Topic: I think it was the wrong tach

[csendker]

I've had many posts regarding MPG, shift RPM, performance, etc.  After a while, I figured out (more properly, it was pointed out to me) that I did not have stock gauges.  For no other reason than it kind of bothered me, I went and scrounged up a set of good gauges from a '78 550 (I think - the odo dial is on the side not back).  Anyway, I swapped them out with no other mods.  Went for a ride tonight and noticed my RPM's up significantly.

I always thought the red-line was way, way too high.  Actually, I now think that the damn gauge was wrong.  I shift at a comfortable level and now I'm seeing 3-4,000 when before it was closer to 2-3,000.  8,000 RPM seems to be in a comfort zone for the engine, before I never got close to redline.  Is there any way to verify whether the new tach is, as I suspect, correct?

[Bob Wessner]

Do you have, or can you borrow someone's engine analyzer? Connect as directed and compare the rpms on the gauge to the analyzer at a couple of points. They should be fairly close I would think, though not exact as the tach is probably not all the precise particularly at lower rpm's.

[csendker]

Will this bad boy work on SOHC4's?  What about my SOHC2?

Craftsman Engine Analyzer: Sears item #00921029000 Mfr. model #21029  -->> http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00921029000&subcat=Automotive+Testing+Equipment

And for that matter, what about this timing light:

Craftsman Inductive Timing Light: Sears item #00902137000 Mfr. model #2137  -->> http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00902137000&subcat=Automotive+Testing+Equipment

[Bob Wessner]

The Craftsman engine analyzer should do for the rpms. You will have to remember it is for 4, 6, 8 cyl autos really and though the SOHC4 has four cylinders, both pairs fire on each rev. You will have to play with the scale selected to find the right one and maybe either divide or multiply the reading.. forget which. There may even be a posting on this as I seem to recall this being discussed before.

[Bob Wessner]

The more I thought about this, if your goal is to determine if you now have the more or less, correct ratio for the tach you just mounted, assuming all else on the bike is stock as to gearing (front/rear sprockets, rear wheel size, etc.) someone with the same model 550 might be able to help. For example, my early 750 is stock as to the items mentioned. At 3,000 rpm in top gear it is going exactly 45 mph and at 4,000 rpm it is going exactly 60 mph. Maybe someone with your same model can give you similar readings and you can compare them to yours. Just a thought.

[csendker]

Good thought.  I'm GUESSING that the rest of the bike is reasonably stock.  Any 550 guys out there with some input; speed vs. RPM?  Considering the perceived differential between my two gauge readings, it should be obvious.  Unfortunately, it's now in the 30's and blowing & snowing out - I can't remember what mine were doing last night.  The thought hit me after I put her back in the garage.