Help Please NC21 VFR400R Engine Flooding

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Wolffe
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Help Please NC21 VFR400R Engine Flooding

Post by Wolffe » Thu May 03, 2018 2:17 pm

I am starting to run out of ideas on this and I was hoping someone here could help me.

The bike was running fine for ages, this flooding issue only started when my brother forgot there was a disk lock on the back wheel and the bike stalled out, it is always flooding on the first cylinder only always on the first rotation of the engine, the engine tries to turn over but then it is pretty much pop and stop.

I have tried replacing spark plugs, and I have also fitted a refurbished set of carbs (something it needed anyway) but it was still doing it, so I decided to try a new battery and it started, ran perfectly no issues at all, perfect idle no bogging down.

And then after a couple days I come back to the bike and decide before I change the radiator I want to make sure it starts, pop and stop again, the engine has flooded on the first cylinder just like before.

The only thing I can think of is maybe the fuel tank is letting fuel into the carbs while it is sitting and this is causing it to flood? but why is it always on cylinder one? The first day it started doing it I did fill up the tank for the first time.

the bike turns over perfectly fine on starter fluid with no fuel tank or no fuel in the tank.

If any of you gents can help me figure this out I would appreciate it a lot.

I would have given up by now but the old girl has quite a bit of personal value to me and I am quite stubborn.

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CMSMJ1
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Re: Help Please NC21 VFR400R Engine Flooding

Post by CMSMJ1 » Thu May 03, 2018 2:28 pm

your float needle in the carb for no1 might have some shit in it -0 and it is open, allowing for the carb to trickle fuel into no1.

You'll want to test that your tank does not flow when the tap is turned to off as well
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Wolffe
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Re: Help Please NC21 VFR400R Engine Flooding

Post by Wolffe » Thu May 03, 2018 2:30 pm

CMSMJ1 wrote:
Thu May 03, 2018 2:28 pm
your float needle in the carb for no1 might have some shit in it -0 and it is open, allowing for the carb to trickle fuel into no1.

You'll want to test that your tank does not flow when the tap is turned to off as well
I believe the tank is flowing when the tap is turned off and it does not seem to turn to Res either as I can hear fuel in the tank even when the bike thinks it is "empty" and I have never been able to get it to use the fuel in the Reserve tank

I am pretty sure it is not the carbs as its a different set of carbs and it is the same issue as with the old set, and the new set was recently refurbished which is why this is confusing me, but then again how is the engine flooding?

I would also like to point out before i changed the battery at least the engine was flooding again after I had cleared the flood, not sure if it still does it, like I would clear the flood put everything back together, wait for the plugs to dry and then try and turn it over only for it to flood again.

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Re: Help Please NC21 VFR400R Engine Flooding

Post by Neosophist » Fri May 04, 2018 1:59 am

How do you know the engine is flooding? Is the cylinder full of fuel? Plug noticably wet? A wet plug can be caused by weak spark failing to ingnite fuel / duff plug not just carb overflow.

The chances of having 2 sets of carbs with identical failures is not impossible but pretty low.

The float pin in the carb as already been mentioned is what turns on and off fuel to the carb... you don't even need a fuel tap in theory, you can just put a funnel in the fuel pipe and dump fuel into the carbs via that, if the float pins are sealing properly the fuel flow will shut off when the floats are full and the float valve pin seals the fuel inlet.

This is probably the long way to diagnose things but since i'm not there and cannot see the bike its probably the most reliable.

Firstly get the carbs off the bike and get them on a bench somewhere... put a funnel into the fuel inlet pipe and put some fuel in until you can see fuel in the funnel (you probably need to tie the fuel pipe to something to stop it flopping over.

Leave the carbs for 30 minutes and keep an eye out for fuel leaking from the carbs.

If after 30 minutes you don't seen any fuel leaking then your "flooding" issue is not related to the carbs and probably due to a bad spark or bad plug.

If you do see fuel leaking then your issue could still be plug / spark related but you need to fix any leaking carbs first. Overflowing carbs will either be the float itself is sticking (gummed up?) or the float needle valve pin is dirty or worn out and not sealing properly.

Or more rare the float height is way off.

Remove the float bowls and clean out the inside with a lot of carb cleaner and compressed air if avaiable. Remove the floats and the float valve needle pins... the brass insert they go into, be careful with this, a cotton bud is a good fit and can be used to clean the inside up.

Check the float heights on all four carbs are set properly (6.8mm from gasket surface with carbs at a 45 degree angle)

Make sure all floats move up and down without binding and re-assmeble / leak test.

If they pass the leak test then you need to investigate spark.

First test the electrical system... the bike could be over-charging as the reg/recs are known to fail over time.. excess voltage will cause al sorts of running issues, as will bad / corroded earths.

Eliminate the basiscs first.

Try swapping the plugs around between the non running cylinder and another one, if the problem moves the plug is your issue.

That should be enough to get started.
xivlia wrote:i dont go fast on this bike so really do not need a rear brake.. /
vic-vtrvfr wrote:Ask xivlia for help, he's tackled just about every problem u could think of...

Wolffe
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Re: Help Please NC21 VFR400R Engine Flooding

Post by Wolffe » Sat May 05, 2018 6:58 pm

Neosophist wrote:
Fri May 04, 2018 1:59 am
How do you know the engine is flooding? Is the cylinder full of fuel? Plug noticably wet? A wet plug can be caused by weak spark failing to ingnite fuel / duff plug not just carb overflow.

The chances of having 2 sets of carbs with identical failures is not impossible but pretty low.

The float pin in the carb as already been mentioned is what turns on and off fuel to the carb... you don't even need a fuel tap in theory, you can just put a funnel in the fuel pipe and dump fuel into the carbs via that, if the float pins are sealing properly the fuel flow will shut off when the floats are full and the float valve pin seals the fuel inlet.

This is probably the long way to diagnose things but since i'm not there and cannot see the bike its probably the most reliable.

Firstly get the carbs off the bike and get them on a bench somewhere... put a funnel into the fuel inlet pipe and put some fuel in until you can see fuel in the funnel (you probably need to tie the fuel pipe to something to stop it flopping over.

Leave the carbs for 30 minutes and keep an eye out for fuel leaking from the carbs.

If after 30 minutes you don't seen any fuel leaking then your "flooding" issue is not related to the carbs and probably due to a bad spark or bad plug.

If you do see fuel leaking then your issue could still be plug / spark related but you need to fix any leaking carbs first. Overflowing carbs will either be the float itself is sticking (gummed up?) or the float needle valve pin is dirty or worn out and not sealing properly.

Or more rare the float height is way off.

Remove the float bowls and clean out the inside with a lot of carb cleaner and compressed air if avaiable. Remove the floats and the float valve needle pins... the brass insert they go into, be careful with this, a cotton bud is a good fit and can be used to clean the inside up.

Check the float heights on all four carbs are set properly (6.8mm from gasket surface with carbs at a 45 degree angle)

Make sure all floats move up and down without binding and re-assmeble / leak test.

If they pass the leak test then you need to investigate spark.

First test the electrical system... the bike could be over-charging as the reg/recs are known to fail over time.. excess voltage will cause al sorts of running issues, as will bad / corroded earths.

Eliminate the basiscs first.

Try swapping the plugs around between the non running cylinder and another one, if the problem moves the plug is your issue.

That should be enough to get started.
Okay so I did a test on the tank, i found the fuel in "off" does stop fuel from flowing freely but any pressure inside the tank causes fuel to flow, I tested the carbs for leaks and they are not leaking.

I did however find switching my spark plugs around did cause the flood to change to cylinder 3, the end of the plug was also black where as the others were clean (i recently changed these plugs myself) I figure I must have gotten a bad plug perhaps? I have ordered another CR8EH9 to see if that fixes the flooding issue.

I will keep this updated if the problem occurs again.

thank you for the help so far.

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Re: Help Please NC21 VFR400R Engine Flooding

Post by Neosophist » Sun May 06, 2018 8:19 am

Clean the plug up and it should be fine... blow torch the end of it to burn off the carbon and wire brush it.. try not to heat it up too much but should clean up ok.

You could have suffered the stuck float issue.

Soemtimes when rebuilding the carbs the float can get jammed open causing fuel to leak into the cylinder and flood that one out.

A tip is after mounting carbs and switching fuel on is to use a long handle of a scwerdriver (handle end) to tap on all of the float bowls to dislodge any stuck floats.

It sounds like this could have flooded and drowned the plug out and the issue has corrected itself.

The fuel tap is another issue but wont cause the flooding, but the tap should get sorted for peace of mind.
xivlia wrote:i dont go fast on this bike so really do not need a rear brake.. /
vic-vtrvfr wrote:Ask xivlia for help, he's tackled just about every problem u could think of...


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