Author Topic: bogging down WOT... 78 550 (Read 6113 times)

uksparky · « **on:** February 16, 2019, 04:44:07 PM »

Been trying to sort this out for some time with no luck, as you know the PD46 carbs need two hand fulls to get full throttle i very rarely need full throttle only on long incline hill, backing off to 3/4 its ok... when this bogging started on my ride today i gave it full choke for a second/no change.... so 5,200 rpm 6th gear long incline giving more throttle and more, rpm now dropping to 5k...full throttle bogging..... back off throttle power comes back. Giving choke for one second means its not lean right. If i change down to 4th it does the same thing...low and mid range its perfect no problems.. when i got the 550 it had this problem
It must be a fuel/carb problem... any ideas guys or is this a 550 thing

stock carbs/jets
stock exhaust
stock air filter
no vacuum leaks
throttle sync
idle mixture set ok
clear tube level just below bowl gasket two mm
jets cleaned two weeks ago..
idles smooth runs perfect plugs brown tan
valve clearance .005
High comp pistons
electronic ign
ign timing spot on
advance working ok
new in tank filter
Could it be the kenny harmon camshaft it has the longer duration lobes could it be running out of gas full throttle .. another idea would be plug chop at top of the grade, only problem i would get burnt to death with the hot engine lol

HondaMan · « **Reply #1 on:** February 16, 2019, 08:07:52 PM »

Not fully sure about the camshaft issue (could possibly be slightly off time?), but ignoring that for a moment...

Next time you try the 'run', maybe pop open the fuel tank's gas cap first, to see if it is just a fuel restriction issue. This happens sometimes when the vent in the fuel cap is rusted shut, or partly shut.

If the cam is an early-open one (intake opens more than 7 degrees BTC) then you may find that the mainjets are too rich. If it is working OK between idle and 2000 RPM then it's not terribly likely to be timing related, but to test this you can first retard the timing slightly (3 or 4 degrees) and try it. In the 550, it is slightly easier to adjust the slide needles than the mainjets, and they adjust approximately 1% per notch position in their slides. So, for example, if you have #100 mainjets and the needles are now in the middle notch, dropping them 1 notch will simulate a #99 jet until about 3/4 throttle, at which point it reverts to acting more like #100 again.

Deltarider · « **Reply #2 on:** February 17, 2019, 12:02:50 AM »

Did you have a look at the plugs noses yet? While you are at it, make sure the gap is OK and not wider than prescribed.

sixthwisconsin · « **Reply #3 on:** February 17, 2019, 05:26:48 AM »

How is your fuel line and what diameter is it? Is it routed properly with not a lot of extra line looping around? Are you running an aftermarket inline filter? These can cause fuel starvation during high demand like WOT runs. Also, make sure your petcock is functioning normally.

MRieck · « **Reply #4 on:** February 17, 2019, 05:40:46 AM »

Your main jet may be to large. You noted the engine picked up when you backed off the throttle....that drops the needle and leans the mixture. Maybe a main jet fell off the needle jet etc too.

uksparky · « **Reply #5 on:** February 17, 2019, 07:30:14 AM »

Thanks for all the info guys..spark plugs set at 30 thou....no in line filter just tank filter proper clear fuel line ..no kinks, checked flow its good... i played around with timing few weeks back retarding, no change.
My thoughts...when the volume of air is coming through the carbs needle jet at 3/4 throttle, the amount of fuel at that point is coming through the main jet and emulsion tube, when full throttle no more volume of fuel can pass through... what about drilling two more holes above the existing ones, only thing is 1/16 is the smallest drill...but would that make it run to rich at all the time...if thats a good idea i would need 4 emulsion tubes in case i screwed up.
When i was doing the carb sync i could see the needle jets were in place...
Needle jet to large ..that is a good point the only way to tell is give it the full throttle up the hill, pull over let it cool down and pull a spark plug check the tip rich or lean...... as far as i know the carbs are stock ....

Don R · « **Reply #6 on:** February 17, 2019, 08:34:56 AM »

Does it reach rpm OK going through the gears? If so, that suggests it is a fuel volume issue. No one mentioned the air filter, stock and recent? You can buy a pin drill set and enlarge the emulsion tube holes slightly, I've done it on 750's. It sounds like you've been thorough in checking and maintaining your bike.

uksparky · « **Reply #7 on:** February 17, 2019, 09:06:22 AM »

Yes Don it reaches rpm going through the gears and is ok.... yes stock air filter... i remember going back in time when i got the 550 it had a foam filter, when going back to stock paper filter it did improve throttle response. Normally i twist my wrist and thats all i need normal riding, why did Honda make it that way having to grab another hand full to get full throttle
Anyone have a link to the drills i think thats the way to go, after plug chop

Just found this link to drilling the emulsion tubes... it will lean out if i do that....i think i will re check float levels again

http://forums.sohc4.net/index.php?topic=168198.0

TwoTired · « **Reply #8 on:** February 17, 2019, 10:27:52 AM »

Are sprockets 17F and 37R?

Suggest holding the "bog" condition as long as you can stand, then hit kill switch and pull in clutch simultaneously. Stop and pull all the plugs to note the spark plug deposit patterns.
This is your window to combustion conditions during the trouble issue, to which you can respond and address.

Do note, the center electrode insulator. If coated with carbon, spark can be shunted away until it burns off. Usually a sputtering sound.

If backing off on the throttle instantly resumes clean firing, it is an indication that too lean mixture is occurring. The plugs ought to be pretty white if that's the case.

Have you considered taking it to a dyno test shop? They can get you a fuel map to tell you exactly what mixture occurs during the "bog".

Cheers,

uksparky · « **Reply #9 on:** February 17, 2019, 11:28:42 AM »

Yes stock sprockets 17/37 i will do the spark plug check.... have to wait cold and rain here in Cali next five days. Dyno not close by where i live but a good idea TwoTired

uksparky · « **Reply #10 on:** February 17, 2019, 12:53:07 PM »

I decided to check the clear float bowl test the two inner ones were right on the gasket line....outer ones shown in picture a little bit low
.. will fiix that today...wet Sunday...... just checked spark plugs all same color, 91 Oct gas that's after freeway run yesterday.... idle mixture screw almost two turns out.... a month ago the plugs were tan color, in the picture it looks a little rich, but it could be the gas

seanbarney41 · « **Reply #11 on:** February 17, 2019, 02:40:19 PM »

If that photo is color accurate, that is pretty weird looking. Never seen that reddish hue before. Are you using some kind of fuel additive?

uksparky · « **Reply #12 on:** February 17, 2019, 03:21:37 PM »

Quote from: seanbarney41 on February 17, 2019, 02:40:19 PM

If that photo is color accurate, that is pretty weird looking. Never seen that reddish hue before. Are you using some kind of fuel additive?

Three weeks ago i did put 3oz of oct booster in the full tank, ........ forgot about that, i will have to run tank low and refill to get true plug check

540nova · « **Reply #13 on:** February 17, 2019, 04:10:00 PM »

Quote from: seanbarney41 on February 17, 2019, 02:40:19 PM

If that photo is color accurate, that is pretty weird looking. Never seen that reddish hue before. Are you using some kind of fuel additive?

I agree, you never see that on any of those charts with 15 pictures of plugs, for diagnosis, from grossly oil contaminated / black, to pure white / lean. Looks like rusty water.

Sent from my Pixel 3 XL using Tapatalk

TwoTired · « **Reply #14 on:** February 17, 2019, 04:34:54 PM »

Looks like you are burning rust. Yikes. Unless you can sand blast those clean, they aren't any good for reading mixtures anymore. imo.

To be clear, You have to use clean plugs and operate only in the "bog" regime to read conditions that apply to "bogging".

Cheers,

HondaMan · « **Reply #15 on:** February 17, 2019, 07:11:37 PM »

Quote from: uksparky on February 17, 2019, 07:30:14 AM

Thanks for all the info guys..spark plugs set at 30 thou....no in line filter just tank filter proper clear fuel line ..no kinks, checked flow its good... i played around with timing few weeks back retarding, no change.
My thoughts...when the volume of air is coming through the carbs needle jet at 3/4 throttle, the amount of fuel at that point is coming through the main jet and emulsion tube, when full throttle no more volume of fuel can pass through... what about drilling two more holes above the existing ones, only thing is 1/16 is the smallest drill...but would that make it run to rich at all the time...if thats a good idea i would need 4 emulsion tubes in case i screwed up.
When i was doing the carb sync i could see the needle jets were in place...
Needle jet to large ..that is a good point the only way to tell is give it the full throttle up the hill, pull over let it cool down and pull a spark plug check the tip rich or lean...... as far as i know the carbs are stock ....

One of your comments above reminded me of one of these I 'fixed' a few years ago. The owner had rebuilt the carbs using Keyster kits, and their needles were (are) the wrong taper. If you did this, try reinstalling the OEM needles again.

ALL of the Keyster needles in the 750 and 500/550 kits I have seen are the wrong taper for these carbs. ALL of them...and their error makes the engines run lean.

uksparky · « **Reply #16 on:** February 17, 2019, 09:47:14 PM »

Quote from: HondaMan on February 17, 2019, 07:11:37 PM

Quote from: uksparky on February 17, 2019, 07:30:14 AM
Thanks for all the info guys..spark plugs set at 30 thou....no in line filter just tank filter proper clear fuel line ..no kinks, checked flow its good... i played around with timing few weeks back retarding, no change.
My thoughts...when the volume of air is coming through the carbs needle jet at 3/4 throttle, the amount of fuel at that point is coming through the main jet and emulsion tube, when full throttle no more volume of fuel can pass through... what about drilling two more holes above the existing ones, only thing is 1/16 is the smallest drill...but would that make it run to rich at all the time...if thats a good idea i would need 4 emulsion tubes in case i screwed up.
When i was doing the carb sync i could see the needle jets were in place...
Needle jet to large ..that is a good point the only way to tell is give it the full throttle up the hill, pull over let it cool down and pull a spark plug check the tip rich or lean...... as far as i know the carbs are stock ....

One of your comments above reminded me of one of these I 'fixed' a few years ago. The owner had rebuilt the carbs using Keyster kits, and their needles were (are) the wrong taper. If you did this, try reinstalling the OEM needles again.

ALL of the Keyster needles in the 750 and 500/550 kits I have seen are the wrong taper for these carbs. ALL of them...and their error makes the engines run lean.

HondaMan i have no idea what the PO over the last 41 years did to these carbs... i never pulled the needles, you could be right, i just cleaned the jets and replaced the float valve and rubber bowl seals.... how would i know if they were Keyster are they stamped... something to keep in mind...

dave500 · « **Reply #17 on:** February 17, 2019, 10:51:21 PM »

that octane booster rubbish will cause that colour,it might be manganese?

Tracksnblades1 · « **Reply #18 on:** February 18, 2019, 05:21:36 AM »

Quote from: dave500 on February 17, 2019, 10:51:21 PM

that octane booster rubbish will cause that colour,it might be manganese?

+1

Magic Mystery Cure in Can...

TwoTired · « **Reply #19 on:** February 18, 2019, 11:08:47 AM »

Quote from: uksparky on February 17, 2019, 09:47:14 PM

HondaMan i have no idea what the PO over the last 41 years did to these carbs... i never pulled the needles, you could be right, i just cleaned the jets and replaced the float valve and rubber bowl seals.... how would i know if they were Keyster are they stamped... something to keep in mind...

The Honda needle have a stamping E2369 or near that number. I didn't look it up for exactness.

Keyster numbers are like 2 or 3 digits.

There is a chart in the FAQ giving Honda numbers found for PD carbs.

Cheers,

BomberMann650 · « **Reply #20 on:** February 18, 2019, 12:22:05 PM »

Gotta remember there is a slight drop in port pressures at WOT. So the engine pulls less air/fuel at that position.

A change in needle jet profile or clip could correct that.

So would artificial aspiration 😈

Tracksnblades1 · « **Reply #21 on:** February 18, 2019, 02:04:18 PM »

UK,
Did you get your timing and advance unit functioning like you want it..?
Have you tried fattening or leaning it up..?
I've never used the full choke momentary method for determining jetting.
I have slowly applied choke to see if a bog situation changes from bad to better or visa versa....
I'm glad you tried fourth gear to rule out long duration camshaft, and low RPMs...
👍

uksparky · « **Reply #22 on:** February 18, 2019, 04:56:44 PM »

Quote from: Tracksnblades1 on February 18, 2019, 02:04:18 PM

UK,
Did you get your timing and advance unit functioning like you want it..?
Have you tried fattening or leaning it up..?
I've never used the full choke momentary method for determining jetting.
I have slowly applied choke to see if a bog situation changes from bad to better or visa versa....
I'm glad you tried fourth gear to rule out long duration camshaft, and low RPMs...
👍

,,...

Yes i have the timing spot on now, plus advance... throttle sync, and idling nice and smooth ... as you know the mixture lean/rich screw is for idle only...the only way is to pull the needles and see if they are stock....if so raising them up a notch will also screw up the sync/mixture... i changed the level of the two outer carbs about 5mm but never had a chance to test, i dont think that will solve it.. plug chop will be my next thing....in the next few weeks... i sure dont like these PD46s ...my gut feeling is its running out of gas WOT.... How about the stock exhaust is there some kind of restriction in there.... thanks for all the help guys

Tracksnblades1 · « **Reply #23 on:** February 18, 2019, 05:59:01 PM »

Quote from: uksparky on February 18, 2019, 04:56:44 PM

Quote from: Tracksnblades1 on February 18, 2019, 02:04:18 PM
UK,
Did you get your timing and advance unit functioning like you want it..?
Have you tried fattening or leaning it up..?
I've never used the full choke momentary method for determining jetting.
I have slowly applied choke to see if a bog situation changes from bad to better or visa versa....
I'm glad you tried fourth gear to rule out long duration camshaft, and low RPMs...
👍
,,...

Yes i have the timing spot on now, plus advance... throttle sync, and idling nice and smooth ... as you know the mixture lean/rich screw is for idle only...the only way is to pull the needles and see if they are stock....if so raising them up a notch will also screw up the sync/mixture... i changed the level of the two outer carbs about 5mm but never had a chance to test, i dont think that will solve it.. plug chop will be my next thing....in the next few weeks... i sure dont like these PD46s ...my gut feeling is its running out of gas WOT.... How about the stock exhaust is there some kind of restriction in there.... thanks for all the help guys

Spark,
I don't have a cb550. The threaded jets in the round tops make it quicker and easier.
While reading your inference that the stock exhaust may be affecting the jetting, I would think the Norris long duration deep breathing cam would have a greater effect.
Without having knowledge of the factory 550 exhaust performance limits, I'm not sure a quality 4/1 will be of any great benefit barring peak power.
My Yoshimura pipe came with .120 larger primaries and no inner dual wall pipe.
I tend to believe, as other great tuners have published, the percentage of power gains from a good exhaust, to a great exhaust is marginal as compared to an intake side upgrade.
I like your incline grade A/F testing, i think it helps exaggerate shortcomings.
👍

Tracksnblades1 · « **Reply #24 on:** February 18, 2019, 10:53:02 PM »

Forgot to mention. Have you access to 100% gasoline. We have a few stations still selling it.
I have not done the math but have read E10 needs 4.5% more fuel to equal that perfect 14.7:1 stoichiometric. But E10 stoichiometic is around 14:1. And the 10% part ethanol carries near 30% more oxygen in it. E10 has 18,500 btu's per gallon. Straight unleaded gasoline 23,500 btu's per gallon to complicate it some more.
👍

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Author Topic: bogging down WOT... 78 550 (Read 6113 times)