GZ250 exhaust backfire no start

[gz4me +]

I have a 2000 GZ250. The rectifier went up in smoke. I changed out the rectifier, stator, and pick-up coil. Now when I attempt to start it, all I get is exhaust backfire. It ran before I changed everything. Any thoughts??

[alantf]

Difficult over the internet, but it sounds like some kind of timing problem. :hmm:

[jonathan180iq]

I agree with Alan.

Any more details? Anything at all rotate while you were changing out the stator?

[gz4me +]

Nothing rotated while changing stator. Timing is auto controled by the CDI. Trying to find information on testing it. I have been told that there is no way to test the CDI. Told to buy one and keep fingers crossed that solves the problem. I do not have that kind of money. Trying to find someone local who will allow me to put one on to see if it corrects the problem. Not many GZ's around. I have checked all the wiring connections and comfirmed good contact and connectors are locked in.

[raul10141964]

the aliment key on the crank may be missing

[gz4me +]

Thanks, I will check on that. I was also advised to test the stator and make sure it was working. I had already done some basic test on it after the install. I will recheck that as well. Still trying to find a loner CDI. Negative results so far.

[blaine]

Thanks, I will check on that. I was also advised to test the stator and make sure it was working. I had already done some basic test on it after the install. I will recheck that as well. Still trying to find a loner CDI. Negative results so far.
The stator is part pf the charging system & has nothing to do with the bike starting.I kinda leaning towards flywheel key sheared off. ;) :)

[gz4me +]

I agree with you and Raul. This makes alot of sense. I will be checking this out first. Thank you for your input and I will let you know what I find.

[gz4me +]

Sorry it took so long to get back with information. It took some time to find a 35mm flywheel puller. A local motorcycle shop was nice and pulled it for me. The flywheel key was not sheared. This shop owner went out of way to pull the flywheel and install it back on the bike at no charge to me. Hard to find someone like that these days. He thinks it is the CDI Box. Still searching for that. I will keep you updated as I continue to get this GZ going. MY Grandson has learned alot on this project and really hope we get it sarted soon.

[gz4me +]

Receieved CDI from E-Bay today. Installed it and have same problem. Exhaust backfire no start. It sounds like a 12ga. going off. Neighbor behind me called cops and reported gun fire. Two squad cars reported to my house and interrupted my work on bike. Funny after the fact, but not at the time. Anyone have any thoughts on what to check now???

[raul10141964]

check if the valves

[jonathan180iq]

Gun shot sounds mean it's blowing through the exhaust - most people confuse some sputter and popping with backfire, which technically blows back into the intake...

I'll agree with Raul - there is something about your timing. You can check the valve clearances and make sure the timing marks are doing what they're supposed to be doing.

...Did we ever figure out why the rectifier just suddenly burned out? It wouldn't go out without something else failing along the way, right?

[gz4me +]

Will check valve clearance as suggested. Will read up on timing marks and go from there. As for the rectifier burning up, that is why I changed out the stator and pick-up coil. I was told if rectifier fails, replace stator at same time. I checked for frayed wires, made sure all connections were clean and locked in place. Really never did find a reason for it burning up. It was suggested to me yesterday that prior to attempting to start bike, I should advise neighbor so no more squad cars will show up. At least I got a laugh at the end of the day.

[gz4me +]

I was not able to work on bike today. Going to pull gas tank tomorrow and check valve clearance. Seems like one step foreward and three steps backward. Learning alot from this forum. Hope some time I can assist someone like all of you have done for me. Thanks.....Will let you know what I find tomorrow.

[Water Warrior 2]

Seems like one step foreward and three steps backward.

Sometimes you have to learn to dance to the music in unexpected directions.

[gz4me +]

Removed gas tank, valve inspection caps and generator cover cap. It took awhile to get the generator cover cap off. I used a flang that holds the discharge tube in Insinkerator garbage disposer. It was strong enough for the force I had to use to get the cover loose. lThe large hole in the center gave me plenty of grip. I guess I will be adding that to my tool pouch for future use. The real problem came when I went to my toolbox for the 22mm socket to rotate the crankshaft. After searching my garage, my truck, my work trailer and back to my garage, it finally popped into my head!!!!! I let my next door neighbor use the socket set last month. Of course he is not home for me to recover the socket set. Project on hold for now.

[jonathan180iq]

Just got get one from Walmart as a rental and then take it back... I don't think that's TOO unethical.

[gz4me +]

I checked valve clearance today. Exhaust valves were thight. No clearance at all. Adjusted them to specs. Timing marks appear to be right. Put tank back on and attempted start. No backfire, but also no start. Did not have time to do much more. Will brainstorm more tomorrow.

[gz4me +]

After reviewing ImaginativeFig and ShaunCW78 posts, I decided to pull the right side cover on mine. Everything was fine. No shaving, sheared off bolts, etc. After I put new gasket on side cover, I will pull the head cover and check for any damage. From there, I guess I go back and recheck everything I have checked 10 times already. (spark,carb., wiring, timing, clearances,etc.)

[jonathan180iq]

Do a compression check. If it was popping and after firing then it's definitely getting fuel.
See if you can get it to turn over or hit using the old lawn mower mechanic's special tool "starting fluid".

That said, there is still no reason for the rectifier to suddenly just go up in smoke and then expect everything to work fine after that.

AlanTF will be in here once his old man body heals back up. He is our resident electrician. If anyone knows how to break down the wiring schematic for that thing it will be him.

[gz4me +]

Between mowing lawns and dealing with medical issues, have not had any time to work on bike. Things starting to slow down, so I might be able to get working on it next week. Will be doing compression check and cam timing check. Need to find information on cam timing before I go any further on that. I see from the postings that several members have solved their problems and out enjoying their bikes. Hopefully ImaginativeFig and I will be in that group soon. If anyone has info on cam timing, please let me know.

[ImaginativeFig]

So this one's your grandson's?
For me, all my timing issues arose from allowing the woodruff/alignment key to be destroyed/displaced.
Checking compression was probably the most useful thing I ever did. It's what led me to the discovery of both the shorn camshaft (which is probably the only one of the problems with my bike that weren't my bad) and the again-misplaced key...
Using starter fluid is how I found out that I still didn't have my carb right.

[gz4me +]

Yes. I bought the GZ for him after he layed down a Yamaha 650 custom. After laying the bike down at a stop sign 1 block away from house.( No damage to bike or Grandson.) He knew he was going down and was able to get off bike and lay it down softly. Only thing hurt was his pride and confidence in riding. He felt the GZ would be better until his riding skills developed a little more. We enjoy working on the bike, but both of us would enjoy him riding it more than working on it. Both of us have gained respect for you as we followed your posts. You have gained the respect of many on this forum for not giving up and working hard to get that GZ back to rolling down the road. We hope to have his running in the near future. Had to take a break from it. Lack of money and time were the main reasons for taking break. Still not exactly sure why it will not start. Will go over every possible reason until she works.

[ImaginativeFig]

Haha, well I wouldn't have needed to do nearly as much as I did had I not made so many mistakes!

[blaine]

Haha, well I wouldn't have needed to do nearly as much as I did had I not made so many mistakes!
Mistakes are Lessons well learned. ;) :)

[Water Warrior 2]

Yes. I bought the GZ for him after he layed down a Yamaha 650 custom. After laying the bike down at a stop sign 1 block away from house.( No damage to bike or Grandson.) He knew he was going down and was able to get off bike and lay it down softly. Only thing hurt was his pride and confidence in riding. He felt the GZ would be better until his riding skills developed a little more. We enjoy working on the bike, but both of us would enjoy him riding it more than working on it. Both of us have gained respect for you as we followed your posts. You have gained the respect of many on this forum for not giving up and working hard to get that GZ back to rolling down the road. We hope to have his running in the near future. Had to take a break from it. Lack of money and time were the main reasons for taking break. Still not exactly sure why it will not start. Will go over every possible reason until she works.
A 650 custom is a little more than a starter bike for most folks. The weight factor alone is a danger when coupled with little to none experience.
Send your young descendant to an approved riding course and also buy him a copy of Proficient Motorcycling. The grandson should learn the proper way before developing any bad habits that can make riding dangerous or less enjoyable.

[gz4me +]

Grandson has already taken the course and read the Proficient Motorcycling book. Did well in the course and was riding a few bikes prior to getting on the 650. He had been riding the 650 around the neighborhood(gated) for about a month before the lay down. The Assocation installed speed bumps just before every stop sign. I think he was worried about the new speed bump and tensed up. I agree the weight of the 650 did not help. The 650 is a nice looking bike and he did not want to lay it down anymore. Both of us decided to drop down in weight for awhile. We decided on the GZ and he was doing fine until the bike had issues. Now we just need to get it going so he can get back to riding.