Cylinder porting problem?

[Ivan168]

Hi again, after getting a lot of good advice on buying an engine I have already overcome the first problem, after starting the engine everything seemed fine, but it seemed good to port the cylinder and grind the head with 1mm after doing all the work and fitting everything in places and tried to start the engine, the piston hit the electrode of the spark plug, it turned out that I had ground the head more than 1mm, and I had to remove the extra thin copper gasket and put the original one and that solved the problem, after starting the engine it turned out that runs much worse than before, almost no bottom end and top speed is down, i don't know what this is, and i really don't know what to do, i feel like i have filed the intake and exhaust hole too much and that is causing the problem, i removed the spark plug and it was white on the electrode if that matters i tried all the carb needle positions but still that didn't fix the problem what can i do??

 

[robe]

You may have killed it. Doesn't take much to wreck it. I don't want to be the bearer of bad news but there you go.

 

[Chainlube]

When it comes to porting, 1 mm is a lot. If you take 2 or more mm off the roof of an exhaust port, the chances of the fresh charge passing through the engine unburnt increase. A little wider is always helpful, but to increase the height of the port you need a degree wheel. Then you can measure how far the piston will move before the cylinder just becomes a hole and holds nothing back.

 

[DAMIEN1307]

When it comes to porting, 1 mm is a lot. If you take 2 or more mm off the roof of an exhaust port, the chances of the fresh charge passing through the engine unburnt increase. A little wider is always helpful, but to increase the height of the port you need a degree wheel. Then you can measure how far the piston will move before the cylinder just becomes a hole and holds nothing back.

Yeah, I remember your warning to the OP on one of his other threads when you tried to warn him how to do the porting the right way to begin with.

Only change the width of the intake and exhaust ports, or you'll make a nice paper weight.

 

[Ivan168]

When it comes to porting, 1 mm is a lot. If you take 2 or more mm off the roof of an exhaust port, the chances of the fresh charge passing through the engine unburnt increase. A little wider is always helpful, but to increase the height of the port you need a degree wheel. Then you can measure how far the piston will move before the cylinder just becomes a hole and holds nothing back.

Yeah I think that's the reason, I've been reading a lot of threads about porting but I haven't made a distinction between top and side, and apparently I've taken a lot from the top of the exhaust port, and now most of the crap mixture leaves the cylinder before it burns, the only option i can think of is to fill the holes with JB weld and after it dries to file them again but this time properly, but i'm not sure that the glue will withstand the temperature in the exhaust hole, although it's worth a try anyway.

 

[Ivan168]

All in all I'm very disappointed, now I don't know what to do, I obviously shouldn't have been doing this, and I don't know where to find what a properly ported cylinder should look like, I've read a lot of people saying come on it's easy but apparently not it is so.

 

[Chainlube]

You can try filling the hole, but like you say, I don't think the JB will last very long. You need a new cylinder, and if you try gluing it, probably a piston too.

 

[Gordy]

There's so many books, articles, videos, and such on porting. Porting is a science of it's own. This might not be what you want to hear, but you should have looked into porting alot more than you did.

 

[Ivan168]

I bought a new cylinder and widened the exhaust port to the sides as you said instead of up, I did the same to the intake port but down, now it works better but I still feel like I can't get the most out of the porting, apparently I don't have enough knowledge to do such complicated things on the engine.

 

[DAMIEN1307]

I did the same to the intake port but down, now it works better but I still feel like I can't get the most out of the porting

Again, did you not see what chainlube said before that I also pointed out to you once before???

Chainlube said:
Only change the width of the intake and exhaust ports, or you'll make a nice paper weight.

He did not say up or down on either of the ports, he said "width" only.