Guess the Jet size (Pleeeeeaaaase!!!)

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Manfriday

Guess the Jet size (Pleeeeeaaaase!!!)

Post by Manfriday »

Hi guys,
I'm making a TR Tribute (not replica as I have neither the skills nor the money) out of my GT750 for Australian roads.
I dragged the rusted GT out of a barn a couple of months ago and began a simple refurb job to get it through 'Rego' which is our road-worthiness examination.
Obviously the carbs will need cleaning and overhauling. I am planning on buying one of Baz's DVD kits, but...........

What jet sizes shall I ask for?

1. I don't know how well the bike ran on current jets.
2. I want to use bellmouths/open carbs.
3. I am in a huuuuuuuuuge country with no dyno anywhere near.
4. The bike has expansion pipes on, similar to Allspeeds.
5. The barrels are unlikely to have been ported.

I need jets to get it going, somewhere to start.
Surely someone else has run this configuration before.
Is estimating new jet sizes likely to be more dangerous than running current sizes?
I understand people's reluctance to recommend sizes because of the implied responsibility for a damaged engine, but there is none.

You guys have got a much better chance of making a more accurate estimate than me, that's why I joined this forum; you've done it before.

I have spent very little money on the bike so far and the previous owner told me she was going to 'Put a match under it' if I didn't want it.
I need to hear it run semi-reasonably before I invest any more in it. I can't afford, and this bike doesn't warrant thousands throwing at it.
There are good, running examples available locally, quite reasonably priced.

This is an experiment and experiments sometimes blow up in your face. I'm doing what I can to prevent it, and welcome your advice.

Thank you,
Lozz :? :? :? :? :? :
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by teazer »

Bit of a challenge there mate. Allspeeds were fairly restrictive and typically didn't need much larger jets. open intakes could upset things though.

Assuming that the bike runs and crank seals are fine etc, if it's a 74 on with BS40 CV carbs I'd start with 117.5 main jets are 47.5 pilots. They must be the correct jets though. Check http://pinkpossum.com/GT750/carb/BS40carbs.htm for more info on the carbs and jets. It will not necessarily answer every question, but it will get you started on the road to poverty. :shock: :lol:

It is possible that you will need larger jets but not likely. If you want to start really safe, you could go with 120s on all 3 pots to start. Use new fine wire plugs, preferably throw the old points and condensors out and fit an Accent ignition from Uwe in Germany along with new plug caps. You could home brew a DYNA S sysetm like this http://pinkpossum.com/GT750/Dyna%20S.htm I have done two of those plus a Newtronics and a couple of Ignitech systems and I am using Accent on the current Dunstall GT build.

You do know that without pictures it didn't happen..... ;)
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Manfriday

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by Manfriday »

Thanks loads for that advice mate. I will look at the links.

I was planning on getting everything I could from Baz as I believe he is the expert.

I having to make some assumptions.

I also don't need the bike to run like a dream at this moment in time, just run.

Electronic ignition is certainly on the 'to do' list, but I'll need some reassurance from the bike that it is not a waste of my time and money.

Crank seals, water pump, the whole lot will get done in time; I just need some signs of life!

Thanks again.
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by teazer »

I believe that he is. In Oz, the local go to guy for jets is Ian Williams at IWT in SA. He's a kart race guy and Mikuni dealer.
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canaletto5
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Location: Derbyshire

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by canaletto5 »

teazer wrote:I believe that he is. In Oz, the local go to guy for jets is Ian Williams at IWT in SA. He's a kart race guy and Mikuni dealer.
"Local"...... :lol:
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by teazer »

To the orstralian guy in WA that asked the question? Yes.

To you? Not so much. :roll:
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Manfriday

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by Manfriday »

canaletto5 wrote:
teazer wrote:I believe that he is. In Oz, the local go to guy for jets is Ian Williams at IWT in SA. He's a kart race guy and Mikuni dealer.
"Local"...... :lol:
The world is a tiny place. I for instance, used to work on Burton Road in Derby!
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canaletto5
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Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by canaletto5 »

Manfriday wrote:
canaletto5 wrote:
teazer wrote:I believe that he is. In Oz, the local go to guy for jets is Ian Williams at IWT in SA. He's a kart race guy and Mikuni dealer.
"Local"...... :lol:
The world is a tiny place. I for instance, used to work on Burton Road in Derby!
And I used to live near Perth WA ! :lol:
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PaulD738
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Joined: Thu Sep 25, 2014 6:57 pm
Location: Warrington Cheshire

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by PaulD738 »

canaletto5 wrote:
Manfriday wrote:
canaletto5 wrote:"Local"...... :lol:
The world is a tiny place. I for instance, used to work on Burton Road in Derby!
And I used to live near Perth WA ! :lol:
I've been to Blackpool on a day trip does that count? :lol:
They're rubbish them Jap bikes lad they won't last five minutes! you want to get yourself a nice Royal Enfield!
A quote from my old dad 8-)

I started out with nothing and I’ve got most of it left!
Roger Ackery
Posts: 3693
Joined: Wed Jul 20, 2011 3:40 am
Location: Sydney NSW Australia

Re: Guess the Jet size (Pleeeeeaaaase!!!)

Post by Roger Ackery »

I've been to the Isle Of Man........10,599 miles from Sydney, I think I win :tw :P :P :P
Cheers,
Cheers.
Roger
GT750A.
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