Carburettor refitting and tuning – 7 Sep 16.

After rebuilding the Dellorto VHB carbs on my V7, and bench-testing the one which previously leaked as best as I could, It was time to refit them to the bike.

I smeared a little copperslip on the carb mounting stubs. This made it easy to refit the carburettors to the manifolds and hopefully they’ll come off easier next time. I also screwed on the aluminium intakes (which connect to the rubber boot) before fitting the carbs to the bike. New gaskets were used between the intake manifolds and cylinder heads. Old Guzzis with solid (rather than the later rubber) inlets use two gaskets stacked on each side to act as heat insulation. There are also insulating washers under the heads of the intake mounting screws for the same reason. I have wondered about getting some PTFE (Teflon) to make insulators from. These might not stick to the inlet manifolds and cylinder head and be destroyed like the conventional gaskets on dismantling. For the moment, I just used lightly greased replacement gaskets.

Once I was sure the carbs were at the angle I wanted, I tightened up the fixing clamps and fitted the fuel hoses.



I turned on the fuel at both taps and thankfully everything was fuel-tight.

I reconnected the throttle cables


and those for the enrichers (chokes)


Just after taking this photo the choke spring was launched before I could get the piston back into the carburettor. Once inserted it can’t get free. It only took 40 minutes to find where it went!

I got the rubber intake boot back on but, as I expected, I had to remove the battery before I could refit the air cleaner box. To do this the other side panel had to be removed and was left dangling on the speedo cable.

I put a little grease on the air cleaner box before offering it up to the rubber boot. This fits around the outside of the lip on the box, just pushing up against it.




Once the air box is back on, I wipe off any grease I can see so that it doesn’t attract the muck.

Once the battery and side panels had been refitted I gave the carburettors some initial settings so I could get the bike running and warmed up before tuning the carbs properly. I set the left carb mixture screw to 1½ turns out and the right to 1¾ as per the workshop manual. I set the throttle stop screws to about 12mm out on each side.


It’s important that these screws are never turned while the carburettor slides are resting on them. Always hold the throttles open with the twist grip when altering them to prevent damage to the slides or the tips of the screws.

I checked there was slack in all the cables and started the bike. I had to turn both the throttle stop screws in a full turn to get the bike to run, albeit very badly. It was time to get the vacuum gauges out again.


I’ve described how to set the carburation using vacuum gauges before when I did this on The Racing Rhino so I shan’t do so again. You can refer back to it here.

Later, I took the bike out for a short run to make sure it behaved properly. By then it had cooled properly so I was able to start it using “choke” and ride it to warm it up. It seems to be running well.

However, before going for a ride I tackled another job I’ve been meaning to do for a while. I’ll post about that in a minute.


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