Turbo dr200 carb help

[bartman]

I built a dr200 up with a turbo a little bit ago. And I have been annoyed with the carb not working properly. After looking through all the forums here and other places online I think I narrowed it down to the vacuum slide. It looks relatively the same as the one on the 87 gsxr750 carb. 

I have put a pitot tube coming from the turbo to the carb vent. And I have a plenum before the carb. And it is a blow through setup. 

When I am driving it will ramp boost slowly then suddenly come on. And as I'm cruising the vacuum slide seems to close and lose all boost. Is there anything I would need to do below the membrane? I was thinking to block the passage at the back and drill a hole and tap a line to the pitot tube. 

Is that a bad idea?

That's the dr

https://www.reddit.com/r/Suzuki/comments/15rvap1/turbo_dr200/

 

 

[Gixer1460]

4 hours ago, bartman said:

I have put a pitot tube coming from the turbo to the carb vent. And I have a plenum before the carb.

Not sure how you have installed the pitot? Blow thro carbs should need little modification to work with a turbo - so something ain't right.

[bartman]

14 hours ago, Gixer1460 said:

Not sure how you have installed the pitot? Blow thro carbs should need little modification to work with a turbo - so something ain't right.

There's no other modification on a cv carb?

[clivegto]

Got'any pictures they can say a thousand words without saying owt. 

[peter1127]

What you describe might just be turbo lag: 200 cc is not much to get a turbo to spool up and no boost at cruising at low speeds/rpm is normal. Then when you open the throttle I expect a delay which can be massive at lower rpms. Cruising at higher speeds/rpm you will see a little boost and when opening the throttle that should raise fairly quick. Anyway for your carb try this for information  https://oldskoolsuzuki.info/?s=carb+turbo

Summary:

• make sure bowls dont overflow, seals, needles and seats must  be MINT. Might need to lower fuel level a bit
• Fuel pressure need to be 1:1 in relation to boost, and only a couple of psi above boost otherwise you have a shower head
• Pitot out of middle of airstream to the bowls
• Below the membrane you need pressure. Depends on your carbs how to do that. Maybe you already have that, if not you could drill from plenum side towards under the membrane. If not possible a dedicated line. I dont expect it makes much difference if that is from a pitot or not.
• Above the membrane all is well: the existing holes take care of that. Plastic caps might crack, alu is better
• you might need weird needle settings or even custom shaped needles. Depends on all kinds of stuff: getting off boost and cruising ok is the hardest part in my experience. Can play with springs too
• Check you enrichment system, plungers can be pushed out under boost messing stuff up

[TLRS]

Is there any chance the pitot pressure is messing with the cv slide position?

[peter1127]

4 hours ago, TLRS said:

Is there any chance the pitot pressure is messing with the cv slide position?

If I translate "messing"  into "influence", then yes, could be if this is used for membrane pressure.

 

The position of the cv slide is a balance between:

• pressure above the membrane solely caused by existing hole(s) in the slides: a result of plenum pressure and venturi effect reducing that pressure. 
• pressure below the membrane which is  plenum or pitot pressure depending on chosen solution.  If there is no connection to boost, or there is a hole/leakage towards ambient, the slide will close once some boost occurs simply because pressure above membrane is higher then under membrane.
• Spring.  Can be played with in combination with needles to finetune offboost/cruise behavior. 

Its also worth checking the membrane for rupture and sealing around the edge. Often overlooked.

Using pitot connection also for "under membrane" pressure is imho not needed. This pitot solution is mainly beneficial for bowl pressure and if done correctly the main jet is close to stock which makes it easy to deal with different boost levels.

Still, its very possible that this is all due to a very low capacity engine having trouble spooling up the turbo.

Edited November 6, 2023 by peter1127
additional info

[Gixer1460]

Most CV carbs work via airflow and will have drillings from the mouth into the chamber over the diaphragm. As air speed increases over / through the venturi, its pressure drops - this lower pressure (if it drops below atmospheric pressure its termed a vacuum) will draw the slide up thus giving more fuel. Even if pressurised air is pushed through the venturi, its pressure still drops so the slide lifts. The pitot should be located and sized to feed a slightly higher pressure air to the fuel bowl so that the boost pressure over the fuel jets isn't more than in the bowl so fuel can still flow. Fuel pressure coming into the bowl needs a psi or so higher than any boost pressure and to follow it hence the use of boost referenced fuel pressure regulators.

Single cylinder engines aren't really suited to turbocharging - one slug of exhaust every two revs as opposed to a 4 or 8 cylinder with a slug every 180 degrees of rotation, It'd need a pretty small turbocharger i'm guessing? I've seen a 'onda C50 turbo'd but more of an engineering exercise than a practical useful bike LOL!

[bartman]

So everything you guys have said I have done. I set up the carb based on that whole web page. I dug I to the way back machine to find the old turbo-bike.com. and that's where I found carbs set up that were not exactly the same. That's why I posted here asking. The carb I looked at was a gsxr 1100 turbo build. Which was different then mine. Now the page that I looked at from here. Said that a gsxr 750 was ideal for that set up. And the gsxr 750 carb diagram area looks identical. 

The gsxr 1100 carb at the top, had a plug in the mouth of the carb blocking the diaphragm. So they drilled and tapped under the diaphragm and put a line into the plenum, not the pitot tube. I also noticed it didn't have an air jet which mine and the gsxr750 carbs did. After reading it was saying that the air would pass through the slide and down into the carb when the throttle was closed. Which would propoperly open and close the slide.

The gsxr750 carb has a air jet like mine. But doesn't have a line connected to the plenum I'm guessing because it's already open at the mouth of the carb so it seems un necessary. Now since the air jet in those carbs I'm pretty sure go to the intake after the slide. They would not return through the slide itself as much. Which is why I was wondering if there was something I was missing. 

It seems to me that as air comes into the bottom of the diaphragm. Air passes through there and goes down the air jet into the intake past the butterfly causing me to lose enough vacuum for my blow off valve to open causing me to lose boost. 

I had this bike running for quite a while but the only way I could hold consistent boost was running really big main jets. I have since lowered my main jet so I'm not as rich. Seems now to be around 11:1 ish. But now I lose boost in that manner.

And I tested another carb. It ran like dog shit. But it was way quicker to build and hold boost. But I can't keep using it as it refuses to idle and run at slow speed.

I know this is long but if you guys have any Ideas what to do that would be great.

[bartman]

That's the gsxr1100 carb I was looking at from the way back machine. It was on www.turbo-bike.com

[bartman]

9 hours ago, Gixer1460 said:

Single cylinder engines aren't really suited to turbocharging 

You wouldn't be the first one to tell me that haha. It does work well when the carb wants to work with me. And it has hit over 20 psi of boost on this tiny little turbo.

[Maggotbreath]

3 hours ago, bartman said:

So everything you guys have said I have done. I set up the carb based on that whole web page. I dug I to the way back machine to find the old turbo-bike.com. and that's where I found carbs set up that were not exactly the same. That's why I posted here asking. The carb I looked at was a gsxr 1100 turbo build. Which was different then mine. Now the page that I looked at from here. Said that a gsxr 750 was ideal for that set up. And the gsxr 750 carb diagram area looks identical. 

The gsxr 1100 carb at the top, had a plug in the mouth of the carb blocking the diaphragm. So they drilled and tapped under the diaphragm and put a line into the plenum, not the pitot tube. I also noticed it didn't have an air jet which mine and the gsxr750 carbs did. After reading it was saying that the air would pass through the slide and down into the carb when the throttle was closed. Which would propoperly open and close the slide.

The gsxr750 carb has a air jet like mine. But doesn't have a line connected to the plenum I'm guessing because it's already open at the mouth of the carb so it seems un necessary. Now since the air jet in those carbs I'm pretty sure go to the intake after the slide. They would not return through the slide itself as much. Which is why I was wondering if there was something I was missing. 

It seems to me that as air comes into the bottom of the diaphragm. Air passes through there and goes down the air jet into the intake past the butterfly causing me to lose enough vacuum for my blow off valve to open causing me to lose boost. 

I had this bike running for quite a while but the only way I could hold consistent boost was running really big main jets. I have since lowered my main jet so I'm not as rich. Seems now to be around 11:1 ish. But now I lose boost in that manner.

And I tested another carb. It ran like dog shit. But it was way quicker to build and hold boost. But I can't keep using it as it refuses to idle and run at slow speed.

I know this is long but if you guys have any Ideas what to do that would be great.

 

Are you running a wideband?

Pretty sure that's the pilot air jet, shouldn't have any effect on higher rpm.

More than likely your fuel pressure/pitot pressure ratio is out. What fuel reg & pump are you using? Can you show a pic of your pitot? 

Edited November 7, 2023 by Maggotbreath
spelig

[peter1127]

 

4 hours ago, bartman said:

It seems to me that as air comes into the bottom of the diaphragm. Air passes through there and goes down the air jet into the intake past the butterfly causing me to lose enough vacuum for my blow off valve to open causing me to lose boost. 

 

If you lose boost due to the BOV opening when it shouldnt, that is different issue than the slide closing once you achieve boost. Not sure how a lost vacuum opens a BOV valve? Lost vacuum means there is more pressure, exactly what you want to keep a BOV closed.   

Edited November 7, 2023 by peter1127

[bartman]

4 hours ago, Maggotbreath said:

 

Are you running a wideband?

Pretty sure that's the pilot air jet, shouldn't have any effect on higher rpm.

More than likely your fuel pressure/pitot pressure ratio is out. What fuel reg & pump are you using? Can you show a pic of your pitot? 

I was using one. The cv carb works good till it doesn't 

[bartman]

3 hours ago, peter1127 said:

 

If you lose boost due to the BOV opening when it shouldnt, that is different issue than the slide closing once you achieve boost. Not sure how a lost vacuum opens a BOV valve? Lost vacuum means there is more pressure, exactly what you want to keep a BOV closed.   

Sorry It closes the slide and vacuum is created not lost. I sort of figured it out. I took out the air jet plugged the hole and it works better. But not how it should cause now when the I close throttle it floods a bit.

Edited November 7, 2023 by bartman

[bartman]

Like it does work. But if I hold the throttle full for over 5 to 10 seconds it will lose all boost and fall on its face

Which is why I suspected the air jet. And took it out.

[Gixer1460]

Maybe ask this dude - only difference I see is he's using a slide carb so avoiding the uncontrolled slide lift issues? 

 

[peter1127]

If you hold the throttle and it builds boost, but after 5-10secs it gives up, I suspect this to be a fuelling issue. If there would be a slide or BOV issue, it would have that problem immediately once boost builds, not with a delay. 

If too rich after 5-10 sec I suspect too high fuel pressure or the floats cant hold the pressure. Plug should indicated this. If too lean it could be not enough fuel flow causing empty bowl. Clogged  needle seat, failing fuel pump, clogged fuel filter, kinked hose, clogged fuel cap vent, vacuum operated tap closes?   

Other thought: you make more boost so ignition fails. Replace plug and reduce gap.

[bartman]

22 hours ago, peter1127 said:

If you hold the throttle and it builds boost, but after 5-10secs it gives up, I suspect this to be a fuelling issue. If there would be a slide or BOV issue, it would have that problem immediately once boost builds, not with a delay. 

If too rich after 5-10 sec I suspect too high fuel pressure or the floats cant hold the pressure. Plug should indicated this. If too lean it could be not enough fuel flow causing empty bowl. Clogged  needle seat, failing fuel pump, clogged fuel filter, kinked hose, clogged fuel cap vent, vacuum operated tap closes?   

Other thought: you make more boost so ignition fails. Replace plug and reduce gap.

I'm not sure about the fueling to be the problem. There's no indication of the fuel being lean on the O2 sensor. But I have been wanting to get a colder plug. Il try the plug but I say 5 to 10 seconds but it varies alot. And the big one. If I shift too slowly I wouldn't be able to rebuild boost again unless I let off for a few seconds then rebuilt boost. I am using a 0 to 30 psi fuel pressure regulator. With a way over kill flow rate fuel pump. The initial pressure is 4 psi and the float holds that fine. 

So essentially if I want to do a hard acceleration. I have to shift without the clutch and hope I do it fast enough or it falls on its face. Now say I did a pull in second. Hit 15 psi of boost. Did my quickest shift to 3rd Id have 12 psi throughout all of third. Then shift again. Id have 8 psi and so on. Pretty much the majority of the bull is I gotta wait for boost to rebuild if I want max boost again. It doesn't always loose boost but it does it a lot. But it has gotten better. I changed the air jet from a 135 to 120 and that has worked a lot better. But it still happens. 

[bartman]

Also. Should the fuel pressure regulator reference line be connected to the pitot or the same line as the bov/vac boost line

[peter1127]

15 minutes ago, bartman said:

Also. Should the fuel pressure regulator reference line be connected to the pitot or the same line as the bov/vac boost line

What I did is have the pitot to the bowls only, and BOV/FPR on carb connector.  

[bartman]

5 minutes ago, peter1127 said:

What I did is have the pitot to the bowls only, and BOV/FPR on carb connector.  

And what exact carb or carbs did you run?

[peter1127]

22 hours ago, bartman said:

I'm not sure about the fueling to be the problem. There's no indication of the fuel being lean on the O2 sensor. But I have been wanting to get a colder plug. Il try the plug but I say 5 to 10 seconds but it varies alot. And the big one. If I shift too slowly I wouldn't be able to rebuild boost again unless I let off for a few seconds then rebuilt boost. I am using a 0 to 30 psi fuel pressure regulator. With a way over kill flow rate fuel pump. The initial pressure is 4 psi and the float holds that fine. 

So essentially if I want to do a hard acceleration. I have to shift without the clutch and hope I do it fast enough or it falls on its face. Now say I did a pull in second. Hit 15 psi of boost. Did my quickest shift to 3rd Id have 12 psi throughout all of third. Then shift again. Id have 8 psi and so on. Pretty much the majority of the bull is I gotta wait for boost to rebuild if I want max boost again. It doesn't always loose boost but it does it a lot. But it has gotten better. I changed the air jet from a 135 to 120 and that has worked a lot better. But it still happens. 

Hmm weird behavior. Basically not closer to a solution. Possible issues are:

• AF wrong  (jetting)
• fuel issue (fuel supply)
• slide issue 
• BOV issue
• Ignition issue

Maybe you can do some tests to exclude stuff:

• O2 sensor should be wideband. If not, its not so useful. Also  rich stumbles often dont show.  Dyno run including shifts with proper sensor might reveil something
• When the issue appears, shut the bike down including fuel pump and check bowl level. If almost empty its clear where to look.
• check with gopro the slide behavior (which with a plenum is troublesome, maybe it fits and add a light;-)
• Slightly more spring on the BOV so you are sure it doesnt open a bit when boost starts to build.
• Change plug, smaller gap. Check/replace coil & wire/cap

Edited November 9, 2023 by peter1127

[peter1127]

4 minutes ago, bartman said:

And what exact carb or carbs did you run?

GSXR1127 1992 model with 40mm carbs

Edited November 8, 2023 by peter1127

[bartman]

4 minutes ago, peter1127 said:

Hmm weird behavior. Basically not closer to a solution. Possible issues are:

• AF wrong  (jetting)
• fuel issue (fuel supply)
• slide issue 
• BOV issue
• Ignition issue

Maybe you can do some tests to exclude stuff:

• O2 sensor should be wideband. If not, its not so useful. Also  rich stumbles often dont show.  Dyno run including shifts with proper sensor might reveil something
• When the issue appears, shut the bike down including fuel pump and check bowl level. If almost empty its clear where to look.
• remove airfilter and check with gopro the slide behavior
• Slightly more spring on the BOV so you are sure it doesnt open a bit when boost starts to build.
• Change plug, smaller gap. Check/replace coil & wire/cap

It will be a bit before I can but definitely couldn't do a dyno run.