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

what would you check first? The fuel pump works just fine.

Another doubt is point 11 of my first message: is it normal the float bowls have a lot of fuel?

 

I would remove the carbs and go through them again. Double check everything... check fuel pump delivery, check fuel filter, check float level and idle circuit.

 

The fuel pump works and the fuel filter is new, I think they’re free to go. I will remove the carbs and check everything again. I found almost everything I need to know about carbs from videos and service manual, but got a few doubts:

1. The main air jet doesn't go all the way in like the slow jet: should I tight it all the way? If it won’t go in it’s because something stops it (maybe dirt or rust)?
2. What could cause to carbs to not send fuel to the cylinder, besides the float needle? Maybe the drain screw is too tight?

 

#1 DO NOT TIGHTEN beyond finger-tight + a very small bit more. no, the threads showing is normal, and additional tightening could ruin the carbs forever. BASTA !

original post # 11: exactly the opposite is true. if gas comes out the fuel is available for sucking into cylinders.

i suggest you remove tank and airbox top so you can see if the vacuum slides all rise to follow throttle increases while engine is running/idling. if not, the diaphragms may be installed incorrectly, having slipped out of their grooves when putting on the cap. use compressed air to blow into the oval-shaped area on carb intake side to check that all slides rise equally.

 

really, thats absurd and misspelled.

 

SM, I don't think English is his first language. I think he's doing OK describing.

But I think we have a first time V4 carb situation here. From a bike that just wouldn't idle great to now a non starter / runner after rebuild.

Time to go back in and perhaps document going back together in steps.

 

I’m sorry, I was tired and didn’t pay attention to what I wrote, I meant the drain screw, does it have to be tightened?

The engine doesn’t start, how can I do this test?

This is something I can do in my current situation. I have manually checked the movement and it doesn’t seem blocked to me, but I will try with compressed air.

 

Thanks Captain.

I think I reported all my steps in this thread.

I didn’t tight the main air jet,
didn’t replace the diaphragm or the jet needle, just cleaned them and checked the movement,
I tried to start the engine with pilot screws tightened (from now on by “tight” I mean “tighten gently until I feel a bit of resistance”) but still doesn’t work.

In your experience, what carburetor failure could cause the engine not to start?

To see if the reason could be “carbs not fully seated”, I “vaped” between the intakes and tried a start to see if smoke would be sucked from them but nothing moved (I don’t know how to test otherwise the proper seat of the carbs).

My main concern is about the idle circuit, since it seems that doesn’t deliver fuel to cylinders. But what to check exactly?

 

I removed the carburetors, I'm gonna double check on them.

Before that I took some videos of the carburetors during starting attempts:

• No choke, no throttle
• No choke, a little bit of throttle
• Full choke, no throttle

I felt air coming from the air chamber, from all the four holes.

In the videos, a bit of gas can be seen coming from the needle (I took just one of them after I checked that all were behaving the same), so the fuel goes in the cylinder, am I supposing right?

 

I blown compressed air and the slides rise only if I get air into this banana-shaped part pointed with the screwdriver. So are the slides ok?

 

yes, slide diaphragms are installed properly but float levels [or float needles] are wildly out of control if any wet fuel comes up around the slide needle.

since the world's best carbs are made in italy {WEBER] you should do some studying. read the book "weber carbs:tuning and maintenance" by john passini to understand how carbs work. i have 2 weber 40DCOE carbs on my '63 alfa giulia spider, and ive done alot of tuning for performance.

 

Will do as soon as I finish to check all the pieces, I want to clean the choke valves and grease them (the only part I didn’t clean).
Since I got the carburetors removed, could you tell me how to check if idle circuit is ok like suggested by sixdog?

 

Blow some carb cleaner through it and make sure the spray comes out the intake side of the carb.... small pilot hole. If it does then some compressed air to make sure .

 

So I have to spray it in the idle jet and make sure it comes out from those little holes where the throttle valve is?
Sorry for silly questions but this is my first time

 

Not a silly question…

Yes … should be a nice strong stream


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Also from the hole where the air mixture screw goes in


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ok sixdog, thanks. I’ll do this test.

During starting attempts I can see some fuel coming from the slide needle (I think it shows in the videos above), so I have to check float needle too?

Cool, thx for the tip

 

Idle circuit is perfect, spray comes out flawlessly from both the little holes in the throttle valve housing and from the mixture screw housing…
Rebuilding again, setting the air mixture screw at 3 and 1/2 turns like squirrelman suggested and gonna try again

 

Are you sure you have a nice clean spark at the plugs ??


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Yes, checked and cleaned all the four of them yesterday: spark is present.