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FCR41 Nightmare!

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I started this post in the Honda section a few days ago and got a few replies but I'm new to posting on TT so I'm not sure how far the exposure goes in that section. The original post is as follows:

I have an 89 dominator 650 motor (in a chopper/bobber frame). I just rebuilt it boring it to a 675cc, hot cam stage 1, performance rod and a kicker setup off of an old xr600. At the same time I installed an FCR41 and can not get this thing to run. It does have an airfilter simler to a pod filter and some pretty open pipes so I anticipated having to richen it up some but this thing is running super lean. It also has trouble idling even though I have the idel screw all the way maxed out. There is some obvious education on my part as this is the first flatslide I've owned. I've tried the following with no positive result:

50 slow jet

Multiple adjustments on air screw

OCEMR needle on 3rd, 4th, 5th, etc clip

170 main all the way up to a 230

Got JD tuning guide and figured out I needed to try different needles.

48 slow jet

Air screw 3/4 turns out

FMS 2 turns out

OCFHR needle on the 6th clip

230 main

= LEAN!

55 slow jet

Air screw 3/4 turns out

FMS 2 turns out

OCFHP needle on the 7th clip

230 main

= LEAN!

I've been pulling the plug after each run to see how it is and is super white. I don't dare ride it more than a mile or so in fear that I'll burn this motor up (again). It doesn't pull like it should. My best result was when I drilled out the slow jet to a 1.016mm (#60 drill) 170 main with the OCEMR on the 5th clip. Ran rich as hell at the bottom but pulled like a tractor and had no issue bringing the front wheel up. Plug looked pretty good but thats obviously a crazy size slow jet. That's when I tried the other setups above. I've checked for any vacuum or intake boot leaks and came up with nothing. I'm seriously struggling with this one and any help would be great! I'm sure I'm missing a bunch of info so ask all the questions you need to to help problem solve. Thanks

The latest run (5-4) was:

55 slow jet

Air screw 2 turns out

FMS 1 turn out

OCFHP needle on the 7th clip

185 main

It idled ok but would stall randomly. I restarted it without hitting the throttle and it would start back up. I did this for over 5min and then pulled the plug. Not bad, looked kinda lean but still wouldn't idle correctly. I took it for a run (less than 2miles) keeping it at 1/4 throttle 98% of the time. Pulled the plug and it was VERY white!

I've been hearing about the NCV needles but not sure if it'll help. I can find any taper/length/diameter specs so I don't know how it compares to the OC needles. I'm ready to buy a NCVN and a NCVQ to try.

Feeling desperate... Haha

Any help would be great. Thanks!

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You cannot tell air fuel mixture by looking at the plug anymore, unless you are using racing fuel.

Gas additives  burn in multiple colors.

 

Is the FCR new or used? 

If it is used, you should replace the Needle jet, as they wear out.

 

You are aware that not all FCR41's are the same?

 

 

You mention fuel mixture screw and air screw; it does not have both.

 

One is idle (slide position) and one is fuel screw (+/- 10% pilot circuit adjustment)

 

You may never get it to run properly with an air filter pod, as the intake is too short and too turbulent.

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It is a new FCR ordered from pro cycle.

I'm aware of an MX version of the FCR.

I may not have the terminology correct but when I say fuel mixture screw I'm talking about the one under the carb by the bowl. When I say air screw I'm talking about the one in front of the carb.

I have seen these carbs on other bikes running velocity stacks and I assume they run well. I did tape off most of my filter so only 1" or so was exposed and a do have an intake tube approximately 2.5" in diameter by 8-10" long with a 90* smooth bend. With the air filter taped off it didn't make a difference at the 1/4+ throttle area of operation. It was still lean. I say lean because the plug was white as a piece of paper.

I can modify my intake tube to add restriction but I'm unsure it will help based on taping the filter off without a positive result.

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You don't want restriction, you want a Bell mouth into the carb, to reduce turbulence.

 

I don't think your jetting is as far off as you think.

 

If you go up and down as many sizes as jets as you have done already, I would focus directly on the Jet Needle, using an NCVS (rich).

 

Does you motor drop back to idle quickly after whacking the throttle?

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It came with a bell mount that I have bolted to the front if the carb. I ordered a NCVQ (be here in a few days). The motor returns to idle fairly quickly but won't consistently idle (randomly stalls). I have the idle screw (black knob) all the way in just to get it to do that.

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1. Back the black idle knob all the way out: that is why you are so lean

2. set the fuel screw at 1 turn out

3. start the motor, and get it to just barely idle with the idle screw

4. raise the idle with the FUEL SCREW to reach proper idle. This is your fuel screw setting (usually 1.5 turns out)

5. If your fuel screw is more than 2 turns, you need a bigger pilot / less than one turn, you need a smaller one

6. Fuel screw and pilot jet are for IDLE ONLY

 

When you say you bolted a bell mouth on the 'front' of the carb, you mean the back / air cleaner side, right?

Or are you just referring to an adaptor plate that is bell shaped, and less than 1/2" deep?

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Do you know what the measurement from the bottom of the slide to the bottom of the carb needs to be? When I adjusted the black idle knob out last night it seems that my throttle was set at about 1/8 throttle. Which is probably why the fuel screw had no effect turned in or out. I'll mess with it more tonight. What should the screw on the front of the carb be set at? Or does this not come into play until later?

And yes. The "back" of the carb. Air cleaner side.

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Yeah, I adjusted before I turned the idle screw up. I have my throttle positions marked on my throttle assy. With the idle screw in as far as it it's now its it has a lot if play. But if I back the idle screw all the way out its just right.

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Installed a n Innovate air/fuel gauge. Going it drop the NCVQ needle in and reset my pilot/slow circuit tomorrow. Pretty pumped about the A/F gauge. I'm interested to see what #'s it throws out.

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Alright, making some progress. I did most of my tuning with the AP disconnected. After everything look ok I hooked it back up and it only improved my lean spots(hard fast pulls). After a few runs and a few changes this is where I'm at:

-NCVQ needle on 3rd clip from top

-Black idle screwball the way up(tried a shitload of settings to get it to idle with anything less. No dice)

-185 main

-Slow jet 50

-Air screw 1.5 turns out

-FMS 2.5 turns out

Throttle positions

1/4-1/2 A/F = high 12s to mid 13s

1/2-3/4 A/F = mid 13s

3/4-WOT = mid 13s under load. 14s at higher RPMs

I'm thinking about leaving it a little rich for now with the fresh motor until I get it broke in a little.

Shoot me some feedback

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