NO VACUUM on #4

[lee_dutcher]

been trying and trying to get vacuum in the #4 carb/cyclinder...getting a decent amount of smoke coming out of the breather tube.... ot 1,2,and 3 carb sync'd well but #4 just hangs in the red were it says, something about leaking in the intake, valve clearance , something something, lol. i have the EMGO carb sync tool fyi. so am i looking at a engine rebuild? or just a valve adjustment?

[mlew]

Do a compression test on the engine, that will help to see what is going on. Could be valve adjustment or a stuck valve. Any history on it? Have you had it running before?

[TopCatGr58]

Hey Lee,

Our memories are a bit short, we need more background info about any service that you have done to the bike, ie. valve clearance check/adjustment reshimming? Had the bike been running before..I think it had, have you had good temps on the exhaust pipe for the #4 cylinder...good sizzling when spritzed with water vs. 1,2,3?

Next, have you checked the gauge to make sure it's reading vacuum properly by putting in on one of the other cylinders?

Next, have you done a compression test on that cylinder? If so, and you got good compression readings, then it should create vacuum, so then you have a vacuum leak. Most likely the interface of the carb boot with the engine since you have the vac. gauge connected to the synch port!

T.C.

[BA80]

All good advice to follow.....unfortunately the lack of vacuum and smoke from the breather do indicate broken or seized rings or the dreaded hole in the piston.

Check compression and if it's low or non existant check valves. But, with XSive smoke from the breather it sounds more like a ring/piston problem.

[lee_dutcher]

yea it definitly HOT when it comes to temp on the pipes. only thing i havent done to this bike is a valve clearance check. otherwise everything else i have done. the intake boots are cracked but not all the way thru. i got good spark color mabe a tad bit lean but nothing to horrable. engine runs and always has still does just a little rough

[lee_dutcher]

So good news..bought a compression tester. Test reasults are better then expected....from 1-4

118 110 110 120

Engine was cold and i didnt put oil in the cylinders...so whats nextt?

I know the numbers are not to spec but 142 +-14lbs after 30 years and who knows how many POS and 33 years.

[natemoen]

As you have the sync gauges on there try opening the idle screw up on that cylinder and see if it starts to bring the vac up.

[lee_dutcher]

The idle screw between 3and 4 or the one between 2and3 that is i front of the carbs?

[clcorbin]

One thing I did when I had problems getting one of my carbs to sync was pull the carbs and then set the carb openings to be the same using a VERY fine wire feeler gauge (ok, I actually used the wire from a twist tie...). Sure enough, there was a "big" difference on that one cylinder. When I bolted everything back up, all four cylinders were on the sync gauge and it was very quick to sync it up. Of course, my bike was in decent mechanical condition too, so I knew I was fighting a carb issue, so this might not help at all.

[natemoen]

The idle screw between 3and 4 or the one between 2and3 that is i front of the carbs?

i am talking about the idle screw ON #4

[TopCatGr58]

Those compression readings may even be better, you may have forgotten to crank the throttle WIDE OPEN when doing the test??

Something even simpler could be the problem, take a fine wire and stick it down into the SYNCH port to make sure it's not clogged!

T.C.

[lee_dutcher]

Yea i did the testing wide open. Good idea maybe i have a clogged sync port ill give it a shot in the am. If it doesnt help ill pull the carbies off again and inspect them.