Off idle and mid range hesitation/bog

[ShoMeStyle]

Hello all. First time GW owner here. Been lurking on the forums for a while but could not find a correct answer to my problem.

I picked up a 1981 gl1100i on trade. Had been sitting for who knows how many years. It has about 35k miles so I started to go through it.

Compression is around 160psi ±5 between all the cylinders. Have replaced coils, plugs, wires, battery, tires, rebuilt the carb with new cut off valves and new accelerator pump and polished the slides. I disassembled and boiled the carbs and was able to take out the pressed in idle jets and clean them properly, set float height to 15.5mm. Carbs have been synced, and idle drop adjustment has been done for the mixture screws. I checked and adjusted the valves for .004 intake and .005 exhaust. I cleaned the tank, installed new fuel filter and verified good flow from the pump. I have done everything except check the timing as I am expecting to replace the belts soon because of unknown age and condition.

The bike starts on first crank every time. Idles perfect around 950-1000rpm and throttle response is amazing and she revs to the moon while in neutral. When in gear it's another story. Went around the block a few times and there is a hesitation/bog under load if leaving from a stop sign etc. Also it seems to hesitate/bog and buck a little around 2500-3000rpm. I can rev through both of the spots and it will scream like a banshee. Keep in mind it only does this in gear under a load. In neutral it revs perfect.

I cannot determine if this is a carb issue, fuel issue, spark issue, timing issue or drive train issue.

I am thinking that maybe the timing may be off by 1 tooth but haven't gotten around to taking the covers off to check yet. Does anyone happen to know of anything else I can check?

Thanks for reading and sorry for the long post. Wanted to give as much info as I could.

[OldguyGlen]

Welcome to the forum. I wouldn't rev it to the moon on those timing belts. At 35k miles, but not running for unknown storage time, I bet they are 41 years old. My thought is the carbs. It can rev easily with less than 4 perfect carbs when at no load. But in gear, they all have to help out. Sounds like you did a thorough carb rebuild, but you might want to recheck the accelerator pump, and maybe check for sticking slides. The low speed port and mixture screws are important for idle, but the slides/mains, and pump are important for moving the bike. I doubt the timing is off a tooth, but the advance mechanism might be stuck.

[ShoMeStyle]

Welcome to the forum. I wouldn't rev it to the moon on those timing belts. At 35k miles, but not running for unknown storage time, I bet they are 41 years old. My thought is the carbs. It can rev easily with less than 4 perfect carbs when at no load. But in gear, they all have to help out. Sounds like you did a thorough carb rebuild, but you might want to recheck the accelerator pump, and maybe check for sticking slides. The low speed port and mixture screws are important for idle, but the slides/mains, and pump are important for moving the bike. I doubt the timing is off a tooth, but the advance mechanism might be stuck.

Yeah, I really need to replace the belts. That seemed to be a very important topic with these bikes especially with them being interference engines. I just can't justify to the wife putting anymore money into it until I know I can get it running right. Before installing the rebuilt carb, I did verify accelerator pump function and squirt into the carb throats. I have also pulled the vacuum line off of the number 3 carb and sucked on it and can hear the advance mechanism move. However I have not checked if it holds vacuum for long periods of time.

As for the slides, I haven't checked function of them yet with a mirror because I am not sure how I would do it while the bike is under a load.

Do the slides move while revving in neutral? I feel like I would need to check them while I am experiencing the symptom, which is only when in gear and moving. If the slides were hanging would it still rev up perfect in neutral? Thanks

[OldguyGlen]

Yes, the slide will "pop up" when giving the throttle a sharp "blip" in neutral. They may not open fully, and may not stay up long. And yes, the engine, in neutral can rev very high with less than full function of all 4 carbs. It doesn't need much fuel, or torque, to rev high with no load.

[ShoMeStyle]

Yes, the slide will "pop up" when giving the throttle a sharp "blip" in neutral. They may not open fully, and may not stay up long. And yes, the engine, in neutral can rev very high with less than full function of all 4 carbs. It doesn't need much fuel, or torque, to rev high with no load.

Okay, thanks. I will check the slides with a mirror when I get off work. After I polished them I flipped the caps upside down, put spring and slide in and bounced them up and down, buttery smooth while not on the bike.

If that is not the problem, hypothetically. Are there any other areas I could look into after? I'm stuck at work until 5ish so I'd like to get a game plan in order for when I get home.

I read on randakks about shimming the slide needles on the GL1000. I wonder if it could benefit from that on this '81 GL1100.

I think the bike has stock exhaust and everything, the main jets are #145 which I believe is stock.

Also, not sure if related, but after the carb rebuild, for the 81 it says to start the mixture screws out at 1 ¼ turns, however that was way too lean, throttle would hang, etc. After the idle drop adjustment, they all ended up closer to 2½-3 turns out. Does that seem okay or is something weird going on here?

[OldguyGlen]

I'm about out of suggestions. Maybe someone else will chime in. Your test of the slides, on the bench with upside down caps is typical. The only thing different is the needles drop down into the main jets when fully assembled. Possibly a bent needle is dragging.
Check to see if all 4 head pipes get warm at the same rate, indicating each cylinder is making a contribution. Mixture screws can be different than book values due to air leaks on the runners, or butterfly shaft seals, etc.

[ShoMeStyle]

I'm about out of suggestions. Maybe someone else will chime in. Your test of the slides, on the bench with upside down caps is typical. The only thing different is the needles drop down into the main jets when fully assembled. Possibly a bent needle is dragging.
Check to see if all 4 head pipes get warm at the same rate, indicating each cylinder is making a contribution. Mixture screws can be different than book values due to air leaks on the runners, or butterfly shaft seals, etc.

No worries, thanks for the help. I will reply back with my findings on the slide function. It really does feel like that's the problem. When I go to take off I can hear it almost fluttering during the hesitation/bog like they are trying to work free, sometimes it will do it for a solid few seconds, then it's almost as if they become unstuck and she goes wide open with the power.

[ShoMeStyle]

I was trying to think back to when I did the carbs, trying to remember if anything stood out that could cause this. Then I came across something on randakksblog that has me thinking. I remember when I replaces the air cut off valves and springs, that the new springs I received were ALOT more stiffer than the ones that were in my carbs. I am wondering if this could be my issue.

The blog says, when talking about the air cut off valves: "Often, they fail in a more insidious way by shifting the “function point” of the valve to a higher vacuum / rpm level than designed. So, even though the diaphragm is intact and will hold a test vacuum…you can get an excessively lean condition resulting in poor off-idle throttle response."

I am wondering if my springs are so stiff that they have moved the "function point" of the valve to the wrong spot. Can anyone possibly confirm this as a possibility?

[ShoMeStyle]

Checked the slides with a mirror and they are moving up and down smooth as butter. Although I did notice now, with the air cleaner off, the hesitation is there even in neutral when I blip open the throttle. It seems fuel/air related. Really makes me wonder about those air cut off valve springs.

[ShoMeStyle]

Swapped the air cut off valve springs. While I had the carbs off, double checked to make sure they were still clean. Accelerator pump still pumping a nice squirt into all 4 carbs. Cut off valve springs didn't make a difference... so I'm back to square one.

Is there anyway this could be a spark issue? Is there anything that could cause it to lose spark off idle under load? Like I said it has new plugs, wires and coils. Also soldered the 3 yellow wires for the stator I assume(they were corroded and plug was starting to melt).

It still fires right up and idles/revs great in neutral. Spark plugs are all the same light brown/tan color. All the cylinders seem to heat up evenly, they are all contributing when not under a load.

But this hesitation/bogging/bucking/miss or whatever is going on right off idle in gear makes it near impossible to ride safely. The only way to take off from a stop is to rev it up to over 3.5k and let the clutch out super slow, which I don't think is very good for it.

Any help is appreciated.

I think I will take the carbs off and apart one more time and boil the ever loving shet out of them again, praying there is some tiny internal passage I missed during the rebuild, but I highly doubt it. If that doesn't fix it, I'm done chasing a carb issue that doesn't exist.

[OldguyGlen]

Just guessing now... Maybe it's not a carb issue. Spark plugs can fire more easily at lower compression conditions. It's harder to fire them under high compression as in aggressive acceleration. Do you get the hesitation only at those limited mid range rpms, or does it also occur at higher rpms if you sharply go wide open throttle. In my normal driving I rarely go wide open throttle when already at the higher cruising rpms, like starting a passing attempt while already at highway cruise condition. If your riding style is more relaxed where you ease off the throttle to shift or cruise as the rpms get above 3000-4000, maybe you haven't really tested that? If the hesitation is related more to high load, rather than specific rpm range, then ignition could be the problem.

[ShoMeStyle]

Just guessing now... Maybe it's not a carb issue. Spark plugs can fire more easily at lower compression conditions. It's harder to fire them under high compression as in aggressive acceleration. Do you get the hesitation only at those limited mid range rpms, or does it also occur at higher rpms if you sharply go wide open throttle. In my normal driving I rarely go wide open throttle when already at the higher cruising rpms, like starting a passing attempt while already at highway cruise condition. If your riding style is more relaxed where you ease off the throttle to shift or cruise as the rpms get above 3000-4000, maybe you haven't really tested that? If the hesitation is related more to high load, rather than specific rpm range, then ignition could be the problem.

It pretty much does it only under a decent amount of load. I'm a big 300lb guy and it feels like it is struggling to pull my weight. If I do a highway pull, let's say testing the power of the bike etc, shifting up in the higher rpm ranges, it does great. Now if I am cruising let's say at 2500-3000rpm and shift, it will hesitate/produce the symptom when I reopen the throttle after letting the clutch out.

Basically the best way to describe it, because im not exactly 100% on the rpm values;

If I ride it like I stole it, (other than the hesitation under load at initial take off from stopped) it produces no symptoms.

If I ride it like any sensible person with a family to go home to at the end of the day, it will slightly hesitate and "bog" after every gear shift on initial throttle opening very briefly, then as you get the rpms up for the next shift it clears up and acts normally until the next time you reopen the throttle after shifting.

[ShoMeStyle]

I also want to mention that my brakes are not locked up, I rebuilt the calipers and masters front and back and she rolls easily.

[ShoMeStyle]

I figured it out. I finally figured it out...

I became suspicious of the needle holders and slide needles that came in the carb kit I bought after watching a video on YouTube.

So I went and found my old ones in the trash. Cleaned them up real good and put them back in.

Sure enough, she runs absolutely perfect now.

0 hesitation, great throttle response through the whole rpm range and tons of power.

Thank you for the help. Hopefully this helps someone else.

[OldguyGlen]

Congratulations. Good sleuthing work. I bet you can now get that carb rack out and back in, in record time. You followed the advice that an old mechanic once told me...It's got to be something. So if you check everything, you're bound to find it.

[ShoMeStyle]

Congratulations. Good sleuthing work. I bet you can now get that carb rack out and back in, in record time. You followed the advice that an old mechanic once told me...It's got to be something. So if you check everything, you're bound to find it.

You best bet I can get them out in about 2 minutes blindfolded at this point.

I checked alot of stuff. I've read and retained just about everything that exists on the internet with these carbs at this point haha.

That was a solid week of being a troll in my garage, hyper focused on this bike after work and staying up way too late. The wife and kids were glad to see me this evening after I figured it out.

I traded two pit bikes I found at the dump for this GW. So it's not that I spent a lot of money and needed it running right. But there's just nothing like bringing a machine that's older than me back to life and enjoying it, especially when it's that cheap.