Topic: UNBELIEBEABLE, can't find a definte answer! cb350 tach...still!

[kurtanton]

Hi,

I called all over the country, scoured the web. Got confused with the responses on here, is it 1:7 or 1:4?! So I took a drill to them, on the 1:7 i got 2600rpms, then one the orginal I got 3000! So it seems as if the 1:7 ratio isn't the right one, what could it be? Does anyone know ANYONE I could call that would know? I am looking for the mini chrom tach CORRECT ratio...not even the vendors could tell me, so I tried to find the manufacturer, and the vendors said they don't talk to them, can't communicate. What a debacle! Thanks for the input so far, but it seemed inconclusive...or maybe I read it wrong. Sorry to clutter up the forum, but I can't believe this information is not to be definitively found!? Going crazy..maybe have to sell bike....jk!

Thanks,
-Kurt

[eldar]

You are likely to NOT find a direct replacement as gear ratios can vary widely. The ration may not even be a whole number. It sould be 1:4.5 or something like that. So unless you get lucky or go onto tons of websites and find someone by accident who knows the ratios of certain tachs, are are left with trial and error. You may actually want to look into an electronic tach that does not use gearing which would work better but of course be quite pricey and may not actually work well for a bike.
You may even have to fabricate a geared unit that will make the changes needed to use a different tach.

[Geeto67]

if this is a JC whitney tach then you might as well throw it away since it will be junk soon anyway.

First question, Is your old tach accurate? Go get a dwell meter and test the actual RPMs electronically. Something tells me comparing a brand new tach to a 30 year old one for accuracy isn't the brightest idea. (BTW are you using the same cable for the test? is the cable well lubed and the tachs in the same position? any varation in cable makes a huge difference). While you have the dwell meeter out, make sure your timing is on the money.

Second question, why don't you get an electronic tach like the ones autometer makes. If the is a cb350 four (I am assuming it is since this is the SOHC 4 forum) I know they make tachs for 4 cylinder and single cylinder drag bikes, one of those has to work. This way you have an accuate reading not subject to cable flex and stretch.

Third question, you do know that those little chrome gauges are not the most accurate thing on the planet, right? I would consider them closer to suggestions than actual readings. If you bought the JC whitney one you might as well throw it out now since it it will probably be nonfunctional in 6 months. Cobra and drag specalities make high quality mini tachs that are reasonably accurate, you might wanna contact them (their gauges are more expensive however) Cobra's mini tach has an integral bar mount that is super slick. 

[Clyde]

The ratio is 20:3