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Engine basics => Engine set up tips => Topic started by: Terry Caron on January 12, 2015, 01:56:27 PM
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I recently bought a used TT .46 Pro.
I disassembled, cleaned, reassembled and tried a bench run.
It starts easily but runs backwards, at very low rpm, with a regular tendency to pop forward yet never makes the transition.
The cylinder liner is pinned so it's not in wrong.
Any thoughts, notions, suggestions?
Thanks.
Terry
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I recently bought a used TT .46 Pro.
I disassembled, cleaned, reassembled and tried a bench run.
It starts easily but runs backwards, at very low rpm, with a regular tendency to pop forward yet never makes the transition.
The cylinder liner is pinned so it's not in wrong.
Any thoughts, notions, suggestions?
Thanks.
Terry
Check for and add an additional head shim, use a cooler plug, prime about 2 times then flip the engine over 10 times very fast to aerate the charge, then flip the prop backwards, it should fire front ways.
Are you running a carb or venturie? nitro % ? size of prop?
Randy
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No head shim, carb w/.295 bore (not sure if factory, marked DV-II, single needle), 6 1/2% nitro 22% oil, APC 11/5x4.
Terry
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Add the head shim, or 2 that should stop it
Randy
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Add the head shim, or 2 that should stop it
Randy
Tnx Randy - do you know (or would you guess) the thickness of the head shim?
Don't have any, but can try making rather than wait.
Terry
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Tnx Randy - do you know (or would you guess) the thickness of the head shim?
Don't have any, but can try making rather than wait.
Terry
You can make one anywhere from 5 to 10 thou, any of those should do it
Randy
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OK, I'll make a couple .005".
Would you explain what's happening?
I assume timing?
Terry
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Ordinarily that's a symptom of being badly flooded and is fairly normal with RC engines with the throttle at, or close, to idle even with just a bit of over priming. Try to ensure the engine is completely dry then prime with a few drops of fuel without the fuel line attached and see if it starts correctly. If so then make sure the needle valve is actually fully closing first before attaching the fuel line. I had one engine (brand new) that would run in a slobbering 4 stroke with the needle fully closed. Actually it was the barrel bottoming out on the threads, not the needle itself.
It's extremely unlikely to be a compression problem because I generally run mine at 12-13:1 with no problems.
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I'm gonna agree with these fella's. I had the same issue with the .46 and .25. It was just my starting method. Too much fuel. Mine, i prime it 4 times, then flip it 5 or 6 Then attach the battery and go. Always fires up on that first flip.
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OK, I'll make a couple .005".
Would you explain what's happening?
I assume timing?
Terry
It is VERY likely that compression is helping in causing this, The 46 is very high compressed and if you have ZERO head shims in it, it can make it "diesel " and run backwards
What is most likely causing this is a combination of things ,too high compression,excess oil, afterrun or other oils and /or excess amount of fuel charge inside the engine when you try to start it. the EXTRA COMPRESSION is making this much worse and aids in the running backwards. Sometimes with the very high compression the engine will start without a battery on it.
Try to clean out any excess oil, and fuel before you start it next time, and try one of the .005 head shims that your making.
You will also not blow as many plugs with a head shim in the engine, as with zero shims.
If you start it again and it runs backwards, do not shut it off, instead pinch the fuel line to stop more fuel from going into the engine, it most likely will pop back and run the other direction, even if it doesn't this will clean out the excess
Randy
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What's been said makes rather embarrassing sense, everyone.
I definitely primed it quite wet, several turns open needle, at full throttle.
I've made & installed a .004" shim; I'll try again tomorrow to first see if it'll properly burn just a light prime.
Thanks to all for your interest.
Terry
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My Stalker .81 does just this. I believe it is very much over compressed. I added 1 head shim & it actually 4 stroked at a higher RPM....
Work in progress, John
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What's been said makes rather embarrassing sense, everyone.
I definitely primed it quite wet, several turns open needle, at full throttle.
I've made & installed a .004" shim; I'll try again tomorrow to first see if it'll properly burn just a light prime.
I would leave it alone and try again. This is absolutely classic behavior when the engine is upright and you get the crankcase loaded before there is enough fuel in the cylinder to get it to start. This is why I hate starting upright engines.
If it starts and runs weakly backwards, pinch the line off until it slows and just as it stops, release it. It will probably kick and run forwards. If it stops, release the line and flip forward. Still no luck, pinch the line, put a few drops in the venturi, and then go.
Brett
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The weather is finally cooperative enough to get outside to play, so I ran the engine a bit w/2 .004" shims, cooler plug.
It took a good bit of prime (about a dozen) and didn't diesel but the NV has little effect.
Has to be ~6 turns open to run and won't lean or richen appreciably, 11.8K-13.3K range.
Recommendations for a decent venturi/NVA assy?
Terry
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The weather is finally cooperative enough to get outside to play, so I ran the engine a bit w/2 .004" shims, cooler plug.
It took a good bit of prime (about a dozen) and didn't diesel but the NV has little effect.
Has to be ~6 turns open to run and won't lean or richen appreciably, 11.8K-13.3K range.
Recommendations for a decent venturi/NVA assy?
Terry
Hi Terry
I of course make them, let me know If i can help, but did the engine run the correct direction? and is the TT ventuire NVA setup or aftermarket or carb?
Randy
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Hi Terry
I of course make them, let me know If i can help, but did the engine run the correct direction? and is the TT ventuire NVA setup or aftermarket or carb?
Randy
It ran the right direction Randy.
It has a carb w/.295 bore, not sure if factory, marked DV-II, single needle.
It dies w/no leaning at less than ~ 4 turns, dies at ~8 turns w/little richening, when the needle unseals from it's body.
You mentioned excess oil in an earlier post - is 22% too much in this engine?
Terry
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It ran the right direction Randy.
It has a carb w/.295 bore, not sure if factory, marked DV-II, single needle.
It dies w/no leaning at less than ~ 4 turns, dies at ~8 turns w/little richening, when the needle unseals from it's body.
You mentioned excess oil in an earlier post - is 22% too much in this engine?
Terry
NO The oil content is not what is causing the poor needling unless you have old fule, or fuel with water in it
Randy
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NO The oil content is not what is causing the poor needling unless you have old fule, or fuel with water in it
Randy
Fuel is good - I was thinking of the high compression/dieseling issue.
Terry
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Forcefully flush the spray bar from both the threaded end and the fuel nipple with your fuel syringe.
Is there a funny shoulder in the needle like it was crushed in over tight? Was there any trash on the needle? Is the needle straight?
Phil
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Forcefully flush the spray bar from both the threaded end and the fuel nipple with your fuel syringe.
Is there a funny shoulder in the needle like it was crushed in over tight? Was there any trash on the needle? Is the needle straight?
Phil
Passages are clear, needle straight and tapered Phil.
Terry
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sounds like you do have something wrong with the carb, is this an engine you will use with a carb? or NVA for CL along with venturie. we can guess all day at what is wrong, but if your going to use it, sounds like you need a new carb or venturie setup
Randy
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PM sent Randy.
Terry