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  #16  
Old 04-08-2016, 06:32 PM
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BlackoutSteve BlackoutSteve is offline
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Do you have one of those IR temp guns to point at the bowl/s when this happens?
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  #17  
Old 04-08-2016, 07:05 PM
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guffer guffer is offline
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I had very similar problems with mine, I had a reg and gauge but had fuel p1ssing out of the vent tubes, I thought it was a faulty reg, so changed that and ignored advise to run a return line
fitting a new reg didn't fix the issue and I had a problem that ended up causing a big engine fire due to fuel pouring out of vent tubes
after I had my car repaired I fitted a return line and the problem is now 100% fixed

I hope you too don't learn the hard way
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  #18  
Old 06-08-2016, 03:59 PM
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69ISH 69ISH is offline
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Took the stang to Munchies llast night and used enough fuel to test my theory today and it was wrong, I replaced the 3 sections of hose between the pump and the tank as well as double clamping them I also fitted the fuel pressure gauge and removed the barbed fitting from the pump and resealed that as well, I have not yet refitted a fuel filter.
If there is air getting in now it is either at the pump or in the fuel line itself which is doubtful.
I took it for a run down the M1service road tye nsat on the side of the road to make sure it was as hot as it gets then drove it revving it through to 6000rpm and it starts missing at around 5600 rpm.
I tried this a couple of times with the same result..
I sat on the side of the road and pulled the air cleaner of and brought the revs up slowly until it hit the rev limiter at 6400 rpm and watched the sight bowls and the fuel still aerated but did not spit out of thevent tubes I also did this a few times with the same results.
I could not watch the tacho at the same time nor could I watch the air/fuel ratio gauge I however could watch the fuel pressure gauge and it supposively was only making 4 psi, I also doubt this is correct, This is the first time I have had it fitted with this pump but with the old pump it use to read 5 to 6 psi but it was only fitted for about a week and the first gayge I bought only read 1 psi and they exchanged that gauge for this one and I believe this one is now far from accurate as well.


Next plan of attack is to fit a regulator and another new fuel pressure gauge, will keep,you all updated.
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  #19  
Old 07-08-2016, 01:02 PM
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With the bubbling in the fuel bowls.. Could it be simply the engine's vibration shaking the fuel and no incoming air/vapor?
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  #20  
Old 08-08-2016, 04:15 PM
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Impalaman Impalaman is offline
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If your comfortable that you've exhausted all your fuel supply avenues and not knowing your engine build, google camshaft reversion. I am no expert, not even an amateur but might be worth a read.

Good luck and keep us posted.

Cheers
Craig.
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  #21  
Old 10-08-2016, 10:53 AM
350chev 350chev is offline
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Bit of left field thought, is it possible that the carb is getting intermittently starved of fuel at the higher RPM causing the float to rise/lower rapidly - this would aerate the fuel and force it out of the vents. Starvation could be caused by poor tank ventilation (leave cap off for a trial), a hose collapsing due etc etc
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  #22  
Old 10-08-2016, 01:53 PM
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BlackoutSteve BlackoutSteve is offline
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My thoughts are along these lines also, but a factory vented cap (working properly) is supposed to be for 300 or 350hp of fuel displacement.
Also, bear in mind that fuel will become aerated with vapor when subjected to a low pressure/high vacuum, especially in Winter months when the RVP of the fuels is lower.
If you know about nitrogen bubbles in the blood when sea diving (the bends), this is the same principal.
Mechanical pumps, as good as they are, naturally create a vacuum on the entire fuel system behind them.
The stronger the pump, the stronger the vacuum.
This is one of the reasons why a fuel pump in the tank is superior. Electrical or mechanical is irrelevant.
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Last edited by BlackoutSteve; 10-08-2016 at 01:58 PM..
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  #23  
Old 11-08-2016, 08:04 PM
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My internet has been down since Sunday Night and what I have pasted below is what I had typed ready to post when it crashed.

To answer a few other questions, We had similar thoughts about the fuel cap because when opening the cap it is nearly always pressurised. The cap does let air into the tank but does not seem to let it out.
(You can suck air through the cap but can not blow air out)

The cap was removed on the Dyno and made no difference.

As far as the float to rise lower rapidly, this does not appear to be occurring looking through the sight glass.

I am starting to think that aerating is normal up high in the rpm it is just in my opinion no one sees what is actually happening with carburettors without a sight glass or watching the sight glass that high up in the rpm.

This is what I had ready to post on Sunday

Quote:
Originally Posted by BlackoutSteve View Post
With the bubbling in the fuel bowls.. Could it be simply the engine's vibration shaking the fuel and no incoming air/vapor?
I don't think so.

I fitted a borrowed fuel pressure gauge and regulator today (both of unknown age or brand, I can't prove gauge is accurate but have been led to believe it is), the gauge read that the pump was putting out 8 to 8.5 psi before I fitted the regulator.

I then fitted the regulator and set it at 6 to 6.5 psi and then brought it up through the rev range and the fuel still aerates in the bowls but still does not spit out through the bowl vents.

Then test drove it and it still breaks down up above 5500 rpm on my tacho, air/fuel ratio reads around 12.5 but it seems like it runs out of revs then after we backed off to 60 kph the fuel ratio went pig rich. pulled over checked float levels and adjusted the levels as both were low (Which I would have been the other way around) then after adjusting the secondary bowls reversed and went way to high so readjusted it back down.
Took it for another run and same thing seems like it was running out of revs then the fuel went extremely lean on the primary circuit and only just managed to get the car home.
Pulled the front bowl and metering block off expecting to find a blocked jet but could not find anything obvious except that the bowl gasket now needed replacing. Blew the metering block out with carby cleaner replaced the gasket and reassembled.

Took it for another run and the car was running nicer but still has a huge stumble transitioning of the idle circuit on to the primary circuit (I think a lot of this is timing possibly being to far retarded and plugs that have been fouled too much). It still feels like it is running out of revs and I am starting to wonder how accurate my Tacho is as it actually felt like I bounced of the rev limiter at one point which I think I have set at 6400rpm. (MSD 6AL2).
The car pulls really strong through to 5700 rpm approx and then once again the car went extremely lean again but this time on the idle circuit.

Gave up and parked it up to look at another day.



I since have pulled the carby off and pulled the bowls and metering blocks off, cleaned and blown compressed air through everywhere I could get it, I reassembled it put it all back on the car and fitted a new Ryco Z153K fuel filter immediately before the carburetor.
It fired up easily and idled on its own early in the warm up cycle, I adjusted the idle mixture screws to get an approx 14.7 air/fuel mixture ratio once warm took it for a drive and it was the nicest it has driven for quite a while with no flat spot and a nice smooth idle at approx 750-800 rpm, drove it down the service road and the flat spot started to rear its ugly head again, revved it through to around 5000-5200 rpm and it had a small miss but rev it any further and it definitely sounds like I am over revving it. I did a couple of pulls through to 5200-5400 rpm and I spat the fan belt, refitted it (after calling the wife and asking her to bring tools to me) and called it a day.

Warmed it up today adjusted the idle mixture screws so that they are all about 1 to 1 1/4 turns out and ignored the air/fuel ratio gauge (approx 11) added 2 degrees of timing where it is now at 8 degrees initial and 28 total at which when under heavy load on the primary circuit below 4000 rpm it will ping.
The car drove perfectly if I kept the revs below 5000rpm which is where it then seems to start to over rev and it definitely seems to stop making anymore power.

At this stage I am quite happy with where it is at but I am going to find another Tacho to compare the revs. I do know that with 25.8" tyres and 3.25 diff ratio that the at 100 kph by my GPS the revs are at approx 2700 rpm and at 110kph the revs are approx 2950 rpm which calculates out that my tacho is still accurate cruising at these speeds.

I will go to another Wednesday night test and tune and take a few different sets of jets and play with the timing and see how it goes,
Justin from HPS (My dyno guy) is away for a couple of weeks tuning race cars in America so the dyno is out for awhile but would like to break 400 rwhp I am thinking 410 rwhp would be nice to suit a 408W (410cc) but anything over 400 would be nice.

Someone did assume what I was running earlier, estimating my drivetrain loss was.
I have a 408W with a C4 and 4000 rpm stall, 9" with 3.25 trutrac and I am guessing I would be losing an easy 100 Hp through the drivetrain, if anybody would like to correct me please feel free.
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  #24  
Old 11-08-2016, 08:19 PM
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BlackoutSteve BlackoutSteve is offline
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Off-idle transition stumble very likely to be accelerator pump tuning. Maybe try the next size up shooter.

Also, when you think it's running lean/out of fuel, does it backfire through the carb? If so, then lean.
What is your fuel pressure during this time?
Otherwise, if it's not leaning out, I'd be looking at the ignition system.
What are your plug gaps?
Also, how good are your valve springs?
Misfiring and loss of valve control can have similar symptoms.

100hp loss through the drivetrain is typical.
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  #25  
Old 11-08-2016, 09:57 PM
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69ISH 69ISH is offline
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Quote:
Originally Posted by BlackoutSteve View Post
Off-idle transition stumble very likely to be accelerator pump tuning. Maybe try the next size up shooter.

Also, when you think it's running lean/out of fuel, does it backfire through the carb? If so, then lean. No Backfiring
What is your fuel pressure during this time?6-6.5 Psi
Otherwise, if it's not leaning out, I'd be looking at the ignition system.MSD Pro Billet distributor and MSD 6AL2 less than 6 months old and ignition box was was replaced under warranty
What are your plug gaps?34Thou
Also, how good are your valve springs?I am not sure on the brand but they were tested when the heads were machined and reassembled with new scorpion roller rockers less than 2 years ago
Misfiring and loss of valve control can have similar symptoms.

100hp loss through the drivetrain is typical.
See Above
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  #26  
Old 12-08-2016, 08:53 AM
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BlackoutSteve BlackoutSteve is offline
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"...it is now at 8 degrees initial and 28 total at which when under heavy load on the primary circuit below 4000 rpm it will ping.."


Please remind me what size cam and comp ratio is in this engine?
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  #27  
Old 12-08-2016, 09:41 AM
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tex013 tex013 is offline
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fuel in the bowls will always aerate at high rpm . there is some "bottom feeder" needle/seat/float assemblies that help this - for holley type carbs .
Are you getting the breakdown on the dyno ? operator should be able to say if tacho is out .


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Last edited by tex013; 12-08-2016 at 09:44 AM..
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  #28  
Old 12-08-2016, 04:37 PM
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69ISH 69ISH is offline
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I believe the CR is between 10.2 and 10.5

I have had issues since it was built trying to get more timing in it. We did at one stage manage to get 12 to 13 Deg Static and 32 Deg Total but that would still ping under heavy load and lowish rpm. and that was also with a Mallory RTR distributor (destroyed a distributor cap approx every 3 months and then the module went so out it came).

Never checked the Tacho whilst on the dyno but until approx 3 months ago it would rev through to 6000rpm before it felt like it was not making anymore power.
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  #29  
Old 12-08-2016, 10:30 PM
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66FAIRLANE 66FAIRLANE is offline
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So its not a massive cam for the inches and should build good cylinder pressure if installed as per card. Was the cam timing verified? Was true TDC verified on the balancer? I have no magic bullet for you over the internet but it beats me how you can get a "heavy load" on it well below stall speed. If its pinging before it hits the converter then you have real issues. High stalls are very forgiving on timing curves and the curve you have described (unless its all in in a big hurry) is very pedestrian. Even if its all in off idle (which I doubt) the converter should probably mask it. Something not adding up here. What heads?
Also don't try and tune to a number on the A/F gauge. Use it as a guide but give the engine what it wants, I am a little surprised it can idle and tip in well at 14.7.

Last edited by 66FAIRLANE; 12-08-2016 at 10:38 PM..
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  #30  
Old 13-08-2016, 01:32 PM
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BlackoutSteve BlackoutSteve is offline
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Are you sure that's not 8 intitial plus 28 centrifugal for a total of 36?
That would make sense.

Also, I'd have a lot more initial than 8. I'd go 16 then reduce the cetrifugal amount to arrive at what you want your total to be.
You'll have a much stronger idle, more response and a smoother off-idle transition.
I'd also strongly recommend adding vacuum advance for an even stronger idle, part throttle cruising manners and response plus much better fuel economy.
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