Turbo plumbing for a simpleton

[El Gringo]

3 hours ago, Madb said:

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.

Or too much below preventing it from lifting? This is the theory i'm working on at present.

To that end, we now have 5.5mm holes into the bellmounth as per the pictures i found above (5.5 as my 5mm drill is a bit tatered)

It's all back together now so will give it a go, only thing i'm struggling with is a test location without having to take it back to the dyno

Unfortunately living down a dead end in the middle of a sleepy English village isn't conducive to turbo testing, and also, I quite like my neighbours 

Plus it's still pissing it down here and freezing cold, and the idea of testing with an ancient slick on the front wheel doesn't strike me as being very brilliant 

[MeanBean49]

17 minutes ago, El Gringo said:

Or too much below preventing it from lifting? This is the theory i'm working on at present.

To that end, we now have 5.5mm holes into the bellmounth as per the pictures i found above (5.5 as my 5mm drill is a bit tatered)

It's all back together now so will give it a go, only thing i'm struggling with is a test location without having to take it back to the dyno

Unfortunately living down a dead end in the middle of a sleepy English village isn't conducive to turbo testing, and also, I quite like my neighbours 

Plus it's still pissing it down here and freezing cold, and the idea of testing with an ancient slick on the front wheel doesn't strike me as being very brilliant 

Too much below is going to make it lift quicker as opposed to stopping it.

[Gixer1460]

4 hours ago, Madb said:

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.

Carbs don't essentially work with vacuum - they function via airflow.............else how would all those turbo blow through carb set ups work - no vac when on boost!

High pressure is created / generated through the venturi  - a CV carb tries to keep this constant by lifting / lowering the slide.

[Madb]

Thought the slides were controlled by vacuum on cv carb? 

[El Gringo]

In the case of turbo'd CV carbs i'd say it's a case of pressure equalisation above and below to allow it to function as it normally would

*or not, i'm not really sure at this point

Edited January 23, 2018 by El Gringo

[El Gringo]

Right, i've employed the mind of a clever bloke at work and he agrees that the slides lift as a result of a vacuum being drawn through the slide holes and the resulting low pressure above the diaphragm causes it to lift.

Logically then as the underside of the diaphragm sees atmospheric pressure in an N/A engine, in order for it to be able to draw a vacuum on the slide and cause it to lift, in a boosted engine it would need to see the same pressure as passing in to the engine in order for the air velocity to create the depression that raises the slide.

This means i was, in theory, going in the right direction but possibly the hole i drilled wasn't big enough to allow the pressure to equalise quickly enough as the boost increased

I guess i could have closed off one slide hole to compensate as some mentioned above but i like drilling holes in things 

Edited January 23, 2018 by El Gringo

[MeanBean49]

2 hours ago, El Gringo said:

Right, i've employed the mind of a clever bloke at work and he agrees that the slides lift as a result of a vacuum being drawn through the slide holes and the resulting low pressure above the diaphragm causes it to lift.

Logically then as the underside of the diaphragm sees atmospheric pressure in an N/A engine, in order for it to be able to draw a vacuum on the slide and cause it to lift, in a boosted engine it would need to see the same pressure as passing in to the engine in order for the air velocity to create the depression that raises the slide.

This means i was, in theory, going in the right direction but possibly the hole i drilled wasn't big enough to allow the pressure to equalise quickly enough as the boost increased

I guess i could have closed off one slide hole to compensate as some mentioned above but i like drilling holes in things 

That doesnt really make sense. The top side of the diaphragm is open to atmosphere irrelevant of whether you drill the carb or not. You arent changing that at all. All you are doing is allowing boist pressure to build up under the diaphragm making it want to lift even in closed throttle situations.

Whats possibly happening is as soon as a bit if boost builds the slides are going instantly open and making everything massively rich.

Where you say it creates a vaccume isnt really true. What you are creating is a pressure differential. Which with spring pressure is what controls the slide height, which keeps the airflow roughly at a constant velocity all the time. Hence the name CV carbs.

I would temporarily ditch the turbo, block the holes and run the bike up N/A and see if it revs out under load. Rule out electrical issues. Then try again, possibly with the holes blanked

[Madb]

Cool. I was going to ask wether it rev out in n/a mode but that was my next question.

[MeanBean49]

Little bit of info. Ive just dug about on my garage, found the carbs for my GK73a SP they work exactly the same way as bandit carbs. No need for drilling or anything. Not sure if standard GK73's are the same. Ive a few sets of carbs in my lockup will see what they are like. Or Ian and Jim might have some spare. Could save a lot of ballache

[Screwriverracing]

What are the coils and leads like?

just to add another factor in.

Cheers SRR

[El Gringo]

14 hours ago, MeanBean49 said:

That doesnt really make sense. The top side of the diaphragm is open to atmosphere irrelevant of whether you drill the carb or not. You arent changing that at all. All you are doing is allowing boist pressure to build up under the diaphragm making it want to lift even in closed throttle situations.

I've had a look and there's definitely no atmospheric pressure above the diaphragms. It's completely sealed other than the slide holes. What i'm suggesting is the velocity of the inlet passing the slide holes creates the low pressure above the diaphragm which lifts the slide, as you say a pressure differential 

13 hours ago, MeanBean49 said:

Little bit of info. Ive just dug about on my garage, found the carbs for my GK73a SP they work exactly the same way as bandit carbs. No need for drilling or anything. Not sure if standard GK73's are the same. Ive a few sets of carbs in my lockup will see what they are like. Or Ian and Jim might have some spare. Could save a lot of ballache

GK76a carbs are different, the Bandit carbs are the same as GK73a with the oval inlets with the port above the main bellmouth, which does away with the need for the holes.

What i'm saying is if 1100,1200 and now GK73/Bandit carbs have the port that feeds under the diaphragm - be it atmospheric pressure in a NA engine or boosted pressure in a turbo engine and these work well, then surely i need to have the same pressure reference?

The 76 carbs also sit at more of an angle i believe, slightly down draught where as the bandit ones are side draught - Thanks for looking at your carbs, much appreciated. I might try the carbs off my bandit 4 if this doesn't work.

Edited January 24, 2018 by El Gringo

[MeanBean49]

1 hour ago, El Gringo said:

I've had a look and there's definitely no atmospheric pressure above the diaphragms. It's completely sealed other than the slide holes. What i'm suggesting is the velocity of the inlet passing the slide holes creates the low pressure above the diaphragm which lifts the slide, as you say a pressure differential 

GK76a carbs are different, the Bandit carbs are the same as GK73a with the oval inlets with the port above the main bellmouth, which does away with the need for the holes.

What i'm saying is if 1100,1200 and now GK73/Bandit carbs have the port that feeds under the diaphragm - be it atmospheric pressure in a NA engine or boosted pressure in a turbo engine and these work well, then surely i need to have the same pressure reference?

The 76 carbs also sit at more of an angle i believe, slightly down draught where as the bandit ones are side draught - Thanks for looking at your carbs, much appreciated. I might try the carbs off my bandit 4 if this doesn't work.

Thing is if the 76 carbs are designed to work without drilling and the pressure differential needed is created by the air velocity. It should work irrelevant of boost pressure.

Its probably a case of lots of messing to find the sweet spot.

 

[El Gringo]

24 minutes ago, MeanBean49 said:

Thing is if the 76 carbs are designed to work without drilling and the pressure differential needed is created by the air velocity. It should work irrelevant of boost pressure.

Its probably a case of lots of messing to find the sweet spot.

 

I think you're right on the messing around.

I've only based the drilling on the guide on here, as the carbs would appear to be the same theory as the 40mm 11 carbs.

As i say, it's not going to be difficult to block the holes back off to try it, plus it won't take long. I'm pretty sure i can now get the carbs off it blindfolded 

[MeanBean49]

15 minutes ago, El Gringo said:

I think you're right on the messing around.

I've only based the drilling on the guide on here, as the carbs would appear to be the same theory as the 40mm 11 carbs.

As i say, it's not going to be difficult to block the holes back off to try it, plus it won't take long. I'm pretty sure i can now get the carbs off it blindfolded 

Definately think its worth trying N/A just to rule out or confirm electrics

[El Gringo]

40 minutes ago, MeanBean49 said:

Definately think its worth trying N/A just to rule out or confirm electrics

It's worth a go i think too, the only issue i can forsee is the fuel delivery, i haven't got anything other than the pump to run it on, can i just turn the regulator off by removing the reference to it and having it only pump the bare minimum or is that going to cause issues?

We did try it without the turbo connected on the last dyno run, but didn't remove all of the air take offs on the carbs, and obviously it'd still got the holes open (although it would need them with the normal vents blanked off).

Biggest issue currently is the weather and not being able to test it!

Edited January 24, 2018 by El Gringo

[MeanBean49]

Can you not just run a gravity line from tamk to carbs? Without any boost the fuel pressure will only stay at base pressure anyway. Should be fine

[El Gringo]

4 minutes ago, MeanBean49 said:

Can you not just run a gravity line from tamk to carbs? Without any boost the fuel pressure will only stay at base pressure anyway. Should be fine

I'd have to do it from a remote bottle, the tank has got a 1/2" feed, although i spose i could step it down to suit.

I'll have a think. Need to try and test it without going back to the dyno, i can't afford to keep going over there on the off chance it's going to work

[Madb]

Top chamber/diaphram is controlled by a very small hole above the thottle butterflies in the venturi. It's these holes that control the slides.

[MeanBean49]

1 hour ago, Madb said:

Top chamber/diaphram is controlled by a very small hole above the thottle butterflies in the venturi. It's these holes that control the slides.

And the holes in the bottom of the slides

[Madb]

Yes,  quite right.  Should have elaborated a bit more but my head still foggy from this bloody illness. 

Would any of the ecu''s have a rev limiter on them? Maybe..

[El Gringo]

2 hours ago, Madb said:

Yes,  quite right.  Should have elaborated a bit more but my head still foggy from this bloody illness. 

Would any of the ecu''s have a rev limiter on them? Maybe..

I looked into the CDI limit idea, i can;t find any evidence to suggest that the CDI has any fail safe limit and the main CDI i'm running is an aftermarket unit so it probably wouldn't have been included.

Also, having looked at the wiring diagrams, the GK76a does have an extra wire that goes to the CDI from the neutral switch which does something with the neutral circuit - however neither the aftermarket CDI nor the Bandit CDI have this input on the CDI - all the wire does is create an earth so if it's not running into the CDI i can't see that there's anything for it to affect.

Plus, having looked at the dyno runs again, after it plays up at 6.5k rpms, it did carry on recording the rpm signal past this, which suggests, as the clip was on the plug lead, that it was still sparking (or at least receiving an HT pulse down the lead) after the point it stops pulling

[mick-ne]

God I hope you get this sorted soon, its not my bike and its frustrating the life outa me, So near and yet so far. I have everything crossed for you keep at it

Just like to add its a great read and hats off to everyone chipping away trying to help, great example of what its all about here.

[Madb]

+1 . Bang on the button @mick-ne.

I dare say everyone feeling it.

The only place to be.

 

[El Gringo]

14 hours ago, mick-ne said:

God I hope you get this sorted soon, its not my bike and its frustrating the life outa me, So near and yet so far. I have everything crossed for you keep at it 

Just like to add its a great read and hats off to everyone chipping away trying to help, great example of what its all about here.

Me too! After all the hassle just to get it to run i was hoping for an easier time in getting it set up! Obviously not to be. I shall not be deterred.

If it does turn out to be the CDI unit it just gives me an excuse to buy an ignitech so i can fiddle with the retard at the top end.

I was going to save it for v2.0 of the engine but if it needs it sooner so be it 

I've already got plans for a big bore second motor with tuned head, probably a base spacer to get the compression down further, and maybe a bigger turbo, along with one of Ian Cross' lockup clutches - an ignitech makes perfect sense to top it off

However, i'm getting way ahead of myself....

I also concur with your sentiments, this place is awesome, many thanks to everyone again for your help 

Edited January 25, 2018 by El Gringo

[Tombola]

Have you got another set of carbs you can try without the turbo?