CG250 Performance Cam Installation.

[Megadan]

Okay, so I woke up a bit early and decided to try 1 change. Still a 35 pilot, Needle now in second slot, 140 main. Almost perfect until I hit the main jet on the throttle sweep. Now it feels just a tad dull and still struggles to pull past 62mph.

Skip forward to the adjustable CDI I was playing with. When I advanced the timing at the upper RPM ranges it started to pull a little stronger. Got a couple more mph out of it with it's not so perfect state of tune.

Another observation with my motor, it REALLY likes the ignition advanced in the lower RPM ranges. Let me put it to you this way. My big 270lb butt on a Hawk with decently tall gearing just effortlessly pulls away from a stop, and I mean effortlessly. I have to slip the clutch a lot less to get moving. It also idles way more stable.

[JerryHawk250]

Originally Posted by Megadan

Another observation with my motor, it REALLY likes the ignition advanced in the lower RPM ranges. Let me put it to you this way. My big 270lb butt on a Hawk with decently tall gearing just effortlessly pulls away from a stop, and I mean effortlessly. I have to slip the clutch a lot less to get moving. It also idles way more stable.

Funny you mention this. One thing i noticed is that leaving out my driveway this morning i didn't even need to give it throttle to move. i went through 1st, 2nd and third without touching the throttle.

[Megadan]

Originally Posted by JerryHawk250

Funny you mention this. One thing i noticed is that leaving out my driveway this morning i didn't even need to give it throttle to move. i went through 1st, 2nd and third without touching the throttle.

Yeah, me being a solid 100+lbs heavier I don't get that luxury lol. Still, it is much more effortless. I also have to give it a lot less throttle when cruising along, so as long as I can resist twisting the throttle I might see an increase in mileage.

[Megadan]

So, my little gamble on the pushrods paid off. I did some searching and couldn't find anything off the shelf for the CG250 that would work. Most options were either too small (3/16") or too big (5/16"+). Thankfully, Honda builds another engine that uses the same diameter pushrods as the CG engines, which is the GX390.

The good news is that the GX390 is a popular go cart and mini bike platform, so there is a good amount of aftermarket support for them. The downside is that most of the ready made GX390 Pushrods are too long. So that leaves option 3, which is to order a set of cut to length chromoly pushrods.

ARC Racing offers just such a thing. https://www.arcracing.com/dj-3070cl-...-individually/

They came in today, only 3 days to ship too, which was really amazing.



I ordered a set of GX390 lifters to assist with pressing them together. They were cheap, so why not. Prevents me from damaging the ends. I can always pass them along to someone else when I am through with them.

Anyway, I just figured I would prove that the ends are the same dimensions, so this first picture is the GX390 lifter and the original CG250 Cam follower.
The second picture is the end of the pushrod in said cam follower.





So on to the details. The CG250 Pushrods are 153mm long, or 6.024" long. Since I milled down my head 1mm, I am going to cut these pushrods to be a bit shorter at 6 inches even.

The pressed in tip is 5/16" long from flange to end, so I need to cut my pushrods to 5 11/16" long. Pretty straight forward. Hopefully I have the time tomorrow, but I may hold off until next weekend because I want to finish getting my jetting sorted and repack my muffler.

The jetting might not actually take very long though. Currently my idle mixture, pilot, and needle settings are spot on, and the bike pulls strong until you hit the last 1/8th bit of throttle, and it just goes flat, so it needs a bit more fuel. I just got my 142-150 main jets in, so I should be able to get it sorted fairly quickly. I might even take it out tonight and test one or two jets if I feel up to it.

[Megadan]

Jetting update: Ready for this? I ordered a 142, 145, 148, and 150 main jet right? The 145 improved the lean condition, but it still felt flat. The 150 cured it, but I think there is just a little bit more in it so I am going to order a 152 and 155.

Current Jetting Setup is as follows.
Pilot Jet: 35
Mixture: 1 5/8 Turns out
Needle: 2nd slot.
Main: 150.

So, if there was any doubt that there was an improvement in airflow, let's consider that before this point I was running a 132 -135 main jet depending on the air temps earlier this year.

Verdict on the cam. Definite improvement in power from 3000-8000 rpm. My bike will now pull to 8500 much stronger than before. In 5th gear I was able to pull to 8200rpm before I ran into traffic (that's 77mph), which is pretty heavy today being an almost perfect day and a Friday afternoon. I think with enough room on a flat bit of ground I could pull to the factory rev limiter and hit 80mph.

One thing I do think I can get away with now is to drop 2 more teeth on the rear sprocket and go for that 17/43 type gearing. I have enough power to spare to pull that off and have a true road capable highway machine.

If there was a shift in peak power, it was just a few hundred RPM, but more importantly is it helped level off the top of the power curve. It doesn't fall off as quickly as it used to. The best part is, it hasn't really lost any mid range, and maybe just a tiny bit down low, but the advanced Ignition curve on the CDI I have brought a lot of that back.

Do I think the chromoly pushrods are necessary? Not really, but I wouldn't shy away from them if you plan on doing this cam. I plan on installing mine once I get a couple of other things in to do all of it at once. I am then going to install the TT250 head gasket to increase my compression another half a point as well.

[Megadan]

Time for a little bit of educated bench racing. For the heck of it I decided to spend the time doing a little VE calculations based on jetting changes, both from a proper jetted stock bike (105 main jet), which likely made right about 15hp give or take a half a hp. Considering RPS rated them at 14.1hp with their too lean jetting I thing that is a fair assumption.

Now, give me some latitude here, because I already said this is a bit of educated guess work, but that 30% increase in air and fuel at WOT would put my bike right in the 19-20hp range. For a bike with port work, a full exhaust, compression increase, and a cam. I think that would be a fair number to assume. I will try to get a dyno session schedule sometime later this year if at all possible to confirm that number. That would put me around 18ish hp at the rear tire. Obviously that number could be higher or lower because there are so many other factors at work, but if it made around 18-19whp, I would be quite happy. Considering CCW's Heist made 21hp to the rear tire with a more aggressive cam profile and revving out to 9200rpm, I don't think it is that unreasonable to assume.

[mtiberio]

On my race Guzzi I had to tighten up valve clearances when I went to CrMo pushrods. They expand Less than Aluminum .

[Megadan]

Originally Posted by mtiberio

On my race Guzzi I had to tighten up valve clearances when I went to CrMo pushrods. They expand Less than Aluminum .

Yeah, I was actually considering that possibility as well. Not quite sure how much I would want to tighten the clearances, but I had considered going to .05mm intake and .06 exhaust. That would bring both settings in about .01mm from what I run now.

[Megadan]

Update, Part 2. As brought up previously:

Originally Posted by mtiberio

On my race Guzzi I had to tighten up valve clearances when I went to CrMo pushrods. They expand Less than Aluminum .

In anticipation of this I decided to start by setting my valve lash at the minimum spec for both valves, .05mm. On the factory pushrods the motor is usually fairly quiet, with just a faint tippety tap in the background but otherwise not very audible.

As many can attest, when you set the valves to .08-.10mm, the valve noise is more pronounced, but otherwise not bad.

This is how my motor sounds with the valve lash set at .05mm. I could try to tighten it up a little more and set them to .04mm, but I think I will leave well enough alone for now until the new pushrods get worn in a little. I personally don't mind a bit of engine clatter.

Just be prepared for this if you decide to go with chromoly pushrods.

[China Rider 27]

Originally Posted by Megadan

I will try to get a dyno session schedule sometime later this year if at all possible to confirm that number. That would put me around 18ish hp at the rear tire. Obviously that number could be higher or lower because there are so many other factors at work, but if it made around 18-19whp, I would be quite happy. Considering CCW's Heist made 21hp to the rear tire with a more aggressive cam profile and revving out to 9200rpm, I don't think it is that unreasonable to assume.

Alright! It is time for the numbers. How to get a CG motor to approach CCW's results is the quest!

[Megadan]

Originally Posted by China Rider 27

Alright! It is time for the numbers. How to get a CG motor to approach CCW's results is the quest!

If that were my goal, then I would start with this cam. https://wgkindustria.com.br/produtos...-alta-rodovia/

Port the head and use proper multi angle valve seat cuts with back cut stainless valves, The above pushrods, better valve springs because you WILL have valve float issues, mill the block a couple of mm to reduce the quench gap to less than .035" And then have a custom forged piston made because your compression ratio after that jug being milled will be right around 12:1 on a stock one.

Then you just need a 32mm carb.

[China Rider 27]

Sounds like a plan to me!

[Megadan]

So, I wanted to give it a little bit of time to ride the bike with proper jetting to really get a good idea of how this cam changed things.

To start, yes it did make a big improvement. It did not increase the RPM range that my motor can take advantage of, nor did it shift the power curve much at all. It does pull a lot stronger, especially up top, but I am still limited to nearly the same rev range as before. It will pull to about 8200rpm now, and from 7500-8000 is a lot stronger. The mid range power is rather impressive as well.

On the road I find it much easier to reach a top speed of 75 than before and I am less affected by a headwind. Hills present less of a challenge to the bike than before, and I am able to leave it in a higher gear around corners and just tractor away.

They might call this a "race" cam, but on the CG250 I would call it a street cam. It could be run on a motor with no head porting and likely make a decent difference, but when combined with a head ported to maximize low lift airflow through the intake and an uncorked exhaust, it is one hell of a combination.

If this disappoints you, then I would suggest looking into one of the other cam profiles that has added lift. Those camshafts are designed specifically to create power higher in the RPM range, and one in particular will greatly shift the power curve. Just understand that these profiles will require other supporting mods like valve springs, machine work, etc. in order to properly function.

[duck9191]

I wonder if they would give us a break on a group buy.

[duck9191]

or talk peace/csc into stocking them...