Loss of power, torque. Sputters at full throttle

[pillowpants]

I was riding the other day and suddenly my GZ250 just lost power and torque. Now it sputters at full throttle in every gear. I can't get over 45 mph. I changed the oil and filter and it's still the same. I also added Berrymans b-12, but it hasn't changed. Please help. :)

[raul10141964]

Change spark plug

[jonathan180iq]

How does it respond with less than full throttle? Does 1/2 throttle respond better, for example?

[pillowpants]

Hey Jonathan, there is no sputtering at half throttle, but the torque/power isn't there. Raul, I changed the spark plug and it hasn't changed anything.

[jonathan180iq]

Not being able to get over 45 would indicate to me that you have an air leak somewhere, and a big one. Does the bike idle alright? Does it also buck like a bull with a yellow-jacket on it's haunches?

Take some WD-40 or some ether or something similar and give a little spritz to all areas of the carb where a seal or connection exists. If your idle changes at all while you do this, then you need to fix whatever is causing the leak.

[pillowpants]

I sprayed all the boots and around the carb and did not notice an idle change.

[raul10141964]

do you check the air filter
my do that when i mod the filter before i change the main jet to 140

[JohnC]

When it sputters, try full choke. If there is no improvement then the problem is likely ignition or a plugged air intake. If there is even the slightest improvement then it is likely carburetion.

[pillowpants]

Raul, I checked the air filter and box. They both seemed fine. I am mechanically inclined when it comes to jets. JohnC I don't have a choke on my bike, I have never noticed one before and I don't see one. Where would it be? I bought my gz250 used over a year ago and never had any problem with it.

[jonathan180iq]

These things have a factory choke... Left handlebar control.

Can we see your setup?

Check the "S" tube that runs from the crankcase to the bottom of the air box.

[JohnC]

It's not really a choke, rather an enrichment valve. The control is just inboard of the left grip. There's another thread by a guy with a broke choke, with pictures.

[pillowpants]

Yeah I have a choke, but the cable is broken. I pulled on it when it was running and it turns off. I checked the S hose and it was fine.

[Water Warrior 2]

Raul, I checked the air filter and box. They both seemed fine. I am mechanically inclined when it comes to jets. JohnC I don't have a choke on my bike, I have never noticed one before and I don't see one. Where would it be? I bought my gz250 used over a year ago and never had any problem with it.
Did you remove the air filter and check the inside surface? The airflow is from the inside to the outside so the bugs and crap plug the inner surface first.

[JohnC]

I pulled on it when it was running and it turns off.

And what turns off?

[alantf]

I imagine that he means the engine. Suddenly enriching a warm engine will shut it down. I learned this the hard way, one day, when I forgot to turn the choke off, and when the engine got warm, it spluttered. Turned off the choke, and back to normal.

[JohnC]

Yeah, but he said the cable is broken.

[alantf]

He said "the cable is broken. I pulled on it" I reckon that means that he pulled the broken end, and operated the choke.

[JohnC]

If he can do that then maybe he can pull it while the bike is sputtering to perform the test I suggested.

But, then, maybe we should stop speculating and let him speak for himself...

[jonathan180iq]

Either way, first things first, fix your choke. It's going to be hard to maintain a properly running bike when all of the things that are supposed to be working on it aren't working...even if it was running fine while it was broken before, this needs to be corrected.

Was it without choke when you bought it? How did the PO get it start without choke? I see you're in Florida, but all it takes is a slight chill and these things simply won't run without choke. Did he adjust some carb settings away from the factory default that could play a factor in the current issue?

[pillowpants]

I took out the carb and cleaned it, but that wasn't the problem. Come to find out my valves needed to be adjusted. Now it's running great. I still have to eventually change the springs on it. Does anyone happen to know how much those springs run for? BTW Thanks everyone for they're help.

[Water Warrior 2]

Valve springs???????

[alantf]

Valve springs???????

Yes - that's what holds the valves shut. Pressure from the rocker arms opposes the spring, and opens the valves.

[Water Warrior 2]

Valve springs???????

Yes - that's what holds the valves shut. Pressure from the rocker arms opposes the spring, and opens the valves.
I know what the springs do and where they are but how was that determined without removing them?
Pillowpants will have to explain this to us. I can't see a valve adjust being the determining factor for replacing the valve springs.

[alantf]

Whoops! Sorry. I thought that you didn't realise that the valves had springs. :blush:

[Water Warrior 2]

Whoops! Sorry. I thought that you didn't realise that the valves had springs. :blush:
No problem. 2 words and a lot of ???? marks really doesn't convey a lot of info.

[JohnC]

I think he meant more like "what makes you think the valve springs are bad?" I certainly wonder...

[Water Warrior 2]

I think he meant more like "what makes you think the valve springs are bad?" I certainly wonder...
Yeah, that is exactly what I should have said.

[plato1]

I just had a similar issue, except mine was noise based. I initially did a valve adjustment--did not solve the loud tapping noise. How does your bike sound?

If you are getting sputters at full throttle, and you have checked the basics of carb, air filter and etc. You may have a compression issue. Which you mention you valve springs--which sort of put you in the right area. First off what year is your bike and how many miles are on it? This may help you determine how worn some of your parts may be...

If you think your valves may not be closing all the way, this could affect your compression, then you want to check things more deeply before you end up dropping a valve.

You can remove the head cover and the head cylinder without removing the engine from the bike (do it carefully). I would start with the head cover. Open it, and check your rocker arms AND the cam shaft lobes for wear. Use the manual to do this. If you have wear on them--replace them ALL. I had a worn exhaust rocker arm and decided to just replace that initially---It did not solve my noise and lack of power. The intake rocker arm and cam side lobe weren't really that worn. As a result, I bought the whole set of 3--both rocker arms and the cam shaft.

Then since reading on another post here, that a guy had his piston smash his valves, and then also a parts bike I almost bought that had the same issue, and that guy told me his exhaust rocker arm and the corresponding lobe on the cam were worn, but the intake was fine---I thought I better dig deeper because I felt I was about to have a valve drop. Keep in mind all of the mechanics I spoke to said it was NOT likely to be anything wrong with the valve or springs or parts there because when a valve drops the bike will just stop. My argument was what about just before it "drops" something has to be wrong in there, or it's bent or something. There is a REASON they eventually drop.

So, decided to order the whole top end minus the cylinder head itself and the cover. Then when the parts arrived, I took the cylinder head off, took out the valves and ALL 4 were burnt and swollen. I also had spongy springs as well. I replaced all of it, except the valve seats, they were good...And a good thing I did, because it was a matter of time before one of them valves would have snapped and caused some really bad problems....

Also, while you have it apart, check your cam sprocket and chain. If your issue is there, then you may have your chain jumped a tooth or something which will throw the timing off--leaving valves open when they should be closed which may also be causing a compression issue. Not to mention if you have a valve open at the wrong time, the piston head could hit it and smash everything in there pretty bad.

I know you mentioned that you looked at the carb, but you may want to try a product called SEAFOAM....Put it in your GAS tank....It also mentions stuff on the label that you can also put it in the oil---but everyone I have spoken to tells me NOT to put it in the oil part of the bike, but to use in the GAS tank only. If you have a clog somewhere the SEAFOAM may clean it out a little bit better. After I reassembled my bike, I has an idling issue, partly because of the removal of the carb for the repair. The SEAFOAM helped it.

Also, something to check is your throttle cable itself. If your throttle cable has stretched it may need adjustment. You can do this at the barrel up by the throttle handle. Also, if you look on the right side of the bike, there are two bolts with the cable running through it and it can also be adjusted there. You will also see the little wheel the cable runs through....the end of that wheel has a piece that touches the little idle adjuster---this is the thing with the spring on it, and has a white plastic round piece you can turn the idle up and down on....Mine needs a new spring on it...what happens is that it rotates slightly out of place.....As you turn the throttle handle, that "wheel" down there on the adjuster taps against the top of the adjuster....It may have something to do with your issue....

I was at a light and messing with it the other day, and I didn't turn the adjuster and just started to touch it and it cut off the bike...so on mine it is kind of out of its contact place....You may not necessarily have an idle issue, but definitely check your throttle cable and the adjustment where that cable runs around that little wheel....when you turn the throttle handle you will see it move with the wheel and be able to see slack in the cable.....Anyhow, if that cable is not tight enough, you may have it come back down on that contact on the wheel at the adjuster, which will cut your power and or put your idle down....I would take a look at this before you tear your bike apart going after the valves. However, if the bike has a lot of miles on it, it might be worthwhile to check the valves, rockers, and cam shaft.....

I have 37k on my bike, so it was definitely due to be rebuilt....The guy I spoke to that had the parts bike, that had the piston head hit the valve when it dropped, he only had 10k on his...I have seen and heard of random amounts of mileage regarding the valve issue on this bike.....So, it may be worth checking....

By the way, I ordered all the parts from China-- $200....If you order those same parts from Suzuki, it would have been about $680. The chinese parts, you can tell are not manufactured the same way as Suzuki, but they seemed to look decent like they would hold out for awhile.....Since the repair, I have put about 150 miles on the bike and so far, so good....

Anyhow, I hope this helps......

[pillowpants]

Ok, so I rode my bike after adjusting the valves and blew out my engine... :skull: Grrrrrrrrrrrrrrrrrrrrrrrrrrr!!! I took it apart and found that one of the valves broke off inside and tor up the block and piston head. :cry: Should I try to repair it or just buy a used motor? Does anyone know of a good place to buy one? Any suggestions will be appreciated. Thanks

[pillowpants]

Hey Plato1, What is the website u ordered the parts from?

[jonathan180iq]

......What the hell is going on?

You guys are going to have to describe your valve adjustment process. This is a growing issue around here. Something's not right.

[pillowpants]

Anyone knows where I can find a new or used head cylinder?

[JohnC]

I'm gonna guess the valve adjustment is a complete red herring and, coincidentally, the stuck valve got unstuck in the process. It stuck again, this time hitting the piston.

[dual_uzis]

Hi, I'm just a new guy but I'll describe what just happened to me.

I dont work on bikes much, but I'm a 15 year Master Technician. I know my way around a wrench.

07 GZ250 came in for knocking/tapping noise and wouldn't start. Checked carby, boots, etc. Started fine on alternate fuel.
Pulled valve covers to find super, super tight exhaust rockers. loosened then up, assemble, bike starts beautifully, but still rattles.

Exhaust valves were being held open and the carby wasn't getting enough vacuum to start on.

check compression after valve adjust, still low, so I pulled the head off. Found the r/s exhaust valve seat had come unpinned from the cylinder head and was clanking round on the valve when the valve was opened. I'm not sure how it didn't bind up and break the valve off, maybe got lucky and caught it just in time. The head was beat up badly enough to buy a new one.

Research has shown me that bad valve seats are a common issue with this bike, maybe a suggestion to pull the head and re-do the seats would combat so many failures before they occur.

Sorry to hear about your bike.

[tnastvogel]

Your valve... broke off? Wow.

Ebay is where I would look first, then maybe a salvage yard, then probably a Suzuki dealer. Good luck.

Remember to support the cam chain from falling down into the case and have the piston on TDC on the compression stroke (the one after the intake stroke-watch the valves open).