Bike has 0 power under load when under 4000rpm?

[Cmarino]

Finally got almost everything dialed in besides this issue, hopefully I will have a complete bike soon.

As the title suggests, my 1982 suzuki gs650 is not running right only at low rpm, regardless of throttle position. To get the bike moving, you either have to start on a downhill or feather the clutch at high rpms in 1st gear until the bike is going 10mph and you can release it. It's difficult to ride up my hilly driveway without a running start. The weird thing is that after 4000rpm, the bike rips. It has tons of torque and power once its gets above around 4000. I know that it's not a carb/gas problem because I'll be trying to ride under at said rpm under 4000 and whatever throttle position, and as soon as I pull in the clutch the rpms will shoot up; so it must be getting the gas, right?

It just like bogs down/can't accept the gas underload at low rpm, why? Starting in 1st gear on this feels like starting in 4th gear on my dirtbike at 1/4th of the displacement. It has no problem fully revving out and being responsive in neutral.

Almost confident in no airleaks. New airfilter, intake boots, o-rings, petcock, carbs fully rebuilt by a member of this forum, synced, coil packs/battery are good.

When I had my carbs synced, I believe they were synced from 1.5 turns out. They ran great but had a rising idle for being too lean. I just turned them all .5 out, I can't tell if it made this issue any worse or not but it solved the rising idle.

Again, the bike runs great if you can get it moving. Any help appreciated

 

[Guest]

I see a couple of things going on.

I know that it's not a carb/gas problem because I'll be trying to ride under at said rpm under 4000 and whatever throttle position, and as soon as I pull in the clutch the rpms will shoot up; so it must be getting the gas, right?

Yes, it's probably "getting gas", but is it getting ENOUGH?

When I had my carbs synced, I believe they were synced from 1.5 turns out. They ran great but had a rising idle for being too lean. I just turned them all .5 out, I can't tell if it made this issue any worse or not but it solved the rising idle.

I think you are mixing up a couple of DIFFERENT procedures. You don't "sync from 1.5 turns out". There are NO numbers associated with the "sync", you adjust the screws BETWEEN the carbs to get the vacuum levels all the same.

If you are talking about the PILOT SCREWS, 1.5 turns out from LIGHTLY seated is too lean. On some carbs, 2 full turns might still be a bit too lean. I would suggest going 3 full turns out from LIGHTLY seated as a starting point. That will at least get the bike running. Should start a bit easier, almost like using the "choke". When the bike is warmed up, you can turn each screw IN slowly until the engine speed drops a bit, then turn it back out about 1/8 turn, then continue with the other carbs.

 

[Cmarino]

If you are talking about the PILOT SCREWS, 1.5 turns out from LIGHTLY seated is too lean. On some carbs, 2 full turns might still be a bit too lean. I would suggest going 3 full turns out from LIGHTLY seated as a starting point. That will at least get the bike running. Should start a bit easier, almost like using the "choke". When the bike is warmed up, you can turn each screw IN slowly until the engine speed drops a bit, then turn it back out about 1/8 turn, then continue with the other carbs.

Okay. I'm unfamiliar with the carb sync, I thought it was done with the pilot screws. Okay, so then the pilot screws are all 2 turns out. It is already starting pretty easily, and was even starting a bit easier at 1.5, but I'll spin them out some more and come back with an update

 

[chuck hahn]

use the service manual here and sync them. I rebuilt those carbs and set the bfloat heights per service manual specs and i can tell you the carbs arent dirty. Also a hanging idle IS in fact indicitive of an air leak and most likely at the head / intake juncture. Some STARTING FLUID sprayed on each intake while at an idle will tell the story. if rpms climb theres your leak if not then the issue is elsewhere.

Check timing advancers is free and snaps back when maually twisted. Be sure the springs on the weights arent weak allowing a weight to flop a bit. Do a good valve adjustment. do a compression check with the throttle WIDE OPEN, Many thing can mimic carbs when its not carbs at all


http://members.dslextreme.com/users/bikecliff/

 

[roeme]

I'd attribute such abysmally poor power to one or more cylinders not working. Since your carbs are most likely in order, do a compression check and focus on your ignition system.

You said coils are ok - what are the values?

And what's the story with your spark plugs and plug caps?

 

[Cmarino]

use the service manual here and sync them. I rebuilt those carbs and set the bfloat heights per service manual specs and i can tell you the carbs arent dirty.
http://members.dslextreme.com/users/bikecliff/

Yes! Chuck did a great job rebuilding and I recommend him to anyone needing work done.

I didn't have a hanging idle issue as much as it was a gradually raising idle with temp. But after loosening the pilot screws by .5 that went away. It went from nearly 3500rpm in a 30 minute ride to 1100 with no adjustment to the idle screw so there is no confusion that it was just too lean.

I did just try spinning them another .5 out (2.5 total), and I really didn't couldn't tell if it made the no power issue better or worse, which probably means it didn't do anything (maybe slightly better). I can try again farther out tomorrow.
What's weird to me is that when trying to start moving in 1st gear on flat ground, if you release the clutch while under 2.5k it won't accept any amount of throttle (just simply no response), so I will pull in the clutch and it's still stuck in that mode until it ultimately stalls a few seconds later. Starts right back up and can fully rev out, but you really have to feather the clutch until bout 10mph .

Will also try other tests tomorrow

 

[Cmarino]

I'm positive all 4 run at idle, I can check compression tomorrow. Plugs are new, are good condition ngks, the coil is a dyna coil which seems to give good spark to all 4 but I can measure its power tomorrow.
I'm sure the Dynas aren't ideal but it's what the bike came with and I can't find good oem ones reasonably prices

 

[chuck hahn]

All the plugs out and the engine will spins faster. be sure gauge has maxed out. hold throttle wide open while cranking

 

[Guest]

I'm sure the Dynas aren't ideal but it's what the bike came with and I can't find good oem ones reasonably prices

Actually, Dyna coils are the preferred coil, if you are replacing OEM coils. Just be sure they are the green 3Ω coils.

 

[Cipher]

use the service manual here and sync them. I rebuilt those carbs and set the bfloat heights per service manual specs and i can tell you the carbs arent dirty. Also a hanging idle IS in fact indicitive of an air leak and most likely at the head / intake juncture. Some STARTING FLUID sprayed on each intake while at an idle will tell the story. if rpms climb theres your leak if not then the issue is elsewhere.

Check timing advancers is free and snaps back when maually twisted. Be sure the springs on the weights arent weak allowing a weight to flop a bit. Do a good valve adjustment. do a compression check with the throttle WIDE OPEN, Many thing can mimic carbs when its not carbs at all


http://members.dslextreme.com/users/bikecliff/

Ignition advance is 40 degrees btdc at 3500 and above.
I had a weak magnet in my pulse pickups once that acted like this

The electrical stuff is straightforward easy resistance checks easy to do

 

[Cipher]

Finally got almost everything dialed in besides this issue, hopefully I will have a complete bike soon.

As the title suggests, my 1982 suzuki gs650 is not running right only at low rpm, regardless of throttle position. To get the bike moving, you either have to start on a downhill or feather the clutch at high rpms in 1st gear until the bike is going 10mph and you can release it. It's difficult to ride up my hilly driveway without a running start. The weird thing is that after 4000rpm, the bike rips. It has tons of torque and power once its gets above around 4000. I know that it's not a carb/gas problem because I'll be trying to ride under at said rpm under 4000 and whatever throttle position, and as soon as I pull in the clutch the rpms will shoot up; so it must be getting the gas, right?

It just like bogs down/can't accept the gas underload at low rpm, why? Starting in 1st gear on this feels like starting in 4th gear on my dirtbike at 1/4th of the displacement. It has no problem fully revving out and being responsive in neutral.

Almost confident in no airleaks. New airfilter, intake boots, o-rings, petcock, carbs fully rebuilt by a member of this forum, synced, coil packs/battery are good.

When I had my carbs synced, I believe they were synced from 1.5 turns out. They ran great but had a rising idle for being too lean. I just turned them all .5 out, I can't tell if it made this issue any worse or not but it solved the rising idle.

Again, the bike runs great if you can get it moving. Any help appreciated

Silly question but is it fully buttoned up?
Fully reassembled with exhaust and all intake parts per oem config?

 

[tom203]

Sadly, I?d recommend removing carbs, redo the bench sync and at same time check that none of the mixture (pilot to you ) screws have broken off their tiny tips and left them lodged in carb throat . This critter relies on those mixture holes to enable the handoff to higher loading.

 

[chuck hahn]

If any were broke off its extremely unlikely it would even idle on an offending carb....which doesnt seem to be the case.

 

[Guest]

Possibility that it has a air leak that is lean ning out the mixture on 1 or more cylinders is there
Have you resently changed oil or toped up oil as i found my gs dies not like synthetic oil at all her clutxhes battle to engauge at pull off and this causes ( lerner rider geting clutch control) heasentent take off

 

[chuck hahn]

Good point. didnt think to ask iff te engine bogs down or not. If not i ncan see clutch slippage being so bad it takes forever to get going.

 

[Cmarino]

Okay so I did a compression test and here's what I found. 1 - 110 2- 105 3- 101 4- 118. I'm not sure if that's low enough to warrant the issues i'm having, someone advise please.

Here's the craziest thing I found; the spark plug on cylinder 3 was literally a different spark plug, it was DR8EA as opposed to D8EA. That's what I get for trusting autozone I guess, I was very, very surprised that I didn't notice when gapping and installing. The cylinder was still firing before, but it's definitely a bit better/smoother now.

Chuck; I remember you saying that 2 of my needlejets were different and you drilled them out to the proper size. Something I've noticed is that once moving at low rpm's in first gear(lets say 2000rpm, where youre barely moving), the bike will accept gas so long as it's just where the throttle is first engaged, so you're able to stay coasting and moving (slowly) without a problem. The issue is that it bogs when engaging the throttle anymore than that if it's under like 3500rpm. Do you think this could be the because of the needle jets?

As for the oil, I did change it while I was working on the bike, so maybe that could be the problem? I put in the amsoil dominator motorcycle oil. But I'm not sure if it's a clutch problem because if the clutch was slipping, wouldn't it still rev up and just not accelerate?

 

[Cmarino]

And as a reminder because there seems to be some confusion, bench and vacuum sync were just done, the bike starts fairly easily and idles perfectly, has no problem accepting gas in neutral or with the clutch in, and rides great above 3000rpm. Everything is completely stock, and I feel that there are no airleaks, I have new intake boots o-rings and airfilter and everything is set well and very much tightened down

 

[pdqford]

Here's the craziest thing I found; the spark plug on cylinder 3 was literally a different spark plug, it was DR8EA as opposed to D8EA. That's what I get for trusting autozone I guess, I was very, very surprised that I didn't notice when gapping and installing. The cylinder was still firing before, but it's definitely a bit better/smoother now.?

Howdy neighbor ;-)

How do all the spark plugs look color wise?

Has the tank and intake fuel filter ever been cleaned.

Are you running an in-line fuel filter?

 

[pdqford]

And as a reminder because there seems to be some confusion, bench and vacuum sync were just done,

Which carb sync tool do you use?
And at what rpm did you do the sync?

 

[Cmarino]

Howdy neighbor ;-)

How do all the spark plugs look color wise?

Has the tank and intake fuel filter ever been cleaned.

Are you running an in-line fuel filter?

I can insert a picture of the plugs later today and I'll take a video of how the bike runs tomorrow to make it more clear for everyone, but for now the plugs are black on the metal and a slight dusting of black on the ceramic; no tan anywhere, just black/white. Mixture screws are 2.5 out

Carb sync was done at a local shop so I'm not sure of the specifics, I didn't want to buy the tool so I had them do it.

Brand new petcock with no fuel filter, my old petcock seems pretty clean so I'm not worried about the tank, replaced because it was backfeeding into the vacuum line