Go Back  RCU Forums > Glow Engines, Gas Engines, Fuel & Mfg Support Forums > Engine Conversions
Reload this Page >

Ryobi 31cc won't start. Mystery !! Please help

Notices
Engine Conversions Discuss all aspects of engine conversions in this forum

Ryobi 31cc won't start. Mystery !! Please help

Old 03-25-2020, 11:50 AM
  #1  
alexander.fridlund
Junior Member
Thread Starter
 
Join Date: Mar 2020
Posts: 2
Likes: 0
Received 0 Likes on 0 Posts
Default Ryobi 31cc won't start. Mystery !! Please help

Hi,

3 years ago me and by brother converted a ryobi 31cc weed eater engine for his homebuilt foamcub.
Before building the plane we fired up the engine to se if it was okey.
It ran perfectly ! no problem to handstart. So we began building the plane.
Now to the strange part, when we installed the engine to the plane and got it ready for the first startup.. It wouldn't start !
We tried everything but couldn't get it to run, after many days of tries we gave up on both the plane and the engine and quit the project.

Now 3 years later i found the plane in Dad,s garage and decided to give the engine a new chance.

Things i have done so far without any improvement or sign of life from the engine.
* New cylinder
* New carburator (tried it on another engine and it works perfectly, even the original works on other engines)
* New ignition coil (spark has always been good with both new and old)
* New flywheel
* New gaskets
* New sparkplugs
* Compression test (140 psi)
* Pressure test of the crank case ( 7 psi with intake and exhaust plugged, No leaks)
* Checked if the ignition timing has changed (crankshaft rotated on axel because of hydrolock etc..) Key in flywheel is ok.
* Replaced the reed valve and experimented with the gap between the reed and backplate.
* Different positions of the fueltank.

Please help me ! This is starting to get really frustrating but i won't give up intill i find the problem.
Im using a cordless drill to spin the prop. My bet is on the ignition since it barely puffs when injecting fuel into the carb.
And as i mentioned above i know the carb is fine.

Please help me sleep at night
// Alexander
Old 03-26-2020, 07:32 AM
  #2  
larry@coyotenet
My Feedback: (21)
 
Join Date: Feb 2003
Location: pueblo, CO
Posts: 656
Likes: 0
Received 0 Likes on 0 Posts
Default

Does your drill spin it fast enough? Magnetos need a minimum speed to generate the spark. Pull the plug and put it in the boot and ground it against the case somewhere and spin the motor, you should see a pretty fat spark at the plug. If not, check plug gap, check mag gap ( I use a business card to set the flywheel to mag gap), make sure mag is not grounded somewhere, make sure the timing is right, spark should be around 30 degrees before top dead center. Put some gas down the plug hole and see if it will run, if not it is usually something in the ignition, the old rule of thumb is that you need three things to run, fuel, air and spark. If it tries to run it is probably something like the pressure tap hole is not lined up right with a gasket so the carb pump won't work. It is always something small like gasket sealer in the pressure tap hole or some other dumb thing.
Larry
Old 03-26-2020, 07:46 AM
  #3  
alexander.fridlund
Junior Member
Thread Starter
 
Join Date: Mar 2020
Posts: 2
Likes: 0
Received 0 Likes on 0 Posts
Default

Thank you for your answer.
the drill is fast, it had no problems starting the engine when it was working. The spark is really good, even when flicking the prop by hand.
the timing is also correct.

it must be a ignition problem since it won't even start or puff when injecting fuel into the cylinder.
but i have tried 3 different coils and flywheels which all gives a good strong spark.

I have practically replaced every part of the engine with no sign of life..
Old 03-26-2020, 11:49 AM
  #4  
larry@coyotenet
My Feedback: (21)
 
Join Date: Feb 2003
Location: pueblo, CO
Posts: 656
Likes: 0
Received 0 Likes on 0 Posts
Default

Well if you have the three things needed to run I do not see the ignition being the problem since you have a good spark at the right time. How old is the fuel?
Leaving ignition out it must be one of the other two. Your description of it "puffing instead of popping is interesting. If it were a motor with a liner I would say the liner is in backwards but a Ryobi doesn't have a liner so that isn't it. Can you post a picture of the engine? I kinda hate to mention it but a friend of mine lost a pylon race because he could not get his engine started in 3 of the 4 heats and the problem was his starter was reversed!
Larry

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.