1990 Quadrunner LT-4WD won't idle compatible CDI

[BenderIsGreat]

So my old quadrunner gave up on me a couple years back.  Would run for 20 minutes, and then would die when you let off throttle and wouldn't start again till it was cold.  Should also be noted that at that point, I was having to crank up the idle adjustment screw to keep it running.  So at that time, I had given the carb a partial tear down, looked clean, tinkered around trying to narrow down what was wrong, and eventually got a compression testing tool and diagnosed bad compression, significantly under spec, but still over 100psi.  So I took it to a mechanic who said the cylinder was bad and to get another engine, wasn't interested in me trying to find another cylinder for him.  So I took it back and decided to take the engine apart myself after watching a bunch of youtube videos as reference.  I found the cylinder, piston and rings were all fine, but the valves where fouled and obviously causing my compression issue, so I cleaned and lapped them and I was up to 150psi.  Now the thing seemed to run a lot better, but still won't idle.  So I took the carb apart again, found the o-ring for the mixture valve was disintegrated, and one of the jets was stuck and couldn't be removed, so I just ordered a new carb from amazon.  Put it on, and now I was able to get it to idle like normal (without cranking the idle screw) but only for short times, and then I'd give it throttle and it would bog.  So I went at the electronics.  Couldn't get an ohm reading through the spark plug cap, so I replaced it, coil seemed ok but replaced it anyways because it was cheap, still can't get it to idle and run right.  So I'm thinking it's the CDI.  Now, I found a few search results for the correct CDI (as per suzuki parts house), but they were all expensive, like $200+.  But there was another one, slightly different part number (only the last two digits where incremented by 10) and it looks exactly the same, same connectors, which I determined was meant for the Kingquad 300 and it was only $43.  So I posted on another forum asking if anyone could confirm if they were compatible, and a guy said he has both a quadrunner 250 and a kingquad 300 and he interchanges their electronics for testing and they work fine.  So I ordered one, and am waiting for it now to see if it solves my problems and finally gets this old girl usable again.

 

If anyone has any thoughts or insights, feel free to pass them along

[Mech]

The valve clearances have a bit of a habit of getting out of spec after their first adjustment after a stripdown. I'd recheck them. Sparkplug gap  can effect idle too.

Then the symptoms, if it's only the idle that's playing up, and it runs ok otherwise,   sound like fuel problems. I'd be trying to adjust the idle mixture, which will either cure the bad idle, or reveal a blocked/faulty idle system. Probably requiring a clean and inspection.

I'd very much doubt the cdi is the problem.

[BenderIsGreat]

Still waiting on my CDI, but I will definitely recheck my valve clearances, thank you.  The carb is brand new, I did mess with the mixture though before discovering the spark plug cap was bad, and have been trying to get that right since replacing the cap, but I can't even get a starting point to work from, as in I have to hold some throttle to keep it running, so I'm struggling to adjust to mixture at the same time.  It also doesn't run right with throttle, it misses I think so the power is jittery.  The fuel pump is also new, but even if I prime it by blowing in the gas tank breather tube, it doesn't help.  I just hope it's not a charging issue.

[Mech]

Speed the idle up temporarily, either with the screw or on the cable, then adjust the mixture, in for leaner, out for richer, till it idles fast, then slow it down and readjust, cycle around doing those two, adjust,slow,adjust.slow, till it idles slow and even..

Replacement carbies are hardly ever really set correctly for a bike.. They often need a lot of retuning.. If you get the idle right, then you can ride it and test the performance and let us know how it is and we can suggest what to adjust next..if need be.

[JustRandy]

I've never seen a bad CDI, but problems when hot do indicate electrical issues.  Check the regulator.  All those quads have bad ones or will eventually.  Just pop it off and look at the back.  Another way to test it is to turn the lights on and see if it runs better.  Put a big electrical load on it to lower the voltage.  The problem is the voltage runs up to 16-18 volts and causes the CDI not to function.  Turning the lights on reduces the voltage and restores CDI functionality.

If it is the regulator, don't buy another stock one.  Contact Ricks Electronics and order something bigger.

That engine doesn't care about compression leaks because the stroke is longer than the bore.  The only symptom it would produce is hard starting when cold.

I have the kingquad 300 and have put the 250 CDI on because it has a higher rev limit.

[BenderIsGreat]

Thanks Randy.  The CDI I had already ordered arrived, and it seemed to help, and then didn't....where is the voltage regulator on these bikes?

[JustRandy]

1 hour ago, BenderIsGreat said:

Thanks Randy.  The CDI I had already ordered arrived, and it seemed to help, and then didn't....where is the voltage regulator on these bikes?

It's on the front to the right of the steering stem bearing (would be passenger side if it's a car).  It's hard to get to with the plastic in the way so I cut the plastic and either used zip ties to put the "door" back on or else left it off.   It don't look too bad, whatever I did.  I'm pretty sure your regulator is bad because they all are.

Ricks is the way to go.  https://ricksmotorsportelectrics.com/   Call them and tell them you want something that can handle lots of amps.

[Mech]

The regulators cause a problem when you rev the engine. I've never seen one cause a problem at idle.. Easy to check though.. Put a voltage gauge on the battery and see it's charging, and regulating.

[JustRandy]

Yep the problem would get worse as revs increase.  The way to check is to see if voltage rises beyond 14.4v with rpms.  Once voltage exceeds roughly 16-18 then the CDI stops working correctly.  A quick fix is to turn the lights on which reduces the voltage.  There are threads all over the net complaining that the engine only runs with lights on.  It's such a common problem that I recommend every owner of these 4x4s swap the regulator first thing.

[JustRandy]

Usually the epoxy on the back is cracked or burned.  Here are two examples:

The one in the bag is the one from Ricks.  They said it is for a Triumph and can handle 50 amps.

[BenderIsGreat]

Awesome, thanks guys

[BenderIsGreat]

So, I'm sure this will come as no surprise to Randy, but he was correct.  I got a new voltage regulator and replaced it this afternoon, and it seems to have resolved all the issues.  Thanks again

 

 

[JustRandy]

Thanks but not much credit to me since that is a very common problem.  There should be a sticky about it because every 250 and 300 4x4 suzuki will get the problem eventually.  Look how much trouble could have been avoided.

Congrats on a nice sounding machine!  Try to keep it cool and change the oil often so it doesn't start smoking.  I'd put a fan on it.  Suzuki used to offer one.

https://www.rockymountainatvmc.com/oem-schematic/2

[Mech]

I don't think the regulators are as bad as Randy seems to think.

I'd check the regulator, when you fit it, has a good earth, and that there are no bad connections between the regulator and the battery.

[JustRandy]

23 minutes ago, Mech said:

I don't think the regulators are as bad as Randy seems to think.

Maybe because you haven't seen all the threads about bad regulators over the last decade. 

A quick search:

https://www.suzukiatvforums.com/threads/1991-quad-king-250-runs-well-when-headlight-are-on.8878/

https://atvconnection.com/forums/suzuki/378708-motor-sputters-like-out-gas-then-you-turn-lights-runs-fine.html

Me answering same question from 10 years ago: https://atvconnection.com/forums/suzuki/347075-250-suzki-will-not-run-without-lights.html

Of all the atvs I've ever had, I've only had to change 2 regulators and both were these 4x4s.

The evidence is overwhelming.

[Mech]

I think the regulators fail for a reason Randy.. not because they are inherently faulty.

[JustRandy]

The inherent flaw is they weren't designed to be this old... and that was true 10 years ago.  Or maybe the regulator isn't sufficient for the size of the alternator.

[Mech]

And so you don't think it's a good idea to check for faults that may have caused the failure ?

[JustRandy]

1 hour ago, Mech said:

And so you don't think it's a good idea to check for faults that may have caused the failure ?

The only faults are those within the regulator.  Considering what I've noticed the alternator to be capable of in terms of winching and recharging the battery over the last decade it's my impression that the regulator is too small which is why I bought the biggest replacement I could find.  Over time the oem couldn't handle the amps anymore and I don't consider a strong alternator to be a fault.

I'd recommend anyone considering even a casual restoration of these quads to go ahead and replace the regulator just like I would recommend replacing dry-rotted tires.  Dry-rotted tires may work fine for a while but eventually they will let you down.

[Mech]

Ha.. so there's never any fault except in the regulator..

And so we shouldn't bother checking.

Brilliant !

 

[JustRandy]

What sort of fault did you have in mind?  As far as I know the only fault possible outside of the regulator is too many amps, which isn't a fault.

[Mech]

The faults you don't know are possible..

 

[JustRandy]

Looks like you don't know of any either.

The regulator simply dumps current to ground in order to cap the voltage at 14.4.  So the only possible fault, outside of the regulator itself, is having more amps than the regulator can handle.  Having more amps than a regulator can handle is a good thing and not a fault, so the only fault would be the poorly designed or ill-suited regulator.  Fixing the fault requires upgrading the regulator to match the potential of the alternator.

I don't know why you have trouble believing crappy parts exist.  Industries aren't capable of making bad regulators, carburetors, pharmaceuticals?  That's some remarkable faith you have in corporations.

[Mech]

Read a manual Randy. It's not just my recommendation that the circuits should be checked for faults. It's what mechanics and auto electricians do.. It's what the bike manufacturers say to do. It's the prudent thing to do.

[JustRandy]

Name something that could cause a regulator to fail.  Until you do that no one has any idea what to check for.

Weak batteries are often the cause of alternator failures in automobiles, but if a weak battery were drawing current in this case then there wouldn't have been a high-voltage condition that caused the CDI not to function since the battery would be functioning as a current sink the same as turning the headlights on or having a properly functioning regulator.  And a weak battery would have been evident long ago.

But nonetheless my replacement regulator could happily handle anything my alternator could muster so it wouldn't matter if batteries are weak or not.  Therefore there is nothing to check for.  Simply upgrade the regulator and done.