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JBA Engines

PostPosted: Wed Mar 14, 2012 1:54 am
by pete Stanford
I just bought a JBA 120AR 2 stroke engine. Reviews are good to excellent (for the price). Has anyone out there used these before? I've also tried everywhere to get some tech info on them eg: are they ringed or ABC or what? Any thoughts most welcomed.

Re: JBA Engines

PostPosted: Wed Mar 14, 2012 5:26 am
by RCModelReviews
I hope you got a good one because my own experiences (helping others) with the JBA engines is not good.

Getting them to run consistently is a very difficult task and (like so many cheap Chinese engines) they tend to load-up badly in the mid range, at least the .46-.56 sized ones do and that makes the transition awful.

The carby they're using is unchanged since it was first used on the TigerShark engines -- which were even worse than JBA.

I hope you have good luck with yours -- keep us informed.

Personally, I don't think I'd buy a 120-sized glow engine these days, the DLE20 is just so much better and far, far cheaper to run.

Re: JBA Engines

PostPosted: Thu Mar 15, 2012 3:36 am
by pete Stanford
G'day Bruce,

Geez I hope I get a good one too. Are they on a par with ASP? You may recall I spoke to you (e-mail) about my problems with the ASP 61 and how my experiences differed dramatically from your review of the ASP 52. I am now currently running a ASP 91 which true to form was good at idle, great at full noise but bloody horrible in the mid range. Then a club mate suggested not using caster in my fuel. Its now just 75% methanol, 5% nitro and 20% Klotts oil. Now the 91 runs beautifully at all throttle settings. Can it be that some of the other Chinese engines have similar carby issues? What are your thoughts?

Also, having read your article about oils, should I try reducing the Klotts to say 12 - 15%? If I do, does the nitro stay the same and just increase the methanol?

Cheers and keep up the great work. Love this site, and yes I have donated (where's my prize?)

Pete

Re: JBA Engines

PostPosted: Thu Mar 15, 2012 7:29 am
by RCModelReviews
Kotz is a very mediocre oil so I wouldn't run it at less than 17% -- especially the Techniplate (which is straight synthetic).

We run AeroSave/Aerosynth here at 12% but that's a much better oil.

There are two reasons why many of the new generation Chinese engines run so poorly in the mid-range.

1. the carbies are crap. Replace the Chinese carby with an OS one and the engines often run much better. Unfortunately, an OS carby is the same price as a Chinese engine so it's not really economical to do that.

2. there is a tendancy to overbore engines so as to get maximum displacement from smaller packages. That's why engines that used to be .40-sized are now sporting capacities of .56 or more and engines that were .60-sized are regularly overbored to .90 size. When you overbore an engine like this you end up making the transfer ports much shallower and that produces choking during the transfer process. In effect, all the tiny fuel droplets coming from the carby are squashed through such a narrow path that they bang together and become larger droplets. Large droplets don't burn nearly as well as small ones (due to reduced surface-area to volume ratios) and so the engines appear to run rich. You can adjust for this at the top end and at the bottom end with the high and low needles -- but in the mid-range there is no adjustment so the engine appears to run rich -- mainly because the big droplets cool the plug more than the little ones.

It's a complex bit of gasflow really but the general result is that most overbored engines will have an inferior transition and mid-range. The JBA 120 may have deep enough transfer ports to avoid this (since it's probably not an overbored crankcase) so then you only have the issue of the carby.

The reason that some Chinese engines run better than others that are the same make/size is down to quality control and manufacturing processes.

In a good factory that produces quality product, the tooling is regularly changed -- when you're making an engine to a price, the tooling is often only changed if it breaks or the parts will no longer go together without using a sledgehammer. That's why, with only a few exceptions, you usually get what you pay for with RC engines and cheapest usually means you're playing lotto.

Re: JBA Engines

PostPosted: Thu Mar 15, 2012 8:16 pm
by quarry44
I once had a "Tigershark"engine,a very early Chinese make, that had a similar problem.I think it was a .75.I put a reducing sleeve over the carb inlet,and it ran much better.Not as much power as before,but better transition.IIRC I reduced the inlet to 8 or 9 mm size.YMMV.

Re: JBA Engines

PostPosted: Mon Jun 11, 2012 9:10 pm
by FlyingTiger
elizasteave wrote:I have purchased JBA engine before six months. It's a wonderful engine and JBA applications are not inexpensive, they are just cost that way. JBA has done an excellent job of generating a excellent engine. JBA engine is common of two-stroke nitros. It has a high-speed hook modification, a low-speed modification and a reduce quit modification.



Good Lord, this is bad. But it is a great example of artificial low intelligence. Bruce, you may need to install some kind of confirmation scheme to insure a human is on the other end before they can post drivel such as this.