scoop
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| posted on 20/6/11 at 08:41 PM |
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Overfueling bike carbs
Been out for a couple of runs today. The first was just to warm the engine before doing an oil change and then a longer one this evening. Each time i
came in from a run i smell of petrol! I can smell it on my hands. When starting the car the second carb spits back and when i take off the filter the
carbs seem quite wet inside. So i obviously suspect that the carbs are overfueling.
My question is how do i adjust the fuelling on the ZX9R carbs i have? Is it the size of the jets, the amount of turns out on the air screw underneath
or is it the hight of the needle or combination of all of them?
Cheers.
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David Jenkins
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| posted on 20/6/11 at 08:50 PM |
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What sort of fuel pump do you have? This sort of thing often happens if you're using a car-style pump instead of a bike one.
Otherwise - no idea!
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nearly done
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| posted on 20/6/11 at 08:54 PM |
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First and formost are you using a fuel pressure regulator? You need to use one preferably set to 2.5-3 psi definately no more. Bike ones are ideal but
you can use a facet type one (as i do with a adjustable regulator).
Cheers, Sean.
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scoop
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| posted on 20/6/11 at 09:02 PM |
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No i have bike fuel pump supplied by Bogg Bros. Is it called an interuptor type?
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David Jenkins
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| posted on 20/6/11 at 09:03 PM |
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Another thought - is the car running OK otherwise? If so, have you checked for fuel pipe leaks? (see
this thread. for fuel pipe problems.)
I didn't have a lot of success with a Facet pump and Filter King regulator - if I got the pressure low enough the flow wasn't sufficient.
Changing to a bike pump fixed all of my fuel problems. If you've got a pump from Boggs then I guess that will be fine.
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deltron63
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| posted on 20/6/11 at 09:05 PM |
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Fit a pump from the same model bike the carbs came from. I had the same problem with a facet and regulator.
Make sure it's not a fuel injection pump.
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scoop
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| posted on 20/6/11 at 09:09 PM |
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No fuel line leaks have checked from front to back and back to front. Are none of the things ive mentioned an issue then?
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myke pocock
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| posted on 20/6/11 at 09:13 PM |
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Just to have my sixpennyworth! I have a Filter King, Facet AND a pressure guage in the system on my bike carbed Skoda Estelle engine and dont appear
to have any probs. The pressure guage is to accurately check the pressure is correct but you can get a Filter King with a guage.
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mark chandler
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| posted on 20/6/11 at 09:16 PM |
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Combination of all three, the air bleed screw affects idle, lower the needle to weaken the mixture across the range, the main jet is the master in the
equation.
Did they come jetted for the application?
To much pressure should result in the carbs overflowing BTW.
Regards Mark
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scoop
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| posted on 20/6/11 at 09:20 PM |
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They came predrilled by Boggs. I think they take them out to 1.8mm. I have the air screw turned one and a half turns. This was set by the mot tester
to just get through the emissions test. The needles are one down from the highest setting and i have balanced the airflow today with a flowmeter.
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scoop
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| posted on 20/6/11 at 09:24 PM |
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The idle speed is adjusted by that thing you twist thats attached tot he bottom of the carbs.
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jacko
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| posted on 20/6/11 at 09:47 PM |
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Did Boggs block the air correction hole ? this can make them run rich, but not blocked can make them run weak at high revs
I have a 2.1 pinto zx9r / E carbs and it has 1.7 mm main jets with air correction hole blocked
The air screws are one turn out
All done on Boggs rolling road
[Edited on 20/6/11 by jacko]
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scoop
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| posted on 20/6/11 at 09:55 PM |
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Holes are blocked with snipped off bits of wire by the looks of it. Will try turning in to match your set up and play with the needle setting. Will
look at the jets after that.
Hoping to get the car to Frosts rolling road in ipswich soon. He has an excellent rep. Hopefully he will sort it if i cant 
You say you have E carbs. Thats my other thread im not having any luck with. Dont know which ones i have.
[Edited on 20/6/11 by scoop]
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jacko
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| posted on 20/6/11 at 10:08 PM |
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If it has clips on the needles they will be B,s or C,s photos help us
Just be careful if you remove the blocked holes it may make them to week = holes in pistons etc
Every engine is different to set up
ie what cam do you have / what exhaust what pistons etc etc
Make sure you use a carb bike fuel pump
[Edited on 20/6/11 by jacko]
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scoop
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| posted on 20/6/11 at 10:15 PM |
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Shant be unblocking them then. Standard cam and exhaust manifold. Just cant get photos to upload. Not sure what im doin wrong.
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jacko
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| posted on 20/6/11 at 10:19 PM |
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If std engine i would say the jets are 2 big having said that boggs know what there doing
give them a phone call and have a talk
Is it a 2l engine you have ?
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scoop
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| posted on 20/6/11 at 10:22 PM |
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It is 2l
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norfolkluego
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| posted on 20/6/11 at 10:33 PM |
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Does the engine 'bog down' around 4000 rpm. that's what I got when I was having the same problem last year, also told that Bogg
Brothers (who did mine) do fit oversize jets if they don't have the car to put on a rolling road so as it's not over lean. To be honest BB
didn't tell me that but that was the general advice from here.
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indykid
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| posted on 20/6/11 at 11:28 PM |
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quote:
Originally posted by norfolkluego
Does the engine 'bog down' around 4000 rpm. that's what I got when I was having the same problem last year, also told that Bogg
Brothers (who did mine) do fit oversize jets if they don't have the car to put on a rolling road so as it's not over lean. To be honest BB
didn't tell me that but that was the general advice from here.
Similar to this, my fireblade carbs that they knew were going on a 1.6 pinto came back with 170 main jets. It drank fuel and ran like crap.
After a rolling road session, I now have 150 main jets and the car's transformed.
I'd look at jets first and foremost
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scoop
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| posted on 21/6/11 at 04:40 AM |
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Okay. Now we're getting somewhere. I understand that webber jets fit these carbs. Which ones do i get, DCOE?
[Edited on 21/6/11 by scoop]
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Dingz
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| posted on 21/6/11 at 07:27 AM |
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DGAV/DGAS mains fit Mikuni carbs. They will spit back at times, (overrun) especially if the idle is lean, you could try opening the screws another
half turn.
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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scoop
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| posted on 21/6/11 at 08:00 AM |
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Mine are keihin though?
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RichardK
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| posted on 21/6/11 at 08:16 AM |
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I bought a set of miniture drill bits from the bay and just soldered the jets up and redrilled them.
Cheers
Rich
Gallery updated 11/01/2011
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David Jenkins
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| posted on 21/6/11 at 08:21 AM |
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I made my own jets! 
Quite easy, if you have a small-ish lathe and an existing jet to take measurements from. I made a couple of simple jigs and did a small
'production run'.
They're simple enough if you have reasonable skill with a lathe, but would be a challenge for a beginner.
And to answer the original question - there are a few things to consider when tuning bike carbs...
1. First, get the tick-over mixture right, and balance the carbs.
2. Then get the wide open throttle (WOT) mixture correct - this is governed by the size of the main jet.
3. Then raise or lower the needle (if you can) to get the mid-range mixture correct. My car runs rich at mid-range, but I can't lower the
needles (not adjustable) so I'd have to change the needles. It's not too far wrong so I haven't bothered to take it further, but it
would make a big difference to fuel economy.
4. If you're feeling really swish you could change the needles for ones with a different profile, to get the right mixture at all settings... I
don't know anyone who's done this!
Steps 1, 2 & 3 are the normal sequence though. Ideally you would get all of this done on a rolling road, but I did it with an AFR meter on quiet
back roads.
HTH.
[Edited on 21/6/11 by David Jenkins]
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keljon
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| posted on 21/6/11 at 10:59 AM |
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