Quad 38mm Motorbike carb's on an Astron

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Superscan811
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Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Finally finished installing the carbies on the old wagon and all I can say is :D :thumpsup: ....

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Sorry for the phone pics' but it was all I had at the time.

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Took it for a quick test flog on the M4 and while it's running a bit rich, the amount of get up and go it has compared to the 280 Holley is VERY NOTICEABLE.

It's also very quiet when you lightly use the throttle but when you plant it, there is a nice deep throaty note from under the bonnet.

Because they are CV's, they don't tend bog down, and I didn't feel any flat spots on my 20-min run along the M4.

The other advantage of these carbies is the idle. Happy and Smooth at 450rpm.

I'm getting the carbies properly tuned on the weekend so it should go even better.

If anyone is thinking of doing this, I would definitely say DO IT..

BTW, the engine in the wagon has minimal work done to it.
Standard M7 head but with adjustable rockers.
Extractors
Mild cam . Camtech Stage 2 CT107-712B
Balance Shafts removed.


Cheers.
shuggy
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Re: Quad 38mm Motorbike carb's on an Astron

Post by shuggy »

LOVE IT :thumpsup:

thats what i really wanted to do but seemed like such a head f***..

interesting (strokes imaginary beard)
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rob020
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Re: Quad 38mm Motorbike carb's on an Astron

Post by rob020 »

:thumpsup: :thumpsup: :thumpsup: +1

ive always wanted to do that... now you just need to get it to rev to 12 grand and she'll sound insane...

what bike are the carbies off??

cheers,
rob
"launching missiles? who do they think i am? iraq? where would i get a missile from?" "that means rocks too dumbaass" "oh"
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Cottees
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Cottees »

Are you able to post a vid of what it sounds like?
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

shuggy wrote:LOVE IT :thumpsup:

thats what i really wanted to do but seemed like such a head f***..
In all honesty, it wasn't that difficult. The hardest part (excluding the manifold) was the plumbing for the vacuum and breathers.

Luckily I had several other carbies to pinch the tubing and joiners from, but a quick trip to a wreckers and you could "acquire" enough for several projects.

The only other thing I had to do was modify a Holley low pressure fuel regulator so there was adjustment down to 1/2-psi instead of the standard 4-psi.

All that was needed was to flatten the spring a little so there was almost no tension on the spring when the adjustment screw was fully out.

While I haven't properly sorted out the throttle cable yet, I have it working good enough to be able to drive it.
rob020 wrote: :thumpsup: :thumpsup: :thumpsup: +1

ive always wanted to do that... now you just need to get it to rev to 12 grand and she'll sound insane...
Thanks, but I think 6k will be enough for me.
The engine is a bit tired and I would like it to see another year. Spinning it to 12K may shorten the expected life of the engine, just a little.
rob020 wrote:what bike are the carbies off??
I have no idea, I bought them off EBay several years ago and they have been lying around gathering dust.
I know the 2 sets of 41mm carbies (the ones that have to be mounted on the 30-deg angle) are off a Kawasaki 1100 of some sort but that is all.

I may even sell this setup if I can get some 41mm ID, thin wall (1.6 to 2mm) aluminum tubing, so I can then use the other 41mm motorbike carbies.
Cottees wrote:Are you able to post a vid of what it sounds like?
I'll try over the next couple of days but I would say it sounds very similar to the twin Dellorto/Weber setups.
NICE....


Cheers.
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rob020
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Re: Quad 38mm Motorbike carb's on an Astron

Post by rob020 »

have you drilled out the main jets yet?? what to? i read 1.8mm for a 2l and 1.65mm for a 1.6l and 1.3mm stock for an r1 (1L)... so how much for a 2.6?? ive lost my scientific calculator otherwise id plot a line...

total vauxhaul have a bikecarb.pdf i found ages ago, which you may or may not have stumbled across, which i stole those numbers from

+1 on the vid too!!
"launching missiles? who do they think i am? iraq? where would i get a missile from?" "that means rocks too dumbaass" "oh"
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rob020
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Re: Quad 38mm Motorbike carb's on an Astron

Post by rob020 »

well... ive re-taught myself everything i barely knew about correlation... and those points gave me a formula... o.55(x)+0.75... x being the displacement...

so 0.55(2.6)+0.75 says you need to drill your main jets to 2.18... dont know if what im trying to do is valid though...

ive also read bike carbs are great for turbos.. all you have to do is boost reference the float bowls and shes all apples

cheers,
rob
"launching missiles? who do they think i am? iraq? where would i get a missile from?" "that means rocks too dumbaass" "oh"
conversation recently overheard at police station after big night out
Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

rob020 wrote:have you drilled out the main jets yet??
Yes, I was advised to go to 1.40 - 1.45mm on the mains by the person who is going to be tuning it. The main jets are now 1.45mm from 1.20mm standard.
rob020 wrote:total vauxhaul have a bikecarb.pdf i found ages ago, which you may or may not have stumbled across, which i stole those numbers from

+1 on the vid too!!
I hadn't come across that site yet but that will change shortly, Thankyou.
rob020 wrote:well... ive re-taught myself everything i barely knew about correlation... and those points gave me a formula... o.55(x)+0.75... x being the displacement...

so 0.55(2.6)+0.75 says you need to drill your main jets to 2.18... dont know if what im trying to do is valid though...
With the 1.45mm mains it still runs a bit rich all through the rev range.
At 5k and WOT it's 10.2:1,
cruising at 1/2 throttle it's around 12.5:1
and light acceleration at 1/2 throttle it's 14.3:1

The problem with the motorbike carbies is that they have 3 main metering circuits that can all overlap each other, depending on the air flow AND throttle position.

* pilot circuit
* needle jet and jet needle
* main jet

I wouldn't have a hope in hell of tuning them properly so that is why I am taking it to a pro.
He builds/races/tunes side cars so I think I should be safe.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by EVL076 »

very nice work there :thumpsup:

always good to see someone thinking outside the square
i know early model GSXR 750's ran 38's.... but then again, my guess would be so did a heap of bikes
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Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

EVL076 wrote:very nice work there :thumpsup:

always good to see someone thinking outside the square
Thanks. This wasn't the first time I have done this. The first time was on a 2.0L GE sigma back in '89 with a set of 36mm carby's off a GSX 1100. It worked exceptionally, well so I decided to try my luck again.
EVL076 wrote:i know early model GSXR 750's ran 38's.... but then again, my guess would be so did a heap of bikes
I have found out these are off a '93 GSXR 750.

The issues I am having at the moment are:
1. Because the fuel atomizes a lot better than a standard carby, the re-curved dizzy is making the engine detonate even when it is running a bit rich. The finer the atomization, the less advance you need because the air/fuel mix will burn faster (ie: the difference between lighting a cup of petrol, and throwing a cup of petrol in the air, then lighting it). I've backed the timing off to 0-deg (from 10-deg using the 280 Holley and 12-deg using the standard solex) and I am still getting more power (seat of the pants dyno) but it is still pinging.

2. The other problem is on cruising, it is running a bit rich, around 13:1 and when I back off, the the exhaust is popping a bit too much for my liking.

Idle is perfect, between 14.5 - 14.8
light throttle is 15 - 14.5
1/2 throttle is 14 - 13
WOT is 12.5
Backing off fluctuates between 13 - 16 depending on the RPM
Cruising is 13

The power increase is very dramatic and this is on a tired engine that has been cooked AT LEAST 3 times that I know of (the first destroyed the head, putting 2mm cracks between the valve seats on Cyl 2 and 3, I bought the car like this, but the other times were a lot milder due to heater hose pipes bursting) and when I changed the cam, the old cam and journals were badly scored.

The engine isn't in the best of conditions but it is making a lot more power than it was.
If I can find a cheap dyno in Sydney, I'll post the results as I also want to try a bit of water injection.

Cheers.
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stealth
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Re: Quad 38mm Motorbike carb's on an Astron

Post by stealth »

if your trying to make good power run your mix at 11.8 wide open
cheers stealth (H)
Engineering the unfair advantage !
Red bull , fuelling the fastest race cars on earth !
Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

stealth wrote:if your trying to make good power run your mix at 11.8 wide open
cheers stealth (H)
Thanks for that. I assumed it was on the lean side of max power because the needle has been dropped a fair way to lean out the cruising Air/Fuel mix.

I have a TE wide band O2 device (some where in a box) which is also able to log throttle position, RPM, Water temp, Manifold air pressure and a few other things.

I am trying to make an adapter so I can run a throttle position sensor, to be able to accurately log the info, rather than just remembering what the AEM O2 sensor
was reading and roughly where my foot was at the time.

It will also make it easier to diagnose exactly what changes need to be made.

Cheers.
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GC75
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Re: Quad 38mm Motorbike carb's on an Astron

Post by GC75 »

*waits for vid*
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webby
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Re: Quad 38mm Motorbike carb's on an Astron

Post by webby »

I likey, like ITB's just more old school :thumpsup:
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stealth
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Re: Quad 38mm Motorbike carb's on an Astron

Post by stealth »

no worries scott ,we go down to 10.8 but thats really pushing fuel through but give it a run
with the 11.8 with your wide band
and also whats your all out timing ? shouldnt really need more than 24d ?
btw now all you need is the long engine to be built and you got a speedway engine
cheers stealth (H)
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Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Found the Tech Edge WB O2 Logger and have installed it. I now can log RPM, Throttle Position, Manifold Vacuum and Air-Fuel Ratio.
I'll need to calibrate the MAP sensor before I start logging data.
I also have some accelerometers which I will try and install so I can get a bit better idea on actual power gain/loss on the changes that are made.
stealth wrote:and also whats your all out timing ? shouldnt really need more than 24d ?
What ever is standard. Even the re-curved dizzy only has the standard max advance, it just gets there quicker.

The detonation is mainly happening around 2 - 3k on 3/4 to WOT, but I can still hear a little around 3.5 -4k on a standard dizzy, set at 0-deg advance at idle.

It still pulls hard but always back off to avoid an engine rebuild.

This is what confuses me at the moment:

1). 5-deg less advance than a standard dizzy,
2). Bucket load more power.
3). Running rich.
4). Still pinging.

The only other thing I can think of is maybe the Vacuum advance is doing something strange to cause this.

It will be good to do some logging.


Cheers.
Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Decided that I have had enough with the clutch slipping for over 18 months, and now, not being able to put it into gear when changing up, unless the RPM matched the gear I was selecting, I decided to remove the gearbox and have a look at what would be needed.

I knew the engine had been leaking a fair bit of oil, from the rear cam seal, when I first got her and figured it must have worked its way down into the bell-housing.

I was WRONG, while there was a bit of oil and crap in there, the problem was 4 of the 6 bolts holding on the pressure-plate were undone. 2 weren't even finger tight the other 2 were more than 2 turns out.

There was literally only 2 bolts, side by side, that were holding the pressure-plate onto the flywheel.

Lucky I'm easy on the clutch, otherwise I would hate to see what could have happened.

De-greased everything and off to SupaCheap tomorrow morning to buy some BrakeKleen to finish the job.

I wonder how long this engine/gearbox would have lasted with 13bsigma behind the wheel :lol: . It would have been a nice EPIC FAIL.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Took it for a dyno run today (because my Wideband O2 sensor died) and I'm not disappointed with the result.
This was on 91 E10 fuel BTW.

The red is at Full Throttle.
The green is at 90% Throttle.
The blue is 1/2 throttle.
Just wish I had RPM on there but I will caculate it a bit later from the speed.

Not fantastic but a bit better than normal.
Image

The Air/Fuel still needs a bit of work though.
Image

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by stealth »

mate have you played with the spring tensions in the carbs
looks a little soft ,with all that flutter
cheers stealth (H)
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

stealth wrote:mate have you played with the spring tensions in the carbs looks a little soft ,with all that fluttercheers stealth
I haven't played with the springs but the needle jets/emulsion tubes have a bit of wear in them so I have contacted a company in the US that do performance kits for these carbies and for about US$300- they will "customize" a performance kit.
They say I can expect at least 95KW at the rear wheels, with my current setup running E10.

Not bad for a near stocker, but time (and money) will tell.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

BTW: Just did the calcs and at 83.1KW, at the rear wheels using E10 91-petrol, it's more power than the standard EFI setup running 95 premium (by 1kw :lol: ).

If this all works out, and I get 95KW at the rear wheels, that's a whopping 17kw gain, on a standard magna EFI setup using 95-premium AND a 20kw gain on using 91.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Updated Dyno sheets with estimated RPM values.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Sigmaproject »

Mate, I have a bit of a PCV valve fetish :wut: and I am very interested in your setup.

I can see where it goes to a "t" piece near the carbs, but where does it go from there :\ :\
Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Sigmaproject wrote:Mate, I have a bit of a PCV valve fetish :wut: and I am very interested in your setup.

I can see where it goes to a "t" piece near the carbs, but where does it go from there :\ :\
The "T" piece goes into the manifold vacuum port of the carbies (used to check their balance) which I joined all together.
They are usually blocked off but I joined them so there wouldn't any imbalance caused by just using 1.
It works so well that even if the cap is un-done, just sitting on there, and I give the engine a rev, the cap is still stuck down by the vacuum.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by 81GH »

Fuk Yeah i bet this thing sounds
rad :P
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Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

81GH wrote:i bet this thing sounds rad
I reckon it sounds very nice, especially at round 2500.
It changes note around 3000. Next time it's on the dyno, I'll see if I can record it.

Can't wait for the carby kit to arrive from the US.

The new Wideband O2 sensor arrived on Wednesday afternoon so that is in and I put new emulsion tubes (which are also the needle jets) in it on Thursday.

The cruising AFR's are now quite good around 15.5 - 16.5 and light throttle around 14.2 - 15.5.

All I need is to up the WOT AFR, which has stabilized around 13, even when I increased the main jet size from 145 to 155.

More torque down low (seat of the pants dyno) but I am hoping to come close to 100kw at the rear wheels (with the Carby kit) using 91 E10 fuel.

I may even give it a run on 98 if I make my little surge tank, just to see the difference.

Cheers.
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rob020
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Re: Quad 38mm Motorbike carb's on an Astron

Post by rob020 »

now you gotta go quad carb blow through turbo :) do it!
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Superscan811
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

rob020 wrote:now you gotta go quad carb blow through turbo :) do it!
I'd only do that on a fresh build, not a daily hack with the internal condition unknown.

100kw ATW would be about a 50% gain on standard, and I wouldn't want to push the boundary more than that on an unknown build.

It'd be fun and not that difficult to do with these carbies, BUT a recipe for disaster, unless the engine was pulled down and checked.

I'd also lose the nice Quad carby sound because they would need to be attached to a plenum.

The other thing I would need is a special low pressure, rising rate fuel pressure regulator because the carbs are VERY sensitive on float height. They are used to less than 1/2lb on the seat, so a wildly fluctuating boost pressure won't allow them to work well on a blow through setup.

Cheers.
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Re: Quad 38mm Motorbike carb's on an Astron

Post by Superscan811 »

Well I've just bought 4 sets of 2 (total of 8) 48mm CV carbies for the 2002 Honda VTR1000 V twin's.

Image


Image

These are designed to work with 500CC's per cylinder redlining at 10,000 (I think) so these should work well on a stock engine but would really get up an boogy on a heavily modified engine.

They need to be mounted at roughly 45-deg but as a bonus, there is plenty of pipe and bends for these (2"OD, 1.6mm wall).

I was thinking of making a manifold like this, (Not to scale of course)

Image

and having a large plenum and cold air intake.

Cheers.
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rob020
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Re: Quad 38mm Motorbike carb's on an Astron

Post by rob020 »

hey,

stumbled across some interesting reaqding: http://www.iwt.com.au/mikunicarb.htm explains mikuni (typical bike) carbs and their fuel circuits...

i was actually lookin up info on a tillotson chainsaw carby i wanted to use on a small bicycle engine and i thought of you... isnt that sweet.... if you go to the index (link at bottom of page) theres heaps on there to read... lol

cheers,
rob
"launching missiles? who do they think i am? iraq? where would i get a missile from?" "that means rocks too dumbaass" "oh"
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