What carb ?

fastercarter

This has been bugging me for weeks now; Standard 16 HP clone motor that wont being going past 5000 RPM's. Governor gone and just a lightweight set of valve springs to keep things in harmony. This cart is for golf course use only so won't see any sustained power bursts beyond 15 seconds or so. Has anyone actually dialled in a suitable alternative carburetor alternative to the POS that comes with the clone or are we all just farting in the wind ? I have heard of 30mm Mikuni's that run well but other sources suggest 36mm and above. I understand that exhaust and camshaft will cause issues but surely someone has a basic setting for these engines ? I contacted Hookm the other day regarding his superfluous to requirements bored 390 carb but even that doesn't sound correct and I have contacted several vendors who still cannot be specific. I'm not looking for the definitive answer here, just a good starting point. Mikuni, Keihin whatever. All suggestions gratefully received.

Thanks guys,

FC

BGW

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hookm

FC ,quit using words I have to look up in the dictionary(superfluous)hookm
I'm using a 2007 clone carb that still has all the adjustments on it with a larger jet & it seems just right,we'll see after this weekend.

sho305

The one I put in is all stock except the airbox and exhaust are free flowing (car airbox and car muffler on 1" pipe). I had to hog the main way out to get WOT to run right, then had to hog the idle jet just a little bit and put a new idle screw in so I could adjust it. I richened that up just enough so it didn't pop when slowing down. Right now it runs great everywhere except at about 10mph it will miss here and there. (stock G9 gears with 22s, does about 30gps flat out around 5K rpm just like stock engine would) Worse with choke so I know its too rich in a spot about 15-20% throttle or so. Sometimes at lower speeds if you floor it, it will miss like crazy above half throttle. I might be able to wind the secondary more and get rid of that, it would raise the part throttle rpm a little. Going faster say over 15mph it has more rpm and takes off fine, that makes me think rpm is too low to go WOT. If you floor it from a dead stop it takes off fine. Anything under half throttle anytime works great except that little rich spot.

I've read a ton of stuff and they mostly say get a motorcycle type carb that is made to throttle (run at any part throttle position). They say the lawn carb is made for governor use, never to idle under ~1K rpm, it is very simple. To tune it perfect is difficult and with epa even harder now with no adjustable jets and such, though you can convert them. If you get a mikuni or klein/etc you can tune them in, still work but they can be made to work perfect because you can tune any part of the throttle. Be careful a lot of people are running gokarts and such, they only care about idle and WOT, that is why the bored/etc lawn carb works ok for them....they don't race at half throttle lol.

With all the stuff I'm doing to mine and spring projects I don't have time to get the carb and make a manifold. I have cut the head and got it ported, got a timing key and springs for it. This carb will have to do for now.

There are also PZ carbs they use on buggies and stuff. I think the 30mm and larger are for racing I would not go that big without a cam. I am looking 26-28mm or so. Also the flat slide type carbs are said to flow more for a given size. I think the stock carb is 24mm or so about an inch, I forget I posted it and don't have a rule here to measure a spacer. The venturi in the carb is smaller than the said size on all these carbs they measure the outlet I believe. The air intake side can be larger yet. Larger carb makes better top end flow, smaller carb makes better low torque. So I figure I only need a little more flow since I want best power in 2500-4500rpm range I will use with stock cam, I don't think the carb is keeping rpm under 5K its the cam and timing.....well I think that but can't prove it lol.

fastercarter

I was thinking along the same lines Sho. A 36mm carb designed to power a (say) Honda 400cc motor on a motorcycle pulling 12000 rpm is going to be way to much for a 5000 rpm max clone motor. The people I have spoken with are mostly cart tuners and as you pointed out; with them, it's really pretty much all or nothing as regards throttle opening. I can get a brand new 30mm Mikuni suitable for up to 250cc motorcycles for under $30 shipped. I reckon at that price it might be worth a little trial and error to see how it pans out. I'll give it a go and hopefully the end results will help another member here to get these engines pulling reliably.
Thanks for your input

FC.

sho305

Less than $30 shipped, I better do more shopping not found that one yet lol. I have found this one and some others like it, and some on ebay....all new carbs. You almost need to go by HP/TQ for what size you need. If you don't increase it that much you should not need to make the carb much larger. I've had stuff with too large a carb and it does not work well.

fastercarter

http://www.ebay.com/itm/30mm-Mikuni-...les_Parts_Acce


There you go.

FC

BIKERMIKEYBLACK

will it fit the stock intake ?

hookm

Well I ran my cart this weekend ,it handled anything anyone else could.I did good but it wont rev like a V twin,it gets there but sort of bogs down,may be a cam will do it,good luck,I'm going Vtwin!hookm