CV Carb Issue?

[Westy62]

Hey everyone....I've had this 1980 GS450E for about 3 weeks, I've went through everything (carbs twice), and still have an issue when the vacuum carbs seem to work off the secondary circut. I've searched this site.....have some ideas, but I thought if someone had more experience with this I could at least start with the most possible problem!

Here's some history of the bike and what I've done.....

1980 GS450E, 8,000 miles on bike.....it was stored for years before I bought it.

Carbs cleaned and adjusted (float height 22.4mm)
Adjustment screws about 2 turns out
New intake boots
New intake o-rings
New air filter
Airbox is very tight
Adjust valves
New plugs
Coated tank
New gas
New oil
New oem petcock
All new vacuum lines and fuel lines
140 PSI in each cylinder, warm WOT
Checked intake leaks with started fluid
Plugs are a bit on the light side

This bike idles and runs part throttle VERY nice, it's just when I get into it a little (starts to fall down), or a lot (almost dies), until I return the throttle, then it's just fine again!

It reminds me of an old Chevy I had with a goofed up Q-Jet...!

I don't have a clymer yet, and have done all this work with help here, and the local dealer.....but this problem is driving me NUTS!

I'm going to try running it on prime to see if that helps (my petcock passed all the tests you guys mentioned).....

Here's a pic of the spark plugs (both identical).





It just seems to be the vacuum CV carbs, but the diaphrams were replaced! Any ideas to help would be appreciated!

Wes

[Dave8338]

It sounds like you've been very thorough in you methods. It still suggests that there is an obstruction in you pilot circuit, though, to have both plugs that close in color range, I'm somewhat suspect. Where do you have your jet needles set (you mentioned new diapragms)? Are you sure that you have the float heights set correctly? Can you get the RPM's to hold strong if you ride it with the choke on? Which type air filter are you running? Do you have an inline fuel filter in the bike (shouldn't need one)?

[DimitriT]

These carbs are tuned very lean. Especially were it transitions into the needle jet. Check that your sliders are working properly. I like to blow some compressed air from about a foot out and watch them go up and down. Inspect the diaphragms and make sure there are no leaks.

The color on your plugs was from idle or from the flat spot you mention? Did you get them from a plug chop?

[kctrading]

Only thing I could add is make sure you tank gas cap is venting...check the actual flow of gas to the carbs...it should flow freely. and again where did you set the float level to?...should be against the back of the float (round area) and not where the arm attaches to it as I run across this when doing my carbs on a GS1100EZ.

Good suggestion on adding some coke and seeing how it effects it.

Ken

[SAN]

CV carb issue

Hi. have you tried turning out 1/4 turn at a time to the fuel mix screws. the ceramic and electrodes look slight lean. good luck.[-o<

[Westy62]

It sounds like you've been very thorough in you methods. It still suggests that there is an obstruction in you pilot circuit, though, to have both plugs that close in color range, I'm somewhat suspect. Where do you have your jet needles set (you mentioned new diapragms)? Are you sure that you have the float heights set correctly? Can you get the RPM's to hold strong if you ride it with the choke on? Which type air filter are you running? Do you have an inline fuel filter in the bike (shouldn't need one)?

Jet needles were put back in the same spot....sorry, I don't know what setting it is. Float height is correct from spec, but I soldered a few leaks in them, and maybe they're heavier? Before I rebuilt them, they were flooding and set too high also. I'll try the choke on while I drive....it usually kills the bike when just idling. Air filter is genuine Suzuki and oiled with 30w. No inline filter is used.....

If I just gradually give it gas, it eventually starts to slowly faulter.....if I suddenly open it up, it just bogs with NO power (no backfiring though) and would eventually die, but recoveres to normal when I bring it back.

I'll report back.....THANKS!

[Westy62]

These carbs are tuned very lean. Especially were it transitions into the needle jet. Check that your sliders are working properly. I like to blow some compressed air from about a foot out and watch them go up and down. Inspect the diaphragms and make sure there are no leaks.

The color on your plugs was from idle or from the flat spot you mention? Did you get them from a plug chop?

It sure feels lean (plus I never smell gas). It also really seems to be a transition thing!! Nice tip on the sliders.....I'll try that. Diaphrams are new.....Plugs are from an average ride (I should do a plug chop), but it basically stalls when I get into it.

I can ride this bike around town like nothings wrong, until I give it too much throttle....

Thanks!

[Steve]

Air filter is genuine Suzuki and oiled with 30w.
If I just gradually give it gas, it eventually starts to slowly faulter.....if I suddenly open it up, it just bogs with NO power

Even though the plugs look VERY lean, it also sounds like it's not getting enough air. How much oil is on the filter? It is realy easy to over-oil it. The oil should be a very light misting, just enough to ge the filter a bit tacky, not wet. I don't remember if the stock filter is foam or paper. If it is foam, squeeze out the excess oil. If it is paper, you might just have to get a new filter.

To help with the leann situation, open up the mixture screws 1/4 to 1/2 turn. That should help with the idle, maybe into the pilot circuit a bit. If it still stumbles at mid-range, might have to try raising the needles.


.

[Westy62]

I blew through cap and it seemed fine, float level was around 22-23mm from bowl edge (without gasket) to the bottom of the float (round area). The mixture screws have been moved anywhere from 1 to 3 turns out, with just a noticable diff only to the idle a bit....

I have a vacuum guage.....any use? I'm going to go putz....Thank You for the info! Wes8-[

[Westy62]

Even though the plugs look VERY lean, it also sounds like it's not getting enough air. How much oil is on the filter? It is realy easy to over-oil it. The oil should be a very light misting, just enough to ge the filter a bit tacky, not wet. I don't remember if the stock filter is foam or paper. If it is foam, squeeze out the excess oil. If it is paper, you might just have to get a new filter.

To help with the leann situation, open up the mixture screws 1/4 to 1/2 turn. That should help with the idle, maybe into the pilot circuit a bit. If it still stumbles at mid-range, might have to try raising the needles.


.

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!

[Steve]

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!

Be sure to squeeze, not wring. Wringing the foam tends to tear it and render it useless.

Where to get the washers? Some have found them at Radio Shack, others found them at a hardware store, I found mine in my hardware bin.
What you are looking for is a #4 flat washer. Stainless or brass would be nice, but is not necessary. Might need one or two washers, probably could not fit any more than that in there and still install the clips.


.

[chef1366]

Are your carb vent lines unobstructed? Can you blow into them without resistance?

[KEITH KRAUSE]

Did the bike run fine at one time? Did it only start the problem after the carb clean/rebuild?
If the bike is stock, there's no reason to raise the jet needles. The bike came from the factory a tad lean, but no major issues as you have are related to the jet needles unless you assembled things wrong.
First thought is the diaphragm(s) aren't operating right. But generally, the bike will start and idle fine, but will except NO throttle or very little. But you say you can ride around town at smaller throttle openings??

[Westy62]

Did the bike run fine at one time? Did it only start the problem after the carb clean/rebuild?
If the bike is stock, there's no reason to raise the jet needles. The bike came from the factory a tad lean, but no major issues as you have are related to the jet needles unless you assembled things wrong.
First thought is the diaphragm(s) aren't operating right. But generally, the bike will start and idle fine, but will except NO throttle or very little. But you say you can ride around town at smaller throttle openings??

The carb vent tubes are clear (and off)......This bike has always run decent, but I never opened it up because it needed new tires, so the heavier throttle problem was never noticable. While the tire project was going I did all the other work. It had a major petcock problem with leaking gas all over, and the floats were leaking as well with the height set at 26 (too high). I don't have the leaks anyore.

The bike runs beautifully at idle and part throttle (I can even zip up to 55 or so on 1/8 - 1/4 throttle, but any more and it starts to fall. Last night it seemed unusually hot.....probably from being lean.

Do these carbs fork like a vacuum secondary Holley or something? Vacuum drops and engine velocity allows the diaphram to let the needles open?

So if I blow air into the carbs the needle jets should rise up? Any other way to test them?

I'm going to start putzing today, thanks for the info!

P.S. I registered for repairmanualclub.com and I just get white pages when I try to download...? I followed all the instructions and then had to contact admin....Looks like there is a GS450 manual along with a Mikuni VM carb tuning .pdf Is that the carb I have?

Wes

[Westy62]

Well, I can rule out trying the prime mode on the petcock, and turning the mixture screws. I'm going to work farther in.....