EVO engine with exhaust pop/backfire
Arctic Trooper
He has a '98 Soft Tail Custom (EVO engine) that has had an
intermittent exhaust pop/backfire since it was new. With stock pipes
the popping was noticeable, but no where near as loud as the "shot
gun blasts" he is now experiencing with his aftermarket pipes (yes,
the carb was rejetted after installing the new pipes). It doesn't
seem to make a difference whether the engine is fully warmed up or
cold, or whether it's idling or under power. It's definitely an
exhaust pop, not a true backfire through the carb, and he has
determined that the problem is with the rear cylinder only. The bike
has also been hard to start since it was new. He's replaced the
coil, ignition module, spark plugs, spark plug wires and the cam sensor
cam. He did not replace the cam sensor itself, but tested it with
electrical test refrigerant per the HD service manual. Compression is
OK; VOES valve is OK; no bent pushrods, broken rockers, or broken valve
springs. There does not appear to be an exhaust leak (and besides, the
problem existed with both the stock and aftermarket pipes). Does
anyone have any ideas as to what the problem might be or what he should
check next? Again, the key things to keep in mind are that the problem
has existed since the bike was brand new and that it affects only the
rear cylinder. Thanks!
roach
You left out timing.
roach
Kim Neubert
"Arctic Trooper" <dpg...@umaryland.edu> wrote in message
news:1152887696.9...@p79g2000cwp.googlegroups.com...
Intake Leak.
Noob
Wheel
First thing is recheck timing for starting point. Then I would look
at what jetting was actually done to carb. especially low jet and needle.
you didnt say if it was hard starting just when cold or also after
warmed up.
Wheel
Carl
"Arctic Trooper" <dpg...@umaryland.edu> wrote in message
news:1152887696.9...@p79g2000cwp.googlegroups.com...
If you didn't find a intake leak at the manifold to heads or carb, or any
place that can leak vacuum it could be as simple as backing the air fuel
mixture screw out another 1/8 to 1/2 turn. I've had mine, and seen others do
what your saying until the air fuel mixture screw was out far enough to make
it stop. Mine still has a pop, pop but not a pop pop BANG! If its not a bang
then it to me, is fine. All though you can take more out with the air fuel
mixture screw if its real loud pops. You said it starts hard, sounds lean to
me then. Pull your plugs if you know how to read them it will tell you if
its on the lean side.
--
Carl
99 FLSTF
I started out with nothing, and
I just about have that paid for!
Arctic Trooper
& suggestions: I should have mentioned that the timing was checked and
the plugs look fine. I don't think he's explored the possibility
of an intake or vacuum leak, however. I think we were under the
impression that an intake/vacuum leak would cause a backfire thru the
carb, not the exhaust, but it's worth checking. Checking the jetting
and adjusting the air mixture screw also sound like good ideas to me
(although, I tend to think these would affect both cylinders not just
the rear cylinder). I will pass the information along to my
brother...Thanks again.
Carl
Way lean will sneeze in the carb and bark loud out the exhaust on decel
under a loud. A bit lean will cause a pop or almost a bang out the exhaust,
example, coasting down a steep hill letting the engine break the bike to
slow down, like in 3rd gear with the tach at 3 grand at 40 mph, or 2nd gear
at 30 at 2,000 rpms, that will cause a good pop out the pipes when lean.
I've been there my self and helped another out of it by just taking the air
fuel mixture screw out 1/8 out until it stopped, providing there wasn't a
vacuum leak. And I had to remap a power commander for a friend who had that
same problem. Lean won't necessarily mean just a sneeze in the carb if its
just a bit off.
I live on a hill in town just up from a stop light 30 mph zone, I hear
Harley's go by all the time. Some pop a bit which is fine and some really
get to pop, pop bang bang pop bang!!!! As strange as it sounds its what I've
experienced.
Dan, danl, Redbeard uh Greybeard now
wrote:
Just finished putting new hoses and intake gaskets on my 1996 evo 1200
sportster. It no longer pops thru the exhaust. It also starts great
when cold, runs with the enricher cracked a 1/4" and is now smooooth
at low rpm. If I were you I would try it.
I just hope you don't run into a allen head bolt that someone
stripped. It was the right side front cylinder bolt holding the
manifold. I heated it up and applied PB Blaster on it at least half
dozen times. Banged on it with a punch and hammer. Swore all sorts
of oaths against it and damn near got out the sawsall to clear the
manifold out of the way!!! About 3:00 pm it finally came loose.
Put it all back together and Walla!! Went for a ride and when I put
it in the garage I noticed the bars didn't go over as far as they used
to...Yup, I pinched the throttle F****** cable :<{
Tomorrow is cable change day.
Shirley, if anyone didn't get one yet, set um up now or they can wait
till tomorrow.
Arctic Trooper
Shortly after the original post, my bro actually gave up and took the
bike to a shop run by two former Harley dealership mechanics. Long
story short...there was indeed an intake leak as had been suggested
here. On disassembly it was obvious from looking at the intake gasket
that it had failed to seal. They also found a bad lifter on the rear
cylinder (I forget whether it was intake or exhaust)-- apparently the
needle bearings in the roller had gone bad (very common according to
the mechanic; he said they're only good for about 40k miles!). Anyway,
the bike now starts right up and runs perfectly. Thanks again to all
who replied.