CV Carb Issue?

[KEITH KRAUSE]

Your changing the float height/level from 27mm to 23mm would raise the actual bowl level. So any symptoms you thought were lean related, are not because of your adjustment. You were richening things if anything.
Picture the carb on the bike. The sooner the rising float arm tab touches/closes the float valve, the sooner the fuel stops flowing and the lower the actual bowl level.
So when upside down, the greater your measurement (from carb body without the bowl gasket to top of float), the lower the fuel level.
I don't know what the factory setting is for your model. I'm sure you can find that info in the carb series somewhere in the tech (?) section? Various members have been adding their model/carb stats there.

 

[Westy62]

WOW.....Now I'm really confused!! I'm guessing I measured wrong, and this setting is WAY off. Anyone have a pic? I tried the repairmanualclub.com but had no luck.

Wes

 

[Steve]

Attached is a picture of the way I understand the measurement is to be done.
If anyone can show me that I am wrong, please do so.

.

 

[Westy62]

So is that rightside up? I can see where to measure on the float, but what other surface is that? Is that the carb body? I'm going to take some pics of my carbs later.....TY

 

[Westy62]

Giving up soon!

Giving up soon!

Well, if you read what I've done to the carbs, fuel tank, petcock, airbox, and the bike in general in the beginning of this post, it's amazing to think the problem could be fuel. I just took out the springs in the diaphram area of the cv carbs because of the issue at 1/4 throttle and more (total bog but doesn't die), and the bike ran the same! Idles like a sewing machine, and very crisp throttle around town at low throttle......but when I get on it....blahhhh. You would think it wouldn't run, or very poor at the least without the diaphram springs!

Something is seriously wrong, but as awesome as the bike runs at idle and low throttle, it HAS to be something goofy!! It's kicking my butt.....

Now that I have a Clymer manual, I need to look into the ignition......I've spent a month on the fuel system!

Ideas welcome!

 

[80GS750]

did you try adjusting your needles? it sounds like its not getting enough gas when you hammer it.

if everything is stock, the needle height should be fine. who knows, maybe you just need to tweak the needles and see what happens, it doesnt sound like petcock or vacuum/leak issues.... if everything is air tight that cant be the issue....

maybe your needle jets have an obstruction? something that got caught in reassembly?

 

[80GS750]

it cant be an ignition issue if its only variable is how fast you twist the throttle...

unless you have timing issues? maybe a bad timing advance plate?

just a shot in the dark

 

[Westy62]

The needle setting and bike are bone stock, I'll check into the timing advance plate.....It is SO related to the throttle position, the engine is suffering when the butterflies are opened too far and let too much air in it seems.......A plug chop at WOT shows nothing (dry plugs). I have good spark....Nice and blue at night.

The plug chop is easy to do cause the bike just falls on it's face at WOT and kinda runs about 10 mph in first! I can just about coast home into the driveway.....I'm pretty sure I can hear pinging under partial load cruising also, which to me would be a lean condition.....the gas is premium to be sure.

I have a new float coming soon (I repaired a leaky one, and I don't trust it still).....

I'm not giving up....it's too nice of an old bike! Considering I'm an old drag racer and car guy, I sure feel like a dummy with this bike! Fuel, air, compression, spark.....duh.

 

[kctrading]

One way to verify it's fuel or not is to take out the air cleaner and when you go to wot and it starts to bog stray a shot of carb spray down into the air box...if it revs up you know for a fact you are lean.

Ken

 

[KEITH KRAUSE]

Your description sounds a lot like a vacuum or air flow issue.
The throttle plates open up according to piston/diaphragm assembly position which in turn is dictated by vacuum acting upon the piston. Taking out the springs is an odd test but if it has your decribed results, that's further proof something is wrong with the vacuum and/or the throttle plate operation, or how air is entering the carbs.
Normally, a damaged/incorrectly sealing diaphragm won't accept ANY throttle above basic idle rpm's but will idle fine all day. You say you can throttle it up to 1/4 (?) before it shows a problem.
I can only suggest going back and checking basic assembly and parts condition/missing or incorrectly assembled parts.
Then I'd carefully bench synch the throttle plates and verify smooth operation. The bench synch must be followed by a vacuum tool synch to allow accurate testing/troubleshooting.
The word "bog" can be hard to diagnose because it's often used to decribe both lean and rich conditions. I have experienced personally your bikes symptoms and in at least one case the cure was finding a shop rag that had dropped into the air filter housing and obviously restricting air. His bike literally fell on its face at anything above 1/4 throttle but ran fine below that. Classic air flow problem.
In another case, the owner mistakingly oiled a paper element air filter. Poor air flow through that thing but it did idle fine and accept a little throttle.
In another case, the main jets were left loose and at least one had fallen out completely. This too resulted in your exact symptom. The bike ran fine until approx' 1/4 throttle and then it drowned in fuel.
So there are many things that can cause your problem and I'd just re-check things as I said.

 

[Suzuki mad]

You can set a bike up and it runs well but if enough fuel is not getting into the float bowls as you open up you drain the bowls so the engine bogs down due to lack of fuel.

Ignition system will do the same thing if the CDI/ignitor is faulty.

Start at the top. Check the fuel cap, then the fuel tap then the float heights then the ignition.

The other option is the airbox/intake rubbers seals.

Suzuki mad.

 

[Westy62]

Yeah, about 1/4 throttle.....I now found out if I take the airbox cover and filter off the bike will fly! Put the airbox top on without the filter, and it gets a little better, add the filter, and it's worse.....It's very sensitive to how much air is blocked.

I will look everything over again.....Thanks!

P.S. If I rev up the bike to about 5-6k without giving it much throttle (e.g. 30 mph in second) and then give it the WOT, it will catch and go for a second or two before losing it's umph. Lower rpm blasts usually don't get to the "go" part....so it's really a velocity issue.

I was thinking about moving the needle up to see if any extra fuel could jump start the flow better, I was even told to drill out the hole bigger in the slider (like a jet kit), so it would slide up easier, but I would prefer not to do that yet!!

TY

 

[KEITH KRAUSE]

Hmmm. Not sure what to say. The plugs burn lean but intoducing more air improves performance dramatically?
Plus, removing your airbox improves the performance with CV carbs?? Not the norm, that's for sure.
I think somethings been assembled wrong or adjusted wrong. I'm not sure you ever have adjusted the floats correctly, which could cause a lean mixture and lean plugs and your problem. But removing the airbox shouldn't help if that's the problem. There's more to this than what we've read.
I do think it's a mistake to richen the needles, if the bike is stock and is tuned/adjusted correctly. It should'nt be needed. If it somehow helps, then I think it's just compensating for the real problem and compensation jetting just causes other problems.

 

[Steve]

.....the gas is premium to be sure.

Not that it will fix all your other problems, but "Premium" gas will not help at all. Better to put in "Regular" gas.


"Premium" is not a measure of quality. It is merely a label given to gas with higher octane. Octane does not put more power in the gas. In fact, it makes it harder to light and slower to burn. :shock: Higher-compression engines can create enough heat during compression to light the fuel/air mixture before the spark. This is the "knocking" or "pinging" that you hear while accelerating at lower engine speeds. Increasing the octane level in the gas makes the mixture harder to light, so it waits until the spark sets if off.

By running "premium" gas, you are not adding any power, you are just wasting money. Not just by burning more expensive gas now, but there are also more deposits on the valves and pistons because the fuel is not burning completely. These deposits can lead to very costly repairs, don't ask me how I know.


.

 

[80GS750]

like said before,

you were describing a lean condition, then you took off the airbox and it flew...

i would say your running too rich now, and thats bogging the bike down...

check that filter again, it sounds like your not getting enough air.


i would not richen it however until you kind of have an idea of whats causing your problem....

 

[Westy62]

WOT Plug Chop

WOT Plug Chop

Here are the plugs after 2 WOT plug chops today.....The bike BARELY runs while doing it. They look rich now! About 2 weeks ago, they were very pale just from lightly putzing around town. This is with the airbox and filter in place.....almost everything has been replaced and is new (filter, boots, o-rings, etc.) and I've checked the float level about a dozen times, and I keep it around 23 mm.

I'm going to take the carbs off again tonight.

 

[Westy62]

Bizarre.....I just did another WOT plug chop, and while it was WOT and bogging I flipped the choke on and off, and it made no difference! If I choke it at idle or lower RPM it cuts the motor. I wonder if the choke mechanism is goofed up and does something when the vacuum pulls on the diaphram. Isn't there a choke passage that goes up there on CV carbs? The choke pistons are connected and seem to plunge up and down with the lever......Off they come!

 

[DimitriT]

Yea, you got too much gas. The choke does pull air from the diaphragm. You can check the o-rings on the choke plunger but I doubt that's your problem. I'm sticking to my theory that someone has messed with your needle settings or jets. Maybe you have worn needle jets... but there you would see richness on idle too, I think.

 

[KEITH KRAUSE]

The choke circuit has an insignificant effect (as designed) during full throttle so don't let that bother you.
Those plugs are obviously rich.
Re-reading your posts, you said the bike will reach 55 with no serious trouble so I believe your timing advancer is working since it reaches full advance by approx' 2,000 rpm. Your plugs are newer and I assume the correct heat range and gapped correctly. Have you also checked for a good bluish spark while turning the motor over by hand? Have you taken any resistance reads for the coils? Battery voltage? Are the plug leads and caps in good condition and have you inspected the caps inside for clean/tight connections?
I have a feeling your rich plug reads are mixture related but you should always make basic electrical checks because they are basic maintanance. In this case, even if you don't have a manual and meter to check the coils and ignitor, you can still inspect the spark and all connections and battery condition. If you have the tester and test info, the electrical check is very quick. You just don't want to blame the carbs until you know the electrical is good. Like I said, it needs to be checked anyway or at least do what you can.
If the electrical check passes, then we need to look at the carbs or intake to determine why those plugs are rich at full throttle, and, I suspect, while on the jet needles too.
Going back, it seems possible the bike has never run well at higher speeds since you aquired it. It was stored for years you say and after you started riding it you only rode it slowly without noticing a problem. Only after opening it up more did you notice the problem.
I bring this up because if you inherited this problem and have no real knowledge of any repair attempts to the bike, then the sky is the limit as to what could be wrong. A PO/butcher could have played with carb parts/jets, etc. But if it really did run fine under all conditions but suddenly started this problem since you've owned it, then you'd know if it could be related to something you did or ? It could help us narrow down the likelier causes.
The rich plugs at "higher speeds/throttle openings above 1/4"...
You say the air filter is new and oiled correctly.
I can only assume the airbox itself looks like it's for your model and not possibly off some other model? The box is in good shape and not deformed in any way?
I assume the carbs are the correct ones for your model?
You say the carbs are cleaned inside well.
Fresh inner o-rings I think you said?
Float levels correct and after some question, you're positive the levels are correct.
The floatbowl vent lines are verified open and breathing and routed well with no kinks?
The mixture screws are about 2 turns out, which wouldn't cause your specific problem anyway.
That leaves us with possible PO installed incorrect jets...
This would be quick and easy to check for if you can check the factory jetting info and compare.
Missing parts or incorrect assembly order...
I'm not sure about your specific carbs parts order but if you or someone mistakenly placed any jet needle plastic rings/spacers that go ABOVE the e-clip and placed them UNDER the e-clip or re-arranged them, then you'd be very rich while on the jet needle and there would be an overlap effect that would also effect wider throttle openings to a point. If at all possible, look at a parts illustration of your model and be sure you assembled the entire jet needle assembly correctly.
I assume all jets are firmly tightened and any o-rings between parts are installed correctly.
I assume there are no other signs such as fuel leaks anywhere, including through over-flow lines? This could suggest incorrect float valves or something else involving the float system.
If the jet needle and needle jets have only 8K on them, I seriously doubt you have wear issues with them.
If all above are good, then I'd have to question the carbs being clean, especially the air jets (filter side) and needle jet/bleed pipe tiny holes.
After all this is good, the carbs must still have the throttle plates bench synched and then they should be synched with a vacuum tool.

 

[Westy62]

Amazing to find this done to such an original stock bike!!!

Problem solved.....

Stock 115 on the left from bone yard, hogged out one in bike on right.