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Mikuni Carbs on Holden 6?

Started by _gthr_ , Apr 29 2010 01:19 PM

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34 replies to this topic

#1 _gthr_

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Posted 29 April 2010 - 01:19 PM

Hi,

I am starting into looking improving the performance on the 186 with new head, cam, manifold/carb set-up. Obviously the Weber triple carb set-up is the 'old school' popular choice.

Reading into this further I came across the site below who uses the modern day carbs from Mikuni on early 6cyl Volvo's, Triumphs, etc in the US and UK. They advertise them as technologically superior in design to the typical SU, Zenith Stromberg or Weber carbs. It's a flat slide carb designed specifically as a bolt-on SU replacement and easy to tune compared to the 'standard' carb designs. They are used predominantely in modern jet-ski and motorcycle (Harley & Yamaha) applications.

Check out http://www.v-perform...s/air_fuel.html
and
http://www.mikuni.co...carburetor.html

Has anyone heard of these locally or used them on a Australian 6? Damn cheaper than any traditional triple carb set-up I've seen advertised also.

Geoff

Edited by gthr, 29 April 2010 - 01:20 PM.

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#2 _Ben_

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Posted 29 April 2010 - 03:33 PM

I think there are a few threads on here about these carbs. I have seen a pic of a holden 6 running 6 mikuni carbs. I would love to try this setup one day.

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#3 _gthr_

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Posted 29 April 2010 - 03:49 PM

I have done a search on here however there were no discussions on recent conversions or photos. There was some information on a possible new manifold development to suit the Mikuni's.

They genuinally seem the ducks guts compared to other carbs but without any backing from people who have used them on a local 6, I'm very wary.

Geoff

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#4 Heath

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Posted 29 April 2010 - 04:59 PM

Yeah I've heard it has been done but I don't remember actually seeing it. No reason why you shouldn't try. Hate to do the linkages for six carbs hahaha

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#5 dattoman

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Posted 29 April 2010 - 09:08 PM

Careful using bike carbs
Since most are gravity fed and will grossly overfuel when you try supplying them with a fuel pump

I toyed with the idea of some flat slides on the datto engine
But webers ended up being a more sound idea till efi came along

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#6 _oldjohnno_

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Posted 29 April 2010 - 09:36 PM

Hope to have some HSR's up and running soon, got a couple of projects I'd like to try them on but unfortunately running waaaaay behind schedule and unlikely to catch up any time soon. I've got this weekend off and should try to get something done for a change but I'm tempted to go to WSID instead...
Fuel pressure isn't a problem; they'll easily take as much pressure as an SU so at worst all that will be required will be a regulator. Haven't used HSRs before but used some round slide Keihins many years ago on a Mini with very good results, and various Keihins and Mikunis on bikes. I expect the HSRs to be better than the old round-slides (and the flow figures per sq.mm of area are certainly better), and measurably better than butterfly type carbs. The HSRs flow much better than a similarly sized Weber for example, and the flow path is basically just a clean section of tube. So the carb length and any bellmouth would have to be included in the tuned length of the runner. Probably no real advantage in anything but an IR setup, but this style of carb is becoming the standard in fairly highly tuned bike and some small racecar engines producing around 200hp/litre.
The HSR is a bit unusual for a bike carb in that it was specifically designed to suit cylinder capacities of around 450 - 750cc, so it should be a very good match with the little Holden motor. I'll keep you updated, but don't hold your breath..

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#7 _glenn l_

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Posted 30 April 2010 - 09:30 AM

different car i know, but a friend of mine put yamaha r1 carbs on a mk2 escort with instant gains, had it rejetted and better again.

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#8 orangeLJ

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Posted 06 May 2010 - 01:51 PM

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#9 Heath

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Posted 06 May 2010 - 07:47 PM

K motor POWWWWEERRRRRR!!!

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#10 _triumph202_

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Posted 01 June 2012 - 12:47 PM

I don't know if anyone has seen this before? Posted Image

It's from the V Power site mentioned above, but I haven't been able to find any further info.

http://www.v-performance.com/content_files/j&s%201%20002.JPG

Edited by triumph202, 01 June 2012 - 12:52 PM.

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#11 Peter UC

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Posted 01 June 2012 - 06:05 PM

Below is a email I got from John at Vintage Performance about the installation shown.
" I have changed the throttle adjustment ( he means the idle adjust ) to the short ones and I would recomend that on any others you do for the Holden straight 6 as the long ones get to near the exhaust. I also changed the pilot to a 30 (25 originally in there= idles really well and at 600= noramlly would be 750 to 800 rpm) then took it for a run. Tis a revalation in throttle response- both quick and light. The performance is very good and that is without getting on the dyno. I have a very small flat spot around 3000rpm and a little flat in accelaration from 3500 to 4500, but will wait until I get on the dyno before I change anything else.
Needless to say I have a smile from ear to ear,,,,,
Thanks for your patience and advise. Will keep you informed. Stacey "
"Stacey who did the installation on a Holden 6 ended up his tuning efforts with -pilot:25 ; needle jet :Y8 jet needle : 96-cir-clip at bottom setting (richest) : Main jet 180. Not sure exactly how his engine compares to yours but you can email him to find out."

I am just completing my 202 with the 42 HSRs and at this stage it looks like it will be started Wednesday. I will let you know how it goes although I will have nothing to compare it to.

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#12 _triumph202_

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Posted 02 June 2012 - 11:35 AM

Thanks for posting that Peter.

I'm seriously considering buying two HSR 42's to go onto the Cain twin SU manifold I just purchased. I've already got two SU's, but one need to be rebuilt (and I don't know if I want to invest more $$$ into the SU's?)

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#13 _Bomber Watson_

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Posted 02 June 2012 - 02:16 PM

Like $30 for a rebuild kit/?

$500 or so each for mikuni's??

Unless you guys have found somewhere to get 45mm Mikuni's real cheap, then im really interested, want one for my Harley.....

Cheers.

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#14 _oldjohnno_

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Posted 02 June 2012 - 03:40 PM

I really think SUs would be a better choice for a mildish engine. Carbs like the HSRs really only come into their own with tuned runners.

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#15 _triumph202_

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Posted 02 June 2012 - 08:41 PM

Like $30 for a rebuild kit/?

$500 or so each for mikuni's??

Unless you guys have found somewhere to get 45mm Mikuni's real cheap, then im really interested, want one for my Harley.....

Cheers.

Where can you get a SU rebuild kit for $30? I'll need two spindle shafts, bushes to fit into the worn housings, butterflies, two jets (>$30 ea alone!), new needles etc. I'd be thinking more like $200 or more? And one carby has a waxstat jet and the other isn't- so I'll be up for more parts to make them match.

The HSR 42 is available for well under US$300 on Ebay. I could get two landed for around $700 - unless the AUS$ keeps diving..... They'll also be easier to mount on my particular engine- which is mounted far from level (front to rear). The rubber mount flange will allow them to be rotated level. Linkages will be a problem for both types, but not impossible.

Johnno, I do have plans for a Yella terra style head - and I'm only looking at twins, not triples.

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#16 _Bomber Watson_

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Posted 02 June 2012 - 08:52 PM

Thought you ment basic needle seat jet and gaskets, that kit was $30 from S.U. Midel last time i called up (recently).

Cheers.

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#17 _triumph202_

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Posted 02 June 2012 - 09:27 PM

Sadly, no, I need a lot more than just the basics. The float/ needle / seat in both probably could do with renewing too!

That's part of the reason I'm looking at the HSR option. At least I'll have new - and much better - carbs (and parts seem to be cheaper than SU bits.)

BTW needles alone are $12.50 each from Midel - I emailed them during the week.

Edited by triumph202, 02 June 2012 - 09:29 PM.

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#18 _Bomber Watson_

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Posted 02 June 2012 - 09:55 PM

Why is a HSR a much better carb?

There similar design needle/jet etc, but the SU is variable venturi which seems to make them far less fussy about tune/engine/shitty manifolds etc.

I would put one on my HD if i could be assed fitting a fuel pump etc.....The standard Harley carb is a CV style, with an accelerator pump,and performs well on stock engines.

Same as pretty well every jap sports bike thats ever existed before EFI came along runs variable venturi carbs with no accelerator pump, having owned quiet a few i can say they perform fine.....

Only thing the HSR really has going for it IMO is the fact that when she's open the throttle bore is really open.....

Cheers.

Edited by Bomber Watson, 02 June 2012 - 09:55 PM.

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#19 _oldjohnno_

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Posted 02 June 2012 - 10:37 PM

Same as pretty well every jap sports bike thats ever existed before EFI came along runs variable venturi carbs with no accelerator pump, having owned quiet a few i can say they perform fine.....

Only thing the HSR really has going for it IMO is the fact that when she's open the throttle bore is really open.....

Cheers.

You hit the nail on the head, but for possibly different reasons than you'd think. When she's open the throttle bore really is open as you say, and a 42mm HSR does indeed flow as much or more than say a Weber of a significantly bigger throat size. But it's not just raw flow that make them work.
In another thread here on intakes I said something along the lines of "It's the manifold, stupid". What I meant was that it's the pressure wave activity in a well designed manifold that makes horsepower, not the carburetor. This is where carbs like the Mikunis and Keihins shine; at WOT they appear to the engine to be nothing more than the first couple of inches of runner. As far as the engine is concerned there is no carb. There's nothing there to dampen the pressure waves - no butterfly, no venturi, no booster. Just a thin needle and a bellmouth. Even the Jap CV carbs have a very "clean" bore. Of course this doesn't count for anything without a tuned manifold.
The Jap bike makers had this down to a fine art before they went mainly FI. Remember the original old Honda Fours etc? We'd hack the airboxes up or put pod filters on to make them breathe better. But later the Jap manufacturers got more sophisticated and if you modified the airbox they'd usually go slower. What happened was that at WOT the carbs and airbox were all part of the manifold (which was now basically a plenum ram), all carefully tuned to work together. If you can replicate all this on a 202 you'll certainly end up with a worthwhile boost...

To answer your question of why is the hsr a much better carb, well, it's not. It's only better if you have a manifold that works. And if you aren't prepared to build a suitable tuned manifold you'd be better off with SU's.

Edited by oldjohnno, 02 June 2012 - 10:45 PM.

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#20 warrenm

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Posted 03 June 2012 - 07:51 AM

What "oldjohnno" said. :spoton:

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#21 _Bomber Watson_

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Posted 03 June 2012 - 09:33 AM

http://www.pitstop.n.../query/plu/4029

Read that a while ago.

Bit over my head for a fair bit of it, but i got the gyst of what old mate was on about.

Also very old tech, first written in the late 50's, still cool though, so yeah i get what your on about.

I honestly think for the OP's situation, twin carbs on a 9 port head with im guessing a shitty manifold and from memory a stock engine, unless he's changed it, SU's would perform a million times better.

Cheers.

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#22 _oldjohnno_

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Posted 03 June 2012 - 10:12 AM

I honestly think for the OP's situation, twin carbs on a 9 port head with im guessing a shitty manifold and from memory a stock engine, unless he's changed it, SU's would perform a million times better.

Cheers.

Agreed. With such a low power-to-weight I suspect it'd be grossly overcarbed with 42s.
For more up-to-date info try Blair. And in recent years instrumentation has advanced to the point where it's possible to see exactly what's happening anywhere in the engine at any speed or load. Some old beliefs have have been shown to be myths.

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#23 _hutch_

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Posted 03 June 2012 - 10:36 AM

Seen 2 sets of quad carbies on a v8 in a rodded ute once,looked really schmick,couldn't tell ya what was only that it was small and alloy.
Could you imagine trying to balance 8 of the bloody things

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#24 _triumph202_

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Posted 04 June 2012 - 10:48 AM

I appreciate the responses (no matter how negative / discouraging)

, however I'm loathe to invest any further funds into SU's. I've spent a fair bit of time playing around with the single SU and am finding some of the design features lacking eg. even running thick "dashpot" oil there is a significant lean spike when accelerating. (I've got a digital AFR meter so am able to monitor the mixtures while driving.) As already discussed, SU parts are far from cheap and rebuilt SU's are very costly.

Yes, the engine is largely "stockish" at the moment. However, that will change in the future and I'm not into investing money into cheaper parts that won't satisfy long term. I'm also stuck with side draught manifolds due to under bonnet clearance issues, which doesn't leave me too many options. I'm not interested in a triple set up because maximum power is not my goal.

From the research I've done the HSR option has many advantages with regards to tuning. I've found the SU to be a fiddly thing and after a couple of weeks I'm back to playing around trying to get it running smoothly again. :(

If funds and "vehicle off road time" were unlimited I'd go EFI (forget mentioning VK components- refer back to the previously mentioned bonnet clearance issues).