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Engine / Quad Weber Issues

6K views 64 replies 10 participants last post by  zray 
#1 ·
Greetings from Australia


New to the forum so be gentle :grin2:

Currently having an issue where under throttle at certain rpm i'm getting stuttering, possible misfire and popping through the webers.

It's only started doing this past couple of weeks.

I've changed plugs which were pretty fouled and this made an improvement but its still there.

If i keep the power into it, it does push through it but obviously it's something that shouldn't be happening.


It seems like an ignition/fuel issue, but obviously there's a number of possibilities.

Any help would be appreciated.

Cheers
 
#2 ·
G'day mate! Welcome aboard. It sounds like a possible ignition problem as it wouldn't seem likely that ALL 4 carbs are affected at once. I'd recheck breaker point condition, gap/dwell as well as the contacts on the distributor cap and rotor and condition of the ignition coil tower and spark plug wires. Check under the distributor rotor for spark jumping through it to the distributor shaft and for free movement of the breaker plate/advance mechanism.

If everything with the ignition system seems okay, check for fuel contamination, specifically water.
 
#4 · (Edited)
i assume that the carbs were dialed in and running perfect until this happened, which means i would not be looking at the carbs. at what rpm range does this happen at? is it consistent?

you might have a weak coil, a slightly leaky valve, or you might be experiencing valve bounce depending on the valve springs resonance. are you running an inner spring dampner?

another thing to look at is the pip sensor in the distributor. when they start to go bad, they send a mixed signal to the ignition control module. we had that problem on our drag car many years ago. we finally got the fuel curve dialed in on our injector, and then we started having issues with the ignition breaking up. at first just a mild issue in one rpm range, but it widened up as the ignition system failed.
 
#6 ·
Yeah carbs were fine, ran like a dream. The engine is more suited to track work and does prefer to be driven hard. It's built to handle handle 8000rpm.

Engine was put together by a racing outfit here who run similar combos in there track cars. They run a couple of cars in a big vintage racing series here so i have absolute confidence in there work. So i couldn't tell you if it has spring dampers.

Thing is its entirely random, it can happen straight out of the gate in first but then it wont. Dropping down a gear to overtake and it falls into a hole then won't. Bloody frustrating.

But as i said if i keep the throttle into it, it will push through it and pull like a freight train. It doesn't happen however if you gradually apply the throttle only when you give it the berries.



Again i appreciate all the suggestions and advice
 
#5 ·
The symptom is similar to what you get with a flattening cam lobe. But if you can push thru it, doubtful. Also like a harmonic vibration going thru the valvetrain at certain RPM's. Like when the adjustable rockers lean in too much because the pushrods are too short.
 
#12 ·
If your ignition is converted to electronic this is not applying! But a friend of mine had a similar problem with his 6-cylinder triumph engine. He went through a lot of hassle because the problem kept coming and going randomly.


In the end it turned out to be the condenser that was faulty.


Cheers
Bebob
 
#14 ·
Tell me about it.

Once owned another a 60's Holden here and it would always have a dead battery after a really hot day. Would run for days, weeks without an issue than we would have a hot day and the battery would die. Every other day it ran without an issue.

Even resorted to carrying a spare battery in the boot just in case.

Turns out the headlight switch near the window had a rubber/tar type insulation inside and the sunlight/heat would melt it causing the two terminals on the back of the switch to contact each other draining the battery.


Amount of times i wanted to burn that car to the ground >:)
 
#15 ·
Ok, i 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 ??
 
#24 ·
as i think about it, check to see how much slack you have in your timing chain. pop the dist cap, and hand crank the engine in one direction until the rotor starts to move. then hand crank it in the other direction again until the rotor moves. it should be almost instant, if not then you likely have a timing chain issue.
 
#25 ·
I'll check it tomorrow.

I was starting to now think its a timing issue.

A few times today it was really hard to start after a drive. It will wind over and over and when it does cough and fire theres a alot of burnt fuel smoke coming out of the carbs. Starter etc is fine.

I know webers will pop and crackle alot through the pipes but today it was like someone was tossing hand grenades out the back.

Was running fine a fortnight ago.
 
#26 ·
Usually popping back thru the carburetors indicates a lean condition. I used to have this condition when I ran a pair of webbers on my VW. You might want to remove the idle jets from the side of the carbs and make sure they are not plugged. A plugged idle jet will cause a popping while idleing and go away as you increase speed and the fuel system transitions from the idle circuit to the main jet. Since your problem seems to be at a higher rpm it could be a plugged air correction jet. Webbers are sensitive to fuel pressure, are you running a fuel pressure regulator to reduce pressure to about 4 to 6 lbs?
 
#37 · (Edited)
He said it was popping "out the back", not spitting back thru the intake. So that's not lean, when Weber's are lean you will get spitting or popping or whatever you what to call it out of the carb Venturi, not out the exhaust. popping out the exhaust can easily be a rich conditions, with Weber's that usually means the float level is wrong, often due to a saturated float. He would be advised to put an wideband AF meter on the car and get to bottom of this without a bunch of guesswork

http://www.clubcobra.com/modules/Jig/index.php

The guys on the Internet with the most hands on Weber 48 IDA experience can be found over on the club cobra forum and a few of the guys on the SAAC forum.

Z
 
#27 ·
So the ignition issues continue..

Anyone familiar with the MSD Blaster 2 Specs ?

According to MSD coil should read;

Primary .7 OHMS

Secondary 4.5k OHMS

I'm reading a flat 0.00 on the primary and 5.35 on the Secondary.

Would this be enough variance to potentially contribute and/or compound the problems ?
 
#35 ·
Are you looking at a liquid filled gauge that's under the hood ? The reading on those will drop, often to zero once the engine heat saturates it. That information should've been on the info sheet that came with the gauge. The only accurate reading on those gauges is when the engine compartment is COLD.


Z
 
#45 · (Edited)
Have you disassembled all the accelerator pump nozzles and accelerator exhaust jets to be sure there are no blockages ? When under full acceleration, issues with the accelerator pump circuit can exhibit the symptoms you describe. But so can a weak ignition.

Generally, Weber 48 IDA carbs are very reliable and not prone to going out of tune. I'd be looking elsewhere for an explanation of a sudden change in your cars performance. As mentioned earlier, a permanently installed wideband gauge for each bank of carbs will save you countless hours of searching I the wrong direction.

Z
 
#46 ·
Is it possible that the carbs are out of sync? It may be possible under full open throttle to get acceptable acceleration but have an unequal fuel delivery at part throttle causing popping and snorting. A Unisyn guage will tell you instantly if they are still in sync.
 
#50 ·
I've spoken with Weber here in Aus and they seem to think its leaning out at higher rpm.

Obviously this could also be a fuel issue, pump etc.

But on the off chance its the carbs whats the best plan of attack ?

Im just a bit dubious that the carbs have all of a sudden change when it was running fine and some how its magically changed
 
#52 ·
Unfortunately no mate.

I think im going to have to bite the bullet and get it thrown on the dyno.

Can't get it done till the New Year which is annoying, there busy with race meets etc. So ill have to park her up for the next month :(

It seems to be getting worse. Hitting the pedal in neutral and you can see it spit what i assume is fuel out the carbs.

Its also backfiring out the exhast just coasting along, had its usual pops etc under heavy braking, down shifts which its always done but now it will really crack some big bangs out the pipes.

Also the surging, stuttering, popping out the carbs appears to be occuring alot lower in the rev range now.
 
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