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Discussion Starter · #1 ·
I have a 77 Exciter with a 540 fan from an 80 XLV in it. When the engine was in the XLV it ran like a top with a ton of power.
It backfires through the exhaust when I try to accelerate from an idle. I have replaced the plugs, reeds, and cleaned and reset the carb. It has the exhaust from the 340 Exciter in it. It does not have an airbox on it yet. I was hoping to get it running before modding an airbox to fit.

I was told if the exhaust was not the right size it would create an issue with the performance. It sounds like I am going to have to modify the XLV exhaust. It is going to be a major job, so any help would be appreciated. The XLV pipe is a monster in comparison to the Exciter pipe and chassis.

This project has been one challenge after another. This is a custom I would never attempt again. I just want the mechanics right so I can get the hood done and painted over the summer. I hope to have everything done for next winter as my daily rider.

We affectionately call this Frankensled. It has parts from Yamaha, Polaris and A/C.

HELP PLEASE!!!
 

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Get the right pipe.
 

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bgkid2966 said:
I have a 77 Exciter with a 540 fan from an 80 XLV in it. When the engine was in the XLV it ran like a top with a ton of power.
It backfires through the exhaust when I try to accelerate from an idle. I have replaced the plugs, reeds, and cleaned and reset the carb. It has the exhaust from the 340 Exciter in it. It does not have an airbox on it yet. I was hoping to get it running before modding an airbox to fit.

I was told if the exhaust was not the right size it would create an issue with the performance. It sounds like I am going to have to modify the XLV exhaust. It is going to be a major job, so any help would be appreciated. The XLV pipe is a monster in comparison to the Exciter pipe and chassis.

This project has been one challenge after another. This is a custom I would never attempt again. I just want the mechanics right so I can get the hood done and painted over the summer. I hope to have everything done for next winter as my daily rider.

We affectionately call this Frankensled. It has parts from Yamaha, Polaris and A/C.

HELP PLEASE!!!
I know for the yamahas (phaser and mountain max) that I have worked on the factory manual specificaly says not to run with the airbox off. It creates a lean condition. This may be the cause of the backfire.
 

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The pipe has to be for the engine, two strokes rely on the tuning of the pipe (back pressure) for the specific engine it was built for. A 340 pipe put on a 540 engine is like you trying to crap through a straw..... it will not work, you must use exhaust for the 540 engine, this will fix your problem
 

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Discussion Starter · #6 ·
LOL!! I will be modifying the 540 exhaust to fit the chassis. No better time than the present to get started!
 

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bgkid2966 said:
LOL!! I will be modifying the 540 exhaust to fit the chassis. No better time than the present to get started!
How are you modding the exhaust?

If you mess with the tuned pipe, you will untune it, and may aswell keep running the exhaust from the 440.
 

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[/quote]

How are you modding the exhaust?

If you mess with the tuned pipe, you will untune it, and may aswell keep running the exhaust from the 440.

[/quote]
IE,back to;[;)]
TeamNFG said:
you trying to crap through a straw.....
 

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Discussion Starter · #9 ·
I have to reshape the silencer. I am not messing with the expansion chamber. All work will be after the small pipe at the end of the chamber. This should not mess with the tune, right?
 

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I wouldn,t think it would make a huge difference,maybe a bit of HP.When you do get it running I would check the plug color as altering the part after may change your jetting requirements.
 

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You should be fine with a mod of your silencer and not the pipe itself, aslong as you don't cause a restriction.
are you just trying to fit the exhaust out the belly pan? If yes, just cut a new hole in the pan and cover up the old one with some aluminum
 

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Discussion Starter · #12 ·
How much affect does the length of the stinger have on the function of the pipe? The pipe just does not fit the chassis and I am working on combining the expansion chamber from the 540 with the muffler/silencer from the 340. Will this be a problem or will it work? [baldy] This is getting to be a pain in the a** !!!

Thank you all for the valuable input!!!
 

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is the 340 muff the same size ID as the 540, if so it should work

You basicaly want to run your proper pipe to the engine and then don't restrict any flow with the silencer, or just add a chunck of pipe to 540 silencer to pass through the belly pan
 

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I would get the airbox on there and run it before you go hacking the pipe apart. The pipe designs back then were not that great yet. More than likely those 2 pipes weren't that much different. In the 70s most of the sleds just had mufflers an no expansion chambers.
 

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Discussion Starter · #15 ·
I am in the middle of combining the 540 pipe with the 340 can. Then the airbox mod is next and should not be as challenging. I look forward to riding some of this season and then the hood and body mods for the summer.
 

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Personally I would have tried to get the air box on there first. You should be able to run it without any exhaust (on a stand) and be able to hear if the air box is making any difference. The reference to crapping through a straw, while entertaining, is not exactly true. The 340 pipe is not going to have that much more restriction or backpressure, but it will be tuned for a different power band. It might be more like crapping while sitting on an uncomfartable toilet seat. Good luck on your project.
 

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redwolf_92 said:
Personally I would have tried to get the air box on there first. You should be able to run it without any exhaust (on a stand) and be able to hear if the air box is making any difference. The reference to crapping through a straw, while entertaining, is not exactly true. The 340 pipe is not going to have that much more restriction or backpressure, but it will be tuned for a different power band. It might be more like crapping while sitting on an uncomfartable toilet seat. Good luck on your project.
I partly agree, the 340 pipe will do exactly what his sled will do, seen it many times by people just sticking some pipe on a two stroke and can't figure out why it woun't work, and running no exhaust will make noise, but help with nothing.
He is on the right track with the exhaust first
 

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Discussion Starter · #18 ·
The pipe is finally completed and seems to work pretty well. I have to make a custom air intake system since the airbox is jus to deep for the chassis. I have acquired some parts to make this happen and look forward to some test time in the summer. Then to tear it all apart to do the finish work, the hood, seat, and cleaning up the chassis.
 
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