Hey all,
I picked up a 2004 Gs500 a few weeks back as my first owned bike, and its been a blast. I've taken it out every chance I get and have been fixing up the minor problems as I go. My coworker even lent me an old mercury manometer so I was able to try and sync up the carbs. One problem that has persisted, and which I am having much difficulty diagnosing and solving is the bikes excessive backfires. It backfires when the engine revs up and down and even while driving along at a constant speed. I mean to an extent it's pretty cool, but I think its definitely hindering the bikes performance. The previous owner had clearly done some work on it, with a different exhaust, headlight setup, and a few other things. I assume its down to something they did. I've fully cleaned the carbs, and I didn't find anything startling there. I read that usually backfires are caused by an improper mixture, but I'm kind of stuck on how or what to do next.
Thanks guys for any help or recommendations,
-GSWill
A properly set up GS will crackle quite a bit on deceleration but shouldn't do any kind of popping on acceleration.
There are basically two causes for popping or crackling on acceleration. My gut tells me it has to be too lean, making the exhaust too hot, and causing unburnt fuel to ingnite in the pipe. But it can happen when it's too rich particularly only one specific throttle/rpm/load situation, especially if you have an exhaust leak.
If the bike has mods then it's likely it's too lean. Maybe way, way too lean depending, like if it has pod filters or lunchbox and stock jetting. Too rich IME results in a hard rpm limit and horrible fuel economy and not more popping.
That said, on decel, a GS will do a whole lot of crackling and popping like a 70s IMSA car, even if it's not too lean. That's just normal for a carbureted motorcycle. FI bikes have a hard fuel cut on decel that prevents it. Some of us can't get used to that not crackling so we ride the throttle a teeny bit on decel on a FI bike to get it to crackle, like on a 2012 Triumph Bonneville SE... not that I would know anything about that, of course, just speculating.
Thanks for the reply mr72 :star:,
The motorcycle still has its original airbox on it, but I do think that the bike is running lean. What can I do about it? Sorry to put you on the spot. I like the idea of understanding my bike, and not paying someone to fix it.
-GsWill
Crappy air filter?
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The air filter seems to be in great shape still. I checked the float levels today which seemed to be good as well.
Did you check the float level or the fuel level? Float level is really a proxy measurement for fuel level. Fuel level is what really matters in the end. I use float level to get me close, and then check fuel level to be sure. Are the GS500 floats even adjustable? I think on my '04+ carbs at least they are all plastic and can't be adjusted.
Have you pull the carb apart to see if there are any aftermarket bits? Maybe washers on the needle or larger than stock jets since they messed with the exhaust. In fact, they should have messed with the carbs because an aftermarket exhaust with stock jetting will run lean.
The fastest way to figure it out is to return everything to stock. That means finding an OEM exhaust, making sure all the carb internals are back to factory spec, and making sure you have no air leaks by replacing all the rubber bits between the airbox and intake (carb internals, intake boots, intake boot o-rings). Its hard enough to find the right carb settings for an aftermarket exhaust when the bike was running good before hand, you are trying to do that while simultaneously diagnosing other things that might be wrong. Too many variables...go back to stock first.
totally agree with bluesmudge. But actually I think it's more likely rich and lean, probably both, depending on throttle position, slide level, etc. It's really easy to get the carbs into this state especially if you alter airflow characteristics.
Aftermarket slip-on exhaust will make very little difference in target jetting on main. I have a 13" long yoshimura straight through slip on and I'm actually between jet sizes stock and +1 size, it's a hair rich +1 size and a hair lean on stock jet. I had to tinker with needle position to get it to run just right. But it would be really close with it stock.
I am just not sure this is an actual problem. You could try shimming the needle one washer, or checking it. Main jet will really only purely affect WOT and high revs (like over 6K). Below that, needle position will make a bigger difference, and float level is critical.
Follow the link in my signature for more details :)
My guess is it's lean in some conditions because of a vacuum leak, and rich in other conditions because of what someone did to try to counteract the vacuum leak leanness. So you dump unburnt fuel like at idle and then it goes lean at WOT because of the vacuum leak, heats the exhaust valves a lot, you get crackling and popping in the exhaust, you let off the gas, it dumps a bunch more unburnt fuel, on and on. The symptom feels like it's lean but the real problem is a vacuum leak and you don't fix a vacuum leak by making the pilot mixture richer.
Hey Guys, thanks for the fantastic replies.
I had the carbs apart on Sunday and found that they were relatively clean. It was a bunch of fun to get them out of the bike and not so much to get them back in. That airbox is such a PITA. I wasn't able to tell if the jets in my carbs were stock or not... I couldn't locate any markings on them which is a bit frustrating. You fellas have me convinced it will probably just be worth buying some stock ones and switching them out (let me know a good place to get such items I have no idea where to even start). After I had them back together and on the bike, I checked the float level with the clear tube trick and found both levels to be very close to the top of the float bowl casing.
Flash forward to today I was spraying down the running carbs and boots with a bottle trying to find any vacuum leaks, which didn't reveal anything other than my carbs were covered in dust ;).
I suppose my issues are probably mostly down to an aftermarket exhaust and unknown jetting.
-GSWill
mr72, I had honestly read that article over a few times already and found it useful in setting the idle right. Maybe have to pay more attention to the other parts too :laugh:.
Dont buy stock jets, buy 1 size up - 20, 132.5, 1 washer 3 turns on air screw.
I used to sell them, I might in a week or 2 if I find my stock.
Cool.
Buddha.
If the jets are not marked, I would be concerned that maybe a previous owner put in a "dynojet" kit that included not only jets but needles. Are the needles alloy, or are they stainless?
Backfiring or popping on acceleration or while riding at constant speed is not only a fuel mixture problem. You need to sort whether it's truly "backfiring", that is, ignition in the intake tract, or if it's exhaust popping, that is, igniting in the exhaust port or header. If it's exhaust popping, at steady speed and accelerating, it almost has to be an exhaust leak plus too-rich mixture. The rich mixture may be totally acceptable. Check the plugs, and if it seems to run fine, accelerate like it should, and the plugs aren't black, then I'd quit fiddling with the carbs and focus on how air is getting into the exhaust.
Could the PAIR system cause this? Does the '04 have PAIR? Someone else needs to chime in here, IDK about the later bikes and PAIR. I know removing the similar SAI on my Triumph basically eliminated any popping in the exhaust but this was always on decel.
Yes, the 2004+ GS500s has the PAIR system. Gen 1 Hayabusa PAIR block off plates fit the GS500 (thats how you have to buy them since nobody sells them specifically for the GS500). Removing the PAIR system is lot of pipes and tubes you can remove to simplify working on the bike.
Its a good point mr72, since the purpose of the PAIR system is to help burn the unburned fuel/hydrocarbons to in the exhaust to reduce emissions and I imagine it was carefully engineered to be paired with the stock exhaust. It works by adding air to the exhaust system. Its been a long long time since I removed my PAIR system, but I think I remember that it stopped a lot of popping on decel when it was removed from my bike. That still doesn't explain the popping on acceleration which should never be happening.
GSWill2002 should look at the parts fiche and see if all the parts for the PAIR system are still there. Btw, holly hell were you born in 2002 :o These must feel like antique bikes to you.
I know this forum hates the dynojet kits, but I did have a local shop install it on my bike and checked using an actual dynometer with several dyno runs to dial in the jetting). No offense to The Buddha, but I find this dynojet setup runs better than I ever did with my +1 Mikuni jets from The Buddha.
FWIW I don't hate the DJ kits ;) It's just that once you get in their walled garden, it can be hard to unwind it. It's a bit of an unknown quantity.
If you put bigger exhaust on, or in particular headers without the crossover pipe like stock, then it could potentially screw up the PAIR system operation to the degree that it may cause popping not on decel.
My GS has no PAIR (it's a 92) and big exhaust, lots of popping and crackling on decel. To me, that's just normal. Exhaust is hot, on decel some fuel leaks through and ignites in the exhaust tract. Nothing to it. I think it's not a bug, it's a feature. But on acceleration or steady it shouldn't do it, PAIR or not.
Ok, The Buddha hates dynojet kits. I actually argued with the shop about using it but they swore by it so I let them try it. Probably good in that scenario where it can be dialed in and then its done but for the home mechanic it would be a nightmare if anything needed to be changed. I guess that's now the situation that GSWill2002 is in.
Exactly right IMHO bluesmudge!
What I dont get about DJ kit is - how is the next size up from 128 a 134 or whatever crap they sell ? Is that cos that's the next size drill they had lying around ? I'd like to tell em ... "psss you're missing a lot of numbers between 128 and 134".
Yea you need stock needles for using the formula I posted or my "kit" if ever such a thing materializes.
Cool.
Buddha.
I think the DJ jet sizes are relevant for their needles. You have to pair them together. And they are sized according to other mods they recommend, so it's a kit-by-kit thing.
I understand this as a marketing effort. You can package a whole kit of mods that if you install it all together it'll have a known effect, not requiring the home mechanic to do any diagnosing or tuning. Of course, I'm just not that type of buyer, I'm the guy who puts together my own "kit" and I need to rely on the input and guidance of others like me who have access to the same parts and materials as I do. So putting DJ needles in the mix makes it basically impossible to know what you are doing tuning wise unless you can put the whole DJ "kit" in place that came with the needles. But if you do the DJ kit and then do something like change the exhaust then life gets a lot harder.
I have a friend with some Yamaha 1600cc v-twin cruiser who has been struggling to just basically get his bike to run after putting in a DJ kit. It worked at first, then after a couple of winters of non-use, the bike basically won't run and DJ can't help him. You get a carb rebuild kit and all of the sudden you are wondering, which of these rebuild parts work with the DJ kit? Which don't? So you wind up returning to stock and re-tuning towards your mods using regular parts.
Anyway, probably off the OP's topic. Who knows what the needles are, just something to check. Backfiring or popping on accel or steady is not normal, but backfiring on decel, even if it's light decel, is totally normal.
If you know what each part of rebuild kit is and does, you can tell.
Or put a pic - I'll explain what each is.
Cool.
Buddha.
Hey all,
Thanks for all the great ideas and replies. My boss had a friend over the other day, who just happened to be an avid motorcycle collector. I was talking over some of the troubles I've been having with him, and when I started the bike he was almost immediately sure it was running very rich. Yeah, I think he's right. This means that its time for me to get some jets that are the right size. I read below that I should get jets that are the next size up, but I don't really have any idea where. If anyone knows a good supplier, let me know. Thanks again for the help,
-GSWILL
Next size up would make it run MORE rich.
I've used jetsrus.com because they sell real Mikuni parts. I haven't been impressed by the quality of aftermarket carb parts.
Find out what size jets are currently in the carb first.
Quote from: GSWill2002 on October 31, 2021, 06:16:11 AM
Hey all,
Thanks for all the great ideas and replies. My boss had a friend over the other day, who just happened to be an avid motorcycle collector. I was talking over some of the troubles I've been having with him, and when I started the bike he was almost immediately sure it was running very rich. Yeah, I think he's right. This means that its time for me to get some jets that are the right size. I read below that I should get jets that are the next size up, but I don't really have any idea where. If anyone knows a good supplier, let me know. Thanks again for the help,
-GSWILL
Where are you based?
You've probably got a high or a stuck float. Its hard to get it to be rich via jetting alone - unless someone did a K&N lunch box, then went back to the airbox without bothering to rejet.
Cool.
Buddha.
@herennow I live in the Boston area.
Mr. Buddha, I had heard that the float being stuck could be an issue, so when I took the carbs apart I had the floats off and gave them a real good clean. They seemed to move smoothly, and when I checked the float levels after putting them back together they were both where they should have been.
Thanks guys,
-GSWill
I bought jets form AliExpress, and found them to be spot on. I can share the supplier possibly but it was a while ago. I bought two each of 4 or 5 different sizes.
Quote from: herennow on November 05, 2021, 06:56:48 AM
I bought jets form AliExpress, and found them to be spot on. I can share the supplier possibly but it was a while ago. I bought two each of 4 or 5 different sizes.
I got Jets from Aliexpress, and they were embedded with corona virus. This is just a joke. Couldn't resist taking a dig at my competition and china at the same time LOL.
Cool.
Buddha.