Modded with succes need help to improve fuel supply

F

fattmeeney

New Member
Hi everyone, I want to share a couple of free, provided you have access to tools and ability, Performance mods that really helped me get alot more from my chinese 48cc.
First The obvious is to solder all wire connections, Been said and done, But the next is to add female Bullet style connectors onto the ends of the spark plug lead, Solder and heat shrink. This is a much stronger connection then a screw into the copper core, Very noticble improvement straight away especially with a spark plug upgrade at same time, I went to a bosch platinum UXF79P, awesome....
I also filed and sanded inlet and exhuast manifolds (port and polish) I did not do any Block or "jug" porting, Only on the bolt on manifolds. A very mild improvement
I then cut-up and old car speaker cover, I made 2 seperate piece's that bolted together with the original foam filter between them, I don't use it in wet whether but provides a noticable improvement when in use.
The finial and probably most benificial improvement was to bore the standard NT carb out to 14.7mm (mine was approx. just below 13mm). I completly stripped the carb, cleaned and used compressed air to dry/clean all the components, then reassembled in a clean contaminant free enviroment, after boring. It required a drill press and some wet&dry emery paper but made a noticble power improvement all across the board, Mostly in low rpm's and on hill's underload, but also to top speed. I want to purchase a jet kit, however just with these "free" mods The improvement is fantastic, I really urge people to try them if they have access to the tools, and experience or ability to use them.
The problem I have now is on downhill's under peak RPM's I run the carbie dry, I can't keep up enough fuel. When I had it apart I adjusted the float level to the maxium the carb case would allow, I had to trim the lenght of the "prime-er" button beside the idle screw and all works fine until peak RPM's on downhill runs (peak RPM on flats, uphills with or without tailwinds is okay)
I use Shell V-power with caltex Super2T full synthetic oil at 70:1 mix. If anyone has a good fuel delivary tip or mod that'd help I would be much appreciated, Thanks in advance
 
If you have the stock kit supplied fuel petcock, you can disassemble it and drill all of the holes out one size larger.
 
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Glad you found the problem.....sometimes these tanks have debris in them right from the factory! Thanks for sharing your successful mods as well....im sure many ppl will appreciate it as we all like more power for not much (or none) money!
-Dan
 
Thanks guy's, I was thinking about a petcock mod, good to know it's possible... It's now on the todo list.
I wanted to add that the bosch spark plug I was running caused high operating temps, I pulled it out and am using standard until I find something better. Thanks again
 
instead of modding the stock petcock, just invest 10 bucks or less into a higher quality one. SBP has one, or you can get a good tecumseh one from a lawnmower shop.

i've proven the stock petcock doesn't have enough flow at high RPM's to keep the float bowl full, and after switching to a real petcock i've got no more problems.
 
you dont need an air filter... or you can run a little piece of foam for looks.

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I didnt think you could get away with boring an NT... mine was 14mm, and so was my slide.
 
The bore fine, It was under 14mm to begin with, I used a 14.5 and it then mic'd at 14.72mm, The slide bore on my NT is measured at 15.23, the slide functions fine, I should also mention that I drilled the hole that goes to the bowl to 4mm. I did some maths, and at approx 7000rpm, with a volumetric effeicancy around 80% airflow (a/f) rate is about 217.513 litre's a second, to flow that volume is approx. 17.something mm. As the inlet is larger then the intake there's a pressure drop (and velocity slow) there, To the best of my understanding The venturi effect works on pressure difference's so the bigger the difference the more affective the V. effect? I think....lol. Mine seems to be okay, as stated in my first post, I think it has a little more torque in lower end rev's and a smoother WOT speed and RPM. I have also seen for the very first time, The little grey patch's on the inlet side's of the piston, which I've read is a good indicator of a healthy A/F mix.
I removed the petcock, and intank filter from end, drilled it out to the next lrgest size, There was alot of castring dags even in that small component, I the reinstalled the petcock without the intake filter and used an external inline filter for carburetted 6cyl. ford. Fuel flow is fine and doesn't impeed motor/carb function or performance in any way.
I have also made a copper head gasket, that is .020' thick, slightly increasing TDC copression ratio, I would reckamend people do this also, The engine was quieter, had more compression and sounded more 'crisp' out of the exhaust. I plan on making a copper exhaust gasket asap.
I plan on modifing stock setup to get the best set-up possible before I spend money on after market parts, I beleive getting everything to "mesh" perfect is a good way to power, performance and reliability But to gain real performance then will start with aftermarket components to maximise engine, Having said all this I do want to get my hands on a jet kit, Is there a kit that come's with primary and secondary jet's.
Anyway thanks again everyone, awesome community with great feedback!



I want to thank everyone who reply'd or has contributed to the forum, It has been a wealth of info and very helpfull.
 
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