Carbs popping on GT4

Hi Everyone!
I have developed a problem I hope you can help me with.
My GT4 has been running great, I got stuck in some really heavy traffic and it started missing.
So I went home, changed the plugs and checked the carb balancing, there was a little play between the linkage of the front and rear bank of carbs, so I adjusted them until they all read 35 on a Weber balancer (one of those things you stick on the trumpet and it tells you what the drag is).
But, as soon as I touch the throttle it starts popping and spitting up through two carbs. (cyl 3+4 and 5 + 6)
The timing is OK, tick over is smooth at 850 rpm, no noises, HELP!!
It sounds like a dog, but floor it, it clears and the power comes in.

any ideas?

Cheers in advance.

Nick

 

Wish I could help, mine only pop and sputter a bit while warming up, after that she runs fine. I'll be watching this thread to see what the responces you get are, allways learning ya know! How'd the plugs look?

Cheers!

DT

 

Don't know about the carbs, but it could also be a ignition issue. Are your distributors advancing like they should?

 

The plugs are fine, it just seems though that if you hold the throttle at about 1500 rpm it pops and spit up through the carbs. It isn't on releasing the throttle but at a constant RPM and on mild acceleration. As I said, floor it and it go up to 7k no problem and suddenly you get a kick in the back as it clears and takes off.

Embarrasing driving it at slow speeds!!

 

That's what I thought, but why only on two carbs? I have a euro single dizzy motor with a black stallion ignition system - again new.

 

ahhh..... I assumed twin distributors

 

Could be you're lean on those two carbs. Maybe you picked up a piece of grit or dirt or something from the fuel lines and it's causing a clog in one or two of the jets.

Just a thought...

 

I also think it sounds like you have gone lean on those two carbs. Its time to strip them down and have a little look.
My car spits and pops on a cold start until warm, its very common on the GT4. I hear its best to run them a little on the rich side and it reduces the problem.
Good luck Nick! keep us posted.

Mark...

 

Pull the idle jets and clean them. You may also need to go through the complete synch procedure again.

Birdman

 

Follow the birdman.... 123 ducks can't be wrong!
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Yep, that's what I guessed. Cleaned everything but now just one carb messing about.
Set everything to default, 3 1/2 turm on idle as per manual, disconnected all linkages and one carb showed a major difference between chokes, although I evened it out, at 1500 static and 2000 it started spitting again.

At ths point I had to stop, being 10:00 PM I was getting angry looks out of bedroom windows (due to noise I guess), so packed up for the night.

What could cause a BIG difference between chokes on one carb? I cleaned all the jets, never had this before?
I love Webers!

 

There are air-bypass screws (located above the idle mixture screws and just below the starting mechanism lever/plate. These bypass screws are locked-down by nuts). They are used to balance out air flow between the two carb throats of each carb.

One of these bypass screws could be opened more than the other. Air from these bypass circuits do not come from the carb throat, so would not register on your flowmeter (and therefore, you wouldn't know it). They exit below the throttle plate and above the progression holes.

Listen inbetween the throats of each offending carb with a stethescope for the sound of the flowing air and notice any difference. As an experiment, shut all of these bypass screws and see how the car runs/drives.

I have never used the bypass screws on my carbs, each carb throat flows evenly without the use of the bypasses, so I've left it alone.

 

Hi Peter
I did that last night, all carbs bar one are roughly equal, however this one is vastly different between chokes (one choke read 5 whilst the other 3). I evened it out on the bypass screw but it still pops and spits. Today I will take it off again and see if there is a blokage somewhere, maybe a leaking inlet gasket?

 

Your bypass screws just even out air flow they have little to do with the mixture adjustment which it sounds as if you are running lean, pull some plugs and check them then adjust your idle mixture to stop the popping accordingly.

 

In desparartion I stripped the offending carb down, cleaned everything, then reassembled the lot, including the throttle flaps.
Put it all together and presto, runs like a dream. Must have been either a bit of grit in a jet or an air link on the manifold.

 

What a great thread! I learned a bit more that I new before by following along. Good stuff to know and may help me troubleshoot my Dino if she ever acts this way. Thanks a bunch. Say where does one find one of those carb balancing devices? And would be using more than 1 be more helpful?

Cheers!

DT

 

www.webercarbsdirect.com

 

I learnt a good lesson as well today, when ever you remove the carbs, change the gaskets! Could have saved a whole heap of agro.

Or here.. http://www.superformance.co.uk/308/308carb.htm