Realization...there is no cure for the bog on a '99 YZ400 carb.

As with many others, I have the off idle bog on my '99 YZ400. I've totally cleaned and adjusted the carb. Taffy mod done. New accelerator pump and o-rings. Adjusted everything twice, three times. Although the bog is less pronounced, it's still there. So, what I've realized is there is no cure to the Yamaha bog on the '99 model. Am I missing something?

I've kinda come to the same conclusion. Ended up removing the collar (Taffy Mod) and just let her squirt as designed :cry:

I've kinda come to the same conclusion. Ended up removing the collar (Taffy Mod) and just let her squirt as designed :cry:

Yep, I did too. Nothing against the taffy mod, it obviously works well on some bikes but it didn't do anything for mine. Adjusting it from .3 seconds to 4 seconds on the AP squirt didn't make any real difference.

So, the question is, does that particular carb have a design flaw? It really seems like there isn't enough gas getting to the motor when the throttle is wacked open hard.

I had the same problem for a long time but after putting in a james dean kit and a power now the response is crisp right from idle.

I had the same problem for a long time but after putting in a james dean kit and a power now the response is crisp right from idle.

Hey Rush, that's really interesting. I've been looking at the JD kit, but I've not heard that the powernow improves the bog..interesting. Hey, what jetting specs are you running? Thought I'd ask since we're around the same elevation.

well I did have to play with the jetting to get it right.

Im running 165mj red needle 5th clip( one richer from middle) and my fuel screw is between 1 1/2 and 2 1/2 depending on the altitude I'm riding since I range from 10,000ft to 4,000ft.

But try the James Now Mod , play with your jetting and you might look into A JD kit.

Will do. I'm running the stock jetting, which has the 175 main, I'll try the 165, and keep messing with that dang fuel screw, i'm probably running a bit lean right now. I'm determined to get that BOG outta this bike.

The Power Now does help the bog on any bike. It also helps starting and gives a little better low end.

When the bike bogs do you get a big puff of black smoke out of the exhaust? Chances are you don't most pre 03 FCR carbs don't provide a sufficiant A/P shot ( volume vs timing ). Check it out if you don't get the puff of black smoke then you are not rich, your lean. let me know and I'll tell you how to fix it garraunteed! :cry:

When the bike bogs do you get a big puff of black smoke out of the exhaust? Chances are you don't most pre 03 FCR carbs don't provide a sufficiant A/P shot ( volume vs timing ). Check it out if you don't get the puff of black smoke then you are not rich, your lean. let me know and I'll tell you how to fix it garraunteed! :cry:

Well that is interesting. Most of us here have been resolving issues with bogs for years by shortening the duration of the accel pump by performing the BK/GB Mod or Taffy mod. Seems like the earlier FCR's had too much spray which led to bogging, fouling and flooding. And you want to lengthen the spray?

Your Bike is Jetted WAY TO FAT!

Do a search for the "Jetting Q's" thread and take some time to read it. Many of us did alot of work back in 99 and 2000 to get these bikes running right.

The Taffy Mod works great...Done on my 99 for several years without an issue. Part of the solution IS that you must also have the Pilot Jetting correct or it does nothing except throws in a bucket of fuel from a different location.

Bonzai :cry:

I'm running a tad lean right now I think because I have a bit of backfiring on decel. I have the stock jetting (175 Main, 35 Pilot, and the clip is set one groove up from middle). My fuel screw is set around 1.5 turns out. With the Taffy collar, I've adjusted the AP squirt from anywhere from .3 seconds to 3 seconds, and the bog is still there. The bike runs really well when I roll the throttle on, good power, starts like a dream, etc.

So, James Dean said I should drop the Main to 172, increase the Pilot Jet to 45, take my needle clip down 1 groove from middle, and then really play with the air/fuel screw when the bike is hot.

When the bike bogs do you get a big puff of black smoke out of the exhaust? Chances are you don't most pre 03 FCR carbs don't provide a sufficiant A/P shot ( volume vs timing ). Check it out if you don't get the puff of black smoke then you are not rich, your lean. let me know and I'll tell you how to fix it garraunteed! :cry:

I don't have the black smoke, and i pop on decel so I think I'm lean. What do I do WR426Madness!

How many turns out are you on the fuel screw? I run a 170 main at sea level so you look fat to me. What does it seem like on the big end? Arm ripping power?

How many turns out are you on the fuel screw? I run a 170 main at sea level so you look fat to me. What does it seem like on the big end? Arm ripping power?

I checked it again and I'm 1-1/2 turns out of the fuel screw. The power seems pretty good, and the bike generally starts and runs in all other throttle areas with good response.

Have you tried smaller mains? I would think 168,170,172 and a larger pilot. You are only too lean in the pilot, try the 40-45 James suggested. I would also think you will see a change for the better go down on the main. Try it.

This is just what has happened to me. I tried everything all of the other post have listed and still no help. I was ready to sell the bike due to this problem. I found a brand new Edelbrock carb. on ebay and thought what the hell I'll try it. I installed the Edelbrock carb and have never had a bog or anyother problem at all. I know alot of people on this forum love the FCR but to me it was junk. With the Edelbrock carb. and the 450 cam I couldnt be happier with this bike. Good luck Rob

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When the bike bogs do you get a big puff of black smoke out of the exhaust? Chances are you don't most pre 03 FCR carbs don't provide a sufficiant A/P shot ( volume vs timing ). Check it out if you don't get the puff of black smoke then you are not rich, your lean. let me know and I'll tell you how to fix it garraunteed!

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Well that is interesting. Most of us here have been resolving issues with bogs for years by shortening the duration of the accel pump by performing the BK/GB Mod or Taffy mod. Seems like the earlier FCR's had too much spray which led to bogging, fouling and flooding. And you want to lengthen the spray?

I didn't say lengthen the duration, I said," volume vs timing". You will definately need the B/K mod to help with the duration, and icrease the A/P spring tension by shortening it to increase the volume. Now the trick is to figure out what is your current condition, like I said if there is black smoke after you whack the throttle open then you are rich if not chances are you are to lean. Let me stress that it is important that you make sure that the bike is jetted properly before you start monkeying around with the A/P so that a prolonged duration isn't misstaken for to rich of a needle setting. So make sure the bike runs good from 1/4 throttle on, then set the A/P.

Here is a chart that I created it should help.

fuel%20curve.jpg

If my brain is working properly the BK mod wont work on a 99 or 98. Not sure but I think only the wheel collar mod will help these bikes. Again Im not sure

I have called James Dean a frind now for a very long time, and he was my jetting mentor for a long time. What he says is true for the most part, but there are quite a few variables that affect which way you go. I have sent you an e-mail with the recommended setting for your bike at an altitude of sea level to 5000 feet. This is a tried and true jet set , the only adjustment you should have to make is minor adjustments on the Fuel Screw when the temp swings from one extream to the other.

Bonzai :cry:

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