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Piledriver wrote:

The power is limited only by how much boost you dare put to it.

...and your wallet.

Cuz carb jets and venturis are free........

. I wish they were free.
I have the fuel reg getting a signal from the turbo actuator pipe . If add a bleed valve to that pipe will it take away the signal for the fuel reg.
Cheers g.

Hi guys.
I'm having trouble with an on boost backfire.
Any ideas as to what it could be.
Thanks.

GARRICK.CLARK wrote:Hi guys.
I'm having trouble with an on boost backfire.
Any ideas as to what it could be.
Thanks.

How far are your retarding on boost?
Most likely too much retard and a lot of ex backpressure , overlap makes it more likely.
(still burning mixture (due to excessive retard)> backing up aka reversion (but worse), with a bang)
Small turbo/large cam=worst case.

Hi PIle.
I'm at 10* at idle
20* total
5* retard
Plus svda advance.
I could lock it at 24
And test it.

Does that mean on boost you are at 15 degrees???

What is your max boost you are running right now???

I doubt you would want to go less than 20 degrees advance and that would be at 15 plus lbs boost. If you are trying to stop detonation with retard at high boost you need to change direction and go with intercooling or WI instead.

Hi clone.
Yes basically with boost retard its 15* when on boost.
I'm going to adjust it to 25*total and keep the 5* retard
If it pinks I'll have to get water injection.
I have noticed the on boost AFR is is in the right place. Plugs are a good colour too. The cruise is too rich its like it needs more air adding to the fuel at low speed.10s AFR at low speed going leaner as revs increase with boost.
What causes a lack of air at low revs.
I have to feather the throttle. As boost and revs increase I give it more throttle and all is good. If I give it too much throttle before boost has started it starts hunting. (Too rich)
Could my small cone filter be too small and be suffocating it.also the filter is on the end of the turbo is this the best place for it or is there a better place to have it.
Thanks.

Hi Guys.
A year has gone by and still no further.
I did lower the comp by a few points so should be good for more boost.
Fitted an intercooler.
Fed boost into the float chambers.
So what's it like.
I still have the on boost back fire.
When it starts to boost the AFR gradually goes leaner till it starts to back fire.
Is this fuel starvation.

What do you have for fuel pressure boost compensation????

Your fuel pressure needs to stay probably around 3 lbs. above your boost pressure. For ex. 15 lbs boost would require 18 lbs. fuel pressure.

If you are good on fuel pressure then you are setting your mains for max boost and not getting the carbs set correctly to add more fuel at boost.

Your idles and mains should be set to give you idle and cruise afr's where you want them and the emulsion tubes and other jetting should richen up the boost areas.

Do you have both carb float bowls referenced up into the top hats????

That is what made the biggest difference on my Pict 34 blow through.

I eventually moved to EFI because I knew that I could never get my carb setup to run like I would want to.

I decided I wanted to drive it more than I worked on it.

You should be at 12.5 AFR on boost if not richer.
I kick mine up to almost 11.5:1 when at 20 plus lbs to help cool along with the WI.
My ignition advance is at 19-20 degrees at 21-22 lbs. boost

Hi Clone.
I'm almost going pull through.
I have an FPR 014 pressure reg.
The fuel pump can pressure up to 100 psi.
I've just been out to test the reg. It mainly returns fuel back to the tank. If I block off the REG outlet to the carbs I can set the gauge to 3psi. Is it right that most of the fuel flow and pressure is returning to the tank. I can boost ref the REG and the gauge pressure reading does rise. So am I going to get the correct flow of fuel to the carbs .
I have a boost ref pipe from the actuator that splits into 2 and goes through each hat and directly into the float bowl.
idles are 55's.
mains 142.
Its rich at cruise like 12, as boost comes in the afr goes from 12 to 13 to 14 and higher till it makes loud backfires from the straight through pipe. No pinging tho.
I'm using 8 mm fuel pipe
225 needle and seats.
carb banjos are drilled out
passage ways to the fuel needle are enlarged.
So AFR OF 12-13-14-15 AND UP TILL BANG BANG is telling me what.
Thanks G.

You are going lean on boost......Fix the fuel issue before you hurt the engine.
If you don't have a real good muffler on the engine you will not hear it ping but it could still be doing it.
My advice is to be real careful until you get it richened up on boost.


Your regulator needs to be boost referenced.
Put a pressure gauge on the fuel line to the carbs and take it for a drive to see what your fuel pressure does on boost.
You have to verify that it is indeed working before you look elsewhere.

It's the little things that will trip you up.

Running it at 15 lbs when it is not tuned will certainly give you grief in the long run. Get it working at 6 lbs first and then work your way up a couple lbs. at a time.

Anything over 8-10 lbs. is quite serious and damage will result if you don't have it set up correctly......I've been there.
I have a buggy and a good muffler plus I know what to listen for and I can hear mine pinging at 8 lbs without WI.
I can pretty well guarantee you are getting detonation if you are running that amount of boost with high IAT's


Any blowby that shows up is a sure sign of cracked pistons and will be a ticking time bomb.

Ok. Been testing this reg. 1 Inlet,1 outlet, 1 return to tank. I've put a gauge on the outlet going to carb. If I blow down the fuel inlet the gauge needle rises. if I Blow down the boost ref. NOTHING shows on the gauge, it blows the pipe off.
Have I got the wrong REG.

Post a pic of the regulator......

I've never been good at loading pics.
There's basically an inlet, an outlet, a return to tank and a vac nipple on top. There is a diaphragm inside with a spring pressing down on it. put vac on the nipple and the diaphragm lifts. air cant be blown into it .

Find a pic of it on line and post the link from the address window.