Finally got the Mack Mag built!

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#1
755E204D-5C72-4740-A9FB-F324BF01D5CD.jpeg
46F2BDFF-848C-4FA3-8A84-1769C553A0DF.jpeg
D33D9117-0DE5-44FA-8D37-3853F79FE801.jpeg
F0BF9F86-3EC3-4263-BF9B-65A0F0C7F8F1.jpeg
3F1AB324-3B46-497D-954E-436D1E5BBAE0.jpeg
C24FEE51-3282-408C-8CDD-ED35063436CB.jpeg
02E63D14-D748-4CDA-85AF-3D497C339418.jpeg
Finally got the Mack Mag rollin! Pretty tight fit with the high comp head so I figured out a great, cheap, and easy way to extend the intake. I use a length of radiator hose and wrapped the connection very tightly with EZ fuse tape. This stuff is really excellent stuff and can resist temps up to 500 degrees so it’s perfect for lots of motor bike applications. It created a completely leak proof seal on each end of the extended intake with only 9 inches of the tape each. I wrapped it super tight and then used a zip tie just to keep it in place while it sets for 24 hours. The reason I posted a few photos of the carb is because I cannot figure out how to stabilize/attach the newly extended carb to the bike? I have some temporary Velcro holding it against the seatpost for now but was looking for suggestions!? I have an MZ 65 pipe ordered and on the way and I’m currently looking at a nice banana seat to drop my but down a little lower and back some since it feels like I’m sitting so high on the bike. And lastly does anyone have any suggestions on how to rearrange my handlebar situation? The left side with the clutch isn’t an issue reaching the clutch pad over the shifters but my right side with the throttle and double brake lever is a real stretch to get it to stop and makes me uncomfortable trying to reach for the lever especially at higher speeds. I tend to twist the throttle when stretching for the brake lever and it feels unsafe ha. Thanks in advance!
BE2CD6D3-83B2-4BC8-9395-70D51CDE7E5D.jpeg
A06CF0D7-6871-4EE2-BC4E-44D17939B3F6.jpeg
B6633D78-6CA0-4F1D-B079-9A23AC0F1A11.jpeg
 


FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,192
Likes
517
#2
Looks like it's coming along nicely. I like the idea of the self fusing tape. I have a lot of sticky residue from the electrical insulation tape on my bike lol. :)

Carb: when you tie one cylinder/ convex shape against another it tends to wiggle and rock, so you might make something to fit between the two which will stop that. It could be hot melt glue pumped straight into the space while the carb is in position, or it could be epoxy putty or even liquid epoxy held in shape by some electrical insulation tape.

Handlebars: I think it was @crassius who posted a photo recently in the thread about gears on a mountain bike build of a stub thing that fits to the bars and can be used to mount a gripshifter at right angles to the bar. I would probably try a SRAM trigger shifter, where the up and down levers are both operated by the thumb (as opposed to the Shimano ones that are thumbnail and index finger).
You could also try just putting the gripshifter inboard of the brake, for now. :)

Edit: bloody autocorrect never lets me spell Shimano. Or autocorrect.
 
Last edited:

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#3
Looks like it's coming along nicely. I like the idea of the self fusing tape. I have a lot of sticky residue from the electrical insulation tape on my bike lol. :)

Carb: when you tie one cylinder/ convex shape against another it tends to wiggle and rock, so you might make something to fit between the two which will stop that. It could be hot melt glue pumped straight into the space while the carb is in position, or it could be epoxy putty or even liquid epoxy held in shape by some electrical insulation tape.

Handlebars: I think it was @crassius who posted a photo recently in the thread about gears on a mountain bike build of a stub thing that fits to the bars and can be used to mount a gripshifter at right angles to the bar. I would probably try a SRAM trigger shifter, where the up and down levers are both operated by the thumb (as opposed to the Shipman of ones that are thumbnail and index finger).
You could also try just putting the gripshifter inboard of the brake, for now. :)
Good idea on the handlebars! I’ll check into those options! And as far the carb suggestion are you talking about gluing the intake to the seatpost? Also while I’ve got you I figured I would ask. As I add higher performance parts do I want to be jetting higher or lower? Say if I add an MZ 65 pipe will I want to jet higher(richer) into the 70’s or lower(leaner) into the 60’s, assuming the stock jet in the NT is a size 70?
 
Last edited:

FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,192
Likes
517
#5
Good idea on the handlebars! I’ll check into those options! And as far the carb suggestion are you talking about gluing the intake to the seatpost? Also while I’ve got you I figured I would ask. As I add higher performance parts do I want to be jetting higher or lower? Say if I add an MZ 65 pipe will I want to jet higher(richer) into the 70’s or lower(leaner) into the 60’s, assuming the stock jet in the NT is a size 70?
No I don't mean to glue it on, the hot melt glue would have a very low adhesion to the cold, smooth powder coated frame and the metal of the carb, but it would mould into the shape of the space between the two convex surfaces, so when you use the cable tie to secure the carb there will be no rocking and wobbling. I have a plastic adapter for my plastic air filter so I was able to use a knife to make the appropriate shape to fit against my seat tube, but I did use hot melt glue for steadying a few other bits including the tachometer.

High performance is just a marketing term, utterly meaningless lol, but I believe @gary55 mentioned that the tuned pipe has a leaning effect so you would need a larger jet, assuming the stock jet is correct. But the stock jet is probably a bit larger than it needs to be with the stock exhaust (and that's good for the break-in stage), so you never really know until you try it.

Also for the gear shifters, I find that I like having the rear gripshifter on the left, because I don't want to have to let go of the throttle at all, and I am twisting the throttle back with my right hand to go faster, so it should be natural to twist the left hand gripshifter the same direction to stay in the correct gear.
I actually ended up putting a gripshifter (inverted) on the left side for the rear gears and also a thumb shifter for the front gears on the same side. So at the very least I would say switch your shifters around and have rear gears on the left, inverted.

If you decide to try the sawn off bar end, be aware that of the few bar ends that have a round cross section, most of them have a larger diameter than your handlebars, probably 25mm instead of the 22.2mm that you need to fit a gear shifter. Those that are 22.2mm are nearly all old stock/used early steel ones. When you see bar ends advertised as 22.2mm they are nearly always just referring to the handlebars that the bar end is made to clamp onto, not the diameter of the grip section of the bar ends themselves.
 
Last edited:
B

bike4life2

Guest
#8
I am bike4life, just at school and forgot login credentials as they are auto-saved at home.
Why did you remove the rear disc brakes ? I have a similar mongoose bike w/ disc brakes and you just have to extend the disc brake over 1/2" with some steel plate and then extend the actual wheel over 1/2" with 4 washers stacked.
 

FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,192
Likes
517
#9
Do you by chance have a picture of what you’re talking about?
He means mountain bike bar ends. I guess they were first popular with cross country mountain bikers, uphill cyclists did wear spandex before the invention of lycra but then it is useful stuff if you don't want to chafe to death lol.
Crassius posted these photos:
https://motoredbikes.com/threads/can-you-still-use-your-shifters.52886/#post-463742

Here's my picture of some mtb bar ends, including a pair of rather rarer alloy 22.2mm bar ends. This narrow diameter is usually (not always) steel, and old, since the larger diameter is much more comfortable.
_20180611_140247.JPG
 
Last edited:

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#10
Thanks for the replies! The bike is running great so far took it out on the maiden voyage today! First bike I’ve built with absolutely zero vibration at all RPM ranges. I’m still with the stock jet, which feels rich and four strokes, and did have to move the c clip to the highest notch since it was running really rich. That brings me to my question... at idle with the clutch pulled I can rev the bike and it’ll rev up and return to idle normally just like before, however while I’m riding if I pull the clutch to coast or whatever the bike takes longer than normal to returun to idle... what is causing this? The rpms seem to hang for a bit and then eventually return to the idle rpm... does this have to do with the extended intake by chance? This engine was actually broken in on another bike and the carb was placed normally on the intake manifold so this is my first experience with an extended intake. Just curious if anyone knew what might cause this? Thanks!
 

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#11
He means mountain bike bar ends. I guess they were first popular with cross country mountain bikers, uphill cyclists did wear spandex before the invention of lycra but then it is useful stuff if you don't want to chafe to death lol.
Crassius posted these photos:
https://motoredbikes.com/threads/can-you-still-use-your-shifters.52886/#post-463742

Here's my picture of some mtb bar ends, including a pair of rather rarer alloy 22.2mm bar ends. This narrow diameter is usually (not always) steel, and old, since the larger diameter is much more comfortable.
View attachment 82274
Man Furry you’re always on point on these forums! Kudos to you! That’s a great idea thank you! I did however rearrange my handlebar situation and cut the stock throttle grip down a bit which allowed me to sleeve the bikes actual grip back over it, for now everything seems to be working out well!
7A93F052-2722-4058-B317-5D20EB66805F.jpeg
 

FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,192
Likes
517
#12
Man Furry you’re always on point on these forums! Kudos to you! That’s a great idea thank you! I did however rearrange my handlebar situation and cut the stock throttle grip down a bit which allowed me to sleeve the bikes actual grip back over it, for now everything seems to be working out well! View attachment 82279
Hey it was Crassius' idea not mine!
I still think you should switch the shifters to the opposite side but meh, whatever makes you happy, you know. :)


Thanks for the replies! The bike is running great so far took it out on the maiden voyage today! First bike I’ve built with absolutely zero vibration at all RPM ranges. I’m still with the stock jet, which feels rich and four strokes, and did have to move the c clip to the highest notch since it was running really rich. That brings me to my question... at idle with the clutch pulled I can rev the bike and it’ll rev up and return to idle normally just like before, however while I’m riding if I pull the clutch to coast or whatever the bike takes longer than normal to returun to idle... what is causing this? The rpms seem to hang for a bit and then eventually return to the idle rpm... does this have to do with the extended intake by chance? This engine was actually broken in on another bike and the carb was placed normally on the intake manifold so this is my first experience with an extended intake. Just curious if anyone knew what might cause this? Thanks!
My guess, and it is just a guess, is that the fuel is foaming inside the carb bowl because it is not rigidly attached yet. If it has any wiggle room it can shake like one of those paint mixer things. That's why I was saying about putting something between the carb and the frame so they can be strapped snugly together with a cable tie. The foamed fuel would cause a lean a/f ratio, consistent with the symptoms you describe.
 

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#13
Hey it was Crassius' idea not mine!
I still think you should switch the shifters to the opposite side but meh, whatever makes you happy, you know. :)



My guess, and it is just a guess, is that the fuel is foaming inside the carb bowl because it is not rigidly attached yet. If it has any wiggle room it can shake like one of those paint mixer things. That's why I was saying about putting something between the carb and the frame so they can be strapped snugly together with a cable tie. The foamed fuel would cause a lean a/f ratio, consistent with the symptoms you describe.
But wouldn’t leaner show on the plug? When I pull my plug now it’s dark and oily doesn’t look lean... but I do need to do why you described and attach the carb to the frame more solidly.
 

FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,192
Likes
517
#14
But wouldn’t leaner show on the plug? When I pull my plug now it’s dark and oily doesn’t look lean... but I do need to do why you described and attach the carb to the frame more solidly.
I think it wouldn't show on the plug because the rich condition returns when you slow down or idle the engine at a standstill so the plug would get a fresh coating of oil. We'll see what happens anyway.
 

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#15
I think it wouldn't show on the plug because the rich condition returns when you slow down or idle the engine at a standstill so the plug would get a fresh coating of oil. We'll see what happens anyway.
Hmmm I definitely don’t want to run lean. Sounds like it’s four stroking at WOT but maybe your right about the plug re-oiling itself at idle. Worries me a little bit, I’ll try and temporarily rig something between the carb and frame and see if that changes anything.
 

Carcher

New Member
Joined
May 26, 2018
Messages
10
Likes
0
#16
I am interested in your cylinder head! How is it working/ cost? Also does it produce more RPM? Also what is it called?? Carcher
 

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#18
He means mountain bike bar ends. I guess they were first popular with cross country mountain bikers, uphill cyclists did wear spandex before the invention of lycra but then it is useful stuff if you don't want to chafe to death lol.
Crassius posted these photos:
https://motoredbikes.com/threads/can-you-still-use-your-shifters.52886/#post-463742

Here's my picture of some mtb bar ends, including a pair of rather rarer alloy 22.2mm bar ends. This narrow diameter is usually (not always) steel, and old, since the larger diameter is much more comfortable.
View attachment 82274
Here’s another idea I really like for getting unwanted shifters and accessories off the main bar.... $15
9BF761EA-B022-462F-946B-F9C6803E4C0A.png
ED6FA665-99E1-4168-AE5D-33527D4ABED0.png
DEB4E1B8-5193-460F-A4CC-80B5A88C4172.png
 

FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,192
Likes
517
#19
Here’s another idea I really like for getting unwanted shifters and accessories off the main bar.... $15
View attachment 82282 View attachment 82283 View attachment 82284
I just fitted one of these, but I have plenty of room for (from left to right) rear gripshifter, front rapid-fire shifter, rear brake lever, clutch lever, tach, (extension bar mounts), small light, speedo, bell, front brake lever, and twist throttle all on my new narrower (610mm) handlebar.
The phone, I believe, is better on the top tube of the frame because there's slightly less shocks from the road surface in between the axles.
I am using the extension bar just as a support/mount for the Bluetooth stereo speaker. :D
DSC_0012.JPG

DSC_0014.JPG
 
Last edited:

Kpi890

Active Member
Joined
Nov 6, 2017
Messages
349
Likes
30
#20
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!?
 

Top