Bike wont start after fitting big bore kit

[Ant132]

Bike was running fine (suzuki ts50) but i decided that it i would fit the 80cc big bore kit i had.

Went on fine no problems, but the shop adviced me that i would have to fit a larger gasket underneath (thicker) the avoid the possibility of the piston hitting the head as its alot wider and the cyl. head has a smaller hole that was only big enough for the standard piston.

Anyway, I did, everything was fine and i came to start it and it wants to go and starts up but dies straight away. Sometimes if i held it on full throttle it would stay on very low but it still wasnt really started just kept goin, when i let the throttle go it died.

So, From this i thought it may be fuel? So i checked everything, found nothing wrong so thought about the jet? I had the original jet (70) in it and so i changed it to 82 (only other size i have), Still nothing, just exactly the same.

I did a compression test and i was getting 100psi, when the old cyl.was giving around 130-140, so i thought this was odd and checked the gaskets underneath.

The shop advised a metal gasket (3-4mm thick) with the standard base gasket on either side, so that is what i did..

I changed this to 4 base gaskets made out of gasket paper (2 x 0.5mm and 2 x 0.8mm) as i thought the metal one was no good.

This turned out to be even worse and gave me around 80psi..

This is where im at now, ready to have another go tomorrow

Any ideas? Thanks!
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1980 Suzuki TS50 ~ 1984 Honda CB400N ~ 1992 Triumph Trident ~ 1998 Suzuki Bandit 1200

[hmmmnz]

have you changed your fuelling?? youve almost double the capicity of the engine, it stands to reason that you are going to need a whole heap more fuel,
have you changed the whole head? or just got a rebored original barrel?? if its an original then your port timings are going to be wrong/out and will require you to grind the ports
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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[Ant132]

[Pete.]

Figure-out your piston-head clearance by bolting the cylinder down without the head (use spacers under the head bolts/nuts taking care not to damage the surface). You can use a ruler across the top of the barrel or put the old stock gasket on there, and run the piston up to top dead centre to check for clearance. You need at least 1mm. I'd be surprised if you needed those spacers to be honest, as few pistons project above the top of the cylinder at the outside edge. If you think the clearance might be too close, roll some plasticine out to about 3mm thick then cut it into strips about 6mm wide and then cut the strips to about 20mm long. Place these on top of the piston at places you would expect to come close to touching then drop the piston in the bore, assemble the top-end then GENTLY turn-over the engine BY HAND until either the piston passes TDC without the plasticine touching or the plasticine is squisehd in the gap. Don't force it . This is called 'claying the head'. A thorough description is here:

https://www.c-speedracing.com/howto/claymotor/clay.php
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[MaybeGuy]

are you getting a new crankshaft too? as i cant imagine piling 80% more power would be too good for a crank designed to take the impact of 50cc...

dont expect your bigend, crankshaft or crank seals to last long.
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[iooi]

Stupid question time.....


Where you fitting these extra gaskets under the head ? Or at the bottom.
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Just because my bike was A DIVVY, does not mean i am......

[hmmmnz]

[superslick]

could be that its not getting enough fuel in to combust in the bigger cylinder hence it not firing and not starting?
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aprillia rs125 gp-1 2004

[Finglonga]