Help needed big bore+jets :(

[jamie192]

Right i have a 70 cc big bore fitted to a ts 50 x, ive been told by m1ke and a guy at the local bike shop and my friend who fit the bore that i need a new main jet so the bore gets enough fuel. So today i go down to my local bike place, he has this guide thing that says, 80cc bore on ts 50 + 22ml carb and 80 jet. I dont know exactly what my carb is i think in the area of 16 to 18. The jet i currently have on is 67.5 then one i was given by the guy at the shop was a 85 which flooded my engine( i think). it wont start hardly and to get it to work i have to have the throttle right back and still its only running at about 1k because its flooded, or is this 85 not giving it enough fuel but the hole in the 85 is bigger so im guessing flooding.

When i have the orignal jet in below like 3000 rpm it struggles to keep going, and pulling away in first on the standard gears, it just doesnt hardly, its slower at pulling away then my 50 and there is no more power in it, i can get a little extra top speed but nothing like all the people i have spoken too have been saying. it kind of acts like its got a turbo lag under 3000 rpm. ive been told its doing this because there is more air than fuel being sucked into the engine and i need to sort out my jets.

I hope someone can help because my poor bike is sat in the garage not moving.

Any help or suggestions on this will be greatly appreciated.
Thanks for your time!
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Ride Fast, Brake hard, don't fall off!

[Barker-CBR 600]

*points to workshop forum*

Might get better response there.
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Previous - Gilera DNA50 / XVS125 Dragstar/Honda CBR 600F/GSF 650 Bandit
Current - 2013 Suzuki VZ800 Intruder
'Is this a rhetorical question?'

[jamie192]

oops, sorry didnt realise, feel free to move it any mod's if you have time. thanks again and sorry.
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Ride Fast, Brake hard, don't fall off!

[mrchips]

As the saying goes

"If it ain't broke, don't fix it"
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Northern Irish? www.nibikers.com

[jamie192]

but it is broke, it hardly moves.
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Ride Fast, Brake hard, don't fall off!

[rizo-sri200]

^^^

but it wasnt broke was it
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swift kick to the wing mirror puts em straight..
98' Bandit 600 with Slip on

[Spike_R]

may aswell of been

And matey, when changing jets you will need to adjsut the idle and mixture...
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Derbi supermoto with cr500 engine, niceee

[jamie192]

yeah i know i have to change mixture and everything, but its finding the right jet which is the problem.
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Ride Fast, Brake hard, don't fall off!

[Dom_]

[DM]

Yep, I agree entirely. A 21mm would work well, a 24mm possibly.

[jamie192]

well i put in an 85 and that flooded the engine, it orignaly had a 67.5 and ive been ringing around the shops and they recon about a 70 75 or 80. so im going to order them and hope for the best.
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Ride Fast, Brake hard, don't fall off!

[Kickstart]

Hi

Jet sizes are not standard between different makes of carb, and indeed even if the size is the same the material they are made of will affect the flow (eg, a brass jet compared to a nylon jet).

The jets are quite cheap. I would say to get a range of them and have a play.

The main jet only affects high throttle operation, above about 3/4 throttle. Below that it will have no effect.

Between about 1/4 throttle and 3/4 throttle it is the shape and position of the needle jet that affects the mixture. From 1/8 to 1/4 it is mainly down to the shape of the carb slide (but few people bother to do anything about this), while below aboiut 1/8 throttle the mixture is determined by the idle air screw / idle mixture screw.

Given how it is running I would probably start at something like a 75 main jet and raise the needle jet slightly. However do one thing at a time and see how it goes.

Generally the main jet is the easiest thing to sort out, as it is very easy to find full throttle!

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[jamie192]

Thanks for your help kickstart i have just ordered a 70 75 and an 80 jet, ill see how it goes, my needle is on the second from lowest setting possible, you think i should move it down one more?

Also thanks for moving it to the workshop section.
Its just annoying having to take my carb apart all the time o well, my fault for getting the bore on in the first place.

Thanks for your help.
____________________
Ride Fast, Brake hard, don't fall off!

[Kickstart]

Hi

For the carb, just cheat. Slacken off the mounts for it, twist it through 90 degrees and the you can get at the bottom of the carb from the side of the bike . Just remember to turn the petro off.

I would get it running correctly on the main jet first. Safety wise that is the most important one. Once you are happy with that then play with the needle jet. Dropping the clip down one notch on the needle will richen the mixture up. If this is too much (or not enough)then you can use a small washer under the clip to raise it slightly more than the existing clip positions allow. You could also replace the needle with one with a more suitable shape, but then you are getting into rather more complex areas.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing