GB Mod really worth it?

Seems like a lot of work. I am noticing a little stuble when I crack the throttle. I think I can live with it if this is all it fixes.

If your bike is running well, starts good and does not have the YAMABOG....don't bother. If you suffer from any of the things listed above it is worth doing the mod.

What year bike?

I have a 2000 did two things that brought the beast to life

Number one the GBMod

Number two THE 2001 epj needle

It seems like a lot of work? In relation to what? It takes less than an hour and a few dollars at the most. Maintenance must not be a priority for you. I like to work on mine as do most here. Good luck

My 2000 YZF NEEDED this mod, it would foul plugs on cold starts occasionally, and had the Yama-bog bad....

Afterwards, it ran great, and never fouled another plug.

That 3 second long spray is WAY too long, on my CRF when you hit the throttle it only squirts for a half second or so, which is what you do to the Yammie essentially, the carbs are almost identical.

I say DO IT. :)

Well this really is not maintenace it is more of a mod. I just took the swing arm off and had it repainted if that gives you any idea how meticulous I am over my bike. It is a 2001 and runs like a champ. Last time out it started on the first kick! It starts and runs so well from what I have heard on this forum I don't really want to mess with it. Like I said I notice a slight stumble off idle but that is it. I am thinking the air screw could fix this.

You're the only one who has to ride it. If you're happy with the way it runs, leave it alone. If it ain't broke, don't fix it. On the other hand, if there is improvement to be made, don't be affraid to do it. The mod is simple and cheap.

It does seem some bikes don't need the GB as much as others. Correct me if I'm wrong, but it seems like I remember reading about the durration of the AP squirt being substantially different from bike to bike, even bikes of the same year. Does anyone else know about this? If it's true you may have a bike that doesn't need it. Most people though find the GB mod makes a big difference.

How do you check to see how long the squirt is? Do you twist throttle?


Scotty, I too agree that it is not really a maintenance issue as much as a mod. I have the 2000 as do others it made a night and day difference. The 2001 might not need it. In actuality I think with meticulous tinkering with pilot jets, needles, leak jets, clip positions, fuel screw adjustments, etc you could probably made mine run much better but the mod made it instant. In no way is it a band aid for improper jetting and set up. The fuel screw will make a difference and you should adjust it every ride if you want the best performance. If you have an adjustable fuel screw (4 strokes run fuel screw, 2 strokes run air screws) it makes it effortless and you can do it sitting on the bike and running. :)

I didn't do the BK mod, but I did get rid of all the bog. Combination of a lower pilot jet, A FreePowerNow and a P-38 Ligthning accelerator pump atomizer. The P-38 was the only expense, forgot the cost, wasn't much, looks cool too. I didn't really want to spend a lot of time timing a squirt that is only a fraction of a second...I'm probably just lazy and was interested in how a gizmo as simple as the P-38 would work (actually wanted to get my hands on it and check it out), no need to 'rig' a BK mod when a P-38 takes 5 minutes to install, no re-jetting, no timing, you don't even need to remove the carb.

SCOTTY - My '01 did not need the BK mod to have snappy throttle response. Just a smaller pilot jet when it got warm and the usual amount of fuel screw adjustments. Occasionally I have jetting problems if it is VERY hot and humid at the same time, but this is not what the BK mod fixes anyway.

FWIW - I did the BK mod one day when it was raining. The stock squirt was about 1.5 to 2 secs. After the mod I needed to tweak (seat of the pants) the AP pump squirt delay to get the best throttle response. Once it was dialed in I could not tell a difference from the stock response. I've left it in because it was it took a while to get it finally dialed perfectly.

I noticed an immediate improvement on my '01. The stock squirt duration was about 3 seconds on my bike. I adjusted the squirt timing a duration on the bench and it turned out perfect. Never had to touch it again. FYI...Keihin ( the carb manufacturer) is owned by Honda. Their carbs seem to be a bit more inconsistant on the Yamahas, lessor so on the Hondas. Do I smell a conspiricy here??? :):D :D

BTW... you said you had a noticable stumble...Why live with that if you can make it run so much better with so little work?

2 more cents on the GB mod...This is a known issue on the 426's. Better to at least check the accel pump operation and fix it if it's off than to chase a jetting ghost that may or may not exist. :)

BK mod is a quick $.50 unless you don't have a tap. Didn't notice much difference between the stock 5 second squirt and the 1/2 second squirt on my bike. Bog hasn't been and issue however. No MX on my WR unless I get excited after watching SX on TV and try a small double or something. :)

Hi, I have a yfz450 quad with basicly the yzmotor and the FCR Carb.. I have considerable amount of fall flat on your face yama-bog.. Im curious if the BK mod will help me out also..

Below is a picture of the ACP on the yfz FCR


What year bike?

I have a 2000 did two things that brought the beast to life

Number one the GBMod

Number two THE 2001 epj needle

As much as it pains me to do so, I have to heartily agree w/ Ego here.

In the interest of maintaining a semblance of normality, I'll dispute the order of import: the EJP (not epj) needle is a bigger improvement than the GB mod for the '00 YZF, even if all you care about is just-off-idle response (they just plain goofed on the '00 needle, but recovered in '01 w/ the EJP).

Also, the GB mod is very easy. If you have the tools it is a five minute deal. The difficulty is the mental barrier to drilling a hole in an $800 carb.

It does seem some bikes don't need the GB as much as others. Correct me if I'm wrong, but it seems like I remember reading about the durration of the AP squirt being substantially different from bike to bike, even bikes of the same year. Does anyone else know about this?

I'm sure it has more to do w/ the variance in results from something as wildly inaccurate as using a stopwatch to time the squirt. I always thought that was silly.

I set my pump travel with calipers, but since nobody ever adopted this convention I've long since forgotten what this number was. I want to say that stock travel was 3 mm at the actuating rod, and JD and I both ended up around 1 mm after playing with this when this mod was first discovered here.

Measuring the travel seems much easier and much more accurate than trying to time the squirt.

Oh well.

As for the variation in reported benefit, I've known plenty of folks that spent years on horribly jetted bikes totally oblivious to it. Where I live very few, if any, bikes run to their potential on stock jetting, yet few owners get around to sorting this out.

In short, you don't know what you are missing until you try it.

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