Okay so I believe the issues I’m having with both carbs is fuel backfiring from the carb, not sure how to fix the issue but I put the Runtong carb back on to see if it was the air filter causing the restriction. I put it on there without the filter and immediately upon startup I could feel/see fuel shooting out of the carb onto my leg!? Any ideas on how to fix this or what may be causing this?
Finally got the Mack Mag built!
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FurryOnTheInside
In Memoriam
Did you notch the piston skirt or lower the intake (increase the intake duration)?
Increased intake duration will have the effect of increasing the intake noise and reversion because a piston ported engine has "symmetrical" porting (intake is open while the piston is descending).
The only way to have very long intake duration and zero reversion of the intake flow is to have a reed valve that closes the intake when the piston is descending. Then you can make the duration as long as you want, in fact the windowed piston means it's as long as the pressure difference pulls air/fuel mix in.
A tuned expansion chamber exhaust pipe would help though, by drawing extra a/f charge from the crankcase while the piston is descending, before the piston closes off the intake port.
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I believe most of what you just said went above my head... lol. I’m just a little frustrated with it at the moment, is this normal? I mean when I say shooting gas out of the carb I mean I can put my hand down in front of the carb without a filter and feel gas shooting into my hand and my hand is wet with gas...normal? And to my lovely enjoyment I just was checking the intake area and found that the right side bolt of the intake is stripped now..... ughhhh any suggestions here now? You can see the crack on top of it and then if you look you can see what looks like the end of the bolt pushed the aluminum out near the end.
FurryOnTheInside
In Memoriam
I normally keep my hands on the handlebars so idk lol!
But you didn't answer my question about the porting work?
If you have lowered the bottom of the intake port or notched the bottom of the piston skirt on the intake side (same difference!) then you should get your expansion pipe and see if that helps. My guess is it will help but only at a certain RPM range.
As for the intake, if it's leaking from in between the fins, clean with carb cleaner and lump some JB Weld in there, I reckon (never tried).
Buy a spare cylinder anyway so you can have more fun with porting experiments!
Is the intake stud actually spinning loosely? I'd get the spare cylinder ordered ASAP and watch out for a lean condition caused by a leak of fresh air coming in past the intake gasket area because you don't want to be running lean.
Will'smotobikes19
Well-Known Member
Looks like you overtightened it, shame. Try some of the permatex steel weld. They also make a product that's meant for fuel tanks also in a tube. Or you could find someone that can weld aluminum and put a bead along that crack then you could re-tap the holes for 1/4 inch bolts. A new cylinder is $30 I think.
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For the porting and any piston work it is a stock Zeda80 that’s all I know nothing has been done to it on that aspect. As of right now I don’t notice any intake leaks or lean conditions, throttle revving is normal with normal come down from high rpms. I believe what happened is I switched intake manifolds while the engine was warm... so mad at myself, but I believe that’s what stripped it. As far as the spare cylinder goes I will probably order one tonight, like I said the engine is a stock Zeda80 what cylinder do I need to order for that or will most any stock china girl cylinder be fine? And for the expansion chamber I have an MZ 65 pipe coming soon so I’m looking forward to that maybe it’ll fix the fuel shooting issue like you said. Would getting a reed valve fix the issue, not letting any air/fuel mix back into the carb?
Yea I was looking closer at it and it’s holding tight for now with no air leaks but I don’t trust it for much longer. I may try and thread some spare M6 stainless studs in there and goop them up with some steel weld. I feel like I’d be better off with studs anyways instead of Allen bolts since anytime I mess with the manifold I’m completely unthreading and re-threading into the cylinder. I’ll order a new cylinder tonight. The engine is a stock Zeda80 would any cylinder for these china girls work okay for it, or is it engine specific?
FurryOnTheInside
In Memoriam
So it has actually stripped the threads, not just cracked the cast aluminium?
I was hoping you could get away with putting a grade 8.8 or higher stud into the hole with red loctite and that would be a decent seal for the crack too. The intake does not need to be bolted down particularly tightly, just snugged down as it's a vacuum in there not pressure trying to force its way out like the exhaust and head. The studs rather th an bolts allow you to snug down the first nut and then hold it while you torque down a second nut, which doesn't put the stress on the cylinder threads but is still resistant to shaking loose. Also as you mentioned you don't want to be unthreading and retreading into the (very bad) cast aluminium.Idk about the Zeda engines. I think it'll have the 40mm centre to centre stud spacing on the intake but you'll have to measure that, and the length of the cylinder, but maybe someone can tell you from experience about replacement cylinders for the Zeda 80.
The tuned pipe will surely help but only when it's "on the pipe" not when idling etc. as far as I know from reading this forum. I don't have a tuned pipe.
The reed valve intake is a lot different, you'll need a windowed piston, preferably some changes to the porting, and you'll have different engine performance characteristics that you may or may not prefer. But yes it should stop any reversion of the flow of the intake, reduce intake velocity (so larger jet needed) and thereby reduce noise too.
I haven't ported the spare cylinder to try out my RSE style (small) reed valve yet. I have used red loctite on my intake studs so I can't fit it on my current cylinder lol. It comes with bolts though maybe they can be switched for long studs, I'm not sure.
Will I have to break the engine in again? And I can still use the same piston and rings right in the new cylinder right?So it has actually stripped the threads, not just cracked the cast aluminium?
Idk about the Zeda engines. I think it'll have the 40mm centre to centre stud spacing on the intake but you'll have to measure that, and the length of the cylinder, but maybe someone can tell you from experience about replacement cylinders for the Zeda 80.
The tuned pipe will surely help but only when it's "on the pipe" not when idling etc. as far as I know from reading this forum. I don't have a tuned pipe.
The reed valve intake is a lot different, you'll need a windowed piston, preferably some changes to the porting, and you'll have different engine performance characteristics that you may or may not prefer. But yes it should stop any reversion of the flow of the intake, reduce intake velocity (so larger jet needed) and thereby reduce noise too.
I haven't ported the spare cylinder to try out my RSE style (small) reed valve yet. I have used red loctite on my intake studs so I can't fit it on my current cylinder lol. It comes with bolts though maybe they can be switched for long studs, I'm not sure.
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