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Title: 72 XL250 Misfire at WO Throttle....
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Hardo
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Rank:none
Score: 61
Posts: 61
From: Australia
Registered: 10/29/2004
Time spent: 0 hours

(Date Posted:04/23/2009 06:49:48)

Hey XL freaks!

I have finished my XL Motosport resto (the one in my avatar pic), and she purrs like a baby at idle.

It is rideable if I am easy on the throttle, however go WOT and she coughs, splutters and even backfired a few times!

I am not a carby guru, but my understanding is that it could be the main jet (?) size??

Could it be timing? considering it idles perfectly without any "blipping" of the throttle necessary and is rideable I would have thought timing wasnt the issue. After all I checked the timing a zillion times when I built it!!


Any ideas guys??

Cheers and keep the XL's alive!

-Dave

--------------------------------------------------------------
1972 XL250 K0 Motosport ; 1973 CR250M ; 1977 RM250 B ; 1985 CR250 RF ; 2 x 1974 Honda MR50"s

Strick
1# 



From: USA
Registered:01/29/2008
Time spent: 0 hours

Re:72 XL250 Misfire at WO Throttle....
(Date Posted:04/23/2009 08:52:07)

I am guessing the air filter is fresh.  It is probably the main jet that is partially clogged, but could also be a mal-adjusted float.  Also, make sure that the hose clamps on the intake and airbox side have been tightened.  As an experiment, remove the air filter from the airbox, leave the side open and give it a ride.  It should be even worse if it is a lean condition.

Also, check the point gap.  If it is off, it could cause a high rpm stutter.

Good Luck and let us know what you find.

--------------------------------------------------------------
'04 V-rod,'02 FLSTC,'04 CRF450,'76 XL250,'78 SR500(street tracker),& the pictured 505hp '67 Camaro + a few more bikes

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Hardo
2# 



Rank:none
Score:61
Posts:61
From: Australia
Registered:10/29/2004
Time spent: 0 hours

RE:72 XL250 Misfire at WO Throttle....
(Date Posted:04/23/2009 20:11:38)

Thanks for the reply Strick.

Air Filter New, Main jet New and Float level has been adjusted to what I can best determine to be fine.

I will definitely go and double check the points gap - that was a great tip so thanks mate.

Just another question - If the float level is too low would that potentially starve the engine at high RPM? My guess is that it would which could create a misfire..... hmm...

 

I'd be interested to pick the brains out there on that one.

Cheers again - Dave.

 



(Message edited by Hardo On 04/23/2009 20:13:26)

--------------------------------------------------------------
1972 XL250 K0 Motosport ; 1973 CR250M ; 1977 RM250 B ; 1985 CR250 RF ; 2 x 1974 Honda MR50"s

Hardo
3# 



Rank:none
Score:61
Posts:61
From: Australia
Registered:10/29/2004
Time spent: 0 hours

RE:72 XL250 Misfire at WO Throttle....
(Date Posted:11/01/2009 04:43:05)

Hmmmm... still have the issue guys...

 

I checked the points gap and thats all fine.

 

Can anyone give some ideas to me?
-Hardo

--------------------------------------------------------------
1972 XL250 K0 Motosport ; 1973 CR250M ; 1977 RM250 B ; 1985 CR250 RF ; 2 x 1974 Honda MR50"s

350s
4# 



Rank:none
Score:381
Posts:381
Registered:01/04/2007
Time spent: 0 hours

Re:72 XL250 Misfire at WO Throttle....
(Date Posted:11/01/2009 07:25:58)

Try a smaller main jet. Pat Orman.
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English Phil
5# 



Rank:none
Score:78
Posts:78
From: United Kingdom
Registered:05/16/2007
Time spent: 0 hours

RE:72 XL250 Misfire at WO Throttle....
(Date Posted:11/03/2009 17:37:13)

Hardo,

I know you say you have changed the main jet, but have you pulled out the emulsion tube that sits underneath it to check all the holes are clear?

I take it your advance mechanism is all free to move and located correctly. Its rare, and I have not heard of it on XLs, but the bob weight springs may be to week thus messing up the timing. Could be worth checking the timing using a strobe.

Whats the plug look like?
Hardo
6# 



Rank:none
Score:61
Posts:61
From: Australia
Registered:10/29/2004
Time spent: 0 hours

RE:72 XL250 Misfire at WO Throttle....
(Date Posted:11/07/2009 21:09:48)

Thanks guys, will check the advancer assy. The scupper on the bottom of the main is all good. Might try a smaller main as suggested.

 

Plug is new and a nice light gray.

Will go back to the drawing board ...

 

Hardo..

--------------------------------------------------------------
1972 XL250 K0 Motosport ; 1973 CR250M ; 1977 RM250 B ; 1985 CR250 RF ; 2 x 1974 Honda MR50"s

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