Roll-on break down - SV650.org

07-08-06, 10:36 PM

Folks,

Just recently, on my '00 SV650S, I am having trouble with engine revs breaking down when rolling on the throttle from part-throttle.

It occurs when I have been cruising at a constant speed and then open the throttle slightly, to overtake for example. When I open the throttle, there is a hesitation, revs drop briefly, then it picks up and carries on as it should.

Nothing has changed with the bike at all, same fuel, about 1/2 way between service intervals, weather is a perhaps a little cooler at around 10 degrees celcius.

Any advice on where to start looking?

Cheers,

Chris

northwind · 08-08-06, 09:33 AM

Do you have- race system, slip-on, air filter? That's usually a ymptom of undersized main jets...

08-08-06, 09:59 AM

May I suggest a quick look at the spark plugs?

Not sure how long you were running at constant-throttle, but that can allow deposits to build up on the plugs (particularly if the engine is a bit worn and using a little oil, or if it is running rich for some reason such as air filter condition). These deposits then cause a misfire when you open the throttle, and it's made worse if the plugs themselves are old, not gapped correctly - or if you are using (for whatever reason) a colder heat range plug. Sometimes, running at the same speeds, but in a lower gear (ie higher revs), for a few miles will burn off those deposits.

However, a quick look at one of the plugs (the rear one....it's easier!) will usually give you some indication. Look for a rounded center electrode, widened gap, heavy dark brown deposits on the ceramic insulator (NOT the steel plug body).

The proper cure is to decide on, and fix, the cause but new plugs - espec. the use of "precious metal plugs" eg platinum, iridium, gold palladium etc - may also be beneficial.

Hope that helps.

08-08-06, 10:22 AM

Possibly slight carb icing?

.

johnnyrod · 08-08-06, 11:34 AM

Weather is too warm for that. Sounds like leanness as Northy says. Try putting on a bit of choke and doing it, if it doesn't do it then it's running lean and needs sorting on a dyno (assuming you do have a non-standard exhaust).

08-08-06, 11:42 AM

Quote:

Originally Posted by johnnyrod

Weather is too warm for that.

Well he's saying it's only 10°c, which in the right (or wrong) conditions can certainly bring on a little carb icing from my experience. It might not be this of course, but riding for a fair distance on a constant throttle is definitely a criterion to cause ice build up if the ambient conditions dictate.

.

Sir Trev · 08-08-06, 11:44 AM

Have you checked your choke cables? At that age they may well be a bit sticky and they don't always get checked/lubed on a service.

08-08-06, 10:05 PM

Gold star for Jonboy

It didn't do it on the way home last night. This morning, I listened to the weather report on the radio before leaving home, and it was 2 degrees celcius this morning. The problem was worse than yesterday, the idle was really low, and the engine would stall at traffic lights if I didn't keep the revs up.

Hopefully this cold snap is nearly finished.

Thanks for your replies folks.

Quote:

Originally Posted by jonboy

Quote:

Originally Posted by johnnyrod

Weather is too warm for that.

Well he's saying it's only 10°c, which in the right (or wrong) conditions can certainly bring on a little carb icing from my experience. It might not be this of course, but riding for a fair distance on a constant throttle is definitely a criterion to cause ice build up if the ambient conditions dictate.

.

northwind · 08-08-06, 10:33 PM

I think I ruled it out from sheer prejudice

Nice one Mr Boy. Silkolene FST Pro is the daddy for carb icing, by the way.

09-08-06, 10:02 AM

Quote:

Originally Posted by northwind

Silkolene FST Pro is the daddy for carb icing, by the way.

Yes it works very well, but is hellishly expensive. Also, a higher octane fuel (98 RON plus) does a very good job too, and is a little cheaper.

.

07-08-06, 10:36 PM	#1
pridhac Guest Posts: n/a	Roll-on break down Folks, Just recently, on my '00 SV650S, I am having trouble with engine revs breaking down when rolling on the throttle from part-throttle. It occurs when I have been cruising at a constant speed and then open the throttle slightly, to overtake for example. When I open the throttle, there is a hesitation, revs drop briefly, then it picks up and carries on as it should. Nothing has changed with the bike at all, same fuel, about 1/2 way between service intervals, weather is a perhaps a little cooler at around 10 degrees celcius. Any advice on where to start looking? Cheers, Chris

08-08-06, 09:33 AM	#2
northwind Moderator Mega Poster Join Date: Jan 2004 Location: In the garage where I belong Posts: 17,083	Do you have- race system, slip-on, air filter? That's usually a ymptom of undersized main jets... __________________ "We are the angry mob, we read the papers every day We like what we like, we hate what we hate But we're oh so easily swayed"

08-08-06, 11:44 AM	#7
Sir Trev Member Mega Poster Join Date: Jun 2005 Location: High Wycombe, where the chair factories used to be Posts: 1,479	Have you checked your choke cables? At that age they may well be a bit sticky and they don't always get checked/lubed on a service. __________________ We are the Goon Squad and we're coming to town, BEEP BEEP!

08-08-06, 10:33 PM	#9
northwind Moderator Mega Poster Join Date: Jan 2004 Location: In the garage where I belong Posts: 17,083	I think I ruled it out from sheer prejudice Nice one Mr Boy. Silkolene FST Pro is the daddy for carb icing, by the way. __________________ "We are the angry mob, we read the papers every day We like what we like, we hate what we hate But we're oh so easily swayed"

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08-08-06, 09:59 AM	#3
Anonymous Guest Posts: n/a	May I suggest a quick look at the spark plugs? Not sure how long you were running at constant-throttle, but that can allow deposits to build up on the plugs (particularly if the engine is a bit worn and using a little oil, or if it is running rich for some reason such as air filter condition). These deposits then cause a misfire when you open the throttle, and it's made worse if the plugs themselves are old, not gapped correctly - or if you are using (for whatever reason) a colder heat range plug. Sometimes, running at the same speeds, but in a lower gear (ie higher revs), for a few miles will burn off those deposits. However, a quick look at one of the plugs (the rear one....it's easier!) will usually give you some indication. Look for a rounded center electrode, widened gap, heavy dark brown deposits on the ceramic insulator (NOT the steel plug body). The proper cure is to decide on, and fix, the cause but new plugs - espec. the use of "precious metal plugs" eg platinum, iridium, gold palladium etc - may also be beneficial. Hope that helps.

08-08-06, 10:22 AM	#4
jonboy Guest Posts: n/a	Possibly slight carb icing? .

08-08-06, 11:34 AM	#5
johnnyrod Member Mega Poster Join Date: Jul 2003 Location: Doncaster, oop norf Posts: 2,128	Weather is too warm for that. Sounds like leanness as Northy says. Try putting on a bit of choke and doing it, if it doesn't do it then it's running lean and needs sorting on a dyno (assuming you do have a non-standard exhaust).