Carb Issues

[Fitzy1980]

A question for the engine gurus out there.

I've got issues with the quad webers popping etc under heady acceleration in certain gears/revs.

Will pull like a freight train then start falling into a hole, stumbling and popping through the carbs. Also seems to be running very rich also.

Could it be a timing issue ? I'm under the impression quad webers love lots of timing and if its too retarded it becomes just a rich, lazy engine popping its head off.

Taking it for a dyno/tune this week but just curious as to what it could be in the interim.

Cheers

[shaunp]

Timing increases Vacuum so it can pull more fuel though the jets

[jiffy]

^^ never heard that before ^^

When this occurs, does backing off slightly fix it?

[sms777]

If it's running rich and popping at high RPM it means it's not burning due to ignition issues. What type if ignition system are you running? If you don't already have an amplifier I suggest invest in a MSD or ICE ignition system so it can be supplied with the correct amount of spark that needs at high RPM. Still I would not run more than 36 degrees of total timing unless you are running racing fuel or methanol.

[Fitzy1980]

If it's running rich and popping at high RPM it means it's not burning due to ignition issues. What type if ignition system are you running? If you don't already have an amplifier I suggest invest in a MSD or ICE ignition system so it can be supplied with the correct amount of spark that needs at high RPM. Still I would not run more than 36 degrees of total timing unless you are running racing fuel or methanol.

It's running an msd

[GLENN 70]

What timing are you running ? . What air cleaner set up also ? .

[69ISH]

What timing are you running ? . What air cleaner set up also ? .

Air Cleaner?  have a look for yourself
http://www.mustang.org.au/forum/index.php?action=dlattach;topic=28422.0;attach=9357;image

[GLENN 70]

Gee thanks Rodney ,AIR CLEANERS 

[MACH_ONE]

Air Cleaner?  have a look for yourself
http://www.mustang.org.au/forum/index.php?action=dlattach;topic=28422.0;attach=9357;image

 

[sms777]

Ok.....so you are running an MSD. Take off the cap and have a look inside, it could be full of rust like happens to lots of MSD's. If there is no corrosion than check your spark plugs. Are you running the correct heat range?

[GLENN 70]

  MSD dizzy s  tend to get corrosion inside them .  When I was running webers they would pop and be quite noisy and that's why I asked what air cleaner set up you were running . The ram tube set up make a lot of noise .  I found when mine popped under hard acceleration the fix was a new set of NGK plugs with the right heat range and plug gap fixed it every time . Still don't know what timing you are running ,as the initial timing might need upping but no more total than 34 to 36 max .

[Fitzy1980]

Sorry for the late replies. Honestly cant remember the timing.

I pulled a couple of plugs earlier and they were pretty ordinary so ill put a new set in tomorrow and see how it goes. I'll check inside the msd as well.


I know the quad weber setup is renowned for the pops etc it was more so the surging, excessive popping under throttle at certain rpm.

See what tomorrow yields

[Fitzy1980]

Alright,

Changed the plugs and it made a massive difference, probably 90% difference but there is still a small amount of surging, popping.

Checked the distributer, all good. So im thinking its probably worth putting in new leads ?

[GLENN 70]

Ok the plugs were the problem (common ) . You still need to check the timing and who knows it might be over advanced .  Throw a timing light on it and tell us what the setting are . Timing at idle then at around 3,000 rpm and with the vacuum line blocked from the dizzy if its got one . Hope you put NGK plugs in .

[Fitzy1980]

Ok, i've drained the fuel and it was crystal clear.


I tested the resistance of the leads and i think that could be the issue.

Cyl 1 - 59
Cyl 2 - 74
Cyl 3 - 96
Cyl 4 - 138
Cyl 5 - 70
Cyl 6 - 96
Cyl 7 - 4.5
Cyl 8 - 265

Leads are MSD 8.5 Super conductor. Apparently supposed to read 40-50 ohms per foot, 36" wire between 120-150 ohms.

Thoughts ??

[BAC]

Thoughts ??

The two outlying results (7 & 8) are a bit concerning. 

[Fitzy1980]

The two outlying results (7 & 8) are a bit concerning.

Yeah, im at a loss there.

New leads im guessing yeah ?

[birdman]

Yeah, im at a loss there.

New leads im guessing yeah ?

Rule of thumb,old skool trick,never run #7 & #8 leads along eachother...

[Fitzy1980]

Rule of thumb,old skool trick,never run #7 & #8 leads along eachother...

Interesting.

How far apart are we talking ? The leads have clamps that run them together so how do you avoid this ?

MSD leads apparently prevent this with the there winding procedure and core material.

[shaunp]

Interesting.

How far apart are we talking ? The leads have clamps that run them together so how do you avoid this ?

MSD leads apparently prevent this with the there winding procedure and core material.

It depends on what the fireing order is as to which cylinders cant be routed together , ie that fire consecutively, so 6 & 5 of 351 late 302 and 7&8 on 289 early 302, just run another lead between them. It also important the trigger wires to the MSD do no run with or near plug wires of coil feed wires.

[Fitzy1980]

Still no change to the stuttering, popping, ignition issues. In fact it seems to have gotten progressively worse. I'm getting a bit of back firing now when coasting and occasionally on up and down shift. It's always popped etc under heavy braking etc but now its letting out a few big bangs. Replaced the coil to eliminate that, no difference.

I'll throw timing light on it tomorrow and check that. What am i looking at timing wise, 38 degrees total timing seems to be the consensus.

Spoke with Weber Performance and they seem to think its running lean in the top end or its running rich on the idle side and leaning out when it hits the mains.

I just don't understand how it could be so far out of whack considering it was driven maybe 2 or 3 times over a mth or so. And nothing was touched at all and was running like a gem before.

[GLENN 70]

  

[69ISH]

I am no mechanic by any means but with the experience of the last 3 carbys I have had on my car in the last 12 months (A couple have been on 2 or 3 times) I am betting it is running way to rich which is fouling up your plugs and causing the banging/popping/misfiring. Seems to be exactly the same symptoms and when you throw a new set of plugs in it runs great until they start to foul up again.
I purchased a new Quickfuel black diamond 830, I am currently running Speed Demon 750 (Which when first fitted one of the secondary jets was found sitting in the bottom of the bowl) and both had dumped heaps of fuel and ran great for maybe 50 -100Klms and then fouled the plugs.
If this is the case you are likely washing your bores with overfuelling and I would dump your oil as you do not know how much fuel has ended up going into it.
Another tip if this is the case don't bother trying to save your plugs as none of mine came good after running so rich and just cause tuning issues, Ask Glenn70 he reckons I should have shares in NGK.

[birdman]

It depends on what the fireing order is as to which cylinders cant be routed together , ie that fire consecutively, so 6 & 5 of 351 late 302 and 7&8 on 289 early 302, just run another lead between them. It also important the trigger wires to the MSD do no run with or near plug wires of coil feed wires.

Thanks for the reply shaunp... you beat me to it

[birdman]

Still no change to the stuttering, popping, ignition issues. In fact it seems to have gotten progressively worse. I'm getting a bit of back firing now when coasting and occasionally on up and down shift. It's always popped etc under heavy braking etc but now its letting out a few big bangs. Replaced the coil to eliminate that, no difference.

I'll throw timing light on it tomorrow and check that. What am i looking at timing wise, 38 degrees total timing seems to be the consensus.

Spoke with Weber Performance and they seem to think its running lean in the top end or its running rich on the idle side and leaning out when it hits the mains.

I just don't understand how it could be so far out of whack considering it was driven maybe 2 or 3 times over a mth or so. And nothing was touched at all and was running like a gem before.

What fuel did you top up with last? Always use BP95 or Caltex95 forget the rest...