My 170 CDi is really easy to start once I've primed it quite a lot so the pump has something to chew on. Initially though, the idle is really low, I mean to the point of it barely running and I have to let it heat up with a much higher idle than normal. I rev up to full power and back to idle, and it's easy to find a steady idle before takeoff.

After a 6-7 min flight the idle is suddenly much higher. I have to trim the idle way down to be able to land. It still quits on throttle cut but it's stressing to have to trim the idle as it obviously changes during flight. Why is this?

- Soft home made hyde mount. It's very soft and it's possible it strectches but that problem should be apparent on the ground as well?
- Fuel flow/hot or cold engine- Does it not get enough fuel at idle before it's really hot?
- Prop windmilling - is the speed of the plane and the spinning prop making it idle faster once airborne? I've never had that happen in a plane before.

Has anyone else experience idle differences on their CDIs?

Hi Jon,

Mine is very steady, never had that problem, could it be too lean? (pump) or you might have a pump problem.
Did you check the basics? Valves, spark plug gap, etc? have you tried to prime the pump and get all the air out of it with a syringe or similar method? Is the pump hose ok?

Regards

Thanks, I'll check to see if steadies if I richen the pump. How much do you turn the pump when adjusting? I mean how much, perhaps 1/4 turn is noticeable?
How far out is your high-speed needle valve by the way?

On a new engine I turn the pump about 1/8 of a turn at a time, once I'm very close to the final setting I turn it 1mm at a time, and it is noticeable. My needle valve is usually at 1 turn, on the new engine I'm still breaking in is a little more than 1 and 1/4 turn. The pump on the CDI engines comes with a rich setting, get your engine at at least half power and go to idle, it should establish a steady idle without an increase or decrease in RPM, if it increases the regulator is lean and vice versa.

Good luck!

Jon,

My idle changes quiet a bit due to the mount I am using. It is a Hyde ARI with an integrated nose ring, same mount I used on my 1.40L, but the 1.70DZ bangs a round a little more at idle than the 1.40 did. I was at a meet last weekend with Archie (rcpattern) and he is running the Hyde LR mount and a seperate nose ring and his idle is very stable. This can be attributed to how steady his engine is at idle. My ARI mount will be getting a little help to reinforce the nose ring and settle it down a bit.

Just food for thought.

Pete

Jon,

I would try richening the pump slightly as well. Unless you motor is really bouncy, it shouldnt change a great deal with the mount, but Pete's was really sloppy and moved quite a bit. I would start with richening the pump. Even an 1/8 of a turn will help.

Arch

Thanks! I had five flights yesterday and I tuned it slightly more rich, about 1/8 turn and it helped. Judging from the smoke when airborne I get a feeling that it's lean at full power since there's White smoke in all other throttle settings. Might have to start over and lean the idle while richening it with the high speed needle. I've forgotten to adjust the idle after the csi conversion...

Good news, but Jon, remember to check the idle mixture by going into power then idle and listen for RPM changes, if it stays at idle immediately then leave it and just adjust the high speed needle; then fly, and adjust the regulator if you fell the engine not smooth, I mean it should accelerate softly (moving the throttle slowly), some times is difficult to try to "feel" when the engine is lean in the air(fine adjustment) but try 1mm on the regulator at a time between fights and you will notice the difference in the air.

Regards

one more thing that might be causing it - There's a leak somewhere. I'm almost certain it's the head gasket and will replace it today but I discovered the check valve/fuel injector on top of the engine is blowing out a little bit of air - if you put a drop of oil on top of it you can see it blow a tiny bubble when you turn the prop over. Is it supposed to be like that or can that valve develop a leak as well?

Hello Jon, if you mean the air is coming out of the hole in the top cap of the fuel injector then yes, it's normal, and it's doing its job, which is to remove the air form the fuel entering the injector.
If you have a leak, check the push-rod guide tube O rings, pretty much leaks from them about 90% of the time.

Best regards

hi guys,
has any one had any issues of the fuel getting to the engine but just wont get up to the injector my friend is pulling his hair out , one minute ok, then refuel and problems begin , very strange!!!..

regards
steve

flush your fuel system from the injector back

gary

gary,
we have done all that even new injector!!!......and stii probs!!........

regards
steve

Steve,

try changing the pump or looking at O ring seals in the needle valve assembly

Keith

hi keith,
that was my next thought !! ,.....

rgds
steve

Sounds like it`s running Hot to me,
You can`t run the CDI on the ground for long periods of time unless the cowling is off, setting the high end like the non CDI
If the motor vapor locks from over heating,,you will not be able to get fuel to the injector.

The reason I say this could be your problem?, you said, one minute it`s running fine the next minute ,no fuel to the injector.
It just sounds like it`s over heating.
It it were a pump or o-ring problem I think it would be a constant problem.


Bryan

you can also try pulling the needle and seat when flushing, a piece of trash may have gotten behind the seat ,I have seen this cause the problem you have pointed out. Bryan also has a good point.

gary

hi bryan,
the engine only does this if you complete a schedule 8 mins land refuel and try to restat within a few minutes of landing , you may of hit the nail on the head with the engine be to hot from the flight , i guess run the engine richer on the regulator and main needle.

regards
steve

Yes Good news,! Easy fix.
Richen it,thats a start, however,
Richen the main needle till it starts to run rich (POP) Watch the Smoke trail you can connect the dots,,
If it`s rich and you have some smoke ,and your still runing hot Then,
make sure the intake air inlet is centered on the head, then increase the exit holes if you can.

I quick way to know if your low end is the main problem, start the motor let it idle for at least a minute, then advance the throttle slowly and see what the engine does then advance it a little quicker ,,because it`s now warm you will get a better reading on what to adjust.if it`s sluggish or non responsive at times richen it up, if it pops or burbles lean it a little.if it`s fine adjust the main needle.

The 170CDI is best adjusted for perfection by getting it close on the ground (don`t fiddle with it too long it will get hot),and then flying it and carefully listening to what the motors doing. Using that info and the smoke trail ,,you can eventually learn it`s ways. it`s a little different than the Non CDI,the settings are a little harder to get perfect.

You can also take the foam from your YS engine box and add dams to the engine cowling and compartment, to direct the air directly on and around the head and case.


If after you land and let it set for a couple minutes you can learn to touch the spinner for a quick check of the spinner heat sinking.
If it increases in temp. after a few minutes and gets hot hot! ,,and hard to start,, keep adjusting.
after a while you will get the hang of it.

You can also get a temp gun if you like for better testing.

Bryan

hey brian,
thanks for the info the prop is a 19x11 turning about 7,290 on the ground 30 nitro 22 oil, smoking well , in the air the motor has great throttling all the way through the flight, is only as i said befor about the re-starting issue.

rgds
steve

What temp range do we want to be in ? Using the temp gun.

I was at a contest last weekend with temp up to around 102 plus dry humidity, the engine temp went up to about 150 after the F sequence, and backs down fairly quickly. However, you must place the foam strategically to create a venturi effect & force cold air through the fins & the valve cover.

It also helps to take off the bellypan or use a small electric computer fan to further help cooling the engine after landing on those hot & humid days before your next flight.

Adrian