fj1200 turbo "thug"

[racerrad8]

2 my nice shiney new clutch slave cylinder is no longer nice and shiney as it spewed oil out from the casing when the engine reached oil pressure... i guess this is just an O ring??

Not sure where the oil came form, but there is a seal on the clutch pushrod to seal the oil.

Clutch Push Rod Seal

I wonder if it popped out when the push rod shot out before you installed the slave cylinder.

Randy - RPM

[backstreetheros]

quite possibly, i didn't see that though...
I've just ran the bike again and its coming out from the top bolt on the clutch slave...
i'm hoping the seal has gone and someone hasn't put a bolt too long in there and punched a hole behind the threads?
i guess i could use some thread sealant to put the bolt back in?

randy can you point out the idle adjust on these carbs for me?
surely i can just tighten the throttle cable a bit. i will be looking to have the bike re-jetted and dyno'd properly after I've got it to a ride-able stage.
i'm leaving the clutch pipe and chain till last to stop myself taking it up the road for a cheeky hack. its oh-so-tempting! 

[racerrad8]

quite possibly, i didn't see that though...
I've just ran the bike again and its coming out from the top bolt on the clutch slave...
i'm hoping the seal has gone and someone hasn't put a bolt too long in there and punched a hole behind the threads?
i guess i could use some thread sealant to put the bolt back in?

randy can you point out the idle adjust on these carbs for me?
surely i can just tighten the throttle cable a bit. i will be looking to have the bike re-jetted and dyno'd properly after I've got it to a ride-able stage.
i'm leaving the clutch pipe and chain till last to stop myself taking it up the road for a cheeky hack. its oh-so-tempting! 

Okay, I just drilled a case where the upper bolt goes and there is no way I can see a bolt could leak oil.

Are you sure it is oil and not brake fluid leaking from the banjo bolt?

The idle speed screw is underneath the carbs between the two center carbs. It has a thumb screw that for turn to control the idle speed. if the carbs have been sitting I would say the pilot jets are plugged and the reason for the poor idle.

Randy - RPM

[backstreetheros]

100% its not brake fluid as i dont have the clutch hose connected yet 

it may just be that the oil coming from the clutch push rod choses the easiest path out of the top of the clutch slave cylinder.
its not just a drip, it really flows out. so much so that i had to stop the bike.
im thinking maybe the seal around the pushrod (but saying that i ran the bike for 3/4 hour with the plenum disconnected when checking the oil cooler and turbo oil feeds for leaks?)

maybe because now i can hold a steady high rev with my fuel pump connected
where as before i could only blip the throttle as boost pressure would push the fuel back out of the carbs and it would die?...

i'll pull it apart today and see whats going on... up at 07:00 am on a sunday... thats how dedicated i am to doing some more work on this bike!

[backstreetheros]

heres a better picture of the plenum attached to the carbs
with the idle adjusted (thanks randy) the bike will now idle.


pulled the clutch slave cylinder again today due to the massive oil leak...
it looks as though the oil was coming from the top bolt of the clutch slave cylinder....


i was disappointed to see the clutch push rod rubber intact. 

the oil is clearly coming from the top bolt hole
to me it looks like in the past the chain has come off and pulled off the slave cylinder in the process hence why it was missing.
there is also a gouge out of the engine casing by the push rod

if you look closely you can see the cracks at the bottom of the upper bolt hole

to test my theory that the upper bolt was leaking oil i decided to try and start the bike... then i stupidly realised i had entered the "spear the cat" game...



i don't readily have the availability to weld engine casings so some chemical metal found its way into the hole...



the bike now idles properly, i left it for a while to idle and it seems to not be too far off
i decided to get brave and turn up the rev limiter!

on revving the bike it gets to about 6000rpm under its own steam pretty quickly, spits a good flame when you let off the throttle too,
if you hold the revs at about 6000 it starts to feel almost a bit flat, like there is a barrier while its building boost...
then after probably half a second of being flat the bike hits 9 psi of boost pressure then it literally slams into the rev limiter almost instantly, you can't really hear the revs climb, its just like a huge bark and on the rev limiter the bike spits a steady foot long flame from the exhaust...

if you stay on the limiter for a second then dump the throttle, you get a mix of dump valve and wastegate chatter as the revs drop, but they seem to stay really high after a good limiter bash... doesn't fall back to idle... is it possible that the main jets are too big so its over fuelling and staying high?
a tiny blip on the throttle brings the revs back down to a steady tick over.

[backstreetheros]

done a little bit more today, i went and bought a large rubber diaphram for some milking parlour machine,
cut it up and made a nice rubber gasket to seal the petrol cap plate to the tank...
this was all well and good but after doing this i started the bike, ran ok for a little while then the revs started to climb on their own!.
i quickly turned the bike off before it had chance to start spooling uncontrollably.
turns out the fuel pump is pressurising the petrol tank that much its forcing it past the floats in the carbs and filling up the cylinders!
i took a trip to my local bike mechanic/tuner
explained to him what happened and the hesitation in the fuelling.
he told me that the fuel pressure is way too high, its overfuelling loads before it gets chance to spool up and get more air into it... this explains the foot long flame from the exhaust!
he reccomended i practically open the wastegate to reduce boost pressure as much as possible then slowly edge it all up till it doesnt work right lol

if you've got an adjustable boost pressure switch controlling your ignition retard... make sure the screw isnt backed out so far the contacts inside touch... trying to start the bike with 12 degrees retard makes some extremely loud backfires! (nearly blew the windows out! )

i'm going to try adjusting down the fuel pressure regulator to as low as i can get it before i get carried away and buy new things...
the problem with the tank has annoyed me so much i've just bought parts to make a new 2 part tank.




i thought if i cut 2" off the cap side of one of these tanks... a solid baffle could be welded in to retain the petrol, then the 2" part could be used as a water resivoir for the water cooling side of the turbo.
i'm very tempted to just ditch the copper radiator and have a loop of pipe running right round the outside of the bike to cool the water...
i don't think there is any harm in heating the petrol a little from the tanks transferred heat is there?
two of these tanks would be mounted side by side, then one cap would be for the water and one for the petrol although it would look like they are both petrol caps.

then i could weld the necessary vents, feeds and return lines into the tanks without messing around with the crap tank i have at the moment.

much easier.

i'm now trawling the internet looking for how to adjust the fuel pressure on my fuel pressure regulator 

[Seanextra]

Hi Loving this build,

                      I would say No to Hot Fuel !!! 2 Reasons first being safety, as hot fuel will pressurize the vessel and if its vented it will be spewing out fumes just waiting for a light !  2nd reason would be that HOT fuel is not what you want for making power and sort of makes going turbo seem like alot of effort for less gain, Many old school drag cars use to run a temprite which was a small alloy can with an alloy coil running thru it which was between the fuel tank and Carbs this would be filled with ICE before each run and would pre cool the fuel which created a similar but primitive effect of NOS injection, and also similar to what an intercooler does on a Turbo. By pre heating your fuel you are doing the oposite of this and im sure would create problems with atomization of the fuel in the carbs. This is also why the stock FJ engine ran a heat shield in front of the carbs to stop heated air from the cylinders and head preheating the fuel in the carbies.

I may be wrong but this is what i know to be the situation when it comes to Fuel temp etc... maybe someone else here might know a bit more on the subject.

On another point i see you are pressurizing your carbs from the plennum outer edges do these pipes lead to a venturi into the path of the incoming air or are the just plumbed to the edge of the plennum?

What fuel reg and pump are you running looks like a holley blue pump?    Is your Regulator Boost regulated or just static?    What Turbo is it and the Specs? What Size Jets are you running, Needle position and turns out on pilots ?


Regards Sean   

Keep the posts going  really interesting to see your findings.

[andyb]

A little heat won't be a killer for the fuel, but using it as a coolant or a heatsink isn't a good idea.  I mean, the stock air cooled engine has 5 gallons of petrol directly above it, and it gets decidedly warm at times.  Not a huge problem normally, but you still shield it from heat when you can.

As for the way fuel reacts when heated, there's a couple points.  Hotter gas will lose the lighter components, changing your tune as it gets artificially aged from the heat, and that's going to be the problem, rather than expansion changing density.

Sounds like you need to run a lot, lot less fuel pressure, like 3psi or so during offboost or vacuum times, and then use a rising rate regulator to give added pressure during times of boost.  At idle you'd want say, 3psi of fuel as a baseline, but at 20psi inlet pressure you'd have to have 23psi to maintain the same delivery rate.  Jetting past that is another problem, as it's going to do some strange things at partial boost and so on.  Really the only proper way to even see what it's doing will require a datalogger, possibly a Wego unit.

If you use a normal pressure regulator on the fuel system, as the boost pressure builds, it'll go very lean and proceed to shove air backwards through the fuel pump.  Not a good thing.

[Havoc]

Don't the pitot tubes from the up pipe balance the pressure to the carbs. CV carbs don't need rising rate like an EFI do they?

[Seanextra]

On a Turbo you still needs to balance the incoming Fuel Pressure to Compensate for the incoming charge pressure otherwise as andyb states it will try to blow air back up your fuel line which would lead to a Very Lean run and in short time one Rooted Engine.  $$$


Rising Rate or boost controlled Regulators are plentiful and not expensive i cant see how you could get it to work effectively without one on any carb set up ?


Regards Sean

[Havoc]

My understanding was the pitot tubes 'fool' the CV carbs into behaving like they are opperating at 100,000kPa. They would behave differently from flat slides? and I completely get that EFI require rising rate. Boost would force CV carbs closed by cancelling out the negative pressure provide by the suction of the motor. As long as the float bowls stay full of fuel under constant pressure there wouldn't be a problem with leaning out. It is very early and I'm very tired though 

[andyb]

CV carbs don't really respond to vacuum, they respond to air pressure differential.  You have to give a reference signal to one portion of the carb so that it sees the pressure changes as a function of airspeed through the venturi rather than as a function of boost pressure.

There's no chance you can use a fuel pump to push 3psi into a 10psi bag.  Just doesn't work, and that's why you have to have a rising rate regulator.  Sure, you can run the fuel at a higher pressure all the time, but then it's going to leak like hell past the needle seat anytime you're not on boost.

The problem is at this point you can very quickly do much damage to the motor.  Get things as figured out as you can and take it to a dyno with a good tuner.  Yes, it'll be expensive, but it'll be vastly cheaper than a set of pistons, say.

[bcguide]

How about seting your fuel pump for normal atmospher and then run a line from your plentum to the fuel tank. If your tank is pressured up from the turbo
your fuel should still flow to the carbs
Scott

[andyb]

The tank still needs vented for normal use.  It's not the first time a turbo has been done through carbs, go with what's worked for others, yes?

[Havoc]

Got it. Just having a brain freeze. Ta