CV Carb Issue?

[chef1366]

You have CV carbs not VM.

[Westy62]

That's what I thought....thanks! I'm going to take the carbs off again and inspect them.....from what I've been reading about CV carbs, it has to be something in there. I'm suspecting the float level.....I'm going to pick up a more precise float measuring tool, and make sure the needle seat spring isn't depressed. I guess I'm used to cars where the level isn't so critical!

[Dave8338]

The filter is foam....I'll really give a good squeeze for sure. I'll mess with the mixture screws some more, and I believe out is richer.....Where do you guys get the washers for the needle height adjustment?

TY!

Radio Shack has them, bring in the slide just to make sure you have the right size. If you can make or buy a fitting for your vacuume guage, use it to check the balance between both carbs. There should be a small allen head bolt 6mm I think, on the intake boots. Check to see that both carbs are drawing the same.

[Westy62]

So I'm going to tackle the carbs today an check everything out. I had a flooding issue originally and noticed the float level to be around 27mm, so I put it where it should be (around 23mm) and that seems to be when the lean problems started. If I want to richen it up in steps, could I go 1mm up at a time (eg 23-24) to do so? It just seems the opposite, like the lower the mm height the richer (I hate working on things upside down).

I always have measured the float height like this diagram:



Thanks!

[chef1366]

Measure the float at the stepdown from the hinge.

[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!

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.