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Post by curly001 on Sept 18, 2007 23:33:08 GMT -5
Hi All,
Those that have been on a ride with me will atest to the loudness and frequency of the backfires from my XT.
I didn't know which forum to put it in as i don't believe it to be caused by the exhaust ( have been known to be wrong but only once! Ha Ha!) It is not a leaky exhaust all sealed. It will do it from cold but seems to be more pronounced when hot.
Any ideas please.
Curly
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RD
Full Member
Posts: 176
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Post by RD on Sept 18, 2007 23:45:39 GMT -5
Yes very offputting when trying to set up for a corner and this XT gets stuffed up inside of you then tries to burst your eardrum.
Seriously though you said you were still playing with the jetting, I wonder if it is running rich enough at idle that you are still getting enough fuel on overrun to ignite either in the pipe or combustion chamber.
Cheers
Rich
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Post by curly001 on Sept 19, 2007 0:04:04 GMT -5
Thanks Rich,
Sorry about that but you were holding me up. Thought of that but couldn't get the bike to run with the next size down pilot jet. Might have to look into the jetting side.
Curly
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Post by wotavidone on Sept 19, 2007 0:14:54 GMT -5
You have checked the timing? Still got points?
I followed the book for setting the gap, then did the static timing thing and got it almost spot on. I checked it later with a timing light.
Bike became lots easier to start and bangs on overrun got lots smaller. An observation with my XT is that the best bangs occur when the carb starts running dry when I forget to turn the fuel on.
Mick
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Post by curly001 on Sept 19, 2007 1:06:54 GMT -5
Mick,
running sr cdi but will have a look at timing couldn't imagine it moving to much.
Curly
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Post by wotavidone on Sept 19, 2007 17:52:09 GMT -5
Nah! Can't be timing if you've got CDI. Given the nature of the way they work, if they go crook, you'd expect that they would either not fire at all, or would advance themselves a long way, and you would know about the advance every time you tried to start it.
Must be the carb leaning out, when you shut the throttle.
Mick
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Post by wotavidone on Sept 19, 2007 17:55:48 GMT -5
Second thoughts. And apologies for trying to teach grandma to suck eggs, but
I gotta ask. If you have the SR CDI, then you must have changed to the SR flywheel. You did check that the TDC mark lines up with the timing mark on the engine, when the piston is at top dead centre, when you put it on?
Mick
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RD
Full Member
Posts: 176
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Post by RD on Sept 19, 2007 18:31:50 GMT -5
No problem curly there was plenty of room, and I must admit I seem to have become a bit of a mobile chicane as i've gotten older.
I definitely don't think you have a timing problem the old XT is much to quick for that. mind you I think the nut holding the handlebars has a lot to do with that.
Cheers
Rich
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Post by curly001 on Sept 19, 2007 23:13:30 GMT -5
Mick,
The timing is spot-on checked with timing light and timing marks line with TDC.
Rich,
I think you hold your own quiet well although the guy on the white speed triple did use us both as mobile chicanes. As for the nut holding the bars on the XT! (Hang Thats me!) I don't know it doesn't seem that quick I'm just cruising along.
As for the bike the consensus is it's leaning out will try a larger pilot jet. Here's hoping
Curly
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Post by StewRoss on Sept 21, 2007 2:29:50 GMT -5
Yes, sound about right to me as well. If you've sealed the pipe well it can't be that... Have you tried adjusting the screw to the see the effect? You should be able to screw the adjustment out until you get a point of highest RPM...go further it should begin to slow agan, likewise in as well. If you can't reach that point, then it's probable that it is not the correct size. Go one size larger then try again. You'll find most factories set the bikes up to about 1.25 to 1.5 turns out as being correct. Try to match that setting with your bike....by playing with the pilot jetting sizing. Have fun. See you at the rally. SR  |
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Post by curly001 on Sept 21, 2007 5:08:45 GMT -5
What a day!
Tried bigger pilot Jets, tried smaller pilot jets. Guess what! none of it helped! It is what I feared the exhaust is TOO efficient scavenging exhaust gases. Going to run bike with standard muffler to see if that stops the backfire if that works, going to have to figure out a way of increasing the back pressure without affecting the performance too much. Wish me luck
Curly
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