Really Cheap Trail Rider.

[cannonball2]

So been reading a bit on the Cag style engine. Seems I have bought a 39cc. Judging by the cylinder finning its a 39/40cc 40mm bore. Guess I get to look forward to a big bore kit in the future($26). Bottom line is this engine rocks for is displacement!

 

[cannonball2]

A bit of an update. The chain keeper has worked flawlessly. Have not had a chain derail since its installation. Have switched from the break in 32:1 fuel to 50:1 Klotz R50 mix and the little engine is much happier. Still haven't received my jets but think it will tune with one size smaller jet. Seems its a trade off between midrange and top. I will shoot for a better midrange.

Now for the missing link for the Cag engine. The cylinder air guide. I have never seen one on an engine, but it is designed for it. Its obvious its missing. That's what the weird plug boot is for the seal the plug access hole. Maybe the guide is there when you buy a complete pit bike. This directs the air over the cylinder/head. With out it the air flows straight out the top of the fan shroud and not around the cylinder. With it travel is over the complete cylinder, blows like a hurricane even at idle. This has to greatly extend the life of this hard working little fella.

Theres a story to the guide. Its an Alabama M/C tag from my last BMW. This bike was originally owned by Piet Boonstra and made a trip from up state Ny to Alaska and was written up in one of his books. He put something like a 100k miles on it. He has the AMAs certification of riding over a million miles. I corresponded with him a bit a few years back and he sent me a signed book. I believe he was 88 then and still riding a Suzuki V-strom 650. Super interesting guy! Google him! Hope he is still with us!

 

[cannonball2]

Heres a link to his site and pics of the BMW. If you like M/C adventures hes your man! Go to the home page and read about his crash! http://pietboonstra.blogspot.com/search/label/Photos - Alaska 7

 

[Intrepid Wheelwoman]

That's a good use for an old numberplate (Kiwi for licence tag) CB. I have plenty of those kicking around so I might just do that myself

I'd been looking at the odd shaped plug boot on my engine too and had been working towards much the same conclusion.

 

[Ludwig II]

Have you put the shielding on to protect your extremities from the chains and sprockets yet?

 

[cannonball2]

IWW, the air guide is a necessary part of the cooling system. If you look at the fan shroud it has a slot for a mounting screw/nut and a snap peg to hold the MIA guide as well an an extrusion on the perimeter to engage in a lot on the guide. Don't know why they would remove them?? Kinda like selling a car with out a radiator fan!

L2, the answer on the chain guards is yes and no. The keeper on the right seems sufficient. I am adding a spring idler on the left chain run as soon as the stuff gets here. Will incorporate a guard with that. The pedals actually position the feet well away from the chains, but there is no certainty they will remain there under the rigors of trail riding, so guards will happen.

Rode the thing a bit more yesterday and the guide was forcing heretofore not felt hot air from the side of the engine. I feel more confident about riding slower sections of trails now when there is little ram air for cooling, which it was relying on with out the guide. The jets are to arrive today.

 

[cannonball2]

Got the idler made and rejetted the carb. The idler is spring loaded set at a very low tension just to keep the back side slack in check. The idler arm is half of a side pull brake caliper--love to repurpose! The carb originally had a 70 jet. The proper stock jet is a 64. I installed a 65 and things improved a lot, its snappier across the mid range. The top seems about the same but the low is a bit lean. I need the raise the needle one notch and I think that will have it. I also painted the air guide and laced it to the fan shroud with small cable ties. I believe these will be less trouble some than screws

About the last thing I need to do is add a bit of chain guard below the idler to keep Lud 2 happy, and dab a bit of black silicone around the weld at the small silencer where it is blowing a bit of spent oil. Once done its time to load it on the bike rack and head to the outback to put some real time on it.

 

[Intrepid Wheelwoman]

Way cool CB!

 

[mapbike]

looking good cb

 

[cannonball2]

Thanks yall!

Despite the Cags iffy reputation this one has done well. Always starts easily and has run reliably. Once the carb is totally dialed in should be a pleasant runner. The jetting took away most of the original peaky operation, though it is a banded runner. It could only handle the 70 jet well at the very top end. Im thinking maybe the carb was intended for the 47cc. I don't think the highly tuned engines will provide the same reliable operation as the little stockers and in my opinion should be avoided. The stocker is pretty smooth overall more so than a CG. It only vibes at the very top as it unloads. Mine cruises nicely/smoothly in 6th gear as its constantly loaded, its actually faster in 5th but more buzzy.

If one is looking to build a bike with good top end this is a cheap ticket there. Even a single speed version should produce some pretty good speed. The trick is finding a seller that actually knows the CC of the engine. Never seen one advertised as a 40cc, always a 47/49cc but I bet plenty of people are getting 40s! We will know for sure when I pull the jug on this one.

 

[cannonball2]

Got the carb sorted and the little Cag is running well. So well in fact if you are not well in the seat in low gear it will loft the front wheel. Moved the shifter to the left side and its more intuitive. I am really amazed that such a small displacement engine can produce such an amount of power even if its concentrated in a limited range. This is a sport bike engine for less than a hundred bucks!

 

[mapbike]

excellent cb...

 

[cannonball2]

Thanks Map!

Think I have finally sorted the engine to my liking. At the current temps in the mid 80s It has settled on a 60 main jet with the needle in the last(top) clip position. I finally figured out the Cag is so loud because the "silencer" is just an ornamental can. I stuffed the thing full of stainless Chore Boy pot scrubber and its down right quiet. No louder than the trimmers used daily in the area by the yard services. It seems to have moved the band down a bit, but that may be the reduction in noise. For outback riding the Chore Boy can be quickly removed if wanted. I can now ride the neighborhood with a clearer conscious.

Added a couple of mud boards to try to deflect the sand from the outback roads away from the BB and chains. Seem to work pretty well. The little bike is shaping up and operating well. Way more pleased with the Cag than I anticipated based on all the bad reputation.

 

[Citi-sporter]

I wonder if the CAG engines have a family heritage with the Italian made McCullough ProScaper II's weedie engines. The similarity to the cylinder on my 30cc weedie friction drive is uncanny.

Like your engine my Pro Scaper has a definite 'peak' to it's power, but for a 30 cc engine it also seems to pull well from lower revs. Pulling 'well' is comparative to the older Kioritz 32 cc I was originally going to use, which had hardly any low end at all. My engine is also really mild in vibrations when revved up.

I've looked at the CAG's in the past thinking there would be trouble with that light plastic pull rope starter/shroud. Do you think you could detune the engine some by raising the cylinder with extra gaskets?

 

[Ludwig II]

The designer was somebody called Cagliari in Italy, so there's a reasonable probability they have common ancestry.

 

[cannonball2]

This little bike is basically sorted out. Got it shifting very reliably, running well, and finally quiet enough for the neighborhood. The stainless pot scrubber worked very well stuffed into the "silencer" but the little B&S style muffler is much quieter. Amazingly it threaded into the exhausts end ring with a bit of coaxing and once tightened has yet to loosen.
The bike is very light and easy to load into a standard bike rack to go exploring in the outback.

 

[silverbear]

That's a sweet build. I bet it's a lot of fun to ride. Gears are good & so is inexpensive, too!
SB

 

[curtisfox]

Yep you build so simple and yet so effective, make me want to go dig out my motor and do something like it .....Curt

 

[cannonball2]

Thanks guys! This one is a pretty minimal build. Would really like to do a carbon frame version one day.

 

[Ludwig II]

Oh yes, carbon.