Bike problems!

[tokkela12]

Hi guys. I really hopr you guys can help me! I'm busy with a FJ1200 built. I have some questions as this is my first time working on a bike with 4 carbs. Question 1: does the mikuni vacuum carbs need a air box? Will cone filters work better? Question 2: Should there be air pressed back through the carbs will runnig or is it the timing?

[movenon]

Reading this might help.  http://www.fjowners.com/index.php?topic=1041.msg7676#msg7676.  The third post will answer part of your question.
A LOT of us run UniPods with no problems. The K&N's are not in to much favor here.  Also if you use an aftermarket filter make sure the rubber boots do not block or disrupt the air passage way feeding the diaphragms.  Disrupting or blocking that air flow is one reason some of the aftermarket foam filters didn't work very well with CV carbs.  And gave them a bad name.  The UniPods are well proven.
George

[tokkela12]

Thanks for the info! this explains alot! But what about the air that is pressed back through the carbs? Is this normal or is the timing off?

[FJmonkey]

Thanks for the info! this explains alot! But what about the air that is pressed back through the carbs? Is this normal or is the timing off?

A better explanation is required for "the air that is pressed back through the carbs" is needed here.

The air flow is generated by the engine as it consumes both air and fuel. Pulling air through the CV carbs. Do you have a manual of any kind to help? I think that would be a really good start for you.

[tokkela12]

Hey monkey  I have a manual for the bike, and I consult the manual before I do anything, but my problem is, that when the engine is cranked, it pulls the air through the carbs on cylinder 1, but as soon as cylinder 2 pulls air, air is pushed back from cylinder 1 to carbs to air box. According to me, this should not happen because the valves are suppose to be closed at that stage.

The only reason why I think it does this is because of the timing. I had difficulty setting the timing.  So I just want to make sure that this is the reason before I redo the timing again.

[ribbert]

.......I had difficulty setting the timing.  So I just want to make sure that this is the reason before I redo the timing again.

Are you referring to the valve timing (the cam shafts)?

Noel

[tokkela12]

Hi Ribbert, I am indeed referring to the valve timing. Once I have set the exhaust cam and the intake cam to the correct position, the chain is too short to make a solid fit, then I gave some slack on the chain to make it fit. To the chain connecting the two sprockets is not stiff.

[ribbert]

Hi Ribbert, I am indeed referring to the valve timing. Once I have set the exhaust cam and the intake cam to the correct position, the chain is too short to make a solid fit, then I gave some slack on the chain to make it fit. To the chain connecting the two sprockets is not stiff.

I don't quite understand the above description of what you did.

However, when you set the cams on the timing marks, then install the tensioner, the slack that is taken up on the chain rotates the inlet cam a bit. The trick is to anticipate that amount of rotation and allow for it when positioning the cams initially.

Once timed, turn the engine over several times in the direction or rotation and recheck the timing to make sure it is on the marks.

If you cam chain is worn you will not get the marks to line up perfectly in which case use common sense to "balance" out the stretch evenly. The other option is to install the relatively cheap adjustable cam sprockets to fine tune the timing to spec.

Re check the timing with the marks, as per the manual, before you pull anything apart again.

Noel

[movenon]

Remove the plugs.
Remove the left side timing cover and set the bike at TDC.  
Remove the valve cover.  Look at the little holes in the top of the #3 cam caps.  You should see a "divot" timing mark on the cam shaft when looking down into the # 3 cap holes both in and ex. while at TDC.   If all is there you are good on timing.

While doing this I would check all the valve clearances (write them down) and do a compression check.  You might have a leaking valve. Valve or adjustment.

There is some cam overlap causing some reverse flow but it shouldn't be to excessive.  Here is a statement by Randy that hits on that subject.

"The UNI filters are a better application than the K&N filter for one simple reason. Valve overlap and fuel mist washing the oil out of the K&N filter.

The overlap of the FJ engine generates a mist of fuel spraying out of the carbs. This mist then hits the rigid endplate of the K&N filter and the fuel runs down to the bottom. The fuel then dissolves the oil from the filter, making it useless. The cotton media of the K&N filter prior to oiling has a large mesh. The oil is designed to make the cotton expand to trap dirt particles. If the oil is flushed away, the cotton will allow the dirt to pass through.

The UNI filter media has a dual foam design and the fuel cannot penetrate the filter completely allowing the oil on the outer surface of the filter to trap all of the dirt. "

As a note if you are re-timing the cams it is very important to not turn the engine over backwards during the procedure.  And here is a good read on the cam tensioner.  http://www.fjowners.com/index.php?topic=5620.0

Here is a video on checking valve clearances. https://www.youtube.com/watch?v=zCa556ObEi8

George

[copper]

George, great read I think his cam timing is off. the second thing I read this at the end of Randy's installation instructions "And finally...when you have it all installed you need to turn the engine over in reverse using the 22mm hex on the intake camshaft. That allows the chain to slack on the slack side and set the proper tension. If you listen carefully you usually hear 1-2 clicks from the tensioner."

Do you have something different in mind?

[movenon]

You are correct on that last step after it is all back together.  You don't have to rotate it much.

I don't know what his problem is yet.  I was just trying to do the logical (to me) path to troubleshoot the concern and look for answers.

George