Another Carb Issue??

[foreda]

This is for all of the Carb Guru's out there in xsland. Here we go!!
I decided to pull the carbs off of my 79 Standard and clean. In doing so I broke the tower on #2 carb. No problem, I have 3 sets so I take the number 2 off of one of my backup sets and install. After doing this and reassembling with all new parts (i.e. needles. seats,jets and shaft seals), I do not get a good vacuum and the advance revs the engine, so I can't get a good sync. I remove this set and install another set and the vacuum is fine and I can sync ok I just am having problems with the mixture being too lean. I guess the main question would be what would cause this vacuum difference in these 2 sets of carbs?This one has really got me stumped. Oh, and the compression is good, this bike has only 2500 miles on it. Could stretched diaphrams cause this?
Part 2> Set 2 installed on the bike it idles fine and falls flat on its face WOT?I have standard jets for 79F. I am at sea level and clips should be at center right? When set at center posistion. it will idle ok but will not rev. I moved clips one posistion to a richer setting and this has helped but still plugs are very white. Can I enrich enough with the mixture screw or does this sound like float failure? I do not have a ColorTune plug so I am trying to set this by ear. Ya'll give me some feedback please, especially the vacuum issue because I really want the original set back in this machine. Thanks in advance!!

[CatatonicBug]

You said you replaced the shaft seals. Are they actually sealed? Maybe they're leaking? Have you inspeced the diaphragms and checked for tears in them? As I am not really familiar with the '79 std, does it have the vacuum advance thingy on the #2 carb? If it does, might that be a problem, especially for the WOT thing? Just a few stabs in the dark for ya'.

[Crazcnuk]

The only time the advance will rev the engine is if #2 carb idle is set high enough that the plate does not close. This causes vacuum to pull the advance on.

This is part of the synch process. The #2 is out of synch and not closing at idle.

You can just unplug the advance hose and plug the vacuum port until you get the sync done. The advance has nothing to do with synching the carbs, although you should hook it back up as a final check.

[foreda]

Thanks for all the numerous responses!!

Guess no one is home!!

[TopCatGr58]

This is for all of the Carb Guru's out there in xsland. Here we go!!
Part 2> Set 2 installed on the bike it idles fine and falls flat on its face WOT?I have standard jets for 79F. I am at sea level and clips should be at center right? When set at center posistion. it will idle ok but will not rev. I moved clips one posistion to a richer setting and this has helped but still plugs are very white. Can I enrich enough with the mixture screw or does this sound like float failure? I do not have a ColorTune plug so I am trying to set this by ear. Ya'll give me some feedback please, especially the vacuum issue because I really want the original set back in this machine. Thanks in advance!!

Hey Foreda,

CrazCnuk answered your first part quite well...I think most of us felt, and so no other suggestions were needed.

Your second part wasn't well separated from the first part, so perhaps folks didn't see it!

We don't know what type of sets of carbs you have, seeing that you have 3 sets, are they ALL from the early models, or are they a mixed collection? Also, can't remember your setup....ALL STOCK intake/exhaust, or aftermarket, Indy filters, etc.??

But anyways, if it's falling on it's face at WOT, sounds like it's too lean, like you noticed...bleach white plugs. I don't think you can adjust that much by just floats, and the pilot screws are really for low/mid range, don't really have much affect at WOT! You may need to rejet the mains, but don't necessarily have enough info about your bike to make that suggestion...ie. what jets are in it...I think you said stock, but again, what if any MODS to bike? Many of us don't have or use a colortune, we vac. synch, and then use Ken's By Ear technique to fine tune the idle/pilot circuit.

T.C.

[foreda]

Replies

Hey Foreda,

CrazCnuk answered your first part quite well...I think most of us felt, and so no other suggestions were needed.

Your second part wasn't well separated from the first part, so perhaps folks didn't see it!

We don't know what type of sets of carbs you have, seeing that you have 3 sets, are they ALL from the early models, or are they a mixed collection? Also, can't remember your setup....ALL STOCK intake/exhaust, or aftermarket, Indy filters, etc.??

But anyways, if it's falling on it's face at WOT, sounds like it's too lean, like you noticed...bleach white plugs. I don't think you can adjust that much by just floats, and the pilot screws are really for low/mid range, don't really have much affect at WOT! You may need to rejet the mains, but don't necessarily have enough info about your bike to make that suggestion...ie. what jets are in it...I think you said stock, but again, what if any MODS to bike? Many of us don't have or use a colortune, we vac. synch, and then use Ken's By Ear technique to fine tune the idle/pilot circuit.

T.C.

Thanks TC
I appreciate the response. I was frustrated at myself mainly for breaking the original carb goal post and do apologize for the smart ass comment. Breaking that carb was plain dumb and I knew better. That's what I get for mixing Bud Light and carb rebuilds. I have since removed the lean set as I believe there is a problem with transtion from low speed circuit to the high speed circuit. I reinstalled the original set and have been focusing on getting these right. I still don't understand why I am not getting the vacuum like the other set.?? I also have plenty of compression?? My problem now is fuel mixture. I have sooty plugs on 1 and 4 ( I know this sounds like spark but with the other set all 4 were white). I set the float levels at 25.7 mm but when I checked the levels on the bike, 1 and 4 levels are higher than 2 & 3. I ordered some plastic floats from Mikes and understand they come set a around 25 mm. Somebody correct me if I am wrong. One thing I forgot to mention is that I changed the carb intake boots but I don't think this is an issue?? How would you get carb 2 to develop more vacuum? I don't know any other way to sync as I have probably read ever thread on this sight concerning carbs. I have seen where others have had this problem but never seen where anyone nailed it down. All my carb sets are Minkuni Bs 34's with stock jets. The only component I added was K&N Air filters to replace the stock ones. Again please forgive me for being an ass!

[foreda]

All 78- 79 carbs

All my carbs are 78-79 Mikuni's,

[tw1980]

I have played with these carbs a lot and had similar problems.1st check very carefully for vac leaks.2nd check and recheck float level.3rd get the main jet right.Warm up bike and pull hard 2nd,3rd and 4th(remember the carbs don't know what the rpm is,they only know the position of the slide).Then set the needle.Smooth 1/4 throttle to 1/2 under load.Then last set the pilots,smooth idle to 1/4 throttle.I hope this helps,if I'm wrong I hope one of our carb gurus will set me straight. Terry

[Ken Talbot]

Thanks TC
One thing I forgot to mention is that I changed the carb intake boots but I don't think this is an issue??

Aha! Anything you change can be an issue. This one little thing now introduces four manifolds that might be leaking, four intake sides that might not be sealing against the cylinder bank possibly due to missing or leaking gaskets, four carb ends that might be torn or not well seated to the carb throats, and four clamps that might be over or undertightened. Throw in a new #2 carb in the existing bank, and a bunch of new parts such as needles jets seats and shaft seals and it gets a bit hard to figure out where to start. Oh, and there was also a change from stock air filter to K&N.

Someone much wiser than I once advised here the forum something to this effect:

"When you have a problem, start with one thing. If that doesn't fix the problem, put it back to what it was. Then change something else. If that doesn't fix it, put it also back to what it was. Do it like this, one thing at a time, until you discover the problem. Then fix the problem and leave the other stuff alone."

My advice, FWIW, put everything back to exactly the way it was, to the moment in time just before you pulled the carbs of for cleaning.

BTW - what sort of performance issue were you having that prompted taking off the carbs in the first place? The answer to this might point to a simpler path to the final solution.

Believe me, I'm not trying to chastise you with all this. I'm just trying to offer a more methodical, one step at a time process to try to get you through this.

[DGXSER]

Dude, we all get frustrated and are subject to the "age of instant gratification" effect. Typically you can get ten answers in as many minutes on here so it does seem odd when no one answers.

If you are not getting vacuum readings, and you replaced intake boots, then here are some possible but not probable ideas. 1. Did you use a gasket at the seal to the head, and is that sealing? 2. Are you sure there is nothing plugging the synch port so you do not register vacuum on that carb boot? 3. As to set two, does it idle fine under load? or just idle with no load, then you give it throttle no load and it falls on its face? When I first rebuilt my carbs I found the bike would start and idle up and warm up fine, even did alright with throttle under no load, then under load of riding, it was all fubar. Took some tuning and synching to get it running right.

And now I see some of the true genious folks are getting here and well ahead of me...like Ken.

[Crazcnuk]

Just to add, if your getting different vacuum between two carb sets, all else being equal, have you checked the diaphragms in the set that lacks vacuum?

My last set had several tiny pinholes in the diaphragms on 3 out of the 4.

[foreda]

Original issue

Aha! Anything you change can be an issue. This one little thing now introduces four manifolds that might be leaking, four intake sides that might not be sealing against the cylinder bank possibly due to missing or leaking gaskets, four carb ends that might be torn or not well seated to the carb throats, and four clamps that might be over or undertightened. Throw in a new #2 carb in the existing bank, and a bunch of new parts such as needles jets seats and shaft seals and it gets a bit hard to figure out where to start. Oh, and there was also a change from stock air filter to K&N.

Someone much wiser than I once advised here the forum something to this effect:

"When you have a problem, start with one thing. If that doesn't fix the problem, put it back to what it was. Then change something else. If that doesn't fix it, put it also back to what it was. Do it like this, one thing at a time, until you discover the problem. Then fix the problem and leave the other stuff alone."

My advice, FWIW, put everything back to exactly the way it was, to the moment in time just before you pulled the carbs of for cleaning.

BTW - what sort of performance issue were you having that prompted taking off the carbs in the first place? The answer to this might point to a simpler path to the final solution.

Believe me, I'm not trying to chastise you with all this. I'm just trying to offer a more methodical, one step at a time process to try to get you through this.

The original issue was low speed stumble/ hesitation. It actually ran like a bat out of hades after getting pass the stumble. The new carb boots came from Georges and came with gaskets, but I am pretty sure the gaskets are not needed because of the o-ring seal. The old ones where not really bad, I am trying for showroom condition. I replaced all of the parts including emulsion tubes with after market parts.
I had tried running sea foam before pulling carbs with no sucess so that is where it all started.

[foreda]

Idle

Dude, we all get frustrated and are subject to the "age of instant gratification" effect. Typically you can get ten answers in as many minutes on here so it does seem odd when no one answers.

If you are not getting vacuum readings, and you replaced intake boots, then here are some possible but not probable ideas. 1. Did you use a gasket at the seal to the head, and is that sealing? 2. Are you sure there is nothing plugging the synch port so you do not register vacuum on that carb boot? 3. As to set two, does it idle fine under load? or just idle with no load, then you give it throttle no load and it falls on its face? When I first rebuilt my carbs I found the bike would start and idle up and warm up fine, even did alright with throttle under no load, then under load of riding, it was all fubar. Took some tuning and synching to get it running right.

And now I see some of the true genious folks are getting here and well ahead of me...like Ken.

The idle was perfect on set 2. You just could not give it any throttle until it was really hot and warmed up. Then road test, WOT would fall on it's face. I am going to disassemble this set and put each carb in the carb cleaner. I obvioulsy missed something although I saw cleaner come out of every hole. I bought these on Ebay so you never really know what you get when you buy used stuff??
Thanks for the reply.

[foreda]

Diaphrams

Just to add, if your getting different vacuum between two carb sets, all else being equal, have you checked the diaphragms in the set that lacks vacuum?

My last set had several tiny pinholes in the diaphragms on 3 out of the 4.

Craz
When I removed the lean set and replaced with the original set I did find that I could spin the diaphram on # 2. I am pretty sure you are not suppose to be able to do this. I replaced this slide with one out of another set and this did help.
Another problem I have is my carb sticks are getting low on Mercury. Guess I'll have to fork out more money since you can't get Mercury anymore.

[foreda]

Mikes XS Diaphram/ Slides

Has anyone bought the 34 mm diaphrams from Mikes XS and if so , do they work ok?