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Author: Subject: Overfueling bike carbs
scoop

posted on 20/6/11 at 08:41 PM Reply With Quote
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

posted on 20/6/11 at 08:50 PM Reply With Quote
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

posted on 20/6/11 at 08:54 PM Reply With Quote
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

posted on 20/6/11 at 09:02 PM Reply With Quote
No i have bike fuel pump supplied by Bogg Bros. Is it called an interuptor type?
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David Jenkins

posted on 20/6/11 at 09:03 PM Reply With Quote
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

posted on 20/6/11 at 09:05 PM Reply With Quote
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

posted on 20/6/11 at 09:09 PM Reply With Quote
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

posted on 20/6/11 at 09:13 PM Reply With Quote
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

posted on 20/6/11 at 09:16 PM Reply With Quote
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

posted on 20/6/11 at 09:20 PM Reply With Quote
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

posted on 20/6/11 at 09:24 PM Reply With Quote
The idle speed is adjusted by that thing you twist thats attached tot he bottom of the carbs.
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jacko

posted on 20/6/11 at 09:47 PM Reply With Quote
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

posted on 20/6/11 at 09:55 PM Reply With Quote
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

posted on 20/6/11 at 10:08 PM Reply With Quote
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

posted on 20/6/11 at 10:15 PM Reply With Quote
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

posted on 20/6/11 at 10:19 PM Reply With Quote
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

posted on 20/6/11 at 10:22 PM Reply With Quote
It is 2l
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norfolkluego

posted on 20/6/11 at 10:33 PM Reply With Quote
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

posted on 20/6/11 at 11:28 PM Reply With Quote
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





me? ambivalent? well, yes and no

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scoop

posted on 21/6/11 at 04:40 AM Reply With Quote
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

posted on 21/6/11 at 07:27 AM Reply With Quote
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

posted on 21/6/11 at 08:00 AM Reply With Quote
Mine are keihin though?
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RichardK

posted on 21/6/11 at 08:16 AM Reply With Quote
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

posted on 21/6/11 at 08:21 AM Reply With Quote
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

posted on 21/6/11 at 10:59 AM Reply With Quote
.
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