BTW! I was happy to find Yamaha MSN #394 for all 1973 models. Everything I've read and the videos I've watched on adjusting the oil pump, have shown the guide pin to be aligned with the line on the pulley when throttle is closed.

While my (181) pulley does have an index line, MSN #394 specifies that the oil pump guide pin should be aligned with the small round bump on the pulley and NOT aligned with the index line.

Please correct me if I'm wrong but I've already decided the '74 GT specs should be the same as the '73 GTs, and plan to align my guide pin with the bump rather than the index line..

ZT

It sounds like you've come across more than I have.  I've never seen an index that shows the bulletins cross referenced by year and model.  

I agree that the bump is what I would use, I have not come across that info for 1974 but both 73 and 75 GT80 used the same pump and use the round pulley mark and not the line.  

Biggest mistake on pump adjustment is not following the instructions on warming up, setting idle speed, and then taking up the cable slack in the throttle cable when checking pump mark alignment.  

Update, I just found the 1974 bulletin in a folder.

Thanks Mark!

Your latest 1974 TB is essentially the same as the 1973 MSN bulletin #394 that I found here in the tech library. Does this 74 TB have an M4-xxx number?

And might your newfound folder contain oil output data for the 1973 or '74 GT80/MX (PINK) oil pump? The output data you posted on pg 1, for the 1978 GT(E)s, showed a YELLOW color coded pump.

Thanks! ZT

I posted the pic of the bulletin I had in a folder on my computer.  I don't have any more info than that.  

You have the only pump data I could find.  The 78 engine is identical so oil pump specs should be close.  By 1978 they lost the manual "primer wheel" which is likely the difference in pumps.  

Thanks Mark! I appreciate your follow-up.

I guess I'll go with the '78 data you provided when I get everything back together... unless I can find the actual oil output specs for the 73/74 GT80/MXs. I haven't yet given up on my local Yamaha dealer.

I'll let ya'll know if I find anything.
ZT

I’d suggest, testing the pump on the work bench. How close is it to specs? Compared to all other known 80cc Yamaha oil injection specs. IF it complies, sounds like a great pump to use.

Quote: @Sneezles61... "I’d suggest, testing the pump on the work bench. How close is it to specs? Compared to all other known 80cc Yamaha oil injection specs. IF it complies, sounds like a great pump to use."

Sounds simple enough for you guys thoroughly familiar with all the Yamaha Enduro iterations.  Unfortunately, this is my first "2-stroke rodeo" and didn't know one model Yamaha from another.   So I spent some time better familiarizing myself with pump operation and adjustment as well as the output specs I was able to find.  I decided to shoot for the 1978 GT80/MX specs that MarkT provided and got my McGuyver going.

Bench testing these pumps may be old hat to most of you; but I thought if another rookie like me ever shows up here, they might find my test setup useful.


My cobbled together Setup

The drive;  I chucked up a short length of 3/16" aluminum tube with a slot cut in the end to straddle the cotter pin in the adjusting wheel.  Then placed a mark on the wheel to count the revolutions/strokes.

The idle setting was maintained with the head of a roofing nail in the pulley's cable slot.

The WOT setting was maintained with the cantilevered weight of a screwdriver inserted into the same pulley slot. 

Resulting output after 200 strokes at each throttle setting was a tad more than the max specs for the 1978 GTs (0.63 + 4.27 = 4.89 cc).  After subtracting the 2.1 cc "tare amount" in the vial before starting the test, my total output was 7.3 - 2.1 = 5.2 cc. which included about 0.7 cc @ idle and about 4.5 cc @ WOT.

A little richer perhaps than the 78 GT specs Mark provided but actually a tad leaner than the WOT oil output specs given for the earlier 80cc G5 & G6 bikes in MSN #258.

So, unless advised otherwise, I plan on running the pump as is with its current 0.6mm shim washer.

And while I have new oem Yamaha black inlet and output hoses and clips to install, I kinda' like the idea of clear, "see through" hoses as I used for the bench testing to visually confirm the continuous presence of oil in the system.  Is there any reason not to use clear vinyl tubing on the bike?

Comments, corrections, and advice are welcome. 

Nice work!  I don't know where you heard about "bench testing" but I've never seen a nice setup like yours or done it that way.  I've either spun the primer wheel by hand (tedious!!!) or a couple of times by using a rubber wheel and a drill against the "teeth" on the wheel to spin it with the pump on the engine.  Or usually I just run the engine on premix, cap the oil inlet fitting on the engine (or carb on later models), and run the engine while measuring the output with a syringe body.  

And yes, with emissions laws and probably the improved quality and much better availability of two stroke oil, it's very likely the output could have been reduced slightly by 1978.

(In the 1960's and early 1970's, two stroke oil was not always easy to find and often cost a lot more than regular motor oil.  Many of us used regular automotive 30 weight motor oil which was an option in the owner's manual)

On the hose, clear is fine from tank to pump.  I highly recommend staying with the original tiny black outlet hose with the factory clamps.  Clear hose can cause issues on the outlet side in my experience.  

Thanks Mark! I appreciate your nice comments and all the info you've provided.

Quote: @MarkT... "Nice work! I don't know where you heard about "bench testing" but I've never seen a nice setup like yours or done it that way. "

The "bench testing" suggestion was made by @Sneezles61 above, in post #27. I just put together something that I thought might work. Thanks Sneezles61!