Zenoah ZP38 Idle Issues - RCCanada - Canada Radio Controlled Hobby Forum
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Old 07-22-2016, 09:44 AM   #1
plane crazy
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Zenoah ZP38 Idle Issues


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Looking for some help with my new Zenoah ZP38 Platinum engine.
Bought it new and have it mounted on my Yak, I've run 6 tanks of gas through it, the first 4 at 25:1 now onto 40:1.
Problem is getting this engine to idle without dying.
High end seems good but as soon as the rpm's drop below 4000 it quits, tough to take off and land at these rpm's.
Spoke to Horizon and explained the issue, they sent me a new carb to try and after 5 hours at the field last night nothing has changed.
I'm running a Life battery for the ignition, I've changed out the stock plug to a NGK and am using a B&B muffler, aside from that it's all stock.
I'm just about ready to pull this engine off and send it back for warranty but I'm sure that I won't get it back in time to fly this year.
The engine has been discontinued by Horizon for a while now and I'm wondering if it was due to these issues?
If anyone has any suggestions at all please let me know as this has me stumped. One of the senior members at my club who has been a mechanic until retiring has spent countless hours trying to trouble shoot this and he to is left scratching his head.
I would rather not go to a magneto design due to the weight and doubt Horizon can replace with another so I'd prefer to try and fix whatever may be causing the low idle to kill the engine.
Cheers,
Wayne
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Old 07-22-2016, 09:57 AM   #2
Trumpetman
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Re: Zenoah ZP38 Idle Issues

I would pull the motor off the airframe and mount it to a test stand. If it runs on the test stand (with a different fuel tank) you have found your problem. After that I would try changing one thing at a time: stock muffler instead of the B&B etc., if you can borrow an ignition to try I would also check that. Good luck! I hate chasing these frustrating issues!
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Old 07-22-2016, 10:14 AM   #3
plane crazy
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Re: Zenoah ZP38 Idle Issues

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Originally Posted by Trumpetman View Post
I would pull the motor off the airframe and mount it to a test stand. If it runs on the test stand (with a different fuel tank) you have found your problem. After that I would try changing one thing at a time: stock muffler instead of the B&B etc., if you can borrow an ignition to try I would also check that. Good luck! I hate chasing these frustrating issues!
Thanks Gordon,
It's actually what I'll be spending my Friday night doing aside from sipping Scotch!
My plan is to bench mount it with a new fuel tank (without the felt clunk) bolt on the stock muffler and see if I can locate another RCexl ignition. I've replaced the gaskets on the carb as well as replaced the carb isolator plate.
Another thing I forgot to mention in my post was that the plane won't start unless I inject a bit of fuel into the carb, even when the engine is warm.
I keep going back to fuel as the culprit (not getting enough at low rpm causing it to stall) but it appeared that the carb was spitting fuel out last night when running around 4000
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Old 07-22-2016, 10:54 AM   #4
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Re: Zenoah ZP38 Idle Issues

Just a suggestion: change only one thing at a time. 1. Start with the fuel tank/clunk. Run engine and check. 2. Reset carb needles to the suggested stock settings. Run engine and check. 3. Change the other things one at a time. IMHO
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Old 07-22-2016, 11:56 AM   #5
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Re: Zenoah ZP38 Idle Issues

If you have to prime the engine then I guessing you have a restriction in your fuel system. That could be either the filter, tank clunk etc. suggest removing anything that might restrict fuel flow and try it. I don't use filters in my airplane's as I filter the fuel as pumping it in. You may also have the low end needle to lean which would make it difficult for the carb to pull fuel. Also the carb pump operates on pulse pressure from the engine itself. If it is a high time engine and the compression is low that will cause a low pulse pressure for the diaphragm pump in the carb. When u go to idle there isn't enough pulse pressure to operate the diaphragm an d pull fuel. Replacing the ring would solve that issue. Also u mention that mentioned that u where using a high oil content prior. That may have carboned up the ring seat which results in low compression also.
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Old 07-22-2016, 12:15 PM   #6
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Re: Zenoah ZP38 Idle Issues

If it was running fine the first few tanks and now not, mabey some felt off the felt clunk is plugging up the carb screen. May be worth a look.
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