Carb Synchronizers, Carby Tuners and Vacuume Guages

[MartinMille BANNED]

Hi All

I had a problem the other day where the bike was farting and carrying on backfiring etc , as I had replaced the coil pick up's wiring not that long ago I first thought one pick up might of been damaged, I started with the simplest item first and that being the plugs ,a new set installed and purring away cool all fixed rode down the road and same thing again grrrrr off with the plug leads and out with the ohm meter, nope thats all good as well so I started to play around with the mixture and cable settings BAD mistake no Carb tuner at hand , I started to give it a go mind you this was on Xmas day at 9am in the back yard ,waiting for the not so friendly neighbors to start calling round but nothing came of it so I waited an extra day
It was than that I check the fuel yep nothing in there and only one carb getting fuel mind you at this point the was no return as both carbs were now completely out of sync

I had a look at the SyncPro in Steves shop as I did before but by the time I would have recieved it it would cost me AU$177 , Ok I have 4 Duc's and it would have been $$$ well spent , I did make one of those $4 jobs but couldnt get it to work , after some time using all sorts of wording in Google, trying to find another make or Carby tuner/synchronizer I was just about to give up when I came across one that was called Carbtune (no link will be posted) and they make a 2 or 4 pot tuner there is the go I thought and was well priced to boot , Its on its way to me soon and hopefully it will do want I want it to do

[Vince]

They make 2 types one with Murcury and one with metal rods,I have the Murcury one and it works well but the later is a newer design and is suppose to be better,the one I bought at MCA,in Sydney cost me $150,OZ so Steves ones are cheaper

[MartinMille BANNED]

Yep I have bought the stainless steel rod type as they dont sell them with mercury anymore and at AU$105 landed that will do me just fine

[Vince]

That makes sense,sending Merquiry through the post would be a problem,
I tried to transport mine to a mates place once and had a spill,not good,
but they sell replacement bottle thankfully at MCA

[MartinMille BANNED]

I posted this in another section as it had to do with coils but now its back to fuel

""Ok the old std coils and resisters are back on the bike (for now) and the backfire is gone BUT what a sh!t fight I'm having with the balancing of the carbs. did as per how to tune the carbs written by Steve , back off the cables ,back off the slide screws and mix on 1 1/2 turns out start the bike and get some sort of idle happening and this is where I come to a full stop !

Even with the idle screws fully in I can not for the life of me, get a high idle like they should , yes I'm getting full fuel and I have blown out the all the carb passages and galleries and changed the rubber inlet manifold spacers as well (granted not with a new set, but this is all I had at the time) ,

I'm at a complete stand still HELP Confused""

One week one after obtaining all the part etc etc

I ordered some new manifold gaskets to see if this would improve the lack of vacuum at the gauges, Off with the 34mm carbs and manifolds and on with the 40mm carbs and manifolds new base gaskets and correct length throttle cables, start her up ,quick warm up and how simple is it now to set the base idle, on to the mid range cable adjustments and all is well again

As far as the acc pumps are concerned when should these be replaced ?

[Lumpy]

It sounds a little dodgey I know but I`ll replace mine if they don`t pump anymore. Yes yes I know, they should be changed out as a matter of course. They are heading for over 30 years old and the carbs have seen some 2 kits through them in that time but like my dear old Dad told me, "If it ain`t broke, don`t mess with it son".
Take the air cleaner off, have a look down the throat of the carb while you twist the throttle and see if you`ve got a healthy jet of fossils flying down there on both.
Added to that they are not the sort of thing that will stop you getting home if they fail. Not that I know of anyhow, never had one fail.
I had one instance after the last carb re-kit where one would not prime up after I put the carb back. I thought it`s finally gone and packed it in. I had to go some where that afternoon so thought "she`ll be right". It`s only a short run. Checked it again on my return and it was fine and has been since.

[Craig in France]

I ordered some new manifold gaskets to see if this would improve the lack of vacuum at the gauges, Off with the 34mm carbs and manifolds and on with the 40mm carbs and manifolds new base gaskets and correct length throttle cables, start her up ,quick warm up and how simple is it now to set the base idle, on to the mid range cable adjustments and all is well again

As far as the acc pumps are concerned when should these be replaced ?

Hi Martin,

Sorry to be dense, but ...

So, do you reckon it was the manifold gaskets in the end? Or can't you tell, 'cos you swapped carbs as well?

Re. the pump diaphragms: essentially, the pumps are there to compensate for the temporary loss of vacuum - and therefore fuel - when you open the throttle quickly. This is how the Dell'Orto manual explains it:



Basically, you can run ok without them - and racers, then and now, did/do so; but you will probably end up with larger atomiser and/or main jet to overcome the stumble, and your fuel economy will suffer accordingly.

So, like Lumpy, my approach is, as long as the pumps are pumping, to leave them alone. But if you've got the carbs apart anyway - or you're looking for something to fiddle with - feel free to change the diaphragms, remembering to also re-set the pumps to deliver the correct amount of fuel.

Ciao

Craig

[BevHevSteve]

replace those things, they are hard as a rock by now. To set back correctly, 20 pulls on the throttle cable should yield 5cc gas out the jet.

the pump diaphrams should be soft like a surgical glove to work correctly.

[MartinMille BANNED]

When I cleaned the 40mm carbs I check to diaphragms and they are nice and soft, both primer pumps work as they should with a nice strong stream of fuel,

Now to the 34mm carbs , just to prove a point to myself
I have just removed the 40mm gear and re-installed the 34mm stuff , no problems at all working like they should with the new gasket

The backfiring was by caused by me !!! this came from over-tightening the rubber base blocks and what was happening , air was sucked in through the layers of the rubber where the steel plate is sandwiched and sucking through to the stud holes , this is why there was no rpm increase when I sprayed the rubber blocks , the rubber blocks when looking at them you you had to look real hard to see the split ,this is what through me right from the beginning , anyway all is well and the 40mm gear will go back on later today

[Lumpy]

Alls well that ends well. Doncha love it when you finally find the cause of that pesky problem. I still get a kick out of it even when I`m the cause!!!!

[Craig in France]

<snip>

The backfiring came from over-tightening the rubber base blocks and what was happening, air was sucked in through the layers of the rubber where the steel plate is sandwiched <snip>

Ah, ha! Good find. Glad to hear all is now ok ...

Ciao

Craig

[tony]

Hi

was wondering if you traced the problem for this - I am having same issues now on my 74 GT750 - starts easy, idles and rides away nicely on choke, idles without choke smoothly, but once the revs pick up it backfires and spits along.

I have bought a dellorto re-build kit & rubber manifolds from Steve but before I tackle that, was curious what solved your issues

tony

Hi All

I had a problem the other day where the bike was farting and carrying on backfiring etc , as I had replaced the coil pick up's wiring not that long ago I first thought one pick up might of been damaged, I started with the simplest item first and that being the plugs ,a new set installed and purring away cool all fixed rode down the road and same thing again grrrrr off with the plug leads and out with the ohm meter, nope thats all good as well so I started to play around with the mixture and cable settings BAD mistake no Carb tuner at hand , I started to give it a go mind you this was on Xmas day at 9am in the back yard ,waiting for the not so friendly neighbors to start calling round but nothing came of it so I waited an extra day
It was than that I check the fuel yep nothing in there and only one carb getting fuel mind you at this point the was no return as both carbs were now completely out of sync

I had a look at the SyncPro in Steves shop as I did before but by the time I would have recieved it it would cost me AU$177 , Ok I have 4 Duc's and it would have been $$$ well spent , I did make one of those $4 jobs but couldnt get it to work , after some time using all sorts of wording in Google, trying to find another make or Carby tuner/synchronizer I was just about to give up when I came across one that was called Carbtune (no link will be posted) and they make a 2 or 4 pot tuner there is the go I thought and was well priced to boot , Its on its way to me soon and hopefully it will do want I want it to do

[MartinMille BANNED]

Hi Tony

Start with the manifold spacer/gasket
In my case I had a faulty igniter box spiking a coil both were replaced and my problems were solved

Cheers Martin