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jwdmotorsports
jwdmotorsports HalfDork
2/20/10 9:06 p.m.

So, I just picked up the 84 CRX mentioned in another thread and got to thinking about adding a little more power.

I had this thought that motorcycle carbs might be a good idea.

So, my questions are:

  1. Do I stand to gain much/anything
  2. Has anyone on here done it and how hard was it.
  3. What carbs would you recommend

I'm not looking to gain a ton of power, just wake up the engine a little.

BTW, the engine in the CRX is the 1.3L

aussiesmg
aussiesmg MegaDork
2/20/10 9:32 p.m.

44mm Mikuni carbs rock on a stock or very mild 12a rotary.

End of my knowledge on this subject/

toddgreene
toddgreene New Reader
2/20/10 9:35 p.m.

Check redpepperracing.com. There swhould be lots of info there. It's a dedicated CRX site.

Todd

EvanB
EvanB GRM+ Memberand HalfDork
2/20/10 9:36 p.m.

I would imagine the carbs from a Yamaha FJ1100 or similar big bore inline 4 bike would work and give you some excitement.

93EXCivic
93EXCivic MegaDork
2/20/10 9:45 p.m.

I have six Mikuni 44mm carbs on a Datsun 240Z.

erohslc
erohslc Reader
2/20/10 10:10 p.m.

One issue with MC carbs on a car, is getting proper mixture enrichment from idle, resulting in stumble. Carbs like SU and ZS accomplish this by damping the rate at which the mixture piston rises, briefly enriching the mixture. But MC carbs are typically some variation the slide throttle theme, ie, no accel pump, and no floating mixture piston. A MC is light compared to a car, so it's not a big issue. Careful jetting in car applications can overcome some of this, the lighter the car, the less the problem.

Carter

M030
M030 Dork
2/21/10 12:05 a.m.

I have a really good bike-carbs-on-a-car-engine article from the Britsh magazine, Practical Performance Car as a pdf file. I'll email you the article if you want.

BTW they recommend Yamaha R1 carbs in the article

teamdixonracing
teamdixonracing Dork
2/21/10 6:02 a.m.
M030 wrote: I have a really good bike-carbs-on-a-car-engine article from the Britsh magazine, Practical Performance Car as a pdf file. I'll email you the article if you want. BTW they recommend Yamaha R1 carbs in the article

That would be great. Send it to clemsonjwd04@yahoo.com

M030
M030 Dork
2/21/10 7:13 a.m.

done

jwdmotorsports
jwdmotorsports HalfDork
2/21/10 7:54 a.m.
M030 wrote: done

Got it. Thanks.

wheelsmithy
wheelsmithy GRM+ Memberand Reader
2/21/10 8:02 a.m.

club4ag.com has some recommendations on putting bike carbs on a 4AGE toyota that might help(pics too). My understanding is almost anything 600cc and up will work. Do a CFM proportion in relation to red line(Ie, 600cc X 13K rpm compared to 1300cc and 7K redline). I always figured smaller (like 33mm or so) would be better, but have no data to back up my hunch.

Jensenman
Jensenman SuperDork
2/21/10 8:15 a.m.

Watch the CFM as noted earlier. Lots of late bike carbs have accelerator pump circuits to overcome the stumble issue. The Mikuni flat slide units from many late 4 stroke dirt bikes not only have accelerator pumps but linear throttle position sensors as well, meaning you can now go with 3D ignition mapping.

Rumnhammer
Rumnhammer Reader
2/21/10 8:30 a.m.

If I remember my old honda knowledge, putting Honda motorcycle pistons from a I think it was a 1100 cc honda into that engine, will bump the compression ratio nicely too.... Might want to confirm that with someone more into hondas though.

Chris Rummel

jwdmotorsports
jwdmotorsports HalfDork
2/21/10 9:01 a.m.
Rumnhammer wrote: If I remember my old honda knowledge, putting Honda motorcycle pistons from a I think it was a 1100 cc honda into that engine, will bump the compression ratio nicely too.... Might want to confirm that with someone more into hondas though. Chris Rummel

I believe you're right. However, I'm looking to pull the egine right now. Good reminder for a later mod though.

Jeff
Jeff Dork
2/21/10 9:41 a.m.
aussiesmg wrote: 44mm Mikuni carbs rock on a stock or very mild 12a rotary. End of my knowledge on this subject/

Aussie, or anyone else, any more details on MC carbs for a rotary? Links? M030, I'd love a copy of that PDF.

oldeskewltoy
oldeskewltoy New Reader
2/21/10 9:50 a.m.
96DXCivic wrote: I have six Mikuni 44mm carbs on a Datsun 240Z.

???? the Mikuni's are singles? or do you mean you have 3 - 2 throat mikuni's???

Ian_F
Ian_F New Reader
2/21/10 9:55 a.m.

Yes. Mikuni has single carbs as well. You're thinking of automotive carbs.

www.prirace.com is another guy with extensive experience putting moto carbs on car engines. The set-ups aren't cheap, but you're paying for his set-up knowledge. He used Mikunis for single-carb conversions (replacing the Zenith Stromberg on a lot of LBC's) and Keihins for mutli-carb set-ups.

M030
M030 Dork
2/21/10 11:38 a.m.

In reply to Jeff:

Send me a PM and I'll send you the article. Or, my email address is, Dimetres AT gaxcars DOT com.

Anybody else who wants the article, feel free to send me a message and I'll send it along.

Maybe it's time GRM explores the topic with an article?

teamdixonracing
teamdixonracing Dork
2/21/10 2:28 p.m.
M030 wrote: Maybe it's time GRM explores the topic with an article?

+1

shifty
shifty New Reader
2/21/10 4:26 p.m.

These look interesting:

http://www.v-performance.com/products/air_fuel.html#mikuni_carbs

oldopelguy
oldopelguy Dork
9/18/12 10:19 p.m.
erohslc wrote: One issue with MC carbs on a car, is getting proper mixture enrichment from idle, resulting in stumble.

So I'm bringing this back from the dead because I had an idea to solve both the acc pump problem and the fuel pressure problem that would be the big hold ups and I need some confirmation.

If a holley carb fuel bowl was mounted to a plate, and the plate drilled with holes for fuel lines to the carb the float should be able to stop the flow from a pump and let the fuel gravity drain to the carbs, right? And since the accelerator pumps are also on the fuel bowls, a little linkage and some tubing should allow for a squirt to each cylinder just like the carb would do, right?

petegossett
petegossett GRM+ Memberand UltraDork
9/19/12 5:59 a.m.

In reply to M030:

I'd love a copy please!

It's my username above AT yahoo.com

Thanks!

aussiesmg
aussiesmg MegaDork
9/19/12 6:43 a.m.
Jeff wrote:
aussiesmg wrote: 44mm Mikuni carbs rock on a stock or very mild 12a rotary. End of my knowledge on this subject/
Aussie, or anyone else, any more details on MC carbs for a rotary? Links? M030, I'd love a copy of that PDF.

I was seeking more performance with the original 12a in the red RX7 (now the RX5.0) a friend who has huge knowledge on rotaries bench built the carb, it ran like a dream from day 1 and he had identified and eliminated the stumble issue when he set it up.

With headers and a 2nd gen coil conversion I got 25 mpg from that combo.

GameboyRMH
GameboyRMH GRM+ Memberand PowerDork
9/19/12 9:32 a.m.

Wait do R1s use carbs? I thought they were EFI-controlled ITBs with servo-controlled variable-length trumpets?

Edit: Oh they switched from carbs to EFI in 2002 and had the setup above since 2007.

petegossett
petegossett GRM+ Memberand UltraDork
9/21/12 6:13 a.m.

I've done a bit of research since finding this thread, it seems the Mikuni HSR carbs aren't really a cost savings, even used.

So I'm wondering what would be available cheap off a wrecked/used bike - either carbs or TBI - that could be adapted to a car?

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