Topic: bogging down WOT... 78 550

[uksparky]

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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Not here in California as far as i know.... anyone from Cali in the forum... the highest fuel oct is 91 thats why i was trying the oct booster .. when i had my Aprilia Tuono V4 i had a hard time keeping the front wheel on the ground using same fuel.... could it be different for the air cooled engine, it does get hotter.... oh and the brown rusty spark plugs it wiped off so easy

[sixthwisconsin]

The compression ratio for the cb550 is 9:1. It doesn't need high octane gas. What was the compression ratio for the Aprilia? Much higher I'm sure and required higher octane gas.

The CB's will run fine on 87 and the only reason I use 91 is because that's the only non ethanol gas I can find. Its available in 87 but not common around here and if I could find it close, I would use it. I still have to drive 23 miles to the next county west of me to get it. I ride my "tanker" Kawasaki Concours west and fill it up along with two 2.5 gal gas cans that fit into the side cases. Then I syphon gas out of the Concours and have a supply for the CB's.

[seanbarney41]

Guys, he already said high comp pistons and a cam, so 87 is gonna be a no no

[uksparky]

Pistons HC

[sixthwisconsin]

Ah yes!!

[dave500]

if your cam is stock the compression will be too high with those,the idea of high compression pistons is also to make up for the loss of dynamic compression you get using longer over lap or duration cams,youll have to retard your timing itll ping using the factory settings.

[Tracksnblades1]

if your cam is stock the compression will be too high with those,the idea of high compression pistons is also to make up for the loss of dynamic compression you get using longer over lap or duration cams,youll have to retard your timing itll ping using the factory settings.

Yeh, he posted a Kenny Harmon long duration cam. He listed all the goodies and what's  been done so far in his initial post.
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[dave500]

ok,how much more overlap etc?put the type one carbs on it.

[uksparky]

ok,how much more overlap etc?put the type one carbs on it.

All i saw  that was written on the inside of the ignition cover  Kenny Harmon DE Cam... valve clearance 5 thou .. i bought the bike not running condition, been sitting in garage for some time, it had just over 11,000 miles and was going to get chopped up to make it into a cafe bike    .... after cleaning the carb jets and running i noticed the common oil leaking from the head O rings......... at this point i decided to pull the engine and split the cases change the primary chain /crank seals etc... thats when i noticed the cam and pistons were not stock.... the guy i bought the 550 off was able to give me the name and contact number who he got it off.... he said in the 80s the bike was raced.... ..  with that compression  lol... Kenny Harmon made cams for motorcycles and cars in the 80s

[uksparky]

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.

I decided to replace the mains with replica Keihin SP60-0100  jet size 100..   It bogged down all through the throttle range, ....should i have removed the air filter snorkel ....so went back to the stock 90s and i was back to where it was before i changed them.. took a closer look at my throttle on the hill climb full throttle bog... 3/4 its ok, (thing is i dont notice this on the straight roads) anyway i gave it choke made no difference... so it could be the over rich condition with the KH Cam.... this is the only hill climb i have and there is just dirt and brush to pull over, a mile away i could pull over, but the bloody engine will be hot trying to pull 1 and 4 spark plugs...

[uksparky]

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?

Its the crap california additives the put in the gas here, my truck spark plugs look the same

[rupaulpierce]

Coils?


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[uksparky]

Coils?


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New coils last year, i had one fail, had to drive 22 miles on two cylinders lol.... its not spark problem feels like its running out of gas WOT or too much......been through the whole fuel thing... i have to do the plug chop... so funny though everyone will be pulling over thinking i need help...

[bryanj]

If it has the original PD carbs the pilots are notorious for bloking and they are horrible to get out as they are pressed in

[uksparky]

Yes on the pilots       but they are ok smooth idle...
I did something today, never mind the hill climb.... as i got on the freeway i gave it WOT in 5th gear, would not go past 5,500 rpm just bogged there.... pulling choke full on did not improve, made it a little worse...so on i go... now to the hill climb country road, bogging all the way to the top WOT...turning engine off and coasting to a clear spot pulled 1 and 4 spark plugs .. .. light tan color...not black rich  or white lean.
Now getting back on the freeway giving it hell through the gears pulling almost 10k each gear 1 2 and 3..... NO Problem With Power.. NO Bog... so i am lost what to do next, it has to be a carb problem..... but 

[DaveBarbier]

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.

That happened to me with my 550. What a relief it was to find that little thing in the bottom of the bowl.

[uksparky]

Main jet Dave... running stock 90s

Read this

The 78 550K has lean burn carbs.  In order to appease the EPA, the carbs were set for as lean an idle mixture as they could get away with.
When the throttle slides are suddenly opened, the vacuum depth in the carb throat reduces.  It is the vacuum that draws fuel through the carburetor jets.  Therefore, whacking open the throttle makes the mixture lean and the engine reduces power.
The 750 actually added an accelerator pump to the carbs during this era, that actually shoot raw gas into the carb throats when the the throttle is opened.
The 550 didn't get this accelerator pump for some reason.  Apparently they could leave the idle mix just over-rich enough to allow the throttle to open a "reasonable" amount and still get pickup within expectations.
The earlier 550 carbs were all set very rich at idle, and thus, have more tolerable behavior to throttle opening aggressiveness.

[TwoTired]

Two experiments you can perform.  Since partial choke didn't help.

1- pull off the filter box top cover.  To see if your top end power improves, or gets worse.

2- remove the air filter, as well, for a top end test.

Let us know how it goes.

Do you still have stock mufflers?   ... with no mouse nests in them?  Ha Ha.

Cheers,

[uksparky]

Two experiments you can perform.  Since partial choke didn't help.

1- pull off the filter box top cover.  To see if your top end power improves, or gets worse.

2- remove the air filter, as well, for a top end test.

Let us know how it goes.

Do you still have stock mufflers?   ... with no mouse nests in them?  Ha Ha.


Thanks TwoTired... i will try the air filter test, i remember few years back it had the foam air filter, and got the paper one seemed to run better with stock filter, but never tried WOT...Yes i still have the stock exhaust, maybe the little holes in the rear dont have enough to get the extra hp out... will try later next week...

Cheers,

[Deltarider]

... now to the hill climb country road, bogging all the way to the top WOT...

Check sparkplug gap is not too wide.

[uksparky]

Done that Delta.... i think i have done everything to sort this out  next run out i will pull the air filter/cover

[uksparky]

TwoTired... i could not wait i had to try it without the air filter and lid today sunny 78f... so here goes,,,.. lot more air box intake noise but the rpm was going up at full throttle on the straight much better...  up the hill i was at 6k pulling strong, easing off to 3/4 throttle it did feel smoother power... i could live with that but i need an air filter there of course ... Came back home and fitted the clean paper air filter/no lid.... bog was back again full throttle, wonder why the PO had a foam filter in there.... what could be going on with the carbs ?? the float bowl vent hose is clear not blocked, that was my first thought... i put the foam filter back with no lid, will test another day.

[TwoTired]

If the filter is making it too rich, then you have to reduce the mains and/or lower the slide needles.  What setting of the needles do you have now?

Have to ask, how old is that paper filter, how was it stored, and what brand?

Can you verify the mains weren't drilled?

Is the slide needle orifice still in the carb body?

Cheers,

[uksparky]

If the filter is making it too rich, then you have to reduce the mains and/or lower the slide needles.  What setting of the needles do you have now?

Have to ask, how old is that paper filter, how was it stored, and what brand?

Can you verify the mains weren't drilled?

Is the slide needle orifice still in the carb body?

Cheers,



Good question on the needle jets i will have to pull the tank and the top covers on the carbs to confirm, last time i was in there doing carb sync they were all still in carb body, i am sure they were in third notch down from top...  looked like all mains look stock no drill signs, the 100s i have were larger holes..... air filter is emigo its clear i can blow air through it

[DaveBarbier]

If the filter is making it too rich, then you have to reduce the mains and/or lower the slide needles.  What setting of the needles do you have now?

Have to ask, how old is that paper filter, how was it stored, and what brand?

Can you verify the mains weren't drilled?

Is the slide needle orifice still in the carb body?

Cheers,



Good question on the needle jets i will have to pull the tank and the top covers on the carbs to confirm, last time i was in there doing carb sync they were all still in carb body, i am sure they were in third notch down from top...  looked like all mains look stock no drill signs, the 100s i have were larger holes..... air filter is emigo its clear i can blow air through it

You can verify the jets with some sort of wire that’s the right thickness. 90 mains equals .90mm in diameter. I thought you said these were new jets? Could be mistaken. What brand jets?