1980 CB650 Custom power issues

Guys,
I was working on my bike the other day doing basic maintenance/tuning and then come to find out that I have very little power, my bike sputters constantly and the acceleration is entirely flat, especially after 1/.4 throttle. It bogs like it's running a bad air/fuel ratio.

Please I need help, my bike is worse than when I first got it!

New development, my bike pops really loudly randomly. Do I need to overhaul this bike? It was running great a couple days ago. I put on a new exhaust and K&N filters, 42 slows, 135 mains and now the bike doesn't work at all. Has something broken in the engine that is causing such lack of power?

I feel like there is a whole laundry list of issues with this bike now and I have no clue what they are or why they have come to be. Maybe this video will help:
https://www.youtube.com/watch?v=a-ljAO_2eyU

Here is the setup of my bike, maybe this will help give a few ideas. Please dig deep for this one guys, I really need some expert help on this.

Do you mean that it ran fine right before you made all those changes and it runs badly after the changes?

At the risk of being totally obvious, I would go back to the original set up and see if it improves. If it goes back to working fine, you need to try the changes one at a time to see which is the problem. If it is still bad, at least you have eliminated a whole bunch of possible problems and you have a baseline to work form.

It does sound as if your maintenance and or the mods may be the problem.

For example if the timing was adjusted, it may not like that change. If plugs were replaced, were they the right length and heat range? Good luck

Hmm I think the timing may be the most likely culprit. Here's what happened. I had the stock air box installed with this new exhaust and it was running fine, still needed a little tuning. I figured, screw it, I'll put on the new filters first and then tune so that I don't have to redo it. I started tuning it and things were going great. I installed 42 slows and turned my pilots out 2 turns and the thing was running like a top, save for the top end, which I was in process of tuning. I decided to address the knocking sound in the video I just posted and there were a few things I had done before testing (rookie mistake). I really don't think it has anything to do with what I had done to the carbs. Maybe my timing is too tight? Seems strange considering I did it exactly how the manual instructed. (Loosen bolt, rotate crank 4-5 times while tightening tensioner bolt) I feel like there's something obvious I'm missing?

Ok so I set the pulser air gap and alignment and that corrected my power surges, but I still had shit for power. So then I retightened the cam chain properly and that helped a little bit, but I think what I may be experiencing now is poor carb tuning for this new engine tweak. It appears that now my bike is running too rich? When I turn it on, it'll idle fine, but if I pull the choke out, it kills the engine. When I try to give it a little throttle (with choke pushed down) I get a little bog and then the engine revs a bit, still goes flat around 1/2 throttle, though. I'm thinking maybe the mixture is running a little rich? Retune the carbs?

thwrightstuff said:

Ok so I set the pulser air gap and alignment and that corrected my power surges, but I still had shit for power. So then I retightened the cam chain properly and that helped a little bit, but I think what I may be experiencing now is poor carb tuning for this new engine tweak. It appears that now my bike is running too rich? When I turn it on, it'll idle fine, but if I pull the choke out, it kills the engine. When I try to give it a little throttle (with choke pushed down) I get a little bog and then the engine revs a bit, still goes flat around 1/2 throttle, though. I'm thinking maybe the mixture is running a little rich? Retune the carbs?

Click to expand...

post photos of the plugs.

were the jets stock?

if it ran fine before the changes, it should be lean.

remove the air cleaners and try that . . they may be blocking a hole in the carb throat . . this is a common prob with some filters.

i would jet it without the pods just in case they sre blocking a hole.

What sized jets were in it before? Mains are 90 on the 79 and 80 models and 120 on the 81's 135 sounds like a huge increase over stock.

At idle, why do you have 2 turns out on the air screws? If it runs best at that, it suggests that the bottom end is rich and needs smaller slow jets. Start at idle and get that clean first and try running without those filters just to see what happens. While they are off, take a picture of the carb side of the filters and on the filter side of the carbs.

You old stock plugs won't tell us a lot but if it is as rich as it seems the plugs will be black and or wet.

The plugs are old. I want to get in some baseline tuning based on output power first before I do a plug chop. My bike doesn't even have the power to get past 1/4 throttle without going flat so a plug chop is difficult and a waste of good plugs.

My original jets were 95, but that doesn't apply anymore with the nonrestrictive setup I've got on it now. But before I took the airbox off and put on the new exhaust, I was running 110s, but that was also with a little slack in the cam chain creating that infamous knocking and ticking from the valves.

I know the carb throat isn't being blocked, the inside of those filter boots are flush like velocity stacks so there isn't an issue with any blockages, but I should try to see if the general air flow differentiates.

teazer, I think you're right. Now that I've properly adjusted the cam chain with this new setup, I'm definitely running way too rich. I think going down to 40s slow will help greatly. I was 2 turns out because I didn't have smaller jets to install so I wanted to see if turning them out helped even a little, give me a good idea of which direction to go in. I ordered them already, just gotta wait. I think in the meantime I'll try adjusting the top end. I went back down to 125s mains last night and it didn't help the top end much, so I think I'l go down to 120s, maybe 115s and see what happens. I'll have to adjust the jet needle, too.

The problem is it bogs like it's running lean, but there's lots of popping, so I guess the symptoms point to running rich? If what I've read is correct, popping indicates rich.

What do mean you carb side of the filters and filter side of the carbs, isn't that the same thing? And my plugs aren't definitely rich, save for one of them, perfect brown/tan dry color.

.
changing the pilot will have 0 affect on it not revving up.

going from 120 to 115 is way too small of a change if it is not revving up . . you need to go to 110.

you dont waste a set of plugs doing a plug chop, plus if its too rich on the main, it will burble a bit at wot . . just jet down 1 size at a time until it quits burbling then go down 1 more size.

changing the needle will have no affect on it not revving up because it is a very fine tuning adjustment.

change only 1 thing at a time and retest it.

if your bike easily starts with no choke, your pilot jets are too big . . go down 2 sizes if this is the case.

popping could be several things so you cant jet based on popping sounds unless the jetting affects them.

You are headed in the right direction. As Barnett said, forget about plug color and plug chops for now. mains go up say 1-3 sizes on average with those modifications and in some cases they go down, so 95 to say 100, 105 or even 110 might be right. Old style Keihin jets were calibrated on diameter of the orifice 95 is 0.95mm 120 is 1.2mm which is about 60% larger or so which is just a touch too large. If they are flow rated (I don't think that they are) that would only be a 26% increase.

We are probably looking for a 10 -15% increase in flow which works out to 100 for 10%, and 105 is around 20% increase

Revving even from 0-1/4 throttle isn't effected by the pilot jet? How? Based on Fig 7 in this thread: http://www.dotheton.com/forum/index.php?topic=16745.0, it tells me the pilot jet is off if it isn't even getting going. Yes, not revving in the top end is a result of bad main jetting, something I will attack today after work.

I won't be getting my size 40 pilot jets until tomorrow, so I may just either try the stock airbox again (which I really am against doing because it's a bitch and a half to install) or just keep tweaking it with my current setup. Should I try all new plugs? I have 8 of them, but that may be a waste (by waste I mean foul up the plugs so that they can't be used for plugs chops, I know they will still work, functionally).

Currently, the bike seems to run best, which isn't very good at all, with the choke at about 1/2-3/4 engaged, that tells me the mixture is a touch lean, which doesn't make any sense based on what's been happening.

I'll try changing my jets back down to 110 today and test that, see what happens. Then tomorrow I'll install the 40s and test.

Another big thing I noticed is that the filters get very noisy when the choke isn't on. It's strange, it sounds like it's having a hard time sucking in air, but when I pull the choke out it's a lot quieter, but then the bike dies pretty quickly when I do that. Any idea what it means when the intake/air filter sounds like that? I think you can hear the noise in the video I posted.

Here's something else I noticed, exhaust pipes 1 and 2 are at least 10-15 degF hotter than 3 and 4. I burn my hand on 1 and 2 instantly when on 3 and 4 I can hold the pipes indefinitely without burning myself. Does that mean the mixtures are running better on 1 and 2 than 3 and 4? Or does that indicate that there is something wrong with 1 and 2?

So you'll be happy to hear that your advice has been really helping me to hone in the response of my bike. I'm back to 110s and 40s and it's decent, but not good enough yet. After tweaking the pilot screws some, I've noticed that adjusting carbs 3 and 4 pilot screws doesn't change the rpm of the engine at all, only 1 and 2 seem to do anything. Is this a symptom of some serious issue I might have or is this normal?

thwrightstuff said:

Revving even from 0-1/4 throttle isn't effected by the pilot jet?

Click to expand...

yes it is, in fact the pilot affects the fuel throughout the entire rpm range but it is most noticeable right off the bottom until around 1/8th throttle at which point the needle begins to have affect.

thwrightstuff said:

I won't be getting my size 40 pilot jets until tomorrow, so I may just either try the stock airbox again (which I really am against doing because it's a bitch and a half to install) or just keep tweaking it with my current setup.

Click to expand...

tweek the current setup ir simply jet it with no filters.

thwrightstuff said:

should I try all new plugs?

Click to expand...

it will be better to judge jetting but as long as your other ones aren't too crusty, you can use those but give them sa good scrub with varb cleaner and a brush first then take photos of them before installed.

thwrightstuff said:

Currently, the bike seems to run best, which isn't very good at all, with the choke at about 1/2-3/4 engaged, that tells me the mixture is a touch lean, which doesn't make any sense based on what's been happening.

Click to expand...

yeah, it doesn't...that is odd.

thwrightstuff said:

Here's something else I noticed, exhaust pipes 1 and 2 are at least 10-15 degF hotter than 3 and 4. I burn my hand on 1 and 2 instantly when on 3 and 4 I can hold the pipes indefinitely without burning myself. Does that mean the mixtures are running better on 1 and 2 than 3 and 4? Or does that indicate that there is something wrong with 1 and 2?

Click to expand...

if you can put your hand on ANY pipe after a ride and then remove it and still have skin left, they are not firing.

thwrightstuff said:

So you'll be happy to hear that your advice has been really helping me to hone in the response of my bike. I'm back to 110s and 40s and it's decent, but not good enough yet. After tweaking the pilot screws some, I've noticed that adjusting carbs 3 and 4 pilot screws doesn't change the rpm of the engine at all, only 1 and 2 seem to do anything. Is this a symptom of some serious issue I might have or is this normal?

Click to expand...

these are the same cylinders that you can put your hand on the pipe so i would say they are not firing for some reason.

lay all the plugs on the head and turn the engine over . . if the spark is pale blue, it is good . . if the spark all looks the same they should all run.

try switching the spark plugs between cylinders or install new ones

Well, you're right, the spark plugs weren't sparking, which in turn made the other half of the engine work even harder. I put in all new spark plugs (3 and 4 first to confirm my issue) and now I have responsive power! God it feels great to have my bike back, I wish I had done the spark plugs before. Now I am dealing with fine tuning and power surges. I know the power surges are as a result of running lean with open air filters.

I did a proper plug chop after replacing spark plugs and the reading confirms my suspicion this whole time, it's running lean. I am going to go back to 42s first and possibly 115 or 120s. Currently, the bike runs smoothest when the choke is about 1/2 engaged, so going up a jet size may just fix it perfectly.

Barnett, I did try testing the spark plugs beforehand and they sparked just fine, but I've come to realize that the spark in open decompressed air is much easier than the spark inside a compression chamber with limited oxygen.

I have a new development that I've noticed on the bike since this whole debacle started, though. Randomly, my bike's exhaust makes a quick "Pst" sound and maybe a pop here or there, but the noticeable thing is the pst. I've posted a video of it where you can occasionally hear it, turn your volume up if you listen. You can especially hear it around 30 seconds: https://www.youtube.com/watch?v=GxiyPN5eJqg

I'll be doing all of this work after work today, so i'll let you know how it goes. If all goes well, I could have this fixed by this evening.

Oh and I still have the engine ticking after tightening the valves and the knocks at low rpms. (Sorry for the laundry list of problems, I just want it fixed

I just discovered the strangest thing. Apparently, the positioning of my throttle cable makes a huge difference on the rpms. Generally, if my front wheel is turned to the left, my engine revs up like crazy, but when I straighten it out, the rpms drop and the bike eventually cuts out.

I've narrowed it down to the throttle cable and I believe it has an issue at the twist grip. Why on earth would this be making such a difference? It's not like it's electrical and the damn thing doesn't seem to pull any on the throttle body of the carbs. How is this happening?

.
Either your cable is too short or it is binding or there is not enough play . . Increase the amount of play by turning the top adjustment on the throttle in 1.5 turns.

The exhaust noise is a popping sound caused by bad points or bad plugs or tight exhaust rockers or burnt valves.

Yes, in occasion plugs will spark in open air but not under pressure . . This is very very rare but AFTER I saw your two pipes were not scream hot, it was obvious to me they were not firing.

Also, yes, the jetting will be a bit different for a 4 cyl that actually runs on 4 cyls as opposed to a 4 cyl that only runs on 2 cyls.


Yeah, good luck jetting two dead cylinders!

...............

Gee thanks, fortunately, I've got that detail ironed out. I ran into yet ANOTHER problem last night. My gas tank bolt wouldn't come off so I have to cut it off. Turns out there's this floating nut inside the subframe that the gas tank bolts to. So I'll have to JB Weld that and pray that it holds nicely for awhile. I don't understand why they didn't just weld a threaded nut directly to the frame like they did with the seat bolts, seems pretty stupid to me.

I think maybe my lifters are a little too tight like you said, I'll go through and readjust tonight or tomorrow.