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Discussion Starter #1
hi, I'm writing from Italy and I say first that my English is not very good. I have seen that in this forum are all very good with the bike and I wanted to ask a question.

I have a Bonneville 790 with removed Air Intake System, Uni Filter, Snorkel removed and mufflers Debaffled.


what size of Main Jet should I mount?

I think that the ideal should be around 120/125 with Pilot Mixture Screw turn 2.75. Is it correct? I hope you can help me.

Sorry for my bad English.
 

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120 should be close to the right size.
 

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I agree....120 should be real close to the correct size for your current modifications.

Don't apologize for your English--it is better than mine.:D
 

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Jetting

Be sure to check your pilot jet while you are in there. Use a #42. This will have a very positive effect on your midrange. Your english is fine.
 

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Discussion Starter #6
Be sure to check your pilot jet while you are in there. Use a #42. This will have a very positive effect on your midrange. Your english is fine.
hi, in italy we have a lot of problems to find pilot jets for mikuni...
i'l try to regolate air mixture screw... for now i can't do anithing :/

thank you so mutch ;)
 

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You probably don't need #42 pilot jets with your setup.
 

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I agree with Marty in the post above. The 790 should run fine with the stock 40 pilot jets. Many run 42 pilot jets in the 865's, and I have no comment on that; however, I believe the 42 pilot jets are not needed for the 790 unless one is running header pipes without the crossover pipe. When I ran my bike with this type of header, the 42 pilot jet was needed; but, it is not needed now with the airbox removed and NH Togas. I still have the 42 pilot jets in but the pilot screws are adjusted less than 1 turn out.
 

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Jetting

Not to be argumenitive, but the guys at South Bay Triumph (British Customs) told me that when any mods are done to the intake, they always recommend going to a #42. The main jet is the one that requires more scrutiny because of the many different exhaust systems available, including simply removing the baffles on a stock set of silencers.
 

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Discussion Starter #11
ok, i'l try to find a 42 pilot jet... while I wait try to adjust the pilot mixture screw...

Keihin carburettor... yes...lapsus:p

Thanks to everyone for help:thumbsup:
 

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I'm sure the guys at South Bay know a lot more than I will ever know, and they probably know more than the A/F guage that was used to set mine up. After 21000 miles I still get 50+ mpg and it still runs like a scalded cat, and hits the rev limiter set at 8100 rpm before I can get ready to shift sometimes.:D
 

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Frankie -

I have exactly the same set-up as you.

I run my carbs like this:

- 115 mains
- stock pilots
- thruxton needles

After I debaffled the stock pipes and put in the 115 main jet, I found that I had a flat spot at 3000rpm. The Thruxton needles fixed the flat spot. Now she runs perfectly through the entire rpm range.

P
 

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I have a 790 Bonnie with rear baffle removed and a couple of extra holes punched in the baffles.
snorkel removed and the snorkel hole enlarged.
I find 115 main jets
Stock needles with one .5mm shim
Standard 40 idle jets with about 3 turns out
works well for my bike.
I had Thrux needles but felt it was to rich in the mid upper range and was using too much fuel.
 

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Same opinion here....I had vintage style mufflers installed and my dealer installed 42 pilots as well.Starts easy..I have a 790 motor ...125 mains .. Thruxton needles and great midrange performance,fun to ride.
Hey bonnieowner ,long time no see.
 
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