A little carburetor puzzle.

For all of you to understand I’m going to have to start from the beginning so you get the full picture of my problem/puzzle[:D].

As some of you might know I took my vf into the local garage last year in April to have my carbs synchronized and to have the cam timing looked at, well anyway they made a mess of it and I brought it back home(long story short lol)

Both of the right hand side mixture screws had been so badly drilled[:(!][:(!][:(!] making the carb bodies cracked and untunable, and I had no choice but to find a set of donors from somewhere[:(], luckily[:D][:D] bif helped me out with a set of carb bodies with no parts and mixture screws in perfect order.

I didn’t take me long to swop everything around and to give everything a good clean, because the manifold rubbers had seen better days I purchased 4 new ones and that took a few days to come[|)][|)].

(before I go any further both right hand carb bodies came from Bif, just the bodies…and the left hand side two remained the originals)

If there is one think I dislike and that’s trying to but the carbs back into manifold rubbers[:(!][:(!][:(!][:(!] well I had everything back on the bike and took it for a test ride in the perfect weather(snow[8D][8D]) the response from the throttle was brilliant, 60% better than the carbs before, but when I came to tune her I hit a little problem[xx(][xx(].

When I plumed up my carb synchronizer to the VF the following was reading.

The front right was showing the same as the front left.

The rear right was showing the same as the rear left. (Showing in the red, see below)

It can’t be the fault with the carb bodies Bif supplied me because (I think) Bifs donor right hand side (front) is running the same as the original left hand side (front) which is also the one your unable to tune(master), and Bifs right hand rear is running the same as the original left hand rear which is currently running on the red strip [?][?][?][?][?][?]

The rear two are running into a red strip reading (late valve timing or leak at inlet manifold or heat riser) what does heat riser mean[?][?][?][?][?][?] Balancing calibration vacuum gauges 4 cyl that’s the style if this it makes any difference. Also I’ve checked the pipes for breaks and leaks…

It can’t be leaking at the rubbers because there brand new, and I’ve made sure there seated correctly[:D][:D].

After hours of digesting [xx(] the forum on cam timing [:p][:p][:p][:p][:p](which I thought the problem might be) I spent an hour taking the casings off[xx(][xx(]. I set the rotor wheel on 1:3 (which i hope was right) and all the marks line up apart from the rear exhaust cam which looks to be 1 tooth out facing down, could this be the problem[?][?][?][?][?]

A big sorry to Bif for using his name so many times it’s the only way I could think of explaining myself lol.

Im getting so frustrated lately[:(!][:(!], I know this bike rides beautifully.
I hope you can understand this post and it make perfect sense lol.

Oh dear Brownie, If I understand you correctly you’ve split a set of 4 carbs and mated two pairs of carbs back together again ?
Why did you do that? it’s always always best to leave carbs as god intended them to be, ie mated together for life !!
Your, current balance problems are almost certainly down to your joining them carbs back together, this shouldn’t be an insurmountable problem but it could be very tricky indeed.
I think you might need to check and adjust the throttle linkages between the different bodies, it might even be that you’ve reassembled them wrongly ?
If they’re definitely correctly reassembled then there should be sufficient adjustment to get balance.
Good luck, but I’d recommend in future you regard banks of carbs as one item.

Hi Brownie,

Check the link below for info on carby synchronising, see the note at the bottom of the page regarding Interceptors, they need to be synced to No4 cyl which is non adjustable (front right from sitting on the seat) I imagine F2F is not much different


With regard to the cam timing they should all line up with the casings at 1:3 the rear exhaust doesn’t sound to be quite right. One tooth out either way is quite really noticeable, when I did mine I played around with the tooth position just to make sure I had it right (which hopefully I have!) and one tooth either way was really obvious compared to the others.

Your lard headed mechanic has likely stuffed this up as well!

Is it possible to post a picture of the rear alignment so we can double check it for you?

It can certainly be very frustrating if someone you think has repaired it has actually stuffed it up!!


If your valve timing is out as you describe then you will definitely have a negative reaction on the two vacuum gauges on the rear cylinders. I would make sure you are absolutely certain you have the valve timing correct before you touch any other carb adjustments, you could end up chasing yourself round in circles.
Good luck.

I would check out the exhaust cam position on the rear head as suggested,I cant see how your carb work would produce this symptom.Let us know how you get on,regards BIF