Hello all,
I am trying to get a 2004 Bombardier DS50 running for my grandson's birthday, and am having a terrible time... I'm fairly new to 2-strokes, have NEVER dealt w/oil injection, and am baffled. The quad is at least third-hand, not in great shape, but I had it almost running a few weekends ago and now not a peep. New plug, ignition coil, fuel lines, carb w/choke and starter. The weekend I swapped the carb I had it the closest to running, but it was leaking fuel so I shut off the fuel and quit for the weekend. Turns out the float valve got stuck, and that's hopefully remedied. Turns over slowly, and when I pull the plug and ground it it turns over faster and has nice blue spark, but will not start...

I'm at my wit's end w/this machine, and cannot find any references to troubleshooting things like CDI measurements, so I feel like I'm shooting in the dark.

Can some of you old hats at this give me some advice so I don't keep spinning my wheels?

 

Starting fluid may help get one "primed up" if everything else is ok. Most manuals don't have tests for a cdi but if you have spark(plug laying against the cylinder while cranking the engine over) you don't have a cdi problem.Start at the easy stuff first. Make sure the battery is up to snuff and have it load tested.Even new ones out the box may be bad.Has to be strong enough to turn the engine over correctly.Then a compression check would be next. Not sure on the DS but Polaris had a minimum of 115 psi but I've seen then run at lower readings such as 90-100 psi. Anything below that then compression could be the reason. Also the most over looked item on any two stroke is crank seals.If one of them is leaking bad enough,no way one will start. It has to have a good seal on the bottom part of the crank case so fuel/air/oil mixture can be compressed and pushed through the transfer ports to the top of the piston for ignition. Just like in this simulation.

 

Thanks, old polaris tech... turns out I was doing something wrong in the startup attempt. I saw another post of yours on this forum talking about not using a jumper battery to try and start these puppies - and that's what I was doing. I installed the new battery my son bought when he bought the carb, and within 15 seconds the freaking thing started!!

NOW I have other issues - doesn't always idle, almost no power, hard to transition from idle to full throttle and sometimes hard to get it back down to idle... but at least she starts + runs!!

I've seen on YouTube where a guy whose YouTube name is 90GTVert and is on 49ccScoot.com is talking about the throttle needle setting and idle mixture screw adjustments being fairly critical for these engines, and was wondering if anyone else either supported that opinion or had a better way of describing what's going on with these three interconnected adjustments.

The dude says the idle mixture screw is responsible for 0-1/4 throttle, the needle is responsible for 1/4-3/4 throttle and the main jet is responsible for 3/4-WOT with, obviously, some overlap involved. Is this more or less accurate? I need to be able to set this quad up so there's pretty seamless transition from idle all the way up through WOT (I guess we all need that, though, don't we?!) and would love to hear an efficient way of getting there. I'm not looking forward to having to change the needle position more than one more time...

Thanks!

 

Problem may not be all carb related but on these little machines most fuel mixture screws set between 1-1 1/2 turns out from a lightly seated position. Plus check the jet sizes on the old carb versus the new one. That's where a lot of people have seen differences. Again I would check compression to see where you stand.That plus crank seals is another thing people overlook.If one seal is seeping air it wont idle or run right and some just race and wont idle down.

 

If I could impose upon you on Memorial Day, and please forgive my ignorance, but would you be describing the oil seals where the crankshaft exits the crankcase, or are there others? And what's a good way to check them?

Thanks for all your help thus far, old Polaris tech... wish I could claim "retired and loving it!"

 

Yes,the seal on the clutch side of the engine case and the one behind the stator plate side.Items #9 and 10 under crankshaft/piston.https://www.adlyparts.com/atv-parts/...0-2t-crankcase

 

OK - here goes... compression test showed 130 psi averaged over three tests, needle in the main throttle slider is at highest point (richest setting?), bike starts well and idles pretty well, but still seems to lag up to full throttle. At full throttle it pretty much runs wild, not being too affected by throttle position. Also, there are two holes in the left crankcase cover that I'm not sure are supposed to be there - see the photos below - and I was wondering if those could be the culprits...

Regarding the crank seals, what all is involved in replacing them?

here's two photos of the case holes...
Attachment 12534
Attachment 12535

 

OK - follow-up... I just looked at a case on eBay and see the same two holes, so I assume they're supposed to be there...!


Now I'm back to square one on the run-on condition. Can someone step me through the possible reasons for the run-on? Bike starts pretty easily, runs pretty well at idle, but once I throttle it up it seems to want to stay at full throttle until I kill it. It also seems to run fairly smoothly at full throttle, although I haven't taken it out under load, so no promises there.


A colleague of mine who's owned and ridden dirt bikes for years said it could be the needle setting causes a lean condition, which is why the over-revving - but that seems to me to contradict what a lean mixture would do.


So, what should I be looking for? 'old polaris tech' reckons it could be crank seals, my colleague reckons it's the needle position is leaning the mix too much, and another online reference mentions the possibility of return springs not closing the needle slider down. I just don't know enough to make an educated guess - which is why I'm spending so much time on this forum right now... and the only shop manual I can find - a Bombardier 2002 Manual covering DS50s and DS90s - doesn't go into much (well, ANY) detail on troubleshooting, so I'm at a loss...


???

 

So...to me, at least, it sounds like jetting and it sounds like the needle. If the needle is adjustable put it in the middle. Moving clip up to blunt drops the needle and LEANS the mixture 1/4 to 3/4 throttle...moving the clip down to pointy end RICHENS the mixture for the same range. Sounds like you are lean until full throttle (off the needle and on the main jet)...Do you know how to "read" a plug?

 

DirtDevil101, I'd love to be able to say yes - and I think I might be able to on a 4-stroke - but I'd be lying if I said I could read a 2-stroke plug...

so, from what you've described it sounds like I had the needle position (lean/rich) backwards. I can redo that, no problem. How do I determine whether the carb jets are the correct ones?