Running terrible at low revs when hot

[Rustyas]

Hi all,

I've just got hold of an 1986 FJ1100. In the main it is a great bike, easy to ride, generally smooth and pretty agile for an old girl.

Ive been lurking for a while now and this seems to be a great site and I look forward to getting involved.

My problem is that as it gets hot, say after 30 - 40 mins of city traffic it begins to run really rough. To the point where it struggles to get of the mark and misses and carries on until it hits around 3K revs then it takes off.

Very frustrating and makes it difficult to ride.

The bike was rebuilt about 2000 klms ago and I bought it of the second owner after the rebuild. my guess is he couldn't fix the problem.

I have had a bit of look through here for some info but cant seem to find a similar issue?

any ideas?

[The General]

Hi all,
I've just got hold of an 1986 FJ1100.
My problem is that as it gets hot, say after 30 - 40 mins of city traffic it begins to run really rough. To the point where it struggles to get of the mark and misses and carries on until it hits around 3K revs then it takes off.

Very frustrating and makes it difficult to ride.

The bike was rebuilt about 2000 klms ago and I bought it of the second owner after the rebuild. my guess is he couldn't fix the problem.
I have had a bit of look through here for some info but cant seem to find a similar issue?
any ideas?

Welcome Rusty. If your in Brisbane it may not be the bike`s fault. Bloody hot here lately! What part of Australia you from?
They do get a bit hot in city traffic, but it`d be a good idea to take a peak under the tank to check the fuel line`s not too close to some hot componentry. Does it run perfect out on the country faster roads?  Spark plugs look okay? Not that it helps ya heat prob but are you sure it`s an 86 model? - Love those ambulance colours! Got some pics? we love pics!

[FJmonkey]

Welcome Rusty, we can always use more Red & White 86's.

[red]

Hi all,
I've just got hold of an 1986 FJ1100. In the main it is a great bike, easy to ride, generally smooth and pretty agile for an old girl.
My problem is that as it gets hot, say after 30 - 40 mins of city traffic it begins to run really rough. To the point where it struggles to get of the mark and misses and carries on until it hits around 3K revs then it takes off.  Very frustrating and makes it difficult to ride.  any ideas? 

Rustyas,

It sounds like the gasoline is boiling (vapor lock), when the bike gets hot in traffic.  You should be able to fix this problem with some insulation.  You can make (or buy) a patch of heavy-duty foil-backed insulation material to fit under the entire gas tank, which will help to keep things cooler.  You can also fold a strip of this insulation around the fuel lines, to keep gas cooler inside the fuel lines.  Office staples will secure this folded insulation strip around the fuel lines, well enough.  At some point, the fuel line has to dive through the large insulation sheet to get to the engine, but you just make a slit in the insulation, for that trick (no need to disconnect any fuel lines).  I do not know what types of insulation materials may be available there, but others here can chime in, with that information.

Start up Google.com then Copy-and-Paste this entire line, as the inquiry:
insulation under tank site:http://www.fjowners.com/

You will see what others here have done with this idea.

Cheers,
Red

[Bminder]

From my experience with gunked up carbs that Randy cleaned for me, I would suggest you pull them and clean your pilot jets.
Mine would do the same thing, run ok at first but as it warmed up more, the below 2000 range was rough, and it wouldn't idle well and eventually die if i didn't give it some throttle to keep it going.
It's not a bad job to pull them and clean the jets. Ask if you need help.
Also, Randy diagnosed that my cams were out of time, and if your engine has been rebuilt, they might not have gotten the cams quite in time, and that will do what you're saying too.
It's not hard to check their timing, and it's not too terrible of a job to get them back in time, just takes patience and a little trial and error.

[Dan Filetti]

It is possible that you have a coil that is going bad.  I had this on my '85, where sitting at a light/ very slow traffic, the engine heat (without sufficient airflow) would begin to affect the coil and it would begin to 'cough'/ miss with greater and greater frequency, until it would stall.  Keeping the RPM's up would prevent it.

Simply putting a timing light on it in the garage showed clearly the issue was a no spark from the coil to the spark-plug.

It's a fast/ easy test and will, at worst, eliminate this from your solution set.

Just a thought.

Dan

[FJ_Hooligan]

A timing light?  Awesome idea, Dan!  I didn't even know they made timing lights anymore.  :-)

[movenon]

A timing light?  Awesome idea, Dan!  I didn't even know they made timing lights anymore.  :-)

Cheap one from Harbor Freight. I picked a real nice almost new Penske one at a yard sale for 1.00. Check out the used tool store in your area also. Lots of them floating around. About as useful with the new cars as a dwell meter...      Nice to have for the old stuff.
George

[Rustyas]

Hi all

Thanks for all the replies and the welcome.

As to the bike, its located in Sydney, and from what I can glean from the replies it could be fuel/vapour/heat issues.

yesterday was bloody hot and by the time I got near home it was playing up temps were high 20s low 30s. This morning the temps were a lot lower and I made sure I kept good clear air flow to the bike and it seemed to have improved dramatically.
I'll see what I can do about insulating the fuel lines etc.

Ill keep you posted

Cheers

Rusty

[movenon]

Just a question. Do you have the factory insulation pad glued to the bottom of your tank ?
George

[Rustyas]

Just a question. Do you have the factory insulation pad glued to the bottom of your tank ?
George

George,
from what I could see there was some there but looks as though most is missing. I'll look for something to replace it.
Im now starting to think the problem could be in the fuel line or the vacuum line from the petcock they are pretty old and may open up when hot.

Cheers

Rusty

[movenon]

Just a question. Do you have the factory insulation pad glued to the bottom of your tank ?
George

George,
from what I could see there was some there but looks as though most is missing. I'll look for something to replace it.
I'm now starting to think the problem could be in the fuel line or the vacuum line from the petcock they are pretty old and may open up when hot.

Cheers

Rusty

OK that's a good start. I would replace the heat shield. Try to get a FJ one if you can. If not perhaps a local wrecker has a bike with a shield you can adapt.
Anything rubber under the tank deserves a good look at. No shortage of heat in that area. I would try to protect the fuel line as much as possable.

George 

[Rustyas]

SORTED!!!  (I Hope)


The small hose, I think it is a vacum hose, that runs from the petcock to the carby was split where it attached to the carby and was causing it to run very lean. Took me ages to find it  as it looked ok until I actually removed it.

There was enough play to allow me to trim the split end and re attach. 

Even in todays heat, in traffic it ran much smoother, not good, but much better.


I am wondering if whilst running lean it may have stuffed the plugs? It still has a miss down low but seems to run ok at 3K revs or more.

Thanks for the help, much appreciated

RustyAs

[movenon]

Glad you are making progress and keeping us informed. There is a good lesson in your finding the crack in the vacuum line. There is a big difference between looking at something and doing a good inspection.
George 

[Rustyas]

After fixing the hose from the pet cock to the carb the bike still runs rough when it gets hot.

From what I an see from other posts and topics, it may be running very rich.

The plugs are all carboned up, all the same

The bike runs ok when cold, as it gets hotter it runs worse

All the hoses are now sorted.

My next plan is to strip down the carbs and check the jet sizes. Any suggestions on how far to go with the resizing? Not sure what's in there at the moment

Cheers