Assuming you can get the engine started and warmed up, does it idle at 1300 rpm with the needle jets at the OEM spec settings.

Can you easily restart the engine went it is warm/hot. No "choke" (fuel enrichment) needs to be applied with a warm/hot engine.

Yes to both questions suggests that the idle fuel circuits are funtioning correctly and the cold start issue can only be related to the fuel enrichment system.

Although I believe it may have been mentioned in an earlier post, is the fuel flow from the tap adequate when starting a cold engine. You could try supplying fuel directly to the carbies to bypass the vacuum operated tap. Perhaps there is insufficient vacuum at cranking rpm to active the tap valve and provide sufficient fuel for the enrichment system when the "choke" is operated with a cold engine.

I can make it run / idle at 1300, hot restarting is not difficult.

Ive been using another fuel supply for my testing though as the bulkiness of the actual fuel tank would get in the way.

Few experiments yesterday;

Engine idling, squirt fuel into the trumpets individually and observing results. Front left cylinder sees an increase in rpm. This also happens if i wet my finger with fuel (or a little even if i don't wet it) and then cover the air jets. All other cylinders seem to lumber when extra fuel is given.

Next experiment. Running the thing dry.

Uprighted the bike and let it run for a bit whilst the float chambers burned away. eventually it started to die and by then adding choke kept the engine alive, At that stage i was able to rev the engine via the choke, Then it got to the stage where it wouldn't run without choke, and then it wouldn't run at all (out of fuel).

So i took the carbs out and checked and set float heights with the carbs inverted, sitting on a bench. Rather than the 45* 'needle valve seated but spring not compressed" recommendation, which i don't believe to be an objective way of measuring at all.. the float heights were all over the place so i set them all to 13mm. Didn't touch pilot screws, but didn't check them either but I'm pretty sure they're still at 1 5/8.

All hooked up and choke still not working, a little choke increases idle a little, and any more labours the engine then kills it. I thought it might be from the bike being warm but these results were repeated when i tried this morning before work also.

Ill keep trying, almost there.

From your last post it appears engine starts and runs as expected when warmed up, with OEM spec needle jet and idle settings. The issue is cold starts where the fuel enrichment system appears not to provide sufficient extra fuel to start the engine, true?

From what I have seen of the jet configuration of the NC35 carby, there is the main jet, a pilot jet and a third jet that I assume to be the fuel enrichment jet/inlet. I only have google pictures as a guide but it seems a logical assumption.

I am sure you will confirm that the enrichment jets, assuming that is what they are, are clear through to the enrichment plunger cavity and the associated air bleed are too.

An interesting factor of this problem is the probability of four enrichment systems being so ineffective at the same time. If looking for a common link, fuel flow into the float bowls and actuation of the enrichment plungers are two that come to mind. But you say fuel flow is uninhibited and I am that you will confirm that all enrichment plungers are being fully extracted by the "choke" mechanism.

the only way I can see this as being a choke issue is if there is an issue with it not emulsifying the choke fuel. as choke is definitely at least letting fuel through. This is evidenced by the fact that when the float bowlsare very low, the choke increases revs, and also by the fact that when cold the bike needs choke to start- it just had to be put away as soon as the bike turns over. I've had the choke plungers and bar out many times to confirm they're clear. I've noticed at this stage the bike seems to sound happier with the pilot screws at 2 turns out. With it revving from idle smoother and without the wet noise from the intake that is present at 1 5/8 . choke still kills the engine like this though.

If the engine runs noticeably smoother with the idle mixture screws wound further out it indicates that the initial setting is too lean. IMHO you need to start by adjusting the idle mixture screws and throttle idle to get a stable 1300 rpm idle with a smooth transition to 1/8 throttle, after the engine has reach normal operating temperature. Then any cold starting issue can be investigated.

As a matter of curiosity, your comment "choke still kills the engine like this though" refers to immediately after the engine fires up from a cold start or are you opening the enrichment circuit (choke) after the engine has been operating for some time? Do the choke plungers have needle points or blunt ends?

Its mentioned on here that on rvf's ,winding the mixture screw out leans out the mixture.

As a matter of curiosity, your comment "choke still kills the engine like this though" refers to immediately after the engine fires up from a cold start or are you opening the enrichment circuit (choke) after the engine has been operating for some time? Do the choke plungers have needle points or blunt ends?

Choke plungers arent damaged, choke feed is not blocked at all, and the fuel pickup for choke sits lower in the bowl than the idle jets do. Choke ALWAYS kills the engine, cold or warm.

Sounds like you can get it running and it hot starts, time to ride it and enjoy it for a while

magg wrote:If the engine runs noticeably smoother with the idle mixture screws wound further out it indicates that the initial setting is too lean. IMHO you need to start by adjusting the idle mixture screws and throttle idle to get a stable 1300 rpm idle with a smooth transition to 1/8 throttle, after the engine has reach normal operating temperature. Then any cold starting issue can be investigated.

As a matter of curiosity, your comment "choke still kills the engine like this though" refers to immediately after the engine fires up from a cold start or are you opening the enrichment circuit (choke) after the engine has been operating for some time? Do the choke plungers have needle points or blunt ends?

RVF carbs are backwards to NC30 carbs.

Winding the screw in richens the mixture, out leans it out.

I was battling carb woes with one of my bikes even after a full soak in cleaner, high pressure air cleaner and full new gasket / oring set they still didnt work right, replaced them with second hand set and its bob on now.

you might have phsyical problem with the carbs.

that being said i havent seen your settings.

please post up what oyu have the settings at / air screws / float heights / jets / emulsion tubes / needles etc

After 6 pages of posts, I'm getting confused on what was done and what the actual problem is, but here's another "suggestion": Can you swap the carbs from a running bike to confirm it is somewhere in the carbs that is causing the problem?

vfrman wrote:After 6 pages of posts, I'm getting confused on what was done and what the actual problem is, but here's another "suggestion": Can you swap the carbs from a running bike to confirm it is somewhere in the carbs that is causing the problem?

I dont have access to another set of carbs at the moment. The problem is the the engine quits when choke is added, whether cold or hot, it sounds like it is smothering the engine as chuffing can be heard from the intake when it is added, as in a noise similar to when you suddenly grap a gob of throttle when the engine is cold and barely idling . Other users here have suggested this to be a rich running issue, as also evidenced by originally (but not so much lately although i have HARDLY ridden the bike lately because this is driving me nuts) having very poor milage (6 to 7L/100km).

As the engine wont run when cold due to metal not expending / cold oil thickness, the idle speed screw must be wound on to have the thing idle from start up, since the rpm cannot be increased with dysfunctional choke. Due to this, later in the ride the idle will be quite high (~3000rpm) if not adjusted back down.

The last part is only relevent if it provides hints to the thing as running rich or lean, My main issue is that the choke kills the engine rather than providing extra rpm for a warm-up-idle.

Neosophist wrote:
Winding the screw in richens the mixture, out leans it out.

I was battling carb woes with one of my bikes even after a full soak in cleaner, high pressure air cleaner and full new gasket / oring set they still didnt work right, replaced them with second hand set and its bob on now.

you might have phsyical problem with the carbs.

that being said i havent seen your settings.

please post up what oyu have the settings at / air screws / float heights / jets / emulsion tubes / needles etc

the carbs are standard except for the 112 jets, and it has a full exhaust to suit.

With that said i have many times confirmed the pilot screw settings were correct, as were the float heights, the float needle seats fine and the pilot screws are not missing any parts.
And to go further i have tried other float height / pilot screw settings.
the valve clearances were recently checked to be within spec, as were the throttle syncing.
The spark plugs were new when this was an issue, and have since been fowled a bunch of times, they seem to clean up alright with a wire brush and mek soak. They dont seem to foul up anymore.
Spark caps are new ngk units with the correct sizing and resistance, mounted onto the standard leads and standard coil.
Regulator rectifier is a chinese unit with a CPU heatsink added, and the RR wiring mod performed, 13.5 -14.7v is available to the battery.
Air filter is new honda unit
Exhaust is full yammamoto system.
Oil is new 10W40 nipone brand.

I agree with you that these carbs are rooted somewhere. This bike has passed hands a few times before getting to me, as evidenced by things like holes being cut in the airbox by a previous owner, then being covered up by a more recent previous owner. There is an internal repair to one of the float valve pin holes (still works fine) and one of the emulsion tubes was in the wrong carb, and one of the pilot screws was missing a washer, replaced by another o ring of equal width.

Although id like to get the thing on a dyno to see what its doing, as the bike gets about 6L/100km and doesnt seem to be particularly down on power, even down low. If i am going to write these carbs off i might as well screw with them a bit;
I was considering for my next experiments: Block the choke jets, the effect of this will be that when choke is added, air from the float chambers will be added to the cylinders, but no extra fuel. If this has no effect on the engine, it means that the current emulsifying air feed for the choke is blocked (it isnt, ive already checked), If this has the effect of increasing rpm, it could mean that the choke feeds fuel flow is way too high for some reason, which could be cured by reducing the blocks in the choke pickups to the point where i have a working choke, or by drilling more emulsion holes in the choke pickup to suit.