Carby primary and secondary throttle valve operation

[dom14]

Hi Guys,

Below are the photos & videos of RB30 Nikki carby throttle valve operation, taken from the bottom
of the carby while it's outside.

Does the primary throttle valve look ok?
It looks like it doesn't shut completely & sort of leaves a gap in the bore where the air can sort of leak through.

The valve moves freely and doesn't sort of "stick", but I wonder what we see in below pictures and videos can be thought as a slightly sticking valve?!

Larger valve with vacuum diaphragm attached to it is the secondary.
Smaller one is the primary.

Primary valve operation video.

https://www.youtube.com/watch?v=S3kQdI5B6gY&feature=youtu.be

Secondary(& primary) valve operation video.

https://www.youtube.com/watch?v=RAXwheJ3mUU&feature=youtu.be

I'm sort of happy with the secondary valve operation(mechanical movement and closing), but I can't say the same thing about the primary one though.

I would appreciate few opinions/advice from guys who know about this better.

Thanx in advance guys.

P.S. I posted the pictures on below posts. My issue is the above carby's running too rich on idling(cold or warm).

[dom14]

Primary valve

[dom14]

Secondary valve

[Throbbinhood]

My primary doesn't shut completely either. If you closed it completely though, there'd be no air at idle, no?

[dom14]

My primary doesn't shut completely either. If you closed it completely though, there'd be no air at idle, no?

Yes, of course mate.
I was wondering whether it's allowing bit too much 'cos during the cold start, the choke doesn't shut completely but stays open a bit via choke brake(vacuum assisted).
I thought, it's good to post and seek few opinions.
Mine's running rich all the time on idling(the carby in above pictures and videos).
I'm trying to figure out why.
Thanx

[Throbbinhood]

Oh haha, can't help with that. I wound my choke all the way off :P

[mudnut]

Are you dead sure the carby running rich is for an RB30 and not a TB42?

[dom14]

Oh haha, can't help with that. I wound my choke all the way off :P

That should be fine as long as it doesn't cause any cold starting issues, back fires, etc.
It will run bit lean during a cold start, but I guess it should be fine as long as the engine's running without backfires during take off.
Cheers
Dom

[dom14]

Are you dead sure the carby running rich is for an RB30 and not a TB42?

That's the carby the troll came with.
I'm pretty sure it's an RB30 carby 'cos of the way it's setup, but who knows!
Most of the TB42 carbies came with a slightly different looking choke(same thing but minor differences in the casing).
I've gota a dirty looking TB42 carby with me which I haven't even touched yet, but it looks different. Mainly the choke casing.

It has been running good for a good length of time after I rebuilt it back in 2013 with a rebuild kit.
I think(I mean I guess) the problem started after I increased the float level from quarter to half 'cos I was told at the time
(last year) the float level should be half full all the time, as I see from the sight glass.
So, I bent the float "neck"to increase the float level to half bowl.
I had immediate performance improvements after that.
Now, I'm thinking may be it has turned into a perpetual rich running problem for the idle circuit.
I'm about the reduce the float level a bit & see how it goes.
I don't have a AFR gauge yet, but a Gunson Colortune plug.
According to the sight glass view of the Gunson plug, it's running badly rich on idling and improves when the throttle is applied.
So, my main aim at this stage to get the idle circuit to function properly.
If there're any half and full throttle AFR mixture issues, I can start dealing with that once I receive the AFR gauge kit and install it.

For the time being, I have to get this carby issue sorted out.
It builds up soot within seconds, so it's running pretty rich, and can't be a jetting issue since it's the idle circuit( if I get it correctly).

Basically my issue right now is..

1)Original carby the troll came with is running way way too rich on idling and I still haven't found a way to fix it.

2)The spare carby is running way way too lean on idling and I still haven't found a way to fix that either. And it idles too high
which to me indicates it's actually not idling, but jetting has partially kicked in via slightly open primary throttle.


But, for a start, I must get the original rich running carby issues sorted.
I'm just about the reduce the float and fit it back and see how it goes.

Let me know your thoughts, and tips etc.
Any speculations, wild thoughts, etc are welcome at this stage, 'cos I ain't buying another carby. :D
I'm fixing at least one of the carby to run the way it's suppose to run. :)

[dom14]

Are you dead sure the carby running rich is for an RB30 and not a TB42?

I know, it looks like I'm asking too much when I wanna run both carbies "perfectly" for the same ignition timing & fuel pressure.
So, I've downgraded my expectations to get one carby to run properly for the set fuel pressure & ignition timing.
I'll worry about the other one later.

I prefer the original carby(the one's running rich), 'cos it's the one I put a brand new rebuild kit through and gave lot of TLC through my cleaning and rebuilding and maintenance of it.
If I can get that one running good, then that's enough for me.

[Throbbinhood]

That should be fine as long as it doesn't cause any cold starting issues, back fires, etc.
It will run bit lean during a cold start, but I guess it should be fine as long as the engine's running without backfires during take off.
Cheers
Dom

It's not a daily, I've got the luxury of letting it sit there idling for a few minutes whilst it warms up. Even after camping in the snow, only takes a couple of minutes to warm up and she's good.

[mudnut]

I must admit, I take any carby with issues to the Dyno guy or in the case of ride on mowers the small engine bloke. After the Dyno guy cleaned the carby and put a kit through it, I gained a few ponies and got almost a litre less per 100 ks economy.

[dom14]

It's not a daily, I've got the luxury of letting it sit there idling for a few minutes whilst it warms up. Even after camping in the snow, only takes a couple of minutes to warm up and she's good.

That 'cos your motor & carby is still in good condition 'cos of the low k's. :)
Carby in mine's bit worn & torn from years of LPG without much maintenance on it.

[dom14]

I must admit, I take any carby with issues to the Dyno guy or in the case of ride on mowers the small engine bloke. After the Dyno guy cleaned the carby and put a kit through it, I gained a few ponies and got almost a litre less per 100 ks economy.

Hmmm... I thought you fix your own carbies!!! :p
And your dyno's there to do the tune up for you! :)
I can't see the value of a professional rebuild, 'cos that money's better spent on a brand new one 'cos the price difference
is not that much.
And then again, the money of the new carby's probably better off spending on an EFI dongle. :)

No argument about one thing though, there's no way we can tune as good as a dyno.
Somebody built a dyno in the backyard using a truck axle and wheels for around 2k or so.
The guy was a builder of performance cars. He didn't have 50k for a dyno, so he built his own with scraps. :)

Mine needs a dyno tune some time soon. It's bit complicated in mine 'cos of dual fuel.
In mine, dyno's gotta do two tuneups. The carby & the mixer.
Then again, without a dual curve ignition module, there's not much a dyno can do to tune ignition properly for both fuel.

[mudnut]

I did fix the second stage butterfly, as the Dyno guy said it was sticking. It required a bit of time and patience to smooth the bore and butterfly down and then refit it it so it didn't stick in any position Apart from that, I find the correct tuning is best handled by someone that knows what they'e doing. Him having an O2 meter makes the whole process easy.

[dom14]

I did fix the second stage butterfly, as the Dyno guy said it was sticking. It required a bit of time and patience to smooth the bore and butterfly down and then refit it it so it didn't stick in any position Apart from that, I find the correct tuning is best handled by someone that knows what they'e doing. Him having an O2 meter makes the whole process easy.

Yeah, I already have a reasonably acceptable alternative to O2 sensor(Gunson plug) & then when I get the AFR, it will be even better.
You're right about doing it by someone that knows what they're doing, and I intend to be that person. :)
It's good to know how to fix carbies at home, 'cos bikes & backyard gadgets still use carbies.
Of course, you can't match with a guy's experience of having had the chance to learn from hundreds of carbies. :)
I'm only interested in RB30 Nikki carby at this stage. Anything more than that, I'm happy to leave that with a pro.

BTW, did you notice the secondary valve sticking or did you take the dyno guys word?
I mean if it was sticking, you should be able to see it sticking while the carby's on the bench, right?!
I'm asking that 'cos my understanding of "sticking" is that it's visual and can see whether the carby's on the engine or on the bench.
If the sticking of valve is bit more trickier than that, like for an example that it only happens intermittently, then I will be lost with my endeavour to diagnose it myself.

[mudnut]

When I first got the vehicle, it took 38 seconds to get to 100 kph. It also carried on terribly when cold. I took it to the dyno guy. We watched as the first couple of runs got a whopping 35 kw. On a subsequent run, the graph momentarily spiked. He reached under carby and pushed on the second stage, and discovered it was sticking. He took the carbie off, showed me what was wrong and put the carbie back on so I could take it home and get it working.

[dom14]

When I first got the vehicle, it took 38 seconds to get to 100 kph. It also carried on terribly when cold. I took it to the dyno guy. We watched as the first couple of runs got a whopping 35 kw. On a subsequent run, the graph momentarily spiked. He reached under carby and pushed on the second stage, and discovered it was sticking. He took the carbie off, showed me what was wrong and put the carbie back on so I could take it home and get it working.

Yep.
All the good reasons for me to get at least one carby to work properly on petrol before I get it to a dyno tuning.
The spare carby was apparently on a turbo machine before it was pulled out, so I reckon it's been through bit of fiddling inside.
So, it's probably not a good idea to invest my time on it, but keep it as a spare.
The original carby is the one I'm focusing on now.
I've been told the needle and seat that comes with the aftermarket rebuild kits aren't always that good.
I might have to polish it up with a bit of toothpaste, and see how it goes.

Cheers

[dom14]

DIY, carby dip cleaning methods that I didn't know about last time.

https://www.youtube.com/watch?v=R1DtY2VwSyY

https://www.youtube.com/watch?v=52UQdUvtvT4

[dom14]

Carby is slightly open as above 'cos the throttle linkage rests on the fast idle cam.
But, I might have to adjust the fast idle cam nut.