Starting and backfiring problem - advice please

Dear all,

Its the XV750SE again presenting problems
Having got the beast back on the road and MoTd, I took it for a blat,
stopped off at my son's on way home - couldn't get the bike to start
until it had well cooled off. However, as it had been a *really good
blat* I optimistically assumed that it would be the exception rather
than the norm. I have been lucky in that I haven't had to do 'hot
restarts' again until yesterday - same problem. It won't restart after
doing more than a couple of miles until it has had half an hour to cool off.

Even from cold, the (new and fully charged) battery struggles to turn it
over and often rotation stops dead as the thing first fires.

Another thing, when decelerating fairly rapidly (ie engine on overrun)
there is always humungous backfiring and popping.

Are these three problems related? My 1960s instinct tells me it could be
ignition timing and and in those (g)olden days I would have known it was
time to adjust the points gap - but this beast is all electronicky!

Advice gratefully received!

Chris D

 

Chris Deuchar came up with the following;:

I dunno anything specific to the bike, but with those symptoms I'd check
carburation, ignition timing, and general electrical health, earthing points
and such-like.

 

The failure to hot-start and the popping on overrun could both be
related to over-rich fuelling, unless you're implying that it simply
won't turn over when hot.

--
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..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2
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It won't turn over compression when hot - and is reluctant when cold.
If I try from cold with no choke, it turns over more easily - but of
course it is not succeding in firing then.

When I first got the bike it was running very rich and one float
appeared stuck (ie flooding). It had been off the road for a year. I
found the air filter was crusty (never seen that before) and thoroughly
blocked. I replaced the filter and freed the needle and have also
replaced the (carbonised) spark plugs with new ones. I therefore think
the mixture is now ok - certainly much better than it was.

Cheers

Chris D

 

Thus spake Chris Deuchar unto the assembled multitudes:

Might be worth your while reading the thread "Trident Trubble" in this NG
from a week or so ago, and checking the integrity of the live feed and
earth from the starter relay. Certainly did it for me

 

The problem is that the old XV has an utterly chronic starter motor
(Bendix system) which *always* breaks or fails, and bloody awful
carburetion.

The two aren't related, anyway.

Google for XV starter motor problems - there's a lot out there,
including some cures.

As for the popping and banging - always worth checking for air leaks,
and especially holes in the (more complex than it looks) exhaust.

It ain't ignition timing, though.

 

Don't know the bike but I'd go with the earth and feed issue,

Running rich wouldn't stop it spinning over unless it was hydraulic'ing
which it isn't.

Peter

 

Ignition too far advanced.

the electonics is still triggered by something on the crank or camshaft and
I give you good odds that it's out of place.