1980 GS550L Won't Accelerate

[ddaum]

I've done a lot of work recently and now the bike just doesn't have the power that it had before. From a stop, getting into and through first gear seems sluggish, then when in 5th and 6th it won't accelerate at all. Not even slightly. I can barely hold 60-65 mph when before, she would hit 80 easy and have power to spare. It used to have more power. Here is a list of what has been done.

- Complete carb rebuild using K&L kits, everything is new. Float heights set correctly.
- Brand new petcock, and fuel and vac hoses. (connected correctly)
- New intake boots and O-rings. Clamps are all tight.
- Replaced stock 4-2 pipes with a MAC 4-1 with new header gaskets.
- Plugs replaced and gapped correctly.

Here are some observations and things I've already ruled out.
- Gas tank is venting properly
- No gas in the petcock vent line
- I pulled in the clutch and cut the engine after doing ~60mph for a few minutes, coasted, then checked the plugs. All look very good and normal except #2 was just a little wet from gas (Is this normal?), none were black, and all had very similar color. I did this twice, same results.
- Stock jetting, stock airbox and filter element, very recently cleaned and oiled the filter. All four pilot/mixture screws set at 3.5 turns out as per THIS THREAD.
- Carbs were bench synced using the "bread twist tie wire method" but not vacuum synced yet. (runs good on the bench sync)
- Idles very smooth at 1000 rpm, and starts easy.
- No dead spots or bogging through the RPM range, just underpowered from about 1/2 throttle-to-wide open, but only while riding.

Here are the questionable items:
1. While running the engine, I tried pulling plug wires one at a time to see if I had a dead cylinder. I got shocked through my gloves repeatedly from two of the four wires. Is this normal?
2. Before I cleaned the carbs, the bike ran great with stock jets, filter, and air box with the MAC 4-1 pipe installed. It also has an in-line fuel filter that it ran fine with before.
3. The fuel line from the petcock exits the petcock, then arches up slightly before going down through the in-line filter and finally into the carbs. Should I straighten this out to eliminate the upward arch? (The gas tank is full)
4. I haven't adjusted the pilot/mixture screws on the carbs at all because with the bench sync and pre-setting the pilot/mixture screws at 3.5 turns out, the bike started right away and idled VERY good. Should I adjust these one-by-one for highest RPM while adjusting the idle knob after each one?

Also, the bike now backfires or pops slightly when I let off the throttle in 2nd, and sometimes 3rd gear. It didn't do this before the carb rebuild. No gas in the airbox, and oil level is constant, so no gas in there either. I meticulously cleaned the carbs and replaced, and measured everything correctly, but I am open to comments. Please help if you have ANY ideas on how I can get my power back. Thanks!

[jimg]

I had almost the same symptoms as you have after I cleaned my carbs. However, I have the stock exhaust and didn't have the popping.

Here is what I did. I have read on some threads here that the main jets in some of the carb kits aren't exactly the right size so I took the carbs off and put the old main jets back in. I also raised the floats (more fuel in the bowl) about 2 mm. This put them at the close end (if not just a little above) of the range given in my Clymers manual. I took off the fuel filter.

Don't know which if any of these solved the problem. If you don't mind taking off your carbs you could try each of them one at a time. I would probably start with the float setting since my bike felt like it was running out of fuel. Although it could have been the filter causing it too and that would be easier to do first.

I tell you, I think between the screen on the petcock and the little screens on the float needles that fuel flow is barely adequate. That may be why removing the filter was the actual culprit. Keep in mind, I reused the old screens and cleaned them as best I could. They were initially clogged with the paste of 20 year old fuel. I plan to remove them and go with only a filter one of these days when I feel the urge to remove the carbs again.

[ddaum]

More advice needed...

Jimg,
Thanks for the reply. Since I cleaned everything up really good when rebuilding the carbs, I think I'm going to re-install all the stock jets like you said. (Money well spent huh?)
Or do you think I should just put the stock mains back in and leave everything else?

What about the poor performance getting into and through 1st?

Do you think I need to fiddle with my pilot/mixture screws as stated in my first post?

The bike ran fine with the in-line filter before, so I'll leave that be for now unless I get more disapproval.
I'll also adjust the float settings like you said. Since I didn't re-jet with the 4-1 pipe, this should richen the mixture, right?

For everyone else, please read my 1st post above once more and offer any advice you can about my other questions. What causes the popping? What about the mixture screws? If measured in fourths, throttle response is poor during the first 1/4, decent during the second 1/4, and very poor from 1/2 to WOT... Please help. Thanks.

[jimg]

Jimg,
Thanks for the reply. Since I cleaned everything up really good when rebuilding the carbs, I think I'm going to re-install all the stock jets like you said. (Money well spent huh?)
Or do you think I should just put the stock mains back in and leave everything else?

What about the poor performance getting into and through 1st?

Do you think I need to fiddle with my pilot/mixture screws as stated in my first post?

The bike ran fine with the in-line filter before, so I'll leave that be for now unless I get more disapproval.
I'll also adjust the float settings like you said. Since I didn't re-jet with the 4-1 pipe, this should richen the mixture, right?

For everyone else, please read my 1st post above once more and offer any advice you can about my other questions. What causes the popping? What about the mixture screws? If measured in fourths, throttle response is poor during the first 1/4, decent during the second 1/4, and very poor from 1/2 to WOT... Please help. Thanks.

Like you, I cleaned everything well including the old jets so using the old mains wasn't a problem. My only problem was at 3/4 to WOT. There just wasn't any power, and I think the fuel flow/float level was the problem. If you bought the $70 K&L kits like I did, I think the float needle and seat are a little taller than stock and the float levels need to be changed accordingly. The float level won't necessarily make the bike run rich. You just want to make sure the level of gas is to the point where it completely covers the main jet at 1/4 to WOT so it can pull gas up through the jet. This is why I can't confirm whether the jets made any difference or if it was the filter/float level.

You might try all the old jets to see if it changes anything. Also, make sure you take a small wire and clean out the ports in the pilot jet passage which controls low speed running.

You did remember to put the rubber plugs in on top of the pilot jets, right? You also remembered to put in the jets that are in the carb throats, right?

I don't think the mixture screws affect anything much above idle. I may be wrong about that. If I remember previous posts, I believe the popping may be caused by your mixture being lean. This could be caused by the float level being too low. You might do a search on 'lean mixture & popping' to read the threads.

[chef1366]

Think about this, the bike ran good until the carb rebuild. Make sure your vent lines are clear. Set the float at the step down on the float body, not at the hinge. Check fuel flow. Popping is usually a lean symptom. Full throttle uses main jet and middle throttle uses a combination of main and pilot jets. Did you do any adjustments to your jet needle? Are your diaphragms good? Sounds like a problem with your needle circuit. Still, check for leaks on your intakes with a little wd 40. Did you put new o-rings in the carb during rebuild? If all these check out, first set the main jet (this takes time and patience) till you get good pull at full throttle from 3.5 rpm on, do a throttle chop at full throttle(find a good stretch of road with no cops, hit full throttle in high gear as long as you can and hit the kill switch without letting go of the throttle, coast to the side of the road and pull plugs and check color, grayish is good. Mark you throttle 3/4, 1/2, and 1/4. These carbs operate on throttle position so to get them right you have to do throttle chops on these different throttle positions. If your idle is fine and your problems starts at half throttle position then it comes down to needle position, main jet size and possibly pilot jet size. I adjust each pilot air screw seperately to achieve highest rpm per cylinder.

[ddaum]

You did remember to put the rubber plugs in on top of the pilot jets, right?

Yes

You also remembered to put in the jets that are in the carb throats, right?

The Air jets? Yes, they are installed.

Make sure your vent lines are clear.

Carb vent lines are removed, and I'm positive that the vent tees are clear.

Did you do any adjustments to your jet needle?

You are talking about the needle that extends from the bottom of the slide, right? If so, no, I didn't make any adjustments.

Are your diaphragms good?

All were inspected during rebuild, no discrepancies there.

check for leaks on your intakes with a little wd 40. Did you put new o-rings in the carb during rebuild?

I replaced the intake boots and O-rings with brand new ones. everything it tight and all carb o-rings were replaced.

If all these check out, first set the main jet (this takes time and patience) till you get good pull at full throttle from 3.5 rpm on

How exactly do I do this?

When I used the K&L kits, I noticed the differences between the K&L, and the stock needle valves seats and needles. I ended up using the K&L seats, and the stock needles. This was because the K&L needles didn't extend past the spring retainer on the seat that is designed to hold them in place. Float height was set to 22.4mm +/-1.0mm during the rebuild.
How much should I lower the height (raise fuel level)?
Today I am going to remove the in-line fuel filter and eliminate the arch in my fuel line and note the results. If no joy there, then I'll pull the carbs tomorrow. Please continue with comments or ideas. Thanks.

[ccratin]

If your #2 plug was wet, your bike isn't going to achieve top speed with 3 cylinders hitting. Find out what is going on with that #2. You always should suspect that petcock. Pull and plug off the vacuum line, set the petcock on prime and put in a fresh plug. Run it and see how you go.

[DimitriT]

Used the stock needle's with the K&L valves? I wonder if that's causing you to starve out. Perhaps the stock needles are too tall and you are not refilling the bowls fast enough to keep up with the motor. I used K&L and had no problems with the valves and needles. I believe we have the same model carbs. Could you describe your problem using K&L needles in more detail.

Float height is important not only to adjust the level of fuel in the bowl but also to affects the rate of flow into the bowls. If your float height is too shallow you may never open the valve wide enough to refill fast enough. Make sure you adjust float height with the valves and needles in place and following the method specified in your service manual. Don't forget to account for the gasket if you measure with the gasket in place. If you don't have a depth gauge you can get by with a standard 6" machinist's ruler (with 1/64 markings) just convert everything to inches. The range of adjustment is fairly wide (1-2mm I think).

[ddaum]

If your #2 plug was wet, your bike isn't going to achieve top speed with 3 cylinders hitting. Find out what is going on with that #2. You always should suspect that petcock. Pull and plug off the vacuum line, set the petcock on prime and put in a fresh plug. Run it and see how you go.

See, here's the problem; I have the 1980 model with the "automatic" vacuum petcock. This petcock has no knob. it only has a small internal plastic slot that you can turn with a small screwdriver. It has a PRI position marked on the housing, but I've never been able to turn that thing so it worked. It has no OFF, RUN, or RES positions. Some say that the slot has to be horizontal for "RUN" and others say that it has to be vertical, but it seems to have the same effect anywhere I turn it. So your idea isn't really an option for me. Here's a pic.

[ddaum]

Could you describe your problem using K&L needles in more detail.

Looking at the carb turned upside-down and with the float bowl removed:

The stock needle valve seat as well as the K&L seat have a ring grooved into it above where the o-ring sits. There is a little wire "retainer" that snaps into this groove to retain the needle when it's in place. Well, when you compare the stock seat with the K&L seat, the K&L seat is "taller" when installed, also the K&L needle is just a tad bit shorter than the stock needle. SO, with the K&L needle and seat together, and the stock "retainer" installed, the tab on the float will stop against the "retainer" before completely seating the needle valve. I didn't want the needle falling out, so my solution was to use the new (K&L) seat with the longer (stock) needle, and to install the "retainer." This way, I could see that the needle was being seated correctly with the wire needle "retainer" installed.
The first pic is from the "Carb Cleanup Series" in "The Garage."
The second pic is my setup, the red portion is my seat retainer, and the green portion depicts the wire needle retainer that sticks up about 1-2mm above the top of the seat.

[flyingace]

Go back the post about the spark plugs. Their condition tells you what you need to know about your engine's internal condition. Are they block/sooty, wet, dry/white dry/grey? Are they all the same or do some appear different?

Maybe you mentioned them in your previous posts, but I don't have time to read them. Let the readers know the condition of the plugs and you'll get more help.

[DimitriT]

I guess the retainer they used on the 1980 model is different than later years. My retainer looks exactly like the top pic. There's that loop of metal which keeps the float from swinging down too far (which would allow the needle to drop out). I'm guessing your floats can swing down right to the bottom of the bowls and they use that wire thing to keep the needle in. Still I wouldn't try mixing valves and needles. I would just stick with the original valves.

[ddaum]

Go back the post about the spark plugs. Their condition tells you what you need to know about your engine's internal condition. Are they block/sooty, wet, dry/white dry/grey? Are they all the same or do some appear different?

Maybe you mentioned them in your previous posts, but I don't have time to read them. Let the readers know the condition of the plugs and you'll get more help.

UMmmm..yeah. I posted above that I pulled in the clutch and cut the engine after doing ~60mph for a few minutes, coasted, then checked the plugs. All look very good and normal (gray) except #2 was just a little wet from gas (Is this normal?), none were black, and all had very similar color. I did this twice, same results.

[chef1366]

Use the K&L seat and needle. I have a 1980 and used a K&L and had no problem with the needle falling out.

[ddaum]

Use the K&L seat and needle. I have a 1980 and used a K&L and had no problem with the needle falling out.

Did you also use the little wire "retainer" that I referenced to in the pictures above, or did you leave that out with the K&L seats?