Hi Everyone,

I've been stumped for a week with some strange behavior of my new JBA 120 (ringed) engine, and hope I can get some tips from someone on how to resolve my issues. There are a number of symptoms (which are possible related) that I'll try to present in a clear form below:

a) It's difficult to get started...it's pretty tight (compression) at the first start of the day so I use a Sullivan Dynatron starter on 24 volts. Even then though, the engine just spins over for quite a number of tries before I can get it to start (it feels like a bit of a gamble).

b) Once it gets running, it runs pretty well at the bottom 40% of throttle (from idle up to 40%) and at the top 15% (85% throttle to full throttle). Anything in-between it tends to die. I have checked the idle needle setting by pinching the fuel line and it's fine (the engine continues at the same RPM for about 4-5 seconds before quitting without a change in revs). At full throttle I have the needle open about 3 to 3 1/2 turns and there's a healthy level of oil/exhaust smoke coming out of the muffler. It doesn't like anything less than 3 turns (it just won't run above 40% throttle at about 2 turns). It isn't too rich either as it is in a happy "slightly" rich two-cycle note, not four-cycling. Another funny thing is that to get to full throttle I have to leave the glow igniter on and advance the throttle to full pretty quickly, then take it off. It runs happily at full then - but if I lower to half throttle for more than 5 seconds and try to come back up the engine dies on me. When I keep it there just for a second or two, it can come back up okay, but not smoothly (it struggles a little bit inconsistently then clears up). I have tried 2 OS 8 plugs, 1 OS F plug, and 1 cold plug from a brand I can't remember (recommended by someone). This behavior persists whichever plug I use (and the plugs still appear to be in good condition with the exception of the first one I used - figure it's not unusual when breaking in an engine).

c) The most annoying thing is that after I run the engine for a while (about a 1/2 tank to 3/4 tank) and need to restart it, I can't! It's even worse than at the start of the day - it just won't ignite. I do feel the compression is not as tight as at the start of the day, but still at a decent level so I don't think that's an issue.

I'm just about ready to give up on this engine - I feel I'm the unlucky recipient of a poor quality control process - some JBA engines are just fine I'm sure, but there's also a fair amount of troublesome ones I bet. Please help!!!

Thanks,
Ken

1- How many hours does the engine have? Less than 1 hour is unacceptabe for this engine. It should be run-in at a rich setting to bed the ring and liner.

2- Remove the carb and check o-ring and needles for clogging, reinstall the carb with the o-ring well seated.

Always put a new plug sfter the first run-in tanks as a lot of debris from the running-in process will contaminate the glow plug filament.

My bet is #1, mine runs sweet and has always started first back-flip on the prop.

http://www.youtube.com/watch?v=FL-Z1Iz7S5g
http://www.youtube.com/watch?v=RbGtoVXvHZ8

Hi Patxipt,

Yes, less than 1 hour running time, as I've had so much trouble keeping it going (or even getting it started so far). Is what I've described then normal behavior for the initial running in period? If I may ask, what is your High Speed needle set at?

Thanks for your reply by the way,
Ken

From memory, I ran it very rich for the first few tanks, around 3~4 turns out on the HSN. It sits at around 1 1/2 turns out now.
Just redo the running-in for the engine. and check for leaks and clogged carb and fuel line.

Mine has always been 2 flicks after priming, glow on and then one back flip.

Glad to help Ken

Hi!
It's easy!
Your description tells me of an engine that has the idle screw turned in too far. Just turn it out some (a quarter to half a turn or so).
The idle screw is blocking the fuel comming into the carb!

Pinching the fuel line isn't a good method to set the idle!!! Rather crude methode.
You have to learn how to set the needles by ear...that way is far more accurate.

Ken,
This is actually a sign that you have idle too lean. using the pinch method even at idle you should hear an increas in rpm when you pinch however slight, then it will slowly quit.

Richen that puppy up

Hi guys,


Thanks for the tips. I'll try turning out the idle needle a quarter turn first and continue running it (when I can get it to start). I have checked for carb clogging and seal to crankcase, seems fine so I hope that's not the issue. Will write back if things still don't improve...

Cheers,
Ken

Try another batch of fuel.Maybe bad fuel.

Well, I have good news to report. This morning I was able to get the engine to run through another 5 tanks of fuel (total of 6 now). It is definitely getting easier to start/run (although getting that first start took a bit of patience, every subsequent start was easy). I have the main needle still at 4 turns open and the idle a bit richer than it was before. It sounds a lot more stable than before - looks like just giving it time to run in was the trick.

It can happily run at the top end for as long as there's fuel now, and while half throttle still gets a little gurgly when the tank's more than 60% fuel (I think it's an issue with tank placement) it won't die on me if I carefully get back on the throttle (and don't keep it at half too long). Once fuel sits at 60% or below half thottle is no problem for any period of time. Very nice response and transition from that stage. I'm so relieved after this morning, to not have this engine constantly quitting on me or not even starting.

Patxipt, since it's just about an hour of rich running now, is this where you started closing the high speed? Can I ask how long it took you to reach 1 1/2 turns in? I am planning on adjusting the needle a bit (if the engine will take a leaner setting now) for the next trip out, and if it keeps running happily to take the plane up in the air to continue running it in there.

Any further advice?

Cheers, thanks to everyone for their input..

Ken

Ken, the needle can be leaned progressively around 2nd tank, no sweat, but peak should be tried at around 5th tank of fuel.
Give it 4 short runs with plenty of time to cool in between and lean the carb on each run. Remember to pull the throttle fully open once it warms up at a fast idle (20 seconds?) as the combustion pressure is what will bed the ring in.

BTW, if you check my youtube account, I've started running-in of my JBA .91, also a treat to start and run. Two flips to prime, 3 flips to clear and it starts promptly, just like the 1.20.

Hey Patxipt,

Thanks for your insights and tips. Yes, the runs I did today were mostly full throttle. I'll do as you said and lean the needles out slowly over a couple of short runs with time in between to cool.

I guess if the instruction booklet had your points in it that would have saved me tons of worry! : )

Cheers,
Ken

Just an update from the field today. Engine ran pretty well on the ground, but I couldn't get it to be happy at any less than 3 1/2 turns out on the main needle. I tried one flight at 3 1/4 turns but it wasn't happy - may have been a little lean (though there was still smoke) - it died after about 4 minutes in the air at that setting. After turning out to 3 1/2 it had a happier flight. Very good transition now. I guess I'll just continue to be patient, and let the engine tell me what it likes.

Ken

You can save a lot of time and the cost of fuel on a engine like that. Break-in will be faster...a savings for sure! The thing to do is get a Frank Bowman custom made piston ring for it. About 15 min of running the engine should run great. Go to engine conversions and read about Franks Piston rings.
Best Regards Capt,n

3,5-4 turns of HSN is not normal.It seems your carb. has some blocking.I recommend you to remove the carb.and disassamble fully.Check for the dirt particles especially on the spray nozzle inlets.
Hard start means unproper priming.Also hard turns means possible choke by fuel.I guess your tank is siphoning into engine.