Good idea. I'll try that. I was thinking of changing squirters anyway...

Lou

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Home of Slant6-powered fun machines since 1988

You may want to verify you are actually getting wide open throttle before you start messing with the carb.

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63 Plymouth Valiant Wagon

Verified, many times.

Lou

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Home of Slant6-powered fun machines since 1988

Hi all,

I still have a problem with the 350 cfm 2bbl Holley with my setup.

I have a gremlin at or about just after 3/4 throttle. It sort of misses/pops/dies out at that point for a bit. It has a really nice sweet spot just before 3/4 across the rev range and will pick up if I stab through the 3/4 point and go to WOT (WOT isn't that great - it's still sweeter and more pull just before 3/4). I've played around with different jets/power valves/somewhat blocking off the power valve etc, but none of these things seem to iron out this particular 3/4 issue. This slant runs well apart from that.

What I am finding is that it's nice at cruise, pulls hard at about the just before 3/4 mark (heaps of torque/get up and go say between 30 mph to 50 mph (can give it heaps in 1st and 2nd - also good in 3rd from say 50 mph up to 80 mph, especially from 60-80mph) - You can really hear that Holley sucking air). (It's a 3 stage Torqueflight auto - I don't have a kickdown linkage, just drive it semi-manual if not just cruising - I prefer that in NZ as it's pretty hilly here in a lot of places).

I'll try to give detail as to my setup to see if that helps for any ideas:

* It's a 1967 VC Valiant - Built in South Australia - imported into New Zealand circa 1970 (or at least first registered Jan 1970 in NZ).

* The Slant in my VC is a 1979/80 Slant Six (head caste no. 4104362) not a 1967 slant. Note for the uninitiated (such as myself born 1980) and in case it helps someone else: the heads on a pre-1975 slant six are different than on a 1975-1980 slant six (one uses drool spark plug tubes (gasket style plugs), the 1975-1980 head uses,"peanut" tapered style plugs). if you are in NZ or Australia and you go into Supercheap Auto or Repco or look up the NGK website, they will all tell you that, according to their system, the correct spark plugs for a 1967 Valiant are NGK BPR5ES plugs (they were the plugs in it when I got it). That would be o.k. (but are not the best) IF the slant is a 1967 slant - which in my car it isn't). NGK BPR5ES plugs will work in a newer 1975-1980 head - but not all that well - as I have discovered. You'll see carbonation up the thread and it'll be a bit missy - no surprise.

Thanks to this forum, I've since learned for a 1975-1980 head use NGK UR5 tapered plugs (or perhaps UR4). In my case, I dropped too much cash on a set of NGK UR55IX (which are Iridium) - but being iridium is unlikely to be important (the shop just didn't have any regular UR5s and I didn't want to have to wait to get some normal ones from the USA). Note the NGK UR55IX (rather than a NGK UR 5IX) is gapped wider than an UR5IX plug - i.e. 1.5mm (0.059 inch) instead of 1.0mm (0.039 inch). I'm getting a nice clean burn with only a slight ring of carbon around the base of the plugs. The tips of the plugs are off white/tinge brown.

* I have a high voltage coil/electronic ignition system provided by Hemi Performance (Australia) - which ought to make up for a wider gap in the UR55IX plugs (https://www.hemiperformance.com.au/shop ... sable.html).
* new Taylor ignition leads
* Dual Dutra Duals (front and rear)
* Aussiespeed Hurricane long runner 2 bbl intake manifold
* Holley 350 cfm 07448 carburettor - 10.5 PV - #60 jets. (I've found it pulls/accelerates better with a 10.5 PV rather than an 8.5 PV). I've played around with #58, #60, #61, #62 and #64 jets. It's 8 degrees Celsius at sea level here at the moment (46 F). I've found #60 seems to work best.
* As noted above, I've partially blocked off the enrichment holes under the PV with 0.8mm mig welding wire.
* idle vac in Drive is a pretty steady 16/17 Hg.
* 2 inch pipes to a Flowmaster Y connector through a single 2.5 inch pipe to a Flowmaster 50 Delta Flow muffler then out the back (sounds great - wouldn't want any louder though).
* K&N air filter.
* Otherwise a stock 1979/80 slant six.

I do not have a Wide Band O2 gauge to see what is happening at/just after 3/4. It seems pretty good everywhere else.

One total guess is that the airflow over the carby plate is causing the fuel to cool when it is at a certain pitch and that is causing the fuel to fall out of suspension into the long runner - even when the engine/intake manifold is well up to temperature.

Overall I'm happy with my setup. What I describe above is not a major problem and can be driven around. It's just a little annoying and I'm curious what the answer might be.

Does anyone have any ideas other than change to a different carb?

Cheers
Mark

With the Dutra Duals you do not have manifold heat. You stated outside temp is in the 40's f. Can you try water heating the base of the intake manifold?

PS: Not a good idea to run without the "kickdown" linkage connected. If the throttle lever on the trans is forward, there is not enough fluid pressure in the trans, and can burn up the clutches. If the lever is all the way back, the pressure is too high and causes high and hard shifts. So the lever would need to be somewhere between, but where? It varies depending on driving conditions.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

As a temporary fix you can wire that kickdown lever back 3/4 of the way so your transmission can carry on without burning up parts.



Greg

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http://www.youtube.com/hyperpack

Hi Drgonzo / Lou

Can you recall what jet size you ended up with?

Mark

I want to say 69s are where I ended up with mine.

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“Buy the ticket, take the ride.”
― Hunter S. Thompson

I assume you mean the 500 holley. Depending on the engine tune and build specs, you will be in the range of 66 to 69 near sea level and 25 deg C to be optimal. I would start with 68s.

Lou

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Home of Slant6-powered fun machines since 1988

I'm pleased to report that the 500 cfm 4412 Holley seems to work a lot more smoothly and without any real issues with my setup, as outlined in posts above, more or less out of the box. I have swapped the 74 jets with 68s and the 5.0 PV with a 10.5 PV. That is with an Aussiespeed Hurricane long runner and dual Dutra Duals, high voltage coil etc but otherwise not milled or ported). My slant runs vacuum max about 17 hg in Drive about 20hg in Neutral but I have found it feels more responsive with both the 350cfm and 500 cfm with a 10.5PV at the low end. With the 500 cfm I might dial it back to a 8.5 PV and see how it goes. The stock 5.0 PV felt a bit flat.

I could, eventually, get mileage (reasonably based estimate of 20-23 mpg/10 -12 litres per 100km) and a good pull with the 07448 350 cfm Holley with a 10.5 PV (I did put some 0.8mm mig welding wire in the ports behind the PV as suggested by Aussiespeed), 60 jets, orange pump cam.

For climate detail: The above is at 12 -to 15 degrees C (53 F to 59F), sea level (which is pretty normal winter temperature in Wellington/North Island New Zealand at sea level. Up the mountains/the main State Highway 1 through the Central Plateau is much colder - the Central Plateau is about 1,050 metres/3,500 ft above sea level - up the highest mountain/ski fields on the Central Plateau of the North Island is approx 2,700 metres/9,000ft but I'm not driving there much). 20 degrees C (68 F) to 28 degrees C (82 F) is pretty normal temp in summer at sea level. Temps are both colder in winter and can be warmer in summer in the South Island.

Possibly off a 20-30 mph rolling start at lower rpm was slightly better with the 350 cfm with the above setup, but very hard to feel the difference (as long as not going from zero to hero rapidly) compared with a 4412 500 cfm. But - with the 350 cfm it was necessary to give the throttle a feather to get it to pick up (i.e. I guess that giving it a couple of pumps/feather on the throttle, gives an extra pump shot). The 350 cfm also had a bog at just after or at 3/4 quarter throttle pretty much everywhere, even at high rpm that I could not get rid of. At WOT it pulled out of that. (manual choke on both carbs)

I noticed when I got the 4412 500 cfm that the choke plate "clips" open vertical. whereas the 07448 does not seem to have such a choke plate open "clip". I do not know, but it may be that on the 07448, the choke plate was not opening as far as it should, or staying as far open as it should have at 3/4, causing a cool air pressure difference or otherwise upsetting the air/fuel mix at 3/4. But this is only a partially educated guess. I tried to adjust the choke cable to keep it wide open on the 350 cfm but I don't think the cable alone would hold it in the same way as the 500 cfm "clip".

The 500cfm is definitely a better performing carb in my humble opinion. The only residual issue I have is to dial that in with the right jets and PV for the conditions and balance out with fuel usage with performance. I expect that will mean getting a wide band 02 sensor (pricey to buy but possibly a fuel cost saver in the long run) or a day on a dyno to get the fuel/air mix right with the 500cfm.

In the meantime, I'll play around with different jets and power valves and probably pour a lot of fuel out of the float bowl into a pair of old undies and hauling up and down the highway to test it out with different jets/PV/tune....

Any comments are welcome. Thought it'd be worthwhile sharing. I am not the only one who has had issues with a 350 cfm Holley on a Aussiespeed Hurricane manifold.

Mark.