Author Topic: High RPM problem 5th and 6th gear (Read 5940 times)

devilears · « **on:** September 20, 2006, 08:56:31 AM »

Hi

I have aproblem when running my bike on high RPM with the throttle fully open. In the lower gears it runs through to 12 k but in 4th gear if I open the throttle up full it starts to stutter a bit about 8k and clears up again at about 10k. In 5th and 6th gear if I open the throttle up fully form 8k the bike starts to stutter and loses all power.

When I close the throttle up 1/2 way it runs smooth again but it doesn`t have enough power to accelerate any further. I can't get the bike past 10k in 5th or 6th to see if the problem clears up when I go past that. At any RPM`s lower than 8k it runs fine.

Does anybody have an idea what could be causing this problem and what I could do to clear it up?

Any comments or ideas would be appreciated. I am running a full yosh exhaust sytem but other than that the bike is standard as far as I know.

Thanks in advance

PitterB4 · « **Reply #1 on:** September 20, 2006, 09:31:17 AM »

Full Yosh and stock jetting?

You're WAY lean if that's the case.

Is this something new? Did you just put the Yosh on?

devilears · « **Reply #2 on:** September 20, 2006, 09:43:37 AM »

I got the bike about 2 months ago with the yosh already fitted. Back then the bike flooded all the time and died so I took it to a mechanic to have the carbs cleaned, serviced, and synched. The mech told me my main jets was to big and put smaller ones in as well as cleaning the carbs and balancing it. Since then it started with this porblem. But I don't know if maybe it was like this before I sent it to him beacause I clould never get up to 5th or 6th gear before the bike flooded and wouldn't run anymore.

If I am running lean what can I do to fix this? Install bigger main jets?

Thanx

wyntrblue · « **Reply #3 on:** September 20, 2006, 12:11:26 PM »

is your bike a VVT bike? coz i found i had a very similar problem when the oil got a bit low......

andrewsw · « **Reply #4 on:** September 20, 2006, 12:41:11 PM »

what is your carb setup?

main jet size
needle position (and type-Factory pro, dynojet, other?)

sounds to me like you're still rich on the main jet, but the numbers would help.

devilears · « **Reply #5 on:** September 20, 2006, 01:21:30 PM »

Yes it is the VV model but the oil is full. Does the viscosity rating of the oil make a difference on these engines?

As far as I know the main jet is supposed to be the standard one according to the mechanic that last worked on the bike but I'm not sure. How does one measure the size of the main jet and how can I find out what the needle position is? I will try to find out and get back to you with this info.

devilears · « **Reply #6 on:** September 20, 2006, 01:41:04 PM »

Andrewsw, after I searched a bit saw that you had a similar problem a while back with your bike. What did you do to correct this?

andrewsw · « **Reply #7 on:** September 20, 2006, 10:55:43 PM »

well, my problem was actually quite different in that it was running fine, just not producing much power above 10K rpm in 5th and 6th gear. That was a horsepower problem -- my main was too small and just wouldn't pull anymore.

My problem was solved by going from a 97.5 main to a 105 main. I may still go up to a 107.5 as I was getting some popping today when under hard deceleration down from the redline. Didn't get to check my top end yet, but she was pulling real good still at 100. Also, I synched up the float levels, which were a little off, and I replaced the emulsion tubes, which were worn. now she's SWEET!

To check the main jet size, you have to pull the carbs, drain the float bowls, take them off and look at the jet (brass thing in the middle). It will have a number on it. Check the factory specs (in the service manual) for the stock jet size and compare to what you've got. They move, afaik, in sizes by 2.5 increments with a bigger number being a bigger opening and more gas!! woot!

To check the needle position, pull the top caps off the carbs (watch those little o-rings!!!) and pop the slides out, pull the needles from the slides and look at them. If they have more than one groove to hold the clip, they are aftermarket needles (one groove is stock). Count the clip position from the top and that gives you the needle position.

I would guess that with a full yosh pipe, you should go up 1 or 2 jet sizes on the main and MAY have to adjust the needles as well. Higher numbers for needle setting are richer, lower numbers are leaner. If you have a stock carb setup then you are most likely running lean, but in my experience, stumbling is more of a rich problem than a lean problem. ymmv.

the best way I know to check main jet size is do some top end runs (be safe!) and use the jet that provides the highest top speed, in otherwise similar conditions (same road, same weather etc). When you've got the jet right, it will be the fastest, go up one too many and she'll slow down again.

you should read this: http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html
its hugely helpful. As is the whole factory pro site. check it out.

devilears · « **Reply #8 on:** September 21, 2006, 08:28:52 AM »

OK, as far as I can gather the needles are still the standard ones because they don't have more than one setting for the clip. Also it looks like the main jets are 100. I've checked in the service manual and according to that the main jets should be 100 or 102.5

Any ideas?

Thief400 · « **Reply #9 on:** September 21, 2006, 08:41:47 AM »

WAY bigger on the main jets

devilears · « **Reply #10 on:** September 21, 2006, 08:59:22 AM »

Now I am totally confused. My bike is a 95 vv model, but it doesn`t have the original engine in it anymore, the previous owner swapped engines so I don't know which year model the engine is from. So i checked the manual for the 97 vv model and according to this the main jet should be 90. Now I'm wondering if all the vv models came out with a 90 main jet, if this is the case the 100 main jet i've got at the moment might be causing my bike to run rich?

Is there anybody else that can maybe tell me what the main jet sizes for other years of the vv engine was? I think this could maybe clear up my problem, hopefully!

andrewsw · « **Reply #11 on:** September 21, 2006, 12:19:08 PM »

I think there are some serial number threads that might tell youwhat engine you have. it may be in the manuals too.

You definitely need to gather some more info, if for no other reason than so that you know.

Meanwhile, what size jets are you running now? really, the stock size doesn't matter as you need to move up due to that pipe. It would be nice to know what stock is just so you can have a starting point, but its all by feel anyway.

devilears · « **Reply #12 on:** September 21, 2006, 12:36:27 PM »

Well, as far as my current main jet I think that is a 100, took one of the float bowls off and cheched it. The only writing on it that I could find was 100. If the stock is a 90 it might well be that I am running rich.

And as for the engine serial number I have searched everywhere on the net but can't find anything. I found a lot of websites that can give the year model by the frame number but none that can give me the year of the engine.

If anybody has any info on this it might help, all suggestions are welcome.

andrewsw · « **Reply #13 on:** September 21, 2006, 12:49:56 PM »

maybe just call the dealer and have them look up the engine number? maybe. they could then tell you the stock jet size as well.

devilears · « **Reply #14 on:** September 21, 2006, 04:48:14 PM »

I e-mailed the dealers now. If they don't reply I`ll have to phone them. Hopefully they can give me some info.

I also tried something else today suggested in some of the other topics, I taped a part of my intake in the airbox to see whether this makes things better or worse and went for a ride. It definitely made things a lot worse. Tomorrow I`ll try taking the air filter out and take it for a quick spin to see what this does. But at this moment everything is pointing to a rich mixture. Will see what happens tomorrow.

Thanks