If the intake valve clearance is too large, the valve does not open
sufficiently and the engine can't breathe in the fuel/air mixture. If
the intake valve clearance is too small, the valve may not close
entirely and the engine will not have compression - no running - or the
combustion gasses may come back through the intake system - backfiring.
If the exhaust valve clearance is too large, the valve willnot open
sufficiently and the engine won't be able to get rid of the burnt
gasses. If an exhaust valve clearance is too small, the valve will not
close entirely and the engine will have insufficient compression - no
running - OR (even worse) the engine may run but the valve is never
closed long enough to cool its face off and it will burn, as will the
valve seat.
I don't know this engine, but if a 5/16 nut is all that secures the
valve setting, it might be worth putting a drop of blue LokTite on that
adjustment after figuring out just where it should be so that it doesn't
"adjust itself" while the engine is running.
It could be rings or burnt valves, but I would expect hard starting in
that case. The coil is likely under the flywheel, as part of the magneto
ignition system. That is typical of small engines. To access it, you'd
have to pull the flywheel which is a right pain, so testing the ignition
system first would be wise.
Hope this helps,
Donald.
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On 2020-08-08 9:27 p.m., Scott Hall wrote:
> Update for those of you sadistic-enough to keep reading: the intake
> valve was...loose? Open? The gap was too wide.
>
> The spec is .003 to .006 intake and exhaust - my smallest feeler is
> .006. I adjusted it to be tight on .006.Â
>
> The hard start is totally fixed. Starts great now.
>
> Still won't accelerate. Opening the throttle bogs it and it'll die if
> you don't let off. Curing the starting issue seems to have thrown the
> bogging issue into starker relief.
>
> Exhaust can is clear. Gas is new. Air filter is clean and freshly oiled
> and removing it entirely changes nothing.
>
> I am unfamiliar with valves making something not run--my experience is
> either on Ford V-8s or a Triumph 1147 I-4, or Honda or Kawasaki SS
> motorcycle engines, none of which ever had issues with the valves. This
> thing's valves are literally just adjusted with a 5/16" nut--there's no
> locking nut. Is it possible that making the intake or exhaust valve
> tighter or looser could cause something like this? Like should I shoot
> for one end of the spec of another?
>
> Last thing left would be the coil like Tom suggested. There's no mention
> of it in the owners manual and I don't see it in a parts search so far,
> but I started with Amazon.Â
>
> Seriously. I have built--from rusty blocks--a Ford 289 and 390. A
> Triumph 1147 that came in several Tupperware bins. More rebuilds of
> CBR600 and ZX750 engines than I like to think about.
>
> A leaf blower engine is threatening to best me. I want to back over it
> with the truck just to make it disappear. I think I'm looking for moral
> support here.
>
> Worn cylinder or piston? Bad valve entirely? I could dig out a
> compression tester, but there's no spec for it in the manual anyway. I'm
> kinda at a loss here.
>
> On Thu, Aug 6, 2020 at 7:40 PM Tom Coradeschi <tjcora@icloud.com
> <mailto:tjcora@icloud.com>> wrote:
>
> I had a leaf blower stop running a few years back due to a bad
> ignition coil. Have you verified youâ??ve got spark? I donâ??t see that
> specifically mentioned (yes, you did mention the spark plug)
>
> â??
> Tom Coradeschi
> tjcora@icloud.com <mailto:tjcora@icloud.com>
>
>
> > On 05 Aug 2020, at 5:09 PM, Scott Hall
> <scott.hall.personal@gmail.com
> <mailto:scott.hall.personal@gmail.com>> wrote:
> >
> > The carb is getting fuel. I can see it in the fuel lines and it
> pumps using the primer bulb.
> >
> > The symptoms are identical with the old and new carb. I can't see
> the end of the fuel line but the only remaining fuel issue could be
> that the new fuel filter (a pumice stone-like thing on the end of
> the fuel line) could be restrictive. Working against that theory is
> that it did the same thing with the old fuel filter.
> >
> > I don't think the problem is the fuel system. The problem
> is...what's left? I swapped the spark plug just to do it.
> >
> > It's a four-cycle engine. Might the valves (like the intake and
> exhaust valves in the head) come out of adjustment? This condition
> has been developing over more than a year...perhaps the valves are
> slowly coming out of adjustment?
> >
> > I don't know what conditions un-adjusted valves cause. I can't
> think of what else it could be.
> >
> > On Wed, Aug 5, 2020 at 3:23 PM <alfuller194@gmail.com
> <mailto:alfuller194@gmail.com>> wrote:
> > Can you confirm whether it is actually getting fuel to the carb?
> Try starting it with ether/carb cleaner/gasoline directly to the carb?
> >
> >Â
> >
> > ----------------
> >
> > All the best,
> >
> >Â
> >
> > Al Fuller
> >
> >Â
> >
> > From: Shop-talk <shop-talk-bounces@autox.team.net
> <mailto:shop-talk-bounces@autox.team.net>> On Behalf Of Scott Hall
> > Sent: Wednesday, August 5, 2020 4:06 PM
> > To: Shop-talk@autox.team.net <mailto:Shop-talk@autox.team.net>
> > Subject: [Shop-talk] M*th%&$#c<ing small engines d*mn again
> >
> >Â
> >
> > Troy Bilt four-stroke backpack leaf blower.
> >
> >Â
> >
> > Replaced the carb and plug.
> >
> >Â
> >
> > No change in symptoms: hard start, choke useless, engine bogs on
> application of throttle.
> >
> >Â
> >
> > That sounds like fuel/air to me. That's the carb. The carb and
> plug are brand new. The old carb and plug look fine and it's doing
> the same thing. The carb isn't the problem.
> >
> >Â
> >
> > I am literally out of ideas. Any idea what to look at next before
> I just toss it?
> >
> >Â
> >
> > Thanks and (*&^*&%&#()_#@&*$&#^&^%.
> >
> >Â
> >
> > Scott
> >
> > _______________________________________________
> >
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