Author Topic: So, you think you may need to re-jet......  (Read 3256 times)

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Offline F.Gassit

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So, you think you may need to re-jet......
« on: September 28, 2015, 06:21:38 PM »
Before you go and buy shiny bits of brass with different sized holes drilled in them,

1. What is the base gasket like ? Have you replaced it ? Not "It looks fine/the guy I bought it off said he'd replaced it/ etc...... have you replaced it.

2. Head Gasket, as above.

3. Crank seals, as above the above.

4. Intake boot. Got any cracks ? s it sealed to the cylinder correctly ?

5. Exhaust pipe. What is the fit to the cylinder like ? Have you cleaned it and the stinger/tail pipe ?

6 Coils. All of them. What's the resistance like compared to the specs ?

7. Carby. Wooooah Nelly.....no, leave the jets alone (apart from checking them for clean etc)...... What's the slide like ? What are the threads like on the air bleed and idle screw ? Do the floats actually float ? What is the needle and seat like ? What is the slide needle like ? What is the bore for the slide like ? What position is slide needle in ? Does it need to be moved up or down ?.....and so on....

8. Air filter. Clean ? Reasonably new ?

9. Plug. What is the gap like. Yes, you have to gap them. You'd be surprised how much of an effect an incorrectly gapped plug can have. Is it the right heat range for what you do and where you ride ?

10. Wiring. Any breaks or cracks ? What is the continuity of the wires like ?



Do all that, before you even entertain the notion of re-jetting. If you don't, you are most likely confusing what the actual problem is, with a solution that Bob's cousins Jacks sure fire advice from his best friends friend of a friend who used to work down the road and raced motorcycles in the good ol'days.

The bit that doesn't make it along with those "gems"of advice is that Bob's cousin Jack's best friends friend of a friend who used to work down the road and raced motorcycles back in the day had already done all those 10 things above, before he re-jetted.....and that he had to re-jet because the bike lived at WOT every second of it's life, because he was racing it.


Are you racing it ?


Then jetting is most definitely on the bottom of the list of things to do......if ever.

 :)


Oh,

11.   .......... run the pre mix ratio to spec. Not 50:1 because the oil rep said new oils are blah-blah-blah....... it's jetted to run that pre-mix ratio. We won't go into it now in detail, because it's this simple. If it says in the manual to run 28:1, and you are running 40/50:1....you are way to rich on fuel, and if you feel the need to keep the Oil sales rep happy, then buy a box of jets, get a notebook, and spend a lot of time pissing about trying to figure what jetting you need to run for 40/50:1.


Me ? Yamaha already did all of the notebook, box of jets tedious sh_t for me. I'll run the pre-mix ratio they said, and just enjoy riding my bike. :)



12. It's a 30 year old bike. If you think you can get it to behave and perform like a more modern bike, well.....it's your time and money.


It is what it is, what it was. You can tidy them up, make them real crisp etc, like Brooksies 465, but at the end of the day, a 465 is going to go like a 465 always went..... 175, 250, 400 whatever...

 :)
IT 175 F
TE 300
GR71D......nearly.....should be here in June.....currently taking up the only available space left at a property in Dubbvegas......

Offline 2fITy.J

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Re: So, you think you may need to re-jet......
« Reply #1 on: September 28, 2015, 07:03:03 PM »
I bet jet air pilots don't fiddle with their jets.......  :P ::)
A bike in the bush is worth two in the shed!

BMW-BSA-Ducati-Honda-Kawasaki-Lambretta-Matchless-Norton-Suzuki-Triumph-Vespa-Yamaha.

Dirty Dozen '13 DR650SE - '90 DR650RS - '82 IT465J - '82 IT250J - '80 GT80G - '77 A100B - '76 DT100C - '76 TC125 - '75 TM75 - '73 MX80 -       '73 TC100K - '69 TC120-1

Offline F.Gassit

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Re: So, you think you may need to re-jet......
« Reply #2 on: September 28, 2015, 07:23:00 PM »
I don't fiddle with mine, because I don't have to. I don't race. I use all the revs, not a certain , narrow, range somewhere near the top.

My bikes aren't pigs, and start and stop on a dime. They don't blubber, cough or fart anywhere in the rev range. Most I've ever had to do in regards to fiddling with jetting is move the needle up or down, or clean a spec of crud out of them.



And no, I'm not lucky. It's maintenance, and realising what you need to do and when. If I had the talent, and rode in the type of terrain, where you just basically hold it pinned and feed it gears, I'd be looking at changing jetting. I don't, so I don't.


MBoddy and MTeague are two people, who because of what they do with their bikes, and their talent for being able to pedal one, would have re-jetted (I'd imagine). Like I said, I don't do what they do, and I don't have their ability to use a bike like that, so I don't need to touch the the f__ken jetting.


Especially not because the bike just started playing up............there's 50 other things it's going to be......
IT 175 F
TE 300
GR71D......nearly.....should be here in June.....currently taking up the only available space left at a property in Dubbvegas......

Offline fred99999au

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Re: So, you think you may need to re-jet......
« Reply #3 on: September 28, 2015, 09:36:21 PM »
There is your killer statement right there Fred
Quote
Especially not because the bike just started playing up

If a bike starts playing up all of a sudden then something has broken.

Offline rd400pi

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Re: So, you think you may need to re-jet......
« Reply #4 on: September 29, 2015, 04:12:26 AM »
Excellent post, sir.

  Mike

Offline uk lee

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Re: So, you think you may need to re-jet......
« Reply #5 on: September 29, 2015, 05:02:07 AM »
Good sound advice

I've learned already - i was running at 40:1 premix , a simple change to 33:1 , and returning to stock jetting made all the difference to performance and starting.
I have raised the needle one notch to enrich the midrange - which has got rid of the detonation i was sometimes experiencing - but that's it.

Starts 1st or 2nd kick every time and pulls like a train .

I can acknowledge that jetting questions can pi$$ off some of the more experienced forum members , but a simple search reveals such massively differing opinions - that it's no surprise that the uninitiated get confused.
I may have asked some 'newbie' questions regarding jetting in the past (and probably will in the future)  - but i don't see that as a bad thing  - my granddad once told me "You're not stupid just because you don't know , but you are stupid if you don't ask"   . I reckon he was right.

Lee  :)

Offline killindini1

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Re: So, you think you may need to re-jet......
« Reply #6 on: September 29, 2015, 09:36:24 AM »
If i could add to it ::)

Read the farkin MANUAL 8)

Cheers,
Steve.
Beer is more than just a breakfast drink

Offline F.Gassit

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Re: So, you think you may need to re-jet......
« Reply #7 on: September 29, 2015, 02:51:34 PM »
Yeah, that comment wasn't aimed at you Lee. Every time you're doing something you've never done before, it's easy to get lost in complicated mis-information. The world is full of experts on any given topic...... it's usually only after you've spent money on things, that you've then munted by following said "advice ", that you figure out who is full of sh_t/doesn't know what they're talking about.....and those that do.


Your Grandad's saying is exactly right. Here, I was taught  "The only stupid question is the one you didn't ask ", same thing as what your Grandad said.


The other thing, I have found, to remember above all else when it comes to mechanical things, is K.I.S.S.


Keep It Simple, Stupid.


Engines and mechanical things can be really involved/technical/experimental........the trick is to know when, why and what for. To be honest, there's not much to being a mechanic, on anything.

What Killindini does is no different to anything I have done....... with the exception that if he makes a mistake, the consequences are higher. To do what he does, shows he's well practised, has a lot of experience, and is thorough.


In essence, that is all there is to being a mechanic. Follow the rules, do it right, first time.


A helicopter is a complex bit of machinery. No harder than anything else, just more to it.

These are Single cylinder gas pumps, with a bang stick screwed into the top of them. It's not hard.

Ditch the rumours and advice from experts in the street. Follow the manual, do things spec.


It can't not work if you do that.

 ;) :)
IT 175 F
TE 300
GR71D......nearly.....should be here in June.....currently taking up the only available space left at a property in Dubbvegas......

Offline 4V5

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Re: So, you think you may need to re-jet......
« Reply #8 on: September 29, 2015, 03:23:05 PM »
It's not the jetting, oil mixture, running in threads et al that are the issue as such, as you say there is no such thing as a silly question.

Those threads however seem to attract the silly answers mixed in with the correct advice and thats where it makes it harder to work out what will work for the person asking the question.

Keeping it to what the manual says will get it close, close enough to know what to change and where.. And also if it needs it.

Needs to be a sticky this thread
IT465x4 IT400C IT175F YZ465G YZ250C YZ250WR XJ650G RD350LC RD250LCx5 DT175Nx3 TW200x2 DT200L DT200R RT3 RX100G GT80F YZ80L PW50J KH250B1 KZ250D1 PE175C TS250ER TS185ER AG175B AG100

Offline F.Gassit

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Re: So, you think you may need to re-jet......
« Reply #9 on: September 29, 2015, 04:06:41 PM »
Well....... you're the bl__dy moderator !  ;) :D

It comes down to,

Do you love pulling things apart and putting them back together again ?  Then knock your socks off. Experiment, fiddle and f__karse about.

Do you like to do the required work, so that you can do the thing you really like....... ie, kicking the f__ker in the guts and just riding the b__tard ?


I'm a mechanic. I go for the second one. f__k working on sh_t unless I have to, and when I do..... do it f___ing once, properly, so I don't have to waste time f___ing with it every ten f___ing minutes.


 ;)


Those are your choices. Do the one that serves your interests best.


 :)
IT 175 F
TE 300
GR71D......nearly.....should be here in June.....currently taking up the only available space left at a property in Dubbvegas......