Topic: bogging down WOT... 78 550

[uksparky]

Ok checked the needles  looking from the top third groove down stock setting....all in place, the main jets in the carbs are 90s and look stock the last time i was in there....i remember putting them along side the 100s and the 90s were smaller dia holes... ...
But i have one question guys as we know when doing the carb sync the adjustment on the screw and locknut raising and lowering the needle body to get correct settings.......... is there a stock setting to where the needle body should be... could they be set too high.... i did a carb sync a few months ago. Pulled the jet # E23491..when pushing down on needle body it drops a few mm and springs back a few mm

[TwoTired]

I've never used an Emgo filter.  But, I suppose it is possible that it is more restrictive and causing deeper carb throat vacuum than the stock Honda one.  And, we have had some unverified but negative reports about their products.  Consider trying one from Honda, as it is a lot easier to swap filters than it is to retune your carbs to a filter.

The stock PD46 carbs have no slide adjuster on #2 carb.  So, it is very unlikely you have any option of putting the slides in the wrong place during a carb sync.

Also, it won't matter about slide needle position if the carbs don't have the slide needle orifice jet properly placed in the carb body.  This is what the slide needles dip into in their travel, to vary fuel flow.  It's really going to run like crap without them anywhere outside of idle throttle position.  If you do have them in the carb bodies, check for wear or alterations.

Cheers,

[uksparky]

I know #2 is non adjustable but pushing down on 2 i only get 1 mm movement...pushing down on 1 3 4  i am getting about 3 mm downward movement, would that be enough to rich mixture too much at WOT...... should i ignore that, or set them the same as #2.... or am i making more work for myself...and making things worse...like screwing the sync up... the  air filter i can blow and suck through it no blockages.
I know the PD46s are a pain in the arse to set up idle, the engine has to be hot, to adjust idle speed, its a balance between the pilot jet and main jet, to much idle and it will stay at  3k when shutting off throttle, moving the thumbscrew a few mm brings it down to proper idle around 1200.. thats why i mentioned the above....

[DaveBarbier]

I know #2 is non adjustable but pushing down on 2 i only get 1 mm movement...pushing down on 1 3 4  i am getting about 3 mm downward movement, would that be enough to rich mixture too much at WOT...... should i ignore that, or set them the same as #2.... or am i making more work for myself...and making things worse...like screwing the sync up... the  air filter i can blow and suck through it no blockages.
I know the PD46s are a pain in the arse to set up idle, the engine has to be hot, to adjust idle speed, its a balance between the pilot jet and main jet, to much idle and it will stay at  3k when shutting off throttle, moving the thumbscrew a few mm brings it down to proper idle around 1200.. thats why i mentioned the above....

I wouldn’t rely on pushing down the slides as indication of needing a sync. Just throw some sync gauges on there if you’re questioning it. But I don’t see how slight out of sync carbs would do anything for making the bike more rich or lean. You can bench sync with a 1/16” or 1/8” drill bit, setting the #2 there first with the idle adjustment screw, then the rest from there.

Do you know the brand of main jets? You said you thought the jets were the ones that came with the bike, but are you sure? Have you measured the jet hole? Did you verify the jet needle seat is installed properly like TT mentioned? I had drilled OEM pilot jets a while back and it through me for a loop for a couple weeks until I actually measured them.

I remember my ‘78 550 with PD46C carbs wasn’t temperamental at all regarding idle. You always have to set idle when the bike is fully warmed up, no matter the bike. 

[uksparky]

Dave....you said..... I wouldn’t rely on pushing down the slides as indication of needing a sync.... I am not pushing down because of needing a sync.....i am trying to fix the WOT problem... I just want to get them all aligned like #2 slide .... then start all over setting idle, and starting with 2 turns out on mixture screws... then re sync if needed.......thanks guys for the help...

I set the slides to all the same height  4 and 1 were  4mm higher .....update to follow

[uksparky]

Carbtune tool this morning, got engine hot, and using fan... re set the sync at around 1200 rpm all good and level..... holding it at 3,000.... 1 and 2 cylinders were about 1.5 inches higher than 3 and 4  ..  engine runs smooth and revs ok....    could this be my problem at WOT ...
Update later on ...fitting top covers on carbs and sync again changed things.. in picture 3,000rpm ..going over it the jet body was sitting higher on 1.3.4 before i started.... my thought was could that few mm higher cause over rich, now i know each venturi is getting the same amount of air..

[TwoTired]

....    could this be my problem at WOT ...

seems unlikely

[uksparky]

Yeah scratching my head on this one T T       your prob right... rain coming in for the next two days ... what rain in Cali this time of year      ...so no test run until weekend....  my mind keeps going back to the bowl venting?..... no filter more air coming in, almost bogging gone WOT..... filter in bogging WOT..
If the foam filter works better i will leave it at that as i am lost for ideas.... plus i ain't taking the 550 to the race track lol

[TwoTired]

Still waiting for verification of the slide needle jet....

[uksparky]

Still waiting for verification of the slide needle jet....

Good point there TT...  i will pull all the slides and needle jets today and post pictures with update ..   just in case one of the POs rubbed the taper of the jets down....long shot but worth checking..

[TwoTired]

Unlike the earlier model carbs, PD carbs don't have the needle jets incorporated into the emusion tubes.  The jets can be left out of the assembly entirely, making the slide needles ineffective at metering fuel.  The main jet would be the only orifice to limit fuel delivery over 1/4 to WOT throttle position.   The symptoms fit the crime...

Cheers,

[uksparky]

Here is picture of jets, some wear on 3 and four tubes, jets look ok....... if 100 jets make it worse what jet lower than 90 would you recommend

[DaveBarbier]

There are no jets in that picture. Just slides and needles.

What TT is talking about is the little brass needle seat that you can see if you look in the mouth of the carb. What the needle passes through as it moves up and down.

[uksparky]

There are no jets in that picture. Just slides and needles.

What TT is talking about is the little brass needle seat that you can see if you look in the mouth of the carb. What the needle passes through as it moves up and down.

Oh Dave i worded it wrong  slides and needles....  now i know what your talking about the brass insert above  emulsion tube assy .. so what am i looking for there oblong holes.... they are  O  all four

[DaveBarbier]

Haha, no problem. I’ll leave that to TT but I haven’t heard of them coming loose. That one is definitely present.

[uksparky]

Haha, no problem. I’ll leave that to TT but I haven’t heard of them coming loose. That one is definitely present.

Yes they are all in place and none lower

[TwoTired]

Those are some ugly slides.  Consider finding replacements for those damaged ones.  Were they media blasted?

Are the needles stamped E2349F?  (stock specification)

Are the emulsion tubes between main and needle jet clean and clear?

If you place a needle into the needle jet and shine light from the opposite side, does it fit closely where it is fattest?  Is the jet still round?

Glad to see the slide needle jets are at least present.

Do you have digital caliper to measure the needles?  Do you have a numbered drill set to determine the needle jet size?

The main jet isn't dominant until after 3/4 throttle position.   If you match throttle to the speed that you can't exceed what throttle position is it at?  Have you marked your throttle yet?

Cheers,

[uksparky]

Those are some ugly slides.  Consider finding replacements for those damaged ones.  Were they media blasted?.... looks like someone blasted #3 and part of 4.. stopped, but did the whole outside of the carbs as they are clean for  40 year old carbs

Are the needles stamped E2349F?  (stock specification)   Yes all the same...

Are the emulsion tubes between main and needle jet clean and clear? ..  Yes i had them off for idle jet cleaning few months back

If you place a needle into the needle jet and shine light from the opposite side, does it fit closely where it is fattest?  Is the jet still round?.... Carbs are still on the engine so thats a no to the light ..yes still round no taper

Glad to see the slide needle jets are at least present... yes

Do you have digital caliper to measure the needles?  Do you have a numbered drill set to determine the needle jet size?  .. No

The main jet isn't dominant until after 3/4 throttle position.   If you match throttle to the speed that you can't exceed what throttle position is it at?  Have you marked your throttle yet?..... Yes marked  one inch from  WOT ...   looks like the last half inch of travel at the carburetor slide...to WOT

Cheers,

[uksparky]

Dam i am getting close to solving this       setting idle mixture screws 1.5 turns out better idle...  .... how important is it to have the little rubber washers in the idle mixture screws, they were all broken plus two small washers were missing..
Here we go on the freeway testing flat road.. 4th gear winding to WOT... getting little stumble/bog around  5k... as soon as it reached 6k it took off full power to red line.... rich or lean... i would say rich, tried this a few times through lower gears same results... could it be something else, i do have electronic ignition, dont think its spark related and not advance...i had the paper air filter in with lid.. after ten 70mph mile run...pulled spark plugs after cool down... not lean but darker brown color... float bowl height levels are up to the bowl gasket using clear tube method...is that correct for the PD46... or too high...causing over rich cond

[uksparky]

I decided to pull the float bowls on the engine and check the float heights.... forgetting the clear tube method... 1 and 4 were 14 mm ...2 and 3 were about 19 mm sorted that out... now the idle jets.. two were about 25% blocked.... main jet and emulsion tube were clean.... left mixture screws 1.5 out... i am getting good at doing this without pulling carbs....
Now the test.. rolling on to half throttle from 5th starting about 30 mph, pulled strong... powering through the gears full throttle......1st 2nd 3rd 4th not as bad stumble at 5k ....getting through to 6k it pulled all the way past red line. (of course normal driving i would not need full throttle, or drive like this) Came back home and did carb sync just needed adjustment on 1
I think the problem is the KH DE Cam this is a race cam and i know most cams like this need higher rpms to perform.... plus the crap PD46 lean burn carbs....so i will leave it at that and let the engine cool down after a thrashing lol.... Hill climbing i have to get the rpm past 6k lower gears..... if i am in racing mood...

[BRG-BIRD]

Something you could do is try a thin shim for the needle under the e-clip, raising the needle and splitting the difference from one needle setting to the other. It isn’t quite the right fix but it may help you decide what to do with the carb setting if any. You know the main jet is proper since it pulls so well at WOT. I might have 4 shims to send you to try if you want.

[uksparky]

Something you could do is try a thin shim for the needle under the e-clip, raising the needle and splitting the difference from one needle setting to the other. It isn’t quite the right fix but it may help you decide what to do with the carb setting if any. You know the main jet is proper since it pulls so well at WOT. I might have 4 shims to send you to try if you want.

Thanks for the offer but i will leave it the way it is for now....

[uksparky]

Well i decided to have another go at this, i only ride weekends so i thought it was time, been sorting it for past five days... i decided to play around with the needle jet, it was on the stock third slot from the top, put it on the bottom full rich, each time i change the clip spot i did carb sync and mixture adjustment ...way too rich mid range did nothing with the bogging wot... next day moved up to 4th slot better mid range but had surge through throttle range. Decided to go with the second slot from the top of needle, much better power through throttle range, ...happy so far... if i linger on a grade on freeway at 5k.. fifth gear thats about 65 mph stock sprockets, now go wot, it feels like surge and bog all the way to the top about 60 mph, that was two miles... other road tests if i rev past the 5k then go to 6k and up its ok... in other words i pull on straight road it will rev past the 5k problem spot in any gear, say 4th it will rev all the way to red line and not a glitch... after the grade climb i pulled over and pulled 1 and 4 spark plugs, they looked ok not rich or lean, the sunlight made plug tip bit lighter.... ten mile run home 65 mph pulled same plug and it was same condition..  Costco California premium gas 91 octane ...before i set off i sprayed all around the carbs hoping for vac leak...nothing.  adjusting idle rpm seemed to take a while until it settled down, idle hot about 1,300.. Next fill up i will use middle grade gas and see the plug condition, i think it could be running a little rich, because the plug tip should be a lot lighter color higher rpm... then again we are in the summer blend gas here in C/A $3.75 a gall, with all the additives to stop pollution .... After reading the posts again, there is one thing i did not do that was mentioned.. measuring the lower brass part that's pressed into the carb body  where the needle slides, i will run it for a while longer, next time i have the needle out i will measure the fattest part of the needle.... further tests leaving needle second clip ..idle mixture two turns out, fill up with mid grade 89 oct... pulls great through throttle range and through the lag range up to red line, did notice a little pinging through low speed pulls low to mid throttle, later on try 95 main jet