 Sounds like a back-fire to me. If it's just bangs, then yes. Bangs when you release the throttle is often a symptom of there being a hole, or an open joint somewhere. Check teh system, make sure it's all tight. But do you have actual flames? If so, then I believe the flames are simply caused by hot unburnt fuel igniting when it reaches more air (ie out the back of the pipe). From what I understand, this is one of the main reasons you re-jet when you change the pipes. The other is that this straight-through set-up will KILL your fuel economy. You'll get maybe half the MPG your bike is rated for? Seriously, if you're getting FIRE out the back of your pipes, I'd try re-jetting. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted January 11, 2011 Moderator Share Posted January 11, 2011 Sounds like a back-fire to me. If it's just bangs, then yes. Bangs when you release the throttle is often a symptom of there being a hole, or an open joint somewhere. Check teh system, make sure it's all tight. But do you have actual flames? If so, then I believe the flames are simply caused by hot unburnt fuel igniting when it reaches more air (ie out the back of the pipe). From what I understand, this is one of the main reasons you re-jet when you change the pipes. The other is that this straight-through set-up will KILL your fuel economy. You'll get maybe half the MPG your bike is rated for? Seriously, if you're getting FIRE out the back of your pipes, I'd try re-jetting. Don't you believe it, that 600 went from 180 mile to a tank crusing with 150 if you push it to, ready for it, sure, 120 tops riding like a nun and at the TT i got it down to under 60 doing 28min laps woo hoo never forget that. Wrecked a rear tyre in under a week Link to comment Share on other sites More sharing options...
Paulwhite Posted January 11, 2011 Author Share Posted January 11, 2011 cheers gents il have a look tomoz for any leaks in the system (and not the green leafy kind), and have a play with the timing if it keeps doin it. as to me getting confused.... google sais that a backfire comes from cylinder into carb and a after fire comes from the exhaust..?? and they give many a reason as to why... but hay never-mind it only spits out flames when i take the end can off , but with the end can on it just goes bang. i would of just moved the carb needle to compensate but when i took the carb to bits i found that you cant! its fixed in one position it is running rich but its not too rich if you get what i mean. could of done with moving the needle down a notch. thought if i could try and get the fuel to combust better by doing a combination of timing and iridium spark plug then it might sort it out?? just one more question (if i may) if the timing chain spins the cam sprocket anti clockwise...which way would i need to turn it to correct it? im guessing i need to retard it a notch so clockwise??? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted January 11, 2011 Moderator Share Posted January 11, 2011 That would make it fire nearer TDC and would , i think make it worse. I'd go with advancing it slightly you can safely go upto about 6 deg but you may need full fat fuel to do it for long periods. At least advancing it if you go too far you will know in plenty of time due to it pinking. Although you wont know that for certain till your riding it of course. Link to comment Share on other sites More sharing options...
Paulwhite Posted January 11, 2011 Author Share Posted January 11, 2011 well what i think is happening is the inlet valve is opening on tdc or just b4 (on the exhaust stroke) pushing fuel into the exhaust. hence why i thought retarding it by 1 or 2 teeth (on the cam sprocket) would fix it. but it could be the fuel isnt combusting properly, so might try using some high octane and an iridium plug b4 i play with the timing. im wanting to try and get the engine running as good as possible b4 i wire it up and get it on the road, then i can fine tune it and sort out any problems from there. but im just puzzled as to why its goin bang im short on funds at the mo and need to save up to build the battery box and make the loom so a new carb is out of the question (although id give anything for a mikuni carb ) the main jet is a 118 but think il be better off trying to find a new (adjustable) needle setup. ebay is useless and google isnt much better. just thought... could the wrong fuel pump make it run rich? at the mo im using the dragstar fuel pump (for a mikuni carb) as i cant get hold of one for the cbr engine. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted January 11, 2011 Moderator Share Posted January 11, 2011 well what i think is happening is the inlet valve is opening on tdc or just b4 (on the exhaust stroke) pushing fuel into the exhaust. hence why i thought retarding it by 1 or 2 teeth (on the cam sprocket) would fix it. but it could be the fuel isnt combusting properly, so might try using some high octane and an iridium plug b4 i play with the timing. im wanting to try and get the engine running as good as possible b4 i wire it up and get it on the road, then i can fine tune it and sort out any problems from there. but im just puzzled as to why its goin bang im short on funds at the mo and need to save up to build the battery box and make the loom so a new carb is out of the question (although id give anything for a mikuni carb ) the main jet is a 118 but think il be better off trying to find a new (adjustable) needle setup. ebay is useless and google isnt much better. just thought... could the wrong fuel pump make it run rich? at the mo im using the dragstar fuel pump (for a mikuni carb) as i cant get hold of one for the cbr engine. I'm not an engine specialist but i'd say you have gas left that is unburnt in the motor due to the breathing being improved and the pipe clearing it out. The problem being the combustion chamber just aint burning it all. So you either need to light it earlier or change/adjust the valve overlap to keep the gas in long enough to burn properly. Link to comment Share on other sites More sharing options...
growls Posted January 11, 2011 Share Posted January 11, 2011 my guess is your 'bang' is hot fuel vapour cooking off in your can - hence the bang and flames if no can. Link to comment Share on other sites More sharing options...
2 Wheels Posted January 11, 2011 Share Posted January 11, 2011 I'd be with Cynic on this one. Any popping, banging, backfireing, flames meanes that unburnt fuel is making its way through to the pipe without being burnt propperly. Link to comment Share on other sites More sharing options...
Ttaskmaster Posted January 12, 2011 Share Posted January 12, 2011 I think I'll put up another post, suggesting that it might be unburnt fuel... That much is a given, but finding the location is the key. As others have pointed out, it can be anywhere along the system, so check everywhere for leakage before you start spending money on replacement parts. Link to comment Share on other sites More sharing options...
Paulwhite Posted January 12, 2011 Author Share Posted January 12, 2011 ok will do and cheers il post a reply when iv had a play Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 12, 2011 Moderator Share Posted January 12, 2011 I would fit a new exhaust gasket Paul, you said not long ago your exhaust was cherry red, this could have damaged the gasket and cause an air leak...air leaks cause bangs. Link to comment Share on other sites More sharing options...
Paulwhite Posted January 12, 2011 Author Share Posted January 12, 2011 well it wasnt cherry red it was bright orrange! but il check that 1st thing! could be the leak in the system. Link to comment Share on other sites More sharing options...
barkwindjammer Posted January 12, 2011 Share Posted January 12, 2011 In the first post you said your plug showed rich, and you have a 'freeflow' filter, it sounds like there is a 'wash' of fuel going through the carb-the 'freeflow' filter will allow enough air into the mix to 'gas it' and you get 'ignition' after a few turns, I think (and I know nearly feck all) that you need to turn the mix screw all the way in, then start moving it out a quarter of a turn til it fires, I think you need to restrict airflow too, and get the 'balance' between fuel and air right down to 'lean' and move on from there, if its spitting fire then there is fuel (unburnt) reaching the exhaust, I think your timing is nearly spot on (otherwise it wouldn't fire at all)-not with a 'tsunami' of gasoline going through it Link to comment Share on other sites More sharing options...
Paulwhite Posted January 12, 2011 Author Share Posted January 12, 2011 well iv got the dragstar fuel pump on it which could be forcing fuel into the chamber but the overflow pipe from the carb is dry. it starts up 1st turn of the engine, iv done everything i can with the mixture screw and set it so it dont "pop"... as much. but im gonna put a new exhaust gasket on, take the pump off and see what happens. then set about restricting the air flow in the filter slightly, to try and get it running leaner. but the plug is only reading slightly rich which would suggest that the timing needs a little adjustment but im gonna leave that one till iv tried everything i can think of . Link to comment Share on other sites More sharing options...
Paulwhite Posted January 16, 2011 Author Share Posted January 16, 2011 right been out today and fixed it! you will never guess what it was!! the engine has a secondary air system (PAIR) to reduce emissions, basically its a reed valve on the head cover that lets air into the exhaust to get rid of any unburnt fuel, there is meant to be some kind of control unit that allows a certain amount of air in......but i dont have one lol so looks like im gonna have to come up with an alternative. its always the bloody simplest of things! but yeah cheers for all the help, much appreciated! no doubt il run into more problems along the way lol Link to comment Share on other sites More sharing options...
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