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Author: Subject: a carb question
Dooey99

posted on 11/1/15 at 01:15 PM Reply With Quote
a carb question

right here goes i know carb tuning is fine work of art but... i have zzr1100 carbs on my 1.8 zetec, the main jets i have drilled to 160 as i have been reccommended this as a good starting point however the car will only start and run on full choke. i have wound the air/fuel screw all the way in before i done this i had to tape up half the trumpet and have full choke to get it to start so that told me there was to much air for the amount of fuel, so i wound the fuel screw all the way in and now it starts and runs on full choke without the trumpets being taped up. therefore i must still need more fuel... my question is what would be a sensible pilot jet to buy? the current size is 38 and i was looking at a 50? could anyone re assure me before i go and spend £25 on the jets

Sorry about the essay.





Less weight more speed, more power more speed

If in doubt, give it a clout

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19sac65

posted on 11/1/15 at 01:27 PM Reply With Quote
I have bike carbs on my rs 1800
They will always need full cold start from cold ( its not a choke flap like normal carbs)
3 turns are fine for idle,i drilled mine out as far as 2mm-a little rich,then bought new 1.8s and its great
I did notice that it was smoother cold on the bigger mains
Maybe go to 1.8 and see how it is
I spoke to bogg bros and hes gone over 2mm on some zetecs-its trial and error
I kept drilling till i was happy,then bought jets in the size i drilled to as theyre reamed at the ends and not just a hole that you get with a drill
Less than a tenner a set

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gremlin1234

posted on 11/1/15 at 01:27 PM Reply With Quote
you are supposed to need some choke when starting from cold...

try running it for a few minutes to see if it settles down

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coozer

posted on 11/1/15 at 01:36 PM Reply With Quote
Main jet size has nothing to do with starting, its purely for the top 25% ie, flat out.

Starting is controlled by the air screw underneath, 3 turns out is a good starting point. The idle jet is big enough for a zetec.

Main thing is balancing, float height and a good seal ensuring lift on the slider.

I would also recommend blocking the positive air feed that's under the mouth of the carb and the two feeds that come in between the Twp outside sets of carbs need to be open, that's free to air.

Once I'd had mine set up at bogg brothers I didn't need the choke, just a bit of throttle to get to going.





1972 V8 Jago

1980 Z750

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Dooey99

posted on 11/1/15 at 02:26 PM Reply With Quote
i understand that the choke is for starting cold, but mine seems like it needs more fuel, if i have the screw 3 turns out i have to tape up 75% of the trumpet or it wont run at all, it will only stay running with the choke on and the screw all the way in otherwise i have to block up the trumpets.





Less weight more speed, more power more speed

If in doubt, give it a clout

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Davedew

posted on 11/1/15 at 02:59 PM Reply With Quote
The choke on bike carbs adds more fuel, not restrict air flow.
My pilot screws are out roughly 3 turns, and needs choke to start.
Have you tried adjusting the idle speed screw at all?






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Dooey99

posted on 11/1/15 at 03:32 PM Reply With Quote
it adds more fuel therefore evening out the air fuel ratio? i think i need a wideband lambda and gauge to properly set my carbs up... we have just bought a new rolling road at work but it will be a couple of months before we have the new building up to put it in, im just abit impatient and want it running right now lol i have never been much good with waiting... im not really used to tuning carbs it just seems like i need more fuel but then i also guess i need to know if its rich or lean before buying jets, i just dont wat to pay £150 for a wide band lol as i dont really have that money at the minute.





Less weight more speed, more power more speed

If in doubt, give it a clout

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Davedew

posted on 11/1/15 at 04:04 PM Reply With Quote
I set my pilot screws 3 turns out, needles with circlip in middle groove and 160 mains. Needed hardly any adjusting on the rollers to get it right.
Have you checked for any air leaks that might make it lean?






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Dooey99

posted on 11/1/15 at 05:16 PM Reply With Quote
okay thanks i shall set mine to that in a little while and give it a whirl just before everyone trys to go to sleep.
did you block off the little air hole on the front of the carb? some people say you have to but others say you don't...

thanks





Less weight more speed, more power more speed

If in doubt, give it a clout

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Davedew

posted on 11/1/15 at 05:32 PM Reply With Quote
No left them exactly as standard except for changing main jets






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