Topic: Lack of power at low revs

[scottly]

The needles main jet is clear and needle position was never touched,

The surging happens at ~ 1/8 to 1/4 position. About 45-50 mph or 75-80 kmph. Any nothing higher or lower all is well.

Again thanks for the help.
Blair

Look again at the chart mystic posted; 1/8 to 1/4 is right in the range most affected by needle position. Maybe try raising the needles a notch (by lowering the clips) and see if that helps....

[mystic_1]

Let's take a step back for a moment, and let me ask some questions I suppose I should have asked in the beginning:

Is the bike stock, or has the intake or exhaust been modified?

What sprockets are you using?

Sure the clutch plates are in good condition and that the clutch is properly adjusted?

Ignition system in good condition, including the plug wires and boots?

Are the carb jets stock sizes, and have they been replaced with aftermarket parts?

Beyond this, I think Scottly makes a good suggestion.

mystic_1

[Tdinova]

Is the bike stock, or has the intake or exhaust been modified? Stock, bought aftermarket pipes 9 years ago when he bought it

What sprockets are you using? was never changed by us,  (9 years)

Sure the clutch plates are in good condition and that the clutch is properly adjusted? clutch seems fine, clutch should not make the bike stall out, I have owned bikes since 1970, from honda 50, kaw 100, cb360, cb750 and now a '07ST1300

Ignition system in good condition, including the plug wires and boots? new plugs, new plug wires, new caps. did a resistance check on the pulsars.. ~535ohms on ea., checked carb boots with wd40

Are the carb jets stock sizes, and have they been replaced with aftermarket parts? all original.

Beyond this, I think Scottly makes a good suggestion.

mystic_1

[Tdinova]

The needles main jet is clear and needle position was never touched,

The surging happens at ~ 1/8 to 1/4 position. About 45-50 mph or 75-80 kmph. Any nothing higher or lower all is well.

Again thanks for the help.
Blair

Look again at the chart mystic posted; 1/8 to 1/4 is right in the range most affected by needle position. Maybe try raising the needles a notch (by lowering the clips) and see if that helps....

I don't want to mess with the needles. When I laid the bike up last fall, all was working fine. I going to remove the carbs tomorrow night for the last time and check the clearance of the accelerator pump rod, I did not measure that clearance. I'll have to break down and take the bike to a bike shop if that measures correctly
I always use fuel stable when storing his bike


frustration is setting in.

I have a Clymer manual and it explains how to set the pilot screws, but I do not have a tack. Would a hand held tack for a car work?? or does it need a bike hand held tack?

[Spanner 1]

Before you actually take off the carbs, when you get to having the airbox removed, please check the acc. pump nozzles for operation....... I know you said you ' bench tested ' their operation... it will take you 1 minute to verify that they ( all 4 ) are working or not 

[Tdinova]

Before you actually take off the carbs, when you get to having the airbox removed, please check the acc. pump nozzles for operation....... I know you said you ' bench tested ' their operation... it will take you 1 minute to verify that they ( all 4 ) are working or not  

thanks for the reply Spanner. How do I remove the air box? There is not enough room to force it by the carbs and frame.  

[Spanner 1]

I've never taken-off a 650 airbox.... maybe one of the 650 guys will chime in with the answer.

[scottly]

I don't want to mess with the needles. When I laid the bike up last fall, all was working fine.

If it ran well with those settings before, I wouldn't mess with them either.
As far as pilot screws, I would go back to a baseline of about 1 1/2 turns out from lightly seated.
As spanner said, check the operation of the accel pump. I have seen a stuck diaphragm check-valve on a motor that had been stored over the winter with fuel stabilizer before. (disclaimer: not a CB) 

[Tdinova]

I don't want to mess with the needles. When I laid the bike up last fall, all was working fine.

If it ran well with those settings before, I wouldn't mess with them either.
As far as pilot screws, I would go back to a baseline of about 1 1/2 turns out from lightly seated.
As spanner said, check the operation of the accel pump. I have seen a stuck diaphragm check-valve on a motor that had been stored over the winter with fuel stabilizer before. (disclaimer: not a CB) 

Well I gave up. Took the bike to "The Shop" about 10 minutes from here. While drive there it worked pretty bad at low revs ,, but revved fine once it was over the hump. The guy in "The Shop" went..  "hmmmm, sounds like the accel. pump". I told him what I done and how I checked the pump and he said "Sound about right", So he is going to reset the pilot screws, re-syn the carbs and check the timing..

After I got home my brother asked me if I checked the rotor for ohms. If the rotor had the wrong ohms (shorted out) wouldn't that effect the charging?

[mystic_1]

If your alternator isn't working properly, you could have low voltage throughout the system.

May as well check out the charging system thoroughly, you've checked out just about everything else.

mystic_1

[Spanner 1]

When you get done with the guy in "The Shop' and if it's still not fixed ( my bet!, not being mean, just anticipating )... come back 'cos I have one suggestion about your ignition... se ya later ( but I hope not, nothing personal  'cos I hope he can fix it  ).....

[Tdinova]

When you get done with the guy in "The Shop' and if it's still not fixed ( my bet!, not being mean, just anticipating )... come back 'cos I have one suggestion about your ignition... se ya later ( but I hope not, nothing personal  'cos I hope he can fix it  ).....

Ok got the bike back today and guess what, It's the same, around 3200rmp the bike starts to stumble, but when I crack the throttle she full bore ahead.. He set the pilot screws to 3 turns each and re-syned my carbs. The carbs were almost dead on when he done the syning.

OK Spanner 'Give it up" what is my cure? PLEASE

[Tdinova]

ok did more checking today, At idle the bike is 12.02 volts, at 3000 the volts is 14.10 volts. I checked the resistance of the rotor and it is .43ohms between the slip rings. Never took it for a drive because it's Saturday and the evening should not be spoiled.

I'm thinking by what is posted here , what my brothers 1st comment and the 1st comment from "The Shop" is the accelerator pump is the culprit. But it squirts at very little throttle response.

Does anyone have a source for the accelerator pump? The Stealers would probably want $1 million

[Tdinova]

Today was my very last try before ordering the Accel pump. I checked the connections at the coil, pulsars, and everywhere else. I even checked the spark plug wires and caps (even though they were new 3 months ago 5000ohms). Took the coils off and made sure there was no rust on any connection and checked the ohms on the primary wires of the coil. They were both the same 2200 ohms(If I remembered correctly). I checked the flow coming out of the gas tank to make sure there was no restrictions. I checked the valve clearance, intake all good ~ .05mm and I found 1 exhaust a tad loose .1mm. Went for a spin and the bike was not to peak temperature and did not work 100%, but worked better after completely warm.

I give up so tomorrow I'm called Mr. Honda and order a new accelerator pump.

[Spanner 1]

Dang, forgot what I was going to say about your ignition ( had a very big weekend  ... hey, now I recall..... measure the 'pulsar' to cam gap on your ignition... is it to spec. ?... if so, close them up , like 2 thou.... just a hunch... ( i.e if book says 14 thou., try them at 12 thou. )..... your report that bike runs better when you stop for some time and ride again suggests heat effect on electrics to me 

[Tdinova]

Dang, forgot what I was going to say about your ignition ( had a very big weekend  ... hey, now I recall..... measure the 'pulsar' to cam gap on your ignition... is it to spec. ?... if so, close them up , like 2 thou.... just a hunch... ( i.e if book says 14 thou., try them at 12 thou. )..... your report that bike runs better when you stop for some time and ride again suggests heat effect on electrics to me 

I did check the pulsars. 535 ohms on each. I did check the clearance and was in tol. I never tried to reduce the clearance.
 

your report that bike runs better when you stop for some time and ride again suggests heat effect on electrics to me 

or the accel pump rubber gets more supple as it warms up.. Just thinking. The gas is always cold so that throws that out that thought.. Honda dealer here I come.

[Spanner 1]

I read it in a report about 650/700 Nighthawks.... poor running at low/mid throttle and the fix was to reduce the pulsar/ cam clearance by a couple of thou', don't know why it would be a fix , but worth trying I think.

[Tdinova]

Thanks for the come back. I'll check tomorrow night before ordering the accelerator pump

[Tdinova]

I lowered the gap on the pulsars to .3mm, the book calls for .3 to .4mm. Mine was set at ~.4mm. I put a spark plug on the plug wire and laid it again the engine frame and cheated the pulsar to send a spark to the plug to see if the color was a dark blue. It was on all 4. I remembered to adj the cam chain. Fired her up and went for a spin.. same. At work today I called mother Honda and asked about a new accel pump... discontinued  .. Gotta order one on line.

Anyone have a source for the pump??

[Tdinova]

Hey, I can answer my own post.

I emailed another Mother Honda about 100km from here and they can get an aftermarket accelerator pump for 35.99. I emailed back saying go for it.

Funny how one dealer will go the extra mile..

[scottly]

I'm thinking by what is posted here , what my brothers 1st comment and the 1st comment from "The Shop" is the accelerator pump is the culprit. But it squirts at very little throttle response.

It sounds like the accelerator pump is working as it should, if you mean it squirts with very little throttle movement?

[Tdinova]

Just got an email from the Honda dealer:
Quote
Ahh, I see now. The parts fiche is pretty old and I wasn't able to tell the difference between the cut off valve and the pump diaphragm (they also don't label them particularly well).

Unfortunately I can no longer source you the accelerator pump either OEM or aftermarket for the CB650.


So I took the carbs off again for something to do. I looked at the clearance of the accel rod and she is really really close. I started to open the throttle to watch the flow and yes it squirts gas on all 4 just after I roll the throttle linkage by hand.

BUT

AS you know the end of the rod sets on a flat metal piece connected to springs and as the throttle is open fully the pump will only go so far. But if I give the throttle a really fast snap the rod does not keep up with the linkage, is that normal, like the spring at the bottom of the accel pump is to strong and will not let the gas come up.? or the passage is partially plugged, or am I over thinking the whole thing?

Also .. What does the air cut valve do? Would that be my problem?

[Tdinova]

well, it rained here these 2 past days , about 3 inches total. Did a lot of soul searching... then the rain stopped. Started the cb650 and went for a little spin. same as usual..of coarse. went home and parked the old girl, sat beside her and looked.. took out the air filter--looked new. then I thought height of gas in each bowl. Took a clear tube and put it on the drain of #1. Open the drain slowly. The gas ran down slowly , right to the top of the bowl. Did # 2, the same.. Did #3 and the gas stopped at the 1/4 from the bottom, hmmmm. I thought I had a gas restriction. Went back to # 1 and 2 both were the same. back to # 3 and the same 1/4 from bottom. I then lowered the tube to the floor to get the flow going, then put it back up along side the outer bowl and it stopped at the top of the bowl..<<HMMM>> . I then tried # 4 and that was really bad, about 1/5 the way up the bowl. Then I lowered the tube to get the gas flowing, then raised it by the bowl, and it stopped at the top.. BY JOE I think I found the little  %^&(***). I removed the float and needle on # 3 and 4 for the 1 millionth time and it looked good. So I called "The Guy" at the bike shop and told him what I done. I took the carbs to 'THE SHOP' and he is going to give them a one over early next week.

I Think I can finally sleep peacefully I hope.

[Tdinova]

Well got them back, $70 later, the same. I'm gonna order some air cutoff valves on line. I have to have the carb number to ensure I get the right parts. On #4 carb there is a PD 50 C then an A in a square RIL.


Went out and took some pictures

would these be off a 650 custom?

I put the Comstar Rims on . Spoke was original.

[Tdinova]

The weather was about 65f after work today . Took my sons bike for a small spin.. the same.. So I came home and started to turn out each air screw. 3 turn went for a small run . a tad better, now I have the pilot screws to 4 turns and the bike work really good. The stop and go, no shutter, like it was new again.. but 4 turns out. I happen to meet a biker at the local hardware store and we just happen to talk about bikes and the weather. IT just so happens that he has 2 1980 CB650 customs.. hmmm, we talked longer. 1 he drives and the other is a parts bike. I talked him into me coming to his place, remove his carbs and bringing them home to try this Saturday... ya.. hope all goes as plan.