I have some MT62s, the one I'm playing with now is in a SD260 30% extra.

My problem is it's dieing on rapid throttle advance from idle. I've got the ignition set at 28* BTC static, and have replaced the soft carb block with one from Ralph made from G10. I'm getting 7400 rpm with a Vess22A and 7200 rpm with a BME 20x10, the same as my Brillelli 366GT. The plug looks good, very light brown. The idle is set at 1850, it will idle down to 1350, but it's a little rough there and 1850 works fine while flying. I've gone leaner on the low until it's really hard to start and dies lean on any advance of the throttle, and I've gone richer until it's slobbering. I'm running a KS86 canister with a DA header from TBM, it has no effect on the top-end compared to the stock muffler exactly the same power readings, just halve the noise. When I took the cowl off to tune the transition, the engine was wet with fuel/oil. When I ran it without the cowl I had to re-tune the end for top-end, then I noticed if I blocked the prop-wash from the engine I had to re-tune it. I fly with a cowl, dah, so to tune it without the cowl I strapped on a plate that blocks the prop-wash, as if it was in the cowl. Now I see where the gas/oil mix all over the engine came from, when I pop the throttle open a air/fuel mix fog comes out of the carb, it's not blown away like it was before the blocking plate. So tonight I'm going to turn a velocity stack about 1 1/2" tall and see if that helps the transition when I pop the throttle open. Anyone got any other ideas.

Rich, Sounds like it could possibly be a timming issue. Put a degree wheel on it to verify your 28 degrees BTDC.

Larry LS PRO ENGINES


AIRBORNE RANGER

Did that. I'm using the back of the prop hub as the degree wheel, it's 1.774' diameter so I figure 28* is .4312" on the hub, am I correct on that?

After each idle re-tune, you must set the H-needle again. It seems you are too lean on the top end, and your mixture is mostly provided by the idle needle.
Set the engine at ~1800 with the idle stop screw. Then find best idle rpm with the idle mixture needle. Open up 1/8th turn from there.
Now turn your attention to the high needle. close until rpm sags, open up again until rpm is just a tad off max rpm. If the carb is OK, transition should be OK. If not, dismantle the carb and clean the transition spray holes well. Blow some fuel in the carb and check function of each jet. There should be three or four of them, apart from the main jet.

soarrich,

I've got .4335. For 30°, it's .4644. I'd call it .450 to make it easier.

Sounds to me like the canister isn't tuned. Might be time to start cutting the header.

PE

Thanks I'll try your method.


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I made a velocity stack for it last night, it seems to have really helped, the engine doesn't die anymore, but it's not 100% yet, maybe 99%, it started to rain so it'll have to wait for tomorrow.


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How does the velocity stack work? Is it that it holds the air/fuel mix there to be suck back in? or is it ramming the air keeping the air/fuel mix from coming out?

That would effect the transition? Is the canister really tune-able? It turns the same rpm as the stock muffler, just quieter. I didn't know a canister was really tune-able, I knew tuned pipes are tune-able, it's that what sets them apart?

It could effect the transition. If you have a canister that needs to be tuned--it could be so far out of adjustment that it's causing the rich condition you are describing.

I think it depends on the canister, but I do know that some canisters must be tuned. You have to cut the header off and adjust the canister closer. Just like a tuned pipe.

It's just like a tuned pipe. Eventually, you'll hit the sweet spot on the header and you should see an RPM gain.

This isn't true of all canisters. I admit--I don't know a whole lot about how they work or WHY some of them create a power boost and WHY some of them actually rob a little power, but make it quieter.

Dick Hanson is the guy you need to talk too. Maybe he will chime in.

The guy at Macs Pipes told me that a canister can sometimes be called a Folded Wave tuned pipe. But it depends on the design of the can. Some cans are purely made to get the engine quiet. Others will get it quiet AND increase the power output. But you have to tune those kind by cutting the header off and reading RPMs.

Header length has a direct effect on the transition.

In a very basic sense it holds the escaping charge there until it can be pulled back in, but it also helps the flow of the air into the venturi and can increase power. (if done correctly)

First I don't use the idle stop screw, I have a digital servo on the throttle, if it touches the screw it pushes with full power against it and will burn out, ask how I know that!:^(

I thought no way is the idle set too rich, but if I ask for help I listen and try what is suggested. It turns out somehow with all my putzing around the idle screw was set 1 3/4 out, the H needle was set about 1 turn out[:'(]. So to start I set the L at 1 turn, the H at 2 turns. I started it, then adjusted the H to get 7000 rpm, then set the idle on the radio at 1800 like Pe suggested and popped the throttle open, a little on the rich side, I played with it until it was about 7/8 on the L. Now it's working pretty well, 99.9%. So tomorrow I'll fly and fine tune it.

Thanks Pe.

I flew it today, almost prefect, but it was the best day in four months so I just wanted to fly. It so nice to have an engine you can depend on to continue to run. The MT62 and the TBM SD Extra 260 make a great combo.[sm=thumbs_up.gif]

What is a basic starting point for the needles? Open 1 turn or more?

So to start I set the L at 1 turn, the H at 2 turns.

It worked for me.