Running with no exhaust

[Cigaro]

I am currently running my bike with no exhaust, as I have given my mate the can to have a hole welded up and to have some of the baffles taken out.

What are the long term effects of this? The manifold and downpipe are still on, there is just no can.

It's fooking loud but seems to run OK.

I've heard it will make it run lean - is this true? If so, how do I sort this out? Can I tweak the mixture screw to give it a bit more fuel?

Actually seems to be a bit faster without the can on, the stock one is quite restricted...

[Itchy]

It'll make it run lean, a very very cheap and bodge tastic mod is to put some gaffer tape over the carb inlets or over the air filters to restrict the airflow and it riches it up a bit.

Babyyam's Eliminator the IL4 carb bike had this...

On my NTV the guy who bought it first thing he did was angle grind the zorst off big hole it in anyway and put some beetle chrome exhausts on the down pipes where the zorst used to attach to.

He opened up the air filter and taped up 1/4 of the air filter riching it up again.

At your own risk though.
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[Cigaro]

[Kickstart]

Hi

Likely to have strange effects. Quite likely to make it run lean, but could also cause odd issues with the length (and how pressure waves bounce up and down the exhaust) and land up with it lean in some places and rich in others.

Mixture screws basically change the idle mixture and have little to no effect elsewhere. While the risk would be when the engine is under load, which would likely be on large throttle openings (and could result in a hole in a piston).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[0ddball]

It's possibly running a bit lean but if you are getting the can back in a day or so i'd just ride it as it is and avoid trashing it at high revs and heavy load. Lean isn't always bad, at light to medium throttle and load it saves fuel and can make the bike feel more eagre.

[Itchy]

[Cigaro]

[yambabe]

Itchy is right, I briefly had a 400 Eliminator that we had erm lets just say some problems with! One of which was that the airbox rubbers had shrunk so badly that I ended up putting aftermarket K&N-style filters on it, then even after re-jetting had to resort to gumming them up with silicone to try and get the mixture right.............

Biggest thing about riding the 250 with no end can IIRC would be the vibration and subsequent white-finger lol, I had to get it welded a couple of times and without the can on it got very very buzzy..........
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[Cigaro]

[Kickstart]

Hi

You need to figure out where it is lean and where it is rich and from that determine which jets to change and in what direction.

Eg, a random dyno run for my Bandit:-

https://www.alfa-pages.co.uk/TempPicture/Bandit1200Dyno.jpg

From the graph at the bottom you can see it is running a bit lean until just under 7k and gets a bit rich at the top end (OK, the richness at the very top is probably from backing off the throttle). To "fix" this leanness at the lower end (although in this case it is too close to bother about) might mean lifting the needle up a touch, but that would probably make it too rich at the top end. Or maybe really richen it up on the mixture screws which would probably make it far too rich on idle. Real solution would be to change the needle profile for a more suitable one, which isn't really a realistic option without a large pile of needles.

What I mean is that you could find that the bike is generally lean from (say) idle to 4k, then rich from 4k to 5k, and then lean again above that. And no simple change will make it better everywhere.

All the best

Keith

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Cigaro]

Is there a way to do it without a dyno?

And how do I change the carb needle settings?

Sorry for the stupid questions

[Kickstart]

Hi

Well, you can just guess but the chances of guessing right are limited.

Needles can normally be shimmed up to richen the mixture they control. Aftermarket (eg, Dynojet) and some standard needles often are located with a small circlip in one of several grooves, and you move the clip to a different groove to change the mixture they control. They are also likely to be a different profile chosen to more likely match the requirements of the bike they are sold for when in some state of tune.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[The Shaggy D.A.]

[Stelmer]

Very interesting thread this.

My GSX has been upjetted for the 4-1 Marshall system and I could do with seeing if it's running correctly.