<div class="FTQUOTE"><begin quote>Originally posted by: hayabusaTURBOkiller

hi ,whats this pilot-tube deal

i just have my carb vents plummed into the turbo out lest

could you explain please

yes my regulator is rising rate

i have been thinking on the a/f meter ,just thought i could work around it

but i see it will point me in the right direction fairly quick if it shows its going lean straight on throttle

any other tips you have

thank you</end quote></div>

Hello, Here's a quote from a guy that has done a few bike blow-through setups.

"The pilot-tube deal is the difference between making a blow-through system work or fail. You need a fuel pump and a fuel pressure regulator that increases fuel pressure as the boost increases. The fuel pressure needs to always be higher than the boost level, otherwise you'll be pushing fuel out of the float bowl.

Thankfully, this isn't a new problem and there is plenty of aftermarket parts availible for this. The tricky part is the jetting issues involved with a CV carb under boost conditions. The float bowls obviously need to be pressurized under boost, but the simple answer seems to be to hook the float bowls to reference lines to the air box, thereby keeping the float bowls at the same pressure, so when there's boost present in the air box, there's equal pressure in the float bowls.

But as so many things in life, its not that simple. You optimally want MORE pressure in the float bowls than what is being seen in the throat/air box. The reference lines just don't flow enough or react fast enough to boost changes too, so it creates a lean condition under boost if you are only using reference lines to teh air box.

I discovered the fix for this, and its pretty easy, its called a "pitot tube", which is a smallish tube that you fix so that its in the middle of the intake pipe, pointing upstream, towards the turbo. Due to its position, it creates a ram-air effect, which slightly increases pressure over what the airbox is seeing, and also creates faster reference. This small difference is very big in jetting issues, and crams so much perssure in the float bowls under boost, that you have to step down quite a few sizes in main jets to get it right.

All of this is made much easier with an O2 gauge, which I highly recommend for these kind of home projects."

Here's a pic of the Pilot-Tube

Here's another link with a lot of good info: Turbo 400ex


If you go with a O2 for tuning, do a wideband. The LM-1 from Innovate Motorsports is worth the money. I have it and the LMA-3 (AUX Box) and can datalog rpm, boost, fuel pressure, etc.. In other words, I make a run, press the record button, and when I come back I hook it up to my laptop computer and go over the graphs to see what's happening throughout the RPM range. Makes tuning a snap because you immediately know where to go with the tune. Innovate has a Products page and a Forums page. Research that turbo site and like I said earlier, Use The Green Search Button until you can't find anymore info. Most questions can be answered by searching but if you run into something, register and post it.

BTW, the pilot-tube setup works for all blow-through carb applications. It gets the fuel flowing so that when you come up on boost, the fuel is there eliminating bogs, back firing, lean spikes, etc...

 

hi ,ill fit one of those pilot-turbo pipes ,,thanks for taking the time to put the info on here

 

Post the aftermath of adding the pilot-tube. You can use a piece of 3/16 brake tubing epoxied or welded into the intake pipe. It should/will help alot.

 

ive got the pilot-tube made up and in place
had a small oil leack from the turbo ,ill be trying it next couple of days
ill keep you posted

 

I've been checking out the Edelbrock Raptor 660 kit. Pretty nice setup with the squirter and may be easier to tune than two CV carbs. I think you are/were having a fuel bowl problem. Boost pressure may be overcoming the fuel flow at the metering rod/needle. The ram effect of the pilot-tube will address this situation by putting more pressure into the fuel bowl, "pushing" the fuel up into the carb throat. You should see a difference when you get the vent hooked to the pilot-tube. May get way rich?? Guess we'll see.

 

ive not had chance to test the quad out ,since fitting the pilot tube ...if i blow with my mouth through the float bowl vents tubes that are going to be connected to the pilot tube ..i can see that the fuel comes out the jet were the throttle needle fits it
but also the fuel will come out of the pumper jet..if iam describing it correctly its the one that when you pump the throttle it squirts down the carb venturi ....will this need blocking up ,am i right in thinking that the fuel flow will be too much when it comes on boost because of this....ore is this how it should work

thank you again

 

<div class="FTQUOTE"><begin quote>Originally posted by: hayabusaTURBOkiller

ive not had chance to test the quad out ,since fitting the pilot tube ...if i blow with my mouth through the float bowl vents tubes that are going to be connected to the pilot tube ..i can see that the fuel comes out the jet were the throttle needle fits it

but also the fuel will come out of the pumper jet..if iam describing it correctly its the one that when you pump the throttle it squirts down the carb venturi ....will this need blocking up ,am i right in thinking that the fuel flow will be too much when it comes on boost because of this....ore is this how it should work



thank you again</end quote></div>

Pressurizing the fuel bowl while the rest of the system is not under pressure will push fuel out because it has nothing counter-acting against it. Keep in mind that the rest of the carb will have pressure when under boost. However, I am a little concerned about the squirter pulling over like you're describing. It may pose a problem that will have to be dealt with such as modifying or blocking. Also, it's possible that it will "act" totally different though when everything is hooked up and running. Most carbs have some kind of check valve to prevent the fuel from pulling over. I'm not sure about the Eddy, I'll look up the diagram again and see how it works.

The best way I know to describe the "Pilot Tube" theory is: Carbs are designed to work under vacuum to "suck" the fuel up through the jets. When your system is under boost, the throat and float bowl become equalized making the fuel flow stall. The Ram Effect of the pilot tube will push the fuel out the bowl through the jets making it almost act like fuel injection. Because of this, the fuel flow is going to have to be cut down or it will be pig rich.

I wouldn't worry too much until you try it. Get it together and see what it does, post back and we'll go from there. If it gets really rich, try using the bigger metering rods to lean it back down. Try to see if the squirter is pulling over under boost.

 

hi,ive had the quad out for a run ,what a differnce that pipe makes
its suprising how a simple thing can make so much differnce
it doesnt cut out or splutter like a *****er any more.
it makes good boost now ,theres a stutter as it comes on boost ,i think thats just
the preasure getting up to pace
i carnt tell if i am lean or rich ,,how could i tell the differnce
ive orderd a cheap a/r ratio meter..which should tell me which way its going
its boosting nice but isnt giving the kick it should..would this be because its lean and not getting enough fuel to make the power..
i think my fuel regulator was set a little high ,ive got clear pipe running from the float bowl and after i had the run i noticed there was fuel in the clear pipe
could this be the reason for poor power ,what should my regulator set at ,at tickover ,should i go for around 2psi
ill put some pics of it in my page on here ,so you can see how things are lookin
thanks again

 

<div class="FTQUOTE"><begin quote>Originally posted by: hayabusaTURBOkiller

hi,ive had the quad out for a run ,what a differnce that pipe makes

its suprising how a simple thing can make so much differnce

it doesnt cut out or splutter like a *****er any more.

it makes good boost now ,theres a stutter as it comes on boost ,i think thats just

the preasure getting up to pace

i carnt tell if i am lean or rich ,,how could i tell the differnce

ive orderd a cheap a/r ratio meter..which should tell me which way its going

its boosting nice but isnt giving the kick it should..would this be because its lean and not getting enough fuel to make the power..

i think my fuel regulator was set a little high ,ive got clear pipe running from the float bowl and after i had the run i noticed there was fuel in the clear pipe

could this be the reason for poor power ,what should my regulator set at ,at tickover ,should i go for around 2psi

ill put some pics of it in my page on here ,so you can see how things are lookin

thanks again</end quote></div>


Hello,
Glad to see a test run. I'll bet you was skeptic at first if the pilot tube would make a big difference in running.

Check your plugs. Black sut that will wipe on your finger is rich. The best way in your situation is a Air/fuel meter. If the one you bought is not a wideband I don't think it will be of much use. You are going to really need a good wideband. You could fry your engine really quick by leaning it.

2psi of fuel pressure should be plenty to start with.

Excessively rich or lean will hurt power. That stutter when coming up on boost is likely lean but it could be rich also. Is the squirter adjustable as in how much fuel you can squirt like by changing the nozzle size or something?

Play with your metering rods going up and down on the fuel and see what it does.



Sorry, I'm in a rush and don't have time to give you some really in depth answers right now but play with the carb and change a few rods and see what it does. Go up and down on the fuel but don't push it. Post back and a little later I've have some time to figure out whats going on with it.

Later.....

 

How's the tune coming? Have you got a A/F meter hooked up yet? Have you tried playing with the fuel curve? What about the timing curve? What fuel are you running?