Topic: Baffles removed Jet Size

[parm94]

I've got a 1976 CB550F with stock airbox and the stock 4 into 1 exhaust. I have replaced the muffler end with a hollow aftermarket muffler that has the baffles removed. 

Here's a picture, it's a Vintage Jardine muffler with baffles removed.


The stock jet sizing on here is 100 main and 38 pilot. I've read the guide on the forum regarding jet sizing and would like to confirm before I order.
http://forums.sohc4.net/index.php/topic,58112.msg628659.html#msg628659
My understanding is that the only change I'm making from the stock is removing the baffles which would mean open headers? Does having the hollow muffler mean open headers?

The guide suggests 2 jet size increases for open headers and then to subtract 1 size, giving me a total of 1 jet size increase. Further, the guide suggests to increase the pilot size by 1 for every 3 main jet size increases.

I plan on ordering from this site: http://jetsrus.com/a_jet_kit_street/honda_550_CB550F_1976.html

According to what's on there, I would need a 105 main jet which is 1 size increase and not be changing my pilot size?

[jonda500]

My advice would be:

 - go ahead and give it a try without changing anything

- take note of the throttle position where the problem is if it's not running right e.g. is it bogging down when you give it full throttle? is it hesitating when the throttle is only 1/4 open?

- next note down the number stamped in the carbs (should be 069A for this model), remove the carbs, take out the jets and note down the sizes (standard for this model is pilots #38, mains #98)

- if you have issues running between 1/4 and 3/4 throttle you will also need to pull out the needles and note down the clip position (2nd from the top or #2 is standard for this model) ps also note down the number stamped into the needles if any

- note down how many turns out from lightly screwed in the mixture screws are

Then post the results here along with some pictures if you can- ppl here love pictures!

   My personal experience - I have a '75 cb550F with cb500 carbs, stock four into one with straight through muffler, stock air filter missing the snorkel, carb settings -mixture screws 2 1/4 turns out; pilot jets #38; main jets #98; needle clip postitions #2 1/2(shim under each clip)
   With this setup it idles well and when cold runs great except breaks up when given full throttle- I have cured the full throttle problem! I tried running with the air filter removed and full throttle was no better, so I taped a little tupperware container upsidedown over the air filter leaving only a 2" diameter hole for it to breath through and hey presto she pulls hard under full throttle now. When warm she falters/splutters just off idle or when trying to maintain slow speeds(1/4 throttle).
   My hunch is that in my case I need smaller pilots (I have purchased #35's) and larger mains so I can remove my improvised air restriction (I have some #100's and #105's so I have this covered)

   I found the whole ripping the carbs in and out and resyncing countless times so frustrating I have had to take a year long break from it but I am psyching myself up for another bout............ 

[jonda500]

Also pull out the plugs and preferably post a picture

[parm94]

From top to bottom are plugs 1 to 4 which ran with the stock muffler and no airbox, just naked carbs . These were iridium and 3 are burned out.


My next setup is going to be stock airbox and baffles removed from the aftermarket muffler.

The PO had 100,38 and my rebuild kit also came with 100,38 (which was a CB550K kit) so the sizing is already a size above stock. I only replaced the jets.

The muffler with baffles removed will arrive next week, can I do the tests with no muffler on since the new one will be hollow anyhow? 
I'm going to be buying the cheaper plugs for the testing (NGK 7912) and see what happens without changing anything. I suppose afterwards if I need to re-jet you guys can help decide what route to go.

This site has cheaper jets but I'm not too sure about quality. http://4into1.com/carburetor-parts/?sort=featured&page=2

[jonda500]

Jets don't wear out- I just replace the o rings- the only reason I get new jets is if I need to change the size...

OEM jet sizes are accurately sized, whereas aftermarket ones not always!

Even without a baffle, adding a muffler to the 4 into 1 will change the mixture... edit- I know this because even screwing a three inch long steel pipe extension into the end of my straight through muffler had a dramatic effect- made it run bloody terrible and I couldn't wait to get back home and remove it! Also, years ago I had a 400-4 which I fitted with pods and a straight through muffler- when I went too far drilling out the main jets I found removing the muffler was a great temporary fix while I ordered new jets.

[parm94]

Rode around for half an hour with open headers no muffler, stock airbox on, 100,38 jets, fuel mixture screws at 1.5 and the plugs look like this:


They're black so mixture is rich? I suspect adding a hollow muffler won't change much and I'll need to rejet? To what? Other changes?
I've also got a carb sync tool but that will come last.

A Video:
https://vid.me/e/F2GG

[jonda500]

Unless you rode around for half an hour with the throttle wide open for that plug chop pic, which I am assuming you didn't, I would try raising the needle clips one notch (drop the needles down one position lower).

n.b. the main jet is normally sorted out first but you should be right in the ball park with the #100's IMO

[HondanutRider]

It's been mentioned/suggested several times before here that running with straight pipes or with a straight-through muffler would have the same results regarding jet size.  WRONG!  Any sort of exhaust extension, whether it be a pipe or muffler, can alter the flow characteristics of the exhaust (read: "fluid dynamics") and require a different jet size to maintain the proper mixture.  The mixture can also change with engine speed and/or the load.  Similarly the intake flow can alter this same characteristic, which means that altering the air filter can result in needing to change the jets in the carburetors as well.

Unless you are duplicating someone's results, expect a lot of experimentation in order to get it right.  Even then, there may be situations where it is impossible to "get it right" for all conditions.  BTW "getting it wrong" runs the risk of holed pistons!

[parm94]

The bike turned off after about a 30 min ride after which I turned around. I was under the impression I was running rich but perhaps this may not be the case? From left to right, plugs 1 to 3 are black but plug 4 is white. Before I adjust needles I'd like to have an idea of if I'm rich or lean according to this picture:



The main sizing is 1 size larger from 98 to 100 and it was running stock air box with open headers.

[flybox1]

when you post pictures of the plugs, we need to see down into the tips.   Side view is not enough info.
A plug chop does not mean 'ride around for a bit' and then see what color the pugs are.
This tells you nothing.
Your carbs are comprised of several fuel delivery systems.   Each system engages at different throttle positions.  The systems also overlap....depending on your throttle position.  Your spark plugs collect detonation deposits, and can give you an idea of what might be occurring inside your combustion chambers.
If you just ride around, you are collecting these deposits from many throttle positions, and many jet overlaps.
Your test needs to consist of a new.set of plugs, and 3-5minutes of a specific throttle position while the bike is under load, to collect deposits for that specific fuel delivery part(jet), so you know what change to make.

[HondanutRider]

Good points and great charts, Flybox!

Don't know anymore where this article came from, but it has some further explanation of the theory involved:

[flybox1]

Good points and great charts, Flybox!

Don't know anymore where this article came from, but it has some further explanation of the theory involved:

Good .doc Hondanutrider....i saved that one!

[jonda500]

Good points and great charts, Flybox!

Don't know anymore where this article came from, but it has some further explanation of the theory involved:

Good .doc Hondanutrider....i saved that one!

Me too   Awesome, I'm gonna read the #$%* out of that from go to woe!

[parm94]

Good points and great charts, Flybox!

Don't know anymore where this article came from, but it has some further explanation of the theory involved:

Very informative article Hondanut!

I'll have the pipe tomorrow so I'll likely be posting my plug chops here then. Should I sync the carbs before on an older set of plugs or will that not matter too much? (They are out of sync right now)

[Gooseman]

Yes, you should sync carbs after every-time you remove them/pull the bowls/rejet/etc. Especially if you're jet tuning.
How can you expect consistent plug chop results if the carbs aren't in sync?

List of other things that can effect carb reading that should all be verified before tuning carbs:

- Valve tappets adjusted, points serviced (gap and dwell set), timing set and advance checked and oiled
- new plugs, good wires
- Coils tested and showing good spark/full voltage at the coils/Charging system in good condition/Battery tested good.
- Exhaust gaskets & Intake manifold rubbers have no leaks.
- Compression tested (hot) and shown to be in spec.

Any of the above not being in proper order can cause ghost chasing in carb tuning.

[Trad]

Yes, you should sync carbs after every-time you remove them/pull the bowls/rejet/etc. Especially if you're jet tuning.
How can you expect consistent plug chop results if the carbs aren't in sync?

List of other things that can effect carb reading that should all be verified before tuning carbs:

- Valve tappets adjusted, points serviced (gap and dwell set), timing set and advance checked and oiled
- new plugs, good wires
- Coils tested and showing good spark/full voltage at the coils/Charging system in good condition/Battery tested good.
- Exhaust gaskets & Intake manifold rubbers have no leaks.
- Compression tested (hot) and shown to be in spec.

Any of the above not being in proper order can cause ghost chasing in carb tuning.

I'm going to have to disagree that you need to re-sync your carbs every time you remove them or change jetting. You typically are not touching the slide adjustment screws (Sync screws) for jetting, float height, removal, etc. Unless you are moving slides, taking carbs off of the rack, or doing anything related to that, another sync is not needed.

[parm94]

Okay, I finally got around to doing a chop. Full throttle through all the gears then kill. Jet sizing 105 , 38. 1 turn out. Stock airbox and aftermarket jardine muffler with baffles removed.

1



2



3



4



It's abnormal to see such variation so I suppose it could be misfiring due to poor spark or carbs not clean (I cleaned them thoroughly a month ago) or uneven compression in cylinders?

[Gooseman]

It's abnormal to see such variation so I suppose it could be misfiring due to poor spark or carbs not clean (I cleaned them thoroughly a month ago) or uneven compression in cylinders?

They definitely look lean to me, or just way too clean, especially #3 & #4.  #2 looks like its getting oil, possible blow-by?  Definitely need to do a compression test to see whats going on there.  Doubtful it's poor spark since the others all look so hot/clean.

I'm going to have to disagree that you need to re-sync your carbs every time you remove them or change jetting. You typically are not touching the slide adjustment screws (Sync screws) for jetting, float height, removal, etc. Unless you are moving slides, taking carbs off of the rack, or doing anything related to that, another sync is not needed.

While i agree there really shouldn't be much difference, and admitidly when I check mine after pulling bowls off, there's usually not difference, but i'm under the impression that something like the gasket seal being moved and sealing slightly differently than last time you had it on, can definitely make slight variations in static sync.

[flybox1]

inconclusive test...
I dont think you rode long enough to get good deposits.
you need to ride with OLD plugs, and get your engine to operating temps.
New plugs in.  Get your bike to WOT as quickly as you can, and stay there, uninterrupted, for at least 5 miles before you cut the power, preferably, on a section of road with a slight incline.  your engine needs to be under load.  Uphill is best.
You could even be in 3rd or 4th WOT just to be within speed limits.  Ive done all my WOT chops in 4th gear.

[parm94]

I tested the compression. 130 on all four cylinders. With oil added it was 140 135 135 135.

Should I test the coils after this before doing another chop? Where should I go from here?

[flybox1]

Plug chop.

[parm94]

So, I did the chop again and I didn't see deposits so I re did the chop on the same plugs and they still don't have very many deposits. I think it's really lean? I didn't run WOT for 5 miles because I think it's lean so from what I understand that could do damage plus I don't want to go that fast. There wasn't any blow by this time, last time the valve clearance caps were loose so I suppose that was why it happened.

Again, 105 Main 38 Pilot Air Box and Muffler with baffles removed.

They all have very fine little spots similar to this:



1


2


3


4

[seanbarney41]

Yes, you should sync carbs after every-time you remove them/pull the bowls/rejet/etc. Especially if you're jet tuning.
How can you expect consistent plug chop results if the carbs aren't in sync?

actualy, unless your carbs are grossly out of sync, like you did not even come close to bench syncing them when you put the carbs together, carb sync will have no noticeable effect on anything other than the smoothness of your idle

[seanbarney41]

yep...that's pretty lean...so lean that those little spots are actually bits of metal removed from your pistons/ring lands and fused to your spark plugs...keep going like that and time for new pistons, if not already...

[parm94]

yep...that's pretty lean...so lean that those little spots are actually bits of metal removed from your pistons/ring lands and fused to your spark plugs...keep going like that and time for new pistons, if not already...

And how should I go about fixing my lean issue? Increase pilots and mains? Needles?