80cc kitted minarelli odd back fire By nobodyspecial (Read 3,094 times)

[cyborg]

Pull the starter and bench test it with jumper cables ,,,,as a side note the backfiring may be caused by the cdi,,,I've seen weird firing patterns on a few other forums and it turned out to be the cdi

[nobodyspecial]

Ok I fitted a new starter and relay. It worked like a charm. Started instantly and the problem of the battery draining overnight was fixed as well.

Then this happened. And may account for why it starts backfiring when off the stand.
Near the suspension stop (see yellow tape) while running the bike started arcing like a spark plug between this and the frame. It eventually blew the fuse and now the starter won't work when I bridge where the fuse went.



Is the starter wrecked? This sparking is very strange...

[nobodyspecial]

After three days of doing nothing but giggling various unrelated wires for a total of about 10 seconds, the starter motor sprung into life overnight. It has a strong spark but won't start even though I fired start spray down the plug hole. I pulled the cylinder off and it hasn't seized.

[czmdiver]

Sept 18, 2017 3:23:07 GMT -6 nobodyspecial said:

After three days of doing nothing but giggling various unrelated wires for a total of about 10 seconds, the starter motor sprung into life overnight. It has a strong spark but won't start even though I fired start spray down the plug hole. I pulled the cylinder off and it hasn't seized.

Be great if you can post some Pictures of your Piston and Cylinder.
Did it have enough compression to blow your finger back out the plug hole?

[dav3]

I had the same problem-I had to tune my carb. I turned my air/fuel screw in all the way, then backed it out 2 1/2 turns, tuned it from there.
 I learned this thru the forums, and it worked!

[cyborg]

How's the engine /frame ground strap?

[nobodyspecial]

On closer inspection of the piston it has seized. I only gave the cylinder a casual glance before and that seemed ok. The rings still move freely. The Piston is scuffed on all four corners. This would account for the backfire then not starting. The electrical short is still out there but I need to get the parts and rebuild before addressing that again. There is no earth strap.

I have ordered a new kit from Scrappydogs. This scoot has been an expensive P.O.S.

[czmdiver]

I had a strong suspicion she had Scuffed a Piston.
Even tho the rings are not stuck they have Collapsed a percentage and are no longer good, don't re-use them.
Most often cause of a Four Corner Seizure is too Fast of a Warm up, simply the Piston expands Faster than the Cylinder. #2 reason is your Lean or may have a Air Leak that is most often a Crank seal.
Two Smokers are just not as forgiving as a four strokes that are running in a Bath of Oil with a Power Stroke every other stroke.
Im anal on two stroke warm up along with Two Stroke Pre-Mix oils...
Thank you very much for the pictures and keep us updated of your fix
Good Luck

[czmdiver]

I should also add if the old or new Cylinder is Cast Iron go even slower on the Warm up.
Cast Iron holds much more heat compared too Aluminum, Think, the Best Fry pan is cast Iron because it Holds so much heat, the Worst is a Aluminum because it dissipates heat.

Onto your fresh top end, go slow on the initial warm up with that Cast iron Cylinder.

[nobodyspecial]

Thank you all for your help. Yes I will take better care with the warm ups in future. I was running a #90 main jet. Plug is oily, while its apart I fitted an #80 and have an #85 on order. I will do a plug chop when its up and going. Is there a simple way of telling if there is a problem with the crank seal? Also while its apart I will test the oil pump is working properly. With the 80 kit I am running a combo of oil pump and premix. I think oil is not a problem as I am getting some blue smoke out of the pipe.

[motley]

Are we allowed to run a can of restore in these little engines?

So restore helps bring back compression on scored engines, etc etc. The stuff actually works!

www.restoreusa.com/index.php

[czmdiver]

Oct 6, 2017 19:45:46 GMT -6 nobodyspecial said:

Thank you all for your help. Yes I will take better care with the warm ups in future. I was running a #90 main jet. Plug is oily, while its apart I fitted an #80 and have an #85 on order. I will do a plug chop when its up and going. Is there a simple way of telling if there is a problem with the crank seal? Also while its apart I will test the oil pump is working properly. With the 80 kit I am running a combo of oil pump and premix. I think oil is not a problem as I am getting some blue smoke out of the pipe.

Darn hate when my worst hunch is true sometimes.
I had tell tale signs of the Piston pictures that made me suspicious of what you have going on with the Oil.
Oil is the problem, You have a Fixed Jet carb when you added that extra Oil to the gas you have now replaced Gas with Oil and have leaned the Motor put, all that black stuff is more Coking from the Heat and extra oil not Blow By.
Boom! She Seized... I've seen this so many times..
When you would have done a throttle chop the Plug will read the extra oil you have added and Not the true reading of lean or fat. it will show you a good to go and your dangerously lean..
Never ever do this, More is Not better. you will even run into detonation issues adding oil to two or four stroke gas.
Im big on higher end injection or pre-mix oils for Two stroke's

[czmdiver]

Oct 7, 2017 6:46:10 GMT -6 motley said:

Are we allowed to run a can of restore in these little engines?

So restore helps bring back compression on scored engines, etc etc. The stuff actually works!

www.restoreusa.com/index.php

No sir, this or any other product will never Repair Damaged Components like what you see in his pictures.
When a Piston Scuff's, Stick's, Seizes that material has become Liquid, and now the Heat Treat has now been taken out of the Piston, Tis Butter...
The other thong that happens to that piston is what in the industry call Skirt Crush or Skirt Collapse, the Piston has also now lost its size, so if you had .002 piston to wall you have more than .005 and its all over. No mechanic in a can is going to bring back the size of the Overheated now Butter Piston..
The Rings are Springs, Now overheated you will have collapsed them and lost significant ring seal, this can be clearly seen laying the overheated ring with a new ring, there done.. 
No product is going to put the Heat treat back in a Piston or Re-Spring and Collapsed Ring......

There may be a place for that crap in a old clapped out Farm-All or Don Deere to get the Field Plowed but I get get the same thing done with adding some Gear Lube to my Don Deere crank case...

[czmdiver]

Oct 8, 2017 11:52:48 GMT -6 czmdiver said:

Oct 6, 2017 19:45:46 GMT -6 nobodyspecial said:

Thank you all for your help. Yes I will take better care with the warm ups in future. I was running a #90 main jet. Plug is oily, while its apart I fitted an #80 and have an #85 on order. I will do a plug chop when its up and going. Is there a simple way of telling if there is a problem with the crank seal? Also while its apart I will test the oil pump is working properly. With the 80 kit I am running a combo of oil pump and premix. I think oil is not a problem as I am getting some blue smoke out of the pipe.

Darn hate when my worst hunch is true sometimes.
I had tell tale signs of the Piston pictures that made me suspicious of what you have going on with the Oil.
Oil is the problem, You have a Fixed Jet carb when you added that extra Oil to the gas you have now replaced Gas with Oil and have leaned the Motor put, all that black stuff is more Coking from the Heat and extra oil not Blow By.
Boom! She Seized... I've seen this so many times..
When you would have done a throttle chop the Plug will read the extra oil you have added and Not the true reading of lean or fat. it will show you a good to go and your dangerously lean..
Never ever do this, More is Not better. you will even run into detonation issues adding oil to two or four stroke gas.
Im big on higher end injection or pre-mix oils for Two stroke's

I thank you for the honesty and details,some withhold some things they do and we can env get to the bottom of what is truly causing there failures.

[cyborg]

And there needs to be a engine to frame ground strap