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Discussion Starter #1
Hi guys,
I've been lurking on this site for a while and looking up solved problems of others has helped me a lot in the past.

I have an issue with my '99 SV and tried quite a few things to resolve it, but unfortunately nothing helped. The problem is that the bike idles at around 3000 rpm with the choke off. It's also quite unstable and there are some notable backfires coming from the exhaust. These backfires aren't too loud and pretty regular.

I've tried a few things to fix it:
Replaced choke cable and plunger springs. Plunger now return to the 'closed' position consistently. Choke closes as it should, but doesn't open all the way; starts fine though.
Replaced air/fuel mixture screw (one was seized and unable to adjust), then turned both screws all the way in and from there, turned them 2,5 turns out.
Tried starting with the fuel cap open.
Checked for cracks at the carb boots, but they were solid.
Cleaned the pilot and main jets with compressed air and looked for the sizes - they are still stock

Am I missing something here that causes these problems? Should I look at rejetting as the bike does have a stainless yoshimura exhaust? It wouldn't idle at double the speed because of stock size jets, would it?

I made a video so you guys can see what is happening:
 

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Good eve,

I’m guessing the bike was fully warmed up for the video you posted? I ask this because it sounds like the fast idle needs adjusting.

I’m rather assuming the carburettor bikes do have a fast idle system - my bike is a K6 (so a pointy) which has run much better since adjusting the fast idle and balancing the throttle bodies.

Good fortune,

Alan


Sent from my iPad using Tapatalk
 

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Discussion Starter #4
Oh yes, I forgot to mention that I used the idle adjustment to turn it down, but it is now fully turned out to the point where the screw doesn't touch the throttle assembly anymore, i.e., its lowest idle setting. This is why I wondered how the idle could still be at 3000 rpm.

I also balanced the carbs before I took them apart last time.. does it need another sync after?
 

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Have you sprayed carb cleaner around the carb connections and manifold to check for vacuum leaks?

I would check the sync with vacuum gauges, especially if you made some adjustments.

Because you said the choke mechanism doesn't open all the way I'd double check the reason for that.

If you add some choke when it's idling high do the RPMs go higher or does it sputter and stall?
 

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Discussion Starter #6
If you add some choke when it's idling high do the RPMs go higher or does it sputter and stall?
When I add choke it does increase idle speed and it is a bit more stable in rpm when it's higher up.

I'll give the carb cleaner method a go tomorrow and also sync it again to see if it improves.
 

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Discussion Starter #7 (Edited)
When I started the bike this morning it seemed to have magically fixed the idle problem. It now runs at ~1500 rpm. I also just tried syncing the carbs and it's at an acceptable level now, but I can't get it in sync perfectly. I noticed some new things about the bike that are a bit worrying. When I had the air filter off, the front carb pushed out a large amount of air from the intake side a couple of times. Those were some pretty loud pops.. Could it be that the exhaust valves are totally out of spec that causes this?
I also noticed that when applying too little throttle, the engine was bogging and stalling. Should I be looking at the air/fuel mixture screw for this? I replaced the screws and turned them fully in and 2,5 turns out, but I'm starting to doubt if this is the correct setting for my sv. I checked the resistance of the coils and they seem to be in working condition.

Edit: I just started the bike again with no difference other than the vacuum gauges hooked up and the idle is back to ~2800 rpm again. I'm starting to think it's extremely lean at idle.. Maybe it is unable to burn the mixture and it spews back out through the intake?
 

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Still sounds like a vacuum leak or the choke (enrichener) is hanging up and bumping the idle.

Can you confirm the throttle mechanism isn't hanging-up and holding the slides up slightly sometimes?

2.5 turns out on the idle mixture screws should get you in the ballpark, and should be a decent start. If that's not the case, there may be other factors going on.

I would check the valve adjustment and confirm carb sync also.
 

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Discussion Starter #9
Hmmm... I did the carb cleaner test to look for any leaks but I couldn't find any. It's a bit hard to tell with the irregular idle, but I'm sure there are no significant vacuum leaks. On visual inspection, the intake boots look air tight as well.

I completely unhooked the throttle cables to be sure it's not hanging or anything, but unfortunately there's no difference.

I have a bad feeling about the choke system... I replaced the cable and plunger springs and that resulted in the choke lever not going past the halfway point, i.e., it goes from completely off to halfway on. I wonder what the reason for that can be. When I operate the choke handle with the plunger out of the carbs, I can see that both cables extend and retract.
The picture below shows my plungers in the closed and open position respectively and it looks to me like it is fully closing.

Btw, when I operate the choke while it's installed in the carb I can also hear that it's doing something.
 

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So my recent experience might shed some light. Bike ran perfectly until I replaced the fully functional JB Welded petcock with a new ebay repop. Next morning bike sat in a pool of gas with the front cylinder hydro-locked with fuel. I sent my carbs off to the carb guy for a rebuild, slapped 'em back in with the old petcock and had much the same symptoms OP describes. Turns out my choke cable was not held under securely under the metal cable tie to the left of the steering head, but rather floated forward when the bars were turned to the left stop and then became hung up on the turn signal mount when the bars were turned back to center. By the time I figured it out the front choke plunger cable had become ripped out of the plastic mechanism so that the front choke plunger is now held by its spring in the fully closed position. I secured the cable back under the metal tie and observed there was now sufficient slack in the cable to allow for lock-to-lock handlebar movement. Now when the choke lever is pulled only the rear carb receives the extra dose of fuel, but the cable housing is not being pulled on with handlebar movement and it starts and runs and idles just like before. Choke cable routing was 100% the issue in my case.
 
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