Surgin on steady throttle - Page 2 - SV650.org

johnnyrod · 07-06-06, 01:56 PM

To be honest is sounds more like either it's running lean or as Sid says the carbs are out of balance. Doubt very much a new battery will make any difference. If you roll off the throttle does it go a bit faster? If you roll off then on again is it better than if you'd just whacked it open and kept it there?

On the two curvy SVs I've checked, the throttle position sensor was a mile out of adjustment, not sure how big a difference it could make as when set back to rights neither bike seemed different. Also bin the retarder (TRE mod), no need for this really but might help.

07-06-06, 06:48 PM

Cheers everyone

I'll give the choke cable a going over this weekend, if family and football will allow.

At present I am assuming the carb balance is Ok as has just been done, of course they could have mucked it up but it is certainly better since the service.

Johnnyrod - how could it have started running lean if nothing had been touched? I had thought that maybe a carb diaphragm had split, or maybe there's an air leak between the carbs and the engine. The problem doesn't seem to occur when I whack the throttle open, at least you don't notice it and it accelerates fine, it seems more of a problem on partial throttle opening, not very often I get to ride it at a constant speed with the throttle fully open and it's only really a problem at steady speed. How easy is it to check the throttle position sensor? maybe it is on it's way out.

When I mentioned the problem to the mechanic who serviced it the first thing he suggested was plugs, that's why I thought about the battery maybe being an issue. I changed the plugs myself, and what fun and games that was, last year when the problem first appeared and it made no difference, they changed the plugs again as part of the service, or they said they did.

The rev counter seems pretty steady when idling, if I rev i up to higher revs while stationary the revs do seem to vary , the needle moves about randomly, not a vast change in revs but maybe 500 rpm either way but with no pattern or regularity.

I just want it back to running smooth again, it's not a major problem but it does really irritate, maybe I should have waited a few years and got a fuel injected one, I bought it early 2000.

21QUEST · 07-06-06, 08:05 PM

rwball if you don't mind I'll piggyback on your thread

.

Any ideas guys/gals on why when I shut the throttle the revs go right down(bike almost cutting out) the goes up again a touch and then idles fine.

I'll be checking the usual suspects(air leaks** etc) tomorrow and balancing the carbs again. I did change the carbs and did a quick carb balance check. They were a little bit out but didn't have time to do it so was going to wait till the weekend. I can't recall having experinced the above symptons even with the carbs out of balance

**My experience with regards had air leaks the symptoms have normally been erractic idle or/and the revs taking time to come from closed throttle.

Cheers
Ben

07-06-06, 09:26 PM

Too me it sounds like either the the choke plungers are stuck open. (this would mean no amount of fettling with the choke cable is going to sort it) or you have a tight spot on the chain and have the chain tightened to tight to allow for the tight spot.

If the choke plungers are stuck in the open position, then you will only get the stuttering in lower speeds.

If the chain has a tight spot you will only get the stuttering at lower speeds.

The choke plungers have springs in them, which return the plungers to the closed position when the cable is slackened off. You could always check that when the cable is released (or the choke is switched off) that the plungers are indeed going into the closed position.

Checking the chain, move the bike forward slightly and check the slack on the chain, move the bike forward a little bit and check the chain again. Keep doing this until you have gone round the chain completely. If you find a tight spot adjust the chain tension correctly to the tightest spot. This will probably not eradicate the surging or spluttering like symptoms completely but should make it better until you replace the chain.

21QUEST · 07-06-06, 10:11 PM

Ok , but are you now going to have a go at telling me what's wrong with mine

:P

Cheers
Ben

johnnyrod · 08-06-06, 09:42 AM

Ball, TPS calibration procedure is in the manual, easy to get at, but you need a good multimeter. Difficult to say if it's carbs or ignition without some fiddling, BigApe could well be right as this is a known problem.

Quest not sure but sometimes out of balance carbs could do this. In my experience one carb "leads" the other - if you have it out of balance one way it's almost okay but the other way and it's a bag of crap. Is the idle speed set a bit low? Does it stall occasionally if you pull up at a junction after zooming along?

10-06-06, 10:41 AM

Hi Big Ape JohnyRod and everyone
Thanks for the suggestions, I don't think it's the chain, if I rev the bike up 6 or 7 K when it's in neutral and hold the throttle steady the revs don't stay steady they jump around erratically.
Thinking about the choke plungers, is it possible to check them with the carbs still on the bike or is a carbs off job? when you say "You could always check that when the cable is released (or the choke is switched off) that the plungers are indeed going into the closed position." do I need to take the plungers out of the carbs or is it possible to check that visually?
This is driving me mad , all I want is my bike running nicely and I'd be happy to pay to get it sorted if I knew someone who I could trust!

johnnyrod · 13-06-06, 11:25 AM

Can't remember if you have to take the carbs off, but once the airbox is out of the way it's much of a muchness. You might find the securing screws a bit sticky, be careful with them. Follow the choke cables and you'll find where they enter the carbs, remove the securing screw and pull out, clean and grease, whack back in.

13-06-06, 02:51 PM

back when these bikes first came out this problem appeared a lot and the common cure was to drop the carb needles (usually have two or three notches on needles for adjustment) which richened the mixture. Of course this does also affect mpg as well but usually cured the problem.

13-06-06, 07:46 PM

I had a look at the carbs over the weekend, I could see the rear choke quite easily, had a go with a screw driver but could not shift the screw and did not want to shred it, didn't have a lot of time, will try again.

But the front one is hidden in the bowels somewhere so the carbs would have to come out which bother me as I get the feeling they would need balancing when put back, and it doesn't look that easy.

I have read somewhere else that sv's run a bit lean but this problem didn't seem to be there before, maybe I should just ignore it. The increase in MPG wouldn't bother me to much if that is the answer, not sure if't something I'd want to do myself.

I did think maybe I should bite the bullet and get a renegade exhaust put on, they aren't to far from me and could probably 'tune' the carbs at the same time as fitting the exhaust if I took it down to Brands, mind you not a very cheap option at all.

Many thanks again for all your help/advice on this, just wish there was an SV650 specialist mechanic/shop near me in Essex that I could get to fix it.

10-06-06, 10:41 AM	#17
rwball Guest Posts: n/a	Checking choke plungers Hi Big Ape JohnyRod and everyone Thanks for the suggestions, I don't think it's the chain, if I rev the bike up 6 or 7 K when it's in neutral and hold the throttle steady the revs don't stay steady they jump around erratically. Thinking about the choke plungers, is it possible to check them with the carbs still on the bike or is a carbs off job? when you say "You could always check that when the cable is released (or the choke is switched off) that the plungers are indeed going into the closed position." do I need to take the plungers out of the carbs or is it possible to check that visually? This is driving me mad , all I want is my bike running nicely and I'd be happy to pay to get it sorted if I knew someone who I could trust!

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07-06-06, 01:56 PM	#11
johnnyrod Member Mega Poster Join Date: Jul 2003 Location: Doncaster, oop norf Posts: 2,128	To be honest is sounds more like either it's running lean or as Sid says the carbs are out of balance. Doubt very much a new battery will make any difference. If you roll off the throttle does it go a bit faster? If you roll off then on again is it better than if you'd just whacked it open and kept it there? On the two curvy SVs I've checked, the throttle position sensor was a mile out of adjustment, not sure how big a difference it could make as when set back to rights neither bike seemed different. Also bin the retarder (TRE mod), no need for this really but might help.

07-06-06, 06:48 PM	#12
rwball Guest Posts: n/a	Cheers everyone I'll give the choke cable a going over this weekend, if family and football will allow. At present I am assuming the carb balance is Ok as has just been done, of course they could have mucked it up but it is certainly better since the service. Johnnyrod - how could it have started running lean if nothing had been touched? I had thought that maybe a carb diaphragm had split, or maybe there's an air leak between the carbs and the engine. The problem doesn't seem to occur when I whack the throttle open, at least you don't notice it and it accelerates fine, it seems more of a problem on partial throttle opening, not very often I get to ride it at a constant speed with the throttle fully open and it's only really a problem at steady speed. How easy is it to check the throttle position sensor? maybe it is on it's way out. When I mentioned the problem to the mechanic who serviced it the first thing he suggested was plugs, that's why I thought about the battery maybe being an issue. I changed the plugs myself, and what fun and games that was, last year when the problem first appeared and it made no difference, they changed the plugs again as part of the service, or they said they did. The rev counter seems pretty steady when idling, if I rev i up to higher revs while stationary the revs do seem to vary , the needle moves about randomly, not a vast change in revs but maybe 500 rpm either way but with no pattern or regularity. I just want it back to running smooth again, it's not a major problem but it does really irritate, maybe I should have waited a few years and got a fuel injected one, I bought it early 2000.

07-06-06, 09:26 PM	#14
Stig Guest Posts: n/a	Too me it sounds like either the the choke plungers are stuck open. (this would mean no amount of fettling with the choke cable is going to sort it) or you have a tight spot on the chain and have the chain tightened to tight to allow for the tight spot. If the choke plungers are stuck in the open position, then you will only get the stuttering in lower speeds. If the chain has a tight spot you will only get the stuttering at lower speeds. The choke plungers have springs in them, which return the plungers to the closed position when the cable is slackened off. You could always check that when the cable is released (or the choke is switched off) that the plungers are indeed going into the closed position. Checking the chain, move the bike forward slightly and check the slack on the chain, move the bike forward a little bit and check the chain again. Keep doing this until you have gone round the chain completely. If you find a tight spot adjust the chain tension correctly to the tightest spot. This will probably not eradicate the surging or spluttering like symptoms completely but should make it better until you replace the chain.

08-06-06, 09:42 AM	#16
johnnyrod Member Mega Poster Join Date: Jul 2003 Location: Doncaster, oop norf Posts: 2,128	Ball, TPS calibration procedure is in the manual, easy to get at, but you need a good multimeter. Difficult to say if it's carbs or ignition without some fiddling, BigApe could well be right as this is a known problem. Quest not sure but sometimes out of balance carbs could do this. In my experience one carb "leads" the other - if you have it out of balance one way it's almost okay but the other way and it's a bag of crap. Is the idle speed set a bit low? Does it stall occasionally if you pull up at a junction after zooming along?

13-06-06, 11:25 AM	#18
johnnyrod Member Mega Poster Join Date: Jul 2003 Location: Doncaster, oop norf Posts: 2,128	Can't remember if you have to take the carbs off, but once the airbox is out of the way it's much of a muchness. You might find the securing screws a bit sticky, be careful with them. Follow the choke cables and you'll find where they enter the carbs, remove the securing screw and pull out, clean and grease, whack back in.

13-06-06, 02:51 PM	#19
Chatterbox Guest Posts: n/a	back when these bikes first came out this problem appeared a lot and the common cure was to drop the carb needles (usually have two or three notches on needles for adjustment) which richened the mixture. Of course this does also affect mpg as well but usually cured the problem.

13-06-06, 07:46 PM	#20
rwball Guest Posts: n/a	I had a look at the carbs over the weekend, I could see the rear choke quite easily, had a go with a screw driver but could not shift the screw and did not want to shred it, didn't have a lot of time, will try again. But the front one is hidden in the bowels somewhere so the carbs would have to come out which bother me as I get the feeling they would need balancing when put back, and it doesn't look that easy. I have read somewhere else that sv's run a bit lean but this problem didn't seem to be there before, maybe I should just ignore it. The increase in MPG wouldn't bother me to much if that is the answer, not sure if't something I'd want to do myself. I did think maybe I should bite the bullet and get a renegade exhaust put on, they aren't to far from me and could probably 'tune' the carbs at the same time as fitting the exhaust if I took it down to Brands, mind you not a very cheap option at all. Many thanks again for all your help/advice on this, just wish there was an SV650 specialist mechanic/shop near me in Essex that I could get to fix it.