Turbo plumbing for a simpleton

[latheboy]

The black rubber joiner at the top that is part of the breather system, if your carbs have this make sure it is sealed properly. 

I machined up some parts with o-rings so they sealed no matter what.

Again, these are Ø38mm CV's so i don't know how they differ from yours.

[El Gringo]

7 hours ago, latheboy said:

The black rubber joiner at the top that is part of the breather system, if your carbs have this make sure it is sealed properly. 

I machined up some parts with o-rings so they sealed no matter what.

Again, these are Ø38mm CV's so i don't know how they differ from yours.

 

Cheers Boss, that's very helpful

I think the GK76 carbs are very much like the 38s - they do have the breather set up between 1&2 and 3&4 (but not between 2&3). I have this blanked off with a blanking plug on each inlet at the moment.

Is the hole in the picture above at the top of the inlet the one you drilled? If not have you got any pictures of that hole please?

I've got a single pitot that I opened up to 7.5mm last night both ends although there is a spot in the middle on the bend that is still narrower

The FPR input is coming from the pressure reference on the manifold that would normally go to the vacuum tap, it does raise the fuel pressure when it starts to boost.

There's several things it could be as far as I can see/others have suggested

Pitot isn't working right to compensate for the boost in the float bowls

There wasn't enough base fuel pressure when running

The holes in the inlet don't need to be there (although i'm still pretty sure they do)

I think i'm going to have to book a day on the dyno, take all the stuff with me and go through it systematically

If you've got any more pictures of your carbs and that extra hole in particular that would be great

Edited May 3, 2018 by El Gringo

[latheboy]

It's been a long time since i've been on the dyno or any tuning.

I think you should unblock the breather ports and link them between 1 and 2, 3 and 4

Yes they are the holes i drilled.

Base fuel pressure on mine is 2.5psi and 

Is your pitot facing into the airflow? slash cut?

I'll get back to with more.. i need to get shake my kids 

[El Gringo]

13 minutes ago, latheboy said:

It's been a long time since i've been on the dyno or any tuning.

I think you should unblock the breather ports and link them between 1 and 2, 3 and 4

Yes they are the holes i drilled.

Base fuel pressure on mine is 2.5psi and 

Is your pitot facing into the airflow? slash cut?

I'll get back to with more.. i need to get shake my kids 

Cheers Chap, thanks for the reply

Pitot is into the air flow but flat end on rather than slash cut, that might be something to look at

I feel a conversation with my tame machineist coming on, i hadn't thought about cross linking the ports.

My drillings are straight up and down as opposed to face on to the air flow like your which might also be something to look at

 

[latheboy]

If it's inline with the air flow you shouldnt need to slash cut it.

Don't know if the direction of the drilled holes would make a difference, it should see pressure even if facing backwards.

I'm going to go look at it and see if i can think of anything else important i did.

[El Gringo]

Cheers Chap, Much Appreciated 

[latheboy]

All i did to the carbs was follow the guide from the old site and i'm grateful for that information, thanks everyone.

If this is all old news ... sorry it's just how i did it.

Right then, i drilled a hole in each carb to get boost under the diaphragm.

I did NOT modify the slides at all. This concerns me that you have.

Boost referenced the fuel bowls (overflow) of each set (1/2 and 3/4) of carbys via its own pitot pipe

Floats at Stock height 

Sealed the diaphragm breathers all together.

Removed the fuel cock (hehe) and made new one that is  free flowing out and a return that goes to the TOP of the tank. This is a must as the fuel return must be free of pressure.

Trade off with the fuel cock (hehe) i made is i don't have a reserve now. STD one is a massive restriction.

If its returning to the bottom of the tank you are fighting the petrol level pressure already in the tank.

I sealed the petrol cock (hehe) feed pipe thingy on the carb rubber.

I used ALL 4 ports in the carby tops  to get vacuum for the blow off valve.

I didn't cut the spring in the fuel Reg... bad idea in my  opinion as it changes the spring rate to make it harder, i made a spacer for the reg that let me lower the std setting.

Fuel Reg has it's own Pitot pipe.

Wastegate controller has a reference off the plenum

I machined the ignition plate so i could get up to 5 degrees retard

When tuning, i had 1 AFR in the pipe and 4 EGT's, 1 in each exhaust port on the headers. I got the exhaust temps within 20 Degree C and the AFR happy 

each carb has different Main Jets and different needle heights 

Boost and Fuel Pressure hooked up too and made sure i had 2.5 to 3 PSI more fuel pressure at all times.

There will be a test after you finish reading this  

[El Gringo]

9 minutes ago, latheboy said:

All i did to the carbs was follow the guide from the old site and i'm grateful for that information, thanks everyone.

You Sir are a legend! - i also followed the instructions on the old site/in the vault

Right i can answer most of this now

Right then, i drilled a hole in each carb to get boost under the diaphragm.

Yep done that, 5.5mm hole straight down into the inlet

I did NOT modify the slides at all. This concerns me that you have.

I haven't touched the slides, they're all stock

Boost referenced the fuel bowls (overflow) of each set (1/2 and 3/4) of carbys via its own pitot pipe

I've got 1 pitot feeding the 2 float bowl vents via an 8mm hose and tee'd down to the over flow connections

Floats at Stock height 

Yep, stock float heights, holding 3psi when running

Sealed the diaphragm breathers all together.

I've got the 2 breathers blanking capped - will look to link these with inserts

Removed the fuel cock (hehe) and made new one that is  free flowing out and a return that goes to the TOP of the tank. This is a must as the fuel return must be free of pressure.

I've got quite a long return hose but it's an 8mm bore and returns above fuel level

Trade off with the fuel cock (hehe) i made is i don't have a reserve now. STD one is a massive restriction.

Fuel delivery block houses the flow at 14mm bore to the pump and the 8mm return

If its returning to the bottom of the tank you are fighting the petrol level pressure already in the tank.

Nope, above fuel level

I sealed the petrol cock (hehe) feed pipe thingy on the carb rubber.

I'm using that for the FPR boost feed

I used ALL 4 ports in the carby tops  to get vacuum for the blow off valve.

Yep, got all 4 linked that feeds the BOV and a line tee'd off that feeds the boost gauge

I didn't cut the spring in the fuel Reg... bad idea in my  opinion as it changes the spring rate to make it harder, i made a spacer for the reg that let me lower the std setting.

Might look at getting a new spring so i don't have to wind it up as far

Fuel Reg has it's own Pitot pipe.

As above, from the manifold take off

Wastegate controller has a reference off the plenum

Currently got a line from the turbo outlet to the wastegate via a boost controller - this is currently backed right off - i might take it off to rule it out

I machined the ignition plate so i could get up to 5 degrees retard

Ignition is currently stock but i do have a modified pick up that allows 3 degrees retard to be fitted when it starts working properly

When tuning, i had 1 AFR in the pipe and 4 EGT's, 1 in each exhaust port on the headers. I got the exhaust temps within 20 Degree C and the AFR happy 

Nothing fitted at present, AFR on the Dyno was pretty good until it hit the bit it wouldn't pull through

each carb has different Main Jets and different needle heights 

Will Faff with this bit later

Boost and Fuel Pressure hooked up too and made sure i had 2.5 to 3 PSI more fuel pressure at all times.

I think part of the issue might be the base pressure was too low in the first place, will re test, holds a steady 3psi when running now but haven't tried it since this

I'm pretty much bang on the same as what you did so i'm a bit puzzled as to why it's not working, 

Thanks for your help, will give it another go and report back

[Madb]

almost there. The sun is out, hurry up.  At least ya got some pointers to look at. hoping ya nail it shortly. looking how many people are reading your project , I would have thought you'll hear the cheers when it's sorted. 

[latheboy]

16 minutes ago, El Gringo said:

I sealed the petrol cock (hehe) feed pipe thingy on the carb rubber.

I'm using that for the FPR boost feed

I think that is a bad idea, you are getting your boost reference from a place that sees a vacuum and reversion. 

It's too close to the valve.

Hook up a fuel pressure gauge next to your boost gauge and while riding along trying to get on boost and watching the road for car/buses/animals/ other things that could jump out in front of you, hold your phone up and video what the gauges are doing... then on the way home watch the video while riding. 

No don't do that.

I have 2.5PSI fuel pressure at idle

 

[latheboy]

25 minutes ago, El Gringo said:

I did NOT modify the slides at all. This concerns me that you have.

I haven't touched the slides, they're all stock

Hmmm i must have read that bit wrong.... carry on

[El Gringo]

10 minutes ago, latheboy said:

I think that is a bad idea, you are getting your boost reference from a place that sees a vacuum and reversion. 

It's too close to the valve.

Hook up a fuel pressure gauge next to your boost gauge and while riding along trying to get on boost and watching the road for car/buses/animals/ other things that could jump out in front of you, hold your phone up and video what the gauges are doing... then on the way home watch the video while riding. 

No don't do that.

I have 2.5PSI fuel pressure at idle

 

 I am known to do stupid things!

8 minutes ago, latheboy said:

Hmmm i must have read that bit wrong.... carry on

That might have been the bit where i compared the size of the hole i drilled to under the diaphragms to the 2 slide holes - originally the drilled hole was a smaller area than the 2 slide holes combined - hence why i made it bigger

[latheboy]

This was my first attempt at a pitot pipe. Like yours i had 1 that split to the 2 different fuel bowl circuits. DID NOT work and I feel like i had similar issues to you.

I have drunk a lot since then sorry.

 

Also i've a read through the thread and a couple of guys said to reference your Fuel reg of the petrol cock thingy thing so you get a vacuum, this is where you have yours now.

Yes vacuum is great for the reg on shut throttle but i found it was pulsing and gave me the shits. I put the blow off valve right next to the Pitot pipes so the reg would see a pressure drop on closed throttle.

[Gixer1460]

Just an observation - carbs with a FPR don't need vacuum - the float bowls should be filled regardless of what the engine is doing. Fuel metering is done by the carb design not fuel pressure.

EFI on the other hand can benefit with a vac referenced FPR as the squirt pressure at the point of injection is proportional to what the engine is doing / needs.

Re the picture above - I wouldn't be surprised that the pitot gave bad results due to airflow disruption from the tube welded on beside it?

[MeanBean49]

44 minutes ago, Gixer1460 said:

Just an observation - carbs with a FPR don't need vacuum - the float bowls should be filled regardless of what the engine is doing. Fuel metering is done by the carb design not fuel pressure.

EFI on the other hand can benefit with a vac referenced FPR as the squirt pressure at the point of injection is proportional to what the engine is doing / needs.

Re the picture above - I wouldn't be surprised that the pitot gave bad results due to airflow disruption from the tube welded on beside it?

You do if its a rising rate FPR, otherwise if you have 3psi fuel pressure and 4psi boost you cant get fuel into the bowls.

Otherwise your fuel pressure needs to be set a bit higher than your max boost permanently. Cant see carbs holding 20psi 

[El Gringo]

8 hours ago, latheboy said:

This was my first attempt at a pitot pipe. Like yours i had 1 that split to the 2 different fuel bowl circuits. DID NOT work and I feel like i had similar issues to you.

I have drunk a lot since then sorry.

 

Also i've a read through the thread and a couple of guys said to reference your Fuel reg of the petrol cock thingy thing so you get a vacuum, this is where you have yours now.

Yes vacuum is great for the reg on shut throttle but i found it was pulsing and gave me the shits. I put the blow off valve right next to the Pitot pipes so the reg would see a pressure drop on closed throttle.

I'll try and remember to take a picture of my pitot later but it basically looks the same as above.

It's mounted in the straight section of the ally tube before the bend where it goes to the plenum - the BOV is just infront of this bit in the silicone tee

[El Gringo]

I think the next course of action will be......

Remove the plugs I put in the drilled holes

Get some link bits turned up to go between the breather ports

Re-test with 2.5-3 psi base fuel pressure, opened out pitot and boost controller removed

If that doesn't illicit the correct response then i'll look at moving the FPR pressure feed somewhere else and add another pitot and run one to each pair of carb bowls

 

[370steve]

Keep at it mate, the end is in sight 

[Gixer1460]

2 hours ago, MeanBean49 said:

You do if its a rising rate FPR, otherwise if you have 3psi fuel pressure and 4psi boost you cant get fuel into the bowls.

Otherwise your fuel pressure needs to be set a bit higher than your max boost permanently. Cant see carbs holding 20psi 

READ IT ! - I said VACUUM !

And a rising rate regulator is completely different to a boost referenced one ! The first is used as a 'band aid' for EFI systems that can't be remapped - increasing fuel pressure uncontrolled and unrelated to boost pressure / engine requirements. The latter will increase FP to match boost pressure so that the fuel pressure will remain at static + boost to avoid wild swings in fuel mixtures / flooding.

[Blubber]

Keep the info coming 

 

Nice to read all this stuff and... including the errors 

[latheboy]

4 hours ago, Gixer1460 said:

Just an observation - carbs with a FPR don't need vacuum - the float bowls should be filled regardless of what the engine is doing. Fuel metering is done by the carb design not fuel pressure.

EFI on the other hand can benefit with a vac referenced FPR as the squirt pressure at the point of injection is proportional to what the engine is doing / needs.

Re the picture above - I wouldn't be surprised that the pitot gave bad results due to airflow disruption from the tube welded on beside it?

The welded pipe on the side is for the BOV, so its a dead end while running and boost but has a massive pressure drop for the pitots when the BOV opens

[El Gringo]

55 minutes ago, Blubber said:

Keep the info coming 

 

Nice to read all this stuff and... including the errors 

That's kind of why i started the thread, there's a lot of info available on the subject, some of it more helpful and relevant than other bits, and as seen in the post through the thread there's more than one way to skin a cat.

I had a vague idea of where to start with it but it's been (il)logical trial and error really

This has certainly been a journey and it's not over yet, but if it helps other people looking to go through the process over come some of the pitfalls that's great.

It's also testament to how awesome OSS is with the level of replies and advice received 

[El Gringo]

One thing that has just occurred to me, would the bore of the pressure reference hose to the FPR affect how it operates?

[MeanBean49]

1 hour ago, Gixer1460 said:

READ IT ! - I said VACUUM !

And a rising rate regulator is completely different to a boost referenced one ! The first is used as a 'band aid' for EFI systems that can't be remapped - increasing fuel pressure uncontrolled and unrelated to boost pressure / engine requirements. The latter will increase FP to match boost pressure so that the fuel pressure will remain at static + boost to avoid wild swings in fuel mixtures / flooding.

The Vaccum they are talking about is from the placement of the pressure reference for the FPR,  the vaccum comes from when the carb butterflies are shut because the reference pipe is after the butterflies. So they arent actually talking about a vac pipe. Its a reference pipe that will see vaccum

And a rising rate regulator is not different. You just using the boost as the reference for how much the rate rises. Hence rising rate. Boost rises, fuel pressure rises

[Gixer1460]

Beg to disagree - Rising Rate regulators increase pressure based on their settings 1:1.2 or 1:1.5 and i've seen them upto 1:1.7 so for every 1psi boost the fuel pressure increases by 1.2 or 1.5 or 1.7 - as I said this is maybe not what the engine wants - sort of if more is good even more must be better!

A boost referenced FPR stays 1:1 so the FP stays exactly as it was without boost in relative terms - you are trying to achieve a constant fuel level in the bowl, how can that be accomplished if the FP is constantly changing compared to the boost pressure within the float bowl?

Re-reading an earlier post this " carbs with a FPR don't need vacuum " was badly worded. It should read " carbs do not need vacuum regulated FPR's"

@El Gringo- pressure is pressure and vacuum is vacuum whatever bore of pipe - only the response time is likely to vary although probably not as you could measure it reliably