Clone cam performance options

cclingma

It's been a while since I was able to do much reading around on here or messing with my cart but I've been thinking all the while.

My 96 CC with 16hp clone has me pretty happy. The opportunity for improvement occurs in the 3000 to 4000rpm range where the motor seems to get tired. I don't expect to have pin me back hp when already rolling 20+mph but would like a little more grunt in that very nice cruising speed range. I'm curious to see if others have similar thoughts. I see these performance kits....cam, valve springs, associated parts that sound like alot of fun. If this little motor pulled a little harder at 3000+ rpm and maybe even pulled up to nearly 5000 rpm I'd be in love. Any experience/thoughts out there?

Thanks.

BGW

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CC-John

A trick I used to do on the old Briggs & Tecumshit flatheads was to retard the cam timing by one tooth.. This will move the stock cam's effective powerband higher in the RPM range.. You'll also need to find some stiffer valve springs or shim the ones you have.. This will help stave off valve float at the higher RPM's.. You could also try shaving a bit off of the flywheel key to advance the spark timing.. This will make throttle response a bit crisper and will boost power in the higher RPM ranges..

Those little Chonda clones should respond to all the same tweaks we do to the Vannys.. You'll just have to get a bit creative on some of the parts, since there isn't really a demand for performance parts for these engines.. Search out some go-kart forums online, some of those guys have been playing around with these clones for a few years, and have learned a few tricks to boost power and keep them alive while doing it...

cclingma

I may have to tinker with the timing thing. I honestly don't think I ever really got the idea behind until I just read your post. That makes sense to keep the stock cam and it's power curve just move it around a bit.

Thanks for the explanation!

shawn.m

their is a link to the honda 16hp performance parts someplace on the site here. cant remember where it was

cclingma

Found some good info on advancing spark timing on these clones. When time permits I'll have to tinker with both spark and cam timing. Thanks.

shawn.m

found the link
http://www.parsonsracingengines.com/...0gx390%20parts

sho305

http://www.affordablegokarts.com/mm5...gory_Code=GPPX

Another link, pretty nice guy too.

I have the same thing though the guy is very happy with it right now once I get the jetting right. Going to put one in my cart and wondering what mods I could do before the install. It pulls hard from the bottom to around 20mph then begins to let off. It still will run 30gps or more pretty quickly, not gps'd over 29 been afraid to really wind on it hard for that long....with 22 tires in a G9. The thing will powerslide in gravel when you take off even with it being damp and the trailpro tires that bite pretty good, and stock clutch. Torque is far greater than stock engine.

I know a timing key or file one down can advance it some, you can also hog the holes out on the coil, they list that on AGK's site iirc. I'm not really sure other than a cam what will help top end. He told me a good flowing air intake and exhaust should let it see 5K. I have that but since my tach broke not sure on rpm, but seems very similar to what the stock yamaha would do in twice the distance. I have a 2" air intake to a car airbox, and over 1" exhaust to a car muffler, it should flow well. A larger carb seems to help top end on most of these engines too. I set the lash to .004 but it didn't seem to matter, it was looser factory. I don't know if its valve floating or just not breathing well, or out of cam. The stock yami seems to rev more even though it has less power....this has more power then lays down...they come out close on top except the yami is far behind.

Freezeman

It all sounds fun. With cam timing I would be careful about moving a tooth on the crank gear. First count the number of teeth on the crank gear. 360 divided by that number will tell you the degrees of change one tooth will be. When changing it be sure you note the cam gear is running the opposite direction of the crank in order to place it in an advanced or retard state. After you do change the cams timing you should recheck the internal clearances of the flywheels counter weights and rod to the cam lobs and lifters to be sure you still have at least .030 clearance between them through out all 4 cycles. It is easiest to check this if you have an old cut up inspection plate side cover to position the cam and crank while still being able to see inside. Clay could also be used. Clearance issues can become more of a issue if changing to billet rods, larger lift cams and stroker cranks. You could also file/grind/sand down the heal or base circle of your stock cam in order to gain more lift or better yet would be higher ratio rockers along with stiffer springs. Shimming the springs can also add valve control at higher rpm's, but always check to see how much gap remains between coils before encountering coil bind at max lift. A .030 feeler gage between the coils is a pretty safe number.
When gaining lift and spring pressure the quality of the cams lobe material comes into play. You start to use the outer edges of the lifters with higher forces which can mill a cams soft nose down in a hurry which will not be seen as increases in lash yet rather only seen if you measure max lift or when draining lots of metal out with the oil.

With flywheel timing no key is needed at all. The tapper is made to hold the timing point well if it is lapped to gather with some valve lapping compound, cleaned then torqued down well. I have only had them slip while starting a motor on methanol with 36-38 degrees of advance.
All modifications come with the risk of shortening the life of the motor. Most the OHV's are designed with a poor rod length to stroke ratio which makes for high friction half way up or down the cylinder bore. The friction is quadrupled to rpms. A longer rod with the correct piston pin height would help a lot in the rpm department.

The Valve lash can be set as low as zero, just as long as the valve isn't open when cold. The lash grows as the motor heats up. Something good to try out would be to open up the exhaust lash to about .010 and set the intake to .001 or so and see if with the correct jetting it moves the power band a bit higher in the RPM scale. That is changing the opening and closing events with out moving the cams position on the crank.

Sorry for blabbing too much.

sho305

I don't see any babbling at all....all great info.

I wondered about higher ratio rockers and the springs, but car engines don't seem to gain much from it unless these are different. You can also shim springs in a stock engine for a little more rpm before float. With a car engine (in a boat) I could hear the exhaust note change with valve float but not run this hard enough to tell. I'm not worried about wear that much, we really don't drive around at max speed much at all, its just a blast here and there mostly. On trails we never seem to run over 1/3 throttle continuous which is maybe 20-25mph not sure.

Trying to get an adjustable jet now, jeez, they want 35 plus shipping when I can buy an entire new carb for 40 shipped. The cams seem to be around 150 for these 16hp, though for the 6.5 some are only 50. Actually cheaper if you could fit a pair of 6.5s in a cart.

Bad part about GC is the engine is not near as accessible as say a gokart or minibike....far as mods and adjustments.

I will try changing the lash and see what it does thanks for the tip.

Freezeman

OK, I'll blab some more then.

I live at 9100 feet and all the fun stuff with motors liked to be leaner here. When without a jet selection to try, I have just soldered them up and drilled them out smaller to lean them. Not the best way to do it but it's better than being fat.

On Bobs kart site there is a good recent post about changing the fuel ratio curve. That may be another thing to explore with your carb for a better blend of rpm's and throttle position. As far as I understand most of these things were mainly designed for constant rpm use.
Main jet changes the fuel curve ratio yet working the air bleed and emulsion tube could be worth looking at.