Tuning a CB77 with vacuum gauges??

DJM · Post by **DJM** » Sat Oct 27, 2018 12:57 pm

Anyone ever used vacuum gauges to set up the carbs on a CB77, or any other Honda twin for that matter?

I know the CB/CL engines aren't fitted with anywhere to connect the gauges but it would be very straightforward to drill the carb. spacers to fit the necessary adaptors.

Just wondering if it's worth the effort and if anyone else has tried it.

My CB77 has never run quite as well as the CL77, I think it's carb related and I'm just (thinking about) exploring all avenues during the winter.

DJM

Geoff Hastings · Post by **Geoff Hastings** » Sat Oct 27, 2018 1:43 pm

Here,s an alternative Dennis, use a small computer fan. Make sure you get a good seal, place the fan up against the inlet tube, connect a volt meter to the fan wires, measure the volts which will be dependent on how fast the fan spins and so how much suck each carb is subject to.

DJM · Post by **DJM** » Sat Oct 27, 2018 1:50 pm

I have a computer fan kicking about but too big I think at approx. 75mm square.

Not sure if I'm understanding this correctly Geoff, are you suggesting I remove the air filters and put the fan over the end of the rubber connecting tubes?

If so, whilst I might get the optimum setting this way for running without the air filters, would this still be the 'correct' setting once the air filters were replaced?

Geoff Hastings · Post by **Geoff Hastings** » Sat Oct 27, 2018 2:07 pm

The big computer fan might be a problem sealing it to the carb inlet hose. The small ones fitted onto the main prosessor chip would be easier. The main object is to balance two or more carbs, the extra small depression caused by the filters shouldn't affect the balance unless one filter is very different in the amount of air it will pass.

G-Man · Post by **G-Man** » Sat Oct 27, 2018 3:03 pm

DJM

I had the same thought. I have used a Morgan 'carbtune' on my Guzzi V50 and that was fine. Also worked a treat on the CB400F. Happy to lend you mine if you want to experiment.

G

DJM wrote:Anyone ever used vacuum gauges to set up the carbs on a CB77, or any other Honda twin for that matter?

I know the CB/CL engines aren't fitted with anywhere to connect the gauges but it would be very straightforward to drill the carb. spacers to fit the necessary adaptors.

Just wondering if it's worth the effort and if anyone else has tried it.

My CB77 has never run quite as well as the CL77, I think it's carb related and I'm just (thinking about) exploring all avenues during the winter.

DJM

revlover · Post by **revlover** » Sun Oct 28, 2018 1:27 am

Geoff Hastings wrote:Here,s an alternative Dennis, use a small computer fan. Make sure you get a good seal, place the fan up against the inlet tube, connect a volt meter to the fan wires, measure the volts which will be dependent on how fast the fan spins and so how much suck each carb is subject to.

Have you actually done this with success? I have trouble believing an electronically commutated (DC brushless) fan motor can be used in reverse like a wind generator. Nonetheless, I'll grab a fan and a meter and try it for myself. Seems like a better idea would be to use two identical mass air flow sensors from some kind of fuel injected engine and compare their outputs.

Geoff Hastings · Post by **Geoff Hastings** » Sun Oct 28, 2018 2:51 am

It worked perfectly well on a four carb engine. Some of these brushless motors are so efficient you can connect two together and turn the spindle on one motor and the other motor will turn also. Two airflow mass control units? it would be cheaper to book the bike into a dealership and get them to sort it.

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Tuning a CB77 with vacuum gauges??

Tuning a CB77 with vacuum gauges??

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