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Two '05 WR250F Questions

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Hello all,

Two quick questions I am sure members can provide some advice on.

I have a '05 WR250F and have had several modifications done to it by the dealer who was advised by Yamaha racing. I still however have an ever so slight "bog" in the throttle when I totally get off it and hammer back on. The dealer is trying to sell me the Boyesen QuickShot accelerator cover claiming a defect in the original from the carb manufacturor in which it only lets 60% of the gas through on initial throttle, has anyone had any success with this bolt on mod??

Second is the use of Mavel oil in the gas, I have heard good and bad but the dealer I bought the bike from says no, not needed in the WR. Any thoughts?

David

:banghead:

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Hello all,

Two quick questions I am sure members can provide some advice on.

I have a '05 WR250F and have had several modifications done to it by the dealer who was advised by Yamaha racing. I still however have an ever so slight "bog" in the throttle when I totally get off it and hammer back on. The dealer is trying to sell me the Boyesen QuickShot accelerator cover claiming a defect in the original from the carb manufacturor in which it only lets 60% of the gas through on initial throttle, has anyone had any success with this bolt on mod??

Second is the use of Mavel oil in the gas, I have heard good and bad but the dealer I bought the bike from says no, not needed in the WR. Any thoughts?

David

:banghead:

NO oil in the gas. If you do a search for bog in this forum, you will find several threads and fix to your problem. It is common. I can tell you that with the free mods done, YZ pipe, and JD jet kit, mine bogs off idle but not when I am riding it. I don't worry about it. You don not the boyeson cover though. I believe a lot have found success with a #40 leak jet and setting the acc pump squirt, 2 things I have not had to do. Also, look on thumperfaq.com, it is filled with valuable info.

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I changed the leak jet and the pump was adjusted by the dealer when they did a bunch of "free" mods for me. The first thing Yamaha racing says is to do both these mods, makes you wonder why they are not done at the factory if it is such a common problem.

The bog for me can be a real pain. I ride out in PA and there are lots of hill climbs and just a slight bog or lack of instant throttle response can make or break you on some of those hills. I do trust this dealer but I wanted some input on the QuickShot before I purchase since it is a $100.00 part.

Thanks

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I was messing around with my jetting and inadvertantly induced a severe bog. Going to WOT off idle, the thing would really puke out. It happened when I had the carb set too lean. Raising the needle jet eliminated my bog.

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I can make the bike bog just sitting on it wacking the throttle open, but I have yet to experiance it while riding/racing and we have out share of hills to climb :banghead:

But as have been found out, these bikes vary widely in performance for each user.

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https://thumpertalk.com/forum/search.php

Search the word "bog" and you will find out everything you will need. Here is a hint, you can fix the bog for less that $10.00. Just order yourself a #40 leakjet, I have the #35 in there now and I also tried the #40, they both are pretty good fixes for the bog.

Oh, and don't "trust" the dealer when he tells you that there is no such this as a leakjet.

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I have a '05 WR250F and have had several modifications done to it by the dealer who was advised by Yamaha racing.
Here is the link for the free mods. http://www.thumperfaq.com/free_mods.htm#WR Make sure that your dealer has:

1) Cut the throttle stop

2) Removed the intake snorkel from the air box*

3) Unplugged the gray wire

4) Removed the exhaust baffle*

* This symbol means that the instructions in the FAQ may differ slightly in describing how these mods are done on your 05 WR. These mods still need done, but you may have to search this forum on how they are done on your 05.

These are the four mods that make the most difference in performance for your WR. Also you can make huge performance gains by replacing your stock WR cam with a stock YZF cam (~$120) and also by buying a used YZF exhaust off of someone here on the forum ($50). The JD jetting kit is also highly recommended, and can be had for ~$70 at the TT store.

I still however have an ever so slight "bog" in the throttle when I totally get off it and hammer back on.
When you flick the the throttle open from low RPM, the Accelerator Pump (AP) delivers a quick squirt of fuel to compensate for the sudden loss of vacuum caused by the opening of the slide. The bog happens for one or more of the following reasons: Improper fuel screw position, improper clip position, improper AP squirt timing or improper AP squirt duration. All of these conditions need to be satisfied before you're bog-free. Definitely fixable, but it takes a little work. Here are the primary considerations.

1) Make sure that you have your needle clip in the right position, and adjust your fuel screw so that your bike idles crisply. A Zip-ty or other aftermarket fuel screw will allow you to make adjustments on the fly, and you'll be able to hear what is meant by a "crisp" idle.

2) Time your AP squirt so that when you flick the throttle open, the AP squirt just misses the slide. See your manual for details.

3) Replace the stock leak jet with a #40 leak jet. This sets the squirt duration to at or near the proper length.

These three things have cured the bog in 95% of all our bikes. For more details see https://thumpertalk.com/forum/forumdisplay.php?f=104

The dealer is trying to sell me the Boyesen QuickShot accelerator cover claiming a defect in the original from the carb manufacturor in which it only lets 60% of the gas through on initial throttle, has anyone had any success with this bolt on mod??
Although it would be nice, a simple bolt on won't cure the bog. Several folks on this list and on the 450 list have found this out. It appears that the Boyesen cover DOES allow the AP resevior to refill faster, which helps keep the AP from running out of fuel if you have to flick the throttle lots of times in rapid succession. For instance this would be a good mod if your riding includes skipping over the tops of long whoop sections. If you're ripping through the woods though, the stock AP cover performs just fine. Unless you have a specific need, as I described above, save your $100 for something like the YZF cam, YZF exhaust or JD jetting kit.
Second is the use of Mavel oil in the gas, I have heard good and bad but the dealer I bought the bike from says no, not needed in the WR. Any thoughts?
Never heard of it, so can't help you there.

Welcome to the forum:thumbsup:

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Thanks to all!!!

Barton,

The freebie mods you listed were all performed by the dealer, they actually replaced the throttle screw with the YZ screw instead of just cutting it, I think I read of some problems with cutting it on this site. It can sometimes "catch" in the wide open position if not done properly.

I also put in a #40 leak jet, the JD kit, and had the dealer adjust the accelerator pump squirt timing and it has eliminated the "bog" by 99%. It just seems that I still have a tiny bit of bog when I am really hard on the throttle and totally let off quickly and then get back on it hard.

I will try some of the other mods, especially the exhaust and see what happens.

Thanks again for everyones input.

David :banghead:

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I'm not taking a chance on a $2000+ engine by putting "mystery" oil in it when it runs great. :banghead:

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gmoss,

I have never used it just threw it out there because my brother in law just bought an 05 KTM 450 and the dealer highly recommends using 2oz of Marvel Mystery Oil per gallon of gas in any of the new four strokes and was wondering if anyone else has heard of this.

The reasoning he gave was that this stuff is sorta of a combo of a lubricant as well as mild solvent. He claims it helps to keep the valve seats and needle lubricated while at the same time keeping the valve stems clean. The owner of the dealership is a hard core KTM guy and swears by it :banghead:

David :applause:

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I know you hadn't used it by your previous post. I would need some proof as to its benefits. Yamahas don't go thru valve like the other brands so I am not worried. I've been on my 03 since new and never have had to go into the engine. I will this winter when I put in a YZ cam, checking everything then. Maybe the other bikes need some "mystery" oil. :applause: Sounds like you are on top of everything, so go :banghead: .

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