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95 or 98 Octane for SU carb's?

Started by _ASLTO_ , Nov 14 2016 08:41 PM

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#1 _ASLTO_

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Posted 14 November 2016 - 08:41 PM

Hi Guy's,

I recently got the boys from Faber / SU Midel at Lakemba to do a major restoration on my HIF 1 3/4" triple SU's and I have been given mixed opinions on which gas to use.

Tim, the boss out at Carbuburettor Service Centre (Parramatta Rd Burwood) who knows his carby's mentioned to me that I should be running 95 octane as it is less likely to foul plugs and it also mist's better than the apparently heavy 98 octane.

I'm finding my engine is ever so slightly pinging when the rev's get up compared to when I ran 98 before the resto and I think that I may even get a little more power from the 98 possibly ? I don't remember ever having fouled any plugs on 98 even with carb's that ran very rich from worn jets before the resto.

so your thoughts PLEASE ????

#2 hanra

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Posted 14 November 2016 - 08:46 PM

Ive been happy with 98 with my twin 1 1/4's.

Edited by hanra, 14 November 2016 - 08:47 PM.

#3 _ASLTO_

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Posted 14 November 2016 - 08:46 PM

not sure how detailed the attached pic's came out but.. Louie from Faber... hats off to you mate! an awesome job, they look even better from the inside...

Attached Files


#4 _ASLTO_

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Posted 14 November 2016 - 08:48 PM

Good to hear Brad!

no fouled plugs by any chance?

#5 hanra

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Posted 14 November 2016 - 08:52 PM

No. I tuned my carbs at idle with my colourtunes. Used an LM-2, and then experimented with different viscosity dashpot oils, spring colours and needles and got it running really well.

#6 _Bomber Watson_

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Posted 14 November 2016 - 08:53 PM

If your cam and compression ratio are ok on 95 when the engine is correctly tuned run 95. 

 

If there not, run 98 and retune it. 


#7 _ASLTO_

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Posted 14 November 2016 - 08:58 PM

That's the shit..

Yeah, I've already played with the colourtunes, springs, oils & needles and I can say there running really well right through the rev range it's just that slight pinging I'm concerned about, and the timing is spot on... I'll be taking out the left over 95 from the tank and fill up with 98 this weekend

Thanks' for the input Brad

#8 hanra

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Posted 14 November 2016 - 09:00 PM


No worries. Sounds like your onto it. Yeah maybe pull some timing out?

I ended up using the proper SU oil in the end after mucking around with so many different viscosities.

Edited by hanra, 14 November 2016 - 09:02 PM.

#9 _ASLTO_

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Posted 14 November 2016 - 09:01 PM

DJ,

do you think I'll throw things way out with putting 98 back in the system?

It's not hard to tune now with the carby's, dizzy, plugs etc all like new...

#10 S pack

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Posted 14 November 2016 - 09:02 PM

If your cam and compression ratio are ok on 95 when the engine is correctly tuned run 95. 

 

If there not, run 98 and retune it. 

Agree, it's about what your engine requires not your carbs.


#11 S pack

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Posted 14 November 2016 - 09:07 PM

DJ,

do you think I'll throw things way out with putting 98 back in the system?

It's not hard to tune now with the carby's, dizzy, plugs etc all like new...

You probably won't have to touch anything to run the 98. If she's pinging with the 95 then you probably need to pull a bit of initial advance out as Brad has said.


#12 hanra

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Posted 14 November 2016 - 09:12 PM

Get yourself an LM-2 geez it makes life easy. Just need a GoPro and mount rather then hold a phone and the LM-2 and change gears and steer.

https://youtu.be/PF1S3KJZt04

#13 _ASLTO_

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Posted 14 November 2016 - 09:13 PM

Thanks once again Gents',

I'll let you all know how it goes this weekend for anyone else who has the same issue...

Thanks',

#14 _Agent 34_

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Posted 16 November 2016 - 03:58 PM

did you do the dizzy, as this may be contributing to the pinning.- just a question.

 

mine does it on a hot day with poor fuel.


#15 _ASLTO_

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Posted 16 November 2016 - 04:14 PM

Hey Grant,

Yeah I got 'Performance Ignition Services' from Melbourne do a full restoration on my electronic dizzy that was an original Bosch..

The pinging is only every so slight when the rev's get right up there and I can here 'sometimes', I'll be putting in a fresh tank of 98 in the next couple of days and I'll post how it goes.. might slightly adjust the timing as suggested by the gurus !

Love the feedback guy's, keep it coming ! for everyone's sake !

#16 LC-GTR-1969

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Posted 16 November 2016 - 05:08 PM

Hey Grant,

Yeah I got 'Performance Ignition Services' from Melbourne do a full restoration on my electronic dizzy that was an original Bosch..

The pinging is only every so slight when the rev's get right up there and I can here 'sometimes', I'll be putting in a fresh tank of 98 in the next couple of days and I'll post how it goes.. might slightly adjust the timing as suggested by the gurus !

Love the feedback guy's, keep it coming ! for everyone's sake !

 

Nothing wrong with 98 as long as the engine needs it. No point running it though with a low comp ratio, high LSA cam combo as cylinder pressure will not be high. Its really shooting darts in the dark without these figures. Could simply have a touch of ping due to too much advance as mentioned by others. 

 

Initial may be right but total advance could be a few degrees too great. Not all engines want the same. I would run 98 as is and if she runs well with no pinking, sweet. If she still pinks your timing is off bud.

 

Also, just be mindful that if you can actually hear pinking above above about 4500rpm its really not very good. Point being that you cannot always hear it due to engine noise etc. 


Edited by LC-GTR-1969, 16 November 2016 - 05:09 PM.

#17 _ASLTO_

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Posted 16 November 2016 - 08:26 PM

Nothing wrong with 98 as long as the engine needs it. No point running it though with a low comp ratio, high LSA cam combo as cylinder pressure will not be high. Its really shooting darts in the dark without these figures. Could simply have a touch of ping due to too much advance as mentioned by others. 
 
Initial may be right but total advance could be a few degrees too great. Not all engines want the same. I would run 98 as is and if she runs well with no pinking, sweet. If she still pinks your timing is off bud.
 
Also, just be mindful that if you can actually hear pinking above above about 4500rpm its really not very good. Point being that you cannot always hear it due to engine noise etc. 


Thank You for your knowledge mate!

You've got a point about hearing pinging at "very" high rev's, that is a worry, though I'm meaning more around the 3 1\2 getting closer to 4K mark and that's if and when I do hear it, (this is a big maybe comment) might it have something to do with the weather at times "possibly" or the fact that I do a lot of stop-go driving and waiting at the lights may heat up the carbs bowls and petrol inside the bowl and then when I tramp it of the lights i' m not getting enough petrol through the carbs hence the pinging?? "possibly"

Regardless, I'll be putting in a fresh tank of 98 and hopefully "let there be light" !

#18 orangeLJ

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Posted 17 November 2016 - 10:56 AM

Get yourself an LM-2 geez it makes life easy. Just need a GoPro and mount rather then hold a phone and the LM-2 and change gears and steer.

https://youtu.be/PF1S3KJZt04


You do realise you can data log right?

Rpm input and a tps and you can log throttle percentage and rpm against your AFR

#19 S pack

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Posted 17 November 2016 - 12:31 PM


#20 hanra

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Posted 17 November 2016 - 01:18 PM

You do realise you can data log right?

Rpm input and a tps and you can log throttle percentage and rpm against your AFR

Sure do, but I had a loaned LM-2, no TPS fitted and didn't have the extra harness for the RPM input.

But I wanted to see in real time what was going on.

#21 orangeLJ

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Posted 17 November 2016 - 03:08 PM

Ahhh! Fair enough haha.

If I am doing direct monitoring it find it heaps easier at night with the backlight on.

Usually wedge it up on the dash pa infront of me.

Laptop display is also useful when road tuning

#22 _Bomber Watson_

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Posted 17 November 2016 - 05:16 PM


I think John is a complete cockhead.

But thats actually pretty good, dumbed down just enough for the average consumer.

#23 N/A-PWR

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Posted 17 November 2016 - 06:43 PM

Hi Brian,

 

 great thread, and a beautiful engine bay.

 

 

 

 

 

like button for your engine bay pictures :)


#24 _ASLTO_

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Posted 17 November 2016 - 07:33 PM

Thanks Dave,

AND Thanks to you all !

I've just realised how much of a bloody novice I really am... well I am just an Air Conditioning Service Technician after all...

Hat's off to you all...

This thread took off a little i guess Dave

Thanks' again Gent's

Brian

#25 _Bomber Watson_

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Posted 17 November 2016 - 09:43 PM

Hmmm fridgey ey.....


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