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Carb question

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DavidZ1R
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Re: Carb question

#16 PostAuthor: DavidZ1R » Sat May 26, 2018 5:27 pm

Update

Well got some acid z1b man suggested, thanks Paul, put in all the ports, after I had stripped the carbs, again, noticed a fair bit of fizzing on 3 and 4 . Flushed out with clean water, dried off.
Checked the screw holes on 3 and 4, noticed the mixture screw did not go in as deep as in 1 and 2, used an old screw, bit of 3 in 1 oil and screwed back and forth, it must have cut through old contamination or cleaning medium, went through all 4 and the screws all went in further.
Taped up the holes on the air box, made sure the filter lid was fully on, carbs vacuumed again, bang on, put the gunsun tune on again, nice blue flames on all 4, whey hey, took it for a spin, bloody flat spot, but not as bad as before, starts at 2k revs, clears at 3.
The only thing which was supposed suggested by the guy at nrp carbs was that the rubbers the slide spindle goes through could be worn, letting to much air in, so that is the last thing I could do, but not going to bother for a while, just going to ride the damn thing for a bit. So thanks for all the tips guys.
CB125 GT380 CB750F1 Z1R GPZ 750 Turbo Z1R

johny brando
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Re: Carb question

#17 PostAuthor: johny brando » Mon May 28, 2018 12:58 am

zed1015 wrote:Too much air via open carbs, modified airbox or pods etc will cause a flat spot just off idle at around 2000 rpm and no amount of jetting will fully sort it.
The solution when using bellmouths etc is to fit the air corrector jets i mentioned earlier to richen the mixture in that area .
These are m5 brass grub screws with a 0.6mm drilling that screw into the air bleed to the emulsion tube and were available from LEDAR/Armstrong engineering back in the day.


Rob as usual is 100% correct ..... .Z1bman is also bang on too because like he correctly says...Ultrasonic cleaning + using v/hot fluid = even just near boiling water with say Washing up liquid ( this will softens & loosens the Varnish so that with the bombarding shock waves of the Ultrasonic ... for about 8 Hours will then seem em clear ! ) this is the only way to 100% clear PARTIALLY blocked drillings that are 'appearing' to be clear, as air or fluid can & will still pass through a partially obstructed passage & that will then display itself as a carb defect.
I have 29mm VM Smooth Bores on mine & I did a fare bit of experimenting with Slide Cutaways- Needles even Pilot jets ...as the pilots contrary to normal believe do on VM Mikuni's !... operative & contribute over the entire rev-range but primarily they come into play up to about approx 2000 revs . ( I had open bell Mouths then Pods & I found .6 is the size that was best ) & taping out your your Emulsion tube Air supply bore & fitting a set of .6 Air Corrector jets... as the std holes are not correct there & need the reducing jets fitted to restrict the air to the elusion tube so as to RICHEN up the mixture in the crucial needle area range thats causing the flat spot. Mine was then much crisper.
As Z1bman states best to preserver as just buying another set of carbs could easily just give yet another set of issues to address ..who knows what would be wrong with them & any set of carbs left laid up with fuel in them for over about 9 months will definitely have Varnishing occurring within them ! Good luck ......hang in there as your nearly there ! Cheers Lee.

DavidZ1R
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Re: Carb question

#18 PostAuthor: DavidZ1R » Sat Jun 23, 2018 2:49 pm

Issue resolved, was going to give up with these god damn carbs and the flat spot, so last thing to try was , as been suggested , was raise the needles one notch, while I had them in pieces I thought I might also change the needle springs, the existing ones which were the originals I think, and also seemed very light compared to the ones in the keys ter kits. Put them all back together and back on the bike, took it for a spin, perfect, not a bit of stutter or bogg, at last, result, so thanks guys for all the tips, don't know if it was the needle height or the springs, and now it's right , I ain't going to find out.
CB125 GT380 CB750F1 Z1R GPZ 750 Turbo Z1R

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zed1015
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Re: Carb question

#19 PostAuthor: zed1015 » Sat Jun 23, 2018 3:37 pm

Lifting the needles is what has hidden/masked the lean condition flat spot but this is not ideal as you will also be running rich in all other areas .
You will be slightly down on power and also use more fuel than you need to although you probably won't notice and it won't really do any harm.
To be correct you really need to either put the airbox back to stock to restrict the air intake and drop the needles back to the middle position or fit air corrector jets and drop the needles back.
The corrector jets can give between 2 to 6 HP ,improve overall running and in some cases allow you to reduce the size of the main jet.
If you want to go the corrector jet route i still have a set for sale.

DavidZ1R
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Re: Carb question

#20 PostAuthor: DavidZ1R » Sat Jun 23, 2018 4:41 pm

zed1015 wrote:Lifting the needles is what has hidden/masked the lean condition flat spot but this is not ideal as you will also be running rich in all other areas .
You will be slightly down on power and also use more fuel than you need to although you probably won't notice and it won't really do any harm.
To be correct you really need to either put the airbox back to stock to restrict the air intake and drop the needles back to the middle position or fit air corrector jets and drop the needles back.
The corrector jets can give between 2 to 6 HP ,improve overall running and in some cases allow you to reduce the size of the main jet.
If you want to go the corrector jet route i still have a set for sale.


Yes I know it may run richer, the airbox is stock, with snorkel and air filter fitted, am going to see how it performs for a while, maybe the fuel today is not as good as years ago, anyway much happier it runs smoothly.
CB125 GT380 CB750F1 Z1R GPZ 750 Turbo Z1R


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