Quad 38mm Motorbike carb's on an Astron

[Superscan811]

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

It's good reading and I had found it a while ago but it's not for the CV style carbies. Very close but there are some differences between the CV carbies and these.

Cheers.

[caboonatlarge]

very nice build and great the see the HP increase!!!

Im doing somthing very similar in my LA lancer. using the 48mm R1 carbs on a AMG DOHC 4g63.Redline around 9000rpm (maybe higher)

I noticed your manifold idea.Im in the middle of thinking about how to do my manifold, what sorta difference do you guys think there would be between superscans "downdraft style" mani as apposed to a "sidedraft" style with the correct 45 degree angle flow wise?superscans would allow much more room and be alot easier to make up and airbox etc for.

nice

[Benharjon]

Hey mate sweet lookin setup i bet it sounds awsome! i am thinking about doin something similar on my datsun a12... i was wondering how is the economny? cheers and keep up the good work!

[Superscan811]

Bought a K&N DYNOJET kit for the 38mm carb's, only to find these are for the carbs with the "Power Jets".
Not too big a problem, just need my lathe back to re-shape the needles a bit.
Need to richen up the main jet a bit but surprisingly, it still ran fine, even if it was quite lean.



EDIT: this was a 40kph start in 2nd gear up to 110kph in 3rd. The entire graph was 16.5 seconds, 40kph to 110kph in 10 seconds, starting at 2600rpm

Cheers.

[SharmCos]

Oohh I love these carbies, easier to tune than 'traditional' sidedraughts..
I will seriously consider installing a set to my next olskool ride as I have two pairs of them under my bed

Here's a video of my brother's Proton Tiara (Citroen AX) with 16v Saxo VTS engine and a set of 40.8mm ZZR1100 carbies.. Sounds real nice, better acceleration than a pair of DCOE IMOs.. and you don't need to tune them every 1000km! Engine revs to over 9500rpm.. unfortunately being completely standard, the flywheel's centre went loose, two pistons melted, 8 valves gone etc.. lol

Lesson 1: Balance the bottom end before fitting these carbs!

Here's a test video of it:

http://www.youtube.com/watch?v=dxJuPSKs6vY

The busted flywheel:

[Superscan811]

The busted flywheel:

OUCH.


I'm impressed with the 38mm carbies on the 2.6L Astron but the 48mm VTR-1000 carbies,
while they will require a bit of fabrication to fit them, I believe, will work even better.

This is the 30 second graph going up a slight incline then back down at 100k's in 5th gear.

I know I'm running very lean but there is no knock and only an occasional hesitation.





This 15 second graph is 3rd gear at 100K's
There was a little bit of backfiring.


In both of these graphs the car was just cruising

Cheers.

[Superscan811]

Changed the main jets, needle height and the float height.
Getting closer, but I still need to modify these needles so they can run on a non-powerjet carby.
Wide Open Throttle is still around 14:1AFR

The following graphs are all just cruising along.

5th gear at 100kph




4th gear at 100kph





3rd gear at 100kph





Another nice thing about the motorbike carb's is the idle speed.
Cold engine, started with the manual choke, but then closed the choke after 30seconds.

It idles nicely at around 400rpm cold, and 550rpm hot.




Cheers.

[Superscan811]

Had a bit more of a play with the idle.
It now idles nicely, cold, at 350rpm.


The 40-110kph is now 1/2 second faster than before (about 9.4 seconds).

The AFR and throttle response is better now.

I love the TE widwband logger.

Cheers.

[BAD-SIG]

You mentioned you used to have a 2 litre GE Sigma with quad motorbike carbies. What carbies were they and what other engine mods did the car have? I have a bog stock GE Sigma 2 litre with 2 1/4" sports exhaust. Would it be possible to fit similar motorbike carbies to it? What motorbike carbie do you recomment for my application? Any help is greatly appreciated

[Superscan811]

You mentioned you used to have a 2 litre GE Sigma with quad motorbike carbies. What carbies were they and what other engine mods did the car have?

The carbs I used were quad 34mm Mikuni's off a GSX 1100 (from memory). The engine had a little bit of work done to it and also had a 35-75 long duration Waggot cam.

I have a bog stock GE Sigma 2 litre with 2 1/4" sports exhaust. Would it be possible to fit similar motorbike carbies to it?

Yes.

What motorbike carbie do you recomment for my application? Any help is greatly appreciated

Any of the carbies from 34mm to 40mm would be fine.

Here's the
A "HOW TO QUAD CARBY" THREAD PLEASE!
thread I was asked to do, to explain the steps.

Cheers.

[BAD-SIG]

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 . It would have been a nice EPIC FAIL.

Cheers.

How did you fix the leaky rear cam seal? Mine is leaking too...

[Superscan811]

How did you fix the leaky rear cam seal? Mine is leaking too...

I used silicon on both the cam seal AND on the rocker gasket, in the corners on either side of the semicircle at the back of the head.

The rubber gasket doesn't seem to seal right in those sharp corners and it tends to leak.



Cheers.