Gas engine tuning for newbies....

[mikeh]

I have an Evolution 58GX2 and I also have the midrange burble. Been playing with the needles and its gradually getting better. Here's the real question, when the plane is inverted why does the motor go rich? There is a nipple on the carb to run a vent line inside the fuse. Will this help even if there is a 3" hole in the firewall? The hole is there because the carb is sitting inside the motor box. I was under the understanding that the vent line is to help the motor get undisturbed air. Wouldn't the air still be disturbed because of the hole in the firewall?
Thanks
Mike

[stommerd27]

	Quote: Originally Posted by mikeh
	I have an Evolution 58GX2 and I also have the midrange burble. Been playing with the needles and its gradually getting better. Here's the real question, when the plane is inverted why does the motor go rich? There is a nipple on the carb to run a vent line inside the fuse. Will this help even if there is a 3" hole in the firewall? The hole is there because the carb is sitting inside the motor box. I was under the understanding that the vent line is to help the motor get undisturbed air. Wouldn't the air still be disturbed because of the hole in the firewall? Thanks Mike

My 116 was the same way until I followed this method to a T. Now it is awsome. Your 58 is half of my 116 so they should tune a lot alike. When you first start your engine it should have that hesitation and not want to transition until it is completely warmed up. If it transitions well right away she will burble in the midrange when she is warmed up.

[Slam]

	Quote: Originally Posted by RTK
	Hmm, they must have invented some new carb. I have never seen an engine where the high starts feeding around 3/4, most of the time at 3/4 throttle you are just about at max rpm unless you have a throttle curve.

The low jet on a Walbro carbs works the entire range, using a bigger version of the walbro in karting, we have raced on some circuits where to get the most out of the engine,the low jet was out 2 turns and the high jet just cracked open and we still hit 16,800rpm at the end of the straight. Although i haven't tried this on my planes engines as they work well by tuning in the methods described here

Duncan

[rcmergler]

	Quote: Originally Posted by mikeh
	I have an Evolution 58GX2 and I also have the midrange burble. Been playing with the needles and its gradually getting better. Here's the real question, when the plane is inverted why does the motor go rich? There is a nipple on the carb to run a vent line inside the fuse. Will this help even if there is a 3" hole in the firewall? The hole is there because the carb is sitting inside the motor box. I was under the understanding that the vent line is to help the motor get undisturbed air. Wouldn't the air still be disturbed because of the hole in the firewall? Thanks Mike

The fuse trick use to work on better built aircraft, but with the new arf's out there the fuse looks like swiss chesse due to the lightening holes. a well built fuse like a carden or dalton or there about that little trick will still work, but for the newer fuses something else has to be done. Quique showed me a cool trick where you run the line from the diaphram hole to the vary opening of the carb.... pritty much that is what 3w is doing with their carb stack they are puting on their engines now... and to my knowledge< which is not much> 3w is the only company doing it so far

[rcmergler]

	Quote: Originally Posted by Slam
	The low jet on a Walbro carbs works the entire range, using a bigger version of the walbro in karting, we have raced on some circuits where to get the most out of the engine,the low jet was out 2 turns and the high jet just cracked open and we still hit 16,800rpm at the end of the straight. Although i haven't tried this on my planes engines as they work well by tuning in the methods described here Duncan

you are correct about the low jet, however on the walbros on these gas engines the low jet does not provide enough fuel to the engine above say around 3/4 throttle, so that is were the high jet comes into play. if the high jet is not open enough then the high rpm range will be way too lean and die out. that is at least the answer i got from da

what class of karts do/did you race in?

[rcmergler]

	Quote: Originally Posted by mikeh
	I have an Evolution 58GX2 and I also have the midrange burble. Been playing with the needles and its gradually getting better. Here's the real question, when the plane is inverted why does the motor go rich? There is a nipple on the carb to run a vent line inside the fuse. Will this help even if there is a 3" hole in the firewall? The hole is there because the carb is sitting inside the motor box. I was under the understanding that the vent line is to help the motor get undisturbed air. Wouldn't the air still be disturbed because of the hole in the firewall? Thanks Mike

also i dont know what type of airframe your using but some cowl
arrangements do it more than others. if you build some baffling it will help with the airflow and keep the engine cooler, also has to do with your hot air exit on the bottom of your cowl. for one dont make it bigger than it needs to be. there are many rules to follow for your air exit, but i have always used the same size or slightly bigger then the air intake. it all changes if you run cans or a pipe though

[rcmergler]

	Quote: Originally Posted by RTK
	Hmm, they must have invented some new carb. I have never seen an engine where the high starts feeding around 3/4, most of the time at 3/4 throttle you are just about at max rpm unless you have a throttle curve.

That is what i thought too, but when da told me this, i tested it out on my da50. with ln at factory setting and hn all the way closed the engine would run until you reached almost peak rpm, then it would just die. i then did the same thing on my 150 with the same results

[Ed Hornbuckle]

	Quote: Originally Posted by Slam
	Hi All I've got a new DL50 that i'm running in at the minute, i've been following the tuning methods described, but it has a misfire at WOT every 5 seconds or so, do i need to lean it out a bit more? cheers Duncan

Both of my DL-50 had the same problem, until I got them tuned. The way I found to tune that works on the DL's, is to set the needles to factory. Warm up the engine and lean the low end until it hesitates when you quickly advance the throttle. Richen up the low end a little. With a tach, lean the high to when it just gets to the highest rpm. Fly the plane and you'll probably notice that it burbles on the low / mid rpm and misses sometimes on the high. Land the plane and turn the high end needle only in a 1/8 turn. (If you try to use the low end needle at this time to tune out the low end burble, it does not work.) Fly the plane again, keep leaning the high needle until both the low end burble and high end miss goes away. When you get it right, the motor will really rip. Check your head temp after each adjustment to make sure you don't over lean the high end.

[mikeh]

	Quote: Originally Posted by rcmergler
	The fuse trick use to work on better built aircraft, but with the new arf's out there the fuse looks like swiss chesse due to the lightening holes. a well built fuse like a carden or dalton or there about that little trick will still work, but for the newer fuses something else has to be done. Quique showed me a cool trick where you run the line from the diaphram hole to the vary opening of the carb.... pritty much that is what 3w is doing with their carb stack they are puting on their engines now... and to my knowledge< which is not much> 3w is the only company doing it so far

I will give this trick a try. I have nothing to loose. Thanks for the tip.
mikeh

[Slam]

Hi rcmergler

I used to race in a British formula called TKM a 100cc direct drive class and now race in Easykart 125cc direct drive with 28bhp. They are great fun, getting near 100 mph on some circuits.

Cheers for that Ed i will try it this weekend. Last night i made some guides in the cowl so it's possible to adjust the carb with the cowl on. i'll remove them when it's set up and cover the 2 small holes with a bit of vinyl.

Cheers

Duncan

[rcmergler]

	Quote: Originally Posted by mikeh
	I will give this trick a try. I have nothing to loose. Thanks for the tip. mikeh

Let me know how it wooks out for you... i have done the carb trick on both of my 50 and 150 and so far it wooks great.

[mogley]

Hello, I'm running a g62 with a toni clark muffler, stock ignition. I finally got it to run. The high end ist at 3/4 and low end is at 1 1/4 turns out. When adding thorttle, there is alot of hesitation. I get no burbble anywhere like I get on my DA 50 w/slimline. The g62 is very quiet with this setup. While choking, fuel comes out of the carb (probaly out of a gasket). This motor is brand new (although in box for 5 years.)

Is it normal for the high end to be only open 3/4 of a turn.

thanks for any help