Honda VFR 750 RC24 '86 doesn't start after carburetors overhaul

Today's updates, the bike started.

I did something that you may not like...
The floats height of carbs #2 and #3 are set at 8mm,
while carbs #1 and #4 are set without any measurements, just with the clear tube test. They are still not perfectly at the ideal line, but now they are less than 5.0mm above (instead of the previous 9.0mm/12.0mm).

I polished the float valve seat housing and cleaned everything with carb cleaner and compressed air through the pipes, then tightened good the float valve seat.

I haven't rebuilt the bike completely for now, I want to observe it for a couple of days by injecting fuel into the filter and fuel pump to see if there are still leaks or other malfunctions.

 

I started the motorcycle, but I noticed that when I turn it off, white smoke comes out from cylinders #1 and #4 (much more from #4), while nothing comes out from #2 and #3. What could it be in your opinion? Unburned gasoline, indicating potential issues with leaks in the respective carburetors? I don't see them as clearly as before, maybe they have decreased but not enough to allow proper functioning. What do you guys think?

edit

in the picture, cylinder #4 after 1 minute of idle

 

now you need to let the bike idle choke off for about 2 minutes then check for heat on all 4 headers, looking for one alot cooler than the others.

 

Guys just a quick info: could you explain me what these holes are? The ones circled in red and blue.

I read that a overfilling carburetor could be that the air is clogged so there’s too much pressure, and I want to check if it is so: are these two holes even related?

thank you

 

I managed to start the bike again, but the same issue persists: initially, it starts wonderfully, until the rpms begin to decrease gradually and eventually shutting off completely and making it impossible to restart. There are always at least 2 cylinders emitting a lot of white smoke while the other two do not, but I noticed that they change (this time it's cylinders 3 and 4).

So I'm able to answer this: it idled for about 5 minutes before stalling as I mentioned above, but all 4 headers were equally hot

 

Disregarding everything else white smoke could be humidity in the fuel, a blown top gasket, a leak in the cooling system or water in the exhaust system. Check cooling water and engine oil appearance and maybe do a compression test.

 

My guess is that one hole is a vent to the float chamber and the other is air intake to the starting circuit - but I am no specialist.

 

I would exclude a blown top gasket, ‘cause last time was the carb #1 and #4 who emitted white smoke, whilst now is #4 and #3.

Another right guess could be humidity in the fuel, since is now a month that my tank is parked in the garage, and now the cold season came

I did a compression test before reinstalling the carbs, and they handle 10psi perfectly.
I will check oil and cooling water level, is there another method to check cooling water leaks, beside level checking?

 

Vapour in the exhaust gasses ;-) Technically the system could be pressure tested but only with the right tools. Check the workshop manual.

 

Oh ok, my exhaust doesn’t flow any
smoke whatsoever, and don’t smell like fuel neither.

 

Did you mean engine cylinder compression test?

 

No, I meant this

 

have you tried bypassing the fuel pump relay as described in the FSM ? do you hear the pump clicking ?

 

yes, I first tried with the carbs filled directly in the T shape tube then through the fuel pump, but it took 3 minutes at least idling perfectly with fuel pump before it stalls.
And neither payed attention to any sound coming from the fuel pump, I'm gonna check on that.
What are you thinking that can involve the pump clicking?

 

do you mean this test?

 

low compression is not a problem here.

 

I think that too, I ain't touched anything but carbs.

 

The fuel pump is an interrupter pump type which will "tick" or "click". The loudness and frequency of which will clue you in to what is happening.

If stopped with the relay bypassed then (once the carbs are full) it should only occasionally click, when idling the timing between those occasional clicks/ticks will decrease (ie the frequency of them will increase). If the fuel is turned off (or it runs out) then it will increase in both volume and frequency. When riding I can tell by sound alone if I've run onto reserve (or run out) from the clicking/ticking of the pump above the engine noise!

If it's silent then it's not pumping. Equally if it's frantically clicking away at idle then it's struggling, maybe the filters are blocked or there are holes in the internal pipes etc.

You should also be able to see the pulsing in the fuel filter as it pumps (some air in there is fine, I know some go to great efforts to purge it but there is no need).

Finally, there is a test in the manual for fuel flow. Pop the hose to the carb off, stick it into a graduated container and bypass the relay for a measured length of time. Measure the quantity and then multiply appropriately to get the amount per minute (eg if you ran it for 5 seconds multiply the volume by 12).

Off the top of my head it should do something like 900cc/minute.

 

Good explanations Fast druid. And correct on the fuel pump flow. The pump also clicks frantically if it is not primed i.e. it is full of air not fuel.

 

Hi everybody, some updates.

The bike is finally (and definitely) alive. The issue was that during the starting attempts, I apparently burned out the spark plugs. After replacing all of them, the bike started like a brand new bike, and I'm no longer experiencing any idle problems or difficulties with cold starts.
I've been driving it for a week now and I'm not experiencing any issues.

Thanks to all of you for the support