khodges

My Feedback: (1)

I've had my Fuji BT-32EI running for 5 tanks (16 oz each) and still can't get it to run smooth at high rpm, it wants to get lean and cut out and miss. If I richen it enough to get it to run smoothly, it's too rich and won't make more than about 4500 rpm. Bottom end doesn't seem to be a problem, it will start cold after 3 flips with the choke and 2 after opening the choke. Once warmed up, it will start 1st or 2nd flip every time, and idle smoothly at 2100 rpm, and transition well until about 1/2 throttle, when the missing starts.

Initially, I started out with Amsoil Sabre at 32:1, as the manual said not to go with 50:1 unless using Fuji oil. Dang thing would hardly even run at that rich a mix ratio, so I went with 50:1 on the 3rd tank, and it ran much better. I even had it going smooth enough on the 5th tank that I decided to fly it, was getting 7150 rpm with a 18-6 MA Classic. Once airborne, after 1/2 lap of the field, it started the same missing, cutting out, so I quickly landed. Ignition is okay, I believe, because for the time it was running very well, it was flawlwss. The battery has plenty of juice, fuel feed is clear with no large bubbles in the line. Spark plug is clean, and looks on the lean side, with a gray insulator and no carbon or oil buildup, gap is correct, but it really doesn't have enough run time on it to change the looks of the plug.

Just a slight tweak of the needle radically changes the mixture, less than an 1/8 turn, and it's about 1-3/4 to 2 turns out right now. I really think the low end is very close, because of how well it idles and transitions without sagging or blubbering. The low needle is about 1-3/4 turns out. Granted, it's running much, much better than when I first started it, reckon it just needs more run time to get smoothed out. I feel like leaning out the oil mix a bit more might also help, but want to make sure i get adequate lubrication during the first couple of gallons until the ring is well seated and bearings run in, etc. Then I'll probably go to at least 75:1, maybe even 100:1. Fuji says to go to 100:1 with their oil after a gallon, even 150:1 if well cooled.

Advice, suggestions, ideas?........insults?

bubbagates

My Feedback: (32)

One thing I noticed in your description is you mention no large bubbles. Is there any bubbles at all. Gas engines do not like air at all and you are describing a lean condition possibly due to an air leak on the high end or possibly the fine mesh screen in the carb is clogged. Also, what size fuel line. You could be restricting flow with too small of line

It's not uncommon for 1/8th or smaller turns to make a change. Every 3W engine I have ever tuned needed 1/16th urns when you were close

hauckf

(Deleted)

hauckf

I had a similar problem with my Fuji 32 EI. On my engine, the problem was the carb mounting screws. You can read all about it here, [link]http://www.rcuniverse.com/forum/m_6499642/tm.htm[/link], but in a nutshell, if the screws are too long they bottom out on the cylinder casting and air leaks by the carb and spacer gaskets.

khodges

My Feedback: (1)

Thanks for the ideas, guys. The fuel line is Tygon and is medium size, same stuff I use on my US-41 with no problem. The clunk line is neoprene, same inside diameter as the tygon. I can visualize about three inches of the fuel line between the firewall and carb nipple, and can see no bubbles at all while the engine is running. This is in bright sunlight, and I'm as close to the fuel line as the spinning prop will let me get without taking an ear off.

hauckf--I remember seeing this thread, and I looked at my carb screws; sure enough, they are seated against the cylinder head. The carb feels tight, no movement relative to the cylinder, but that doesn't mean it can't get enough of an air leak to affect higher rpm. The engine is rock solid from idle to almost half throttle, and has improved , however slightly, each time I've run it. But I'm going to pull the carb, shorten the screws by about 1/8" and while I'm at it, pull the carb screen and check it out. Maybe it's got some mfg. gunk in it, I've been very meticulous with my gas. I have a filter clunk in the tank, and also a filter clunk in the gas can I fill from. Won't get a chance to run it again until T'giving weekend, but we shall see what we shall see. I'll also use a bit of gasket sealer when I reattach the carb. This thing has about got my goat; I didn't have this much problem tuning 4-cyl racebike engines.

hauckf

My carb was tight too, but when the screws bottom out they act like jack screws and pull the spacer away from the cylinder head. Make sure your spacer is flat and not cracked. Another way to solve the screw-too-long problem is to add washers; that's what I did.