Quantcast
Jump to content

  • Do you own an ATV, UTV or SxS? Join our Community Forum!

    QUADCRAZY ATV Community and Forum are FREE to join! We keep our ATV, UTV, and SxS forums clean and user friendly. All first time posters in our forums will have to wait to have their content reviewed and approved. Once your first ten posts are approved, you will no longer need to go through a forum post approval process. To bypass the approval process with immediate access and a NO ADS experience in our ATV, SxS, and UTV forums, consider subsribing to a Premium Membership

Project Quad - Will not start


Recommended Posts

Hi All,

I hope this is the right area to post looking for help.

I've got an old Yamaha Big Bear that I'm trying to get running as a bit of a project between jobs, but I've run into a problem that my novice mechanical skills cannot get around.

  • Compression test on the engine looks good.
  • I am getting spark from the lead when I press the start button. (and the fire suggests there's spark from the plug)
  • Various bits and pieces are spinning (behind recoil starter for example).

So things are not looking bad, but while I don't have the new carby in yet, I wanted to test with a little spray of Engine Start (like I've seen on all the Youtubes :p) and instead of sucking the spray in the intake manifold and burbling to life, it seems to backfire (explosively) and catch on fire.

I know you can do damage if you go crazy with the Engine start, but this happens with even a tiny spray.

What should I look for that might be the cause of this, anyone?

 

Thanks so much

 

Link to comment
Share on other sites

If you were to assume that timing could be set when the piston is at the top, it is possible to set timing on the exhaust stroke and not true TDC which is the compression stroke. This, it's 180 out. I've done that years ago. Both valves have to be closed and the piston has to be at the top to be at true TDC. 

Link to comment
Share on other sites

Not all spark systems are wasted spark. Some only fire every second rotation.

Some cdi systems that run off the crank, that is get their low voltage off the stator, need more than one rotation before they will fire. They have to see several low voltage pulses before the trigger coil will fire them. The cam might need turning 180 degrees so the valves are closed on that second rotation of the crank.

MarkinAr sounds like he's familiar with these yamahas..  I'm not, but I'd check what he's suggesting.

Link to comment
Share on other sites

I don’t like starting fluid to diagnose or make conclusions about an engine. Get the new carb or clean out the one you got and then see what’s happening. I’d only run it with the air filter on, if possible. When cranking it over, feel for air blowing out the exhaust to be sure there’s no mouse nest in the muffler. Also, when spraying the starting fluid, open the throttle wide open to get the mist past the plunger/butter fly valve. 

Link to comment
Share on other sites

First I say "most of these types of atv's are wasted spark", and then Mech comes back with " not all spark systems are wasted spark. Weird.

Of course not all spark systems are wasted spark, but I am guessing this one is. If the atv only has a pickup coil on the crank then how would it know what stroke it was on?

Link to comment
Share on other sites

You make a good point there about opening the throttle wide open to lift the slide Cookie. If it's right down the ether isn't going to get in there.

And I agree, starting fluid isn't a good test really. It's full of oil or kero or something and can foul the plug. A teaspoon of fuel down the sparkplug hole is better.

Stale fuel can also foul sparkplugs. Have you got fresh fuel CJ ?

Link to comment
Share on other sites

"Of course not all spark systems are wasted spark, but I am guessing this one is. If the atv only has a pickup coil on the crank then how would it know what stroke it was on? "..

Don't guess, be sure.

If you  want to know how the electronics involved work read up about "voltage doubler", and digital logic "flip-flop".

The stator sends out pulses of alternating power, they get "stacked" to charge a capacitor to a higher voltage, then the trigger coil triggers a discharge of the charged up capacitor. On a two stroke they fire every revolution, and on some four strokes that's fine too and they do run a wasted spark. Some engines though, because of a combination of valve overlap and ignition advance, don't like that, so they count the low voltage pulses as they charge the capacitor, and don't  let the trigger coil do it's thing till more than one full revolution has happened after the last firing, then it triggers at the next trigger signal.

Your backfiring with the engine start spray is likely because of what Cookie was saying..

 

Edited by Mech
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Similar Forum Topics

    • By HSTAR
      Hey I have a 1997 big bear 350 4x4
      I replaced the shifter shaft and the shift arm linkage and the rod when I installed them all I was unaware that you had to line the dot on the shifter shaft with the gap on the linkage arm gap put it all back  together and rode it I can't get it to shift in the right gears  I can move the shift cam by hand and goes in different gears but with the shifter shaft in it riding I can't put it in R or N 
      Anyone know how to line up the shifter shaft and the shift cam s
       
    • By McG75
      Hello I’m new here and was wondering is anyone knew of good replacement part numbers for front struts and rear shocks for this atv? I think I’ve found a new rear shock, that looks like the original but there is no dimensions or anything and was wondering if there are any afterMarket new front struts available. I know it’s a long shot but any help would be appreciated. 
    • By kiriyaaoi
      Hello everyone, I just picked up an 02 LT-F250F the other day and have been in the process of tearing it down to fix some stuff- one of which was the cylinder base gasket leaking like a sieve. Well, I know why that is now, and I also discovered that someone had been in there before. I didn't take pictures, but it looks like it was probably run low on oil at some point, the cam journals and the "bearings" (for lack of a better term) in the head and the valve cover are totally wiped out, very deep grooves.  From what I know it's very difficult to repair aluminum in this way, so I'm trying to figure out where to go next.
       
      1. Have someone grind down the head and valve cover and fit actual bearings in since the aluminum is screwed, and have the cam ground down to match.  I have no idea what this would cost.
      2. Buy a replacement head+cam+valve cover.
       
      #1 I was hoping someone might have some advice on, but #2 seems like it'll (probably) be the more cost effective option.  However I'm running into some difficulty, it seems like the 2001 and 2002 models specifically use a different head part number,  11100-19B10, instead of  11100-19B01 like for all earlier models.  What exactly is the difference between them? There are obviously far more of the earlier heads because it ran for over 10 years.  Are they actually interchangeable? I've also noticed there are heads from the LT250EF that has 4 valve heads but also otherwise look identical.  Would those work as well possibly?  I'd like to not have to drop $500 on machine work or new heads on a $1300 quad that I'm already putting a bunch of new parts on.  Oh, and it has a new piston and the cylinder itself looks pretty good too, as I said someone was in here before me.
       
      Any help or advice would be greatly appreciated. I'll post pics of the carnage tomorrow.
         
       
    • By Suzukiquad
      If you had to choose one mod that you couldn't live without, or had to recommend one what would it be? 
    • By Drillbit
      Hey all,
      I need some input on a problem I'm having with my Kodiak 400 that keeps fouling plugs. First off, I've done a lot of work to this thing, most of it all in good fun. Brake work, cv joints, u joints, carb kit, checked valve lash, compression good, changed all fluids, etc... My problem is it keeps fouling plugs very quickly. I can put a new (manual recommended plug) in and it starts right up, runs great, idles great, picks up good. Doesn't stutter at all. I ride it for 1/2 a mile, it cuts off and won't start back up. I let it sit overnight thinking maybe it got to hot. Try to start it the next day, nothing. Put a new plug in, fires right up, runs great for another 1/2 mile or so, dead. The plugs come out and look carbon fouled with dry black soot on them. I don't know if this is a fuel/air mixture problem or a ignition problem. A couple of things that I noticed is I never need to pull the choke out to start it. Also, when it starts it automatically idles high like an automatic choke would do, then it comes back down to a good idle. Also I noticed that the air/fuel mixture needle valve screw does nothing when I adjust it in or out. I can screw it all the way closed and the motor still runs and idles good. Any advice would be greatly appreciated. I'm almost leaning to a ignition breaking down the plugs??
      Thanks! 
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...