So I have the FCR Flat Slide carbs installed and the car running. So here's what I've learned so far (some of this is fairly obvious).

First I would not use FCR carbs for a street car, there is no provision on my manifolds for vacuum advance or a pcv valve. Also unlike CV type carbs you cannot simply slap the pedal to the floor........you wouldn't do this on a road race car so it's not an issue.

Like any other carb the FCR's need tuning, I would recommend A/F ratio gauge on the car. I've gone in the wrong direction twice, not a big deal as I've been tuning 1 hour at a time and one of those was intentional.

The carbs were off a D-Sports Racer that probably belted out 50-60 more horsepower than my car. Carbs came set up 170 main, 185 main air, needle clip in center position, 45 slow jet, 90 slow air jet, pilot screws 2 1/2 turns out.

The motor fired right up idled but little else, opening up the throttle would stall the motor, dropped to 155 mains. The throttle could be opened to half above 4K but not full till 5K. Went to 145 mains improved, then dropped to 130 mains seemed better but still just OK. At that point I had to order smaller jets. So while waiting for the parts to arrive I played with settings..........kept turning the pilot screws in until the motor cleared up, 1/4 turn from bottomed made the engine work. I needed smaller slow jets but had none soooooo. I put in a 100 slow air jet, this allowed the pilot screw to be turned 2 turns out. This resulted in idle to 1/4 throttle working very well. Next I played with the lowering the needle, after a couple of one notch at a time changes I went full lean..........this made things worse so I went back the other way and 1/4 to 1/2 was working well. Next while still waiting for parts I tried a bigger main air jet. The car now worked through the whole rev range but still didn't feel right...............parts arrived and I put some 120 mains in (what little I could drive the car on the Cul De Sac in 1st gear) the car seemed to flatten out. Well with the 120 mains the car now stuttered at around 5K................now I at least know I need to go back the other way (richen). Tomorrow I'm headed out to an abandoned stretch of highway. Will be doing the old fashioned plug chop method but I expect one of two things: With the 200 main air jet I'll likely be back up to 145 mains and will have to adjust the needle or I will be putting the smaller main air jet back in along with the 130 main and then making subtle adjustments from there.

I'm not put off by the trail and error method as this is how I've always had to do my MX bikes but frankly for most folks I would recommend the aforementioned A/F ratio gauge and plan on some dyno time to fine tune the motor. (I will likely put the car on a dyno to get the last bit fine tuned).

The plus side for me has been with a left hand drive car I don't need to move the brake master cylinder and I got the carbs cheap.Also with years of bike experiance, despite my NOT being a tuner I at least have a clue of what to try. The one nice thing is the motor picks up revs much faster than with the SU's. So moral of the story, whether it's Webers or FCR's get a tuner and plan on some dyno time....................what I goofed around with for 3-4 hours could have been figured out in about an hour with a dyno.

Tom

but some times better to play round trial and error, at least you get to learn stuff and know exactly what set up you have put in.

Well after a couple of runs I've gone back to the original main air jet and of course I need to order some more jets...........car is very close, maybe two steps off on the main jet.

On the drivability front actually disconnecting the accelerator pump made a huge difference. From 1/2 to 3/4 throttle still needs work, it's just OK at this point.


Tom

So the orginal motorcycle main jet are OK with an A12? I'm guessing you changed the air jet?

Why is it that they don't like flooring the throttle? On a bike maybe you wouldn't do it, but with a good accelerator pump seems like it should work.

The dyno is a tool, just like an exhaust gas analyser & a vacuum gauge are tools.

Just dickin' about with trial & error is doing it the hard way if a dyno is available as you can get readouts in real time & you can see what's happening with mixtures under repeatable test conditions.

If you have a dyno available to you, then I suggest that you should use it, otherwise, be prepared for a lot of time fiddling about.

Dodgeman , dickin around, fiddling around???? It's more like pissing up a rope, messy and it doesn't accomplish much!!! Part of why I posted this is because we often discuss this set up or that set up and folks are looking for the easy way............which basically there isn't

Part of why I was playing around was two fold; I have various possible combo's of jets and wanted to see what each combo did in some actual driving, the whole air correction/air jets part of FCR are new to me. I understand emulsion tubes, needles and slide cutaways etc. I had a couple of Sunday afternoons open as was reeeeeeeealy bored. Truth be told our favorite riding spots are now mud holes and rivers plus the local MX track practice has been cancelled two weeks running.......imagine that in one of the driest deserts in the world.

I hadn't really intended to start on this until after our April 10th event but well with all that pent up energy from not riding I figured what the heck. On the plus side I got to hear the motor pick up revs like never before................with it raining again all this week I'll have lots of pent up energy to see me through putting the old carbs back on for our next two events.

Tom

Quote:I hear ya mate, I hear ya.

Trial & error will get the job done, ........ eventually, but as I said, if a dyno is available then things just work out better.
When it comes to pioneering a new install like this then like you said, there's no easy way.

Young Aiden started out with four m/cycle carbs that would always run lean at full noise.

It was set up on the Boss' dyno & the problem was traced to falling fuel pressure as the rvs went up.
An electric pump was installed in concert with the mechanical pump [separate feed] & this became another problem solved. The mixture became much more stable & further tuning got it reving like a Ferrari.

Without the dyno this problem may well have not been found for a long time, if at all.

Looking forward to seeing how this one turns out.