Ready for a Real Head Scratcher? (Carb & Vacuum Related)

[syscrusher]

Back in January I used my digital carb sync to balance the carbs. When I pulled the vacuum plug off of the right rear carb (izzit #3?) there was no change in the way the engine ran. No stumbling or hesitating, nothing. There is good vacuum on that port, etc. and I balanced the carbs very closely, nearly perfect.

 

Well today I had the lid and filter off the airbox while it was running and when I throttled it the slides on the left both opened a little wider and pulled the needle with them. The slides on the right side didn't move, neither one of them. I used a long screwdriver to move them manually just to ensure they weren't stuck but the return spring provided more force than vacuum in the cap and so they closed again. This is beyond my understanding, except for one thing, it seems like my right cylinders are only getting the pilot mixture and nothing more. I am sort of optimistic that someone here knows just what's going on and when I fix it I'll have somewhere close to twice the power I have now. But I am stumped.

 

What is going on with my carbs? I had new diaphragms a year ago. At the time I didn't know that the small hole in the slide lines up with the hole in the carb body but I have to admit I didn't think that could be tremendously important because vacuum should be even throughout the carb and not require lining it up. If we expected it to spray a jet of fuel through the two holes when lined up it would be different but I don't think we're expecting that to happen. Could I have two damaged diaphragms on the same side after a year? Did I really install them incorrectly? I can't find my tamper resistant torx bit, I hope it's available at Ace Hardware.

 

Please help??

[Great White]

First thing I'd do is pull the caps off that side and check the diaphragms. They may not be damaged, just separated from the slides.

 

As far as showing vacuum on the gauge, even a non firing cylinder will show vacuum if its mechanically sound. As the other cylinders drag it through the cycle, it still pumps air. The vacuum signal is (primarily) determined by the throttle blade opening and that's what you are adjusting when you synch the carbs. More open blade, less vacuum signal and vice versa.

 

[Flyinfool]

The tamper resistant torx bit is available at Harbor Freight.

When You put it back together do not reinstall the tamper resistant screw, You can get a new set of screws at most any hardware store and not have to deal with tamper resistant again.

 

If the slides move easily but do not move with engine running, then the first place to look is at the diaphragms. Hopefully they just were not on all the way and slipped out of the groove. The slides should not move slowly in and out with the throttle, they should be dancing in there. I would pull and check all 4 diaphragms.

 

I never tried, but is it possible to have the diaphragms installed inside out?

[videoarizona]

Everything I've read says the little holes MUST be lined up properly.

I don't remember why...just remember it needs to be.

 

SV carbs are very simple in theory and operation. Crap gas and time clogs the little holes and eats the diaphrams...so the theory remains viable just not sustainable.

 

Since you have the problem anyway...my suggestion is to at least go back and check the diaphrams to make sure they are still mounted on the slides then turn them so they are lines up properly. At least from there, you can start troubleshooting knowing those two parameters are spot on.

[syscrusher]

I must have found her 'G' * Spot!

I didn't know she had such an appetite**.

 

I guess I may have not gotten one or both of the diaphragms on the right side seated correctly. When I opened those two the diaphragms popped right up out of the ring groove. I hate dealing with the damn things because they tend to come out of the groove and if I use my fingers to hold it in place there's enough room to let the ring pop out when I remove my finger and put the cap down. I needed something thinner than my finger to hold the diaphragm until the cap could hold it. I invented a diaphragm installation tool as seen in the attached photo. It's made from thin sheet aluminum roofing material. I knew that cutting with the shear would leave a rough edge so I used the Dremel with a cut-off wheel and then smoothed the edges of the cutout with the Dremel. I got them very smooth as they need to be. Before attempting to use it I spray the side that will make contact with the rubber with WD40. I get the diaphragm in the groove underneath the sheet and then bring the cap to it and put in a couple screws just loose enough to let me slide the sheet out from under the cap. With the sheet removed the screws all get tightened down and on to the next one.

Everyone reading this make a note to remove the fake tank cover, start up the bike and then remove the air cleaner and cover. Rev it up a little and make sure you see all of the slides move. If you don't then take a look at the diaphragms for those. I never knew this was happening. When I got the VR there were pinholes in the diaphragms and the loss of vacuum made the idle rise to 3000 or so when warm. I opened the caps up and put Super Glue over the pinholes. Those diaphragms were well behaved and stayed in their grooves easily. This was probably the best performance I experienced with the bike before getting new diaphragms and messing up the install on some of them. At the time with the Super Glue my carbs weren't balanced so it was still a little off. There really was nothing to hint at what was happening other than to look, which I never had. I guess looking at the slides when revving should be a part of the procedure. I had been thinking I needed new plug wires because of a slight miss.

 

Thanks to all for the help!

 

* the Gassy spot

** appetite for the Gas

Edited July 28, 2015 by syscrusher
added two letters

[syscrusher]

Everything I've read says the little holes MUST be lined up properly.

I don't remember why...just remember it needs to be.

 

Since you have the problem anyway...my suggestion is to at least go back and check the diaphrams to make sure they are still mounted on the slides then turn them so they are lines up properly.

 

When I had it open I looked into the carb body and I didn't see any holes to line up with. The only hole on the "bottom" of the carb body was the needle jet itself. I also didn't want to risk tearing the diaphragms by pulling them loose from the slide. I'll have to be told all about why to line up the holes in some scientific jargon that sounds like it must be way over my head before I try lining up anything. Then I'll have to try and find a hole to line up with. It runs pretty good WITHOUT lining up anything, I'm not sure I could stand it if the holes WERE lined up!

[lonestarmedic]

To keep the diaphragms in the groove try this. Pop the air filter cover off and the air filter out. Look down and see the slides/needles. Take a long thin object such as a long screwdriver or dowel rod and stick it into the carb. Avoid the needle. Now, when you set the diaphragm in cup it so the slider protrudes. Call it convexed out. Slide the unit in until the diaphragm is in the groove but the slide is still protruding. Us screwdriver to keep slide in this position. Put spring in. Grab cover and make sure springs are around the tabs inside the cover. Push cover against carb body as you use dowel to keep slide locked. Hold cover flat and install screws. Tighten down then remove dowel. Keeps the edge in the groove. I have done this so much I lay the cover, spring, and screws out and can have a slide in and cover tightened in about 2-3 minutes. I keep a 1/4" wooded dowel around for this. However a long cabinet screwdriver works well also. The dowel holds the slide great and does not need to be pushed on at all.

 

JB

[syscrusher]

The tamper resistant torx bit is available at Harbor Freight.

When You put it back together do not reinstall the tamper resistant screw, You can get a new set of screws at most any hardware store and not have to deal with tamper resistant again.

 

 

My local HF had the 100 piece Security Bit set on sale for a few cents less than a Hamilton today.

I bought 16 M5x0.8x12mm stainless socket head cap screws for $3.20 at Fastenal locally. Ace Hardware wanted $1.19 each in stainless.

[syscrusher]

To keep the diaphragms in the groove try this. Pop the air filter cover off and the air filter out. Look down and see the slides/needles. Take a long thin object such as a long screwdriver or dowel rod and stick it into the carb. Avoid the needle. Now, when you set the diaphragm in cup it so the slider protrudes. Call it convexed out. Slide the unit in until the diaphragm is in the groove but the slide is still protruding. Us screwdriver to keep slide in this position. Put spring in. Grab cover and make sure springs are around the tabs inside the cover. Push cover against carb body as you use dowel to keep slide locked. Hold cover flat and install screws. Tighten down then remove dowel. Keeps the edge in the groove. I have done this so much I lay the cover, spring, and screws out and can have a slide in and cover tightened in about 2-3 minutes. I keep a 1/4" wooded dowel around for this. However a long cabinet screwdriver works well also. The dowel holds the slide great and does not need to be pushed on at all.

 

JB

 

That's a great way to do it. I didn't think of that. I don't know how many times the diaphragm ring practically fell into the groove when it was inverted that way, until I pushed in the spring. It sure is easier to cut the end of a dowel than it is to polish the edge of the aluminum sheet. I guess I won't be able to sell many Diaphragm Installation Tools here.....

[jasonm.]

keeping the outside edge of the diaphragm in place...use a little waterproof grease. It holds the diaphragm in place long enough to allow the cover to be put on and squeezes out w/o causing issues.