Back Fire issues
 

Ok, Im not new to gas, but Im sure Im missing something.

I got a sweet used ZDZ80 Super J I got off this site. I was testing a prop a few months back and it throw a blade, and broke off the mount lugsoff the rear of the motor.

So I got a replacement rearblock/plate. from Troybuilt Modles Great guys.

I finily got around to putting it in its bird a TopFlite P47 With the Scale Belia 22X10 4 blade prop.

I have not tuned it for this prop, and I know some peaple have a hard time staring, but she gave me no issues.

While trying to get the high end set she backfired on me once at 3/4 power but once I got it leaned out no more top end issues, she is running sweet/scarry at 6900RPM on this prop with no drop off in RPM.

But some times I can bring it down to idel with no issue, I had it ideling at 2000rpm for 30sec or so and was going to run it up and it started back fireing like crazy and sut off.

I richend the low end a little and it would still back fire like crazy.

So now that im typeing this out, Im thinking I need to lean the low end?

Before it would back fire I had no transishion issues.

What you guys think?</p>

RE: Back Fire issues
 

If its truly backfiring, it's probably too lean. Try richening it up and try running it again. If after runing WOT it stuffers or backfires dropping back to idle, your idle mixture is too lean.

RE: Back Fire issues
 

Thanks I will try, its a deff backfire, like a shot gun!

RE: Back Fire issues
 

backfiring, most times means a timing issue,or a bad ignition.try all the easy things first.

RE: Back Fire issues
 

You may be getting odd ball out of time sparks?

RE: Back Fire issues
 

Thanks guys. All good it was a little over 1/2 turn lean in the low needle !!

I have never had a low end so far off. But it's smooth and loves the 22x10 4 blade
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RE: Back Fire issues
 

An otherwise good running engine will almost always backfire if 'slightly' lean, it'll just quit if its 'way' too lean. 2 and 4 stroke doesn't matter. Surging isnt uncommon either depending on the carb. This has been my experience even on engines with adjustable timing like outboards and fixed timing lawn engines.

Other parts of the country with different climates will see slightly different behavior.

My philosophy involves starting with the easiest fixes first. No need to jump to replacing ignition components right off the bat other than spark plugs and fresh fuel.

RE: Back Fire issues
 

Mike, check your timing. This will help. Dan.
http://www.youtube.com/watch?v=GBXFpxWg7vY

RE: Back Fire issues
 

It looks like he fixed it.

RE: Back Fire issues
 

Surprised that it transitioned well being that lean on the low end. ???

RE: Back Fire issues
 

Know Im lost guys,

I had this big boy running infront of my house, with the back fireing issues, open the low end a little over a 1/2 turn and all seem ok, I let it sit at 2000rpm for a min then rev to max with no issues and transhishions seemed great. Put the cowl back on, gave it 5 min to cool down, re starte and run it all over the rpm range with no issue.

So I pack up the P47 for its maden flight today, and got to the feild with my new baby a nice looking and what a disapointment.

It started with no issues, gave it a full 2 min a little above idel around 3rpm to warm up, but while trying to run up to wot, it would stumble up top, run a ruff with little back firing surging sounds would not hit full wot.

Weard as it was fine yesterday, even thow today was a little hotter and muggy,

This sucked as I did not put a door for the needles as it would be on the very top of my cowl.

added some fuel on the top end and it still ran accted weard, I open the top end over a 1/2 turn with no good, then leaned it out over 1/2 turn from yesterday with no diffrance.

I tried to add some fuel on the low end as no diff, but after about 3min of this chaseing my tail, my throttle servo fried Im glad it was on the ground....

The guy I got it from said it was running it great.. but now I wonder.

RE: Back Fire issues
 

Maybe you should go over your backplate repair. Take it off and put everything back together and try again.

Sometimes a small assembly error and drive us nuts.

RE: Back Fire issues
 

Thanks guys, I found a flying buddy who got one of these motors new, he is more of a collector of planes than a flyer so I have never seen him fly this motor yet, but he had the directions.

It states in his manual that my starting point for my needles should be at 1,1/4-1,1,5 on L needle and 1,3/4-2 on the high needle

So I check were I was and I was at like 2 1/2 on both needles so I was way off.

I only kept adding more fuel on the low needle becouse it was said the backfireing and poping could becouse it was lean, but maybe it was just to rich.

So I will try this, if not, Im going to check the timeing, ( Becouse it will be easy to do with out pulling the motor off this bird.

IF not pull the motor, wihc is a pain! to check the carb screen.

Thanks for all the pointers.

RE: Back Fire issues
 

It helps to know if the engine is truly backfiring or if its just misfiring. There is a difference.

Could you take a short video of the engine "backfiring" and post the link?

RE: Back Fire issues
 

You need to get someone to help you tune the engine that truly knows how to carefully listen to the engine and carefully adjust it to run correctly or to make a decision as to whether it is mixture or ignition?

All this talk of turns out of the needles tells me that you actually have little clue as to what you are doing in adjusting the carburetor?

I have more than 60 two stroke engines and could not tell you how many turns out the carb needles are on any of them. But they run correctly.

RE: Back Fire issues
 

60 ENGINES! Jim you need help.:D

RE: Back Fire issues
 

They are not all model engines. I have a lot of chainsaws

RE: Back Fire issues
 

Well I got about 10 gassers all DLE's except this ZDZ , BME50, and 2 ASP 1.80 4c I converted to gas for my ESM B25

and except for the ASP. All have been real easy to work with with only small adjustments needed, I don't clame to be an expert that's why I was asking for adadvice

I only richend the low end because I have never had a motor that pop and shut off before.

I only found out how many turns my needles were because I wanted to comparing them to the manual stock settings

anyways I put them at the stock settings had to lean the high end a little and now she is running like she shshould I even gave it 20mim to cool run it up with no issue. Then gave it 3 hours and still running great what I don't understand is the day I thought it was good and ran great was almost 3/4 of a turn out in both needles from we're it is now


thanks guys<br type="_moz" />

RE: Back Fire issues
 

The important thing is that it is running good.

I've had some that were touchy on the needles and would send out confusing signals.

There have been times that I had to touch up the needles on three or four outings before the tuning settled down for me.

But any time there is a big temperature change you will likely need to change the needles some.

A sudden real cold spell will make the engine suddenly lean and a summer like day in the winter will suddenly make the engine rich.

Enjoy.

RE: Back Fire issues
 

Well, I am not sure about his use of the word "backfire" either. I have rarely heard a gas two stroke engine actually backfire unless it has an ignition malfunction, though a four stroke engine will readily do so if it is too lean, especially upon acceleration.

However, part of the mystery with this particular case could be this; sometimes when a carb sits for a good while, the regulator diaphragm dries out. Sometimes not all the way dried out so that it is so stiff that it won't work, but enough that the diaphragm is stiffer than it should be. This can change carb settings and/or cause erratic running. Then sometimes once the diaphragm has been wet with fuel for a while, it limbers up and the necessary carb settings change again; usually back to more "normal" settings. I've seen this fairly often, though anytime I have a suspected carb problem I just pull it right off and completely rebuild it, including verifying all the passages will flow, etc. It doesn't take much time, nor cost much, and then you know it is "good to go".

AV8TOR

RE: Back Fire issues
 

+1