engine running in reverse

[pgkevet]

This was a frustrating day. The 91 engine started easily and runnign right way round but within 2-3 secs of pulling the starter wand it'd flick into reverse running and up it's rpm a bit as clutch load came off. Blipping throttle didn't sort it.
I uderstood this could be a function of being too rich but leaning the mixture needle, leaning the high needle, starting it with the fuel clip on all made no difference.
I did manage one flight when i richened the mixture cam right up, started on my flight-line, pulled wand and gave throttle almost together. The flight itsef was fine..plenty power and engine sounds sweet, no bearing rumbles etc, decent sensible exhaust.
I used up the rest of a fully charged align starter on refuelling ..and gave up.

I did notice a bit of clutch drag on the head and the bearing has been unchanged over a year.. so if no-one has a better answer i suppose it's pull it, service and bearing change, check clutch shoes and back to basics????

[KevDavies]

too rich on idle/low speed needle causing over fuelling. Which inturn explodes in the exhaust and spins the motor back the wrong way. Id say your wayyyyyyyyyyyyyyyyyyyy too rich bud. Also a failing plug can cause pre detonation and a backfire, maybe why it wouldnt start?? My money is rich tho.

which 91 is it by the way?? is ita pumped with 2 needles aor unpumped with 3 or one of them YS devices?

[ROSSCO]

I sounds like the clutch could be on its way out, I would probably replace the clutch. It might be worth replacing the clutch liner also. What can happen is either the liner has become worn and the clutch shoes are extending further than normal causing them to fracture and then grab causing the engine to backfire and run backwards or it could be just a matter of the clutch getting fatigued and cracking around the flex points cursing the same symptoms.

[smokingtommy]

as above from kevdavis bang on reply also to much compression in the engine can do this easy way take the plug out and turn the engine a few times just to clean out any fuel that may be in there so its not flooded

[pgkevet]

OS91 unpumped. Clutch drag only marginal..as in can feel it 'cos looking for it. As for way rich... can't see it if the mixture was leaned as much as possible and the top needle leaned way more than I'd normaly have it and when it did run there was no x/s smoke etc.

I'll pull the engine and check clutch and check the bearing on principle..

[electricsceadu]

i'd say its over rich
and don't forgat if its way over rich the engine and exhaust doesn't get hot enough to cause lots of smoke
also check that the exhaust isn't blocked and over pressurizing the fuel tank

[KevDavies]

as above from kevdavis bang on reply also to much compression in the engine can do this easy way take the plug out and turn the engine a few times just to clean out any fuel that may be in there so its not flooded

Cheers Tommy.

One thing I do notice a lot with helis is theyre run exorbitently rich when there is no need to. and it causes a lot of aggro with starting etc. Dont be afraid to lean it out abit. You want smoke coming from the pipe yeah but you dont tune them by the smoke.

You need the heli to idle nice for a minute or so and to respond to a punch of throttle without bogging (thats how you set the bottom end)
It needs to run nice and clean at a hover yet still not get majorly hot (if you can hold the back plate for 3 seconds before its too hot then its fine. Much more is too rich IMO) <--Main needle
and mid needles I tend to do last of all and very sparingly as theyre usually not too far off from the factory. This needle controls the trabsition from the low end needle to the main needle. So if its been idling and you punch the throttle and initially it pulls clean and then starts to stumble that means the mid needle it rich so you lean it incremently till it pulls through the whole rev range nice and clean.

[KevDavies]

OS91 unpumped. Clutch drag only marginal..as in can feel it 'cos looking for it. As for way rich... can't see it if the mixture was leaned as much as possible and the top needle leaned way more than I'd normaly have it and when it did run there was no x/s smoke etc.

I'll pull the engine and check clutch and check the bearing on principle..

See my little tuning guide on here but by the sounds of that the top needle is on the lean side but the middle and lower too rich

[trillian]

I think in this weather it's not very easy to tell by the backplate because the cooling is working very efficiently due to the colder denser air.

First of all I'd say, make sure the needles and idle mix are close to the factory recommended start points. The pinch test is probably the best way to get an idea if the idle setting is too rich or lean because in this weather the backplate on a .91 engine is likely to stay very cool regardless.

(I would imagine you have seen the pinch test but if not it's basically getting the engine into a steady idle and then pinch the fuel line close to the carb and the engine will speed up and then die. If it starts to speed up around 3 to 5 seconds from pinching the line it's OK, if it takes longer it's too rich and if it happens sooner it's too lean)

Are you using a hotter plug, like the OS7 or something hotter than the 8?

In my experience if an engine is too slobbering rich on the idle setting it just won't idle at all.

[pgkevet]

See my little tuning guide on here but by the sounds of that the top needle is on the lean side but the middle and lower too rich

As I said it still did the same thing with the lower mixture cam fully closed and the top needle (if I recall ) was 1 and 3/4 open on that set of attempts.

Eit extra: I should add that i generally view any weird engine ebahviour as time to fit a new bering even if it sounds OK and looks OK.. can still affect crank pressures and flows?

[KevDavies]

As I said it still did the same thing with the lower mixture cam fully closed and the top needle (if I recall ) was 1 and 3/4 open on that set of attempts.

Eit extra: I should add that i generally view any weird engine ebahviour as time to fit a new bering even if it sounds OK and looks OK.. can still affect crank pressures and flows?

If your regarding front bearing, then yes it would cause running issues, but generally that leans the engine.

But your plan of a quick overhaul and start again is definately a good one. That way every possibility is eliminated

[pgkevet]

Finally got around to looking at it (doing the hobby shed meant a backlog of other stuff to make)
I'm pretty sure I;ve found the reason..Doh!...both shoulder bolts holding the engine frame mounting one side missing and one broken on the other side!!

I was talking to local tractor engineer the other day and he says that he often sees diesel egines that bog and then reverse run..anything that kicks it while idel will do. clutch dragging, odd output loads.. a fair chance that my engine rattling on it's mounts was snagging the clutch. I'll check bearings while it's out anyway since there's a lot of neglected maintennace on this heli to do..