Vac diaphragm test question

[dbeardslee]

Arrow - the secondary resistance readings on your coils are pretty strange - should read 15,000 ohms resistance. Could be bad plug caps or wires. The 8 ohm reading on the pickup coils is probably 800 (depends on your multimeter), which is within spec. If it's reading correctly, you've probably got pickup coil wire issues, or wiring issues in general. Given the secondary resistance readings on your ignition coil high tension wires, the first thing I would do is trim 1/4" off the end of the wires and replace all four caps and see what happens. I'd also get a little better digital multimeter. They don't cost much, and they come in very handy. Are you still running the stock coils and caps?

[randy]

I have a sneaking suspicion that the wierd meter readings have something to do with the 'autoranging' action of the DMM? They can sometimes be confusing to read.

[Guest]

retest

DB yes orig. stock coils and caps,found hairline crack in 4 retested secondary on coils after trimming and no caps just over 13ohms on both coils![ lesson learned ] bad caps??? that to low for the secondary? 2 run right?
the pu coils still a little over 8, and the wires without taken it apart which i'll do look ok.
now on the tci 4 prongs with pos. probe on left prong reads just over 22, when pos. probe on right prong reads just under the 1k mark guessing 750 whats with that????? bare with me i don't know jack about elec testing

[dbeardslee]

When I test the 4 prong I use an alligator clip with a male spade connector in the end of it. I stick those in the slots, and that way I can connect my multimeter and have both hands free to jiggle the pickup coil wires. If you see the resistance reading jumping around when you wiggle the wires, redo the pickup coil wire fix.

[TopCatGr58]

Hey Arrow,

There isn't any different specs for the vac. adv. for the 81 vs. the earlier models, so the 5.9in spec should be correct, so as suggested, removal and cleaning/lubrication may be needed to allow for proper rotation at the proper vac level.

I would think if you look a bit closer at your gauge, you should see a little "K" show up on the display when you are testing the secondary high tension side/leads of the coils. While you have the caps off, test them as well. Should be about 5k ohms. The specs in the manuals don't tell you that the 15 k spec +/-10% is WITHOUT the plug caps in place!! So...with them on, should read about 25k ohm. You can even take the plug cap apart to inspect the internal resistor, measure it's resistance, clean of corrosion and retest till you get 5k. but if you still get much higher, then the resistor is damaged, time for new cap.

The 13k may be within spec since using an "inexpensive" DMM!
T.C.

[Guest]

testing

hey guys i was wondering about the cheap dmm !! bought it at menards like lowes will check and do some cleaning this weekend once again thanks for the help its well appreciated !

[Guest]

Vac diaphragm

ok guys i pulled off the ign adv mechanism and found no weights to lube so it is different from the 78-80. checked all wires looked fine pulled on them while ohm meter hooked up and no change. now when i turned the mec by hand oil came out of the diaphragm??? called a automec friend of mine and he said never heard of such a thing! so is that oil suppose to be in there? if not is that the reason why i cant get the right vac spec

[randy]

Sounds bad, never heard of oil coming out of one. It may have seeped for a long time down the vac line. It may have started out as fuel vapor and congealed into something resembloing oil? In any case, sounds like a bad diaphram. Do you have a replacement?

[Guest]

oil

hey randy it feels like oil who knows maybe the po's mechanic got ticked off at him and did it on purpose? just check the one on the 80 parts bike and it's good will it work on the 81? and the problem with 2-3 coil was plug caps so i will change all 4 out

[randy]

I don't see why it wouldn't work, check them side-by-side for dimensional comparison. I have a feeling that the yamaha service bulletin about them had more to do with the internal damping corrections rather than some physical dimensional difference. If you still have some pingin, retard the timing a few degrees. BTW, I had the pinging problem on my '81SH back in '90 and I cured it by raising the carb needles with small washers (richening mid-range). JAT