Topic: won't rev past 6000rpm???

[cbme]

hey guys, got an 81 650C, the bike starts instantly, warms up quick, idles smooth, accelerates through 1st and 2nd great. once I hit 3rd it won't rev past 6000, gets there quick then pops and farts and kinda surges. If I roll off a bit it will slowly pull but if I crack the throttle it sounds bad.

I've cleaned the tank which was spotless. bypassed my vac fuel shutoff. checked that the cap was venting. Set the valves cleaned and set the gap on the pulsar generators. I've also tried advancing and retarding the timing but it didn't seem to change the problem. Oh and the air filter is new. Any thoughts?

[Green Goblin]

Carbs cleaned? "My bike won't rev past XXXXRpm" usually means the carbs need a good cleaning.

[seanbarney41]

...also make sure your ignition advancer is working....easiest to hook up a timing light, note  timing at idle, rev to around 4 grand and note whether the timing advances, if yes it's back to the carbs, if no pull out the timing advancer, clean it and lube it...then...be amazed

[Hush]

Exactly what he said, my CB650 was same till I took the advancer out and cleaned it all up and very lightly greased it, couldn't believe how rusty and dry it was even tucked away behind the timing plate.

[wardenerd]

I know this sounds crazy but....remove the cover from the air filter and use fender washers to hold the filter in place.  I also went to a K&N filter and now mine revs thru the rpms.  I saw this remedy on one of the forums earlier

[bollingball]

cbme: Are you saying it goes past 6k in 1st & 2nd. is the filter stock not pod filters. Does pulsar generator=points?

wandererd: Are you thinking it is not getting enough air? If so it does not sound crazy. But I don't know any thing about the 650 filter system.

                     Ken

[flybox1]

these are carburated bikes.  cracking the throttle wont get you anywhere no matter what gear you're in.
your pulsar generators need new power crystals.  you can get them at auto zone.
please do a good cleaning of your carbs, set the timing/advance on your points, and do a good vacuum sync of your carbs.

[wardenerd]

I had the problem of not reving over 5500.  I tried everything.  Took it to my trusty mechanic.  He had already been through the pulse generator and the electrics. He was baffled too.  We even tried rejetting.  I saw this remedy of removing the cover from the side of the filter box where you insert the filter.  I had a new paper filter in place and after taking the cover off I was not satisfied so I put in a permanent K&N filter and left the cover off.  I use the stock air box and K&N filter.  Runs strong and idles perfectly.

[bollingball]

OK flybox what are power crystals

[TwoTired]

these are carburated bikes.  cracking the throttle wont get you anywhere no matter what gear you're in.

Um, Cb650's have accelerator pumps on the PD 50s or CV carbs.  Both have pretty good throttle response if all is working well.

[wardenerd]

my 650c has CV carbs and it will snatch you off the seat if you snap open the throttle and do not hold on.  My 650 is much stronger than my 550 although the handling and seat position are not as good for me.

[flybox1]

OK flybox what are power crystals

it was a silly reference to the movie Napoleon Dynamite, but it sure would get a laugh if you asked at the parts counter for them.

[bollingball]

I guess they would be next to the muffler bearing or bulb stretcher.

+1 TT the working accelerator pump makes all the difference. I thought my bike was working pretty good then I got my pump working on all four instead of just one (my pipes were plugged) WOW

                Ken

[Hush]

Number 3 carb has the accelerator pump as part of it's moulding on the 650, if the skirt is ripped like one I had on a set of carbs then it will do jack so if you ever have to remove the carbs again undo the 3 small screws that hold it on and check that it hasn't hardened and is unserviceable.
Also the trick with the air filter cover off will feed more air to your carbs, use some big penny washers to hold the filter in place and just leave the real filter cover on your work bench, ride bike and see if it helps.
A clogged filter will give you bad acceleration too, they sometimes look great but are clogged with crap and a new one every now and then is a good idea.
I would definitely check the condition of your advancer mechanism though, I had all of these problems with my 650 when I got it so curing one didn't fix it and I had to keep looking until I had done the lot, if you don't want to upset your timing just mark the plate with a sharpie pen and the casing as well, when you finished cleaning up the advancer you can just stick the timing plate back in same spot....good luck...Hush.

[ak58lp]

I am having the identical problem on my 82 650.

Here's what I have tried so far.

-new air filter
-soaked carbs in Pinesol for days
-drained rubber hoses near the kickstand which were FULL of water and crap (helped a bit)
-removed the air filter cover and used the washer mod (helped some too)
-cleaned tank
-added Seafoam

Problem is still there and from what I have been able to determine from people who work on these carbs, it is likely the T tubes that are cracked or rotted between carbs the carbs at the bottom. This is a high failure rate item with this model of bike. There are two in total. I can confirm mine are rotted out and need to be replaced. Problem is to fix them you need to seperate all 4 racks of carbs which is a fairly big job. Honda part numbers are below and they range between 35 - 50 dollars each!!

JOINT (1,2) (3WAY)  16036-460-771

JOINT (3&4) (3WAY)  16047-460-771

Until I get some time in the fall I am going to remove my carbs and just put some high temp silicone on them to get the air leaks sealed up.

[Hush]

Hey ak58lp, I feel your pain but maybe you are looking in the wrong direction, you don't mention cleaning up the advancer unit which is located behind the electronic pick-up plate on the right hand side of the motor.
This made a massive change to my old 79 650's performance and is a very overlooked but important part of the acceleration for these bikes.
I took mine apart, cleaned it all up and lightly greased the pivot points that the counter weights swing on.

[ak58lp]

Hey ak58lp, I feel your pain but maybe you are looking in the wrong direction, you don't mention cleaning up the advancer unit which is located behind the electronic pick-up plate on the right hand side of the motor.
This made a massive change to my old 79 650's performance and is a very overlooked but important part of the acceleration for these bikes.
I took mine apart, cleaned it all up and lightly greased the pivot points that the counter weights swing on.

I''ll look at that too. Is there a procedure some where for this?

[Hush]

Nah just remove the cover from the side of the motor (3 screws) then mark the position of your electronic pick-ups with a felt tip pen that won't rub off, mark the plate and the engine casing so you can align it right back at that point otherwise you will need to retime the bike.
Remove the pick-up plate and there you will find the advancer unit, remove that and give it a birthday, reverse of this is reassembly instructions.

[cbme]

the bike chokes out around 8k in 1st and 2nd. Then at 6k in 3,4,5. seems to have lots of power below 6k in each gear but feels like something is restricting it. either fuel or air.
I've never ridden this bike in working order but it feels to me like the engine is kinda hot.

If I roll of the throttle slightly it will very slowly accelerate past 6k. If I slowly open the throttle to much it bogs down. Thinking fuel starvation? If I accelerate and cut the throttle the bike pops and sort of backfires. Some guy told me that's a sign of running to rich.

I'm gonna try a new filter and see if that changes anything, otherwise i'm giving myself a crash course in carbs.

Advancer works, Previous owner said he replaced all electrics. He also cut a big hole in the air filter cover.

[ak58lp]

Whick also makes me think this is an air flow or carb problem. Do a search here for 82, 5550 rpm, or bogging down and you will see multiple posts. For some, the air filter trick worked, but also try draining the tubes by the center stand. Look underneath, you can't miss them.

[Hush]

Also try spraying some clear coat, not sure what you would call it in the States but some form of spray on coating that will seal up the carb isolators (the bits that connect the carbs to the head), these tend to perish and crack causing air to enter the system and upsetting your carburation, just a thought.

[ak58lp]

Hey ak58lp, I feel your pain but maybe you are looking in the wrong direction, you don't mention cleaning up the advancer unit which is located behind the electronic pick-up plate on the right hand side of the motor.
This made a massive change to my old 79 650's performance and is a very overlooked but important part of the acceleration for these bikes.
I took mine apart, cleaned it all up and lightly greased the pivot points that the counter weights swing on.

Thank Hush I think I am ready to try this. I just took off the tops of the carbs and the float bowls and cleaned, but no difference..runs worse now. Before I start into a total tear down of the carbs, can you give more more info as to what I am looking for? I have taken the pulse generator cover off and know the plate but no idea after that.

[flybox1]

the bike chokes out around 8k in 1st and 2nd. Then at 6k in 3,4,5. seems to have lots of power below 6k in each gear but feels like something is restricting it. either fuel or air.......

Previous owner ........... He also cut a big hole in the air filter cover.

ummm...did you mention that before and i just missed it?     what else did the PO mod that hasnt been mentioned?
did you try sealing up that gaping box hole and test riding?
have you done a plug chop under load to see if you're lean because of this hole, when it bogs at 6k in either 3rd, 4th or 5th gear?

[Hush]

Sorry, left you high and dry there mate. Mark the timing plate with a felt tip pen so you can line it back up in the same position with the engine casing when you have finished.
OK you need to hold the large nut with a spanner and undo the small middle bolt, careful it isn't a strong thing.
The auto advancer unit should be removeable now, slide it out to you and take it apart, the springs and counter weights will probably be dry as, clean it with whatever you have and then lightly grease the pivot points where the wieghts swing on, reassemble and away ya go.

[ak58lp]

I had a look at this tonight and I'm still a little worried. I can see someone had the timing plate off before because they scratched a straight line across both sections. I took that off and sanded the contacts down abit but I'm pretty sure that's just for the stator. My Haynes book is not very clear either. It also mentioned taking the 6 mm nut of while holding the larger one.

The thing I am worried about....If the engine turns over even just a little bit while I get the smaller nut off, am I goin to screw the timig up? I do not have a timing light.

What exactly am I going to clean in there? I can see the small springs but that's about all I know.

I took the carbs off once more and gave them a good soaking in Pinesol. Removed the float bowls and took the top vaccum and all parts inside apart. They all got a good soaking. Blew compressed air out of every spot I could see. Same thing at high end and also a lot of surging at normal speeds in any gear.

This bike is killing me..so frustrating. Next will be the tees to replace but I want to try this fix first..looks a lot easier than a carb tear down.