Quick video of my Honda Cub clone

[Adjuster]

This is the very first video I have ever posted on the net.

View My Video (http://tinypic.com/r/k0h92h/8)



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[Weldangrind]

That's a sweet little bike.

[katoranger]

I would ride that.

[Adjuster]

Its very fun and extremely easy to ride. Everyone that sees it loves it.


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[alex_in_az]

that looks like fun

[KooKooBean]

Very cool bike....

[Adjuster]

Ok so mentioned in other posts I replaced my 49cc engine with a 125cc engine. Increase in power of course was dramatic to say the least. I then became concerned my original 49cc exhaust would/was/is too restrictive for the larger engine. My exhaust has that single little outlet pipe maybe the size of a nickel in the center of the exhaust plate. So I finally purchased some step drill bits and I drilled 4 holes all as the same size as the original hole evenly around the exhaust plate. Immediate improvement on idle, performance and sound. Power lag when taking off from a stand still is significantly reduced. All 5 holes have what feels like an equal amount of exhaust pressure coming out of them. So my question is how far do I go with these holes? Do I stop right where I'm at well enough to leave alone? I have seen YouTube videos where you now take a long drill bit up to 18" or so and drill in through the new plate holes and you will be able to drill through all the plates inside the exhaust to open it up even more. How do I know if I need to open it up more?


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[jct842]

When the exhaust starts to lean out. Check plug possibly or add just a little choke to see if it runs better?

[Adjuster]

I do know its running leaner as it was backfiring during deceleration. I am waiting for it to cool off before I pull the plug. So does this mean I stop or open it up a little more?


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[Weldangrind]

If it starts to lean out, you can always step up the main jet to compensate. Super easy and cheap.

You can determine the ideal size with a little math. Remove the header from the cylinder head and measure the ID. Once you have that, you can calculate the area of the inside of the pipe. When drilling holes, determine the area of the bit size you've selected, and then drill enough holes to equal the header ID area.

Make sense?

[wheelbender6]

That's a cool project. Looks like a better riding position than a Grom or Mad_ss. I bought a 1969 Honda S90 a few years back but never restored it before selling. It was too big of a project for me. Did the original 50cc engine have pedals like a 70s moped? Was the 125cc engine a simple bolt-on?

[Adjuster]

Riding position is great and I am 6'1" 220lbs. No pedals. These Honda horizontal engines mount with 2 thru bolts and it falls right out the bottom of the bike. Its not easy but I was able to change out the engine myself by cradling the engine in my arm like a baby lifting it into place and sliding one of the bolts in. There is a video of a guy on YouTube that straddles the bike and simply reaches down with both hands and liftis the engine into place then traps it with his foot while he slides the bolts in. Of course you still have to deal with the chain and exhaust but thats simple stuff. You can not believe the compliments I get on this bike by anyone in the 50 years old range and especially anyone that is Brittish/English.



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[Adjuster]

This just arrived today from China. New Mikuni with fuel lines, throttle cable and pod filter package. They should have thrown in a fuel filter for the ultimate package. Not a bad deal for $40.00. I don't know anything about throttle cables. I hope it will work on my bike. Its a vinyl covered braided cable, I like it.

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http://i63.tinypic.com/al3ssk.jpg


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http://www.aliexpress.com/item/125cc-Dirt-bike-Pit-Bike-Mikuni-VM22-Carburetor-38mm-Air-filter-56-2-intake-manifold-for/32217872075.html




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[Weldangrind]

Good deal! It's cool that the choke is on the left side; several of the Mikuni carbs I've seen for horizontal engines have the choke on the right.

[Adjuster]

Ok I got my new carb on installation went good. However it is idling way to high. I can turn the idle screw in and make it idle even higher but when I back the screw out I can't drop the idle down into the 1500rpm range. It stops dropping around 2000rpm. Do I need to purchase a couple smaller pilot jets? While I'm at it do I need to purchase a couple smaller main jets? I currently don't know what size jets I have. But the reason I bought this Mikuni carb is so I can re jet it and hopefully get the optimum tune. Also where should I set the needle position? My needle has what looks to be at least 6 or so clip positions. Thats whats good about these Mikunis is they are so adjustable.

Thanks for the help.



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[Bruce's]

Check to make sure the slide is in the correct position and able to close ,the symptoms you have are classic for the slide being installed 180* out .
I can't open your pictures on my iPad ,is the bike an original Honda with a clone engine ,or did you purchase a clone bike then upgrade it with the larger engine ?

[Adjuster]

Thanks purchased a clone bike came with a 49cc and put in a 125cc. Tomorrow I will check the slide like you said but I did look at the slide and worked the throttle and it appears to be working correctly. But tomorrow I will spin it around and see if it seats correctly and if that solves the problem.


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[Adjuster]

I did just go out and check it removed the slide and spun it around and then the throttle wouldn't work correctly. Spun it back around and it fully seated down in the carb and throttle works correctly. So I am pretty confident I have it installed correctly. The more I think about how the carb works I think I need to change my needle position. I need to 'shorten' the needle so the slide will move farther down into the throttle body. That should lower my idle. Right now my needle is in its longest position. The clip is at the top most position on the pin. I need to move it to the bottom most position making the needle shorter and see what that does for me.

Does this make sense, am I imagining it in my mind correctly?



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[Bruce's]

Sounds like you're on the right track ,give it a try .

[Weldangrind]

Check both the main and slow jets for size. I suspect you'll need both to be smaller.

[Adjuster]

Yes will check jet size and get a selection of smaller. Will a too large pilot jet cause the high idle that can't be adjusted down? I have also been reading since I changed the carb and messed with the throttle cable I may not have enough slack in my cable. Although to me it looks like the carb slide is working through its full range of motion.


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[Adjuster]

As another diagnostic I used a propane torch around all my carb fittings and the idle did not increase so I am hoping that means I have no leaks. I can't get the idle to drop below 2000rpm. Even if I fully remove the idle speed screw.


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[Weldangrind]

Will a too large pilot jet cause the high idle that can't be adjusted down?


Indirectly. I found that out the hard way this summer, when I tried to install a carb on a 50cc horizontal clone, and the carb was too large for the application. So much air passed through the carb when the throttle was closed, that it would draw fuel through the main jet. That's not supposed to happen. A switch to a smaller carb solved the problem.

I have also been reading since I changed the carb and messed with the throttle cable I may not have enough slack in my cable. Although to me it looks like the carb slide is working through its full range of motion.

Simply remove the cable from the throttle tube, and you'll know if the cable is affecting the idle at all. You might have a cable adjuster at the carb end as well; make sure it's backed off.

[Adjuster]

Not related to my current new carb idle issue. But with the help of you guys and the link to the micro drill bits. I just took the jets out of my original carb and using the drill bits as a gauge I drilled out the jets to the next size up bit that would not fit thru the jet. Do you guys think it was okay only going up one size large or should I have went for two sizes larger? The pilot jet was the hardest only because the hole and bit are so small. The bit is so small it doesn't get a good bite in the brass material. I just kept at it and it finally punched its way through. The main jet was much easier and faster. The bit is bigger so it got a good bite in the brass and quickly drilled through. I did everything by hand. I have a Dremel tool that may have worked but I was very afraid of breaking the very fragile bits. I will switch out the carb over the weekend and let you guys know if I can detect a difference.

With my original carb I was getting a slight bog hitting the throttle from a dead stop. I think that is the pilot jet range. Maybe I should have went up two sizes larger on the drill bit.

More is always better right!? :doh:


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[Weldangrind]

I think you did the right thing.

Before drilling any further, try adjusting the pilot mixture screw.

[Adjuster]

Yep I will get the original carb back on and make the required adjustments and see how she does.


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[Adjuster]

Stupid aluminum or stupid me I have stripped out one of the manifold pipe to engine bolt holes on my Honda horizontal clone. I have it holding right now with some thread sealant and some exhaust gasket sealant but I don't like that. Anyone have a quick fix? Anyone know what size thread this bolt hole is in case I want to try an insert?


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[Weldangrind]

JB Weld?