R & D power bowl

26 replies to this topic
  • tcuda499

Posted October 31, 2008 - 08:15 PM


Does anyone have the R&D power bowl? if so was it worth it or should I just keep trying to rejet to to get it running good?I just have the normal hesition during a wot.I'm new to jetting but willing to learn.I have an 07 yz450 with stock jets but the pilot i went to a 48,colder weather at sea level.

  • grayracer513

Posted October 31, 2008 - 09:13 PM


No, I don't have one, and no, it's not worth it, IMO. I have no problem with either of my '06's stumbling, but that's because I don't cause it to. You can fiddle with things enough and finally get it to the point where you can smash the throttle from idle to WOT without it hesitating, but you'll have other problems as a result. Getting it jetted right, and learning to roll the throttle open instead of snapping it will get you much better results in the long run.

If you want an adjustable leak jet, use the Merge Racing ALJ Kit, which replaces your accelerator pump cover. Much less expensive, if nothing else.

  • Justin89

Posted October 31, 2008 - 10:02 PM



  • jspeed

Posted October 31, 2008 - 10:11 PM


Love mine, worth every penny!!
No more carb bog and easy to jet.

  • rexbond007

Posted November 01, 2008 - 07:26 AM


i just do the 0-ring only mod it works excellent,
http://www.thumperta...ight=o-ring mod

stock jetting summer, 48 pilot winter and 160 MJ

  • tcuda499

Posted November 01, 2008 - 08:12 PM


thanks everybody.I can learn to roll the throttle instead of snapping it.I will still try to rejet again but time is a problem,12 week old baby doesn't give me much time to play around with the bike right now.:worthy:

  • grayracer513

Posted November 01, 2008 - 08:27 PM


Have you looked at the jetting DB for ideas?

  • Wes Woodin

Posted November 02, 2008 - 04:50 PM


Have to tell you that it was the most performance improving mod I have done yet.

  • tcuda499

Posted November 02, 2008 - 06:01 PM


I have looked at the jetting DB an found some info. I still dont have a service manual for my bike,I have only owned it for 10 days now,wheres a good place to get one online?

  • grayracer513

Posted November 02, 2008 - 06:19 PM


Look in the Common Threads Sticky. Down the page under "Misc", there are two links for downloading manuals from Yamaha. The Euro link is the preferred one.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • tcuda499

Posted November 04, 2008 - 06:22 AM


let me change the question a little, if they giving power bowls away free, who would try one?

  • Holigan

Posted November 04, 2008 - 07:04 AM


Joe Gibb's Racing raced with our product (Merge ALJ) on all of the team's YZ 450's last year and will again this year. We do not pay them to use our products, they purchase the units from us.


  • grayracer513

Posted November 04, 2008 - 07:38 AM


let me change the question a little, if they giving power bowls away free, who would try one?

Let me ask you what you imagine the Powerbowl might be capable of accomplishing. What it really does is 3 things:

> "Improves" the control of fuel sloshing in the bowl to some extent. Does anyone really have a problem with this?

> Provides and externally adjustable leak jet. Leak jets are NOT intended for the modification of the accelerator pump performance, but they can be used for that purpose. The thing is that once you get the AP working right, you rarely, if ever, have to change the LJ after that, so other than saving a little time while getting it dialed, what is the point? On an older, '04 and earlier model, it does add a leak jet to the circuit, which could be an advantage.

> Improves the function of the accelerator pump check valves, which, with the stock pump cover, can be a little less than precise at times. At last, something it really does do.

But the adjustability of the leak jet and the better check valve performance are both provided by the Merge ALJ at about half the price. Their stiffer AP linkage spring is an excellent, much more reliable substitute for the O-ring mod, too.

  • tcuda499

Posted November 04, 2008 - 07:35 PM


Great info grayracer513! I think I understand it better now.As you can tell I'm new to thumpers,just came off years of 2t's.never had any major problems with the m 2t carbs,small adjustments and VERY easy to get at!!!

  • Pilfer8

Posted March 31, 2009 - 08:54 PM


I know I am flogging a dead horse here guys, but my quest for no bog is finally over with the purchase of the Powerbowl. Grey, I respect your opinions and you know a heck of a lot more than I do about these things, and I think a pro like yourself is able to tune a bike to run just as good as one with the PB installed. That said, I'm not a pro, but I have read, researched, and performed most, if not all of the carb mods on this forum. Including, ZipTy, O-Ring, JD Jetting ( I have more jets than I know what to do with) the AP mod, Quickshot 2. Man, I have lost sleep over this.:confused: Last week I finally decided, in a last ditch effort, to install the Powerbowl and the result was instant gratification. The bog, is gone 10/10. So IMO this product is worth every penny and the money and time wasted trying other mods, well if nothing else I have been educated in jetting 101.:thumbsup: And my wife is happy because she thinks I'm going to stop spending money on my bike. Never.:excuseme:

  • grayracer513

Posted March 31, 2009 - 08:57 PM


So, are you saying that you had the Zip-Ty mod done, and it still bogged?

  • Pilfer8

Posted March 31, 2009 - 09:12 PM


the simple answer is yes. I may have had bad luck with that.

  • grayracer513

Posted April 01, 2009 - 06:43 AM


Interesting. Even so, the Merge Racing ALJ pump cover will do everything the Power Bowl will do for half the money. If the PB cleared up your bog, that can only mean that it was caused by incorrect AP tuning, and could have been fixed for less than $20. The bowl simply doesn't do anything else.

  • Brad_Aus

Posted April 02, 2009 - 12:01 AM


You can fiddle with things enough and finally get it to the point where you can smash the throttle from idle to WOT without it hesitating, but you'll have other problems as a result..

Like what?? on the bikes ive tuned, im not happy if you cant snap the throttle at idle, and have the engine respond accordingly...

There is no reason you arent able to have zero bog from idle, and also, have the engine tuned perfectly on the track.. I spent a LOT of time on the YZ450 with the ported head i did, Ill admit, it took some time, and wasnt easy, but the result was great. I was reading about it at the time, and someone was saying that due to the rpm rise rate, there was no way to stop that hesitation while on the stand..

That 450 was the hardest one to tune, ive found the 250's a lot easier..

Do you use a lambda meter when setting up your carbys?? Because, the best advice I can give to anyone is, you have to have the mainjet, the needle type and clip positition and pilot jet all set perfectly before you try tune out the accel pump... If you have a rich spot in the needle around 50-80% throttle, you will struggle to get the idle to wot response perfect.

And without a lambda which logs TPS RPM, you will also struggle to get your above items set perfectly too... You may get it to work ok, but im sceptical itd be as nice as it should be. To quote someone else from the forums "The FCR's live by the needle" and they are dead right.. I also use the Merge leak jet, money well spent

Would you expect to smash the pedal on a NASCAR, or any other carb race engine and have it bog on you from idle?? No, it wouldnt happen, they are dialled in perfect... No reason to live with poor throttle response on your MX'er either

My .02c worth, either you are one of the people with a poorly setup carb and claim 4-strokes bog and are hard to start hot, or you are one that enjoys the pleasure of a bike behaving as it should..

As for the power bowl, i wouldnt be buying one, cant understand the need, but the ALJ does have a need, and works great

  • grayracer513

Posted April 02, 2009 - 08:49 AM


Do you use a lambda meter when setting up your carbys?? Because, the best advice I can give to anyone is, you have to have the mainjet, the needle type and clip positition and pilot jet all set perfectly before you try tune out the accel pump... If you have a rich spot in the needle around 50-80% throttle, you will struggle to get the idle to wot response perfect.

The statement of mine that you quoted is perhaps a bit over simplified, but I stand by it as a practical matter. The reason is partly due to exactly what you have said above. Far too many DIY tuners will try to address an incorrectly calibrated main circuit by over compensating with the accelerator pump. Accelerator pumps have their place, to be sure, and they are more necessary nowadays, with the very aggressive cams and large carbs required to produce a 50 hp 450, but they never used to exist on motorcycles, and tuners and riders alike had to learn to deal with that.

Neither of my '06 450's will respond favorably to an idle to WOT throttle snap in neutral, nor in gear, for that matter, but I don't care. The reason that I don't is because it never causes me any difficulty while riding, and that's simply because while I'm riding/racing, whatever, I am never idling in neutral, and I always have more finesse than to snap the throttle open that abruptly. Now, I am a very old-school, experienced rider of large displacement thumpers who learned long ago how to roll a throttle quickly, rather than snapping it, so you could say that the fact that this condition doesn't bother me has to do with my style, and wouldn't apply to someone else. However, my son, who has been riding for only 6 years, and has never been on anything more archaic than an XR600, has never had any difficulty with it, either, so I'll boldly say it just isn't really a problem that needs to be worried about.

When you say "lambda", the only thing it means to me in the US is a reference to the original closed-loop Bosch FI systems, where fuel delivery was managed by an oxygen sensor equipped processor. Since the YZ450 has no such equipment, I will guess that you mean what we here call a gas analyzer. That being the case, the answer to your question is no, I don't use one, because I don't have one available to me, but you are correct that it is a very useful tool to accurately gauge the fuel mix throughout the throttle/engine load range. It isn't absolutely necessary, but it will save a lot of time.

I'd like to also mention, for the benefit of those who don't know, that the TPS has nothing at all to do directly with the carburetion on a YZF; it controls the ignition advance relative to the engine load state.

As to the Merge ALJ, it accomplishes two things. They are the same two things the Bowl does, and at half the price. These are that it improves on the operation of the AP check valves, which can be a little imprecise in FCR's at times, and to the extent that your particular carb has a problem with this, it can be beneficial.

The other thing is external adjustability of the leak jet. This is of very questionable value. The only thing that it really offers is a savings of time involved in the selection of the ideal leak jet size, as this jet almost absolutely never needs to be changed after it has been selected. Still, time is worth something, so perhaps that's worth $125.

The thing that I object the most to is that this whole thing encourages the improper use of the leak jet as a means to adjust the AP delivery volume, which is not its primary function. That is supposed to be done with selective button lengths on the AP diaphragm. Using the leak jet for this can, in extreme cases, interfere with its main job of preventing AP fuel from entering the air stream during minor throttle movements. (read: http://www.thumperta...330#post4415330
http://www.thumperta...966#post6081966 )

So, to address the original question of what sort of problems one might introduce by the 100% elimination of any stumble on snapping the throttle, it is simply that too much accelerator pump function can interfere with part throttle sharpness.

Nevertheless, you make several very important points regarding FCR's in general and the importance of the correct needle. The effect of the needle of overall carburetion is poorly understood by most people, and it's a good idea to look over that section of chapter 7 of the manual to try to get a better understanding of it. Throttle response, in the sense of avoiding a stumble as the throttle is opened involves transitioning from the idle state, in which the idle circuit is delivering fuel, but the main circuit has no fuel moving through it, to a condition where fuel is moving through the main circuit and being properly metered, depends a great deal on the needle. And, the major diameter, and minor diameter (and thus the taper) can be selected to affect this, in addition to the position. I believe that the carb must be tuned as well as possible independent of the AP, and then the pump adjusted to do what it's really supposed to do by dialing in the pump volume and timing first, and the leak jet last.

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