CV Carb Issue?

[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

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.

[KEITH KRAUSE]

Well, I did mention to check and verify the jets as part of my list of possibilities. I tried to include every possibility.
Hope it helped.

[Westy62]

You did Keith, that list I printed out and went through very methodically.....THANKS!! I'll remember in the future to not just assume the "115" stamped on the jet is what it really is!!

Thanks again!!

Wes