Carb Tuning Questions

[Marsh White]

And all I'm saying is exactly what Frank said: you can't skip step 1 and go to step 2.  That's all!  You're still complaining about the bike running bad at low RPM and even talking about maybe taking it into a shop and paying money...all WITHOUT having synced the carbs.  No negativity intended...just trying to help!   

Oh, and I picked up my vacuum restricters things up at Pep Boys - I would think that any NAPA, Autozone type store should have them...you'll probably have to look hard, but they should be there somewhere.  I never saw them at a hardware store.

[drawkward]

Understood. I was under the impression that the vacuum leaks due to the bad boots were the collective culprit as the bike ran great using the old starter fluid trick. After I replaced them, I realized more carb work is needed...and I stated that. I never said I wasn't going to do the sync as everyone had originally told me to do, I was just saying I hadn't done it yet. After I got the boots on is when I started messing with the idle screws again (after it was bench synced too), thinking that the vacuum problem and hence my loss of power problem would be resolved. It obviously wasn't. And that maybe I'd have to take it to someone if I can't figure it out. Which again, makes me want to puke.

I understand you guys know your stuff when it comes to these great machines. But I do know how to follow directions. I'm an engineer after all. I just wanted to update you guys is all. I am a firm believer that forums are the best vaults of knowledge on the internet (besides a good porn site!) and my train of thought updates are my little contribution.

On topic:

I'm gonna have to jet out of work early to get those restricters from auto zone or the pet store tonight, cause at 6pm Ron Paul is going to be speaking at some Tax Day Tea party near my house and I'm dying to go. I just hope it all gets done before too late cause I want to get those carbs synced. If I can find restrictors I'm going to try my 4 hose setup again...I mean, I spent the time building it, so why not see if it works (got the design from someone who liked it better than a pro one). If it doesn't I'll hack it to pieces and try the two line version for sure.

I'll hopefully have an update tonight if not tomorrow. I'll try to take pics for archiving purposes as I'm sure someone in the future may find it useful. (not sure if anyone has taken pics of a sync job on an FJ before).

Thanks again!! 

[racerman_27410]

the screws on top of the carbs (right at the carb joints) are not idle screws..... they are idle MIXTURE screws and a base setting 2.5 turns out to start with.

the one and only idle screw is underneath the carbs as they sit on the bike.


you do know where the synch adjustment screws are?

[drawkward]

Sorry my carburetor lexicon isn't up to par. I assure you I know the difference between an idle mixture screw and an idle adjustment screw.

And yes, I do know where the sync adjustment screws are.

Thanks

[rlucas]

FWIW, the so-called "restrictors" on the Morgan CarbTune are nothing more than a quarter-inch insert with a tiny hole in it, drilled longitudinally. About the size of a hypodermic needle. Cut hose, install restrictor. Done.

The Morgan's a bit pricey, but IMHO well worth the cost. I'm a cheapskate, but I try not to cheap out on tools. The Morgan works better than any homemade rig or mercury manometer that I've ever used. Worth the money...if you intend to use it regularly.

It's cool, and you can charge your friends. "Balance your carbs?  Sure...twelve pack and lunch." 

Rossi

[drawkward]

That's not a bad idea Rossi. I don't drink, but I can get some good chinese out of it. Speaking of which...

I went ahead and did the carb sync and got it pretty close to center across all the lines. But, to no avail. The bike still has the low end bog when I blip the throttle. I'm going to go ahead and do it again tomorrow because my brain is fried right now and maybe I overlooked something.

I was cool seeing the carb sync tool actually working though I must say.

[MyFirstNameIsPaul]

What I really like about the Morgan is how fits in a tiny little case.  Don't have to have some huge wooden plank with tubes and junk.

[drawkward]

What I really like about the Morgan is how fits in a tiny little case.  Don't have to have some huge wooden plank with tubes and junk.

Haha, I can see the advantage there. I didn't feel like cutting the board I had in two so I just kicked it in half. The Morgan would definitely have been cleaner.

[drawkward]

I finally got the carbs sync'd and the idle mixture screws set correctly and bike is still bogging a bit during the blip test and during the first minute or so of warming up. After total warm up it idles nicely but is still a tad rough.

I took the carbs off again and cleaned them out entirely by taking all the jets out and running some guitar string through them and the usual carb cleaner (again, I think this is the fourth time). I figured out an interesting fact about the jets that makes me think I may have found the problem. Each jet seems to be the stock size across the board (37.5 pilot /110 main). When I bought the bike I was told that the mufflers were aftermarket but I can't remember what specific brand he thought they were and there is no indication of brand on the mufflers. And frankly I don't think it really matters. What does matter is that I think I may need to rejet the carbs to make up for what I can imagine is a loss in back pressure. When I decided to take the muffler off my Buell and run straight pipe, I noticed a slight loss in power through the rev range and I know for a fact that the stage one/two jet kit for the Harley CV or perhaps going to the 42mm Mikuni solves that problem. I can only imagine that the same is true for this bike. I have no power loss through the rev so I think my main jets may be fine, but I feel that the pilot circuit may be running lean, no matter where my mixture is set.

Any thoughts?

p.s. Even with the carb problems, I like this bike more and more each day. This thing is full of power. I just need to get a 17 on the rear!!

[RichBaker]

 Every big-bore sportbike made in the '80s and early '90s was jetted lean at idle and off-idle carb settings for emissions reduction. I put the DynoJet air correction jets(smaller than stock) and #40 pilot jets in my '90 and she's very happy now....
I currently have the S&S exhaust, UNI airbox insert, DJ needles(Grv2) and 114(I think) MJ. A Dyna 2K ignition module and coils light it off.

[Ratchet_72]

I finally got the carbs sync'd and the idle mixture screws set correctly and bike is still bogging a bit during the blip test and during the first minute or so of warming up. After total warm up it idles nicely but is still a tad rough.


Any thoughts?

4 cylinders need a warm up and the FJ is especially cold-blooded, so it will not pass the blip test until its totally warmed up.  After adjusting the mix screws especially on carb 3 you're gonna wanna resync.  If all 4 carbs mix screws are not set exactly the same don't worry about it too much. When you hit the sweet spot and it passes the blip test who cares if one carbs screws are out 3 turns and another is 2.5 turns out.  Again this works for me. It may or may not work for you.
Make damn sure all your vacuum hoses are good/not cracked and plugs on the carb holders are holding vacuum.  The stupidest shit will trip you up and you'll find you didnt even need to pull your carbs that 5th and 6th time. Yeah I've done that a million times.
Again warm up on this bike is crucial.  These bikes are over 20 years old for F*&ks sake. They get grumpy quicklike.

[drawkward]

Rich:

I need to do some research on what is available for these carburetors cause I am unsure of what the air correction jet does or how that specific jet helps. I think I also need to look through some documentation on the different mods you guys have done with these things. I don't know what the UNI airbox insert is, DJ needles or what ignition modules are available. But what you've mentioned sounds like a bunch of small things one can do to bump performance significantly. Thanks!

Ratchet:

I think I misspoke when I was talking about the warm up. When I did the carb sync, I rode the bike for about 15 to 20 minutes beforehand to warm it up as was suggested earlier in the thread. That made a huge difference and I was able to sync rather easily (minus the problems I had with leaks in my sync tool which I fixed). However, one thing I didn't do was reset the sync after adjusting the mixture screws. So I'm going to try that again. I also didn't think to adjust the mixture screws independently of each other. I always thought they should be set together. I'll try that too and hope that I can get the bog out, but I have a feeling that it won't work. Who knows though. If it does, fuck ya. If not, I'll get some jets or something.

Thanks for the suggestions 

[rlucas]

The UNI insert is just a UniFilter replacement for the stock air filter. No big deal.

As far as jet kits go, I'm a huge proponent of Factory Pro over DynoJet (DJ) or Cobra...same thing, actually. But the DJ\Cobra kits use proprietary jet sizing...the Factory Pro kits use genuine Mikuni jets. I've used the FP kits on 3 bikes and they've always been spot-on.

If you're running the stock exhaust, stock airbox...Factory Pro Config 10.

Factory exhaust with pod filters (a lot of us have done this...) FP Config 20.

Aftermarket exhaust and pods...FP Config 30.

IIRC. Which is somewhat unlikely, usually. If you spring for the Config 30 kit, it comes with all the bits from the other two, so you're set for future mods.

It made a huge difference in how cleanly the FJ ran.


Rossi

[drawkward]

Thanks for the heads up Rossi.

I am guessing since I have stock airbox and aftermarket exhaust I should just go ahead and get the pod filters then run the config 30. I don't see any good reason not to have pod filters, so that's most likely what I'll do.

[SlowOldGuy]

Have you checked the fuel level yet?

DavidR.