David Jenkins
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| posted on 20/1/08 at 09:40 AM |
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Bike carb main jets?
Ok - the long-running saga of my bike carbs continues... I am fast approaching the stage where I fit them to the manifold (couple of little jobs to do
first) so I now need to modify the main jets while I can easily get at them.
In the past people have suggested drilling them out to 1.7mm - it's a 1660cc crossflow that will hopefully give around 100BHP after these mods,
if that helps.
Is 1.7mm a reasonably good starting point? I have a range of small drills, if required.
Also, anything else I need to do in the area of jets and needles?
Any guidance would be appreciated!
David
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viatron
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| posted on 20/1/08 at 09:42 AM |
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I have used a dynojet kit on both my bike carbed projexts as without i found it impossible to get the fuelling right at the bottom and top end.
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David Jenkins
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| posted on 20/1/08 at 09:44 AM |
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How much do they cost, and from where?
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MB CUSTOMS
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| posted on 20/1/08 at 09:53 AM |
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Dyno jet kits cost between £85.00-£126.00 depending on bike make and model.
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garage19
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| posted on 20/1/08 at 10:08 AM |
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I would start with 1.6mm.
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David Jenkins
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| posted on 20/1/08 at 10:56 AM |
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Thanks Doug.
(and I might call on your help later on, following on from your comment a while back...  )
As for the dynojet kit - bit rich at the moment, as all I really want to do is to get into the right ball-park so that I don't muck up the
engine. Later on I'll go to a rolling road (if I can find one who's comfortable with bike carbs on a car engine, together with megajolt.
Shame that Bogg Brothers are so far away, as they would be ideal.)
Cheers,
David
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GaryM
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| posted on 20/1/08 at 10:58 AM |
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Hi David
I had a chat with a very helpfull guy at Bogg Bros on Friday about them making me a manifold for my similar upgrade.
As part of the service they would drill my FZR600 (Mikuni) carbs jets to 1.6mm which is their recommended (starting) jet size for my engine 1600cc GT
xflow.
They then suggested fine tuning with a rolling road and CO meter.
Cheers
Gary
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David Jenkins
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| posted on 20/1/08 at 11:07 AM |
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Ah - 2 votes for 1.6mm as a starting point! 
That'll do for now...
cheers all.
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Danozeman
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| posted on 20/1/08 at 12:03 PM |
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3 votes for 1.6 David. I dont reckon youl need bigger that 1.65.
Dan
Built the purple peril!! Let the modifications begin!!
http://www.eastangliankitcars.co.uk
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rusty nuts
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| posted on 20/1/08 at 12:59 PM |
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If you start with the 1.6mm you can always drill it out bigger if needed, easier than reducing from 1.7mm.
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jacko
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| posted on 20/1/08 at 03:52 PM |
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Hi i have a 2.1 pinto on zx9r carbs the engine is modded a lot and it has 1.7 main jets so i dont think you will need 1.7 mm as above try 1.6 mm but
get it on a r/road before giving it some stick it may go weak at full rev's
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x_flow57
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| posted on 20/1/08 at 05:41 PM |
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Hi David
I spoke to these people (Rolling road) a short while ago they told me they had had experience
of bike carbs and megajolt.
Boggs sugested 155 mains on my R6 carbs by the way.
<<<<<< For Sale
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Gaz 1977
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| posted on 20/1/08 at 07:08 PM |
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hi David,
Bogg bros drilled my zx9r jets to 1.6
they said it would be a good staring point.
Gaz
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vinnievector
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| posted on 21/1/08 at 01:52 AM |
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I to was recommended 1.6 by bogg bros as a starting point for my 2ltr pinto.
If i was you i would start around the 1.5 mark and work up in .5 inc good luck
iam embarking on the same trip, soon as i get my manifold rubbers
Let me know how you get on .
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DarrenW
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| posted on 21/1/08 at 10:54 AM |
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My pinto is 1.6mm on ZZR1100 carbs. iused brand new 1.6mm drill and twisted them in by hand (no power drill used). They didnt need any further opening
up when Dave Bogg set it up on rollers.
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David Jenkins
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| posted on 31/1/08 at 12:44 PM |
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One further question!
I believe that Bogg Brothers also change the needle position when they set up carbs - should I also do this?
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DarrenW
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| posted on 31/1/08 at 08:54 PM |
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I drilled jets, needles in mid position, blocked off some air holes, air screws all way in then one turn out. Car fired up no issues whatsoever. On
the road it was sweet compared to the DGAS (albeit i had to mess on getting the carb tops to seal but a smidging of rubber grease in the groove worked
a treat). Took it all to Boggs asap and found out it was running way too lean. Dave spent ages tweeking to get it good through the full rev range -
charged next to nowt and even had a working museum to look around.
If you like sugar in your coffee you may need to take some of your own!
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