Once running the bike performs well, no signs of loss of power and starts normally the same day.

The problem I have is that after about a week, I turn on the fuel, wait a few seconds for anything to fill, put it on full choke, it has to be cranked repeatedly about 10 seconds a time, for about 5 times. Is this normal ?
When it does start it picks up after a few seconds and sounds normal for the rest of the warm-up phase.

It feels as though the carbs had no fuel and had to be filled by cranking the engine to signal the pump relay to run the pump.
I don't know if my assumption is valid.
I have considered putting a priming push button switch to bye pass the relay to "Prime" the carbs before cranking to start if this is the case.
My concern is that there is a lot of extra wear and tear on the starting system and battery because of this.

The bike is a genuine 21k miles, very original and well cared for. I've got the fairings off at the moment just to give everything a good clean and preservation, ready for some summer riding.

Thanks for any help, experiences or opinions.

Kind regards Dennis

 

It sounds like you might have a slight vacuum leak somewhere which is essentially de-pressuring the fuel system when left for a while hence the need to keep cranking, definitely not right. You could try to squirt some easy start around the pipes / intakes to see if that makes a difference and might point to where you have the problem (could also be a slight tear in one of the diaphragms).
You could also crack the fuel drain on each carb after it has been sat for a while to make sure they still have fuel in them.

 

Thanks for your helpful reply Al.
I am keen to give it all a thorough check.
When you say vacuum leak and de-pressurizing I am not certain what to look for. If you could explain a bit more for me please ?

Thanks Den

 

Look at the pipes around the carbs for any signs of tearing or cracking as they do become brittle with age.

 

Thanks for the info Al

I have been doing detailed checks of all the aspects of any air/vacuum leaks - all good. The way she runs once started is good. I did the following to narrow down the problem:-

1. bye-passed the fuel cut off relay - temp wired pump direct to ignition feed. Instant result - the pump ran strongly and the fuel level in the Temp fuel supply tank dropped instantly by 6mm, indicating that little or no fuel in carbs before. Engaged full choke and pressed the starter button - instant starting.

2. Concluded that the fuel is evaporating while the bike is standing for longer periods - there is no battery feed to run the pump until you crank the engine over - and even then the pump pulses slowly and delivers a smaller amount because it is only rotating at cranking speed - hence cranking for so long.

3. My remedy has been (A) to design a separate ignition fed Bye-pass circuit operated by push button that will allow me to "Prime" the carbs before starting and (B) For long period storage - to incorporate a pump cut off switch which will allow me to turn off the pump and fuel tap and run the engine until the carbs are empty. This will avoid fuel going stale in the carbs over winter.
All done now and ready for the biking season.

Thanks for your help and I would be interested to find what experiences you have had with yours ?

Cheers Dennis

 

Great to see that you have found a workaround to your issue, however it is a workaround. You must have a small air or fuel leak that is causing the carb bowls to empty.
The system is designed to hold sufficient fuel in the bowls to start the bike which then gets topped up by the fuel pump.
You should not need the workaround if everything is functioning normally.
The bike should even start and run with a direct feed from an aux tank completely bypassing the fuel pump, indeed the F1 did not even have a fuel pump and was just gravity fed.
Have you had the carbs of and given them a very thorough clean as I'm still sure it is a carb / hose issue.

 

Thanks again for your reply Al,
I will have a second check to see if I can detect any signs of fuel seepage from hoses during standing.
I haven't had the carbs off because they were all checked and balanced by a specialist just before I purchased (seen video of him doing it.) Its also likely that I let it stand more like 2 + weeks in a fairly warm garage which would cause more evaporation. This would have the same effect as low float levels which would make difficult cold starting.

How is yours ?

 

I current have an Old 1999 CB500 that was my old mans that is mechanically sound (ish) but cosmetically challenged and one of the last F4i's which I imported from the US when I can back from working over there in 2017. Both are running well although my CBR does need the fork seals doing as the L/H fork is weeping a bit.

 

Two nice bikes Al and I think they will become sought after in the near future and well worth holding on to. The CBR's generally seem to be a well respected bike and well engineered. I am am just going to enjoy mine sensibly and keep it in good fettle.

Hope to hear more from you and more Brits on the forum.

Best regards

Dennis

 

Just to add to my comment at Paragraph 3 of my Mod above.

Observations of behavior
1. I checked the actual voltage being delivered to the fuel pump when the engine is running, this is shown as 8.5v (fed out from the Cut Off Relay feed wire going to the pump) shown on a basic test meter. The same test carried out when cranking a cold engine before it starts shows 5.7v. (The lower voltage could be, lower batterey voltage when starter is in operation, and/or slower pulses from the HT coil)
2. The pump pulsed very slowly at 5.7 volts so this would cause the solenoid and spring return on the diaphragm to be sluggish and slow. This in itself will cause prolonged cranking to fill 4 carbs.
3. At 8.5 volts the pump pulses in a controlled and calm manner, pumping as needed.
4. My Prime Switch mod of course delivered full battery voltage 12v+, on partially emptied carbs you can hear the fast, loud and strong pumping action, which reduces to a quiet "tick" once the carbs are full. At that point the "momentary Press switch" is released. Activate the starter press button and the engine starts immediately on full carbs.

The engine performs well and shows no signs of fuel starvation when running.

FWIW In my opinion.
In summary I would say that a continuous full, unregulated voltage 12v+ would likely cause pump damage after a while. The 8.5v seems to be the comfort zone for the pump and at this performs as it should, and is likely the correct output from the ORIGINAL relay unit.

Although not needed, I purchase a cheap £9 spare relay as a standby (china manufactured). I tested it on arrival and it actually does NOT regulate the voltage to the pump. This means it would push 14/15v into the pump on starting due to the high output from the alternator. It only acts as an On/Off switch.

I am well satisfied with the outcome and hope the info may help someone.

Regards Den