Should I replace carb, intake, or hood?

C3 Specific - Technical and Performance

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68ragtop
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Should I replace carb, intake, or hood?

Postby 68ragtop » Wed Apr 06, 2011 3:52 pm

Hi all,

Over the past month or so I've been atttempting now and then to get the '68 tuned so that it's a nice driver, compared to the poor idling, rough cruising, weak accelerating beast that it was when I picked it up. Through a combo of working on it myself and a carb tech taking a crack at it I now have a car with a smooth but fast idle, rough cruise, but brilliant wide open throttle acceleration. Unfortunately I don't think anything can be done with the current setup to make it any better and so am trying to work out my next step. Let me explain.

After doing some decoding I found my Holley 650 DP (list 4777-7) is riding a 69 Z-28 hirise aluminium intake, on top of a 1968 327 block running mid 70's heads. The problem here for me is the hirise intake and my limited underbonnet space.

Image

From the pic above you can see the intake adds a few inches to the height that I've seen from pics of standard intakes which led to a hood clearance issue. To counter the lack of hood clearance the previous owner has removed the underhood insulation and added a dropbase air cleaner to try and get the clearance. Even with this the front of the lid of the aircleaner is just touching the hood when closed, as is the nut on top of the cleaner.

The big problem that I saw and the carb guy agreed with is that the actual carb lid is sitting way too close to the top of the choke tower and the vents from the fuel bowls. As a result we believe it's really messing with the airflow into the primaries (the butterflys on the secondaries have been cracked open a touch to allow slightly more airflow to try and counter things). You can get an idea of how close it is in this pic when you compare the heigh tof the threaded rod with the butterflies on the choke tower.

Image

So what I have come up with are three possible options:

1. Find a carb with a main body that sits a lot lower so that it can get the airflow into it correctly (or get someone to mill down the choke tower and shorten the vent tubes)

2. Find a replacement intake for the 327 that is lower so that I use the extra room to add a higher airfilter to clear the top of the carb correctly.

3. Add a (short) big block hood to allow me to run a taller aircleaner (or one without a drop base on it).

So, does anyone out there have any suggestions, recommendations, or something I haven't thought of yet?

Cheers,
Azza

Of course I've always wanted to put a C2 style stinger on a C3 like this but that is way off in teh future.
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australi
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Postby australi » Wed Apr 06, 2011 4:16 pm

Well my C3 holley sits on high rise too, but hood was made out of 3 different hoods, then CUT to allow ramflo intake to sit high atop same.

I guess you could use a BB hood, would mean you'd have to paint it of course...

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Postby silver383 » Wed Apr 06, 2011 7:23 pm

I don't have a choke and have never needed one, 2 pumps and she fires every time.
I use the same airfilter set up without a problem.:o
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Postby shipy59 » Wed Apr 06, 2011 7:38 pm

I agree with SILVER chop off the choke tower!!!! wont need a choke with a gas guzzling holley on there. Or for better drivability put on a dual plane edelbrock manifold with a q/jet or edelbrock carby :o all probs solved in one go. How much cam has you 327 got?stock/mild/warm/hot.

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Postby Bazzas77 » Wed Apr 06, 2011 10:05 pm

maybe just try it first after taking all that choke stuff off ..thats what I did ,dont need no stinking choke in W.A

you can get bowl vent lines bent 90deg. as well.

K&N make tops that are a filter as well , that might help .

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Postby 68ragtop » Thu Apr 14, 2011 10:10 am

Thanks for all the replies guys. The Qld Auto Spectacular last weekend proved useful for finding a few things out as well. Did a wander round the trade and swap meet sites and found a few answer to questions I had. The K&N filter tops they had add an extra 1/2 inch or so to the air cleaner assembly so that is out as an option. Also found that most of the Holley's at the swap sites had had the choke butterflies removed so will be starting with that when I get a chance to work on the car this weekend.

One of the oddest things was discussing the clearance issues with a guy at one of the swap stands. He proceeded to tell me how he had issues with a clearance in an old Torana he used to have. His solution then and suggestion to me was just to get as tall an air filer as I could, then find a suitable piece of foam to cover the top of it and use the closed hood to hold the whole thing together. :shock: Don't think I'll be going down that path.

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Postby australi » Thu Apr 14, 2011 11:04 am

Yeah, I've seen that done :?

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Postby ernbuild » Thu Apr 14, 2011 6:47 pm

68ragtop wrote:Thanks for all the replies guys. The Qld Auto Spectacular last weekend proved useful for finding a few things out as well. Did a wander round the trade and swap meet sites and found a few answer to questions I had. The K&N filter tops they had add an extra 1/2 inch or so to the air cleaner assembly so that is out as an option. Also found that most of the Holley's at the swap sites had had the choke butterflies removed so will be starting with that when I get a chance to work on the car this weekend.

One of the oddest things was discussing the clearance issues with a guy at one of the swap stands. He proceeded to tell me how he had issues with a clearance in an old Torana he used to have. His solution then and suggestion to me was just to get as tall an air filer as I could, then find a suitable piece of foam to cover the top of it and use the closed hood to hold the whole thing together. :shock: Don't think I'll be going down that path.



I had the same problem with my 78. Lose the choke or get a proform throttle body. You can buy a smaller diameter standard airfilter and fit a K&N filter top and it will fit under the bonnet. It worked well for my 78. :D
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Postby CraigH » Thu Apr 14, 2011 9:03 pm

Getting rid of the choke may be an option in Brisbane but in Canberra it comes in useful :-)

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Postby ernbuild » Fri Apr 15, 2011 5:47 am

CraigH wrote:Getting rid of the choke may be an option in Brisbane but in Canberra it comes in useful :-)

Very True!!! :D
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Postby 68ragtop » Fri Apr 15, 2011 9:09 am

A quick search on ebay has turned up a guy in the US who sells the main bodys for the carbs with the choke tower nicely milled off. At $115 AUD delivered(gotta love the exhange rate) it looks cheaper than finding someone locally to do the work (or finding a main body locally), with the bonus of still having the old one intact in case I ever need it.

http://cgi.ebay.com.au/Holley-performan ... _838wt_907

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Postby silver383 » Fri Apr 15, 2011 11:33 am

CraigH wrote:Getting rid of the choke may be an option in Brisbane but in Canberra it comes in useful :-)

never needed the choke in Canberra either :o

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Postby australi » Sat Apr 16, 2011 11:10 am

Used to get ice on my windscreen when I lived in Canberra.

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Postby 68ragtop » Tue Aug 09, 2011 10:28 am

Been a while since I first posted about this, but I finally got around to doing something about it at the weekend. After tearing down the carb I found it was missing the fuel filters on the inlets which had left in just enough small rusty bits of debris to get stuck in the primary jets in the metering block and to mess up the valve on the accelerator pump. unfortunately also noticed the base plate is slightly warped 0.5 mm or so which may not be helping.

Threw a holley rebuild kit at the carb to replace all the gaskets, power valve and accel pumps and put it back together and adjusted to as close as I could figure (with the help of the net) was stock. Also put in new Holley bronze fuel filters to stop any more crud getting in the bowls. Put it all back on the car, primed the bowls with fuel and fired her up and it started first time, although a few backfires seemed to indicate it was running lean.

Had put in some clear sight plugs to set the fuel levels and they worked great. However after adjusting tham I noticed a fuel leak from the primary acceperator pump so had to take it all off again to tighten things up. Went to replace the sight plugs with the brass and both of the B@5tards shattered when unscrewing them. End result taking things apart again and cleaning out the plastic shards from the bowls. Finally got it all back together and adjusted the idle screws a bit richer and things settled down. Took it for a quiet test spin aroundd teh block and found I don't need the choke on full to start it ay more and it idles/cruises without smelling like I am trailing a leaking fuel tanker behind me. Sweet. However I tried to give it a quick dose of WOT and was quickly scared by a nasty bang that came from under the bonnet (didn't seem as sharp as a backfire through the carb I had earlier). Might be time to hand it over to someone with more tools and skills than me to check out the timing and adjust the Holley right I think.

Azza

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Postby DOC » Tue Aug 09, 2011 10:09 pm

Just one more thing, something I learned on my 77. notice the nice hood on mine. High rise plus sharp kick in the throttle makes the rubber mounted engine move! If your air filter wing nut is close to, (just clears) the hood. The first time you really launch it = cracked hood!

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Postby 68ragtop » Wed Aug 10, 2011 8:32 am

DOC wrote: If your air filter wing nut is close to, (just clears) the hood. The first time you really launch it = cracked hood!


No need to worry about that. Prev owner had put a stud in the top of the carb that was 1mm taller than the gap under the hood so I already know all about cracks there :evil:

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Postby australi » Wed Aug 10, 2011 11:02 am

I do0n't get that problem with the shotguns protruding from it.

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Postby DOC » Thu Aug 11, 2011 8:35 pm

Mine cleared just fine, untill the first good burn-out!

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Postby australi » Fri Aug 12, 2011 10:41 am

:-x 8)

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Postby 68ragtop » Mon Sep 26, 2011 9:56 am

Thought I'd post an update about this as I know I hate coming across threads that ask questions and then never say how things turned out or if the problems were ever solved.

End result is I have the car running fairly nicely after a bit more playing with the carb and plugs. Put in a new set of NGK BPR5FS plugs as the old ones were well fouled from all the testing and bad running. Gapped them to 0.040 and it seemed to like that. Initial settings on the Holley that got things running first up were as follows (loosely based on Lars' Holley tuning guide from the net):

- Idle screws 2 full turns out.
- Primaries opened to show about 0.020 of the transfer slot
- Secondaries cracked open at idle (as per Lars suggestion for initial setup)
- fuel bowl level set just below sight plugs.

This got her starting nicely without the choke after a couple of pumps of gas but idling up around 1600. Took her out for some spins up and down the highway and she was finally starting to behave like I thought she should. Good pull through all gears and didn't look to be leaning out and backfiring any more. :-) Checked the plugs and found a good amount of oil on some of them which indicated the valve guide seals are going. Some Wynns stop smoke has worked nicely to minimise this as a temporary measure until I can get the heads and seals looked at. Idle was too high so started adjusting things to try and get things better. Settings I have ended up at are like this:

- idle screws 1/8th turn in from 2 turns out (any more causes stalling at idle)
- primaries have about 0.015 of the transfer slot showing
- secondaries are almost fully closed

Idle is now sitting around 1000 although there is a little more rich gas smell to it, but driving it is great. Have been doing a lot more driving in it (200 miles or so in the last 2 weeks) and am no longer afraid if it dying on me any time which leaves me with a big smile on my face when driving (especially on the way to work this monring while looking at all the depressed workers sitting in monday morning traffic and thinking to myself how much happier I was to be in the vette). Still think there is a lot more tuning to do on the thing to get the idle and gas milage (not expecting a lot here being a double pumper carb though) sorted but for now, I have a nice running car and the intake and stinger hood mods can wait for another day. Cheers for all your suggestions.

Azza

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Postby 98lux » Fri Jan 04, 2013 1:34 pm

I think you should get one of them there stinger hoods :) :) :)
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Postby 68ragtop » Fri Jan 04, 2013 3:53 pm

98lux wrote:I think you should get one of them there stinger hoods :) :) :)


Hmmm, almost a year after posting that I got one, now maybe in another years time it'll be on the car!

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Postby 68ragtop » Thu Mar 13, 2014 1:31 pm

68ragtop wrote:Hmmm, almost a year after posting that I got one, now maybe in another years time it'll be on the car!


Nope, one year later and still not done. However I did get some sawhorses to put it on at the weekend and have started the sanding back process.

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Postby LRC89 » Thu Mar 13, 2014 5:30 pm

well done mate, glad to see you can still find some time for the old girl. :D

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Postby DOC » Thu Mar 13, 2014 6:14 pm

That Hood is going to look great on your Red Vert Mate!
Keep with it.

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Postby australi » Fri Mar 14, 2014 9:28 am

...Sounds like MY rate of progress! :-x ::

I dreamed last night that I was selling my C3 hood for $50!!! :shock:
(But I'm NOT!) :)

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Postby bfit » Fri Mar 14, 2014 1:49 pm

mate the cover being to close to the top of the chock etc wont give you any noticeable problem at idle or mid range
it will give s_it lots of problem up high and at full power.

Depending on what you call fast idle.
if you have fast idle look for air leaks in your manifold carby and vacuum system.

rough running mid range could be looks of thing,
but tying it into your idle problem,
make sure your distributor advance is working correctly and you are not running to much initial advance.

Bfit

just read some of the rest of this thread I see you are getting on top of it

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Postby 68ragtop » Fri Mar 14, 2014 2:13 pm

Actually after messing with the idle screws and butterflies for the past year I've got it reasonably good. Possibly still need to drop a primary jet size, and have never even looked at the timing yet which adjusting could help. But in terms of performance, idle and midrange are ok, and top end, well I tested that at the 1/8th mile the other week and yes it does drop off at high revs which meant I was only getting to about 71mph in 2nd gear before I ran out of puff and track before I could hit 3rd.
:C

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Re: Should I replace carb, intake, or hood?

Postby 68ragtop » Mon Aug 10, 2015 1:07 pm

Well after 4 years I finally got round to getting some slightly smaller jets to test what going down a size or two would do. All going well until I started undoing the nuts on the flared fuel line at the carb. One went fine, the other did this :shock:

Image

Annoying as hell but seems as good an excuse as any to replace my dodgy lines with a nice chrome fuel rail and maybe a pressure gauge :-)

Next thing I found after pulling the carb was this puddle which I suspect is what is being pulled through the port at the back of the carb from the breather on the valve cover (yes the covers have baffles in them under the breather plug and yes the breather is a pcv style that should only open from pressure under the cover).

Image

The fun never ends with these things.

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Re: Should I replace carb, intake, or hood?

Postby riverracer » Mon Aug 10, 2015 7:01 pm

that don't look good :shock:
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Suddenly becoming stationary that's what gets you.


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