HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jun 13, 2012, 11:31 AM
Registered User
Estonia, Harju County, Tallinn
Joined Jun 2012
8 Posts
Question
Asp FS91AR with spark ignition

I converted my asp to spark ignition with rcexl and it is running great on glow fuel. To save money I want to run gasoline in it, however this idea led me to some questions.

1. Would it be possible to run gasoline in it with stock carb? If so, what kind of oil ratio should I use?
2. Would gas ruin my engine faster than glow fuel?
Georgseema is offline Find More Posts by Georgseema
Last edited by Georgseema; Jun 13, 2012 at 03:31 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 13, 2012, 12:39 PM
Dieselized User
gkamysz's Avatar
Chicagoland
Joined Feb 2000
7,387 Posts
You can try to run the stock carb. It may or may not work well. I converted an ASP FS91 for a friend and it didn't work so well on methanol fuel. He just went back to glow. I never looked it over to see what the issue was.

On gasoline you'll not have problems with rust in the crankcase. It will run hotter though. That engine has less cooling fin area than the OS FS-91 so pay attention to how hot it gets. I never tried the asp on gasoline. I would run 20:1 or 5% oil in gasoline, minimum.

Greg
gkamysz is offline Find More Posts by gkamysz
Reply With Quote
Old Jun 13, 2012, 01:31 PM
Registered User
Estonia, Harju County, Tallinn
Joined Jun 2012
8 Posts
OK. i dont know how long the conrod bushings will hold on when running gas. I think i will use Remote Needle ( this one: http://www.hobbyking.com/hobbyking/s...dProduct=12978) before the carburetor to reduce the fuel flow, so it will be easier to tune the engine. will it be good idea or just a waste of money?
Georgseema is offline Find More Posts by Georgseema
Reply With Quote
Old Jun 13, 2012, 01:31 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,177 Posts
Give it a try and see what happens.
Methanol is used at a much higher more rich mixture with air than gasoline is used at. Usually you can get the low speed needle and the high speed to work, but the mid range may be too rich. But some carbs have a more lean mid range and may work, more or less, acceptably. The other problem that occurs is the taper on the needle may make it very sensitive to adjust, but it depends on the carb and needle though.

Methanol is used at a fairly rich 8:1 ratio mixed with air, the ratio can vary a lot as one can add nitromethane to the mix too.
Gasoline is used at a much leaner 14:1 ratio and it doesn't allow for much variation in the ratio either. It pretty much has to stay at around 14:1.

The old time engines got away with using gasoline OK as they were a fixed speed non-throttle type of engine. so you simply adjusted the needle until the engine ran acceptably for you. Ganted you had spark ignition and timing that you could adjust, so you had some control over engine speed, but the engines didn't have a carburetor like we use today on RC engine.

Since you converted a 91 engine to spark ignition, you could use one of the smallest Walbro carbs on it, such as the carbs from a SV 17cc or a RCGF 15cc or a NGH 17cc engine, maybe even the DLE20 or other 20cc engine carbs would work too. You will have to make an adapter for the carb though.

As long as you run around a 20:1 oil to gasoline ratio and use a decent two stroke engine oil, you will be fine. Quite a few gasoline engines used bushed conrods on the engine and it wasn't a problem. A well broken in engine might be able to go with a 25:1 ratio for oil too.
earlwb is online now Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old Jun 13, 2012, 01:51 PM
Registered User
Estonia, Harju County, Tallinn
Joined Jun 2012
8 Posts
Thanks for the help so far, is there more tips that i should know.
I will buy rcgf 15cc carburetor form hk when it will be back in-stock , and make the adapter. I think that it will work the best. Walbro carb works on the crank-case pressure, can i use the pressure from muffler.
Georgseema is offline Find More Posts by Georgseema
Last edited by Georgseema; Jun 13, 2012 at 02:07 PM.
Reply With Quote
Old Jun 13, 2012, 01:56 PM
Dieselized User
gkamysz's Avatar
Chicagoland
Joined Feb 2000
7,387 Posts
I've found that the rod bearings seem to do OK. There is no need for another needle on the carb.

Idle and full throttle will tune just fine with the needles if the carb is good. The trouble is that the idle needle taper or the shape of the fuel jet slit (cateye) control the midrange and this can't be adjusted.

I used a Walbro WT-298 which has a 7.14mm venturi on an OS FS-91. This particular carb has no choke or primer bulb though.

Greg
gkamysz is offline Find More Posts by gkamysz
Reply With Quote
Old Jun 13, 2012, 02:17 PM
Registered User
Estonia, Harju County, Tallinn
Joined Jun 2012
8 Posts
Walbro WT-298 looks like the one one rcgf 15cc engine. Is walbro backwards compatible with methanol, in case if i don't get the engine run on gas?
I found that himodel sells the 15cc carb. Any place to get it cheaper (they must send to Estonia).
Georgseema is offline Find More Posts by Georgseema
Reply With Quote
Old Jun 13, 2012, 02:33 PM
Dieselized User
gkamysz's Avatar
Chicagoland
Joined Feb 2000
7,387 Posts
Walbro carbs will last a while with methanol, but the metering diaphragm fails rather quickly. Plan on replacing the diaphragm annually. I'm not sure where to buy them, I usually use Ebay.

Greg
gkamysz is offline Find More Posts by gkamysz
Reply With Quote
Old Jun 13, 2012, 02:39 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,177 Posts
Walbro does make a WT-499 carb that is setup to work with methanol. Probably for go kart engines or something.
The other Walbro carbs are for gasoline and not methanol useage.


earlwb is online now Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old Jun 13, 2012, 02:41 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,177 Posts
Try Just Engines in the UK, they sell the parts for the NGH engines and may have it. Plus they are a lot closer to you than HiModel is (being in China of course)
earlwb is online now Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old Jun 13, 2012, 02:55 PM
Registered User
Estonia, Harju County, Tallinn
Joined Jun 2012
8 Posts
I will wait when HK re-stocks the 15cc carb and buy it from there.
Anyways if the engine wont work with the walbro i can put the original carb back and run on my chemistry (motul micro 2T 15% + meth) the methanol cost here 0.4 euro per litre and oil (2L) costs 40~42 euro

Are there other 4stroke gas engines than saitos, asking because they are very pricy
Georgseema is offline Find More Posts by Georgseema
Last edited by Georgseema; Jun 13, 2012 at 03:22 PM.
Reply With Quote
Old Jun 13, 2012, 03:19 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,177 Posts
Yes there are some others but they are relatively more expensive though.
RotoMotor is one, Valach is another, Moki has some too, there is a German company making some giant scale engines that sound great, especially their 3 cylinder inline engine that is being release soon. But I forget their name at the moment.
earlwb is online now Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old Jun 13, 2012, 03:26 PM
Registered User
Estonia, Harju County, Tallinn
Joined Jun 2012
8 Posts
I hoped that there are some cheaper ones to , but thats okay when we can convert engines our selves witch i think is more fun than buying completed engine!
Georgseema is offline Find More Posts by Georgseema
Reply With Quote
Old Jun 13, 2012, 05:00 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,177 Posts
I actually have most of the conversion done for a 30cc four stroke weed trimmer engine. I only need to make the engine mount for it and setup the electronic ignition on it. I keep meaning to finish it, but something seems to get in the way, so it has been stalled for a while now.
earlwb is online now Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old Jun 13, 2012, 09:50 PM
Registered User
Reginald's Avatar
Belgium
Joined Aug 2004
3,776 Posts
Quote:
Originally Posted by Georgseema View Post
I converted my asp to spark ignition with rcexl and it is running great on glow fuel. To save money I want to run gasoline in it, however this idea led me to some questions.

1. Would it be possible to run gasoline in it with stock carb? If so, what kind of oil ratio should I use?
2. Would gas ruin my engine faster than glow fuel?
The mix proportions fuel/air are different in a glow versus gas engine
Reginald is online now Find More Posts by Reginald
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Off Site Siedel 7 cylinder Gasoline Spark Ignition 250CC Radial RC Airplane Engine icharus Aircraft - Fuel - Engines and Accessories (FS/W) 9 Apr 22, 2012 01:24 PM
Sold C&H Synchro-Spark ignition system needacheaphobby Aircraft - Fuel - Engines and Accessories (FS/W) 1 Apr 01, 2012 10:03 AM
Discussion Spark Ignition, but still Glow fuel.... any tricks to it? Brutus1967 Engines 8 Oct 18, 2011 01:43 PM
Help! Identitifying old spark ignition motors modlflr Engines 4 Sep 21, 2011 06:25 AM
Discussion Problems, problems, problems! 46 AX, FX and Magnum FS91 AR lehma Engines 20 Jun 17, 2010 06:01 PM