Engine stumble when revving from idle

[Errol62]

Looks to me like you either have the wrong lever on or throttle is half open. Like the custom marine ply inlet manifold.


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[DCE80]

Errol is onto it. Throttle is open. The butterfly inside the body is on the same plane as the flats shown on the end of the shaft. If the assembly on the other end that controls the plunger is incorrect it could maybe prevent the throttle from returning to the idle position (just cracked open).
Dan

[Harv]

Looks like idle vent valve is pressing on top of the pump stem, pushing the pump stem down (i.e. pump piston is halfway down the pump bore). The circlip on the top of the pump stem engages the pump rod, driving the throttle part open. With the pump piston halfway down the bore, you will only get a "half shot" of fuel when you stamp on the loud pedal. This could be why it misses when revving. The idle is probably pretty high on the vehicle, as the throttle plates are much further open than normal (idle screw should connect with idle cam).

I wonder if this is the correct pump stem for the carb... feels like the pump stem is waaaay too long. The motor and fittings look like Holden red motor, but there is a chance that this carb has been Frankensteined.  Can you please let me know the following:
a) There is a small reinforcing bar that sits on top of the float bowl... looks like a small 4" long piece of light angle iron. Stamped into this bar should be some numbers (eg 23-3015). Please also check the leading edge of the float bowl. (there is a picture of these locations on about page 12 of the Guide). May have to clean some of the gunk off to read the stampings.
b) Near the brass fuel inlet fitting to the carb is a little circle cast into the carb. It should have a fraction number cast into it (eg 5/32).
c) On the cast-iron throttle body are some cast numbers (eg BXOV-1).
d) On the service kit, there will be a part number (eg SSB-652).

With these four bits of info, we should be able to work out how far the thing has been butchered.

Where are you located Wilcey? I may be able to lend a hand if you are close enough.

Cheers,
Harv

[Harv]

G'day Wilcey,

Did you end up solving this problem?

Cheers,
Harv

[Wilcey]

G'day Wilcey,

Did you end up solving this problem?

Cheers,
Harv

Hey Harv!

Unfortunately I've had to put her away since Easter as I just haven't had the time to look at her. I'll aim to have a look by the weekend.

Thanks,

Wilcey

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[Wilcey]

Hi Harv, Ive finally had a chance to have a look...
Yes, i should point out it is a 161 red motor.

On the reinforcing bar there are no markings at all that i can see. Refer to pictures... The fraction cast into the carby near the fuel inlet reads "1 3/32"..
On the throttle body It is quite hard to see the markings, but the bottom figure is BXV-2.. Im not sure what the service kit was, it was purchased from rare spares in newcastle following their advice for a 161 red motor.

It does seem the engine is running a bit rich too, as the exhaust is quite smelly and coated with black soot. She has also been dieseling/running on quite a bit when shut off. Not sure if these issues would be related or not..

Im in Stockton, Newcastle if that is anywhere near you.

Thanks,

Wilcey

[Wilcey]

I also should note that according to the kit instructions, on bxov-1 carbys the pump stem has a part that needs to be broken off to shorten the rod so it sits flush. As mine had markings of bxov-2 I left it, and found the vent valve was far too open, breaking it off, seemed to remedy the issue. The stem that was in there prior also had the part broken off... Seems strange.

Wilcey

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[ardiesse]

Wilcey,

Your carburettor is a parts-bin special.  From looking at the photos -

The accelerator pump link is on backwards.  It normally should pull out towards the front.  There's a chance that the throttle won't close properly with the pump link around the way you have it.

You said the engine's a 161.  The float bowl (1-3/32) is correct for a 161.  The air horn's the right type, as it has the bowl vent.  But the throttle body (BXV-2) is from a 179 or 186, HD to HG from the looks of the throttle lever.  The correct throttle body for a 161 would say BXUV-(and I forget the suffix).

Dieseling (aka running on) after switching off is usually caused by the idle speed being set too high.  In the bad old HX-HZ days, the carburettors were fitted with an idle-stop solenoid to combat dieseling.

It would help to make sure that the choke is completely open.  Looking at the third photo, I'm not sure that the choke is completely open.  Push the choke knob all the way in, then loosen the screw holding the cable inner to the choke lever and gently bring the lever forward until it stops.

Here are a couple of sanity checks: (1) It should be possible to make the engine idle too slowly and then stop running by unscrewing the idle speed screw.  If that doesn't happen, something's holding the throttle partially open. (2) It should be possible to make the engine idle roughly and finally die by screwing the idle mixture screw inwards (aka tighten for a right-hander).  If that doesn't happen, and the engine still runs with the idle screw turned in until it stops, again, something's holding the throttle partially open.

I've got a few BXUV throttle bodies at home, but I don't know whether the throttle shafts are worn out on them.  I'll look this evening.

And finally, in what general condition is your engine?  Does it feel like it has a decent amount of compression when you turn it over by hand?  Worn-out engines are inclined to miss on acceleration.  But yours doesn't appear to have the clagged-red-motor-oil-slick down the rocker cover.

And also - ignition timing.  An engine with retarded timing is more prone to stumble on acceleration too.

Let us know how you go.

[Harv]

The accelerator pump link is on backwards.  It normally should pull out towards the front.  There's a chance that the throttle won't close properly with the pump link around the way you have it.

Agree. The pump arm (little lever with three holes in it) is not on correctly. The photo shows the pump link (c-shaped bit of wire) at a cock-eyed angle.

You said the engine's a 161.  The float bowl (1-3/32) is correct for a 161.  The air horn's the right type, as it has the bowl vent.  But the throttle body (BXV-2) is from a 179 or 186, HD to HG from the looks of the throttle lever.  The correct throttle body for a 161 would say BXUV-(and I forget the suffix).

GMH made 7 carbs for the 161ci motors. They were all BXUV-2 throttle bodies. Wilcey's carb has a BXV-2 throttle body on it. This means his throttle body will be 1/8" larger in diameter than the normal carb. Not the end of the world, but not great either - there may be a "step" where the large throttle body meets the smaller manifold, which can lead to fuel drop-out.

The HR and HK economy (taxi) engines had 1 1/32 venturis, all other 161ci carbs were 1 3/32". So Wilcey's venturi is about right.

I'm assuming there is no stampings on the carb, either on the fuel bowl lid or the main body, where the reinforcing bar left screw is missing? Looks like the area has been cleaned up in the 3rd photo.

I've got a box of red motor carbs at home, so probably have the parts you need. If you are interested, happy for you to send your carb to me by mail. I'll strip and clean it, kit it out (use most of your parts) then send it back to you, gratis. The only caveat is that it may take a few weeks for me to do it (I travel for work so my time is rarely my own).

And also - ignition timing.  An engine with retarded timing is more prone to stumble on acceleration too.

Amen.

Cheers,
Harv

[ardiesse]

Wilcey,

Just checked.  I have a BXUV-2 throttle body, and the shaft's not too worn either.  It looks like it's from an EH 149, judging on the throttle lever.

Rob

[Wilcey]

Hi Harv, that sounds excellent!! Shoot me an email if youre concerned about posting your address here. james_wilce@yahoo.com.au

Although I'm no longer having the stumble under acceleration issue anymore, I am having trouble starting and keeping the engine running for the first few mins (regardless of running temp) and the engine idling too slowly and eventually stalling if i dont give the accelerator one quick pump. Idle speed doesnt seem too slow...

I guessing these are all related to that lovely carby of mine.

Ardiesse, thank you greatly for your offer... at this stage i probably wont need that throttle body unless Harv cant find one suitable in his collection. Ill let you know if in the future i need one 

Thanks,

Wilcey

[Harv]

No drama.

I am home this weekend, so will take a look in the box of red motor carbs. If I have a suitable candidate, I'll overhaul it and swap it over for yours.

Cheers,
Harv

[Harv]

G'day James,

I took a look through the red motor carb box, and I have a suitable candidate (HR-HG 161ci carb). The only drama is that the airhorn on my carb is stuffed (someone has managed to pull out the power valve retaining thread  .

If you still want to go ahead, the plan would be to send me your carb, and I will make a complete one using the best of the bits to the correct design. I'll then send it back to you. Only cost should be the postage to send it to me. I'll send you my address now by email - let me know if you want to go ahead.

Cheers,
Harv

[Harv]

A quick update. Wilcey shipped his carb to me, and I stripped it down for a look see. It’s a 23-3019. These carbs were fitted to Holden HR, HK, HT, HG and LC Torana 161ci engines with manual transmissions.

The issue he is having is cold or warm starting and running. The engine will not fire unless the throttle is pumped and revs increased, or the choke used. The engine stalls if he turns off the choke before the engine is completely hot, between 10-15 mins. This also happens when the engine is still warm, but hasn't been running for 20 minutes or so. The engine also sometimes stalls (even when hot) at idle unless the throttle is tapped. He also has a slight stumble upon initial acceleration. It got better when he kitted the carb, but isn't perfect

When I stripped the carb done, I found
a)   The vent valve had no lift. Probably not causing him any problems, but needs setting properly to prevent issues under hot operating conditions.
b)   Some dodgy screws used on the airhorn, including a woodscrew. Probably not causing him any problems, but ugly.
c)   The choke spindle retaining nut was loose (brass spindle had been stripped). This will allow the choke to wobble around, and can cause erratic running. Might be part of the problem, but not a big contributor. I ran a die over the spindle, and rethreaded it to 10-24UNC.
d)   As we saw earlier in this thread, the throttle body is a BXV2 (wrong one for this carb – should be BXUV-2).
e)   The throttle shaft was loose (needs reaming out and oversized shaft fitted). This will allow air leaks, and makes idling harder. Might be part of the problem, but not a big contributor.
f)   The pump link was installed back to front. Not a big deal (pump operation was not affected), just doesn’t look right.
g)   Power and pump bypass jets were correct size (#56 drill), as was main metering jet (0.055”), idle speed (throttle plate just cracked open) and float level (1/8” bench test). Idle restrictor rod was correctly fitted.
h)   Idle mixture screw was set OK (1 turn out). However, someone had backseated the needle, gouging the tip. Might be part of the problem, but not a big contributor.
i)   Neither of the two float bowl plugs had copper washers. These will leak fuel into the engine bay as they warm/cool/warm/cool.

So far, some fiddly stuff but nothing that should make the car run so bad. However….
j)   The idle passage in the throttle body were blocked with crap. This means the car was idling on the main metering jet, and explains the poor idle quality. Wilcey had to open the throttle to get a quick squirt of fuel from the accelerator pump, then get revs up so that the main metering jets took over… poor old idle circuit was doing nothing. The choke helped him because it gives better vaccum (more suck) and lets the main metering circuit flow earlier.
k)   The accelerator pump plunger had been installed too roughly (or without twisting the plunger as it is guided into the bore). The pump plunger leather washer was folded on itself. This gave poor pump performance (you only get half the amount of petrol squirt you need), meaning he got a hesitation/stumble on acceleration.

So all up, it’s a carb suitable for his 161ci engine. It’s had a hard life, and needs some major surgery to the throttle body to reshaft it (and is the wrong throttle body anyway). The idle passages were blocked, making it idle like crap. The accelerator pump plunger was twisted, making it hesitate on acceleration.
Plan at this stage is to send him my overhauled 23-3019 carb gratis (he is fortunate I have one in the spare parts department). My carb has been cleaned and kitted out, and has correct throttle body. My airhorn is buggered, so I’ll use his airhorn (after a good clean up). I'll put his used bits back into the spare parts department. Should get the carb into the mail for him this week, then he can install it, set the idle, idle mixture and float level.

Cheers,
Harv

[Errol62]

Jeez Harv. Generous, learned and articulate. You couldn't be handsome into the bargain. Just as well or we'd all be lining up to make an honest woman of you.
Cheers
Clay


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[Harv]

You couldn't be handsome into the bargain.

Nope, I got a face like a busted cabbage 

Cheers,
Harv

[Harv]

James got the carb back, installed and tuned. Looks like we solved the issue - now running well.

I'll put his old carb back into the spare parts department, ready to help the next guy.

Cheers,
Harv

[mcl1959]

Well done Harv, great service.

Ken

[Wilcey]

The old girl has never been happier, more like an FC less like a flintstone car!

Huge thanks to Harv, I couldn't have paid someone to do a better job!

Next step will be inspecting, and most likely replacing a few leaky welch plugs then on to painting the floors for some rust proofing.

Maybe she'll be show ready in a few decades 


Wilcey