Turbo plumbing for a simpleton

[Blubber]

Not the update I was hoping for.

Thats crappy news bud.

Curious to know what causes your 6.5 rev ceiling. 

Sorry, Can't help you with that. 

 

 

 

 

[El Gringo]

Cheers Boss.

I'm thinking it something fundamental that i've got wrong in the plumbing or in the carbs.

The fact it stops at the same point everytime suggests it's not just jetting 

[Blubber]

It is mainly because of your thread ( and Marco's - bruteforce)  I started reading deeper into turbo projects and their setups / arrangements , so I am learning too from your adventures.. Big time.

 

If I got previous lessons translated correctly in my head.... The 6.5 limit sounds like the boost compension on the carb diaphragms is not working like you think it should.  Again very new to turbo's and the associated tubing and control.  Just something that popped up as a brain fart.

[El Gringo]

1 hour ago, Blubber said:

The 6.5 limit sounds like the boost compension on the carb diaphragms is not working like you think it should.  

Yep, this is what i'm thinking. 

We've got the holes in the slides to allow boost above the diaphragms and i've added a hole through the carb body which runs from the inlet of the carb mouth up into the pocketed area under the diaphragms.

I saw this on a thread on a turbo bike group on FB, it seemed a better option than having to use the main under diaphragm vents between 1&2 and 3&4 - which i now have blocked off

Maybe the hole i drilled isn't big enough to counter act the boost effect going through the slide? I dunno

But the fact we changed a load of things and it's exactly the same is what makes me think it's something more fundamental.

I'll pop some pictures up of what i've done in a bit and yesterdays dyno chart

Up to the point where it goes wrong it's absolutely perfect and the A/F looks great

[MeanBean49]

39 minutes ago, El Gringo said:

Yep, this is what i'm thinking. 

We've got the holes in the slides to allow boost above the diaphragms and i've added a hole through the carb body which runs from the inlet of the carb mouth up into the pocketed area under the diaphragms.

I saw this on a thread on a turbo bike group on FB, it seemed a better option than having to use the main under diaphragm vents between 1&2 and 3&4 - which i now have blocked off

Maybe the hole i drilled isn't big enough to counter act the boost effect going through the slide? I dunno

But the fact we changed a load of things and it's exactly the same is what makes me think it's something more fundamental.

I'll pop some pictures up of what i've done in a bit and yesterdays dyno chart

Up to the point where it goes wrong it's absolutely perfect and the A/F looks great

Holes in the slides may be the problem. Your boost matching pressure for the diaphragms comes from the pitot tube. It should pressurise the top of the daphragms. I would leave everything in the carbs stock. On bandit 12 and gsxr 36mm's having a dynojet kit makes it nigh on impossible to get them to run right

[El Gringo]

Hmmmm, i was under the impression that the pitot tube was there for dynamic boost compensation in the float bowls Rob?

Hence connected to the float bowl vents

The GK76a carbs are more like the 40mm mikunis - they have a vent to atmosphere from under each diaphragm. This is what i've got as it stands

The little hole in the middle of each inlet mouth is 3.2mm and feeds into the void under the diaphragm. You can just about see where i've got the big vent between the pairs of carbs blanked off that leads to the same void.

The theory being that the boost in the inlet should pressurise the underside of the diaphragm through the hole (rather than feeding it through the vents from the plenum which was going to be a ballache)

Each slide has 2 x 2.5mm holes - maybe the hole in the carb body needs to be bigger to match or maybe one of the slide holes needs blocking?

 

Edited January 21, 2018 by El Gringo

[El Gringo]

The last run with the horrible line is with the turbo up pipe disconnected, so no boost

Edited January 21, 2018 by El Gringo

[Gixer1460]

If it ain't running right even without boost and with the sharp stop, i'd guess it's more electronic rev limiter'esc - the rich AFR is likely uncombusted mixture?

[Blubber]

1 hour ago, Gixer1460 said:

If it ain't running right even without boost and with the sharp stop, i'd guess it's more electronic rev limiter'esc - the rich AFR is likely uncombusted mixture?

He did swap to another cdi to rule that out.

Maybe the second one is duff too? 

 

I think the 400's have a rev limiter at 13.000rpm.

What if the generator he has is the wrong type and puts out double pulses it ....the Rev counter would read double tooo...right?

[Captain Chaos]

35 minutes ago, Blubber said:

.right?

stock revcounter, yes.

CBF going throught the whole thread,  but if Gringo has an aftermarket tacho he might not have noticed when programming it. This could explain the 6,5K limiter (assuming of course the pulse generator is somehow not of the correct type).

Edited January 21, 2018 by Captain Chaos

[Captain Chaos]

On 03/05/2017 at 11:38 PM, El Gringo said:

Apparently they swapped CDI and trigger wheel in '93 - guess which muppet didn't know that when he bought a '91 CDI...........

worth investigating further I guess

[MeanBean49]

4 hours ago, El Gringo said:

Hmmmm, i was under the impression that the pitot tube was there for dynamic boost compensation in the float bowls Rob?

Hence connected to the float bowl vents

The GK76a carbs are more like the 40mm mikunis - they have a vent to atmosphere from under each diaphragm. This is what i've got as it stands

The little hole in the middle of each inlet mouth is 3.2mm and feeds into the void under the diaphragm. You can just about see where i've got the big vent between the pairs of carbs blanked off that leads to the same void.

The theory being that the boost in the inlet should pressurise the underside of the diaphragm through the hole (rather than feeding it through the vents from the plenum which was going to be a ballache)

Each slide has 2 x 2.5mm holes - maybe the hole in the carb body needs to be bigger to match or maybe one of the slide holes needs blocking?

 

Sorry my bad. Being a mong again.

I cant see why you would need to drill holes in the carb body at all. 

Does seem more like an electicalissue though

[El Gringo]

16 hours ago, Captain Chaos said:

worth investigating further I guess

I did start wondering about swapping back to the original pickup wheel, but i'm 99% sure that with the new wheel matched to the CDI it should work.

15 hours ago, MeanBean49 said:

Sorry my bad. Being a mong again.

I cant see why you would need to drill holes in the carb body at all. 

Does seem more like an electicalissue though

The holes are to get a boost reference under the diaphragms - unlike the 36 and 38mm GSXR and Bandit carbs these don't have the extra oval bit with the port running into the area under the diaphragms. That info was from Marco's article in the Vault about setting CVs up for turboing.

There's also an article on the old turbobike forum about R1 carbs which are the same principle if i've interpreted it correctly

I'm still liking the slide not lifting for the stop but will investigate the electrical possibility further.

Thanks to everyone for the suggestions - gives me a few more ideas to chase down

[El Gringo]

Putting the electrical possibilities to one side for a minute and thinking a bit about the holes i've added, ages ago i found a thread on one of the FB groups about adding this hole to the 40mm GSXR carbs and they went with a 5mm diameter.

I believe the guy who posted it was the bloke from Proboost in Finland (whether this is a good thing or not remains to be seen)

I went with 3.2mm as i didn't want to over do it just in case it went wrong. However, comparing the area of the new inlet hole to the area of the slide holes would it makes sense that for it to be balanced they need to be at least the same cross sectional area?

For example my 3.2mm holes is 8.02mm2 whereas the 2 slide holes add up to 9.82mm2 - not a huge difference but give the location and size of the extra hole, could the velocity of the intake air be causing a vacuum as it passes over the hole and holding the slide down as opposed to equalising the pressure??

Having looked at a set of Bandit 12 carbs the dyno guy had handy, you've got the top of the oval which feeds directly under the diaphragm so it sees equal air velocity to whats passing into the carb (and having checked my 36mm GSXR11 carbs they are the same) - working on the theory that when people turbo 11s and 12s they just add the silicones and this port sees the same boost as the main mouth of the carb logically (and as per the various guides for turboing CV carbs) the underside of the diaphragm needs to see boost and that the area/size of the port to get it there can be as big as it needs to be if you see what i mean.

The obvious thing would be to use the 2 big air vent points between carbs 1&2 and 3&4 but i haven't got an easy way of adding a take off to the plenum to facilitate this.

I suppose i could tee into the pitot tube line that feeds the float bowls and use the 2 main vents to test it, the addition of the small hole should affect it as it's doing the same job

Sorry for rambling, this is me trying to get it straight in my head as much as anything

Below are the pictures i saved from that FB thread

Fortunately the 400 carbs don't appear to have the bit shown in the last photo where it breaks through into that tube that then needs re sealing

[Captain Chaos]

7 hours ago, El Gringo said:

I did start wondering about swapping back to the original pickup wheel, but i'm 99% sure that with the new wheel matched to the CDI it should work.

99% is not enough

actually I also thought about this ignition stuff last week but I assumed the rev limiter on a 400 would be 14000 or 15000 or thereabouts so did not think about it further. But since Blubber mentionned it's 13000, it seems very plausible (although he too seems not 100% sure about the number).

 

[Madb]

Rev limit is 12000rpm 53bhp 93 and after. Before 93 was 59bhp and 12500 rpm. Gk76 models. 

[Madb]

Silly question. Have the carbs been balanced? 

[nlovien]

bloomin ek this can really do your head in trying to think out CV carbs with a variable positive pressure supply - home work time but i'll ramble on anyway

you got holes to create a pressure diff to enable lift and you got holes to bleed off ( balance ) to enable a controlled lift inline with fueling needs

bigger balance holes = quicker equalisation = no lift when it does - too small holes here and it lifts too quickly - out of sync with the carb jetting circuits - you would have thought by going down main jet - if it was too small holes i.e. getting a main jet slug of richness too early, you should have seen more improvement with smaller mains - ok then is it as you suspect = holes too big, balance too quick - slide not lifting to enable transition to mains - makes sense since you didn't get a measured response by lowering the mains - i.e. is it ever getting to the main jet - wonder if you removed it completely would you see any difference on the dyno ? - no if all its doing is fluttering around the needle fueling only - so suggests smaller balance holes

bit I can't get my head around is pressurising the venturi - this also pressurises the negative pressure to the top of the piston  via the engine vacuum route =  the press diff hole - so i'm thinking your relying on positive venturi pressure to lift from bottom versus engine draw to suck from top as said i'm guessing as I go -- anyway -sooo in this case you want to vent the top of piston to atm. to create press diff to enable lift - now again though - if the balance holes are too big - but now relative to the atm vent hole size then its like above

ok so you need to match the equalising hole size to the atmospheric vent size, the bigger the vent is relative to the equalisation the quicker it will lift - but it needs to sustain boost to achieve this - it can't sustain boost if it ain't working hard and it can't work hard if you can't get it to transition via lift from N/A to positive pressure and it will not achieve this if the vent size is too big for the engine vacuum to work

holy shit this can get complicated - but the same point seems to keep coming back - smaller equalisation holes = plug off / reduce the holes in the slides

i need a dram

 

[Gixer1460]

I don't know what the problem is but I always thought that the carbs should stay pretty much bone stock with a minor MJ increase to start with. The Dynamic boost over the fuel is to keep fuel delivery constant - the std. bleeds and air vents to the diaphragm work via air flow so either NA or turbo it's self compensating or use a heavier spring to slow the lift providing the needle can cope.

[El Gringo]

1 minute ago, Gixer1460 said:

- the std. bleeds and air vents to the diaphragm work via air flow so either NA or turbo it's self compensating or use a heavier spring to slow the lift providing the needle can cope.

I think that's the critical thing, on these there isn't a bleed to the underside of the diaphragms from a boosted or non boosted air point of view.

The underside of the diaphragms vent to atmospheric pressure, but above will see boost through the slide holes.

From reading the various guides the underside needs to see boost too, hence the holes. On an 11 or 12 carb set this is taken care of by the extra port above the main inlet mouth, hence leaving them stock as this pressure reference is already there.

Next idea is to open the holes up further and try it. If it doesn't work i'll block them up and try again. At this point there isn't much to lose in trying both

 

[El Gringo]

1 hour ago, Madb said:

Silly question. Have the carbs been balanced? 

Yep, made quite a difference to the idle

[El Gringo]

I'd also like to say a massive thank you again for everyone's help and thoughts on this 

[Gixer1460]

33 minutes ago, El Gringo said:

I think that's the critical thing, on these there isn't a bleed to the underside of the diaphragms from a boosted or non boosted air point of view.

Don't know the carbs but if the above is true - as stock - I can't see how they work? Normally the slide holes adjust lift speed - and no I don't know how that works LOL!

[El Gringo]

1 hour ago, Gixer1460 said:

Don't know the carbs but if the above is true - as stock - I can't see how they work? Normally the slide holes adjust lift speed - and no I don't know how that works LOL!

I've not explained that very well. The underside of the diaphragms is connected to the airbox so it's only an indirect atmospheric feed.

Anyway, I will not be deterred! We're nearly there!

[Madb]

So is there not enough vacuum above the diaphragm to lift the slides? Is this the cause of the Rev ceiling 6.5k.

Air leak on that side maybe or am I well off the mark.

Me just learning about forced induction but sounds like not enough vacuum  above diapham.