Hyper vtec spec II issue

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Tarlowb
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Bike owned: CB400SF Hyper VTEC Spec II
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Hyper vtec spec II issue

Post by Tarlowb » Sun Apr 02, 2017 11:53 am

Owning this beauty for 6 months has been great, done a few little jobs to tidy it up which I will work on doing a list of the changes, but it's basically flushed brake lines, coolant change, replace brake caliper bolts to stainless etc.

However three times in the last two months I have been riding along for at least an hour, in top gear at around 60-70mph and suddenly It starts bogging down, isn't too bad if throttle is held open a quarter turn, but any more, it's struggling, had to pull over sharpish! :(

All times I have had one bar of fuel on the display, but as soon as I have pulled over and turned it off, restarted it, it runs fine? Very odd.

Kindly Royster81 advised me to check the Sidestand cut out switch and the clutch switch but apart from being a little grubby, I cleaned them and it still happened. I'm not very mechanical, but it sounded to me like it was bogging down which I presume is carb related, and the engine note changed, might have been running on two cylinders which I feel may be something to do with the ht leads/spark plugs as I think the work in pairs?

Could anyone help? Im not sure how to proceed, I'll give anything a go to fix it but I don't want to make anything worse!

Thanks for reading!

Tarlowb
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Re: Hyper vtec spec II issue

Post by Tarlowb » Sun Apr 02, 2017 11:55 am


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JZH
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Re: Hyper vtec spec II issue

Post by JZH » Sun Apr 02, 2017 12:31 pm

Nice looking bike. Silver... (They all seem to be silver!)

Tank breather line pinched?

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JZH

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www.vsource.org

Tarlowb
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Re: Hyper vtec spec II issue

Post by Tarlowb » Sun Apr 02, 2017 11:42 pm

Thank you! I have checked both of the tubes connected to the rear of the fuel tank and they are unpinched, and I can also blow into them no problem so they are not blocked *head scratches*

I added some of the red fuel cleaner stuff with a fresh tank, and Rode for a few hours today and it didn't happen, hopefully that's sorted it

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craigs23
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Re: Hyper vtec spec II issue

Post by craigs23 » Tue Apr 11, 2017 7:38 pm

I had a similar issue once upon a time on a stock Super4. It ended up being linked the the speedo restrictor - the 180kph limiter was kicking in around 60mph for some reason. Bypassing it with a resistor cured the issue (pardon my electrical numptiness, Dad did the wiring that day!).

Tarlowb
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Re: Hyper vtec spec II issue

Post by Tarlowb » Tue Apr 18, 2017 12:22 pm

Thanks for the reply Craig, I'm not sure how exactly it has been converted, but my speedo goes up to 180 and would appear to be the KPH clocks, however someone has covered the KPH and there is now a MPH sticker on the inside of the clocks. I presume it was done when sold new, I will have to look inside and see if the resistor mod has been done, there's no little blue box visible externally!

The result is that when in top gear on a long straight (private of course) road, its just north of 110 on the gauge. I have heard this completely bypasses the stock restrictor, as if it was still reading in mph it would be round the gauge at 180.

have to admit its a little odd looking down in top gear at redline and having the speedo at just over half its written capacity :|

Tarlowb
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Re: Hyper vtec spec II issue

Post by Tarlowb » Mon May 01, 2017 7:38 pm

Alright, I have identified the source of the issue, seems a little silly but I'm posting in case anyone else has this symptom and searchs.

Since I had taken the tank on and off a few times, disconnecting the fuel sender cable, two breathers at the back, and both the fuel hose and the vacuum hose, the ends were starting to show wear.

After showing Royster81 the photo he immediately said to sort it out as if might not be making a good enough seal. So I snipped the end off with wire cutters and it gave a fresh new edge to seal to the fuel tap. Problem solved!ImageImage

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Tarlowb
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Re: Hyper vtec spec II issue

Post by Tarlowb » Mon Feb 12, 2018 4:59 pm

ok

This seems even more silly now, so apologies further! the bike has got a powertech end can on which is allowing the bike to breathe better. this is causing it to run out of fuel in the carb bowls at WOT in top gear. this issue has nothing to do with the seal of the rubber hose I trimmed (I'm sure that will help but whatever)

The solution will be to simply go up one size on the main jet and see how it goes when I get the engine back (unfortunately the bike has broken 6th gear and is being repaired which is a separate issue) Royster81 has the spec 1 bike with the same end can and has had no issues.

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Re: Hyper vtec spec II issue

Post by CB1pod70 » Tue Mar 13, 2018 3:19 pm

If the carbs are running out of fuel at WOT, it could be a failing fuel pump or clogged fuel filter which is causing the problem. Might be worth checking them out.

Tarlowb
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Re: Hyper vtec spec II issue

Post by Tarlowb » Tue Apr 10, 2018 1:04 pm

CB1pod70 wrote:
Tue Mar 13, 2018 3:19 pm
If the carbs are running out of fuel at WOT, it could be a failing fuel pump or clogged fuel filter which is causing the problem. Might be worth checking them out.
Thanks for the reply, the NC39 doesn't have a fuel pump, didn't say earlier, but as part of my troubleshooting I took the tank off, drained the fuel and unscrewed the fuel tap from the tank, pulled out the fuel filter, it was starting to yellow but was all clear of debris. :) appreciate the suggestion!


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