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Author Topic: Kind of backfire when decelerating or changing gears  (Read 1342 times)

darxmurf

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Kind of backfire when decelerating or changing gears
« on: July 19, 2012, 03:02:51 AM »
I'm brand new here, so hi to everybody !

I'm riding a Bullet 500 Indian model from 2007. I think it was the last year of this "old style" model.

She is running perfectly well when the engine is cold but after something like 15 minutes of ride, I start to have kind of explosions noises in the engine when I decelerate or even during the "clutch time" between 2 gears.
If I put the gears on neutral position and I play with the throttle, it bangs too when the engine slows down.
It sounds like backfires but I'm not sure about it.
I checked the valve adjustment and everything looks fine.

Here is a sample of the noise https://www.omch.ch/hfr/noise.mp3

Don't know what to do to fix that  ???
Do you have any info about that or things I can try ?

Thanks !

Darx

Arizoni

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Re: Kind of backfire when decelerating or changing gears
« Reply #1 on: July 20, 2012, 05:38:04 PM »
As your bike is a 500cc Bullet your posts about it really should go in the "Bullet Classic Models" area of the forum but, that's OK.  Folks here aren't too fussy about exactly where a post is made.
(The "Indian" referred to in this area is the old American Indian motorcycles.  During the last days of that company the motorcycles sold under that name were made by Royal Enfield and Matchless.)

Anyway, what you are hearing is the engine backfiring as it decelerates.
This is caused by a lean air/fuel mixture ratio where there isn't enough fuel in the mix.

Most often, this is the result of installing a silencer with too little back pressure or a air inlet filter with a very low resistance to airflow thru it.

The mixture usually burns hotter than a normal mixture so a lean air/fuel ratio will not only cause the backfiring you are hearing but it may damage the exhaust valve and exhaust valve seat.

To fix the problem, larger sized carburetor jets need to be installed.

If you tell us what size and the Brand name (manufacturer) of your carburetor  is I'm sure the guys here can tell you what jet sizes you will need.
Jim
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JVS

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Re: Kind of backfire when decelerating or changing gears
« Reply #2 on: July 22, 2012, 08:31:01 AM »
With my experience of backfiring, I don't know why, but I think this is not the average 'backfiring'. This must be something else? It's a sharp peculiar cracking noise, tappets and what not. Like something is loose and is just flying around somewhere, hitting the sides and making that noise at certain revs.

And this is coming from a UCE owner. No experience at all with iron barrels lol. :|

 ???  ::)
« Last Edit: July 22, 2012, 10:34:53 AM by JVS »
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GreenMachine

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Re: Kind of backfire when decelerating or changing gears
« Reply #3 on: July 22, 2012, 10:05:56 AM »
I get a bit of backfiring from time to time..It depends on high high the RPM'S are when I drop in gear...Being what it is, I like the carb setup that I have (127 and 27.5) and only have to tweaked the air mix for the summer humidity...Check to see that their are no leaks in the exhaust or carb intake path..I'm using the 50 style Brit exhaust system and have the baffle installed for a bit of backward pressure....Even my 1100 with the Bub's aftermarket mufflers, stage 1 kit  and re-jetted carbs produce a bit of bubbling but I like that..  ;D
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carlo

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Re: Kind of backfire when decelerating or changing gears
« Reply #4 on: July 29, 2012, 10:06:40 AM »
With my experience of backfiring, I don't know why, but I think this is not the average 'backfiring'. This must be something else? It's a sharp peculiar cracking noise, tappets and what not. Like something is loose and is just flying around somewhere, hitting the sides and making that noise at certain revs.

And this is coming from a UCE owner. No experience at all with iron barrels lol. :|

 ???  ::)

That kind of backfiring can be caused by an air leak where the exhaust pipe enters the cylinder head.

I don't own a single-cylinder Royal Enfield, but I do have a BSA 441, and if I don't take great care to make sure the exhaust pipe is well sealed when I put the pipe on after working on the engine, it will do this.
The pipe on my BSA just pushes into the head, similar  to the way Royal Enfield does it, and in order to guarantee that it's sealed, I use the red hi-temperature RTV sealant on the section of pipe that goes into the head, and I also add some to the face of the clamp-on finned collar. When I tighten the collar, I pull out on the pipe, so that once the clamp is tightened, the pipe will want to spring back, and hold the clamp against the cylinder head more securely.
Then I wait a few days for the RTV sealant to cure before I start the engine for the first time.
If done right, this method will assure that there are no air leaks to cause backfiring.