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Discussion Starter · #1 ·
I just replaced the spark plugs on my '05 650 and have been noticing that at low RPMs around town I get a bucking or surging feeling when I am holding a dead constant throttle. Nothing too bad, just feels like I am running over little bumps more or less (the road is flat, so I know its not that). Also, I feel like I am getting more small back fires when I decelerate and sort of a low gurgle at times that sounds like it is just on the verge of being a backfire but doesn't do it. But this just might be my imagination since I am actively listening for it now, but I am like 90% sure I am backfiring a little more now.

My first thought was that it may be a bad gap on the plugs since I didn't have a gap gauge and thought the new ones looked about right, so tonight or tomorrow, I am going to pull the plugs and check the gap to confirm.

The second thing that came up as I was searching was people kept mentioning TPS adjustments might be the problem, but I already adjusted mine at the end of last year, and it was running fine until I changed the plugs. Do you need to readjust the TPS when you change the plugs? sort of makes sense I guess ???

The plugs are the only thing I did that would have changed anything. Is there something else, that may have coincidentally happened at the same time, or that I may have hit while changing the plugs that could cause this problem? Anybody have this issue before and figured out where it was coming from? Thanks in advance! And sorry for the long post.
 

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Any chance you adjusted your chain recently? Check for consistent slack in several locations around the length of your chain, looking for a tight spot. if you don't have a rear stand, use an approximately 12" long 2x4 to wedge under the right side swingarm to lift it a little bit (this works well for lubing the chain too.) This may not help but it's something that took me weeks to figure out, even after taking it to the dealer to check.
 

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Discussion Starter · #3 ·
Funny you should mention the 2x4 method, I just tried that out yesterday actually to lube my chain, because I didn't have the time to start anything major, but had a little time to lube the chain up nice and good to make sure that it was not just in need of a lubing. Didn't seem to make a difference, and chain seemed alright slack-wise, but I guess I could give it a check in a few more spots to make sure its not bound up anywhere or over-stretched someplace.
 

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I'm thinking TPS needs adjusment

Made a huge difference at low speed on my bike

Can't say it better then this guy did
http://forums.sv650.org/showthread.php?t=55459

2nd thought.. did you use the right temperature plug? Did you use a Japanese plug?.. I know it sounds dumb but I put Bosch plugs in a Subaru once and it was missing at low speed talked to subaru mechanic and I was told "never put German plugs in a Japanese motor" I had to swap them out even though bosch claimed they were meant for my vehicle. I sent them back to bosch for a refund as they guarantee them to work.. nothing ever came back.. live and learn!
 

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I second the chain. It may need to be cleaned. when you are checking it you may see that the links may loom like they are slightly zig zagged or lightly kinked rather than being in a nice straight line. If it is kinking youll find tight and loose spots like svscott mentioned.
 

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You might have damaged a sparkplug wire taking them off when you changed the plugs. Please check them all carefully as a misfiring plug will do what you are experiencing.

The TPS sure CAN cause you grief....and it wouldn't hurt to check it again....but if it wasn't missing like you have now before you changed the plugs, my money is on the plugs or installation. It is possible to crack a plug too...so a double check there is in order too.
 

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Discussion Starter · #7 ·
Renderw - I did get the right plug, right temp. got an NGK CR8E which is what the manual calls for as the standard plugs. Will check the TPS just to be sure today.

Recoil - I am leaning towards something with the plugs. I am going to pull them and take a look at them and the boot/wire.

Thanks again for the help guys!
 

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That's weird man, mine has been doing something kind of similar to that as well since I did my plugs that day. Let me know what you find.
I'm also due for a new chain and sprockets, mine is starting to bind up a bit so I'm getting a replacement tomorrow.
 

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Discussion Starter · #9 ·
That's weird man, mine has been doing something kind of similar to that as well since I did my plugs that day. Let me know what you find.
I'm also due for a new chain and sprockets, mine is starting to bind up a bit so I'm getting a replacement tomorrow.
Maybe some bad mojo from the garage lol
 

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Discussion Starter · #10 ·
So this afternoon I started the process of figuring this out. First went out to pick up some new plugs just in case, but the local stores didn't carry the correct size, but on the way noticed my idle was a touch on the low side, so brought it up a bit while at the store, but it was still was acting up on the way home. Then I pulled the plugs and checked all the cords and boots, they looked good, the ceramic on the plugs didn't look cracked. Checked the gap on the plugs and they were a little wide, maybe by about .05-.07 mm, so nothing crazy, but brought them back to within spec. Put some dielectric grease on the plugs and boots, and made sure I really pushed the boots on when I reinstalled them, just in case I didn't get them all the way down. Checked the TPS but it was spot on, hasn't moved a hair since last year. Went for a lap around the block, and it seems to be pretty good, but not 100% sure yet, need a little longer ride to figure that out, but I was hot and sweaty and full of grease, and no gear on, so that will have to wait for later tonight. I will see how it goes after that to see if I got it all settled out.

Darrin, I would say just go over everything again when you get a chance, just slow and make sure all is fine, especially the gap on the plugs and the boots are pushed all the way down. I need to do my chain too, the more I look at it the more nasty it looks, and I really just want to change it for some peace of mind, since I think the PO didn't really show it as much TLC as I would have liked.
 

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Discussion Starter · #11 ·
Well, although I had thought I had solved the problem a couple weeks ago, as soon as I went more than just around the block, I realized that while it had gotten better, it was still there. It is RPMs waver up and down a bit while it is just idling, so I am pretty sure it is misfiring a little bit. Now I am thinking that it either has something to do with the plugs themselves (ordered a new set of plugs since they are cheap, so cant hurt to change them) or the wires/boots/coil. I guess what I am looking to see is, is there any way to test with a multi-meter or something to confirm which plug is misfiring, and then to test if its the wire that is misfiring and not something else? I ask because the wire/coil is around $60 each so I don't want to just go and throw $120 at it without being sure that it is what is wrong or if I only need one, then $60 would be better than $120 at least.

Once again, Thanks all!!
 

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Hmmmm.....doesn't sound like the coils/plugs/wires are at fault now if the engine runs well at higher rpms. It does, doesn't it?

A little idle instability is to be expected of an engine with such a high state of tune...relatively speaking. Any operation below 3K is just there to allow you to get to the higher rpms.:) Does it run smoothly from 3K up?

You don't show your mileage on your information....how long since a valve clearance check? If you are interested in smooth low rpm running, setting the clearances to max. will help. Synching the TB's should be checked too if you haven't lately as them being off can cause some instability.
 

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How low of RPMs are we talking? Are you just lugging around, because that would feel like what you have described. Does the problem go away when you are going same speed, one gear lower.
 

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One thing that's easy to check, that also causes low speed weirdness is a vacuum leak. Check the vacuum caps on the throttle bodies. They go bad after a few years, crack and leak. I've had to replace mine twice. The first time the bike was running bad, surging, missing and not very happy at low rpm.

I'm working on some "bullet proof" vacuum caps that will last a long time. The OEM Suzuki caps will last a few years; the kind you get at the auto parts store might last a few months, tops.

Anyway, check the caps.
 

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Discussion Starter · #15 ·
Recoil - I have about 12K miles on the bike. Usually it smooths up after about 4.5-5k RPMs, and once I clear that, I don't feel any more misfiring. Might not hurt to check my valves, they are due at 12K aren't they?

Trace - Not too low of RPMs, and depending on what speed I am at, it usually goes away with a down shift, but then I am hitting 5-6K cruising around apartments, which I try not to do too much.
 

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Discussion Starter · #17 ·
RD - Are you talking about #6 on this fiche? Is there only one cap to check, or one per TB?

Twins - I am 100% sure now its not the TPS. Checked it the other day, and without loosening the screws, just checking the activation point, it hadn't moved since the last time I did it at the end of last year, so I know its not moved for sure.
 

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There should be 3 of those caps, 1 on one TH and 2 on the other. I have had to replace those before and when they start to get old and crack it will have issues. My bike was missing and stalling due to the vibration making those cracked caps leak air in.
 
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