learjet45xp

Both of my evolution engines....a PTS and a 61NT....always want to start backwards. I have no idea why they are so hard to get to run the right way. Seems like as soon as the engine fires it kicks back and then runs backwards. Anyone got some ideas? ....my 91FX does the samething, just not as offen.

asmund

Do not flipp them through the compression, but use the back-flipp tecnique. One flipp backwards against the compression and it will fire and run in the right direction. easy peasy

Flyboy Dave

My Feedback: (21)

....you are not getting the prop flipped through completely. It is firing, but actually firing
and turning the engine backwards. Using an electric starter eliminates the problem.

FBD.

BarracudaHockey

My Feedback: (11)

Its often a symptom of an overly rich low end mixture setting.

Turk1

It mostly indicates,overpriming.Try to less prime it before flipping.

blw

My Feedback: (3)

Using a plug that is too cold will aggravate the over priming as you keep flipping.

daveopam

My Feedback: (9)

Try the back flip first. It is how most guys hand start in my area. It is much safer than flipping through.

david

MJD

My Feedback: (1)

IMHO the #1 reason is that the crankcase is loaded with excess fuel, resulting in a large fuel charge in the cylinder igniting prematurely - enough before TDC to kick back and continue running. This can be caused by more than one reason, such as overzealous priming or a too rich low end mixture. A fuel tank too high can cause gravity fuel feed into the spraybar thereby loading the case, or fuel plumbing/filling issues could also force excess fuel through the spraybar. Another possible cause is plug heat problems, i.e. where the filament is not getting enough current, allowing fuel to accumulate during cranking without firing, then firing after excess fuel has accumulated. In any event the result is that the case accumulates excess fuel.

With the excess fuel in the case, the issue of reverse rotation is somewhat negated by the readily available fuel and whatever air it manages to inhale. I don't know the mechanism of how the porting and all that behaves when it is spinning backwards. I'd say the issue is overpriming or other forcible entry of fuel into the crankcase when the problem is immediate, i.e. the first attempt to start either by hand or starter burp. I'll bet most people have experienced the starter kicking back at you as a wet engine took off backwards? If the problem surfaces after a false start or two, that is, where there has been an opportunity to get some fuel draw happening, I would then look at the idle mixture setting instead.

If the engine is really loaded up I generally disconnect both the fuel and vent line from the engine, check that the plug is up to a good bright orange, then bump it backwards (not through compression) with a chicken stick (oh yeah - this is definitely the time when the oft-printed advice to use a chicken stick should be heeded) - if it kicks off running in either direction, I let it go. It will burn off the fuel in a few seconds, and if it is running backwards (usually it will be since that was the problem in the first place) as the fuel dwindles they often hiccup and run forward briefly. I've been known to experimentally plug the fuel line back onto the carb just as the engine is dying - btw to suggest doing this is stupid advice but at least follow the reasoning here at least - and watch the response. If it keeps running and seems to be running smoothly on the normal to lean side, I then plug the pressure line back to the carb. If it still seems to run okay, then it was likely not mixture but fuel loading for a reason I would then have to determine. If however it progressively richened and died, then obviously I need to lean out the idle mixture. If this happens I usually repeat the fuel burn-off procedure before trying to continue, in other words to get a fresh start with a chance to analyze what's going on again.

Just my two cents. MJD

NM2K

My Feedback: (14)

Most of the folks that have this type of problem are using a glow plug ignitor set up that provides too much voltage to the glow plug. Or, they are using a really hot glow plug. Increasing nitro content may also aggravate the situation.

As Asmund has suggested. Choke the engines and then flip them several times without the glow plug booster power applied. Connect the booster leads. Now flip the prop backwards so that it bounces off of compression. That should start your engine in the proper direction.

Or, if your voltage is adjustable, lower it a bit and flip through compression normally.


Ed Cregger

blw

My Feedback: (3)

The Evolutions will load up too much with OS 8 plugs. Been there too many times myself.

estradajae

It's quite funny how engine works...when a 2stroke engine is overprimmed or rich, it turns backwards...and when a 4 stroke is set too lean it will backfire (maybe preignition ???) I was thinking that backfiring in 4 strokes was caused because a too lean mixture could lead to preignition if the chamber is too hot, pushing the piston down before it reaches TDC...


I have seen that my engines will eventually backfire if the engine is overprimed/flooded....and found the best solution to prime and flip many times before i use the glow driver, when I put it on, it starts inmediately, by hand or by the starter (les than a second with it).

Jorge

DarZeelon

The setting of the low-speed needle (or that of the high-speed needle) does not directly affect this.

While the engine is being flip-started, it does not draw any fuel through the carburettor...
It only runs on that fuel that is already inside it; whether from priming, or from the last running seconds before it was shut down.

All shaft-valve two-stroke engines have a limited capability to run in the opposite direction, although in a very ineffective way...
If an engine does start backward, you will be able to advance the throttle to about 20-25% open, but no more...

If you're lucky, at that point the engine could 'kick-back' and begin running normally. Or it will just conk-out...


Over-priming is the main reason for this to happen.
I have seen cases where over-priming with forward-flipping, caused a kick-back so strong that the prop was jarred loose.
(Kick-back on back-flipping will only tighten the prop in place... Besides, this is how all my engines are started...).

With a single nut holding the prop, you would have no way of knowing, until the engine begins 'shrieking' in flight, after the prop flew off...

Sport_Pilot

As others have said overpriming is the usual culpret. But also sometimes not flipping the prop hard enough can do this as well. It sometimes happens when the chicken stick slips off before it carries it through.