update on my 2000 sv650 backfiring/popping problems

Anyone who didn't read my first post here is my situation: I had an issue with the bike backfiring at lower revs, especially on decel and in lower gears. It had a Yoshi pipe and a K&n filter fitted....

Well I ordered a new OEM-equivalent filter that is a bit shorter and seems a bit more restrictive than the k&n. There is a lot less backfiring on decel and although there is still some I believe that it's in the normal range for a vtwin/sv650. Anyway, now my problem is with the idling...with the k&n filter it would pop every few seconds if the bike was left at idle or at low revs (anything under 3000rpm)...the bike now pops and backfires a lot more, but at even lower revs...probably under 2500 it pops every 5-10 seconds and then at idle it pops every second or maybe less. In traffic this is very annoying.

I'm wondering if someone can direct me as to where the air/fuel screw is? I believe it's also refered to as the idle mixture screw. I have a shop manual, but it only has a picture of the pilot screw. Is there a plug covering it that will need to be drilled?

Other than idling the bike runs really well now with no surging when held at a constant speed. Open/closed throttle is still a bit harsh, but maybe slightly smoother.

I'd go as far to say my bike is running great but i'd still say open/closed throttle is a bit harsh. It's possibly just part of the charm of the bike.

Originally Posted by klohiq

I'm wondering if someone can direct me as to where the air/fuel screw is? I believe it's also refered to as the idle mixture screw. I have a shop manual, but it only has a picture of the pilot screw. Is there a plug covering it that will need to be drilled?

from the haynes manual:

"The pilot screws are located underneath the carbs between the float bowl & the intake duct on the cylinder head"

it goes on to say that for certain emissions-conscious markets:

"...the pilot screws are pre-set at the factory & in some cases have a limiter cap fitted to prevent tampering"

if you're going to get into any of this stuff yourself, I would strongly recommend investing in a haynes manual before you start drilling anything out:

http://www.amazon.com/gp/product/B00...116116?ie=UTF8

rgrds

~andy

[northwind]

US spec bikes have a plug covering the idle screws... Good link here:

http://www.geocities.com/catpoopman/airfuel.html

after posting that I was finally able to view that site...I found it on a few searches before but the hosting site said it's bandwidth had been used up for that period (hour, day, I dunno) so I couldn't view the site...

And you are correct...both the air/fuel screw and needle has a cap to stop tampering...that's what I was refering to when I said drill out...no mods to the carbs...yet lol. Although I am a bit intrigued by the 700, 750 and 800cc conversions I read about in an article of Two or maybe it was Ride...one of those brit bike mags.

As for the popping at low revs, it appears there is a leak around the fitting from the can and pipe...I tried high-temp silicone and that work to relieve 95% of all backfiring. The remaining backfires were during closed-throttle engine braking so I assume they were normal and there weren't very many. I went to start it the next day and the backfiring returned, so now I purchased some exhaust leak cement which is supposed to create a semi-permanent weld between the two parts.

Anyone have any other products I should try if it doesn't work? I've heard about copper silicone, but have yet to see it at any autoparts stores in my area.

Hopefully that was the problem, my friend had me worried when I described the problem saying "It sounds like you may have a bent valve."...Needless to say I was definitely not looking forward to an engine rebuild any time soon.

I will be investing in a Haynes or Clymer manual very soon, but for the moment I have a suzuki repair manual it doesn't have as much info about the bike or about removal/assembly, but it has most of the info I would need for basic repairs, maintenance, and adjustments.

Originally Posted by andym8

I'd go as far to say my bike is running great but i'd still say open/closed throttle is a bit harsh. It's possibly just part of the charm of the bike.

Have you shimmed the carb needles, adjusted the air/fuel screw to ~2.5-3 turns out, gone up one size on the pilot jets (from 15 to 17.5), and jetted the mains (from 137.5 up to 140)? or is your bike all stock? just wondering so I can see whether that is really necessary for a nearly stock bike and whether it will actually produce a noticeable result.

[northwind]

Originally Posted by klohiq

Have you shimmed the carb needles, adjusted the air/fuel screw to ~2.5-3 turns out, gone up one size on the pilot jets (from 15 to 17.5), and jetted the mains (from 137.5 up to 140)? or is your bike all stock? just wondering so I can see whether that is really necessary for a nearly stock bike and whether it will actually produce a noticeable result.

European bikes come with the 17.5 pilot jet as standard, which is nice. Also, slotted needles so less mucking about with shims. I reckon bigger jets in a standard bike would be a mistake (and also, wouldn't affect low revs, or at least not enough to be detected by the human bum) but a half-step shim on the needles might get rid of the power dip on some stock bikes.

put one shim under the needle and adjusted the air/fuel screws to 2.5 turns out (front was about 1/4 turn out...so I imagine that was most of the problem)...fueling seems to be better and overall when under load and with the throttle even open a hair I get basically 0 backfires...high revs...low revs...any gear...

BUT without load I can rev it a little (say 1700 or more) and it will still backfire some. Also backfires while idling and pretty bad on engine braking (esp if I downshift without rev matching).

Should I try going up on the pilots, turning the mixture screw out more, adding the last shim to the needle or just say **** it and get it dynoed? I really would like to avoid that since it's a stock bike with a full exhaust...not really much different than a stock SV and those don't NEED dyno time...it just helps with power a little...

[northwind]

Originally Posted by klohiq

(front was about 1/4 turn out...so I imagine that was most of the problem)

I really would like to avoid that since it's a stock bike with a full exhaust...not really much different than a stock SV and those don't NEED dyno time...it just helps with power a little...

A stock bike with a full exhaust is pretty different from a totally standard bike tbh... The difference was night and day for me. Not because of backfires, but because of the hole in the midrange.

With the pilot scrwe, chances are the front one was tightened in durning the drilling- got bound up with some swarf or bumped with the drillbit. Seems to happen a lot...

Sadly I can't compare this bike to a stock one, but it's becoming more and more sorted as I go through it. Hopefully with a little luck I'll be able to mount some clip-ons and purchase a real tail-tidy/undertail soon(currently I have a slab of plexi-glass painted black for the undertail and two sets of blinkers...one on the diy tail tidy and the other flush mounted on the rear plastic).

Wierd, but the backfiring has pretty much gone away completely. I rode it for about 40-50 miles a few days ago, then didn't ride it until today. The idle went up quite a bit (500-1000) so I had to adjust that and so far I have ridden it for about an hour and only one noticeable backfire happened and it was closed throttle/downshift.

Can anyone explain this? My only guess really is that maybe I had an exhaust leak before (which I thought I cured) and that the exhaust may have finally sealed from being ridden for that length of time...metal stretching and flexing from all the heat and the exhaust sealent maybe becoming liquified somewhat and together finally fully sealing the leak...The only problem with this theory is that the idle went up too. So...maybe the carb gaskets or airbox gaskets weren't properly sealing?? Water in my gas? I have no clue...