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Running pre-mix. do i need to upjet?

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spitfire123
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PostPosted: 14:49 - 11 Nov 2009    Post subject: Running pre-mix. do i need to upjet? Reply with quote
hi all,

want to run pre-mox on my cagiva mito as i just dont trust the feble oil pump.

Now ive heard someone before that if you dont run injector and go on to pre-mix you have to upjet the carb?

if se do u upjet it by 5 or somthing, and run a 50:1 ratio?

sick of heat ceizure and the oil pump failing.

cheers Thumbs Up
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ms51ves3
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PostPosted: 15:42 - 11 Nov 2009    Post subject: Reply with quote
When running pre-mix up-jetting is just simple maths.

Let's say you run 30:1 petrol to oil and you have a 120 main jet (to keep the maths simple).

120/30 = 4

4 is the amount you should up-jet by in this case. So you would want a 124 main jet if you could get one.

So just divide the size of the jet by the bigger number in the fuel to oil ratio and then up-jet by the answer.
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Kickstart
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PostPosted: 16:21 - 11 Nov 2009    Post subject: Reply with quote
Hi

Not so sure. Oil will add to the viscosity of the fuel and change how it flows (although probably not that important). However main jets are marked in different ways. Sometimes by flow (in which case your calculation is probably right) and sometimes by diameter (in which case your calculation would mean a 6~7% larger main jet to make up for the 3% oil).

All the best

Keith
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MarJay
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PostPosted: 18:17 - 11 Nov 2009    Post subject: Reply with quote
Umm. I was thinking of writing out hundreds of reasons why its a totally dumb idea to go premix, not the least of which the oil pump continues to oil the engine on a closed throttle, unlike premix.

But I'll distill it down to three words for you:

Trust the pump.
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spitfire123
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PostPosted: 18:31 - 11 Nov 2009    Post subject: Reply with quote
MarJay wrote:
Umm. I was thinking of writing out hundreds of reasons why its a totally dumb idea to go premix, not the least of which the oil pump continues to oil the engine on a closed throttle, unlike premix.

But I'll distill it down to three words for you:

Trust the pump.



LOL

i know quite a few ppl who dont trust pumps.

she does pump....just dont trust it realy.

im spending another £200 on a new topend for the engine and i dont want it to blow in 500 miles because of lack of oil.....atleast i no 2st is going in with pre-mix.
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MarJay
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PostPosted: 18:45 - 11 Nov 2009    Post subject: Reply with quote
spitfire123 wrote:


im spending another £200 on a new topend for the engine and i dont want it to blow in 500 miles because of lack of oil.....atleast i no 2st is going in with pre-mix.


At least you 'no' that your engine is being lubricated on a closed throttle. If you dick about with this you are MORE likely to seize. Autolube systems are good. If they weren't the world and their wife would change to pre-mix as soon as they could but they don't.

Racers only change to save weight and because its not hassle to pre mix the fuel each time they fill up.

on the road its a total faff. You'll never be sure you've got the right amounts unless you pre mix it in a jerry can with a known quantity of petrol. Its a completely stupid idea. Its not practical, its worse for your engine and its more likely that you'll make a mistake.

If you still want to do it, sell me your mito and do it to a shitter. I'll give you a tenner.
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Blue_SV650S
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PostPosted: 19:22 - 11 Nov 2009    Post subject: Reply with quote
MarJay wrote:
You'll never be sure you've got the right amounts unless you pre mix it in a jerry can with a known quantity of petrol. Its a completely stupid idea. Its not practical, its worse for your engine and its more likely that you'll make a mistake.


You will know exactly how much petrol you have put in, coz it will say on the pump ... Wink

But yes, you then need to do some maths and measurements to get the mix correct, get this wrong and indeed BANG! Shocked

Like you I'd prolly stick with the autolube, but to answer the OPs question, YES you WILL need to up-jet. As has been discussed above the exact amount would depend on the jets you are ccurently running, the way they are numbered/rated and the oil ratio you want to run, the rest is just maths.
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spitfire123
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PostPosted: 19:52 - 11 Nov 2009    Post subject: Reply with quote
MarJay wrote:
spitfire123 wrote:


im spending another £200 on a new topend for the engine and i dont want it to blow in 500 miles because of lack of oil.....atleast i no 2st is going in with pre-mix.


At least you 'no' that your engine is being lubricated on a closed throttle. If you dick about with this you are MORE likely to seize. Autolube systems are good. If they weren't the world and their wife would change to pre-mix as soon as they could but they don't.

Racers only change to save weight and because its not hassle to pre mix the fuel each time they fill up.

on the road its a total faff. You'll never be sure you've got the right amounts unless you pre mix it in a jerry can with a known quantity of petrol. Its a completely stupid idea. Its not practical, its worse for your engine and its more likely that you'll make a mistake.

If you still want to do it, sell me your mito and do it to a shitter. I'll give you a tenner.


i see what you mean mate but ive never trusted auto-lubes.

im using the RS rotax carb on the mito engine on a duel feed unlike the mitos 1 feed 2st oil feed.

when i pre-mixed it for a bit before it seemed to like it better.


as for selling it...no thanks....its staying in my hands for a long time yet Laughing .
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spitfire123
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PostPosted: 19:55 - 11 Nov 2009    Post subject: Reply with quote
Quote:

But yes, you then need to do some maths and measurements to get the mix correct, get this wrong and indeed BANG! Shocked

Like you I'd prolly stick with the autolube, but to answer the OPs question, YES you WILL need to up-jet. As has been discussed above the exact amount would depend on the jets you are ccurently running, the way they are numbered/rated and the oil ratio you want to run, the rest is just maths.


yes i totaly know what you mean.

im no novice to 2st mixing to be fair.

ha da few mini motos i used to race which needed constant supervision.

especaly the belovid polini Laughing
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MaybeGuy
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PostPosted: 19:56 - 11 Nov 2009    Post subject: Reply with quote
spitfire123 wrote:


im spending another £200 on a new topend for the engine and i dont want it to blow in 500 miles because of lack of oil.....atleast i no 2st is going in with pre-mix.


your engine would seize a lot sooner than 500 miles if the oil pump gave up.

if you keep blowing top ends through seizure in say 500 miles i'd say your pump is set up wrong.
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Kickstart wrote: Hi I tend to agree with Matt. All the best Keith
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spitfire123
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PostPosted: 19:58 - 11 Nov 2009    Post subject: Reply with quote
mattsprattuk wrote:
spitfire123 wrote:


im spending another £200 on a new topend for the engine and i dont want it to blow in 500 miles because of lack of oil.....atleast i no 2st is going in with pre-mix.


your engine would seize a lot sooner than 500 miles if the oil pump gave up.

if you keep blowing top ends through seizure in say 500 miles i'd say your pump is set up wrong.


i would have thought the same,
but the setup appears to be all working Confused
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Kickstart
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PostPosted: 20:31 - 11 Nov 2009    Post subject: Reply with quote
spitfire123 wrote:

im using the RS rotax carb on the mito engine on a duel feed unlike the mitos 1 feed 2st oil feed.


Dual feed? RS uses a single feed like the Mito (just on the other side).

All the best

Keith
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spitfire123
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PostPosted: 21:54 - 11 Nov 2009    Post subject: Reply with quote
Kickstart wrote:
spitfire123 wrote:

im using the RS rotax carb on the mito engine on a duel feed unlike the mitos 1 feed 2st oil feed.


Dual feed? RS uses a single feed like the Mito (just on the other side).

All the best

Keith


hi keith,

well the carb i have is suposidly off an rs125 but it has a thin oil feed on the right hand side of the carb (from standing at the back of the bike) and a bigger oil feed on the other side of the carb, both create a vaccume.

i did have the left hand side (bigger with feed) hooded up on that side only and blocked off the smaller one.

seemed to work okay and smokey on startup as you'd expect.

but have now made a T connection from the single pipe comming out of the oil pump for them both.

Thanks
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Kickstart
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PostPosted: 21:58 - 11 Nov 2009    Post subject: Reply with quote
Hi

Something wrong there. Possibly the cause of your problems.

All the best

Keith
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spitfire123
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PostPosted: 19:27 - 12 Nov 2009    Post subject: Reply with quote
Kickstart wrote:
Hi

Something wrong there. Possibly the cause of your problems.

All the best

Keith


hi,

yes i see what you mean but both have allways taken oil with no probelms, smokey on startup etc....

what side do you think (standing at the back of the bike) the oil feed should come out of on the RS carb?

cheers again mate Thumbs Up
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MaybeGuy
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PostPosted: 19:35 - 12 Nov 2009    Post subject: Reply with quote
cagiva mito carbs are for cagiva mitos
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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!! Mr. Green
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith
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Blue_SV650S
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PostPosted: 19:53 - 12 Nov 2009    Post subject: Reply with quote
Wow Spitfire123, have you porked Buddy's missus or smmin?!? Shocked
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spitfire123
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PostPosted: 20:20 - 12 Nov 2009    Post subject: Reply with quote
Blue_SV650S wrote:
Wow Spitfire123, have you porked Buddy's missus or smmin?!? Shocked


yea, hes a bit Rapey.

a strange little boy. Confused
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Last edited by spitfire123 on 20:26 - 12 Nov 2009; edited 2 times in total
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spitfire123
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PostPosted: 20:22 - 12 Nov 2009    Post subject: Reply with quote
mattsprattuk wrote:
cagiva mito carbs are for cagiva mitos


famous last words Laughing

the rs and mito carbs are allmost identical.
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Kickstart
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PostPosted: 20:37 - 12 Nov 2009    Post subject: Reply with quote
spitfire123 wrote:
yes i see what you mean but both have allways taken oil with no probelms, smokey on startup etc....


Although one could be something important such as a breather for the float bowl

spitfire123 wrote:
what side do you think (standing at the back of the bike) the oil feed should come out of on the RS carb?


Sitting on the bike on the left.

All the best

Keith
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spitfire123
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PostPosted: 20:46 - 12 Nov 2009    Post subject: Reply with quote
Kickstart wrote:
spitfire123 wrote:
yes i see what you mean but both have allways taken oil with no probelms, smokey on startup etc....


Although one could be something important such as a breather for the float bowl

spitfire123 wrote:
what side do you think (standing at the back of the bike) the oil feed should come out of on the RS carb?


Sitting on the bike on the left.

All the best

Keith


hi keith,

yea the one on the left if the one its allways been hooked up to.

however.....both of the inlets create a vaccume.

ive had the smaller one blocked off and just had the 1 side going, i seem to remember i had problems with it running at higher revs a while ago if the right hand side wasnt blanked off.

any ideas?

cheers
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Kickstart
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PostPosted: 20:56 - 12 Nov 2009    Post subject: Reply with quote
Hi

Would need to know what it is connected to inside to even guess. Could be a mod someone has done to fit a scot oiler (for example).

Could be that it ran a bit lean with it open to the air.

All the best

Keith
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spitfire123
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PostPosted: 21:08 - 12 Nov 2009    Post subject: Reply with quote
Kickstart wrote:
Hi

Would need to know what it is connected to inside to even guess. Could be a mod someone has done to fit a scot oiler (for example).

Could be that it ran a bit lean with it open to the air.

All the best

Keith


ahhh yes keith youve hit the nail on the head there,

i remember now anything after 1/2 she was coughing (to lean obv) and had to block off that tube and she ran fine as she did before with the old carb.


its in no way a mod....factory done.

cheers Thumbs Up
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Kickstart
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PostPosted: 21:12 - 12 Nov 2009    Post subject: Reply with quote
Hi

Not sure then. Never seen an RS carb with 2 points to connect the 2 stroke oil line.

All the best

Keith
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