Cuyuna 440 First Test

[Groundhog]

Finally able to get a really old Max running with a cuyuna.
I have a few questions:

Are the cuyuna 440's really hard to pull start?

Is it normal for the power to be kina shallow thru the middle rpm range, then violently coming in at really high rpm? It is a challenge to drive, sorta like a modified 125 2 stroke. The power goes from ~10 hp to ~50hp right around 5500rpm like a switch. When power band hits, all 6 wheels spin and things get scary. Are these engines known to be this jumpy?

My last ride today spapped both of my rear chains and whadded them up on my rear sprockets. It was a great 20 minutes tho!

[6X6]

Hi: The Cuyuna is a powerfull little motor, but I don't know about it being that peaky. I have 2 but neither installed in something, YET. If you're off on your low speed adjustments, you'll also have poor low end and then as the engine clears out it'll start hauling. Poor clutching or a worn belt can also do this. Worn belt- Once the engine gets the clutches open and winds out it'll go, but it'll be starting in too high a gear. Poor Clutching - ??? really depends on whats off, but a worn secondary spring may be allowing it to open to high gear too quick. THAT would also do this. Just a few possibilities.

[hydromike]

There really isn't a "powerband" on the Cuyunas when they're installed in our sorts of machines, unless you have a very well tuned pipe, which is a real rarity. The JLOs/ Cuyunas I've run seemed to make quite respectable low end (<3000) rpm when the drive and driven clutches are set up correctly. Do you know if you're running stock clutches? Are they both in good condition (springs/rollers/shaft)?

The horsepower curve for a VERY similar engine (made by 2si, who bought cuyuna, who bought JLO) is here.....
.

They used to publish the curve for the 2si ULII02, which is basically a better breathing 440 Cuyuna. The curves were basically identical, but they're just shifted a bit. You can see it's basically a nice climb to advertised redline. Again, this is stock. No tuned pipe, which makes a big difference, but not always a better difference.

Is the engine just hard to pull over because it's physically difficult, or do you have to pull it over for a long period of time before it starts? A fresh Cuyuna should have at least 140psi per cylinder, but I don't think it's really difficult to pull over. If the issue is the latter, try squirting a little gas right into the carb with the throttle open and pull it over. It should fire right up if everything else is in order.

~m

[LarryW]

Hey Groundhog, You need to kick me in the XXXX's! I forgot all about your parts again. I'll try to get them ready by this weekend.

[Groundhog]

6x6, Thanks for the info! The driven clutch is not in the greatest shape. I can see where the hub is sliding up the ramps, but the spring may be soft. The belt surface has some rust, maybe that makes things jumpy.

hydromike, Thanks for the info, awesome power chart! The Cuyuna motor has the clutch it came with. The Max had a JLO440 originally with the stock driven clutch used on that combo. The engine just seems physically hard to pull start. I guess as I get it running better it wont seem so hard.

I did make an expansion chamber for the Cuyuna. It is just some various junk welded together. In the past I have carefully followed the expansion chamber design book and made useless crap. This time I just hacked things together, and it is possible I made something useful. You will also notice a very dumb intake design. I did not have a good way to connect a Mikuni carb to the flange, so I knocked the insides out of the walboro carb and made it into a mikuni adapter. I suppose the long intake runner may wake up at higher revs. I attached a picture of my creation/mess! Comments welcome, you may even have a good laugh!

[George]

What's the deal with the carbs GH?

[6X6]

Interesting Mikuni adapter there, groundhog. Also, tuned pipes are very finicky. You are honestly better off with a muffler designed for the motor than a tuned pipe from something else, unless you know it to be compatible. Some members, including myself have posted up some pipe theory, but it's very involved, best to find a pipe off a 440 sled and modify it to fit without changing the length and not altering the shape of the expansion chamber itself. Still, the sled pipe may be more high-rpm depending on it's design.

[amcfreek]

I think its the walburo adapter ...
Nice pipe i think the pipe is working and probablly will work with the porting depending on how heavy a load is on it it actually looks about right for the ap eyballing it
also the exciter 570 yamaha sled from like 1987 was a plauge with bogging where it was almost un rideable as it used the butterfly carb rather then the std mic slide , well they got rid of that and it ran , also the dam engine had crappy lowend on some machines on the last model engine they prodused the sx , they shortened the flange for the carb and made the carb closer and the thing was a dam new sled . Like 15 more hp over the original model , and a down right screamer on lower mid..
Learned that reading some of the forums
again nice pipe dont change annything right away . Was planning on doing the same myself . For an engine that didnt have a pipe on it ....
Thanxz laterz

[Groundhog]

Thanks amcfreek, yea that is my mikuni adapter. I am feeling a convincing improvement in power with the alien, modified pipe. I ran it with flex pipe and it had a more mellow linear power curve as the posted curve shows. I have talked to some old time 2 stroke racers who had various thoughts on ex chambers. They all suggest some constant diameter section directly out of the engine. The worst area to shorten a pipe is in the first foot. If you start to expand too early it just wont work. They also say bends are generally good, as long as they are smooth.

The machine is completely torn down now. I am doing a complete restoration. I am strengthening the frame to make things more reliable. The welds were all broke loose in the back section and this is why I was throwing chain.