Author Topic: 1975 CB550f stock carb jets  (Read 2456 times)

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Offline ceebass68

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1975 CB550f stock carb jets
« on: December 28, 2016, 06:42:13 AM »
Hey Guys,

Happy Holidays! Unseasonably warm in VA (almost 70 yesterday). Spending a little time on 2 wheels while I can. Making it hard to focus on my cb project...

As I work to focus... Looking for some insight on carb jetting. I know this has been covered a few times here but, 1 piece of info I can't seem to locate... STOCK jet sizes for my 1975 CB550f.

I ordered rebuild kits off 4into1.com (they are great btw). The kits came with a 98 main and 38 pilot. This is also what I took out of the carbs. Ok so, I should leave it at that right? BUT, I'm confused... Their kit (and the svc man I have) says the cb550k model comes with a 100/40 combination. Higher #, larger orifice right?

Why would the supersport (f) model have smaller jets than the standard (K) model?? Could that be right?

2nd question:
I am confused on the rejetting. Where is my baseline? Zander's nice recommendation chart suggests 2 mainjet sizes up for 4into1 exhaust. Since this bike came stock that way, do I count that..?

I am installing a Uni foam filter in stock airbox and looking at buying the Delkevic 4 into 1 megaphone (unless someone talks me out of that). By looking at Zander's rejet recommendations, 2 mainjet up (4into1 exhaust) - 1 mainjet up for Uni filter then subtract 1.

I should go from 98 to 105 then? (Sizes appear to go 98,100,105) Pilot jet suggestion is 1 size for every 3 main jet increases. Do I upsize from 38 to 40?

Thanks for any help! You guys are great with the advice and I appreciate it!!
1975 CB550F (long term project)
1976 CB750F (short term project)
1976 CB750A (future project)
2006 VTX1800C (primary rider)
1995 VN800a (son)
2001 VN1500LC (highly modified - for sale)
Lots of others now gone

Offline Deltarider

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Re: 1975 CB550f stock carb jets
« Reply #1 on: December 28, 2016, 06:58:32 AM »
Quote
The kits came with a 98 main and 38 pilot. This is also what I took out of the carbs. Ok so, I should leave it at that right? BUT, I'm confused... Their kit (and the svc man I have) says the cb550k model comes with a 100/40 combination. Higher #, larger orifice right?
Why would the supersport (f) model have smaller jets than the standard (K) model?? Could that be right?
 
Yes, it's because of the different exhaust. If you've ordered imitation parts you might as well leave them in their packages, clean and the replace the originals.
Quote
I am confused on the rejetting. Where is my baseline? Zander's nice recommendation chart suggests 2 mainjet sizes up for 4into1 exhaust. Since this bike came stock that way, do I count that..?
Hard to say, but I remember the days that all aftermarket 4-1 manufacturers communicated in their ads that no rejetting was required.
Quote
I am installing a Uni foam filter in stock airbox and looking at buying the Delkevic 4 into 1 megaphone (unless someone talks me out of that). By looking at Zander's rejet recommendations, 2 mainjet up (4into1 exhaust) - 1 mainjet up for Uni filter then subtract 1.
Why so many turn to an inferior foam filter remains a mystery to me*. The genuine Honda airfilters (also for your model) are widely available, they filter best and in fact become better in process up to the very end of their lifespan.
Quote
I should go from 98 to 105 then? (Sizes appear to go 98,100,105) Pilot jet suggestion is 1 size for every 3 main jet increases. Do I upsize from 38 to 40?
Why bother? Buy the genuine Honda filter. You'll have it in within ten seconds and that includes raising the seat, removing the tooltray, etc.
On second thought... now, if you've bought already inferior Keyster carb parts and you're going to buy an inferior foam filter, why not complete it by ordering inferior Daiichi breakerpoints and turn a good bike into a rotten one (like so many did before you) but he, he, he... you will have saved a buck.  ;D
* You may read this for some more info on filtering and filters. http://forums.sohc4.net/index.php?topic=98901.msg1102737#msg1102737
« Last Edit: December 28, 2016, 07:33:09 AM by Deltarider »
CB500K2-ED Excel black
"There is enough for everyone's need but not enough for anybody's greed."

Offline Stev-o

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Re: 1975 CB550f stock carb jets
« Reply #2 on: December 28, 2016, 07:17:49 AM »
FYI - I have a 550F and had a hard time tuning it last year.  The PO used aftermarket carb kits and the bike ran bad.  I could not find genuine parts but was lucky enough to get a used carb rack from a buddy with all original parts in it.
Changed out the rack and the bike ran great - it was like night and day.

BTW - I have the stock airbox and would not consider taking it off and changing to another filter system.
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline ceebass68

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Re: 1975 CB550f stock carb jets
« Reply #3 on: December 28, 2016, 07:42:16 AM »
Ok, wow. Keep in mind that I'm learning here. I do appreciate the educated advice. Note that the more I read, the more confusing it can become.

I hear you about the aftermarket parts but the old ones were not in great shape. Is there NOTHING from the new kit you'd use then? O-rings, gaskets float needle...nothing?

I could probably swap o-rings on the main jet and reuse. The pilot jets are ok except completely blocked up.

Delkevic exhaust DOES say no rejetting required. Wasn't sure to trust that? (The reputable folks that sold me the carb rebuild kits said they'll work fine). Again, more info I get, the more confusing it can be.

I read the old post listed about air filtration. Appears that some like k&n, some like paper.

Bike isn't running yet but close. Trying to do the research so I don't have to keep taking carbs off and making changes.

1975 CB550F (long term project)
1976 CB750F (short term project)
1976 CB750A (future project)
2006 VTX1800C (primary rider)
1995 VN800a (son)
2001 VN1500LC (highly modified - for sale)
Lots of others now gone

Offline Deltarider

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Re: 1975 CB550f stock carb jets
« Reply #4 on: December 28, 2016, 07:52:51 AM »
Quote
I hear you about the aftermarket parts but the old ones were not in great shape. Is there NOTHING from the new kit you'd use then? O-rings, gaskets float needle...nothing?
I assume the O-rings and gaskets will be OK to use. The point is that the brassware inside the carbs hardly wears if at all. No wonder; not that much gas passes when there are 4 carbs for just a 550cc engine. Maybe the jets are OK to use, but I've read complaints here about the needles.
Inspect the little O-rings on the main jets. It's a must they seal well.
I wrote something on getting the needle jets out for cleaning, the easy way. The search function here is down so give me some time.
Ah, here it is.
 For who is interested, below you'll find the directions for a complete inspection.
1. Unscrew the 4 floatbowl screws (later to be replaced by same size allen screws)
2. Pull floatbowl carefully downwards in a straight line. If you number the floatbowls 1,2,3 and 4, you can use them as containers for all the brass parts of that particular carb.
3. Remove springleaf
4. remove float by carefully(!) extracting it's swingpin. Do not exercise force. Some manage to break their whatever it is called (towers?). If the swingpin is hard to extract, spray some WD-40. Caution: whilst removing the float, have your free hand cupped under it to collect the tiny floatneedle that will fall down. Don't loose it! They are expensive.
5. Pull the main jet using your thumb and finger. Some wiggling does it.
6. After removing the main jets twist the throttle wide open in order to raise the slides and with them the needles. Now with your free hand insert from below a match or wooden toothpick into the needle jets (aka emulsion tubes). When that is snug in the needle jet, cant or turn the wooden toothpick a mm or so and you can wiggle the emulsion tube out easily. Some WD-40 at forehand can help. Essential in this procedure is that you open the throttle to have the needles raised. BTW, sometimes the needle jets just drop by themselves after the main jet is removed, so start with your hand cupped under it.
7. Use a small screwdriver 'slid in sideways (horizontally)' to unscrew the slow jet. Think first and make sure you turn it in the right direction. Gently!
8. All parts go in 1,2,3,4, numbered floatbowls or little containers
9. Now all parts can be inspected and cleaned. Don't forget to carefully inspect the tiny O-rings that seal the main jets.
10. The airscrews (in the sides of the carbs) can be removed at all times. Caution: do not loose the little spring under them. On these carbs they don't have tiny O-rings.
11. Back to the carbbodies. Use a can carbcleaner with a straw and spray from below the carbbodies upwards in all it's orifices. Don't forget the openings where the airscrews sat.
12. Install in reverse order. Do not overtighten the slow jets!
13. Install floatbowl using new little allen screws instead of the old dreadful crosshead screws. Much easier for future removals.

You need to be at ease and well concentrated. Don't hurry. On a CB500 carb #1 and #2 are a bit harder due to the presence of the clutchcable. Make it a Zen exercise (that's how Soichiro designed motorcycles, with Zen). I can do it blindfolded and after the first time so can you.
This method can be exercised with 022A, 069A, 087A, 627B, 649A carbs

« Last Edit: December 28, 2016, 08:08:00 AM by Deltarider »
CB500K2-ED Excel black
"There is enough for everyone's need but not enough for anybody's greed."

Offline Stev-o

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Re: 1975 CB550f stock carb jets
« Reply #5 on: December 28, 2016, 08:00:56 AM »
Let's make it simple:  dont use aftermarket brass parts!

orings and gaskets should be fine.
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline ceebass68

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Re: 1975 CB550f stock carb jets
« Reply #6 on: December 28, 2016, 08:16:02 AM »
Ok, gonna take your advice and try my best to clean up and use the original brass. I'll see how that goes.

The original air filter was chewed up like some mice got in there at some point. Only reason I replaced. Guess I should reboot on the Uni-foam...

Thanks
1975 CB550F (long term project)
1976 CB750F (short term project)
1976 CB750A (future project)
2006 VTX1800C (primary rider)
1995 VN800a (son)
2001 VN1500LC (highly modified - for sale)
Lots of others now gone

Offline Stev-o

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  • Really Old Timer ...
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  • Posts: 34,432
  • Central Texas
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline ceebass68

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Re: 1975 CB550f stock carb jets
« Reply #8 on: December 28, 2016, 08:58:47 AM »
Get yourself a new air filter...

http://www.ebay.com/sch/i.html?_odkw=cb550F+air+filter&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xcb550F+air+filter+uni.TRS0&_nkw=cb550F+air+filter+uni&_sacat=0

I do appreciate the advice but, this link directs me to a bunch of foam filters. Are you suggesting that's ok vs paper? Back to my original post, the Uni filter is what I have purchased and was planning to use until directed otherwise in this thread...

1975 CB550F (long term project)
1976 CB750F (short term project)
1976 CB750A (future project)
2006 VTX1800C (primary rider)
1995 VN800a (son)
2001 VN1500LC (highly modified - for sale)
Lots of others now gone

Offline flatlander

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Re: 1975 CB550f stock carb jets
« Reply #9 on: December 28, 2016, 09:05:08 AM »
i tested one of those uni foam filters against a regular, OEM paper filter on the dyno. the OEM filter flows better and produces more power.
the only advantage i see with the foam filter is that you clean and re-oil it instead of replacing it. then again, the paper filters are cheap enough.