2003 Yamaha Blaster power issues

[Jared]

So, I bought my son a 2003 Blaster to learn on. It's a great size for him and the quad was in very nice condition. It came with a Vito's pipe, and had the factory TORS deleted (throttle override system, a problematic system designed to cut out if a stuck throttle is detected). When we test rode it, it was really boggy on the top end but I figured it was just a jetting issue.

After we got it home, I started playing with jetting. I couldn't find a manufacturer recommended main jet size specific to that pipe, but I found similar pipes were in the 270-310 range. It had a 320 main in it already, so I figured I'd start going down from there. I've tried every jet size down to 250 and it still won't ever hit solid in the powerband. It is strong right off idle, but tapers off very quickly. If there's any drag on the motor, like riding up the easiest of grades, it never even goes above half RPM in any gear. I can get it to rev out somewhat while riding downhill, but it has no power whatsoever. I checked the reeds and they looked good, and passed the tried and true "blow through them both ways" test.

So, I did a compression test, and got a measly 88 PSI cranking pressure. This seemed horribly low, so I went ahead and put in a fresh top end. I haven't checked the compression since, but you can feel a reasonable increase just from the feel of the kick starter. I probably ought to check it again, but these bikes don't have a huge amount of cranking pressure to begin with. The bike runs no different now than before. Coils are cheap, so I replaced that and again no difference. Obviously, I've also replaced the spark plug with an NGK BR8ES, the factory spec.

The TORS setup was my next suspect, but after looking it over the previous owner did everything right. If I jumper the system (which he did) the bike runs, but poorly. If i remove the jumper, it dies immediately after starting.

I'm pretty much stumped at this point. I don't really feel like this one is a jetting issue. Timing isn't adjustable, but I guess somehow the key could be sheared and yet the flywheel isn't freely spinning on the crank?? Crank seal leak? I know the base and head gaskets should be good, I just replaced them. I'm open to ideas.

Thanks,
Jared

 

[Gravy]

Check the compression again perhaps. Were the cylinder walls scored?

 

[Jared]

Check the compression again perhaps. Were the cylinder walls scored?

They were some on the exhaust side, but not bad. I probably could have just honed it. But I used a new cylinder, piston and rings, so I suppose that's a moot point now. I set the ring gap properly, and chamfered the ports as well.

 

[Gravy]

What's the clutch look like?

 

[Jared]

What's the clutch look like?

It looks like a stack of flat rings, alternating bare metal and fiber plates, running in an oil bath. They all fit in an aluminum basket and are pressed together by a group of springs.

Why do you ask?

 

[Jared]

Anybody? I'm about to drop this off at the dealer... which makes me cringe to even type.

Stratton - just giving you crap about the clutch, I haven't opened it up ever. Is there something I might find in there that would cause it to lose all power at above about 2500 RPM?

Thanks

 

[Rot Box]

The parts breakdown lists the main jet as #230 stock.. Even with a aftermarket pipe I don't think it would run with a 320 main unless that was a typo.

What is the needle clip position?
Is the exhaust smokey?
Does it run better with the choke on or off? Excessive blue smoke could be a bad wet side crank seal (sucking transmission oil into the combustion chamber).
What color is the plug?
Is the reed valve assembly in good shape? And is that boost tube (or whatever that hose/bottle thingy on the reed valve is called) in good shape? If it leaks you'll have a major vacuum issue.
I'm assuming the air filter is clean...

Air, fuel and ignition is all it takes. It sounds like you've verified the ignition side of things is working.

A blown dry side crank seal will cause all sorts of problems as well. They will typically run very lean though. I guess it depends on how much smoke you're seeing and how wet/dry that plug is.

Andrew

 

[Gravy]

If it's slipping, definitely. That's how my bike would act if I revved it out or was climbing a hill when the clutch was roasted.
Check the springs and the friction plates.

 

[Jared]

The parts breakdown lists the main jet as #230 stock.. Even with a aftermarket pipe I don't think it would run with a 320 main unless that was a typo.

What is the needle clip position?
Is the exhaust smokey?
Does it run better with the choke on or off? Excessive blue smoke could be a bad wet side crank seal (sucking transmission oil into the combustion chamber).
What color is the plug?
Is the reed valve assembly in good shape? And is that boost tube (or whatever that hose/bottle thingy on the reed valve is called) in good shape? If it leaks you'll have a major vacuum issue.
I'm assuming the air filter is clean...

Air, fuel and ignition is all it takes. It sounds like you've verified the ignition side of things is working.

A blown dry side crank seal will cause all sorts of problems as well. They will typically run very lean though. I guess it depends on how much smoke you're seeing and how wet/dry that plug is.

Andrew

I want to say needle is in the middle position (of 5), I set it to the specs listed for a Toomey B1 pipe as it's a similar, large volume, top end type pipe. The recommended main jet size for the B1 pipe is 310 at sea level, meaning about a 290 up here. I know it sounds huge, but most of the similar pipes have similar jet specs for this machine. The stock pipe is very, very conservative.

Reed valve assembly looks good, and so does the gasket. I'm not sure what the boost tube you mention is, the only inlet to the reeds is the main hole for the carb. The reeds sit basically closed at rest, and when I blow/suck through them they open and shut as expected. Air filter is clean and lightly oiled.

The new plug is light brown after a couple WOT passes, but it was a bit on the wet side. I ran WOT for about 10-15 seconds and then pulled the clutch and hit the kill switch before pulling the plug to check.

The bike does smoke a lot more than I think it should, and it's blue. But, I've been blaming that on the cheapo Maxima oil I used. I'm running 40:1 premix.

I've never had a machine with a crank seal issue, so I'm not terribly familiar with the symptoms. I'd assume the wet side is between the crank and tranny, and the dry side is behind the flywheel. Wet side leak sucks tranny oil, dry side leak sucks air and leans the ever-loving crap out of things. Is that pretty much accurate? Does it require a leak down test to verify crank seal leaks?

I've been leaning toward a weak spark problem, but where I've tried a different plug and coil I'm not so sure. Could a pickup coil cause weak spark?

 

[Jared]

If it's slipping, definitely. That's how my bike would act if I revved it out or was climbing a hill when the clutch was roasted.
Check the springs and the friction plates.

The bike won't rev up under load in gear, so I don't think the clutch is slipping. It pulls hard (meaning engages as you'd expect, not pulls hard on the lever) when released and can easily stall the motor in any gear. I can pull in the clutch (or be in neutral) and the bike will weakly rev to the rev limiter.

 

[rholbrook]

Jared,
Do a throttle chop on it. Run it hard and then kill it. Pull the plug and look at it. I would bet you will need to be 270-280.

Also, it is a ATV. It has a lot of weight to move so maybe you are expecting too much out of the small bore ATV. For the price of a main jet I would grab a 280 and start there. I am able to do some jet swapping if you want to give me a call.

 

[Jared]

I've tried all jet sizes down to 260 with no improvement. Actually, it runs best (but still awful) at about 270-280. I believe I've got the 280 in it currently. The bike also has the air box lid removed for more air flow, which supposedly is pretty restrictive in stock form. I didn't answer earlier, but the choke absolutely makes it run worse. This is the 3rd Blaster I've owned and my others would completely destroy this thing... like triple or quadruple the power. This thing won't even pretend to enter the powerband. I'd be surprised if it's putting out more than 5HP wide open, literally.

The throttle chop is what I've done to check the plug. New plug, ride wide open through all gears for 10-15 seconds and immediately hit the kill switch, pull the plug and have a look at the ceramic by the electrode.

 

[rholbrook]

Have you looked at the reeds closely? Do the blasters have a power valve to clean or adjust? I just dont know enough about them.

 

[rholbrook]

Did you change your number? Call me.

 

[Jared]

No power valve. Think 1982 two-stroke, air-cooled technology and you've got a good idea of what I'm working with.

 

[Rot Box]

Hmm, I'd try moving the clip on the needle. Try moving it down on the needle first (richer) and see if that helps. If it gets worse go the opposite direction (leaner) and try again. Hard to say without being there :-\ I do know removing air box lids, adding pipes etc will have a huge impact on jetting. The main jet might be in the ball park but the needle is just as important.

Beyond that another compression test and a leak-down test might be a good idea. A leak down test would tell you if your crank seals and top-end gaskets are good to go. There are several youtube videos on this if you decide to give that a shot. Cranks seals can cause all sorts of weird jetting issues.

 

[rholbrook]

Hmm, I'd try moving the clip on the needle. Try moving it down on the needle first (richer) and see if that helps. If it gets worse go the opposite direction (leaner) and try again. Hard to say without being there :-\ I do know removing air box lids, adding pipes etc will have a huge impact on jetting. The main jet might be in the ball park but the needle is just as important.

Beyond that another compression test and a leak-down test might be a good idea. A leak down test would tell you if your crank seals and top-end gaskets are good to go. There are several youtube videos on this if you decide to give that a shot. Cranks seals can cause all sorts of weird jetting issues.

Spray some starting fluid around the motor as its idling.

 

[Jared]

I was under the impression the needle has very little to do with jetting at wide open throttle, and that's where I'm having issues. So the pilot jet controls idle up to about 25% throttle, the needle/main jet combine to control about 25-75% throttle, and primarily the main jet controls roughly 75% to wide open. Am I off base with that?

Any other thoughts on weak spark being caused by a pickup coil or even the computer/ECU thingy before I dig deeper? Otherwise I think my next steps would be another compression check, then a leak down check. I'm really badly hoping I don't need to split the cases on this cheap little learner bike!

I can try the starter fluid trick looking for vacuum leaks tomorrow. If I find something I sure hope it's on the top end!

 

[Rot Box]

Starting fluid will work great for the top end gaskets. If there's a leak you'll definitely hear it. You'd need to do a leak down to verify the crank seals are good.

I was under the impression the needle has very little to do with jetting at wide open throttle,

Any other thoughts on weak spark being caused by a pickup coil or even the computer/ECU thingy before I dig deeper?

I'm really badly hoping I don't need to split the cases on this cheap little learner bike!

I can try the starter fluid trick looking for vacuum leaks tomorrow. If I find something I sure hope it's on the top end!

You're right about the jetting.

Pull the plug out and kick it over. If you're getting healthy spark and it's running good everywhere except on the top end you can probably rule that out for the time being. Not saying it couldn't be a ignition problem but.... I kinda doubt it. The ignition is simple on this bike and for the most part it will either work or it won't.

You shouldn't have to split the cases. Even if the crank seals are bad they come out the sides and don't require too much effort the change.

I'm outa ideas

 

[rholbrook]

I was under the impression the needle has very little to do with jetting at wide open throttle, and that's where I'm having issues. So the pilot jet controls idle up to about 25% throttle, the needle/main jet combine to control about 25-75% throttle, and primarily the main jet controls roughly 75% to wide open. Am I off base with that?

Any other thoughts on weak spark being caused by a pickup coil or even the computer/ECU thingy before I dig deeper? Otherwise I think my next steps would be another compression check, then a leak down check. I'm really badly hoping I don't need to split the cases on this cheap little learner bike!

I can try the starter fluid trick looking for vacuum leaks tomorrow. If I find something I sure hope it's on the top end!

But if its too rich or too lean in the needle it may not let it build the RPM. What about timing? Did I miss what needle you are running and what position the clip is in?