Modified stock exhaust: won't idle

[baddkat]

Hey everyone, so I modified the stock can on my bike ('06 750) because I'm saving up for a new lid, eventually I intend to get a Scorpio slip on but here is my problem.
I modded the can pretty well the same as Rock Star Bars explained here; http://katriders.com/vb/showthread.p...+stock+exhaust
I also removed the header from the head and ground-off all the slag and excess weld from the pipes, once I put it all back together she will not idle.
Some points to take into consideration;
* Before I started the job I did not start the bike because I didn't want to burn my finger tips while doing the job,
* it is a Canadian production bike so the advance is already at 10 BTDC,
* outside temperature is -40C but the bike is inside a heated garage
* I have fuel preservative in the tank and the fuel is about 2-3 months old

I have a feeling it is a combination of the fuel in the tank and the cold air, eventhough she is in the garage I opened the door once the fumes got thick.
The bike sounds great while it is running, she just won't idle. Are these motors really this sensitive to the drop in back pressure? and am I really going to have to put in a carb kit?
Any ideas?

[Newbie2it]

Since you ground down the welds, and all the other stuff, your letting your kat breathe a lot more. However, Its not taking in more, you've not mentioned any changes to the fueling of it. As in a jet kit. The outside air is a mute point,since its a heated garage. So isn't the fact of the advancer. You jumped the gun without doing a little research here. More air in with same fuel intake results in a lot of issues.

A lot of this can be addressed with a jet kit, Right now, from what you've said above, Your kats way too lean. Not enough fuel vs. air to support ignition.However, there is the one variable you tossed into the mix.... You hogged out the exhaust. To what extent, no one knows. Yeah Back pressure here. But until you correct the amount of air vs. fuel and get it running, No one will be able to help you get things in order till it runs. After its running, then its a lot of adjusting and metering, toss in a few Dyno runs to make sure your on the right track...

You know.

[Randy G]

If all else fails I have a stock can for a 06 750 I will sell you CHEAP.

[scottynoface]

I'm thinking if you fatten up the mix a little bit it should be better. IIRC most bikes run lean at idle. I'm assuming it hasn't been running regularly for a bit (-40C and stabilizer) which could have something to do with it. I say richen out the A/F screws in small increments and see if it doesn't get any better.

[jdm5770]

Your only problem is grinding out the headers, that's what did it...jet kit...problem solved. There is no issue with back pressure since all that comes from the collector anyway. Same reason you don't have to do any mods to add a slip on, unless you change the headers.

[GSXfs600]

You could remove the complete exhaust and the bike would still start and idle. It's not your exhaust mods! tear into the carbs.

[baddkat]

I'll try draining the fuel and topping up with fresh fuel, playing with the mixture a bit.

However, Its not taking in more, you've not mentioned any changes to the fueling of it. As in a jet kit.
You jumped the gun without doing a little research here. More air in with same fuel intake results in a lot of issues.

It is the same amount of air going in, you said it yourself. The back pressure will affect the torque band and combustion efficiency not the initial combustion without load right? otherwise you would need a jet kit with an after market slip on. Unfortunately it is too friggin cold and snow and ice on the road to take it for a rip and burn the fuel out of it. Even with conditioner in the carbs I'm guessing that they could be gummed up.
Newbie2it, I hope that I don't need a jet kit, it will cut into my new helmet fund.

I'll keep you posted. THANKS!!
Jorge

[brooder]

Grinding out the headers will affect the back pressure. Not sure why people would think otherwise. You're affecting the flow volume prior to the collector which is where most of the backpressure comes from. I would reread Cyber's page regarding the welds and see what effects it had on the bike. I don't remember them off the top of my head.

[GSXfs600]

Grinding out the headers will affect the back pressure. Not sure why people would think otherwise. You're affecting the flow volume prior to the collector which is where most of the backpressure comes from. I would reread Cyber's page regarding the welds and see what effects it had on the bike. I don't remember them off the top of my head.

Whether or not the back pressure has been effected will not effect the performance much (if any)at idle.

[baddkat]

Whether or not the back pressure has been effected will not effect the performance much (if any)at idle.

I completely agree, obviously grinding the welds will reduce back pressure, otherwise why do it, right?
I just ran the bike again with the same fuel, this time I did not open the garage door and let it warm up for a minute or two before taking the choke completely off;
she stalled, I ran it again and added some artificial back pressure by holding a board at the muffler and played with it as if I was manually choking it. It made little diference but did not allow it to idle.
After a few minutes of this she just started to idle on her own, a little rough but it idled.
At this point I had to open the garage door because it was getting a bit thick in there and I found that I did need a small bit of choke to get it to build up RPM.
This tells me that as one of you pointed out, I am probably running lean. I'm not quite ready to adjust the carbs yet, not until I can run it with totally fresh fuel. I closed the garage door and she started to purr at 1100 RPM but still had problems building up when I snapped my wrist.
I am convinced that this motor is very sensitive to the cold air which is why she would not idle yesterday.

[hardlydangerous]

pipe mods won't affect the idle

-40o temps will though.
it's going to be way lean and will need the choke for quite some time before it will idle.
Normally you use the choke to start it after 30 seconds or so shut the choke off and warm it up using the throttle, after 2 minutes it should idle on its own. however it might be a lil lower then normal.
With that much choke and poor combustion from the poor atomization of the cold carbs, and the lower compression of the air cooled engine design, these engines tend to load up a lil in cold weather and usualy takes a 2 minute ride up and down the street to build up the proper amount of heat to clean it up.

[baddkat]

Thanks for your input guys, I put in some fresh high octane fuel and after a 2 minute warm up she is purring as usual, this time I ran it with a 4 inch dia 6 foot long exhaust hose from work so I could keep the door closed. Once the new fuel started running through the carbs there were no problems snapping up the RPM.
Funny thing is, I might still get the slip on before my new helmet.

[Rok_Stars_Bars]

Thanks for your input guys, I put in some fresh high octane fuel and after a 2 minute warm up she is purring as usual, this time I ran it with a 4 inch dia 6 foot long exhaust hose from work so I could keep the door closed. Once the new fuel started running through the carbs there were no problems snapping up the RPM.
Funny thing is, I might still get the slip on before my new helmet.

Im glad to see another member. Do this exhaust mod. It really does sound great. But no one can deny the looks, sound, and lightweight on an aftermarket. But as you and many others on this forum. Its a way to get some noise and make it till you can afford what you really want. Or like in my case a used yoshimura for $50 comes by.

[baddkat]

how do you like the Yoshi? I've been considering the Scorpion