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SV650s 99 New Exhaust, Now back firing... a lot!

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The Blackbaron
Two Stroke Sniffer



Joined: 22 Mar 2010
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PostPosted: 21:45 - 27 Jan 2011    Post subject: SV650s 99 New Exhaust, Now back firing... a lot! Reply with quote
Hi guys,

I've fitted my SV650s 99 with a new stubby exhaust (short can) from Fuel, and now the bike is doing a lot of back fire when left at idle. It's a mild backfiring (no flames or anything and not loud enough to piss everyone off, but quiet enough to make me worry that I'm wasting fuel...in this case petrol)

I understand that the new exhaust is not providing enough back pressure so I will need to do "something" with the carbs.

My question is the following:

Do I balance the carbs? If so how will I do that without a vacuum thingy... and how much will that cost if I get one?

Do I get a new jet? If so which one?

How do I make the carbs run a little dry without replacing any parts?

Thanks guys, there's nothing in the hayne's manual so I thought this would be the best place to ask.
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Ed Case
World Chat Champion



Joined: 01 Mar 2009
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PostPosted: 21:47 - 27 Jan 2011    Post subject: Reply with quote
Before you buy anything make certain you have no air leaks in the exhaust joints, they can cause backfiring.
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The Blackbaron
Two Stroke Sniffer



Joined: 22 Mar 2010
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PostPosted: 21:53 - 27 Jan 2011    Post subject: Reply with quote
I thought about that, but all the joinings seem just fine,
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 21:58 - 27 Jan 2011    Post subject: Reply with quote
Ed Case wrote:
Before you buy anything make certain you have no air leaks in the exhaust joints, they can cause backfiring.


This ^^^.

Air leaks tend to cause a lot of popping and banging, especially on the overrun.

A more free flowing exhaust would tend to make the bike run lean rather than rich. This can also cause backfiring and popping.

The easiest way to jet it appropriately is to buy a stage 1 dynojet kit. This will usually have replacement main jets, throttle needles and springs to suit that bike with a sporty exhaust. Often a couple of different ones depending on if you have a K&N air filter or not. That'll take it pretty close to correct (possibly even close enough) but ultimately the only way to get the fuelling bang-on is a dyno run with an exhaust gas analyser after you've fitted it

Dynojet kits aren't cheap though. You're paying for them having done the dyno runs and worked out what settings to use rather than the componants themselves.

EDIT: The exhaust itself really shouldn't affect the fuelling at tickover much unless it was horrifically restricted. There isn't much gas going through it to impede at lower revs, it's at high revs when it's trying to bung out large quantities of gas that having a bigger hole helps. This is backed up by the fact that dynojet kits do not usually contain a different slow running jet and they advise you to leave the idle settings alone.
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The Blackbaron
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Joined: 22 Mar 2010
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PostPosted: 22:07 - 27 Jan 2011    Post subject: Reply with quote
So I am looking at spending more than 50 pounds to resolve this issue? From your point of view is this a worth while fix (I think I meant popping rather than backfiring)?
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 22:27 - 27 Jan 2011    Post subject: Reply with quote
The Blackbaron wrote:
So I am looking at spending more than 50 pounds to resolve this issue? From your point of view is this a worth while fix (I think I meant popping rather than backfiring)?


Upshot. No, because I seriously doubt your new exhaust is affecting carburettion at tickover. It may be that they all make that noise on an open can and you just couldn't hear it before. Or it may be that there is an air leak.

However, it could well be running lean at higher revs, in which case a dynojet kit is cartainly the easiest way to sort it without resorting to a dyno run.

I'd have a look on youtube and see if you can find what they normally sound like on an open can.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 22:32 - 27 Jan 2011    Post subject: Reply with quote
The Blackbaron wrote:
So I am looking at spending more than 50 pounds to resolve this issue? From your point of view is this a worth while fix (I think I meant popping rather than backfiring)?


I wouldn't worry about it. As long as the bike is running rich rather than lean, you won't do any damage.

If you rejet the carbs you'll need to remove them, rejet, test the bike on a dyno and then adjust. Its not a simple process, and you may just as well leave it as it probably won't gain a lot of performance.

The other thing to note is, backfiring is usually a consequence of running rich, whereas changing an exhaust can usually makes the bike run lean. The backfiring is a good sign, it means you aren't in danger of doing any engine damage.

If it were me, I'd leave it as it is.
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Livefast123
Nearly there...



Joined: 15 Mar 2010
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PostPosted: 22:38 - 27 Jan 2011    Post subject: Reply with quote
Why don't you just do a plug chop then you'll find out what the mixture is running at and possibly save the expense of a jet kit.
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The Blackbaron
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Joined: 22 Mar 2010
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PostPosted: 00:17 - 28 Jan 2011    Post subject: Reply with quote
Sorry I don't understand what a plug chop is.

Thanks guys, at least I understand that it's not a bad thing. I'll look for air leaks somewhere.
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clancy
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Joined: 11 Apr 2009
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PostPosted: 01:33 - 28 Jan 2011    Post subject: Reply with quote
Quote:
It may be that they all make that noise on an open can and you just couldn't hear it before.



that would be my bet if you cant find any air leaks, had an open pipe on my car and it backfired everytime i took my foot off the excellerator, mechanic told me its normal, you just dont normally notice it
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Suntan Sid
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Joined: 07 May 2009
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PostPosted: 09:55 - 28 Jan 2011    Post subject: Reply with quote
The Blackbaron wrote:
Sorry I don't understand what a plug chop is.

Thanks guys, at least I understand that it's not a bad thing. I'll look for air leaks somewhere.


Plug Chop

Take your bike out for a run, get it fully warmed up.
Run the bike at the red line for 5 to 10 seconds.
Hit the kill switch and pull the clutch in simultaneously.
Do not let the clutch out until you’ve stopped.
Pull the plugs immediately and check their condition.
This should give a good indication of how the bikes fuelling!
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c_dug
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PostPosted: 10:01 - 28 Jan 2011    Post subject: Reply with quote
Watch your fingers on the plugs, they get a wee bit hot! Embarassed

edit:

Also I don't think you need to run it on the limit for so long.

With my TDR it was just full throttle in first gear until it touches the redline, then clutch in and kill switch simultaneously, then plugs out.

Whitey = Lean (Bad times)
Brown = Perfect (Good times
Black = Rich (Not perfect but acceptable)
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The Blackbaron
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Joined: 22 Mar 2010
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PostPosted: 23:03 - 28 Jan 2011    Post subject: Reply with quote
Hi guys, this plug chop sounds promising, but when you guys say pull the plugs out you mean check the fuel lines yes? (take off fuel tank, check fuel filter etc...) or are you taking about another plug?

Umm... I redlined my bike on neutral on stand for fun and flames are coming out of it!!!... awesome!!! But should I be worried?
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clancy
World Chat Champion



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PostPosted: 23:06 - 28 Jan 2011    Post subject: Reply with quote
they mean take the spark plug out and check the colour Thumbs Up

flames sound cool Laughing no idea wether you should be worried
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The Blackbaron
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PostPosted: 23:14 - 28 Jan 2011    Post subject: Reply with quote
Ohhhhhh!!! Got it, I should probably clean them out before I do this huh?
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c_dug
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PostPosted: 02:29 - 29 Jan 2011    Post subject: Reply with quote
To be honest without doing a chop the colour is still a pretty sound indication of how it is running.
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Blue_SV650S
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PostPosted: 14:13 - 29 Jan 2011    Post subject: Reply with quote
If the carburation was fine with the old pipe, then it will be fine with this one. It is only a 'slip on' right?? If so, I wouldn't worry, jet get out there and ride! Thumbs Up
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sickpup
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Joined: 21 Apr 2004
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PostPosted: 16:10 - 29 Jan 2011    Post subject: Reply with quote
onsidering the popping is happening at idle the chances are it is the mixture screw that needs adjustment initially. In fact it is absolutely pointless messing around with anything else until the mixture screw is at the correct setting.

Easiest way to chack it is to use a gunsons colortune.
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HD
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Joined: 16 Dec 2009
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PostPosted: 19:14 - 29 Jan 2011    Post subject: Reply with quote
I thought backfiring was too lean (too much fuel?) as excess fuel is ignited and instead doing this in the cylinder it happened in the exhaust?

So surely running it too rich would mean it would just tick over high?

Help Confused
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stonesie
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PostPosted: 19:21 - 29 Jan 2011    Post subject: Reply with quote
Rich = too much fuel, can cause backfires

Lean = not enough fuel, can cause backfires (not enough to get a complete burn in the cylinder so fuel goes down the exhaust then ignites) Thumbs Up


Clear as mud really...

A colour tune or simply checking the plugs will help you narrow down which one you have, do not thrash a lean running engine excessivly as it can send the cylinder temperaures way up and melt pistons.
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Old Thread Alert!

The last post was made 15 years, 159 days ago. Instead of replying here, would creating a new thread be more useful?
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