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Discussion Starter #1
Hey all! I have one of those gofit $50 "big bore" top end kits that are sold on Ebay and Amazon, the kit came with everything needed to do the top end, and it came with a dell'orto sha style carb. Although this isn't any bigger than the stock piston on my mototec demon 50, but it is windowed, so I'm hoping it helps out a little bit. My question is, I've installed a high performance pumper style carb on the bike with a velocity stack, it starts and runs great and makes more power than the stock set up...do I really need to swap it out with the dell'orto sha knockoff when I rebuild the top end? I took the advice of a poster here with the carb, and since it works so well, I'd like to keep it on. Thanks for your input!
 

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Some people like the pump or carbs and some people like the Delorto carbs. From what I’ve read on these forums and have tried, the pump or carbs are easier to tune in. If you have a 15 mm pumper, the delortos are 14and 16mm. You would be fine sticking with the pumper carb
 

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If it ain't broke, don't fix it. Do you have the 13mm piston carb now?? Many ways to mod that carb to work even better. Need a bigger main jet from .64mm to .68 or.70mm, Wait till you try to hook the throttle cable to the 14/14 dell, makes me Crazy.
 

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The pumper carbs are better simply because the tune changes as the engine wears...

The tune also changes due to weather conditions humidity temperature and such.
 

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Yes most people think you set it and forget it but thats not true. Will it run with varying temps and humidity, Yes! But not ideally. Tuning needs to be done a lot on any carbed application but especially 2 strokes to maximize performance and engine life as well.
 

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when I was drag racing bikes, rich in the morning and leaner as the day goes on and the temps rise, cold air is denser than warm.
 

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GB2020, there is no big bore kit now. They all have a 44mm bore. I have many engines w/ hp alum finned heads, round alum allow heads, and the Billet Winged head kit w/ 3 upper port cyld and full circle crank. Did your kit come with a new crank?? The round alum alloy kit has more compression than stock. You can remove material off the top of the cyld for more. The big bore kit was to replace the 40mm bore 47cc cyld with a 44mm bore cyld and piston with 10mm pin to fit the 47cc crank. The 49cc engine has a heavier crank than the 47 with a 12mm pin. Big Bore Kits 101. I still have one or two stored here somewhere, lol.
You can still buy 44mm piston w/a 10mm pin. I used the lighter crank and 44mm piston instead of the heavier crank & heavier piston and 12mm pin, get more rpms that way.
 

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Discussion Starter #9
Thanks guys, Im gonna finish the top end as soon as a new cylinder gasket arrives, I accidentally ripped the new one. I was advised by a poster here before that these kits are not a bigger bore, but since the piston is windowed (the stock piston is not) and since the kit was fairly inexpensive, I thought it would be a fun project to do anyway &the red cylinder head looks nice, too. This kit did not come with a new crank...though I did see a few kits for sale that do. Just trying to do anything to squeeze a little more power out of the bike. I've added better reeds, an NGK plug, and a "racing" coil/plug wire as well. I also placed an order for an adjustable clutch with hd springs. We'll see how it all goes!
Thanks again for the tips! Will share my findings when it's back together.
PS: I looked the Dell'orto style carb over, the throttle cable set up looks tedious to do haha, my current carb (pumper) was a piece of cake to install.
 

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Yeah, you are on your way. It is always exciting. The pumper carb is the way to go. You will get there, try and test different things. Thats what its all about. Can't wait for the final product.
 

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You don't need a base gasket, I use Yamabond, very thin on the cases and let the cyld sit on it 24 hrs then tighten it down, you will have a lot more compression, there is only case pressure at the case.
 

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Discussion Starter #12
You don't need a base gasket, I use Yamabond, very thin on the cases and let the cyld sit on it 24 hrs then tighten it down, you will have a lot more compression, there is only case pressure at the case.
Ok thanks, I didn't know that. would high temp rtv like Permatex work?
 

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I had some so I used Yamabond is rubbery, Yamaha uses in an intake gaskets and stuff, I would look for Moto Seal, it is used for puting cases and parts together, Its takes very little of it, I can still see the case material underneath, I spread it thin with my finger. Once it is seated, put the 4 bolts back finger tight, If you have 2 piece cyld, Put the head on with the four long bolt lightly finger tight, wait 24hr, take it a[l apart and finish assembly.
 

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Here is a pumper carb project carb I never tried, I bored out a 16mm Cag alum pumper carb manifold to 20mm and mounted a 20/21mm Boss Hog chop saw carb, had to bore out the V-stack also. Its a little big for a Cag, waiting for the right engine, lol. On one of my Crazy engines has a 19mm Walbro HDA223D pumper carb on a bored out Cag $18 alum manifold. There are so many mods you can make it never ends, lol.
 

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I still have it, you can see where I put a 19mm Walbro HDA223 purge carb on my 50cc C1 W/C, That carb was never use there, its on another engine now. The 20/21 was mark for that engine which has the 19mm now. Had to drill a hole and add brass fitting in the cases above the intake area to feed it, right off and above the reeds. That engine has a teflon coated 40mm piston. Before I got all kinds of chainsaw carbs from hlsupply .com I got a 16mm clone 603 w/ accel pump carb for less than $12, the 20/21 was $14. There are some carbs that only have 1 an inlet perfect for a Cag.
 

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Discussion Starter #19
Finished putting the top end together, was a fairly easy job, was fun....the last time I put a top end together was on a Kawasaki KX80 back in the late 90's. Ahh the memories haha. Anyway, haven't tried starting the engine yet, pulled it over once just to see how it felt. Definitely a bit more compression. Thanks for the advice here, it helped! Will let you know how it runs when I fire it up. I've gotta fix a pinched rear tube, adjust the chain, and do a few more things before I take it out of the workshop.
 
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