Rising revs.

Woodsman · May 04, 2014, 04:12:26 PM

My 87 fj had a slight problem for a while which has got a little worse. Bike starts fine and will idle steady and pulls fine all through the range.
The issue was getting the revs to return to idle, as i changed down coming to a junction the bike would come to a halt and hold around 2k revs. Let the clutch out and put the bike under load and it would return to idle 1100rpm. Have driven it like this for months but putting the bike under load tonight didn't bring the revs back down.
So,is there something sticking in the carb or could it be a clutch problem?
Sean.

theLeopard · May 04, 2014, 07:02:19 PM

this interests me, i'm getting a similar symptom.

the bike idles great (once it's warm) at 1000rpm. pulls through all the gears just fine.

but I have noticed if I get on the throttle, or do some freeway riding, if I idle at a light after that it will idle around 2000rpm for a few minutes.
I had figured this is to how a heartrate rises after heavy exercise, but bikes aren't human bodies so perhaps it's actually something mechanically unhealthy?

winddancer · May 04, 2014, 11:14:01 PM

I had the same problem with my 92 you need to rebuild your carbs you can get the rebuild kit from Randy at http://www.rpmracingca.com/.

Woodsman · May 05, 2014, 04:40:06 AM

I'm sure you are right about having to rebuild the carbs. I also need to do the valve seals.
However i would like to know what is causing the issue prior to pulling the carbs apart.
It's possible to buy all sorts of bits for the carbs,replace them,put them back together,and still have the problem.
Anyone have a reasonable explanation to what might be causing this within the carbs?
Worn needles,diaphrams,o-rings.........................
Sean.

movenon · May 05, 2014, 05:19:51 AM

Binding throttle cable ? Grip binding or rubbing against the throttle cable housing ?
A vacuum leak ?
Choke cable / circuit problem ?

I know that's not much but things to look at. Wish I had more.
George

Woodsman · May 05, 2014, 07:25:46 AM

All those things seem to be fine George. Started from cold choke operates as it should,shut off choke and bike will idle fine.
When the engine heats up the revs will then climb to 2k, like the mixture has changed.
My guess is that extra fuel is slipping in somewhere and causing the change.

What's the story with the valve seals, does the engine have to be dropped out of the frame to get the cylinder head off?
Thanks, Sean.

movenon · May 05, 2014, 09:03:26 AM

Well I guess if it is nothing external then it has to be in the carbs.. Just hoping it might be something simpler to fix. In the carbs I would check the choke plungers, float height etc.

The valve stem seals are something I would rather approach differently but I want to attend a rally the end of the month so I am going to do (or try) to change the seals without removing the head. The smoking now has gotten to the point it looks like a rich two stroke when cold in the morning. I pulled the exhaust pipes off and can see some of the exhaust valves stems. They are leaking down from the lower part of the shafts. There was some discussion last winter about do this and I started making a tool to do it. Yesterday I ordered new seals and started pulling the cams out. Today I will get back into finishing a tool to do the job.

Here is a guide that I am following on the tool. Open the PDF file in the first post.

http://www.fjowners.com/index.php?topic=10862.msg106443#msg106443.

Here is some other information in a thread, you will have to scroll down to the bottom.

http://www.fjowners.com/index.php?topic=10426.105

Here is another thread page worth reading with good information also.

http://www.fjowners.com/index.php?topic=10426.105

George

winddancer · May 05, 2014, 09:44:29 AM

Quote from: Woodsman on May 05, 2014, 04:40:06 AM
I'm sure you are right about having to rebuild the carbs. I also need to do the valve seals.
However i would like to know what is causing the issue prior to pulling the carbs apart.
It's possible to buy all sorts of bits for the carbs,replace them,put them back together,and still have the problem.
Anyone have a reasonable explanation to what might be causing this within the carbs?
Worn needles,diaphrams,o-rings.........................
Sean.

I believe for my it was the o rings but Randy @ RPM can tell you more specific.

Woodsman · May 05, 2014, 02:02:31 PM

Thanks for all the info on the valve job George. Can i assume the head wont come off without dropping the engine?

In relation to my rev issue. I messed around with it today and found the difficulty was holding anything from 1200rpm to 2000rpm on the throttle almost impossible ( no matter how sensitive i was with it ). As the throttle is applied very softly it will surge between this range.
So the problem is in the very initial throttle application and fuel feed.
What controls the fuel in this range and is most likely to wear? The bike has 64k miles.

jscgdunn · May 05, 2014, 02:19:47 PM

I just pulled and replaced the head without pulling the motor on an 84 1100. On the 84 you have to remove the fairing. We also removed the subframe etc.

Jeff

Pat Conlon · May 05, 2014, 04:11:17 PM

I think you have a couple of issues...

First, if the bike starts and idles fine, only to have the idle increase as the bike warms up, indicates to me that the idle mixture screws are set a tad too rich...try leaning the idle mixture out by turning *in* (clockwise) the idle mixture screws in 1/4 turn increments to see if that helps with the hot idle issue.

Second: Poor transisition response indicates dirty pilots, idle circuit, and/or needle jets (aka emulsion tubes)

Time for a cleaning.

Woodsman · May 06, 2014, 03:06:49 PM

Thank you very much gentlemen. I shall endeavour to get the old girl running as it should.
Sean.

giantkiller · May 06, 2014, 06:35:05 PM

I had a problem with mine when I first got it running. I completely rebuilt the cabs with Randy's kits. Put them back on. And once it got warmed up. So went the R's. No matter what I did couldn't get them down. Sprayed starting fluid to check for intake leaks. Nothing. Even tried spraying down with water. ( thought it might drop if it had a leak) still nothing. Took the cabs apart 3 or 4 more times. Still as soon as it warmed up up went the R's. Well Randy had included the intake orings in the carb kits. So even though spraying it didn't do anything. I replaced the intake orings and it went away. Wish I would have replaced them right away... Would have saved me 2 days of frustration.

Woodsman · May 13, 2014, 03:53:35 PM

Tried leaning out the mixture but revs are still kicking up. From the responses here looks as if replacing the intake o rings should cure my problem.
Can anyone tell me which o rings i need?
Sean.

movenon · May 13, 2014, 05:51:25 PM

Quote from: Woodsman on May 13, 2014, 03:53:35 PM
Tried leaning out the mixture but revs are still kicking up. From the responses here looks as if replacing the intake o rings should cure my problem.
Can anyone tell me which o rings i need?
Sean.

They are the larger o rings in this kit. The kit is about the same price as just buying the o rings from Yamaha and you get all the other o rings you might need at a later date. http://www.rpmracingca.com/proddetail.asp?prod=carbkit&cat=24.
George

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