Rear window out.

[Mad4slalom]

I reall some years back a buddy had an AC Cobra replica with a severely 'cammed' stroker 514 cu in big block Ford engine. He was 'running' a rather silly Holley Dominator race carb too. We took a trip (with me in the Vette following him) at 50 mph or so speeds to the local car meet - perhaps 15 miles distance. His car was running so rich that when we got to the meet his eyes were bloodshot from the intensely rich mixture in the cabin. Anyone who has travelled in a Cobra cabin will be well aware that unlike a Vette you get blown to pieces by the poor areodynamics and back-draught from the side exhausts circulating excess exhaust fumes in the cabin. Me? - I learnt within a few hundred yards of following him about the exhaust fumes and dropped right back.......but even so my eyes were still red from inhaling the fumes when I got to the meet.
Mad4 - It isn't difficult to tune a Holley without resorting to using probes rammed up your tailpipe. Simply put a new set of plugs in the engine (or super cleaned ones) - once the engines warmed-up and off-choke go for a steady 50 mph cruise for a few miles - cut the ignition/engine off - knock it into neutral - and coast to a standstill (ideally in a pre-planned layby) - remove the plugs and note the condition of each one and its position in the engine. Perhaps do the same thing in urban/town use (and again try and record the colour of plugs) - do the same thing yet again at wide open throttle - obviously you'll have far less less time to do this (do it in an intermediate ratio if you have to) but the colour of the plugs should tell you if the fueling is correct. The first two tests should tell you if primary main jets are sized correctly. The third test if secondary main jets are correctly sized. If there are underlying mechanical issues with the engine these should show too.

Thanks Rossc, I gave it a good blast then popped into the garage , gave it a bottle of forte petrol system cleaner, he put his probe up after saying it smelt really rich . The analyser showed that it wasnt that bad , hydrocarbons a bit up but not too bad. He said to have a google and a tweek myself. I will pull the plugs next few days , look at them to note Which if any look oily or fouled. Will fit the new plugs and give her an oil change. Then look again as you suggest. Say for instance if the plugs look good , should I still be looking To lean off the idle mixture as that is when I am more aware of the rich smell . Just giving it a few blasts over 3 consecutive days (italian tune up) has smoothed out the bog over idle to main jet transition a lot. Definitely likes to be used than parked up so am making the best of the high pressure set fair weather while I can. Any good links to tweeking the 650 double pumper with vac secondaries welcome.
I have a bung in the downpipe but will need a meter of some sort And read I need to plug vac line with a golf tee . Have’nt touched a carb for years except for the beach buggy solex. Thank you for input snd advice .

 

[Roscobbc]

Thanks Rossc, I gave it a good blast then popped into the garage , gave it a bottle of forte petrol system cleaner, he put his probe up after saying it smelt really rich . The analyser showed that it wasnt that bad , hydrocarbons a bit up but not too bad. He said to have a google and a tweek myself. I will pull the plugs next few days , look at them to note Which if any look oily or fouled. Will fit the new plugs and give her an oil change. Then look again as you suggest. Say for instance if the plugs look good , should I still be looking To lean off the idle mixture as that is when I am more aware of the rich smell . Just giving it a few blasts over 3 consecutive days (italian tune up) has smoothed out the bog over idle to main jet transition a lot. Definitely likes to be used than parked up so am making the best of the high pressure set fair weather while I can. Any good links to tweeking the 650 double pumper with vac secondaries welcome.
I have a bung in the downpipe but will need a meter of some sort And read I need to plug vac line with a golf tee . Have’nt touched a carb for years except for the beach buggy solex. Thank you for input snd advice .

A 650 scm Holley with a vacumn secondary function.......isn't a double pumper (which has mechanically operated secondaries)
Good news its one thing less to be concerned about. And yes, Italian 'tune-ups' on old school engines are effective. Mine tends to gas-up a bit in town use if the idle speed is set too low (say 550/600 rpm) and eventually after a few weeks of this a plug or two will carbon-up and fail. I find that 800 rpm works best for my set-up. Some of the higher performance Holleys (especially race spec double pumpers) have 4 idle screws (one for each choke) and are extremely sensitive to idle screw settings and will easily over-fuel.

 

[Mad4slalom]

A 650 scm Holley with a vacumn secondary function.......isn't a double pumper (which has mechanically operated secondaries)
Good news its one thing less to be concerned about. And yes, Italian 'tune-ups' on old school engines are effective. Mine tends to gas-up a bit in town use if the idle speed is set too low (say 550/600 rpm) and eventually after a few weeks of this a plug or two will carbon-up and fail. I find that 800 rpm works best for my set-up. Some of the higher performance Holleys (especially race spec double pumpers) have 4 idle screws (one for each choke) and are extremely sensitive to idle screw settings and will easily over-fuel.

Thank you for sharing your knowledge ross , I was just going from memory re the info the original owner sent over with the car, i will re read it to confirm what carb exactly it has . ( it has no choke either) can I report back later

 

[Nick B]

I have a '71 T top and have the tops off, windows down and rear window out whenever possible. I do not ever notice any exhaust smells in the cabin.

 

[Mad4slalom]

Thank you for sharing your knowledge ross , I was just going from memory re the info the original owner sent over with the car, i will re read it to confirm what carb exactly it has . ( it has no choke either) can I report back later

Hi again ross, I was confusing the vac secondries with his instructions for timing the motor and the golf tee thing . Here is some of the info that came with the car . Seems it is a double pump holley although he doesnt mention secondaries at all. What do you think?

 

[teamzr1]

Could not read that, so I reworked it

 

[Roscobbc]

The important thing to remember is that whether vacumn or mechanical secondaries whatever adjustments are made to the side of the carb that has the exhaust bung and which someone will 'read' and ajust any carb settings to achieve optimum air/fuel ratios will need to be replicated on the opposite side of the carb to balance right and left 'sides'of the engine. Once you have done the 'opposite' side you'll need to double check the original side once again as (and depending whether you have a single plane or dual plane inlet) as it may need re-adjusting once more.

 

[CaptainK]

My 68 feels better being driven more as well as a good Italian tune up. Take for example yesterday, its runs "ok" when I first start it up and wants to bog coming off idle (which I set higher than normal as it suits my easier driving style), but if I give it a bit too much welly then it pops and tries to die and I have to catch it and its all good when its starting to move and away from that "stationary to moving" state.
It then feels a little low power driving for a few minutes, have to hang in a lower gear to keep revs a bit higher. Then after 10 mins its warmed up and its generally happy and pulling like a trooper. To be fair, it hasn't been used in a few months now, so kind of expect it.

I ought to check the plugs sometime. When I get chance.

 

[Mad4slalom]

My 68 feels better being driven more as well as a good Italian tune up. Take for example yesterday, its runs "ok" when I first start it up and wants to bog coming off idle (which I set higher than normal as it suits my easier driving style), but if I give it a bit too much welly then it pops and tries to die and I have to catch it and its all good when its starting to move and away from that "stationary to moving" state.
It then feels a little low power driving for a few minutes, have to hang in a lower gear to keep revs a bit higher. Then after 10 mins its warmed up and its generally happy and pulling like a trooper. To be fair, it hasn't been used in a few months now, so kind of expect it.

I ought to check the plugs sometime. When I get chance.

Hi captain, yours sounds like it may be a bit worse than mine from cold. I am sure if I didnt warm mine up for five minutes or so then it would be more like how you describe. Am working on my mezzanine door today but will pull some plugs for a look in the next few days. I have a vacuum gauge coming tomorrow so will try the idle mixture screws and check idle speed too. Great week to get the 68 out for a blast

 

[CaptainK]

Hi captain, yours sounds like it may be a bit worse than mine from cold. I am sure if I didnt warm mine up for five minutes or so then it would be more like how you describe.

I should add mine only does that when its been stood for a while. If I've used it recently-ish then there are no problems. I took it out the last two days in a row - first day not been used in about a month. I get in, drive it out of the garage, close garage door, then immediately drive - no warming up. To be fair, my "10 minutes" I quoted above is probably too harsh - it is more like 5 minutes thinking about it. Once you get it moving and its over 1500rpm its all fine and groovy. Its just if I'm below 1500rpm OFF IDLE then it can be a bit funny until its warmed up a bit. It doesn't bother me.
Second day in a row, it starts up instantly, drive out of garage, close garage door, and its all driving fine no issues at all. I suspect mine is just hinting I should drive it more

 

[Mad4slalom]

I should add mine only does that when its been stood for a while. If I've used it recently-ish then there are no problems. I took it out the last two days in a row - first day not been used in about a month. I get in, drive it out of the garage, close garage door, then immediately drive - no warming up. To be fair, my "10 minutes" I quoted above is probably too harsh - it is more like 5 minutes thinking about it. Once you get it moving and its over 1500rpm its all fine and groovy. Its just if I'm below 1500rpm OFF IDLE then it can be a bit funny until its warmed up a bit. It doesn't bother me.
Second day in a row, it starts up instantly, drive out of garage, close garage door, and its all driving fine no issues at all. I suspect mine is just hinting I should drive it more

Definitely the same, have used mine 3 days in a row which is rare and it is just so much smoother between idle and main jet transition .

 

[Roscobbc]

Definitely the same, have used mine 3 days in a row which is rare and it is just so much smoother between idle and main jet transition .

I've always noted how after to winter 'lay-off' much of what is said above happens but take a 15 mile rum-out and how over that period the suspension 'softening-out'a little, brakes heating-up and more effective, manual gearbox action inproving.......and yes, finally the engine running so much smoother.

 

[Mad4slalom]

I've always noted how after to winter 'lay-off' much of what is said above happens but take a 15 mile rum-out and how over that period the suspension 'softening-out'a little, brakes heating-up and more effective, manual gearbox action inproving.......and yes, finally the engine running so much smoother.

This arrived today, thought it was a fuel pressure gauge and not what I need , then I noticed it is a vacuum gauge as well. Anyone have similar and any tips where to find the vacuum source on a holley 650 double pump carb. I read that I should be l looking for max vacuum on the gauge when adjusting the idle ? TiA

 

[Roscobbc]

There should be one, perhaps two vacuum ports on your Holley - be carefull one isn't a ported source - that only takes vacuum from directly under the primary throttle plates and will read close to zero I think at idle. It'll be the same source that supplies the advance can on the distributor. For the purposes of 'reading' vacuum when setting-up the carb look for where the brake booster vacuum source comes for on the inlet manifold - it may have a 'capped-off' 'T' connection you can use.

 

[Mad4slalom]

Sorry , forgot the pic. , thank you for your guidance ross

 

[CaptainK]

Definitely the same, have used mine 3 days in a row which is rare and it is just so much smoother between idle and main jet transition .

Funnily, yesterday was my third day in a row too. Deffo much better, but I think I might also have a misfire / not running on all 8 when the car first starts up / not used for a while and then when warmed up is all fine. Need to check plugs and stuff.

Where did you get your vac gauge from? Looks quite fancy.

 

[Mad4slalom]

Funnily, yesterday was my third day in a row too. Deffo much better, but I think I might also have a misfire / not running on all 8 when the car first starts up / not used for a while and then when warmed up is all fine. Need to check plugs and stuff.

Where did you get your vac gauge from? Looks quite fancy.

Good old amazon prime, range from 15- 20 quid all pretty much the same