1999 Trailblazer 250. Bone stock, all original. Just picked it up and it didn't have power about half throttle. Fired up GREAT, first click of the starter, even cold without using the choke.

Guy said it hasn't been used regularly in about 3-4 years. Symptoms lead me to believe a gummed-up carb or maybe a plug.

Rebuilt the carb, new oil fiter, new fuel filter and new spark plug.

Fired up immediately after reassembly. Revved great. Seemed to now have full power all the way to top speed (although it did seem just a little on the slow side to me - not drastic, but a little). Had son take it around yard a few times, slow, then a little faster. After 2-3 trips around it when he pulled back up to me, it bogged down and even with adding throttle it wouldn't stay running and stalled.

Restarted it (I think I had to use full throttle indicating to me it was flooded), another trip around and when she pulled up, it bogged and died again. Did this again using various methods - with choke, without choke, etc. Now since I JUST rebuilt carb, I don't have the choke adjusted so that may or may not be a contributing factor.

Messed around with the air/fuel mixture valve. Ran it all the way down and backed it out 2 turns and then tried various positions from that point. Nothing really seemed to make much difference (other than all the way in and it would run...).

Pulled carb off and made sure everything was installed right, didn't see any crap anywhere. Reassembled carb.

Ran compression test (cold) and have 115 psi. Seems enough. Going to go put carb back on and try to warm up engine and text compression again to try to eliminate that.

I have another T/B (2003) and the carbs look the same. If compression test (warm) shows good, I may swap in the carb from THAT quad and see the results.

I am looking for ANY ideas here guys. Big wheeling weekend coming up and I can't spend days d*cking around with this thing...

 

If swapping carbs doesn't help then check crank seals,especially the one behind the front clutch. Especially since it's been sitting up. Gas could have started deteriorating the seals. Must have good bottom end compression along with top end compression or it can bog down,not idle and get to the point it won't crank.. OPT

 

Swapped carbs and I was able to keep it running longer with the other carb but it sounded loaded-up the entire time. That carb has oil-injection on the body so I had to cap that off for this test.

I was able to get the machine warmed up but eventually it, too, seemed to load up and die so I did another compression test. Of course this takes a few minutes with a damn-hot cylinder head and hot pipes to work around.

Cold: 110,115,115
Warm: 105,110,110

So it does drop some. Seems when the other quad was in need of rings I was getting just below 110 as well as if that may be the threshold...

I really don't mind doing a top end so long as I KNOW it is the issue. I have a video that I took (about 35 seconds) before the carb loaded up and died. OK, let me make it clear, I THINK it is loading up.

Sometime I can start it right back up (about a minute wait), othertimes I need to hold throttle wide-open. Now that indicates to me a flooded carb.

OPT, to your point about lower crankcase pressure, I don't even know how to check that, other than to spray some WD-40 around the seal areas that you mentioned.

I didn't mean to make it sound like the quad sat 3-4 years. It just wasn't ridden regularly; if that even makes a difference...

I put a rebuild kit on, but I can't help to wonder if the float valve could be an issue here...

 

You are in the low area of compression which can cause problems atomizing the fuel/oil mixture properly and load up leading a lot of people to think it's more of a carb related problem. I've seen this often to where people would shut down the fuel flow(bending the float arm to restrict fuel,etc) basically the 2 stroke has to have a good seal on the rings and piston against the cylinder (upper compression) and the crank seals must not loose the air/fuel charge that the piston sucks downward and then compresses and sends this atomized charged up through the transfer ports to the top of the piston to where it fires. Then as the piston starts down,the process starts again. Intake/compression,then fire.That's why it's considered 2 strokes or 2 revolutions. When you have to hold the throttle wide open the fuel usually is not compressing good at the bottom end (or has a weak fuel charge from the top end,which usually is more fuel than air) and causes crank cases to "load" up with fuel or just ends up fouling plugs,won't idle after getting warm(heat expansion of the cylinder causing rings not to seal properly,etc) This may or may not be the problem area you're having ,but sure sounds like it. Plus if it needs a top end,I wouldn't trust doing just this alone without rebuilding the bottom end also on a 13 year old machine. To do a leak down test you have to block off the exhaust,have an adapter and gauge for the intake manifold and what I used was a bicycle pump to pump up to 7 psi and it must hold this pressure! Then you can spray soapy water around seals,base and head gaskets,etc to find leaks if it doesn't. OPT

 

OPT since you are all retired now I have to say it's a damn shame to only have 5500 miles on that bike. It should have 55,000 miles on it!!! I've had my Kaw VV for three weeks and will hit the 1,000 mile mark on the way to work in the morning!!

I read your post several times to make sure I'm clear on a few things. Are you saying that it sounds like compression MAY BE the culprit here?

I hear what you are saying but with time constraints right now I don't see me having time to do the crankcase end. I can, however, get the top end off tomorrow night, dropped at machine shop and back by end of day. I could probably have it installed Tuesday night (I have an event that night which is the only reason I am not positive I'd have time).

Do you foresee issues with the bottom end if I only perform a top-end rebuild?

Since it ran just as crappy with the second carb - I actually had the hold half-throttle with the other carb on there to keep it running, I see only two other issues: Ignition Coil (I had nice bright blue spark on my spark gap tester) and compression.

Everyone says "you need three things to fire the engine" but I say you need FOUR:

Spark
Fuel
Air
COMPRESSION

I mentioned I already did a top end on my daughters machine. She, too was right at the 110psi mark. It would start fine, run 10 minutes and die. Wouldn't start for 10-15 minutes and then it would repeat. A top end rebuild cured all the issues. If this machine did the same I would feel more confident that the top end rebuild would fix the issue.

Let me ask you this, OPT; The issue BEFORE the carb rebuild was there was no power gain from 1/2 throttle and up. Because of that, I was afraid this machine wouldn't handle some of the hills we will encounter. However, it continued to run with no idle issues and no bogging.

AFTER rebuild it would achieve top end. However, now I cannot keep it running.

Do those two issues have a connection that you can make? I was positive the lack of power at the top of the throttle was due to a dirty carb. When my kid drove it around the yard a couple laps after the rebuild he was screaming "woooooooohooooooooo" at the difference.

Now I'm afraid I won't have this machine done before our trip and I can tell you my family is SOOOOO looking forward to this upcoming trip!!!

 

Yes you need all "four" things! Air,fuel,compression and spark. Seems like you can eliminate two of them,the fuel problem,and you have spark. That leaves compression and air. Lack of compression means less air also to mix with the fuel! You could get by with a top end "IF" there is no up and down play on the rod,no roughness from the crank bearings as you turn the crank around by hand. This is your call on this!! But I would replace the crank seals also! Like I said it could be also the crank seals causing a lot of the problems even with your lower compression readings and leaking seals could contribute to low compression readings to!. OPT

 

Looks like we're gonna find out if it's the rings b/c I just pulled the top-end off and dropped it off at shop for a bore/hone.

Mic'd it up at 72.3mm What an oddball number. Stock bore should be 72mm. Machining to 73mm and decking the head .25mm

Should be able to get back together by tomorrow night (I hope...).

I detest the engineer who came up with the upper motor mount that attaches to the jug...

 

I detest the engineer who came up with the upper motor mount that attaches to the jug...[/QUOTE]



Welcome to my "ex" World The top motor mount I believe was an after thought! Same thing when they came out with the 300 engine and decided "Since we already have the top motor mount at the rear of the cylinder,then this is a good place to install the fan sensor" NOT a very good idea since it actually didn't get hot enough as they thought to trigger the fan that often! Plus the vibration from this area just tore up the tiny little spade connectors on the sensors. PS Don't forget the crank seals!!! OPT

 

The crank turns very smooth, not rough spots and I notice no play in the connecting rod. I truly only have the time for a top-end rebuild anyway, but I appreciate that you told me to look for this.

When I pulled the plug it was wet. While that alone doesn't tell me that compression is the likely issue, when put with the other indicators, I think he helps me believe that this is the issue.

We should know by tomorrow night!! Thanks for the help, OPT and I'll be posting on the outcome - especially if it does NOT work!!

 

Wow. This is so messed up that if it didn't happen to me I'd hardly believe it...

Got cylinder back and new pistons/rings and all and put it all together. Fired up, halfway around yard it died.

It did EXACTLY the same thing. Started troubleshooting more, checking fuel line to make sure it wasn't kinked, changed to the old fuel filter, took hose off petcock just to see how much fuel would come out of it (a LOT), etc, etc.

We were convinced it was a fuel issue. Tore carb apart again and everything looked good, clean jets, etc, etc. While we had it out we tried blowing air through the fuel inlet...

Nothing... No air was getting through. I thought maybe when I tapped the fuel inlet tube back into the carb I went too far and collapsed it or something. We pulled it back out and it was PLUGGED!!!

We pulled out the culprit and could NOT believe what we found...

This carb has the pins that the floats ride on. There are little red caps that pop on the ends to contain the floats so they don't fall off (presumably during assembly or disassembly).

It fit in there PERFECTLY!!! Un-freaking-believable!! I thought when I got the carb back from the local dealer (had them tank it) they simply lost that cap. I lost the other one when I attempted to snap it onto the pin and it shot across the bench...

Reassembled and not I have a VERY VERY happy boy ready to hit the trails this weekend!!!

I don't regret doing the top-end work b/c it was necessary anyway but DAYUM!!!!

Thanks, OPT, for the help!! Who would have ever guessed that, right???!!!!