Getting the best form your carbs

[baileymc]

Following a great day at Cadwell in September I went away with the intention of upgrading my suspension and getting my carbs cleaned and balanced. The suspension was easily sorted courtesy of NLM who flogged me a pair of Hagon rear shocks and a pair of progressive springs for the forks. Raising the ride height by approx 3 cm over the old saggy Girlings has certainly made a big difference!!

With the suspenders sorted I turned on the carbs. The engine is 375 cc and one of the chokes had never worked. I had also noticed at Cadwell that the bike ran out of puff at around 7000 rpm in top. Stripping the carbs down, cleaning out the crud, replacing the gaskets, O rings and seals brought the absent choke back into play, but performance was still soggy past 7000 rpm.

I checked the tappets and reset the ignition timing by retarding it slightly ( previously, in trying to hit a compromise between both cylinders the front pot was set too advanced). I retarded the timing on the front cylinder so that it was bang on the button when at the point of maximum advance.

My strobe has a digital readout so I can monitor the revs closely when setting the carbs. Vacuum gauges were also employed. Both pilot screws were set, then the idle screws and finally the vacuum gauges response was balanced by a tweak on the throttle cable adjusters. The process was repeated once and I was happy that all was stable. A test run gave better mid range response but showed no marked improvement in top end performance so I changed the 115 main jet for 117s and bingo! It'll now pull right through to 8500 rpm in top. Has anyone else had a similar experience or is it just that the 375 cc engines run better with a slightly richer mixture at full throttle?

[Ralph]

Mines just a standard Strada but when I fitted new as in pattern silencers it went all fluffy and 115 mains up from 112 sorted it but after a few mile as in a thousand or two it had to be put back on the 112s but as to revving it will rev cleanly into the red no problem, carbonation is very clean, it will pull non snatch from less than 30 in top show 100 mph and do 100 mpg but not at the same time.
When checked with a calibrated rev counter mine shows a slight under reading at 1200 rpm the engine is doing about 1265rpm, I always thought it over read but it doesn't.

[Morizzi]

I find it interesting that no one seems to compensate for the different rotational requirements of the 2 cylinders when balancing using vacuum gauges.

The front cylinder only has to rotate the engine 288 degrees but the rear has to rotate it 432 degrees but most seem to give the 2 cylinders equal fuel and vacuum. This is only really relevant at idle, I know. After that the cables take over and the slight difference should be almost insignificant.

Just a thought to get the neurons moving.

[EVguru]

If you set up the idle screws for minimum vibration at idle, then check with a vacuum gauge, you'll be close to equal vacuum. It's much easier to use the gauge of course. Synchronising the cables is just as important. The feel and ridability of the bike is much improved when the slides are properly synchronised. I expect to be able to trickle along at just above idle and then accellerate by gently winding on the throttle with no use of the clutch.