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Triple SU carb info

Started by ribz0 , Jun 08 2016 01:12 PM

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23 replies to this topic

#1 ribz0

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Posted 08 June 2016 - 01:12 PM

Hi all...

Well... I have finally got "stage 2" underway on my LC and all is going well... Im just doing some of the final small stuff and plumbing and have some questions for the the guru's about my SU set up... I have triple HS6 1 3/4 and running the blue motor mech fuel pump.

Firstly, did the LC and LJ's run pressure regulators and special fuel pumps?

I got the standard SU conversion kit which looks HOT!!! but... not keen on the fuel distribution block or regulator which was supplied... so, I am making up my own ally 4 way fuel block and fuel lines and thought why do I need to run a fuel regulator on carbies which have needle and seat?

Also, vac advance for the dizzy, my carbs dont have a port for this so where would be a good spot to tap into?

Cheers

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#2 jd lj

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Posted 08 June 2016 - 06:51 PM

If your fuel pump has too much pressure it can actually force fuel through the needle and seat when it's meant to be closed.

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#3 ribz0

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Posted 08 June 2016 - 10:11 PM

yes... but why would that be different to a normal stombie carb? Im running a standard mechanical fuel pump... did the original lc/lj's have anything different as in type of fuel pump or run pressure regulators?

Has it something to do with pressure on the needle and seats on the SU's compared to a normal carb?

Do early glass bowl type fuel pumps pump more or less that the newer blue/black motor fuel pump?

Just throwing it out there....

Cheers

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#4 _oldjohnno_

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Posted 08 June 2016 - 10:30 PM

yes... but why would that be different to a normal stombie carb?

It's to do with the size and shape of the float, the length of the lever that pushes the needle and the size of the opening in the seat. It's standard practice to run a regulator with SU's; they tend to dribble and overflow (onto the exhaust!) with "normal" fuel pressures.

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#5 ribz0

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Posted 08 June 2016 - 10:43 PM

thanks for that oldjohnno... you have answered my "why"... so no messing around with the fuel pump like spacing it out to reduce the angle of the dangle or anything like that? any pressure differences between glass type and later pumps?

so would you think 3-4 psi would be a good place to start? I will have to do something about getting a better looking regulator and gauge if I must have one fitted....

Cheers...

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#6 ribz0

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Posted 08 June 2016 - 10:46 PM

oh... my SU's have the overflow tube on them which I plan to run to a HJ-Z smog box so the fuel will at least avoid spilling onto the hot headers and have somewhere to go.... a bit safer at least....

:rockon:

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#7 _Bomber Watson_

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Posted 09 June 2016 - 11:08 AM

Only problem with that is you cant immediately tell if there dribbling...

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#8 ribz0

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Posted 09 June 2016 - 05:01 PM

true.... maybe will see it drip out of the canister if there is that much... just playing with a few different ideas...

Cheers...

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#9 Dave6179

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Posted 13 June 2016 - 12:51 PM

I'm only using the std glass bowl pump. Nothing else. No dribbling, leaking, over fueling etc. Have done since 1987.

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#10 _oldjohnno_

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Posted 13 June 2016 - 01:43 PM

That's good to know. I dunno how they go with the later Goss pump but I do know they'll overflow with a Carter SBC pump.

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#11 warrenm

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Posted 13 June 2016 - 05:25 PM

I used to have a pump from a blue motor fitted to mine years ago, had to fit a return line as the carbs would over flow very frequently, I think it had 4psi, which the carbs didn't handle.

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#12 ribz0

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Posted 13 June 2016 - 08:01 PM

ok.. great info thanks!!

Thats what I was trying to get across as Im sure the original triple set up's did not have regulators fitted to them so good to hear that info Dave..

oldjohnno... i have a standard blue motor fuel pump fitted atm but will fit the glass bowl type as dave has done.. I have seen sbc pumps used but thought that the sbc pumps were much higher psi output... no good for SU's as they dont like pressure...

warren... not keen on fitting return lines so if you had a standard blue fuel pump fitted, it seems that type of pump may have a higher psi output than the glass bowl type... maybe for the downdraft the commodores were using??

anyway, will start with a standard glass bowl pump, small fuel block and steel lines and play from there...

Cheers

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#13 _oldjohnno_

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Posted 13 June 2016 - 08:49 PM

Keep in mind that the fuel pressure is determined by the strength of the spring under the fuel pump diaphragm. If necessary you can substitute a weaker spring or at least start with the oldest fuel pump you can find in the hope that the spring might have lost a little tension...

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#14 ribz0

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Posted 13 June 2016 - 08:56 PM

ok great!! thanks for that info johnno... Id luv to NOT use a regulator but if I must... I will.... There will be enough room on the fuel block to run a pressure gauge if I need to run the regulator but will start with a basic set up and go from there.... I have some steel fuel line coming so will be able to make lines as I need them....

Cheers

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#15 _Bomber Watson_

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Posted 13 June 2016 - 09:16 PM

THe "original triple setups" ran Strombergs, not SU's, different carbs with different needs, so your arguement about the glass bowl pump working with them is invalid.

Still worth a go though, but I bet you will end up with a dead head of some description fitted.

Cheers.

Edited by Bomber Watson, 13 June 2016 - 09:17 PM.

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#16 ribz0

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Posted 13 June 2016 - 09:37 PM

Cheers Bomber... I understand they were a different carb .....just a totally different beast compared to the SU.... I reckon from what others are running, I will need to fit a reg but will do a bit of trial and error engineering.... lol.... the fuel block Im making will cater for a reg and gauge if needed...

Cheers

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#17 _Bomber Watson_

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Posted 13 June 2016 - 09:40 PM

Im running the Holley 1-4 psi dead head.

Dont run a return style reg with a mechanical pump, learnt that the hard and embarrassing way.

The clicker style regs work, lots of people use them, but by god there ugly.

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#18 ribz0

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Posted 13 June 2016 - 09:48 PM

ok thanks... yep, got a clicker style in/out reg on hand and no... no return lines....

Yes... they are very fugly...the very reason no to use one... but hey... lots of people use them and they have been around for ages so they work.....

Cheers

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#19 ribz0

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Posted 13 June 2016 - 09:55 PM

care to share the embarrassing story bomber?

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#20 _Bomber Watson_

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Posted 13 June 2016 - 10:51 PM

Couldnt work out why my carbs were spitting fuel no matter how far down I wound my bypass style reg, watching the guage it would spike from 0-4psi and the carbs would spit in synk. Then OJ pointed out that im a frOcking retard and that you should only ever use a dead head reg with a mechanical pump, due to the nature of how they work.

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#21 _ljxu1torana_

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Posted 13 June 2016 - 11:00 PM

at least you admit to being an idiot davey which you are anyway

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#22 SA EH

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Posted 13 June 2016 - 11:20 PM

FFS frOck off

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#23 warrenm

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Posted 14 June 2016 - 06:40 AM

I didn't use a regulator as such, had a small needle valve to bleed some pressure off back to the tank.

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#24 I'm a Red Motor fiend

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Posted 14 June 2016 - 07:16 AM

I don't understand why you just dont fit your reg. Search the forum or google it and you will see most SU guys will be running a reg, me included. I run a clicker type like you have and they're not big and dont look that bad. Mine is set on 2.5 psi which feeds a very healthy 202, never starves or hesitates. Says to me that without a reg your stock pump is giving you say 4 psi which is too much and not required.