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Thommo_400f

400f putter fouling

17 posts in this topic

Tried various needle positions

New plugs

Tps adjusted/unplugged

With a new plug I can ride for 1 min with minor stutter and then it slowly gets worse.

If I run wot then I can run clean but if I back off it slowly gets worse again.

Is it possible I have a head gasket leak causing a misfire and subsequent foul ?

Getting desperate now :(

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Sounding like it might be electrical to me.

But be sure your jetting is correct: moving the needle up and down is only moving one area, the carbs on these bikes are quite finicky, especially the older ones.

What are the complete symptoms, what lead up to it (sudden, slowly got worse, etc.), what a have you done recently to the bike, how modded is it and what all have you done to attempt to fix it?

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We need more info. Are you saying that you actually foul a plug? Or is the stutter just annoying?

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'99 400f

Stock jetting

fuel screw 1 3/8 (per manual)

Stain tune exhaust

Airbox open

Tested electrics, coil, tps, plug lead and all resistance in spec.

Carb removed to clean AP

AP now really good.

Install new plug

Ride for a few minutes with minor stutter at 1/3 -2/3

Then stuttering and really bad miss gets continually worse unless I go WOT and then it's a bit better for 20 seconds.

The plug ends up severely carbon fouled.

Really sooty.

Which would indicate rich. So tried leaning needle up 1 then 2 clips but same symptoms and it starts popping on decel as well.

Only suspect head gasket because I had a 2 stroke do it.

I do get a faint burnt coolant smell when I stop and idle occasionally.

I'm going to get a new header pipe gasket and mid-pipe gasket today to make sure the exhaust isn't the issue.

Edited by Thommo_400f

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Well I think I have found my problem.

When I first cleaned the ap circuit I noticed that the needle valve pin was stuck. So I freed it up and it seemed good.

BUT

Being the noob that I am just put it all back together.

I FORGOT to re-set the float height.

I just checked it ( after 2 months of jetting attempts) and it was 4mm out!!!!

No wonder it kept sputtering at 1/2 throttle, there wasn't enough fuel in the bowl!

Heres hoping my problem now goes away ;)

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Well I give up !! :( :(

Tried everything.

Reset carb to factory spec.

Tried leaning out and going rich.

Always same result.

Sputtering that gets worse.

Can idle or run flat out but nothing in between.

Plug always fouled after each ride.

Time for sending it to the shop. F#%^ it !!!

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Sorry we weren't able to help. Let us know what the shop finds out, so that we can learn too! Lets hope they don't hose ya!!

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I'm starting to think I might have a top end / ring issue.

It's fouling too fast to be a fuel issue.

I'm trying a hotter plug ( CR7EK - love the twin electrodes , helps a lot ) to get me through the weekend and then off to the shop.

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Hello,

I was having similar issues with plugs fouling, but mine fouled so bad the bike couldn't run. Turns out that my cylinder/piston were worn and I was oil fouling the plugs, even though it didn't appear a "sticky" black residue on the plug. Replaced them (new OEM piston and cylinder replated) and the issue was solved.

-Alex

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Well.... I gave up....Bike is in the shop for some "Professional" diagnosis.

I'm hoping it's just the needle/emulsion tube being too worn to tune, or maybe the ignition coil / Stator.

Really hope it's not the Top End.

Oh well, it's only money :cry:

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It's FIXED.

Can't believe it..... I really had no chance of fixing it.

Turns out the previous owner had drilled out the main jet because the Acc Pump wasn't working... it was like having a 300 main!

No wonder I was fouling plugs!

Time for a good ride without carrying 4 plugs :)

Thanks to everyone who tried to help me.

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Couldn't believe it.

Problem returned only after another few minutes of riding.

So I went back to where it all started .. The Accelerator Pump.

I checked it hanging on the bike by the throttle cables, and every time I moved the throttle, even a little bit, it squirted a good stream.

So that's what has been making it so rich.

I disconnected the pushrod on the AP and the bike runs well...... Soooooo

I assume there is a blocked leak circuit to catch slow twists of the throttle, but not a major twist to wide open???

question being where is it?

Mine is the '99 fcr so it doesn't have a Leak jet, but there must be some mechanism to stop flooding?

Any help would be appreciated.

Cheers

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Should be an AP timing thread in the Stickys, that's a good place to start.

***Edit: it's called "The Bog"

Edited by miweber929

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I've read through "The Bog", but unfortunately it's aimed at newer version carbs than mine ('99).

My carb doesn't have a "Leak Jet", so I was wondering if there is a similar cicuit in my carb or it is a one-way deal like a non-return valve?

Love to see a schematic of my carbs AP circuit. Mainly the passage into the AP from the bowl and if there is a leak circuit or if it is just meant to flow back into the bowl with a slow twist vs a strong twist.

At the moment even with the gentlest twist I get a solid stream into the carb which is essentially flooding it and fouling the plug.

Cheers.

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I've read through "The Bog", but unfortunately it's aimed at newer version carbs than mine ('99).

My carb doesn't have a "Leak Jet", so I was wondering if there is a similar cicuit in my carb or it is a one-way deal like a non-return valve?

Love to see a schematic of my carbs AP circuit. Mainly the passage into the AP from the bowl and if there is a leak circuit or if it is just meant to flow back into the bowl with a slow twist vs a strong twist.

At the moment even with the gentlest twist I get a solid stream into the carb which is essentially flooding it and fouling the plug.

Cheers.

The second post in the Bog thread is directly to the 98 and 99 carbs vs. the newer ones in the first post.

Seriously, do some searching as well specifically for the 98 carb, I know others have bad this problem and there was some help given.

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