Loss of power @ +-6000rpm

[Live2Ride]

 
Hi guys!
I'm a proud FJ owner for about 5yrs now - on my 2nd FJ1200 '92 model. Love these bikes, but this one has a problem though... In every gear, at about 6000rpm, the motor surges - loosing power - doesn't go over that rev range... It's not restricted. It feels like it could either be something to do with fuel supply or air intake...? Anybody had anything similar...? Would really like to have a "full" FJ again... Can somebody PLEASE help!!! Thnx guys!

[andyb]

Isn't uncommon for them to have a small flat spot around there if you've got a 4-1 pipe.

I'd suggest checking your fuel line routing to start, followed by checking the fuel filter.

If that doesn't fix it, you'll need to take a good look at the jetting I'd imagine.  Did the bike run well as it is before, last year or whenever?  Anything change?

[Live2Ride]

Hi there!
Its not really a little flat spot...it doesn't go over this mark at all... in every gear -
I've got 4 into 2. Was like this from the start... What must I check on the fuel line...? Is it true that the fuel line should be exactly measured off...? What routing should it follow? How can this cause the problem...? (excuse my inquisitivenes...) I live by the coast...what could/should the jet size/settings be?

[fj1289]

MEDIC!!!

THIS GUY HAS LOST HIS KOOKALOO -- THIS COULD BE TREMINAL!!!!!!!!!!!!!!!!!!!!   

You've been riding an FJ that won't go over 6,000 RPM for HOW LONG? 

Late model FJ's are not as critical for fule line routing (or length).  Reason is the early models were very easy to pinch or kink the fuel line if not routed perfectly.  Late models (with fuel pumps) not so bad.

Speaking of fuel pumps -- does yours work?  You should be able to hear it come on for about 5 seconds when you first turn the key to on and the kill switch to run.  If the fuel pump is dead, that could be causing the high RPM issues. 

For starters, check the things Andy mentioned -- make sure the fuel line is not pinched or kinked anywhere.  Check the fuel filter.  Then check the fuel pump. 

Tell us some more about your setup and use:
Stock engine?
Stock carbs?  Jet kit?  Airbox or filter pods?
Stock exhaust?  Slip ons?  Aftermarket 4-2?  (If so, who makes it?!)
How often/far do you ride ?
How long ago since the carbs were cleaned?  Probably time for a good cleaning - and a great time to pick up the carb kit fro David Raforth (slowoldguy on this list) .

DON'T PANIC!  This group here will help you find the missing kookaloo!

[Arnie]

Really sounds like a dud fuel pump to me.  I had similiar symptoms when my pump died.

Cheers,
Arnie

[mst3kguy]

i've never owned anything other than a '92 (two of them), so i can't compare, but it's been my experience that the late model fj's are very temperamental to fuel routing.  per rock, "i'm just sayin'..."

MEDIC!!!

THIS GUY HAS LOST HIS KOOKALOO -- THIS COULD BE TREMINAL!!!!!!!!!!!!!!!!!!!!   

You've been riding an FJ that won't go over 6,000 RPM for HOW LONG? 

Late model FJ's are not as critical for fule line routing (or length).  Reason is the early models were very easy to pinch or kink the fuel line if not routed perfectly.  Late models (with fuel pumps) not so bad.

Speaking of fuel pumps -- does yours work?  You should be able to hear it come on for about 5 seconds when you first turn the key to on and the kill switch to run.  If the fuel pump is dead, that could be causing the high RPM issues. 

For starters, check the things Andy mentioned -- make sure the fuel line is not pinched or kinked anywhere.  Check the fuel filter.  Then check the fuel pump. 

Tell us some more about your setup and use:
Stock engine?
Stock carbs?  Jet kit?  Airbox or filter pods?
Stock exhaust?  Slip ons?  Aftermarket 4-2?  (If so, who makes it?!)
How often/far do you ride ?
How long ago since the carbs were cleaned?  Probably time for a good cleaning - and a great time to pick up the carb kit fro David Raforth (slowoldguy on this list) .

DON'T PANIC!  This group here will help you find the missing kookaloo!

[Live2Ride]

My previous one I had for 2-3 yrs and this one for also 2-3 yrs... Both had 4 into 2 pipes - 1st one had Kerkers - current one has after market hand made slip-ons - stainless steel - but problem was there even when I had the standard pipes on...
Fuel pump does def. work - I know about that thing...
Yes - stock engin, carbs, jets , air box & filter pods (i think...), I ride almost every weekend when the weather's good - about 140kms or so... Carbs were cleaned and set with last service at 15 000 km...now got 20 000kms on...due again...
Don't know what size jets I should run...? So I don't know if I have standard jets...and what they should be down at the coast...?
This site is awesome! Nice to know that there are lots of FJ-lovers out there!
Hope to hear from you soon!

[ren-dog]

Surges at 6K versus runs really fu&*%* rough at 6K versus simply refuses to rev past 6K.
The surge suggests the engine wants to rev but can't;
so that one word - surge - eliminates electrical and valves.
This only leaves two broad areas to concentrate on, in my mind anyway.
Vacuum leaks and fuel delivery.
If it idles OK then chances are its not an obvious vacuum leak.
But there might be holes in your carby diaphrams.
Of course vacuum depends on rings, so do a compression test.

More than likely however it is a fuel starvation issue.
Mixture fine - revs fine - mixture leans out - revs drop off = surge.
I'm no FJ expert but initially I'd be checking:
fuel pump flow,
kinked fuel lines, &
float levels.

Whilst inside the carbies I'd also check:
needle and seats & diaphrams.

But remember to check for vacuum leaks at each cylinder,
because it could be a synchronisation issue.
Some carbies are mixing correctly and others aren't.

Hope that helps.

[jack02]

Don't know what size jets I should run...?

Main jet should be 110. When I got my FJ back in '02,I got it dirt cheap because it refused to pull above 4K without much spluttering and surging,as if cylinders were cutting out completely then chiming back in. Otherwise it was mint! I figured it wouldn't take much to find out what was wrong. It had original exhaust,airbox and filter but when I pulled the carbs down it had 130 mains. I guess it had been fitted with aftermarket exhaust and/or filters at some point but the jets hadn't been returned to stock along with the aforementioned items,for some unfathomable reason. Whatever... installing the correct mains and a good session with the vacuum gauges rectified matters.

[Live2Ride]

Thnx guys! Got few things to work on... Really appreciate the input! Have a gr8 day! Chat soon!

[weymouth399]

If you have a airbox you don't have pods.  Did the bike sit for a while before you bought it? if so
I would check the air box and filter for a restriction (mouse nest). if you have one, simple but it does happen
fuel other than that   (poss vac line to ignition booster is off) I don't know much about them.
  hope this helps Bob

[Mark Olson]

+1 on the mouse nest in the  airbox , my fj had sat a while and became a mouse house. it would run good till about 6k then nose over similar to what your problem is. A good carb clean and eviction took care of it.

[Knuckles]

Hi, I had a similar problem with my 91 FJ. It pulls like a train up to 6600 rpm and only sometimes would it sort of bog down. It felt like it runs only on two cylinders. It does go up in revs but it feels like it has no power. In my bike's case I found that the diaphrams in three of the carbs had small holes in them. I covered the holes temporary and now the bike is scaring me.
I am now waiting for the rubber stuff to paint the diaphrames, but for now it runs Very well.

[andyb]

I should mention that when I got my FJ it had DJ134 main jets in it from some cowboy.  To say it nosed over at 6k is an understatement.  It pulled well enough, but it was pulling like it had 85hp instead of 105 at the wheel.  The symptom that I noticed was that at 6k it came fully off the needle and nosed over, blubbered like an ugly chick getting dumped for the first time, then slowly cleared up and made some power up higher through the revs.  It'd pull the RPM, but was having a difficult time getting through top gear at speed (uh on a closed track, natch)... around 135mph it didn't want to play much anymore.

Went down to a 125 mikuni jet, which is still on the big side, and the blubbering went away and all 105 horses showed up for the party. 

In more practical numbers, my trap speed at the track went from 118 to 124mph (which is an INCREDIBLE difference if you know about dragracing, otherwise take my assurances).  Mileage went from bad to still bad, but it ran like it meant it.  (Mileage for me on the last tank that I tracked prior to tearing it apart was 29mpg... and that was an improvement!)

If you're running an aftermarket exhaust (full pipe) and pod filters, I'd suggest a 122.5 main jet (V&H recommended spec is a 125) if you're not in the mountains.  If your average corrected altitude is over 2000', you will need to reduce that a bit unless you plan on touring in the lower areas or running in coldish weather (under 70F).  This is what a common starting point is for some legends builders using stock displacement, as a reference.  I actually ran 122 vs 125 mains at the dragstrip and saw no appreciable difference at a corrected DA from 500-1500'.  This indicates a couple of things:  The FJ is a lovely, lovely beast to work on, as it tolerates a pretty wide jetting range well (likely because the carbs are slightly undersized), but also that there's not much reason to go over a 125 main with stock carbs.  Do be aware that the FJ is a wasted spark system (2 coils, four cylinders... it fires on the exhaust stroke when there ain't shit to burn), so the plug can potentially get cleaned more than you'd expect. 

Someplace I posted a howto link on reading plugs.  Short version is, unless you're using a magnifrying glass and/or cutting plugs apart to properly view the base section of the ceramic insulator, they're going to look VERY white to the typical eye... and that's a good thing, means you're close.\

God, I'm rambling.  Too much beer.  There's worse problems to have.

[racerman_27410]

according to sources in the know the FJ has a very inefficient combustion chamber and as such responds well to running a little bit lean.

if you go big bore you may not even need to rejet as the bigger pistons (larger pump) draw more fuel thru the jets.

i actually had to drop jet sizes on my keihins

Frank