lorenzo Posted January 29, 2011 Report Share Posted January 29, 2011 A while back I put a gsxr 1000 exhaust (full system) on my carb'd srad 750. It ran like shit, would barely start unless you partially blocked the exhaust, so I took it down to a local dyno place. He said I'd got 2 torn diaphragms, replaced them and allegedly set it up. Before the exhaust swap the bike started a treat, within a second or two every time, with a whiff of choke when it's cold. Now, despite it being better than it was when I first did the exhaust swap, it's still hard to start from cold, needing 3 or 4 holds of the starter, each about 5 seconds long. Even when it does catch it takes about a minute until I can release the choke and it settles to a very lumpy idle, only smoothing off after about 2 more minutes of idling. Once it's revving it doesn't seem too bad. When it's warm it starts fine, but then there's also a second fault, when coming from a closed throttle to getting back on the gas it seems a bit lurchy at about 6 or 7krpm; the last trackday I did I was cornering in too high a gear to ease any funny business getting back on the throttle, but obviously it meant I was meandering out of corners, rather than blasting out with my usual verve and panache (ahem....). The jetting is all stock as far as I can tell, and the air screws are at the stock position, 2 turns out. I've checked the choke mechanism and it's all working fine. If I do something with the air screws to aid starting, which way should I turn them and by roughly how much do you think? What impact will these air screws have on the rest of the rev range? Once I find it I'l get a photo of the dyno print out too, the a/f ratio is all over the place, but from memory the upper end of the rev range is OK but the mid is really quite lean, which would seem to my mind to indicate that the jets are fine but the needles need lifting slightly. If I tweak the air jets, what happens to the mid range then? Just for further info, I have a baffle fitted to the end can, if I remove the baffle the starting problem gets worse, I don't know about the lurchiness as I've rarely run it without the baffle as I don't want to spend a week trying to start it. Link to comment Share on other sites More sharing options...
lorenzo Posted January 29, 2011 Author Report Share Posted January 29, 2011 OK, here's the dyno, and rather unhelpfully, it doesn't go down as far as I'd have hoped and doesn't show the fuelling at 1500-2k which'd give an idea about its starting problems (although I'm not suprised either). Link to comment Share on other sites More sharing options...
hipringle Posted January 29, 2011 Report Share Posted January 29, 2011 mate why not put the 750 exhaust back on & see how it is from there?. Link to comment Share on other sites More sharing options...
speedy sie Posted January 29, 2011 Report Share Posted January 29, 2011 https://docs.google.com/viewer?a=v&pid=...4ODEw&hl=en need some of these... and a read of this... http://www.gixxer.com/forums/showthread.php?t=286034 Link to comment Share on other sites More sharing options...
lorenzo Posted January 29, 2011 Author Report Share Posted January 29, 2011 mate why not put the 750 exhaust back on & see how it is from there?. Because the 750 exhaust now lives with a bloke in sheffield and the headers were rotten to fuck. The good news is that this titanium system only cost about £30 more than I sold the 750 end can for. The bad news is it runs like shit. Saw that thread Sie, and I also saw this one, which I think helps me out loads. I'm going to find out what size pilots I've got as stock and go up one then tweak the air screws to suit. Link to comment Share on other sites More sharing options...
lorenzo Posted January 29, 2011 Author Report Share Posted January 29, 2011 In fact, having looked a bit more at the a/f ratio on the dyno, I'd be willing to bet that both the pilot and main jets are a size too small and the needles are up on their highest setting, hence it being lean everywhere apart from at about 8000. I need to buy me some jets... Link to comment Share on other sites More sharing options...
BudgetBoy Posted January 30, 2011 Report Share Posted January 30, 2011 OK, here's the dyno, and rather unhelpfully, it doesn't go down as far as I'd have hoped and doesn't show the fuelling at 1500-2k which'd give an idea about its starting problems (although I'm not suprised either). I gather this is the only dyno you got before the bloke repaired your diaphrams?? Without trying to look stupid here.. Anyone can see it is lacking fuel between 6800-10,000rpm (ISH). But the bike picks up after this.So if it were the jetting and the bike was not getting enough fuel would it not stay "lean"? What i am saying is WHY does it pick up after 10,000 rpm when it is under massive load.Do you see what i mean? Anyway..... These are some of the other things that can cause bad air fuel ratios as well as the main jets.If i have missed any off perhaps someone can add it, i can only think of these off the top of my head. Air Filter blocked Air Bleed Holes blocked Fuel level too low in float chamber Fuel tank breather blocked Carb intake manifolds leaking. Main jet Clogged Main Jet Wrong size Pilot screws out of adjustment Fuel pump faulty An inline fuel filter blocked Water in Fuel/Bottom of float chambers Oh and the Air/Fuel mixture screws.. If you do turn these its "Normally" 1/4 of a turn either way (l or R) and no more. Hope this helps Link to comment Share on other sites More sharing options...
fran9r Posted January 30, 2011 Report Share Posted January 30, 2011 I'd be checking for worn needle and needle jets, plus looking at the starter jet sizes. Presuming the 1000 exhaust is a performance benefit, plus a race can, I think the pilot and mains would need some work anyway. Did he not tell you about any jetting changes he made? Link to comment Share on other sites More sharing options...
ccmhunt Posted January 30, 2011 Report Share Posted January 30, 2011 https://docs.google.com/viewer?a=v&pid=...4ODEw&hl=en need some of these... and a read of this... http://www.gixxer.com/forums/showthread.php?t=286034 Hey, Those are both my instructions and my thread......whats going on over here....oh its the interwebs again. Lorenzo....I got your PM, let me go into the garage today and see what I can put you together.... Link to comment Share on other sites More sharing options...
lorenzo Posted January 30, 2011 Author Report Share Posted January 30, 2011 OK, well a bit more progres was made today: I've wound the pilot screws out by a turn and a half (3-1/2 turns out now) and it seems much more like what I'm after in terms of starting it, especially from cold. It's still not quite where it was with the old pipe on there, but frankly after taking the carbs off twice in one day i was starting to get a little bit peeved with it (although I'm getting a good bit quicker at it now) plus from what I've read the start to become less effective beyond about 4 turns out. The dyno printout was from after I had it allegedly set-up (although I suspect it's me he did that to, rather than my carbs). The fact that it's responded well to the pilot screws being altered, and that they're now most of their way out, that the dyno shows it as being lean up to 7krpm and that I get it surging when I'm coming from a closed to a neutral throttle tells me that the pilot jets are too small. To be honest I don't remember all that the dyno guy said about what had been done but I do remember that he said he'd drilled an extra hole in the pilots to get a bit more fuel through at lower rpms and when cruising. Of course, what he really meant was he should've gone up a size on the pilots but he hadn't got any that fitted. Maybe somebody can help me out here, does it look like I want to go up 1 size or two (I'm suspecting just the one size a I'm still within the range of the pilot screws at idle)? Just to run through some of the things listed above: Air filter is a K&N and was cleaned and reoiled about 1500 miles back. I had a quick look at it and it's very clean. The carbs themselves are physically very clean. They had new diapraghms about 1000 miles back. The inlet manifold is airtight as far as I can ascertain and it's not doing any silly things like revving its nuts off etc. Bizarrely, there is no fuel filter in the fuel line, so unless there's one in the tank? I plan on adding an inline filter in the near future, anybody know of a decent source of filters with a 9mm in & outlet? The pipe is a full system off a k4 GSXR thou, with the butterfly valve removed, and then with an Akra oval race pipe on the end, with a baffle fitted (that's a thought, I should've tried it to see how it started without the baffle as it was near impossible previous to my screw tweaking). It's no race system but the logic is that if it can flow enough gas for a 150hp engine, it can do enough on my 115hp lump too. It's also running a K&N and straight through air intake tubes. The airbox is stock. This time last week I knew very little about the specifics of how to set up a carb and even less about air fuel ratios. I put my trust in a guy who makes it his business to set peoples bikes up, and not only was I let down in terms of the time it took to do the job, the more I read into things, the more I realise he's let me down in the work he actually did do. Also, unless I'm totally reading the dyno wrong (and in which case fuck it, I'm giving up!) then it's not lacking fuel between 6.8 and 10K, it's rich if anything, and it's lacking everywhere else. This middle bit is controlled by the needles as much as anything, so what i plan on doing is to run a larger main and drop the needles down a little. This should stop it running lean 10k+ on the larger jet and then the lower needle should reign in the fuelling 7-10k. Anybody agree with my sussing out of things? Any opinions? Like I say, I'm feeling my way about here and just using what i see as logic, I know there's people out there with hundreds of times the experience I have, come on, fill me in if you feel fit to do so. Many thanks for everybodies input too, as frustrating as it is to be clearing up somebody elses mess, especially when I've paid for it, I feel like I've really learned something this weekend, and it feels good. My scraped knuckles will hopefully heal soon. Link to comment Share on other sites More sharing options...
lorenzo Posted January 30, 2011 Author Report Share Posted January 30, 2011 PS. Forgot to say, back to a thread from last week about which do people prefer, carbs or injection, if I had an injected bike this'd be sorted now, I'm sure.... Link to comment Share on other sites More sharing options...
TriGGer Posted January 30, 2011 Report Share Posted January 30, 2011 Without trying to look stupid here.. Anyone can see it is lacking fuel between 6800-10,000rpm (ISH). But the bike picks up after this.So if it were the jetting and the bike was not getting enough fuel would it not stay "lean"? Anyway..... : Anything above the red line is too lean, anything below the blue line is too rich. HTH Link to comment Share on other sites More sharing options...
BudgetBoy Posted January 30, 2011 Report Share Posted January 30, 2011 Sorry mate i read the graph wrong.. You say that everything is clean on the bike (filter,carbs) I dont mean to be funny but have you taken out all the jets and checked them to see if they are spotless? Also the airways need to be blasted with an air line. You will be suprised on just how easy they are to get blocked..Even more so if it has sat for a while.Anyhow.. Lets say you have done all of this.. The extra 1 1/2 turns has made it run richer now. Right then..So as its lacking in fuel i would be inclined to go UP 1 size on the main jet. I think IMO 2 would/might be overkill. By fitting the new exhaust you have improved the air flow of exhaust gases but the fueling is normal. So Up the Main jet 1 size. Very hard to diagnose something Online if you get me.. But i have had a go. All based on what you have told me. BTW what is your bike 750cc Srad (What year?) I have not had alot to do with Dynos, But the AFR.. I am sure that in order for you to get the best you are looking for 13.0 parts of AIR to 1 part of fuel.Thats volume wise.. This is from what i see,because the (stoichiometric) air to gasoline ratio is 14.7 Air to 1 part fuel.Ths does differ a little depending on the model/make of the engine of course. Link to comment Share on other sites More sharing options...
lorenzo Posted January 30, 2011 Author Report Share Posted January 30, 2011 Carbs have been stripped, sprayed with carb cleaner, blasted through with an air line, all spotless. The pilot screws are what I've adjusted, and again, tell me if I'm misinterpteting anything here, this is simply adjusting the mix at idle. Pilot screws work when the butterflies are shut, and act upon 1 of the 4 holes in the pilot jet (although mine now have 6!), then the opening of the throttle gets the fuel going from the other holes. Hence me adjusting the screws has very little to do with what size main jet I want, this is more a relection of what size I want to go up on the idle jets. Again, the surging issue is related to the idle jets rather than the mains I think; it's happening when I'm coming from a closed throttle (when braking up to a bend for example) to a neutral throttle (as I go for the apex and get ready to get back on the gas). As the throttle is shut and then goes onto a slightly open state then the mains wouldn't be coming into play I wouldn't have thought, this is part throttle stuff rather than wide open. I think I know what I want to do with it to correct things, but it's how much I want to correct it that I'm unsure about, which is where real life dyno experience comes in I suppose. It's a 96 SRAD 750, although there's no difference between the two years they were on carbs for apart from paint. Link to comment Share on other sites More sharing options...
ccmhunt Posted January 30, 2011 Report Share Posted January 30, 2011 Carbs have been stripped, sprayed with carb cleaner, blasted through with an air line, all spotless. The pilot screws are what I've adjusted, and again, tell me if I'm misinterpteting anything here, this is simply adjusting the mix at idle. Pilot screws work when the butterflies are shut, and act upon 1 of the 4 holes in the pilot jet (although mine now have 6!), then the opening of the throttle gets the fuel going from the other holes. Hence me adjusting the screws has very little to do with what size main jet I want, this is more a relection of what size I want to go up on the idle jets. Again, the surging issue is related to the idle jets rather than the mains I think; it's happening when I'm coming from a closed throttle (when braking up to a bend for example) to a neutral throttle (as I go for the apex and get ready to get back on the gas). As the throttle is shut and then goes onto a slightly open state then the mains wouldn't be coming into play I wouldn't have thought, this is part throttle stuff rather than wide open. I think I know what I want to do with it to correct things, but it's how much I want to correct it that I'm unsure about, which is where real life dyno experience comes in I suppose. It's a 96 SRAD 750, although there's no difference between the two years they were on carbs for apart from paint. BTW...there were other differences between the two years. The '96 had issues with piston/valve clearance and most '96 were recalled and a 4ply head gasket installed (lost some compression and performance) All the 96/97's responded positively to larger (#15) pilot jets....Factory pro kits came with them, Dynojet don't as they don't like to alter pilot circuit fueling other that the screw. You are likely rich in midrange and lean on top, as others have said. These bike responded well to drilling out the MAJ (main AIR jet) when installing a larger jet.....staggers of 132.5/135 and 135/137.5 are common in cooler conditions. Float height of 7 to 8mm (measured from gasket mating surface to top of float...spring NOT compressed) is critical. Don't get carried away with worrying about the pilot fuel screw...if everything else is RIGHT, that screw has little effect other than idle and off idle cruise. Link to comment Share on other sites More sharing options...
BudgetBoy Posted January 30, 2011 Report Share Posted January 30, 2011 mmmmm.. Just seems strange that it has only appeared since the exhaust swap.IMO this would have possibly increased your air flow a little. Are your carbs balanced? If they have been played about with, then i would also suggest doing this. Whip the plugs out and have a look at them. They should all be a browny grey colour. If they are WHITE you are lean. If they are Sooty black you are RICH. often this simply thing is overlooked, but IMO gives you an idea on how your engine is running. Your plugs should be CR9E type ones.You might find that there is just 1 cylinder running lean or one running rich. That would show you which carb is the problem. While plugs are out i would do a compession test.This is another thing it could be.. Do a dry & wet test.it will also show you the state of your engine. The dyno people (Im sure,never had one myself) dont check the state of your plugs,compession and stuff like that.You sign a disclamer in case it blows up. summat along those lines..I thought when you went to have a dyno you got one as standard then they set it all up to run better? Oh.. Another thing.. They say that K&N air filters sometimes Rob your bike of power and that the OE is better.. You would have to check on that. But the K&N will make you run a bit lean. Anyway.. Thats my input.. Keep us up to date.. Link to comment Share on other sites More sharing options...
ccmhunt Posted January 30, 2011 Report Share Posted January 30, 2011 mmmmm.. Just seems strange that it has only appeared since the exhaust swap.IMO this would have possibly increased your air flow a little. Are your carbs balanced? If they have been played about with, then i would also suggest doing this. Whip the plugs out and have a look at them. They should all be a browny grey colour. If they are WHITE you are lean. If they are Sooty black you are RICH. often this simply thing is overlooked, but IMO gives you an idea on how your engine is running. Your plugs should be CR9E type ones.You might find that there is just 1 cylinder running lean or one running rich. That would show you which carb is the problem. While plugs are out i would do a compession test.This is another thing it could be.. Do a dry & wet test.it will also show you the state of your engine. The dyno people (Im sure,never had one myself) dont check the state of your plugs,compession and stuff like that.You sign a disclamer in case it blows up. summat along those lines..I thought when you went to have a dyno you got one as standard then they set it all up to run better? Oh.. Another thing.. They say that K&N air filters sometimes Rob your bike of power and that the OE is better.. You would have to check on that. But the K&N will make you run a bit lean. Anyway.. Thats my input.. Keep us up to date.. You are right in that you should at least bench sync the carbs when off, but....sync really only comes into play at idle and coming off idle. Remember its primary effect is butterfly valve relative openings and its impact vs pilot fuel holes in the bottom of the venturi. Run the CR9EK plugs with the dual tips....trust me. K&N do indeed adversely affect carburation in some bikes as they can disrupt HARMONICS in the airbox, nothing to do with air flow and yes will make you run lean. I prefer BMC on that model. The exhaust may indeed be a problem, for a reason that has nothing to do with air flow: a well made pipe is "tuned" in length and design so as to prevent negative pressure waves from arriving back at the exhaust port during periods of valve overlap....allowing already burnt mixture back into the cylinder and possible into the intake. I highly doubt that a 1000 exhaust was tuned with your 96 750 in mind. Link to comment Share on other sites More sharing options...
ccmhunt Posted January 31, 2011 Report Share Posted January 31, 2011 Millemille is quite right. Link to comment Share on other sites More sharing options...
lorenzo Posted January 31, 2011 Author Report Share Posted January 31, 2011 You are right in that you should at least bench sync the carbs when off, but....sync really only comes into play at idle and coming off idle. Remember its primary effect is butterfly valve relative openings and its impact vs pilot fuel holes in the bottom of the venturi. Run the CR9EK plugs with the dual tips....trust me. K&N do indeed adversely affect carburation in some bikes as they can disrupt HARMONICS in the airbox, nothing to do with air flow and yes will make you run lean. I prefer BMC on that model. The exhaust may indeed be a problem, for a reason that has nothing to do with air flow: a well made pipe is "tuned" in length and design so as to prevent negative pressure waves from arriving back at the exhaust port during periods of valve overlap....allowing already burnt mixture back into the cylinder and possible into the intake. I highly doubt that a 1000 exhaust was tuned with your 96 750 in mind. All bench balanced tested and it was OK by that and I'd have hoped that as the guy had the carbs properly apart he'd have at least done this. It's OK in terms of response off idle etc once it's warm, I've had unbalanced carbs before and this doesn't feel like that did. It's interesting to see about dual tip plugs and also to see that there were changes between the years. I may get some of the dual tip plugs and see how they go. My plugs at the moment show it to be a bit lean, they're a sandy colour, a bit pale, but they were already 6 months old before the exhaust swap so some of the colour might be from them (how long do the deposits last for?). Lastly, I know the thou exhaust isn't going to be tuned for my bike, it's clearly a very different design to the srad one; the headers are longer by about 2", slightly narrower too. This is one of those things where you read on the 'net "I did this swap and it worked out fine", and you assume what the guy writes is true. I guess that some of the people who did this swap didn't ride their bikes anywhere close to how they were designed to and must just cruise about the street on them. Don't get me wrong, it's perfectly ridable as it is, but as you probably well know, any slight issues tend to get magnified when you're out on track. The plus side is that this is about a third of the weight and doesn't have dirty great flakes of rust falling off it like the previous one did! The plan is to get it ballpark with new jets/needles, do my trackday which is coming up on the 26th Feb, then get it dyno'd and fine tuned with the needle and float heights. Hopefully the effort put in now will save a bit of time on the dyno, but it's still something I want to do, even if it's just to know that between us we've made a half decent job of getting it sussed out. Link to comment Share on other sites More sharing options...
ccmhunt Posted January 31, 2011 Report Share Posted January 31, 2011 Ok I will get into the garage and see what I can put together for you. You offered me too much money in trade. BTW, I hope to hell that if you are taking that bike on the track, that you have replaced the ACCT with an MCCT Link to comment Share on other sites More sharing options...
fran9r Posted January 31, 2011 Report Share Posted January 31, 2011 You are right in that you should at least bench sync the carbs when off, but....sync really only comes into play at idle and coming off idle. Remember its primary effect is butterfly valve relative openings and its impact vs pilot fuel holes in the bottom of the venturi. 9Rs are sensative to carb balance, and I find the corner exit is greatly cleaned up with the right sync. Bench balancing CVs is pointless -they need to be on the bike, running to get them properly setup. Although if they have been apart, it's useful as a very rough starting point. Link to comment Share on other sites More sharing options...
lorenzo Posted January 31, 2011 Author Report Share Posted January 31, 2011 Ok I will get into the garage and see what I can put together for you. You offered me too much money in trade. just because I offered it, doesn't mean to say you have to accept it! BTW, I hope to hell that if you are taking that bike on the track, that you have replaced the ACCT with an MCCT Nope, are they that unreliable? I've done 3 trackdays with it already. If it jumps it's new valves time, at the very least, yes? Link to comment Share on other sites More sharing options...
Tennis Posted January 31, 2011 Report Share Posted January 31, 2011 Looks like the needles are too rich and the main jets are leaning off at the end. It goes like this. Pilots to about 1/4 throttal Needles from 1/4 to 3/4 throttal Mains till full throttal Link to comment Share on other sites More sharing options...
ccmhunt Posted January 31, 2011 Report Share Posted January 31, 2011 Almost all the automatic cam chain tensioners on that year model fail. Typically happens when you chop throttle at high rpm. Not worth the risk when all things are considered, especially since the MCCT is a $50 part. This last summer I had the same conversation with a newcomer at the track. Next track day, there he was standing next to the fire crew as they put out the flames fed by hot oil coming out of the cases, the result of a chain of events initially caused by CCT failure. Link to comment Share on other sites More sharing options...
lorenzo Posted January 31, 2011 Author Report Share Posted January 31, 2011 Almost all the automatic cam chain tensioners on that year model fail. Typically happens when you chop throttle at high rpm. Not worth the risk when all things are considered, especially since the MCCT is a $50 part. This last summer I had the same conversation with a newcomer at the track. Next track day, there he was standing next to the fire crew as they put out the flames fed by hot oil coming out of the cases, the result of a chain of events initially caused by CCT failure. Fires from the oil huh? That's not going to be cheap, is it. Still, most of the bodywork's melted away round the badly fitting exhaust, a little fire's not going to be the worst thing to have happened to it. Seriously though, it's well worth the tip, how often do they need adjusting etc, and it is possible to do it with the carbs on etc, just flip the tank up? The reason I'm on the auto one is that I know I won't bother tensioning it up too often if the job's a horrible one to do. Link to comment Share on other sites More sharing options...
ccmhunt Posted February 1, 2011 Report Share Posted February 1, 2011 Fires from the oil huh? That's not going to be cheap, is it. Still, most of the bodywork's melted away round the badly fitting exhaust, a little fire's not going to be the worst thing to have happened to it. Seriously though, it's well worth the tip, how often do they need adjusting etc, and it is possible to do it with the carbs on etc, just flip the tank up? The reason I'm on the auto one is that I know I won't bother tensioning it up too often if the job's a horrible one to do. CCt fails at near redline, all the valves go, rod goes through case, oils down tire, bike crashes in next turn, fuel from carbs catches fire and mixes with oil = end of bike (it needed to die....as it was a horrible pink bike with the shocker painted on the side). MCCT sticky on GDC Link to comment Share on other sites More sharing options...
lorenzo Posted February 1, 2011 Author Report Share Posted February 1, 2011 According to that article the later revised acct is an upgraded part, if I replace mine with one of these will it be OK for future easy running? Link to comment Share on other sites More sharing options...
ccmhunt Posted February 1, 2011 Report Share Posted February 1, 2011 According to that article the later revised acct is an upgraded part, if I replace mine with one of these will it be OK for future easy running? it is likely possible. Link to comment Share on other sites More sharing options...
speedy sie Posted February 1, 2011 Report Share Posted February 1, 2011 would just like to point out my cct failed on my 99 inj srad,lucky it did it when i parked up,and let the cluch out ibn gear the bike jumped and the cct poped out!...so this is on a 99 fi srad,so be warned. Link to comment Share on other sites More sharing options...
lorenzo Posted February 1, 2011 Author Report Share Posted February 1, 2011 would just like to point out my cct failed on my 99 inj srad,lucky it did it when i parked up,and let the cluch out ibn gear the bike jumped and the cct poped out!...so this is on a 99 fi srad,so be warned. Hmm. OK, I may have to consider my (only) option. Link to comment Share on other sites More sharing options...
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