Hesitation when taking off

[Cliff Ruggles]

You simply need more fuel to the idle system.  This will also put more fuel to the off idle transfer slots and cure your issues. 

Pretty sure that was mentioned earlier at least once.

It could be as simple as effectively cleaning the idle tubes as they tend to get smaller over the years as "varnish" builds up in them with many drying up cycles.

Here I remove them from the main casting and manually clean them with precision drill bits.  For this new fuel I open them up in almost all cases and to date have never had a single complaint from the end user and I'm well over 15,000 units at this point........Cliff

[Kavesh]

Yes you are quite right it has been mentioned before about fuel delivery at idle.

I have removed the idle tubes and used wire to ensure the tubes are clear. I do not have the precision drill bits to be precise on this.

I must say though that the idle tubes were not blocked nor was there any muck in the main body. This is what has me stumped.

I am hoping a fresh set of eyes in my buddy would see what the issue is and sort it for me. Perhaps I have been looking at it for too long now.

I will post an update in due course.

[Kenth]

There is no way around enlarging the idle tubes and idle down channels.
Now is the time to get a set of precision drill bits.

[Kavesh]

What will the impact of the plastic retainer for the power piston be when its installed upside down.

My mate said that he noticed this installed incorrectly. See pic attached.

I have had this in the carb for probably 2 years of longer with no known problems, until the carb issues I am experiencing now.

Will the power piston collar have any effect on the carb when installed upside down?

Thanks

[Kenth]

No real ill effects. Obviously the power piston will not rise the full distance with the retainer upside down but the taper on rod should still leave the jet enough at WOT or heavy load manouvers.

And, this has NO effect on idle and off-idle issues.

[Kavesh]

Thanks Kenth. My mate will have a good look this weekend and hopefully find something else.

He mentioned that he believed the play on the primary shaft was alot. As the carb worked fine before I did not pay too much attention to the shaft.

My mate offered his theory here.....prior to motor being overhauled, vacuum may have been low which was not noticeable at the shaft. My motor is now rebuilt and vacuum should be higher which is now showing itself at the shaft and causing an idle issue. His logic makes sense but my vacuum is pretty low at 13 inches steady at idle. Perhaps i need a bit more timing to increase vacuum.

[Cliff Ruggles]

You mentioned that the engine was "rebuilt".

13" vacuum is pretty low for a "stock" rebuild using a stock camshaft.  Did you use something other than a stock cam during the rebuild?

Another BIG mistake folks make when "rebuilding" engines is not paying attention to quench.

Many oversize aftermarket pistons are shorter than stock ones for pin height placing them deeper in the bores at TDC.  This LOWERS the compression ratio when it should actually raise it with the larger CID.

Most head gaskets found in "builder" gasket sets and THICKER than the stock ones which raises the cylinder heads off the engine and LOWERS the compression ratio.

Most engine "builders" either don't know these things or don't address them during the rebuild, so the engines compression ratio is typically lower than it was before the rebuild.

It's also common to replace the camshaft with an aftermarket cam of some sort instead of using a cam with stock specs.  If a larger cam (more duration) is used this LOWERS dynamic compression, which hurts idle vacuum, idle quality and throttle response right off idle, etc.

Other mistakes I see with engine builds are not degreeing the camshaft and using "double roller" timing sets in them.  Most of the roller sets being sold are JUNK!!!  They are "weak" compared to the factory Morse chain set-ups, they do NOT offer constant tooth contact (smoother), not as accurate and the chains can stretch out very quickly.

Adding a high pressure and/or high volume oil pump is another BAD decision I see made with a lot of these engines.  Stock oil pumps are more than adequate for all stock and most performance engine builds.  Larger pumps rob power and put a LOT more load on the oil pump drive and distributor/cam gear, often wearing them out quickly.

I could add at least a half dozen more items to this list but I'll stop here.

Just throwing a few things out there that may be contributing to your problems........Cliff

[Kavesh]

Thanks for the indepth reply Cliff.

Let me update on my carb first. My mate said that when he stripped it down he noticed that the seat for the needle and seat was not screwed in tight. With me having opened it up so many times i did not remove the seat each time so maybe this is my own doing. Perhaps the reason for the idle issues!
What impact does a not fully tightened needle and seat have on the carb? Rookie mistake I have made.


The carb was assembled by my mate and it is running fine on his test engine which is the same engine I have on my truck. I should have it back in a couple of weeks.

With regards to the low vacuum, I also was not happy with it.
The cam as best I know shoudl be a stock aftermarket replacement.
With the Holden 308 motor the replacement pistons are Chev 327 pistons. All rebuilders seem to use these as the Holden brands are just too expensive, if you can find stock.
My head gaskets are Felpro which as far as I understand are a little thicker.
My timing chain is double row like the original
Also using a standard oil pump.

Once I get my carb back I will try to determine why my vacuum is on the low side.

[Cliff Ruggles]

No direct experience with the Holden engines.

A 327 Chevy, or even a 350 would have came from the factory with a camshaft that made at least 18-21" vacuum at idle speed with very little timing in it.

They NEVER used "double roller" timing sets in any of those engines, they were all the Morse type.

Contrary to popular belief the vast majority of the double roller timing sets being sold are NOT an "upgrade" over a stock type set.  Most have cheap chains (poorly made or not "true roller") and cast iron sprockets.  The "high end" varieties use billet sprockets and a real heavy duty true roller chain, but even those aren't nearly as strong as a factory style chain and probably why the factory used that variety instead.

Morse chains only got a bad reputation because early on they used a nylon coated top sprocket to minimize noise and absorb harmonics between the crank and cam.  Those were actually excellent sets but over time heating/cooling cycles caused the plastic to crack and teeth would start falling off of them and eventually fail.

In my own engines here I will only use factory wide link type (Morse) timing sets and have had zero issues with any of them dating back nearly 50 years.

I tried a "high end" Rollmaster timing set once on my first 455 built in 1999 and it failed after 4 years of pretty hard use.  I loved the ease of moving the cam around (9 keyway variety) and thought it would be a nice set-up for my engine back then.  Sadly the chain got so loose it started "slapping" and retarded the cam so far the car slowed WAY down at the track.

Anyhow, a loose fuel inlet seat if leaking slowly will not provide full control of the fuel level in the carb and issues with fuel delivery as the fuel level has a direct impact on metering.  I see quite a few leaking fuel inlet seats due to damage to the gasket surface.  When the leak is really slow they car typically drives fine, but may "load up" when you stop if/when the leak is faster than the fuel the engine is consuming at idle.

It may also cause flooding after shut-down if there is still fuel pressure in the line between the pump and carb.  For sure it's often difficult to diagnose but more common that folks think........Cliff

[Kavesh]

Hello

Here is a further development on my carb issue. As mentioned before my buddy has leant me his spare quadrajet to use on my truck. For a few weeks now it has been working perfectly.
Yesterday I wanted to go for a drive and noticed that it was not idling like it should. The truck was last used a week ago. It is displaying the same issue I have had with my carb with the erratic idle.
Thinking that some dirt has got in I removed the airhorn and could not find any dirt inside the carb.
Nevertheless I used wire to make sure all the orifices are clear and they were.
Closing the primary flaps did smooth out the idle and the RPM increased. I am really confused guys, am I chasing a carb issue when in fact my issue may be elsewhere, or is this a lack a fuel on the idle circuit. If it is a lack of fuel why would it be fine for weeks and now display these idling issues.
Just to confirm I have not interfered with anything on the motor since last operated.
I will try and upload a video

[Kavesh]

Here are the videos on youtube

https://www.youtube.com/watch?v=WSnqfFfRq9U
https://www.youtube.com/watch?v=Pl9vtBegGy4
https://www.youtube.com/watch?v=_4hrdZREmLU

[Kenth]

Sounds like you´ll need to adjust the valves.
What does an intake vacuum meter show?

[Kavesh]

The Holden 308 does not have adjustable valves like the Chevy motors.

I did not put the vacuum gauge in yesterday but will do.

[Kavesh]

I checked a couple of things today.
As I am using an HEI, i tested the voltage to the wire going to the BAT terminal on the dizzy with ignition on, read 11.93volts. Is this a real problem as it should be 12v?

Started up the motor and she struggled to idle. At higher revs there were no issues. I let the RPM down gradually and down to idle and when it wanted to die I used my fingernail to push down the accelerator pump which gave it a shot of fuel, this kept the motor running, and then another shot of fuel when it wanted to die to help it run.

Will the above test be sufficient evidence that the problem is indeed the carb and on the idle circuit?

[Kenth]

Take a measurement over the battery at idle, should read 13.5-14.5 volts.
This is what you should read at the HEI.

I have forgot how many "carb issues" i have cured for folks by feeding the HEI with correct voltage.
The HEI needs a dedicated feed wire, not the wires aimed for the points distributor which contains a resistor cable reducing volts an amps for the points to live.
You may use the points wires to control a relay from which you feed the HEI.

Been there done that a couple of decades ago, now i´m running the factory points ignition system again since i don´t care for the looks of the big ugly HEI and i don´t mind tinkering with points, checking/setting dwell once a year and replace the points every 10:th year or so.

JMHO