Finally got the Mack Mag built!

[FurryOnTheInside]

Alrighty I’m at a loss at the moment. I re-jetted my NT carb all the way down to 60 and it’s still 4 stroking at WOT. I then switched over to a new dellorto clone carb, which is really nice as far as throttle response and low-mid range, and also jetted it down to 60 and STILL 4 STROKING!!!?? I’m so confused, I’ve tried 3 different plug types and they all come out black and oily after running WOT and pulling the plug for a check. What is going on here? I have since secured the carb to the bike and I know it’s not running lean that’s for sure... what can be my issue I’m about to go crazy!?

Float height.. The little prongs on the needle valve can be bent downward so that the valve closes sooner. It ought to be okay the way it came, so idk.. I try to avoid messing with stuff like that.
Could be a hole in the float.. But not on two different carbs, you would think!
Air filter. Could be blocked, gummed up by oil residue. Clean with fresh gas or carb cleaner. That's the one I'd try first, since it can't harm anything.

I suppose that maybe it's still clearing out fuel from a flooded crankcase? I'm doubting it, but it's just another idea.

 

[Kpi890]

Float height.. The little prongs on the needle valve can be bent downward so that the valve closes sooner. It ought to be okay the way it came, so idk.. I try to avoid messing with stuff like that.
Could be a hole in the float.. But not on two different carbs, you would think!
Air filter. Could be blocked, gummed up by oil residue. Clean with fresh gas or carb cleaner. That's the one I'd try first, since it can't harm anything.

I suppose that maybe it's still clearing out fuel from a flooded crankcase? I'm doubting it, but it's just another idea.

Okay after swapping back to the NT carb I’m beginning to get where I want... I believe he issue came from me switching over to the dellorto clone, whew I think I’m okay haha! Thanks though Furry, my new question is with that dellorto clone I have heard they run rich, I had the lowest jet I have in it (60 size) and it was still four stroking pretty good. I really really love that carb though, the semi auto choke is pretty nice but my bike starts and runs much better until WOT with it. Do they make the 5mm jets for these carbs that go below 60? If I could tune that carb in and run it on th bike I think it’s a much nicer option. The bike idles much better, sounds, and feels better.

 

[FurryOnTheInside]

Okay after swapping back to the NT carb I’m beginning to get where I want... I believe he issue came from me switching over to the dellorto clone, whew I think I’m okay haha! Thanks though Furry, my new question is with that dellorto clone I have heard they run rich, I had the lowest jet I have in it (60 size) and it was still four stroking pretty good. I really really love that carb though, the semi auto choke is pretty nice but my bike starts and runs much better until WOT with it. Do they make the 5mm jets for these carbs that go below 60? If I could tune that carb in and run it on th bike I think it’s a much nicer option. The bike idles much better, sounds, and feels better.View attachment 82293View attachment 82294View attachment 82295

Well I have no experience with that carb. I only have a crappy NTTC carb and a big foam air filter. I would guess that the filter you have on there might be restrictive if the problem starts happening only at WOT. Where did you get the filter? Did it come with another carb? Is it restrictive at all?

 

[Kpi890]

Well I have no experience with that carb. I only have a crappy NTTC carb and a big foam air filter. I would guess that the filter you have on there might be restrictive if the problem starts happening only at WOT. Where did you get the filter? Did it come with another carb? Is it restrictive at all?

The filter came with the carb and I will try and test to see if it’s restrictive... I don’t have it on the bike right now due to it being so rich. Do you think the air filter could make it run that rich?

 

[FurryOnTheInside]

The filter came with the carb and I will try and test to see if it’s restrictive... I don’t have it on the bike right now due to it being so rich. Do you think the air filter could make it run that rich?

The so-called HP or High Performance carb that's all over ebay and everywhere has been widely reported on the forum that the air filter is restrictive, maybe even worse than the awful thing that comes with the NT and NTTC etc stock carbs on the kits.
Yes it could/would start to choke the air flow and richen the a/f once you get above a certain rpm with the throttle wide open because it has reached the limit of how much air can flow through it but your fuel flow isn't being restricted.

 

[Kpi890]

The so-called HP or High Performance carb that's all over ebay and everywhere has been widely reported on the forum that the air filter is restrictive, maybe even worse than the awful thing that comes with the NT and NTTC etc stock carbs on the kits.
Yes it could/would start to choke the air flow and richen the a/f once you get above a certain rpm with the throttle wide open because it has reached the limit of how much air can flow through it but your fuel flow isn't being restricted.

Hmmm now you’ve got my wheels turning. I guess I’ll have to swap it all out again tomorrow lol!

 

[FurryOnTheInside]

Hmmm now you’ve got my wheels turning. I guess I’ll have to swap it all out again tomorrow lol!

Haha, I know that feeling.

 

[Kpi890]

Update on the build! Got my carb running really close to what I think is perfect, got a 68 jet in there and I believe a 67 or 66 may be just perfect. Happy with that for now but I am eventually going to revisit the HP runtong carb. I added the banana seat that came today and I think it looks great on there, not the most comfortable of seats as it’s lacking most any padding at all but I do like sitting lower and rearward on the bike makes me feel like I’m going faster and it feels more stable at high speeds. My MZ 65 pipe is coming soon so prolly gonna have to mess with the carb again once I put that on, would I more likely go richer or leaner with jetting adding that pipe? Anyways here’s a pic! ... yea my wiring and all my cables are just temporarily ran for now hoping to take all that soon.

 

[Carl Walichnowski]

Update on the build! Got my carb running really close to what I think is perfect, got a 68 jet in there and I believe a 67 or 66 may be just perfect. Happy with that for now but I am eventually going to revisit the HP runtong carb. I added the banana seat that came today and I think it looks great on there, not the most comfortable of seats as it’s lacking most any padding at all but I do like sitting lower and rearward on the bike makes me feel like I’m going faster and it feels more stable at high speeds. My MZ 65 pipe is coming soon so prolly gonna have to mess with the carb again once I put that on, would I more likely go richer or leaner with jetting adding that pipe? Anyways here’s a pic! ... yea my wiring and all my cables are just temporarily ran for now hoping to take all that soon. View attachment 82303

Bikes looking good, as you know I have the same frame so I been following your build. Arw you going to do lights for the bike?

 

[Kpi890]

Bikes looking good, as you know I have the same frame so I been following your build. Arw you going to do lights for the bike?

Yea I’ve had my eye out for some cool retro looking motorcycle headlamps!