Topic: any tips on finding and fixing air leaks?

[the technological J]

my carbs have only been bench synchd but last season (before rebuild) this problem has been the same... the bike basically will either stall, idle real nice(rare)or idle at three to four thousand rpms on rare occasions even up to five thou. i often am stopping and will use first to slow the engine down and then it some times sort of catches the slowr idle and idles basically fine... most of this happens when the bike is warmed up.... im pretty sure the boots are ok.. is there a specific gasket for the metal(intake manifold?) that the boots seat onto... and if i have an air leak would this be the reason i get 25 miles to the gallon and run rich? thanks guys i look foreward to ur sharing of wisdom..... or BS

[mlinder]

Not really. THere are ways of checking for air leaks. Pretty easy. Spray some starting flud all around the carbs and boots while the bike is running. If rpm changes, you have a leak. If not, you don't.

[Gordon]

or BS

Whew!  I thought I was going to be left out of this one!

Do like Mark said and see what happens.  If it turns out there are no vacuum leaks, it could still be a carb synch issue.  Even with a bench synch the carbs can still be off far enough to cause idling issues. 

[the technological J]

oh yeah the local honda rep told me that if i spray wd 40 in there  and if  my eyes start to burn i have a leak... i thought  the best this guy can come up with involves facial pain.. gosh..... any body know if keihin pds have a rubber diaphram in the top end ?

[Gordon]

oh yeah the local honda rep told me that if i spray wd 40 in there  and if  my eyes start to burn i have a leak...

Huh?

[mlinder]

Gordon, I always stab myself in the face with a fork repeatedly to help diagnose running problems on my bikes. This seems to be just a variation on a tried-and-true trouble-shooting practice.

[the technological J]

so how do i tell if i got an air leak or outta sync carbs?
will a blown head gasket cause the bike to act this way?
 i did spray the front of the carb boots with starter fluid idle dropped and almost stalled... boot clamps were loose enought to be moved by hand... i tightened them way down and the idle still likes to climb although it settled a little bit
does any one know about the intake manifold... or the metal peice the boots attack to on the engine.. is there a gasket there?

[mlinder]

so how do i tell if i got an air leak or outta sync carbs?
will a blown head gasket cause the bike to act this way?

Not really, no.

As I think I mentioned earlier, with the bike running, spray starter fluid around the carbs and boots. If RPM changes (in this case, would likely increase), you have an air leak.

You tell if your carbs are out of synch by synching them, with a carb synchronizer.

[1timduke]

Vacuum sync is definitely needed, I bench synced several times and was nowhere close, the vac gauges really dial it in well, just make sure you have a big fan.

Have you already checked all the other basic tuneup items, timing, points gap, tappet adjustment, fresh oil and gas, etc?

-Tim