Idling problem

Fired up the bike just now and the problem wasn't there. Revved it a bunch of times and nothing, so I let it warm up completely. Once warmed up, gave it a little rev (to about 2k rpm) and it jumped to 4k and stayed there. I didn't have propane, so I sprayed some carb cleaner around. The idle seemed to raise just a tad when I spayed the #1 cylinder manifold coupler and the throttle seals. Then I went around and sprayed #3 and #4 and nothing happened... Then I went to #2. I sprayed the coupler a good amount and the idle sky rocketed to 4k. Just to make sure it wasn't a coincidence, I did it again, and again, and again. Looks like I'm going to have to crack off these manifold couplers. Hopefully this fixes the problem.

 

Not necessarily there are several ways outlined on this site to fix them on the bike. With the risk of snapping an intake bolt of in the head very great on these I'd try the on bike repairs first.

 

The Number - 1 Rule of Old Motorcycle Maintenance & Repairs.

"DO NOT do something that will make a Bad situation, ... WORSE!"

The Manifold Bolts are prone to seizure.
Making matters worse; they're made of SOFT Steel.
You will "Feel" like the Bolt is >> Turning <<.
Actually, the Bolt is >> Twisting <<, ... and then ... it SNAPS!
Very Bad Situation.

Remove the Carbs.
Smooch some RTV Black, ... into the Mating Crease all-around the Manifold.
Two coats.
Make the Joint ""AIR TIGHT""

Leave removal of the Manifolds for a Winter Project when you can Pull the Head and have a Machine Shop deal with fragments of Broken Fasteners seized in the Ears of the Intake Manifold Ports.

 

I got them off, but only cyl #1 and 2, 3 and 4 didn't want to budge so I left them alone. The gasket was completely dried up and fell apart right when I got the coupler off.

I used some RTV to make a new gasket, just waiting for it to dry. I'll put some more around it, to ensure that it's sealed up on all 4 couplers.

 

hello everyone. i just built my YICS tool, fixed the annoying petcock, Now with the vacuum gauges. I have a big question that i can't seem to find on the internet. How many inches of vacuum should there be when syncing them?

 

Haynes manual says:
...."No specific vacuum reading is given by the manufacturer, but it is essential that the two carburettors (1 and 2) give the same reading."
I've not had to sync the carbs myself, yet. So I'm afraid that's about all the help I can give you. Maybe someone has a shop service manual that has the numbers in it.

 

well it looks after giving it a shot today resulted in utter failure. I can't even get a damn reading on the stupid gauges. Even after throttling it higher. they just bounce all around the stinking thing. tomorrow i'm gonna try it again but i'm gonna use the B12 trick to see if there is a vacuum leak. This bike seems to be in really good condition for it's age. I've seen other ones that are FAR worse shape and giving people all sorts of problems. But this one i got lucky with. I hope that i can sync it up tomorrow. but if anyone knows a way to make the needles stop fluttering all the place, please give me advice.

kinda frustrates me though, should of bought a CB750 since i'm an actual honda guy.

 

maybe there is a vacuum leak. But ALL of the needles are doing it. Could it be the YICS port? i built the tool to the right specs and everything! i don't get what's going on here! and i've reved it to see if it would stable out but it isn't!!! AAAAAAAAARGH!

 

OH MY GOD! i think i found out why it didn't work! i never tightened the YICS tool. DUH! i didn't know that it was supposed to expand in there like that ROFL!

 

xjmike.... don't thread jack start your own.

To answer your question a vacuum gauge will bounce up and down with the engine pulse. You need a restriction in the vacuum line to smooth it out to a useable level. There are also many other home build synch gauges that work.

carbonxe... glad to hear you didn't make it any worse by breaking a bolt off.

 

I did that once before with an exhaust manifold bolt, so I knew the consequences. I only used a standard Allen key, so there was little to no torque being applied. Luckily the one I needed to come off came off, and the gasket was NOT pretty. I just picked up some RTV black, so I'm going to plaster that stuff all over the manifold couplers later, then hopefully I can re-vac sync the carbs and get this bike running properly.

 

oh noes! i'm about ready to steal this thread as my evil secret plot!

"To answer your question a vacuum gauge will bounce up and down with the engine pulse" saying it as if i'm not aware.

also this is a technical discussion forum. people should be able to talk about whatever the need help with.

 

Some people don't know that a gauge will bounce up and down. How am I to know that you were already aware of that?

It is a technical discussion. There is plenty of space for everyone to get their help with their subject in their thread without confusing people by jumping in the middle of someone elses.

 

I DO KNOW THAT. and i already fixed it. there was no reason to be rude.

 

Gentlemen, please.

Mike, it was a pretty rude thread-jack. Chill.

carbonxe, are we talking about a 750 with Hitachis? It's not in your sig, wanted to be sure. If the carbs are still off, take a minute and pop the clips off the throttle shafts on the outside of the #1 and #4 carbs, pluck out the nylon washers, and inspect the throttle shaft seals you can see. If those are toast, you can be reasonably sure the inners are too. If they're fine, it's no guarantee that the rest are but if the outers are bad you know the inners will be too.

No sense putting the bike back together and having to pull the carbs again if the seals are bad too.

 

Take the Rack off the Bike.
Hold the Rack Vertical.
Flush the four Thottle Shafts at the 6 O'Clock position with Isopropyl alcohol.
Invert.
Flush the remaining four.

Employ an assistant.
Have them "work-the-throttles" Open~Closed.
Apply 4 Drops of CaliKleen RBR Rubber Conditioner to the 6 O'Clock Throttle Shafts.
Invert.
Do the other four.

Let set for 30 Minutes.
Reapply Conditioner.

Cross fingers.
Reinstall Carbs.
Light candle.
Pray to Motorcycle Gods and fire that mother up!

http://store.caig.com/s.nl/it.A/id.1671 ... tegory=179

 

Not trying to jack this thread, so apologies if I do......I have read enough posts to know not to dunk the whole rack or soak it due to the possibility of damaging the throttle shaft seals. When cleaning my lowers and spraying lots of carb cleaner from various positioning of the rack, i wondered if the carb spray will damage those seals just from the spraying of the lower parts? Have any of you experienced that or does it seem okay for them to get hit with some spray as long as they don't get soaked with it? Just trying to be proactive instead of reactive, lol.

Thanks!

 

one thing i've learned about the carbs is that it is HARD to find parts for them.

 

Not as long as we have Chacal around it doesn't seem to be, but money on the other hand, is HARD to come by for alot of us, lol, especially if we have joint checking accounts, if you know what I mean, lol.

 

I already checked the outside seals and they're fine, but no clue about the inner ones. At this point, it only takes 5 mins to get the carbs off the bike. I'm waiting on the RTV to dry right now, then I'll fire up the bike and see if the problem went away, if not, I'll check all of the throttle seals. A little more work this way, but I'll be sure of what the problem was.

Also, I have no clue if my carbs are Hitachi or Mikuni, I never figured out what the differences were between the two.