Easy one this time (hopefully) :-)

[Patrol'n]

Hey guys, so over the past few months amongst a busy work schedule I have fixed a bunch of stuff and worked on the tuning of my RB30, now my Aircon is cold, my oil pressure gauge works, and I have improved my engines operation. I have almost got the fuel use back down under 20 per hundred too, 20.3 at last fill (down from 24-26) so that's going in the right direction at least, got a new carb, replaced the inlet manifold gasket and sorted another vacuum leak.

At the moment I am finding that sometimes my idle speed comes up like when the choke is on, but I have checked the choke butterfly and the choke appears to be working, in so far as the butterfly is fully open once warm. No matter what I do though, when this happens the idle speed stays at about 12-1400 rpm.

Once or twice when this has happened I disconnected the plug to the carb and the engine stalled, then once I started it again the idle speed went back to the normal 800 I set it at. Based on this I wondered if it is a solenoid?

After I sprayed cleaner in the plug to the carb the problem seemed to go away for a week or so, but yesterday started doing it again, now pulling the plug Does not restore normal idle speed.

Does anyone know what could be causing the high idle speed in this case?

Thanks all.

[Bidja]

No experience with your eng. Comments provided: New carb, Vac good, certainly running rich IMO. RPM will rise above say 800rpm with full choke, 1400 might be a bit high though.
Think I would look at your throttle valve operation may be it is not functioning correctly. If by spraying cleaner fluid around you may temporarily overcome a high resistance issue. Check your solenoid and connection out.

Came across this thread from mudnut, check it out:
http://www.nissanpatrol.com.au/forum...-Helpful-Hints

[mudnut]

I run a manual choke. I found a fast idle knob from a wreck, cut the cable and mated it to a cheap choke cable setup from Autopro. I use that in conjunction with the fast idle knob to bump up the revs a little. I have no issues with the choke, apart from forgetting to release both knobs when the engine is warm.

Have you checked the choke break diaphragm?

[Patrol'n]

Haven't checked the choke break diaphragm but given the carb is effectively only a couple weeks old and it seems that the cleaner in the connector at least temporarily resolves it, I'm leaning towards a high resistance connection at this point.

I'm trying to source a new connector, but can't find a listing anywhere online, so I'm thinking an interestingly priced genuine might be the only choice... Another thought I had was to buy a new Deutsch plug and wire that up instead

[dom14]

I run a manual choke. I found a fast idle knob from a wreck, cut the cable and mated it to a cheap choke cable setup from Autopro. I use that in conjunction with the fast idle knob to bump up the revs a little. I have no issues with the choke, apart from forgetting to release both knobs when the engine is warm.

Have you checked the choke break diaphragm?

I simply tore apart & repaired the auto choke.
Auto choke in the RB30 isn't bullet proof or perfect though.
It responds to the electrical signal via auto choke relay which only get powered by alternator, which is the way it should be.
However, it's entirely electrical and the bimetal coil in it does not respond well to the engine heat or does not respond at all.

Consider the below scenario.

You cold start the engine and run it for five minutes. During that time the auto choke flaps should fully open
as the bimetal coil inside the auto choke unit expands. Now stop the engine and leave it for five minutes.
During this time the fully warmed up engine doesn't cool down back to be stone cold, negating the need for the
choke flaps to be closed so the mixture is rich. The mixture will ignite fine without needing the richness of mixture IMO 'cos
the engine's still warm. However, the bimetal spring can coil back to cold position during that five minutes, effectively making the mixture rich again when you start the engine after five minute break, even though it's not likely a necessity but only burns extra fuel unnecessarily.

There are bimetal spring auto choke out there that really respond to the engine heat and the engine cold running both at the same time, but in my experience RB30 Nikki carby stock auto choke isn't one of them, 'cos I remember when I cranked the warm engine, the choke flaps were closed(apart from the slight opening from the choke breaker) while the engine's bloody warm from previous run.

In that sense, a manual setup as yours can be an advantage, but not so when you forget to release the choke after few minutes.

[dom14]

Haven't checked the choke break diaphragm but given the carb is effectively only a couple weeks old and it seems that the cleaner in the connector at least temporarily resolves it, I'm leaning towards a high resistance connection at this point.

I'm trying to source a new connector, but can't find a listing anywhere online, so I'm thinking an interestingly priced genuine might be the only choice... Another thought I had was to buy a new Deutsch plug and wire that up instead

If the choke flaps are slightly open when cold start the engine(only slightly) then it's quite likely the choke break diaphragm is working properly, or you can apply a slight vacuum to it to see if it affects the choke flaps to be opened slightly, but I probably wouldn't 'cos you can end up damaging these diaphragms by applying too much vacuum.

I am assuming you bought a brand new aftermarket identical carby off ebay.
These carbies come as suitable for both TB42 & RB30. IMHO, they need slight adjustment, tuning for each engine, even though
it is essentially the same carby, and I doubt the selllers do that on behalf of you.
My suggestion is to take it to a dyno & get it tuned properly or get yourself an AFR gauge kit and have it installed and tune it DIY.
Or you can get a Gunson Colortune spark plug and do it that way. I have both.
Adjusting the mixture without AFR or at least a Gunson plug is a bad idea for inexperienced DIY'ers like us IMHO.

In a nutshell, don't count the factory mixture settings that came with your new carby is ideal for your particular RB30.
Even for different RB30 engine's the carby AFR need to slightly adjusted for the engine to run smoothly.
This is why carby rebuilders generally prefer to have your vehicle with them, so they can tune it while fitted to the engine.

As for how all the above apply to your intermittent high idle issue is that such carby quirks can be very much related to other engine quirks.

It is even possible the primary or secondary throttle valves are malfunctioning regardless of the carby being brand new. You can find this by observing the throttle valve(s) from top of the carby while idling/revving the engine. Of course, I would wear safety glasses. You might need to stand on a chair unless you're seven foot tall.

[dom14]

Haven't checked the choke break diaphragm but given the carb is effectively only a couple weeks old and it seems that the cleaner in the connector at least temporarily resolves it, I'm leaning towards a high resistance connection at this point.

I'm trying to source a new connector, but can't find a listing anywhere online, so I'm thinking an interestingly priced genuine might be the only choice... Another thought I had was to buy a new Deutsch plug and wire that up instead

I'm not sure which connector your'e referring to above, but a picture of that connector along with your new carby would be good.
AFAIK, these aftermarket Nikki identical carbies don't come with a sight glass to see the float level. If that's the case, I would advice you do swap over the one from the old one into the new one, so you can see the float level and adjust it to suit your particular engine.

[dom14]

Hey guys, so over the past few months amongst a busy work schedule I have fixed a bunch of stuff and worked on the tuning of my RB30, now my Aircon is cold, my oil pressure gauge works, and I have improved my engines operation. I have almost got the fuel use back down under 20 per hundred too, 20.3 at last fill (down from 24-26) so that's going in the right direction at least, got a new carb, replaced the inlet manifold gasket and sorted another vacuum leak.

At the moment I am finding that sometimes my idle speed comes up like when the choke is on, but I have checked the choke butterfly and the choke appears to be working, in so far as the butterfly is fully open once warm. No matter what I do though, when this happens the idle speed stays at about 12-1400 rpm.

Thanks all.

That is the ideal time to check whether it's related to sticking throttle valve(s) by looking at the valves from top.