Re: Advice on Honda MC problem?
- From: default <default@xxxxxxxxxxxxx>
- Date: Mon, 04 Aug 2008 21:22:50 -0400
On Mon, 4 Aug 2008 20:43:08 -0400, "Steve L" <srl1215@xxxxxxxxxxx>
wrote:
One coil serves two out of four cylinders and it will run on just two
"default" <default@xxxxxxxxxxxxx> wrote in message
news:5tgc941doba49ds5h7lf0odvo8t1eblrh8@xxxxxxxxxx
I've tried everything I can think of with this problem and have a
fair
degree of confidence that it isn't ignition related.
I have a 1981 vintage Honda dohc CB750C. It won't go in the rain.
The problem occurred gradually over time
with first one cylinder cutting out when wet then two now all four -
and they pretty much die all at once.
The problem is worse when cold or occurs faster when the engine
hasn't
reached operating temperature.
Choking sometimes seems to help (but not always, and that may be my
subjective feeling rather than fact).
It runs for a bit after the rain starts, but once it starts cutting
out, it is likely to fail again with little or no delay.
May spit and sputter for a second or two then acts like the ignition
was just switched off entirely. Once it is having the problem, even
the mist from a wet road thrown up by trucks will cause a failure.
If the bike is stopped it can't be restarted immediately, but will
restart in 5-15+ seconds or so, and idle fine and rev, but
won't accelerate and will cut out again.
No amount of water poured over the engine with the tank removed will
cause the problem. The bike will
continue to idle and will rev fine. I've hit it with a spray bottle
in all the nooks and crannies, a garden hose and
even dumped buckets of water on the running engine. It has to be
under load, and wet before it dies.
Hoses are all good and most replaced. The airbox is good, the
connections between carbs and cylinders and box
are good.
All the usual ignition suspects have been replaced - coil wires,
both
coils, spark plugs, boots. I haven't changed
the spark modules but have added 5 LED's to tell me that the system
is
getting voltage and the modules are firing
when they should (even if the problem is there).
The intake is stock, the exhaust is a 4 into one low restriction
header/muffler. I added the after market exhaust
after the original exhaust got a few holes in the mufflers.
I recently rebuilt the carburetors & accelerator pump, with
basically
no change in anything except it needs to be
synchronized now, and it vibrates a little more. (ordered four
vacuum
gauges and will build a carb synchronizer when
the parts get here). BTW: no need to drop $100 on a vacuum
synchronizer - four new vacuum gauges only cost $21.
The bike seems to be running lean judging from the color of the plug
insulators - but doesn't overheat noticeably. But I did experience
some vapor lock problems on 100 degree days when sitting at a
traffic
light . . . that could be heat or gasoline related.
I plan to drill out the main jets a tad when I can locate some
suitable drill bits. The local stores only have
fractional sizes and I want to start with something smaller than
1/16". (still have the old jets from the rebuild so
I'm not burning any bridges - current jet size is stock: 1.02mm.)
My training is in electronics but I've been riding and tinkering
with
motorcycles for 40+ years, and have rebuilt a
few engines in that time. - valve jobs, cylinder bore, rings,
transmission bearings, rewound alternators, built voltage
regulators,
fork seals, etc..
I don't know how many total miles are on the bike. It was bought by
someone who fancied themselves a MC
rider - crashed once then sat in a garage for 15 years. I bought it
from the second owner, who rode it very little,
and it worked fine for about three years for me. In spite of its
age
the mileage is something on the order of 10K miles - odometer died
in
original crash.
I'm pretty much convincing myself that this is related to lean
running
as a result of the original muffler having holes and now the new low
restriction muffler.
Any guru out there with some other suggestions, things to try, and
would lean running cause a problem like this?
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I think it's the coil, the stress under load may be shorting a winding
and killing the engine or causing it to misfire.
cylinders - but I already replaced the coils with new ones just in
case. The plug wires are new silicone ones with new NKG spark plug
boots - everything assembled with silicone grease to prevent water
from getting past the rubber parts.
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- From: default
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