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post #1 of 20 (permalink) Old 04-18-2019, 08:18 PM Thread Starter
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Starved for power, Alfa gurus needed!

Hey guys!

My 74 GTV 2000 has developed a strange issue while at the shop having other things fiddled with, Iím scouring the forums here for similar symptoms but have yet to turn anything up just yet. I figured I would share my story and see if anyone has any input / suggestions!

Ok, so... i brought my gtv in for some minor adjustments/fixes. New dash, pull out aftermarket AC components, new steering box, and finally a new set of jets ect for the carbs that Gigem recommended i try out, as i have his old car and it has an identical engine as his blue one with the exception of the jetting on the carbs. He said his latest endeavor to retune the carbs led to big improvements over what i currently have....

Anyhow, we go about replacing the jets and tubes and venturis, upon firing it up, the idle is fine, same as it ever was. Seems to rev freely and act as it did before... that is until we pull out of the shop to shake it down. As soon as load is out on the engine it just Boggs down, no power. No matter what the pedal position is. No missing, no detonation, just feels... well.. plugged up... it drives fine on the lift, it revs and idles fine. This only happens under load... so we reset everything in the carbs back to how they were. Tried to drive it again, same issue...


Things we have tried so far:

Swapped coils, swapped plug wires, swapped distributors for an original mechanical style, bypassing the street fire and msd unit... basically did this one by one and also together, in essence bypassing all of my ignition system with a new one, well known working one...

So We hooked up a color tune and gave the above methods another shot...

No matter the distributor/coil/ignition box that was hooked up we noticed a flicker of spark on the color tune on cyl 1&2 (closest to front) and strong bright sparks on 3&4 (closest to firewall.)

We swapped the color tune plugs around and got the same response...

All grounds on the car were checked, voltage was checked to each unit down the line, it all checked out fine.

Removing the cap on the front cyl carb, we found the seal gasket (rubber) was distorting, like brake fluid on paint kind of distorting. I am wondering if i got some bad gas the day before i brought it over and maybe the accel pump is in a similar state on that carb? Havenít pulled them yet to see...

Honestly Iíve heard from two people to check the exhaust for blockage, as thatís what it feels like when you try to drive it... but it only has one muffler in front of the stinger and the flow out of the tail pipe seems to be ok when idling/revving....

Also found a bunch of rust in the filter/carbs. Cleaned all the jets ect, need to do a more thorough job, but just trying to get it back to 1 right now before i tear it all apart for a HG (weeping oil down the back of the block)

Any ideas?? Help? Offers on the car i kid i kid...


Here are some specs..

74 gtv 2k
Weber 40dcoe151 (Spanish, ugh i know)
Euro manifold
Msd coil
Street fire cdi
Electronic distributor ( not a 123, canít rember the brand right now, started with an H?)
Motronic 10.1
RJ Cams
1mm upsized intake valves
Ported head
Shankel headers

Before i was seeing an AFR of about 12-13.5 at idle, 13.5-14 under load
Idling around 11-12 now... at about 900-1k rpm


Happy to provide more info if i can, hopefully someone has some input! Thanks!

Current Garage: 18' TRD Pro 4Runner (DD), 13' Ducati Hypermotard (Canyon Express), 74' GTV 2000 (Soon to be Outlaw'd) Work: www.trahanphoto.com
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post #2 of 20 (permalink) Old 04-18-2019, 08:53 PM
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The car is falling on its nose so to speak. This means that there is a fuel delivery problem. The car idles as it is running on the minimum pressure. When you open the throttles to meet demand the pressure isn't there to run the car.

check the fuel pressure. (2-3 psi for carbs) The inlet pipe to the fuel gauge sender/fuel pump pick up could be clogged with sediment. It is a fine brass screen.
Check the tank filter to make sure it is clean and flows.

Next, make sure the inlet screens are clean by removing the tops just above the inlet pipe on each carb.

Next, check the jets to make sure they are clean and that the passages are free flowing. You can use carb cleaner in a can with the plastic pipe to do this.

Lastly, report you findings.

Christopher

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post #3 of 20 (permalink) Old 04-18-2019, 09:19 PM Thread Starter
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Quote:
Originally Posted by velocedoc View Post
The car is falling on its nose so to speak. This means that there is a fuel delivery problem. The car idles as it is running on the minimum pressure. When you open the throttles to meet demand the pressure isn't there to run the car.

check the fuel pressure. (2-3 psi for carbs) The inlet pipe to the fuel gauge sender/fuel pump pick up could be clogged with sediment. It is a fine brass screen.
Check the tank filter to make sure it is clean and flows.

Next, make sure the inlet screens are clean by removing the tops just above the inlet pipe on each carb.

Next, check the jets to make sure they are clean and that the passages are free flowing. You can use carb cleaner in a can with the plastic pipe to do this.

Lastly, report you findings.
Yes! Falls flat on face, big time.

Thanks! The shop isnít open tomorrow for Good Friday, but he is thinking he is going to come in Saturday to investigate this further, was going to over to help poke around again. Will certainly investigate these items, i was leaning this way too but i couldnít explain the idle and ability to rev freely in neutral. If that is because itís getting by on minimum flow, during those occasions i understand but, doesnít the fuel demand go to the same levels when bringing the engine speed up regardless of load on engine?? i.e revving vs. driving

Current Garage: 18' TRD Pro 4Runner (DD), 13' Ducati Hypermotard (Canyon Express), 74' GTV 2000 (Soon to be Outlaw'd) Work: www.trahanphoto.com
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post #4 of 20 (permalink) Old 04-18-2019, 09:39 PM
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Sounds like maybe water in the fuel. It gets stuck in the jet passages and doesn't come out easily.


P. The water settles
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post #5 of 20 (permalink) Old 04-19-2019, 11:35 AM
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did you put the original jets back just to try
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post #6 of 20 (permalink) Old 04-19-2019, 12:16 PM
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74 US models have a rear inline filter on the underside of the fuel tank, if still present have you changed it?

Cars ruined my life! 😱
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post #7 of 20 (permalink) Old 04-19-2019, 12:44 PM Thread Starter
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74 US models have a rear inline filter on the underside of the fuel tank, if still present have you changed it?
Yes, Pulled the filter that was there, had alot of debris in it. Swapped it out with a fresh unit. I should mention after about 2400 miles of driving, I havent had an issue with crap getting blocked up in the carbs, that I know of at least. Maybe it had a slight issue all along and the simple action of the jets and other work done, caused some grit to go somewhere it wasnt before?

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did you put the original jets back just to try
Yep, tried going back to original, as well as swapping one jet / tube / ect at a time in each carb to no avail

Current Garage: 18' TRD Pro 4Runner (DD), 13' Ducati Hypermotard (Canyon Express), 74' GTV 2000 (Soon to be Outlaw'd) Work: www.trahanphoto.com
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post #8 of 20 (permalink) Old 04-19-2019, 01:59 PM
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Could you have put an aux venturi in backwards? Don't ask me how I know. Before you pull them, use a mirror to confirm that the cones are all the same. If not, there's your problem.

Last edited by gmjohns; 04-19-2019 at 02:05 PM.
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post #9 of 20 (permalink) Old 04-19-2019, 02:21 PM
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Either that or your chokes are too large. Did you confirm you swapped new with same same?
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post #10 of 20 (permalink) Old 04-19-2019, 02:53 PM
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Lack of airflow? butterflies not opening fully - try removing the air filter and look (or use your phone) to check. Or a big blockage on the intake - try running without the air filter?

Ignition - are you getting speed advance?

1975 GT Junior with 2 litre lump
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post #11 of 20 (permalink) Old 04-19-2019, 03:17 PM Thread Starter
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Quote:
Originally Posted by gmjohns View Post
Could you have put an aux venturi in backwards? Don't ask me how I know. Before you pull them, use a mirror to confirm that the cones are all the same. If not, there's your problem.
Will double check, but they were swapped twice during the testing. 97% sure they are in order.


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Either that or your chokes are too large. Did you confirm you swapped new with same same?
Same Same, ran fine previously. Same chokes.

Quote:
Originally Posted by malcolm1 View Post
Lack of airflow? butterflies not opening fully - try removing the air filter and look (or use your phone) to check. Or a big blockage on the intake - try running without the air filter?

Will check on this, but it seems to rev/open up ok in neutral. Under load is when the issue occurs.

Ignition - are you getting speed advance?
How do i check for this with a digital distributor?


Any ideas on the dim looking spark on 1&2? Could this be happen because itís not getting enough fuel from that carb due to blockage?

Current Garage: 18' TRD Pro 4Runner (DD), 13' Ducati Hypermotard (Canyon Express), 74' GTV 2000 (Soon to be Outlaw'd) Work: www.trahanphoto.com
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post #12 of 20 (permalink) Old 04-19-2019, 03:34 PM
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How do i check for this with a digital distributor?

With a timing light aimed at the front pulley - assuming the timing marks are visible. As you rev the engine the timing should shift towards the M (max advance) mark


Any ideas on the dim looking spark on 1&2? Could this be happen because itís not getting enough fuel from that carb due to blockage?[/QUOTE]

Not sure. When it "bogs down" does it misfire - I would have thought it would misfire if running lean (lack of fuel)

1975 GT Junior with 2 litre lump
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post #13 of 20 (permalink) Old 04-19-2019, 04:02 PM Thread Starter
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Originally Posted by malcolm1 View Post
How do i check for this with a digital distributor?

With a timing light aimed at the front pulley - assuming the timing marks are visible. As you rev the engine the timing should shift towards the M (max advance) mark


Any ideas on the dim looking spark on 1&2? Could this be happen because itís not getting enough fuel from that carb due to blockage?
Not sure. When it "bogs down" does it misfire - I would have thought it would misfire if running lean (lack of fuel)[/QUOTE]

When it bogs down it doesnít seem to miss or detonate at all. AFR was reading a bit rich... not excessive though. We swapped distributors, boxes and coils to no avail..

Current Garage: 18' TRD Pro 4Runner (DD), 13' Ducati Hypermotard (Canyon Express), 74' GTV 2000 (Soon to be Outlaw'd) Work: www.trahanphoto.com
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post #14 of 20 (permalink) Old 04-19-2019, 05:13 PM
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Misfiring will cause the wideband to read high (lean) even if it is not really lean. AFR is based upon oxygen in the exhaust. When the engine misfires the oxygen in the cylinder is not used up in combustion, the sensor reads higher oxygen and the AFR meter interprets that as high AFR.
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post #15 of 20 (permalink) Old 04-20-2019, 09:51 AM
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How old are your plug wires?
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