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

Hello everyone, I had decided to overhaul the carburetors since my VFR 750 RC24 was not idling well unless I kept the choke open for a while, and it would only start if I gave it some throttle.

I disassemble, work on them and reassemble, and the bike starts: perfect idle. I put it in first gear, release the clutch, and give it some throttle, but the bike dies. I try to start it again, but it doesn't work anymore, and I don't even hear the combustion sound.

I'll list in detail all the operations and doubts:

1. Replaced all 4 intake manifolds with original parts 16211-ML7-000.
2. Ordered a compatible carburetor overhaul kit, realized it's for the RC36, and used only the compatible parts (float bowl gasket, drain screw, idle jet, mixture screw, main jet, float needle). The first time, I had installed a too large main jet (135 instead of the factory 118), thinking it was the problem. I tried both the compatible 115 and the original 118, but the issue of not starting persists.
3. Replaced all the gaskets on the connecting tubes and the O-ring gasket in contact with the air filter box.
4. Cleaned all the carburetors with a compressor, blowing air through the jet housings, and air comes out without any issues.
5. All 4 spark plugs (new) produce a spark, have been cleaned, and are not wet.
6. Replaced the fuel filter and cleaned the fuel pump with compressed air (I see fuel being pulled through the filter during start attempts, and the pump-to-carburetors hose is always full of fuel when I disassemble the carbs).
7. The battery is always fully charged every time I see the voltage drop below 12.20 on the tester.
8. During prolonged starting attempts (max 5-6 seconds with the ignition button pressed), I hear a clicking noise from the starter motor (could it be the relay?), but I believe it's normal (is it?).
9. Mixture screw adjusted to 2 and 1/2 turns, float bowl drain screw tightened.
10. I tried to push-start it twice without success (unfortunately there are no slopes nearby at home). I thought I heard a slight combustion sound during these two attempts, which I don't hear during normal starts.
11. I read that if I loosen the drain screw and gasoline comes out, it means that gas is not getting to the cylinder. When I loosen it, I have quite a bit of gasoline to drain from all 4 float bowls. Is what I read true? If yes, is it possible that the float needle gets stuck? It's the compatible one, but the dimensions are exactly the same as the factory one. I don't think it's the issue because it started the first time, but I'm not sure.

If I think of anything else I'll update the post.
I hope you can help me because I'm going crazy.

 

CCA ( cranking amps ) are the key to the equation…


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I deleted my first post, and it was regarding the battery. When SO MUCH work has been done on such a critical part of the bike, there are SO MANY variables that could cause issues.

But, a bike that can idle should restart pretty easily. Hook up your bike to a car battery, either out of the car or from a non-running car. You should be able to crank more than you describe before your relay just clicks. Sometimes after sitting for a while my VFRs can seem like they are turning over OK but not fire. As soon as I hook up a jumper battery they instantly start.

It doesn't matter if your charger says it's charged or what the volt meter says...

 

Thanks a lot for both the answers.

So to solve this equation, are you also suggesting that I should try jumping a car battery to my bike?

 

Like Captain said … yes but if the battery is attached to a car do not have the car engine running


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Ok then Captain, I'll follow your advice.
I'll keep you updated

 

Please do that …

 

Sure will!

Ok guys, I got the cables. How to proper jump, now? My try is:

1. Car engine off, red cable on red donor battery and on red bike battery
2. Black cable on black donor battery and black on a metal piece of bike
3. Start bike engine as usual by pressing start button

My car is not a diesel, fyi.

Am I missing something? Any more advice?

 

I think you’re good to go


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Correct. You can connect to the negative battery terminal on the bike too.

 

Nothing to do…still won’t start up. What could it be the reason?

 

NOW we are in the realm of all the work you performed.

Was this your first V4 carb rebuild?

Vacuum slides - not installed correctly or damaged.
Circuits in the carb bodies not thoroughly cleaned. - Did you remove the pilot screws and keep track of the tiny washer and o-ring in there?
Carbs not installed properly - not fully seated.

Possibilities are endless.

 

Plug wires are in their correct cylinder?
I mean it’s like Captain said … you are going to have to retrace everything you did…


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Ok, give me just a couple of minutes and I’ll be back with every tracks of my actions

 

Part of the problem in a situation like this is that you can tell us what you did, it doesn't mean it was done right.

Again, was this your first V4 carb rebuild? I have done DOZENS and I still have to be very vigilant in my actions and steps.

 

Ok, here we go.

Yes, I get how to remove them from this YouTube video and how to remove all pieces from this and this video

Don't think this could be the problem because I didn't replace the jet needle or the diaphragm, I just opened them, removed carefully spring and diaphragm and cleaned them with compressed air

I didn't actually cleaned the plastic pipes, but I blowed air through those and air came out without any issues. I could give a try when I get the carburetor out again, but the first time the bike started...not at first try because I didn't tight the drew screw properly and was leaking fuel, but after tight them it started.
I did get track of the pieces of the pilot screw and get them in order as chapter 4-9 of the service manual shows (pilot screw, ring, washer, o-ring), removed the old cracked o-ring and replaced, every four of them. I didn't wrote down the number of turns though. I read somewhere that 2 and 1/2 turn is a good set (maybe on the service manual but I'm not sure).

That's could be something near the problem. I had problems to fit them back in, so I first get the two on the front, then with a flat screwdriver and some of silicone spray made some room in order to fit them. I pressed firmly once every carburetor fits in their insulator. I saw them every time I unmount the carburetors to see if I cracked them, but I'm very gentle with these and so far didn't make any damage. Maybe the silicone spray in the cylinder head?


One thing came to my mind is that I installed o-rings of the "T" shaped pipes that are a little bigger than the factory ones, so I had to squeeze a bit the carburetors together in order to reassemble them. Maybe could be this? But the first time it started, it should be a problem at first try, shouldn't it?

 

Some more:

The main air jet doesn't go all the way in like the slow jet: should it go?
I measured the float level and I had to set just one of them, set it at 7.0-7.1 mm like the others.


I feel like fuel doesn't get into the cylinder but I can't prove this sensation

 

Are the plugs wet?


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Last time I checked they weren't, tomorrow will check again (here in Italy is 11:10 p.m.) but I doubt because the other day I checked multiple times between one start attempt and the other. I even put a little bit of fuel in the spark hole with a syringe but nothing happened (I cleaned and dry the spark plugs after this attempt)

 

Sounds like a fuel delivery problem... get some rest and we can continue tomorrow