Tachometer Ratio

[Trogdor]

Hi folks, Repost - posted to the wrong board a minute ago, sorry for that!

New to the board, first posting. Got a 78 GS550 in a trade that needed a top end rebuild. Did that last winter, now I'm trying to get it working right. Previous owner replaced stock airbox with pods. Smells and looks (plugs) like its running really rich, but thats another story. I got the bike without gauges and I'd like to put a tach on it now to know what RPM's I'm running at when it bogs down etc.

Aftermarket Tachometers all have a Ratio, 1:4, 1:5 1:7 - I'm wondering if anybody knows what the ratio is for this model bike. Anybody have experience putting an aftermarket tach on their GS?

PS - I have a tach and speedo cable, just not the actual original gauges.

Thanks for the help!
Luke

 

[Chuck78]

1:4 tach ratio, speedo is 2240rpm=60mph, & I believe that is occasionally referred to as 2:1 as well

 

[Chuck78]

if you get aftermarket gauges, make sure that you mount them in some very very good rubber vibration isolator mounts, as they will not take much jarring or sudden harsh movements/bumps. I mounted some very nice stainless mini gauges on the gs550 with just the 37 year old rubber mounts on the upper triple, & all it too to take out the speedo & make the tach needle very bouncy was the bike's kickstand sinking into the grass & the bike falling over. Bouncy needle and then no readout, first 150 miles.

Be sure to set the float heights to spec and then check the actual fuel level (shows you in manuals) using a short piece of clear tubing attached to the drain screw threads on the fuel bowls - attach the hose to the drain port on the fuel bowl, & then hold the other end of the hose up so that it makes it a sort of u shape, so that fuel flows out in up to a level in the hose that it also resides in inside of the fuel bowl. An m5 threaded hose adapter works on bs32 carbs (80+), and m6 hose barb adapter for the 79&earlier 4 cylinderbikes with vm26 carbs.

some people just take a piece of clear tubing and shave the end down to a cone shape and a jam it in the threaded hole and then turn the petcock to the prime position. You will find the specifications of the proper fuel level, I believe it is a measurement off of the gasket surface of the carb body as well, same as the float adjustment.

if your needle&seat set are not sealing properly, they will be flooding the carbs and making everything run too rich. what year 550 is this? On the 77 through 79,raising the needle one notch, taking the fuel screws out 1/8 turn or so more, and going about 5-7 sizes up in the main jets works pretty darn well. it really depends on the exhaust restriction (stock,4-1, open header?) and air filter quality and flowability, as well as piston ring condition and proper valve adjustment, as well as valve and valve seat condition.doing a proper valve adjustment is always the first step before any tuning work has to be done. Then do a compression test. clean carbs with all new o rings and intake boot o rings in good condition (intake boots also in good condition) are also very very crucial baseline maintenance items that must be done before you can tune the bike properly. best of luck, hope this is all helpful to you.