Rich/Lean, Backfiring XR400 - Help
bcd...@my-dejanews.com
(I hope this isn't a repost - something screwy going on)
For the first time in 2 years my 96 XR400 is causing me some serious anxiety.
It's never had a jetting problem (baffle/snorkel removed/K&N), but starting a
few weeks ago it started back firing a little on downhill deceleration at
3500-4000 ft. Not having had jetting problems b/4 I adjusted the valves.
Subsequently I had no problems on MX track at 1000 ft, until my last ride. For
starters, it's been getting harder and harder to start cold (10-15 kicks).
And suddenly on my last ride it shows up with a major case of the @!#$%. At
acceleration it is missing, popping and back firing, which with the downhill
problem seemed like a lean problem, but the spark plug is black sooty and
there's lots of carbon blowing out the exhaust - so I think rich. But why the
sudden jetting problems? The changes between rides (4 days apart) was a clean
air filter (not too much oil), an oil change, and a wash job. I took it to my
local mechanic, whose not totally up with the times, but pretty enlightened.
He thinks it may be ignition/electrical - we've had some wet weather in Wash.
I checked all the lines for a short - kill button etc, cleaned all connections
with compressed air, clean out the carb, etc. No luck. So the mechanic thinks
maybe it's a CDI or stator problem. Of course he doesn't have the "peak
voltage adaptor" to really check the electric system. So, before I let him
continue to explore the possibilities or trek it 2 hours to the Honda shop for
what will probably be an extended stay I thought perhaps the collective wisdom
of rmd might point me in the right direction. ???
Thanks for any help (and while I'm at it a big hand to rmd for the
entertainment value of the Decoster thread).
Brett Dumas
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Uwe Hale
Brett :
> For the first time in 2 years my 96 XR400 is causing me some serious anxiety.
> It's never had a jetting problem (baffle/snorkel removed/K&N), but starting a
> few weeks ago it started back firing a little on downhill deceleration at
> 3500-4000 ft.
Back firing is often caused by exhaust leaks.
> Not having had jetting problems b/4 I adjusted the valves.
> Subsequently I had no problems on MX track at 1000 ft, until my last ride. For
> starters, it's been getting harder and harder to start cold (10-15 kicks).
Which is usually a lean condition. Or a lack of one of the 3 requirements -
fuel/air, compression, spark. Is it getting easier and easier to kick?
> And suddenly on my last ride it shows up with a major case of the @!#$%. At
> acceleration it is missing, popping and back firing, which with the downhill
> problem seemed like a lean problem, but the spark plug is black sooty and
> there's lots of carbon blowing out the exhaust - so I think rich. But why the
> sudden jetting problems?
The warmer weather will make your bike run richer. But if you haven't had this
problem in the last two years I doubt that this year is any different.
Have you replaced that black sooty spark plug?
Do a compression test. Make sure motor is warm. Kick with throttle wide open.
Get readings. Then repeat after pouring a tablespoon of oil into the sparkplug
hole. If the readings with oil are much higher, then you have ring problems.
If they are the same or close, use a leakdown tester to check valve leakage.
Check the cables and workings of the compression release.
Uwe Hale
89 YZ250WR
76 BMW R/75
WCA
> It's never had a jetting problem (baffle/snorkel removed/K&N), but starting a
> few weeks ago it started back firing a little on downhill deceleration at
> Subsequently I had no problems on MX track at 1000 ft, until my last ride. For
> starters, it's been getting harder and harder to start cold (10-15 kicks).
> acceleration it is missing, popping and back firing, which with the downhill
> problem seemed like a lean problem, but the spark plug is black sooty and
> there's lots of carbon blowing out the exhaust - so I think rich. But why the
> air filter (not too much oil), an oil change, and a wash job. I took it to my
> local mechanic, whose not totally up with the times, but pretty enlightened.
> He thinks it may be ignition/electrical - we've had some wet weather in Wash.
> I checked all the lines for a short - kill button etc, cleaned all connections
> with compressed air, clean out the carb, etc. No luck. So the mechanic thinks
> maybe it's a CDI or stator problem. Of course he doesn't have the "peak
> voltage adaptor" to really check the electric system. So, before I let him
> continue to explore the possibilities or trek it 2 hours to the Honda shop for
> what will probably be an extended stay I thought perhaps the collective wisdom
> of rmd might point me in the right direction. ???
>
> Thanks for any help (and while I'm at it a big hand to rmd for the
> entertainment value of the Decoster thread).
>
> Brett Dumas
>
> -----== Posted via Deja News, The Leader in Internet Discussion ==-----
> http://www.dejanews.com/ Now offering spam-free web-based newsreading
Here is a simple rule of thumb: If the backfiring is through the
carburetor it is a lean running condition. If the backfiring is out the
exhaust pipe it is an ignition problem.
A wet plug certainly seems to indicate an ignition problem.
Jack Rhodes
Nitrous Oxide
On Wed, 27 May 1998 23:10:53 GMT, bcd...@my-dejanews.com wrote:
Suffering XR4 owner..
>(I hope this isn't a repost - something screwy going on)
>
>For the first time in 2 years my 96 XR400 is causing me some serious anxiety.
>It's never had a jetting problem (baffle/snorkel removed/K&N), but starting a
>few weeks ago it started back firing a little on downhill deceleration at
>3500-4000 ft.
Backfiring? Clean carb, check air cut off diaphragm not punctured,
leaks on exhasut but you say rich when backfire is more lean on
overrun? Hmmm! Correct setup for '96 bike at your alt (guessing temp)
would be #408 slide, HRC needle on middle, air screw 2 1/4, 160 or 162
(with K&N) main, 60 pilot, air box baffle out and assumes no insert or
freeish flowing tip such as Vortip or Thumper. Stock plug.
My only other guess assuming clean filter, carb and all in order e.g
plug, coil, HT lead is the reg/rectifier on top right of top yoke. I
know this is lighting system and I'm a mechanical eng not elec but
this unit did give me probs.
Test as follows for DC reg voltage. run motor at 3,000 rpm and you
are looking for 14 to 15V. Use 4 P (White) connector with positive
lead from multimter on black wire and negative on green wire.
AC reg voltage Headlight on Hi Pos on blue green - neg, run 3,000 rpm.
looking for 12.5 to 13.5 V on AC scale.
I had one of these units breaking down which was replaced under
warranty on my old 96 bike and gave me all sorts of confusing misfire
probs till I tracked the problem down. How this affected my ignition
system - don't ask. ask an elec guy that can truly understand wiring
circuit components.
Maybe you've dropped the bike on the unit. After my prob I made a
guard up and that has saved it on a few occaisions. Also I made a
guard for CDI as a stick smashed that connector too and you cannot buy
connector as a separate.
Good luck.
Tip if you break kickstart use 98 one as stronger than 96/97. Also use
98 clutch springs and 98 clutch lifter as different if you ever have
to replace.
My 97 XR now done 13,500 miles and going strong. Just back from 1,000
miles around Pyrennees offroad up to 7,000 feet. Jetting was
interesting fun....as was playing in the snow and watchuing the eagles
soar. Oh! it's a hard life....
>Not having had jetting problems b/4 I adjusted the valves.
>Subsequently I had no problems on MX track at 1000 ft, until my last ride. For
>starters, it's been getting harder and harder to start cold (10-15 kicks).
>And suddenly on my last ride it shows up with a major case of the @!#$%. At
>acceleration it is missing, popping and back firing, which with the downhill
>problem seemed like a lean problem, but the spark plug is black sooty and
>there's lots of carbon blowing out the exhaust - so I think rich. But why the
>sudden jetting problems? The changes between rides (4 days apart) was a clean
>air filter (not too much oil), an oil change, and a wash job. I took it to my
>local mechanic, whose not totally up with the times, but pretty enlightened.
>He thinks it may be ignition/electrical - we've had some wet weather in Wash.
>I checked all the lines for a short - kill button etc, cleaned all connections
>with compressed air, clean out the carb, etc. No luck. So the mechanic thinks
>maybe it's a CDI or stator problem. Of course he doesn't have the "peak
>voltage adaptor" to really check the electric system. So, before I let him
>continue to explore the possibilities or trek it 2 hours to the Honda shop for
>what will probably be an extended stay I thought perhaps the collective wisdom
>of rmd might point me in the right direction. ???
>
>Thanks for any help (and while I'm at it a big hand to rmd for the
>entertainment value of the Decoster thread).
>
>Brett Dumas
>
>-----== Posted via Deja News, The Leader in Internet Discussion ==-----
>http://www.dejanews.com/ Now offering spam-free web-based newsreading
Nitrous Oxide
http://www.motorcycle.co.uk/