Vac diaphragm test question

[Guest]

can i test my diaphragm on my 81 with the ign. mech. all together on the bike? the reading is to be 5.9 in. but i notice the adv mec is different on my 78 with the 81 having 2 springs pulling it back and forth would there be a different spec for the 81?

[randy]

Your 78 centrifugal advance mechanism is seperate from the vacuum mechanism. They work in tandem to provide the advance, but they dont affect each other mechanically. you can test your vacuum diaphram while installed. Basically, if the diaphram holds a vacuum, it's working. There are other factors that may hinder it's performance such as the moveable plate sticking, or a vacuum leak in the line from the carb.

The 81 doesn't have a centrifugal advance mechanism, it has the vacuum diaphram and electronic advance in the TCI.

[Guest]

hey randy thanks a friend is bringing over his vac tester to check out the 81. does the 81 have the weights on it ? the reason for my testing it doesn't seam to move as much as my 78 when raising the rpm,s.

[randy]

The 81 doesn't have a centrifugal advance mechanism, it has the vacuum diaphram and electronic advance in the TCI.

[dbeardslee]

I just tested my vacuum dashpot about a week ago. There is one screw and a circlip on the linkage that hold it in place. Remove the screw (just under the dashpot) and the circlip, advance the pickup coils with your fingers, and you will then be able to lift the assembly and get the linkage off the pin and remove the dashpot. Push the plunger up and put your finger tightly over the vacuum pipe. Release the plunger. If it stays put the diaphram inside the dashpot is fine. If it moves back out you've got a leak in the diaphram.

[randy]

No need to even remove it, rotate the mechanism and put your fingertip on the pipe, if it holds....

[dbeardslee]

Randy - Now you tell me . Gotta love the KISS method.

[Guest]

vac

hey randy & db just checked and holding vac thanks

[TopCatGr58]

Hey Arrow,

I'm kinda late to this thread, but the reason the 81's plate doesn't turn very far is like Randy said, the Cent. Adv. Curve is built into the TCI, that's 36 or so degrees, and the vac. adv. only provides another 16 degrees, so the plate only rotates enough to generate that much, the rest is provided by the programming in the TCI. On your 78, the plate needs to be able to rotate a maximum of 52 degrees worth for the max cent. and vac. adv of 52 degrees! Glad you figured it was working ok.

You can put a timing light and watch the timing plate as you rev the engine with the vac. adv. capped, and you should be able to see the adv. curve indicate/show it moving more advanced IF the TCI is working properly.
T.C.

[79XS11F]

As per the manual the vacuum advance should be fully advanced at 5.9 in Hg
Test it with a hand operated vacuum pump
Rob

[Guest]

vac on 81sh TC& ROB

so TC your saying to plug the vac hose that goes to #2 CARB AND REV THE ENGINE? which i cant do till i get i get new coils 2-3 quit! ROB that 5.9 reading is that for my 78 because on my 81 it doesn't start to move till 9 in hg and is fully advanced at 13.5 this is a borrowed mighty vac goes from 0 to 30 in.hg

[dbeardslee]

Arrow - are you sure it's the coils and not the pickup coils or the wires that feed them? If you put a digital multimeter on the wires at the TCI you should get a reading of 3.3 ohms primary resistance for the coils (large connector - grey to red/wht, and orange to red/wht IIRC). If you pull the plug wires on 2 & 3 and check the resistance from plug cap to plug cap you should get a reading of 15k ohms secondary resistance. If you test the resistance on the pickup coils at the TCI you should get a reading of 720 ohms - plus or minus 20%. That's checked at the four-wire connector. If you hold the connector so that the slots are parallel with the ground, test the top two together, and the bottom two together. JAT

[Guest]

elec testing

DB never used a tester before so here's what i came up with
coil2-3 secondary 0 ohms
coil1-4 secondary 30 ohms why? should this be 15 ohms?
at tci 4 prong conn. upper&lower both just over 8 ohms
on tci 4 prongs upper and lower almost 1k my meter goes from 200-1k here cheapo!
on tci gray to red white just over 3ohms
on tci orange to red white same as gray
now off a 80 parts bike i pulled 2 accel 140404 coils that the secondary read 12ohms are they to weak?
on large tci connector it's self gray-rw o ohms, orange- rw 0 ohms

[79XS11F]

so TC your saying to plug the vac hose that goes to #2 CARB AND REV THE ENGINE? which i cant do till i get i get new coils 2-3 quit! ROB that 5.9 reading is that for my 78 because on my 81 it doesn't start to move till 9 in hg and is fully advanced at 13.5 this is a borrowed mighty vac goes from 0 to 30 in.hg

That spec applies to 79 and likely 78 standard models. I do not have specs on others. If out of spec it does not mean the vacuum device is not working. If that device will hold a vacuum, which can also be tested with the vac pump, it likely means the timing plate is not moving smoothly / easy enough. Disassemble, clean, lube and re-test. look for lead wires too tight or rubbing on stationary parts.
Rob

[Guest]

thanks rob she holds the vac and will check the others
dick r.