Looking for a little advice for Carbs.

[Guest]

Hello!! I recently started riding my rebuilt 1981 GS450L around. I found it for pretty cheap and it needed a lot of love. Its my first project bike, and Ive made a lot of mistakes along the way. It runs and rides fine-ish. I can get up to 50-55mph no problem in 3rd gear. When I shift for 4th, my power basically just disappears. Have I rejetted / tuned my carbs incorrectly? They are on pod filters. (Yes I know, I should have left it alone, but to late for that now, this ship has set sail)

I rejetted the first time with pod filters and had a lot of trouble getting it to run. I rejetted again to 135 / 40 and I got much better results. However, I still have trouble making it in to highway speeds. Ive also noticed with choke on, during cold startup fuel dumps out of the exhaust, and I noticed some bubbling from a spark plug thread which i found strange. Am I just dumping way to much fuel now? I tired to dial the air fuel adjustment back. I did increase the float level too since I thought i was fuel starving at around 6-7k rpm? (tach is broken haha)

Maybe my floats are to high still? The gas evaporates and when choke is off, its seeping gas anywhere. Im also getting around 30mpg currently. Aside from adjusting the floats a little more, has anyone done pod filters with a GS450 and had success? What sizes did you use? Any advice / suggestions at all? Thanks in advanced!

[Big T]

It's difficult to determine your problem from your description.

What throttle opening is giving you problems?
What brand of pods did you use?

CV carbs need smooth air flow to create the vacuum necessary to lift the slides.

Main jets only affects over half throttle

[Steve]

Greetings, welcome and all that stuff.

As Big T asked, the brand of pods is rather important. Besides the different ability for air flow, some pods tend to block the air ports on the carb intakes. With those ports blocked the carbs can't work properly.

Now to jetting: stock jetting is 115 on the main and 45 on the pilot. Float level should be 22.4mm ±1.0mm.
Depending on the pods, the 135 mains might be good, but why go DOWN on the pilot jet?
You say you increased the float level. From what to what? Numbers are important here, because if you used larger numbers, you actually lowered the floats. No matter what jetting you settle on, you should ALWAYS use the stock float level, and verify that it provides the proper FUEL level. And, you should know that there is no need to change the pilot jets when you install pods.

The reason you have to change jetting at all is because you have removed the restriction of the airbox, so more air can go through the carbs. Along with the extra air, you need to provide more fuel. At idle and low-throttle openings, the airbox does not impart any restriction, so removing it would not change the airflow past the throttle blades. However, there is usually a need to richen the mixture in the mid-range, so you need to at least raise the needles, if you can't find needles with the proper taper.

Also keep in mind that whenever you make changes, make ONE at a time, and record your observations. By the time it is done, you will know which change worked and which one (or several) didn't.

Might also need to go back to square one. Have the carbs been properly cleaned?

.

[TinkersCustom]

The jets i pulled out of there were very small. I am using UNI pod filters.

its hard to describe. so shes got get up and go from 1st 0-25mph, shift 2nd 25-40, 3rd 40-55, 4th 55+ but thats where the power drops off, I feel like if i full throttle i go no where, i drop down to 3/4 or 1/2 and its got a little more power or atleast enough to maintain speed. Maybe my mains are to large?

The jets i had previously were 127.5 / 30. Im pretty sure the jets in there were even smaller, maybe im wrong, i also didnt know the stock size and didnt have any resources to find it. Do you think i should change my sizes a bit? I can order new jets or mix and match the sets i have now.

[TinkersCustom]

Greetings, welcome and all that stuff.

As Big T asked, the brand of pods is rather important. Besides the different ability for air flow, some pods tend to block the air ports on the carb intakes. With those ports blocked the carbs can't work properly.

Now to jetting: stock jetting is 115 on the main and 45 on the pilot. Float level should be 22.4mm ±1.0mm.
Depending on the pods, the 135 mains might be good, but why go DOWN on the pilot jet?
You say you increased the float level. From what to what? Numbers are important here, because if you used larger numbers, you actually lowered the floats. No matter what jetting you settle on, you should ALWAYS use the stock float level, and verify that it provides the proper FUEL level. And, you should know that there is no need to change the pilot jets when you install pods.

The reason you have to change jetting at all is because you have removed the restriction of the airbox, so more air can go through the carbs. Along with the extra air, you need to provide more fuel. At idle and low-throttle openings, the airbox does not impart any restriction, so removing it would not change the airflow past the throttle blades. However, there is usually a need to richen the mixture in the mid-range, so you need to at least raise the needles, if you can't find needles with the proper taper.

Also keep in mind that whenever you make changes, make ONE at a time, and record your observations. By the time it is done, you will know which change worked and which one (or several) didn't.

Might also need to go back to square one. Have the carbs been properly cleaned?

.

Is there a write up or guide on needle adjustment?

Yes the carbs are clean.

Shame on me, i just slightly increased the float level. I didnt measure it. But I will revert to stock then for float level.

[Steve]

There might be a write-up, but save that adjustment for fine-tuning. ONE ADJUSTMENT AT A TIME.

First thing to do is to set the floats to 22.4mm ± 1.0mm. I usually set them close to 22.0 to make them slightly rich.

Next thing to do is to put in #45 pilot jets.

Finally, go ahead and leave the 135 mains in there, just use them as a starting point.

While you have the carbs out, do a bench sync. Look through the carbs from the engine side toward a light that is on the intake side. Adjust the idle speed screw so #2 carb is just barely open. Check that there is a small sliver of light visible past the butterfly. Compare the size of the light sliver in #1, adjust to match, if necessary.

Install the carbs, go for a ride.

Report back with your findings.

.

[TinkersCustom]

Just a quick update. I have set the floats back to stock, synced the carbs, changed the plugs and oil and restricted the air more using some electrical tape on the filters. I considered doing intake runners / velocity stacks with the filter on the end, but i dont have enough space. The carbs are responding much better to the mixture screws now. I tuned it the best I could on the center stand but have not had a chance to do a test ride due to bad weather. Ill be trying to test ride her tonight to see if what happens.

My thought process is, the air is simply to turbulent for the carbs to be able to use effectively. Restricting the air / adding runners would allow the air to stabilize more before entering the carb it self.

(Oil change isnt related to the issue, I just wanted to change it haha)

[Rob S.]

Just a quick update. I have set the floats back to stock, synced the carbs, changed the plugs and oil and restricted the air more using some electrical tape on the filters. I considered doing intake runners / velocity stacks with the filter on the end, but i dont have enough space. The carbs are responding much better to the mixture screws now. I tuned it the best I could on the center stand but have not had a chance to do a test ride due to bad weather. Ill be trying to test ride her tonight to see if what happens.

My thought process is, the air is simply to turbulent for the carbs to be able to use effectively. Restricting the air / adding runners would allow the air to stabilize more before entering the carb it self.

(Oil change isnt related to the issue, I just wanted to change it haha)

I don't think the air is too turbulent, there's just too much of it. When I installed pods on my 11E (which already had a 4-into-1 exhaust with the air cleaner lid removed), I had to cover up (with black electrical tape) roughly 90 per cent of the pods before it would run properly.

I promptly rode it to professional tuner who had a dynamometer.

[TinkersCustom]

I don't think the air is too turbulent, there's just too much of it. When I installed pods on my 11E (which already had a 4-into-1 exhaust with the air cleaner lid removed, I had to cover up (with black electrical tape) roughly 90 per cent of the pods before it would run properly.

I promptly rode it to professional tuner who had a dynamometer.

Yeah I taped them up about 90% and it was way to much. 50% covered is my current sweet spot. Subject to change! Lol

[Steve]

Just a quick update. I have set the floats back to stock, synced the carbs, changed the plugs and oil and restricted the air more using some electrical tape on the filters. I considered doing intake runners / velocity stacks with the filter on the end, but i dont have enough space.

OK, I must be missing something, but I would like to see some numbers.
What are your float heights?

How did you sync the carbs?

If your goal is to get the bike running right and making more power by eliminating the air box, why are you restricting the intakes?
Also, you mentioned something early about pods, then asked about some runners with filters on them, but you don't have room. Do you have ANYTHING besides tape on the intakes of the carbs? Keep in mind that bare carbs will barely run above idle unless there is something to smooth out the airflow. Pod filters work. Even a folded rag works, but you have to have SOMETHING. Blocking the intakes with tape not only restricts what the engine can breathe, but adds a LOT of turbulence in the carb throat. On top of all that, when the gas fumes eventually dissolve the adhesive on the tape, guess where the tape is going to go? Very few engines work well with a gob of tape around the intake valve.

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[Rob S.]

We (or at least I) covered up (some or most of) the pods with tape. Not the bare carbs.

[Steve]

I know that is the usual practice, but in post #4, Tinker said he is using UNI pods, then in post #7 he said he didn't have room for velocity stacks and filters. That is why I asked rather specifically if the tape is over the carb intake. If the tape is over pods, there is at least a small chance that air flow will be reasonably straight by the time it goes through the carb. If the tape is over the carb, it could easily be blocking vent ports that are critical to proper operation of the carb.

.

[TinkersCustom]

Yeah the tape is on the filter it self.... But the bike is down now, I went to change the oil and stripped out the pan it self.... So I can't get a drain plug in, just strips new plugs. Even strips +1 plugs... Not decided on if I want to tap it or replace it

[Steve]

I can't get a drain plug in, just strips new plugs. Even strips +1 plugs...

They make +2 plugs.

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