Some of the most popular performance mods with videos

How I have my exhaust on my Kulana Moon Dawg bike, it ain't pretty but gives my good all around performance low is good for hills and top speed on the flat is 43+MPH

Same here... Not pretty but it gets me to 40mph, still using the 44 tooth rear sprocket too... this is a modified KTM50 pipe that's been cut up and re welded so it would fit, and I've added in a 4" section to the belly from a pocketbike expansion chamber for better low end power...

Davezilla said:

Same here... Not pretty but it gets me to 40mph, still using the 44 tooth rear sprocket too... this is a modified KTM50 pipe that's been cut up and re welded so it would fit, and I've added in a 4" section to the belly from a pocketbike expansion chamber for better low end power...

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Wow Dave, 40mph with a 44T tells me that little china girl is twisting up like crazy, I've thought about putting a 41T I have on mine just to see how it will pull and what the Top speed will still be, the pipe on mine gives it good low to mid and does sacrifice some on the top, I had another pipe on this pipe that I build and it would do 45-46mph on the flat with it and I had a Puch Hi Hi 70cc head on it then also, dont think the head had anything to do with it but the exhaust that flowed better for sure gave it the better top speed and with a bigger carb I think it would have got a little more.

I'm pretty happy with how it is now, pulls me up the hills no sweat and will cruise low to mid 40's, this bike doesn't need to go faster than that for me, I came, I saw and I done 50+mph on the Western Flyer and now I'm done with that kinda speed on the current bikes I have.

I do like that pipe though Dave, the beauty of Red Neck engineering is a good things in my book.

Yup.. She's a screamin at this speed... just over 9k rpm if my math is right... And did it with the stock NT carb since I wasn't fully happy with the CNS, I took it off until I can get a better intake for it since I was spending more time fixing leaks than riding when I had it installed. It did work good when not leaking, but it barely got me home a few times so I ordered up a NT, bolted it on and went with it. It does 4 stroke on top with the NT, but I'd rather let it 4 stroke a little while the engine is still not fully broken in. I'd much rather add in a cylinder head temp gauge before rejetting too just to play it safe, but I'm really happy with the way this one turned out so far.

Davezilla said:

Yup.. She's a screamin at this speed... just over 9k rpm if my math is right... And did it with the stock NT carb since I wasn't fully happy with the CNS, I took it off until I can get a better intake for it since I was spending more time fixing leaks than riding when I had it installed. It did work good when not leaking, but it barely got me home a few times so I ordered up a NT, bolted it on and went with it. It does 4 stroke on top with the NT, but I'd rather let it 4 stroke a little while the engine is still not fully broken in. I'd much rather add in a cylinder head temp gauge before rejetting too just to play it safe, but I'm really happy with the way this one turned out so far.

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Nothing wrong with the NT carbs at all, for best all around reliability I think it would be hard to beat the NT and NT speed carb which I really like since fuel line size isn't an issue and I can use regular 1/4" line if I need to.

The Dellorto clones have given me good performance and reliability also and I like the choke that will kick off with a quick wrap of WOT when bike warms up a bit, the RT carbs do seem to give a tad better low end pull at low rpm's and will flow just as good if not a little better than the NT's.

I have a new older model CNS and I have a shorty manic type intake special made just for the CNS, I may try using it on one of my next builds just to see how it acts, I bought a good used GT5 lower from a forum member today, I've never built a GT5 and he said this engine was a really good performer when he was running it before a wris tpin retainer clip came out and ruined the piston and jug, I'm just getting the lower and I'll build it up from there to replace the oldest and worse vibrating engine I have on the old Black Mountain bike, the member I bought the engine from said he ran a Pk-80 jug on this GT5 lower and it ran very strong, I dont know enough about the GT5's to know why this worked for him and what the actually differences are in the type A jug and the Type B jug, it seems I remember that there are about 2mm difference in port position or something like that but I dont know.

Sounds good with the GT% bottom those engines can make some surprising power at rpm... I know Roger built a few and he swears by them.

yeah, the NT carb is best when it comes to simplicity and reliability, I had a speed carb and like it but was always clogging up the jet with rubber from the built in fuel valve so I got the CNS, liked it when it was working, but without the right intake it kept leaking every few rides so I took it off and ordered the humble NT to get the bike broken in... I'm still on my second tank but it's running really strong and each ride is starting to get a bit stronger or faster.
I've also got an older Morini engine I hadn't decided what to put it in, but it came with a genuine Dellorto 14-14 sha carb so it'll most likely find it's way on this engine and a bigger Mikuni for the Morini when I decide to build something around it.

YesImLDS said:

The bottom end was able to hit 47mph slightly downhill with 45 being the fastest it hit on flat. This was with a 36T on a 26 inch wheel which I think is right around 9k rpm and was very strong indeed! That was with the PK80 jug on there and a heavy huffy cranbrook. At the time I didn't know there was a difference between the jugs so I just bought one from BGF on ebay. Ran great before the retaining clip destroyed it! Was looking at it yesterday and the crank was very well cast and was very true. Should be a good contestant for a top performing bike!

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LOL, I figured you would chime in here, I wanted you to be the one who said who I'm getting the lower from, I didn't want to mention you without your permission, I have a couple extra Pk-80/Type A Jugs in my stack of stuff so I may look and see how thing line up when I'm ready to go together with the engine.

Thanks again, YesImLDS

By the way, not to be disrespectful in any way here but, when I just types out your user name something came into my head and made my laugh.

I'm just hoping this engine works out good and I'm not say YesIneedLSD by the time I get it done...LOL!

Sorry I know that is dumb humor but it came to mind and made me laugh so I thought I'd share.

Peace, Shan

Davezilla said:

Sounds good with the GT% bottom those engines can make some surprising power at rpm... I know Roger built a few and he swears by them.

yeah, the NT carb is best when it comes to simplicity and reliability, I had a speed carb and like it but was always clogging up the jet with rubber from the built in fuel valve so I got the CNS, liked it when it was working, but without the right intake it kept leaking every few rides so I took it off and ordered the humble NT to get the bike broken in... I'm still on my second tank but it's running really strong and each ride is starting to get a bit stronger or faster.
I've also got an older Morini engine I hadn't decided what to put it in, but it came with a genuine Dellorto 14-14 sha carb so it'll most likely find it's way on this engine and a bigger Mikuni for the Morini when I decide to build something around it.

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Sounds like a good plan Dave

Knock on wood I have never had any issue with any rubber or anything else breaking loose on the NT Speed Carb, I got mine from BGF but I'm assuming they're all made with the same gaskets/seals but maybe not.

47 sounds about right with the 36 tooth and a strong enough engine... From what I've heard from Roger and a few things Fred has mentioned on his site, the GT5 does offer a few advantages when it comes to making more power than these things are built for... Fred's pretty secretive about what upgrades give the most effect... until you buy a few parts from him, then he'll open up some. Roger on the other hand is more than willing to share and he also knows a lot about the GT5... he actually prefers them over the pk80 type when we got into deeper conversation before. I know part of the secret is the bigger 40mm bolt pattern makes for lots of room to widen ports, The shorter stroke and higher piston pin hight may also play into how the port timing can be set by raising or lowering the jug to suit the bike's needs etc...

The shorter stroke does play a little in how much max rpm you can run, but it also has another effect on port timing and duration which also contributes some to it. The PK80 type does take a bit more coaxing to get good power out of them but simple stuff like a good pipe, and cleaning up the transfer ports is enough to really be noticeable. I tried running just one ring before too and it was a bit sluggish at low speed but got really strong once the rpm's rose up, it did lose compression after a really sort time tho, but that's the strongest I felt the bike pull going slightly uphill.
What I've done to the engine I got in it now is a 6cc Fred head and set the squish clearance to .75mm, extensive intake, exhaust, and transfer porting, raised the roof of the exhaust side 1mm and rampped the piston down 1mm, then widened the port 1mm on both sides. the intake side I brought the floor down by 1mm and widened 1mm on both sides, then cut 5mm off the back of the piston skirt. The transfers both got the casting ridge cleaned out, some slight re shaping, and streamlining at the bottom of the jug, then the transfer openings at the bottom ob the jug and top of the case were match ported, gaskets needed some serious trimming to stay out of the way too. All gaskets for the base and head are copper and I had to use a .040" thick aluminum spacer at the base along with a .025 copper gasket, then up top I'm using a .016" and a .025" copper gasket on the head all sealed with gasket shellac before assembly and torquing. The jug had .055" milled off the top and about .040" milled from the bottom which gave me enough room to put the ports exactly where I wanted them to be, but the main reason for shaving off so much up top was just to get a nice true flat surface, the bottom was more for seting the squish on my first engine, but I needed a spacer for it to work on this bottom end, the piston protruded out of the top of the jug about 1mm hence the spacer, but it worked once everything was in place.
The intake manifold is stock but i bored it out to 16mm on my lathe so no restriction there, then the pipe is off a KTM50 dirtbike that was cut up and welded to fit, I also added 4 more inches to the belly section so the pipe would hit at around 5 to 6k rpm and it stays strong well past the 9k mark. I don't remember of the top of my head what the port timings were, but the durations were about 12 degrees higher than most people recommended, and the static compression ratio is 12.7:1, actual is lower than that so it still runs ok on 93 octane on these cooler days. take off from a dead stop is smooth and decent but as it reaches past about 15mph it starts to pull harder and harder all the way up to top speed where it begins to break up and 4 stroke a lot, but backing off the throttle just a little will usually clear up the 4 stroking and net me a few extra mph... until I can jet it a bit leaner and clean up the top end performance, but for now I want it rich and blubbery so I don't blow it up before I even get it broken in...

I got some posts in here somewhere showing how I made a degree wheel and a dial indicator mount fixture to set the port timing and I set the squish clearance using a piece of solder and dial calipers, it's also really easy to do and you just need a variety of different thickness head and base gaskets... a bit tedious, but pays off nicely.

You can actually do some pretty good porting without all the measuring and math, just raise the roof on the exhaust port 1mm then widen it 1mm on both sides and keep it as round as possible, same for the intake, but lower the floor, then just clean out that nasty casting ridge in the transfers. That along with a decent pipe should get ya well past the 8500 rpm mark or better. If you still want more, you can ramp the piston since the piston is cheap just replace it for about $11 if you go too far, but once you get everything working as desired, you could cut out the same amount you ramped into the piston and put an uncut piston back in for a little better compression and a complete squish band, just gotta cut out the 5mm from the bottom of the skirt on the intake side to complete the job each time you swap pistons.
The important thing is whatever you do to one transfer port, try to get them as exact to eachother as possible, whether is.s just a casting ridge cleanup or raising the top a little more, they need to be very close to the same or exactly the same size shape, and angle.

The math really came into play a lot on mine because I cut so much off the top and bottom of the jug but raising or lowering the jug moves all the ports up or down which can move the opening and closing timing and duration pretty far. A high jug will give more power on top but lose some bottom end and bringing the jug down lower moves the power to the bottom end and can limit the top end rpm... Fairly easy to do by swapping out base gaskets, but bringing the jug too low and then ya need to add more head gasket thickness so the piston don't hit. You can go as close as 0.25mm piston to head clearance, but if a bearing wears out prematurely it'll hit so keeping it above 0.5mm but below 1mm is considered in the good range. The tighter the squish, the better. but if one gets too greedy they may hit the head and ruin the engine on short order either by letting it get too hot or if a bearing has too much play etc. But there is also a good amount of power to gain just by setting a tight squish clearance, it helps prevent detonation so you can get away with more ignition timing or lower octane fuels and higher compression etc, there is a limit to how well this works, but it's usually well enough to run a 6cc head on 93 ocrtane with the stock cdi.