81std no top end - ignition unit??

[dbeardslee]

I never hose my carbs. I just carefully set the float levels on both sides of the floats with a caliper and they work just fine. They don't suck the bowls dry at WOT, and the plugs don't show a rich condition when I'm just putting around. And it runs like a scalded dog. And to me, that's the real world.

[mro]

Sorry motorman,
that post was a little rude of me.
On the 78 to 80 models the manual has you measure the float height and adjust it to 25.7 mm + - 1mm (carbs turned over with the bowls off)

That fuel level will be about 1 mm below the bowls flange.

The instructions for the 81's have you level the bike/carbs and attach the clear tubes, start the engine for a couple minuets and shut it off, then check the fuel levels.

What I do is set the floats then check to be sure that the fuel level is all the same on all the carbs and adjust them as needed.

[motoman]

These bikes should take off at 5k, mine bogs out and will not go over 7k rpm. Feels like a 78e with centrigul advance issues, but the 81 does that in the magical black box. Tried a spare unit and same thing, so either both are bad or it is something else. Any other way the advance might not work besides bad igniter? Bike is new to me so do not know when this started, spare igniter is off a bike I bought but never ran so could be two bad units. But want to double check everything before I spend money on another one.
Going to check timing but doubt that is it, bike runs just fine in 1500 to 3500 rpm. Then is ok 3500 to 4500 but does not accelerate as fast as it should.

Your too rich either in the mains, fuel levels to-to high(have to hose them and check while running at an idle), or metering rods not matched up with main jets. Oh, and plastic floats in place of original brass floats.......not good my friend.

[yamtom]

messed up mains, clogged

Hey Scott,

I did not read the whole array of responses so I may be repeating something. I once bought a 79, that had almost exactly the same problem, it was clogged up main jet holders, cant remember the right name for them, but cleaning those all out, made the bike run fine. Its those little tiny holes in the sides that were clogged up.

I still have your old triple 750 up here in Midland .

These bikes should take off at 5k, mine bogs out and will not go over 7k rpm. Feels like a 78e with centrigul advance issues, but the 81 does that in the magical black box. Tried a spare unit and same thing, so either both are bad or it is something else. Any other way the advance might not work besides bad igniter? Bike is new to me so do not know when this started, spare igniter is off a bike I bought but never ran so could be two bad units. But want to double check everything before I spend money on another one.
Going to check timing but doubt that is it, bike runs just fine in 1500 to 3500 rpm. Then is ok 3500 to 4500 but does not accelerate as fast as it should.

[TopCatGr58]

Greg,
Looks like you win the trouble shooting contest. Last night I started the basic checks and found all 4 cyl had low compression, all at 90. Tonight pulled cover and cam timing is out, likely one tooth. Will reset tomorrow and recheck compression.

Hey again,

Okay, that's a good find. Just have to ask(no aspersions intended...more for newbies following) you did have the thottle Wide Open while measuring? Have had others report similar comps and thought their engines shot only to find that they forgot to open the carbs butterflies, and once done, they actually had good comps.

T.C.

[motoman]

Easy with a timing light.....
Should get to it this weekend when I either find mine or borrow one. Been two relocations since I last used it.

I actually was easy with the timing lite............till it slipped off the seat and hit the concrete floor.............killed the neon lite. Still have an even fancier timing lite. Good thing I wasn't using it. That would of cost me a couple bills or more to replace.

[RS Thornton]

T.C.
Pulling against closed butterfly valve everything reads low
I have good compression across the bank now. When I saw low readings one #1 I was very sad as I really was not wanting to be tearing down this motor, when they where all low I was pretty sure it was cams being out. While possible for rings or valves to all be bad I have never seen 4 cylinders all equally worn. Have before and after pics and will post them when I get a few spare minutes. Checked with timing light and CDI is advancing properly so hoping to put it all back together this weekend.
Will likely do a more detailed carb check while it has the center stage in the shop. It had a stutter/stumble at idle so cleaned sticky brown goo out of one pilot and from float pins as floats did not move freely. The levels and mains may be fine but rather be sure and done.

[RS Thornton]

Hi Tom

Hope you are riding it by now. I swapped the 850 I got in that 3 bike deal for the other venturer I have. Need to get that one revived someday. I had checked the pilots and found one plugged so that was likely a contributor to the idle issue that is now gone. Hoping it was cam timing but if there is a carb issue it will would be in main circuit as that is the one with biggest impact above 5000 rpm.

[RS Thornton]

On an unrelated note the garage got smaller over the weekend. I added a 79 standard to the fleet, so finally have E through H.

[motoman]

Good use for a set of cr%py carb boots

I really dislike having to do things over and then sometimes having to do it again... Carbs in particular, so I made this.




Shows actual fuel level in the bowls, plus if one leaks you don't have to pull em again and again.

OK, but still not correct way to check fuel levels of 81's nor XJ's. Bike HAS to warmed and idling for the hose check for fuel levels while running. 'the teeny spring in the needle seat IS the issue when not running. Motor off they compress a bit more raising the float, pinching off whatever fkoat needs shut off.............just gonna get lots of practice removong floats cause I've yet to see 'any float needles, even though statisally set ending up all four bowls being the same fuel levels, Important fuel levels are identical(while running} height in all four carbs. 'to high fuel levels cause a rich cond,.......to low cause a lean cond. It only takes a 1/2mm off one way or another to create either cond. mentioned...........so your gonna get lots of practice R/R the carbies.

[motoman]

motoman


Would you enlighten me motorman?
How about a video of you adjust the fuel level while it's idling.
Could be that the factory manual is just wrong again?

Yhe manual shows it all for these model yrs. as an apendage.

[RS Thornton]

cam timing photos

So finally getting around to posting. There should be 4 pics, intake cam before, intake cam after, exhaust cam before, exhaust cam after. The difference in that the arrow points to the dot, just like in the Clymers photo. In the before pics they are not lined up so cams were a little out of sync.

[motoman]

Sorry motorman,
that post was a little rude of me.
On the 78 to 80 models the manual has you measure the float height and adjust it to 25.7 mm + - 1mm (carbs turned over with the bowls off)

That fuel level will be about 1 mm below the bowls flange.

The instructions for the 81's have you level the bike/carbs and attach the clear tubes, start the engine for a couple minuets and shut it off, then check the fuel levels.

What I do is set the floats then check to be sure that the fuel level is all the same on all the carbs and adjust them as needed.

Those are RUNNING fuels that are supossed to be checked.