[Cyclops755]

You mean visually sync the carbs again to kind of "reset" everything? And as far as tracking down a vacuum leak, should I just spray carb cleaner on all the boots between the carbs and the engine and look for rpm changes to indicate a leak? I'm a little concerned about spraying that on/around a hot engine, anything to be worried about?

Are there other places I should be looking for vacuum leaks? My thoughts would be the only place(s) that a vacuum leak could affect performance is either within, or AFTER the carbs (i.e. the intake boots or diaphragms). To that end, is it ok to be testing/sync'ing the carbs and so on without the airbox and filter installed? (I have been working so far with everything installed) I would think that the carb sync wouldn't depend on it. I could see idle being affected by it, due to the added restriction of the filter and airbox, but that shouldn't affect the sync. Is this correct?
Sorry, lots of questions I know. Thanks for all the support

[05RedKat600]

You mean visually sync the carbs again to kind of "reset" everything? And as far as tracking down a vacuum leak, should I just spray carb cleaner on all the boots between the carbs and the engine and look for rpm changes to indicate a leak? I'm a little concerned about spraying that on/around a hot engine, anything to be worried about?

Are there other places I should be looking for vacuum leaks? My thoughts would be the only place(s) that a vacuum leak could affect performance is either within, or AFTER the carbs (i.e. the intake boots or diaphragms). To that end, is it ok to be testing/sync'ing the carbs and so on without the airbox and filter installed? (I have been working so far with everything installed) I would think that the carb sync wouldn't depend on it. I could see idle being affected by it, due to the added restriction of the filter and airbox, but that shouldn't affect the sync. Is this correct?
Sorry, lots of questions I know. Thanks for all the support

Try and sync again first. Be sure the engine is warm, not cold. If that fails, spray around any and all hoses, including where the boots meet the airbox. Only do one at a time so you can isolate the specific carb. Don't forget the vacuum line to the petcock!

The airbox and filter MUST be installed while syncing carbs. Especially with the Kat having CV carbs.

[Badfaerie]

You mean visually sync the carbs again to kind of "reset" everything? And as far as tracking down a vacuum leak, should I just spray carb cleaner on all the boots between the carbs and the engine and look for rpm changes to indicate a leak? I'm a little concerned about spraying that on/around a hot engine, anything to be worried about?

Are there other places I should be looking for vacuum leaks? My thoughts would be the only place(s) that a vacuum leak could affect performance is either within, or AFTER the carbs (i.e. the intake boots or diaphragms). To that end, is it ok to be testing/sync'ing the carbs and so on without the airbox and filter installed? (I have been working so far with everything installed) I would think that the carb sync wouldn't depend on it. I could see idle being affected by it, due to the added restriction of the filter and airbox, but that shouldn't affect the sync. Is this correct?
Sorry, lots of questions I know. Thanks for all the support

The idle is definitely affected by the air box and filter.

If you can get it to sync but the idle still hangs, your problem is likely to be on the airbox side of the carbs. If it won't take or hold a sync, it's likely to be on the engine side.

Common points of failure are having the carbs not quite seated on the boots on either side, the O-rings between the intake boots and motor (especially if the problem gets worse the warmer the bike gets) and not having the drain like from the air box blocked off.

Starter fluid, wd40, or something spray in/around your motor while it is running shouldn't be a problem. If you have enough heat in that area to cause combustion you have MUCH bigger problems. Try to use something with a straw or other precision placement so you can be sure exactly where the problem is.

[Cyclops755]

Don't forget the vacuum line to the petcock!

Isn't this just the carb 4 sync port?

[05RedKat600]

Isn't this just the carb 4 sync port?

Yes, but if you don't use the vacuum line as part of your sync, it could be a source of leakage once you put the tank back on and connect all the lines. It's something to be tested as it is a vacuum line.

[Cyclops755]

well I spent a few hours tinkering with it again today. Tried sync'ing again, pretty much the same results as before. Got the carb cleaner out and started spraying stuff down, and got a pretty repeatable significant rpm change when I flooded the connection between the motor and the carb boots. Looks like its off to Ron Ayers for new o-rings. On the plus side, I inspected the boots pretty closely while I was at it and they looked to be in ok shape, so that looks like $80 saved... I'll get the new o-rings in and report back.

I also was able to get a rise out of spraying down the intake side of carb 4, and on the sync pro carb 4 is the one that consistently pulls less than the other three. I can see what looks like good contact with the carb body all the way around, so that leads me to believe its probably seated fully. Pulled the airbox back off and checked the seal - no cracks or anything else of note there. Tightened the clamp down the whole way and no change. What else can be done to address this?
This is frustrating, but at least its progress

[Cyclops755]

FINALLY got the o-rings and things in from Ayers today. Got everything swapped in, and pulled the carbs out and did another bench sync to "reset" them for a new vacuum sync.

One question I've got is what is the torque setting for the intake air boots (if there is one)? I figure if there's a seal involved, there should be a "proper" torque setting to ensure its even all the way around. I can't seem to find it called out in my service manual though.

[Cyclops755]

bump

[Cyclops755]

Update - with Pics

I've been messing with it more and I've narrowed down what might be the problem, but at this point I'm not sure of how to solve it other than to blindly throw money and parts at it

At this point I've RTV'd the inside of each of the airbox boots to help ensure a good seal to the front side of the carbs, and have sealed each of the airbox boots to the airbox (both of which were places I was detecting leaks before). So seal airbox leaks - check. Got some notable improvement there in how the bike ran.

After replacing the O-rings mentioned above though, I still get RPM changes when I flood the connection at each cylinder with carb cleaner... So aside from the head being warped or the mating surface for the intake boots being marred, the only thing left to blame is the boots themselves so far as I can tell. My reservation is, since all 4 of the boots seem to be intact (no cracks, and still somewhat soft) I don't want to just drop $120 for a new set. I took some pictures to see what you all think. Replace them? Is there another possible solution?



Cyl 1


Cyl 2


Cyl 4

[Cyclops755]

bump

[05RedKat600]

LIGHTLY RTV o-ring side then install. Probably not the head that's warped but rather the boot itself.

[hpjc10]

My 1990 kat seems to be doing the same thing. At my last sync, The idle hangs at ~3k rpm, with the idle screw all the way out, and doesn't go down unless I use clutch brake it or turn off the engine for a few secs. I know it has an air leak at a couple of the boots, I sprayed starting fluid and my rpms shot up. Let me know how the rtv works out for you. I work at advance auto parts and can get the stuff basically free, but it's pretty messy...

[05RedKat600]

RTV is only messy because people use way too much of it. Less is best with that product. Used it on mine, worked like a champ. Just a thin film on the head surface is all that's required.

[ManQu]

...I'm waiting with baited breath as to what happens next......