Bike Carbs on a SR20DE; how (notice I did not ask why?)?

Reference: Bike Carbs

Why: The E36 M3 pile of hoses, the giant manifold, the computer mumbo jumbo (I deal with that at work, I don't want to on my car), the ugliness. Carbs are sexy, carbs are cool.

Car: 1995 200sx R race car, may (big may) get the rally car treatment as well.

How to do this: The article is pretty good, has anyone tried it? How do I handle timing and spark? What other things to worry about?

Yes, this could well turn out to be a winter time waster of time thread (see my build Lola and 935 replica threads ). But maybe not. Every time I go to the garage and pop the hood on the race car I cringe. Selling would be an option,though race cars are a pain to sell. And it's a pretty sweet little car as is. I just want to make it sweeter.

As always, I appreciate your cheers, jeers, and leers.

Jeff

I would think a problem might be big bike carbs are sized for 1-1.2 litres. They might be undersized for what you want to do.

But they're sized for 1-1.2 litres at twice the RPM. So they should roughly be able to feed the flow rate required for a 2.0 car engine.

I've thought about doing this myself. I can't think of any particular hang ups.

I recommend taking a look at the linked PDF as they talk about engine size and flow. According to the folks quoted, bike carbs are constant velocity and flow much better. Yes, you could run into an upper limit in a crazy build, but my motor's got a bit of cam and a header; I don't think the carbs are the limiting factor.

Anyone here use something called 'mega jolt' or 'weber alpha' (cited in the article)?

If you want no more computers to worry about, does you engine have a distributor with mechanical or vacuum advance? If not you're on to a MegaJolt setup at a minimum I'd imagine.

Not sure I would want to go away from fuel injection but why not individual bike throttle bodies and standalone? The ~2ltr motor size fits right into what a lot of folks do in FSP class with the VW's on the 1.8 16v. They sound amazing and keep the best of both worlds as soon as you get them sorted.

I desire the hp and sounds but I have not been brave enough. Taking on another motor swap and fuel injection setup gives me nightmares as I just recently have mine 90% of the way sorted.

84FSP wrote: Not sure I would want to go away from fuel injection but why not individual bike throttle bodies and standalone? The ~2ltr motor size fits right into what a lot of folks do in FSP class with the VW's on the 1.8 16v. They sound amazing and keep the best of both worlds as soon as you get them sorted.

+1. ITBs are tidier and sexier than carbs. IMO the only advantages of carbs are relatively graceful failure modes and roadside repairability.

ITB's and Megasquirt. Handles all the issues. Or, if you want the carbs, some way to mount them to the manifold, fuel lines, regulator to drop the pressure to 3 PSI and/or different fuel pump, something to control the spark like megasquirt or megajolt, throttle cables off a splitter thingie or some kind of linkage. May lean out on left or right sweepers.

In reply to 84FSP:

This is what Im doing on my miata. Bike itbs are pretty cheap and should clean things up nicely.

do it! then rally it!

Although I haven't done a bike carb conversion (though I'd like to someday), if I were using the typical CV carbs I would also try to build an airbox/plenum as large as you practically can. CV carbs tend to like big airboxes with nice smooth flow. A lot of motorcyclists will remove or modify the factory airbox and usually make their engines run worse.

Dr. Hess wrote: May lean out on left or right sweepers.

This. Bike carbs do not see side loads, cars do. To avoid problems, look into sled carbs (RX1 carbs should work)

BA5 wrote: But they're sized for 1-1.2 litres at twice the RPM. So they should roughly be able to feed the flow rate required for a 2.0 car engine.

You can take the carbs from a 1,000CC twin.

An upgrade for a 900CC air cooled monster or supersport was the 41mm Keihin FCR. I imagine that 4 of those would flow well enough, not sure how a flatside would effect drivability in a car.

The guys that ran the Tercel at the Challenge had it running on bike throttle bodies and MegaSquirt, I think.

I have a set of CBR900 carbs hanging off the side of a Zetec, but I've yet to run it. I built a simple manifold but I spaced the carbs (the write up says not to, but I did). I kept the pairs together and added a spacer in the middle. I preferred having the intake runners the same lengths, rather than having the outer runners different than the inner runners. The plan is to use a Megajolt ignition system, as I have used one in the past. I'd like to find a good used one, but I've had no luck so far.

I have, however, had a set of the same carbs running on a 4AG, but only very briefly. I didn't adjust them, and when the throttle was blipped, they came off the manifold. I could have sorted them, and made them work, but I already had a set of DCOE's on the motor. The bike carbs were more of an experiment (I paid $10 for the set a number of years ago).

Now, as for why I'm using them, mainly cost. I priced out a Megasquirt set up, and by the time the dust settles you're getting close to $1k (MS unit, throttle bodies, fuel pump etc). For the bike carb set up I'll be into it for about $275 (MJ unit, carbs, fuel pump and bananafold). I'm sure tuning the carbs will take a fair amount of trial an error, but my time is cheap.

Rod

I like that access panel so you can check on the front of the motor while you're driving, Rod. That could be handy.

Looking at ITBs now as well. Not much more money for the hardware (less the mega squirt).

Forget it.

Buy a SR20VE. They are $800 on ebay. They easily bolt in and you will see 170 to 190 whp all day long.

I've always wanted to play with bike CV carbs on a car engine, but to be honest, now that used bike ITBs are readily available, I'd go that route on a car that was already set up for EFI.

Killing me with the motivating thoughts. I pressed El Rabbito into service this week as the V is waiting on new brake lines to show up.

Searched itbs online and found a bunch of stuff about a specific cycling injury and this.

https://grassrootsmotorsports.com/forum/grm/bike-carbs-vs-bike-itbs/119937/page1/

Kit

fanfoy wrote:

Dr. Hess wrote: May lean out on left or right sweepers.

This. Bike carbs do not see side loads, cars do. To avoid problems, look into sled carbs (RX1 carbs should work)

Ding ding ding,we have a winner.

Rx1 carbs are the ones to go to if you want an affordable set of let model CV carbs and don't want them sticking out of the hood as pretty much any late model carbed sport bike set will require.

I did them on a 4ag with boost,worked just fine without all the headaches of trying to make a standalone actually work when your a tool like me with computors.

The easy button is dropping itb's,standalone,your car and visa card to a proper shop and picking up and enjoying it.When I did that I picked up my 20v AE86 non running after 5 months and threw it all in the trash and went with free Rx1 carbs and had it up and running well without any drama.

On a related not I ran a carbed R1 in the geo,not loads of grip on ice but never a hiccup.

Not sure I have much useful to add, but I like the idea!

Actually, I may have some perspective. I modified the intake manifold, installed and balanced ITBs, built a harness for my Megasquirted car, assembled an ignition system, finished all the setup and have it running and driving. In the same rough timeframe, I bought a non-running motorcycle with four CV carbs. Unlike the car, everything else was there. I've rebuilt the carbs three times and it still doesn't run right!

Carbs might seem simpler, but my experience seems to indicate otherwise.

Anyone have a good idiot's guide to installing ITB they like? Share link if you do. Still leaning to snowmobile carbs though; so Canadian