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Discussion Starter · #1 ·
So last weekend I yanked off my carbs to give them a cleaning, and I noticed backfiring pops in one of my pipes when idling. Carbs are cleaned and mounted on the bike, and the air leak has been fixed, eliminating the popping at idle. Now that I was satisfied, I decided to take the bike out for a testride.

Problem 1:
Before I put the bike in 1st I gave the throttle a bit of gas and instead of hearing the rumble, I heard a strange noise like the bike was underpowered. I look at the carb slides, and they were jiggling up and down when I would roll on the throttle.

Problem 2:
In the CB450 carb synch guide, it specifies that if you have no air leaks and you get maximum RPM with the air screws all the way in, then the carbs need cleaning. I cleaned out the carbs and I have the same situation. What should I do?
 

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Discussion Starter · #2 ·
Background: Bike is a Honda CB360, carbs are the 5-speed Keihin 14H carbs from a CB450
Main Jet#150 Slow Jet#38
 

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I would suggest (first of all) that 150 is way too big for the motor - that's a big size for a 450, much less a 360.
You'd have to get some plug readings to make sure.
In that context, the low speed jets are also probably too big, that's what's going on with the "air" screws.
The needle on 450 carb is not adjustable, so all you have to work with is the two jets.....

What sort of air filters and mufflers??
 

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Discussion Starter · #4 ·
Ok so I had a keyster carb rebuild kit (yeah shitty quality I know) that had 130 jets in it. I put those in...no change. Idle/slow jets are #38. Should i be going up or down in size? I am running w/o air filters and EMGO dunstall pipes (essentially straight exhaust)

I think the needle is adjustable, since there is a "set"screw where you can move it up or down. Am I correct in saying that moving it up = lean, down = enrich?
 

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krukster86 said:
Ok so I had a keyster carb rebuild kit (yeah shitty quality I know) that had 130 jets in it. I put those in...no change. Idle/slow jets are #38. Should i be going up or down in size? I am running w/o air filters and EMGO dunstall pipes (essentially straight exhaust)

I think the needle is adjustable, since there is a "set"screw where you can move it up or down. Am I correct in saying that moving it up = lean, down = enrich?
The set screw just holds the needle to the slide. The tiny little circlip that would allow adjusting is buried in that nylon thing on the end of the needle.

Just as a start, "early" stock 450's had 130/135 and 38 in them.
I would guess that a substantial lowering of both numbers would be indicated.

What about the plugs, again??
Are they obviously "rich"????
 

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Discussion Starter · #6 ·
I promise I will get spark plug info sometime today, I have been really lazy in pulling them out even tho it is a real simple job :lol:

Anywho since my digicam took a nosedive and broke I have to do all my picture taking with my laptop's webcam, so sorry for the low quality...
I have been looking at this website, http://www.jetsrus.com/main_page.htm for purchasing individual jets, but based on the picture of the jets, I am not seeing the ones that I have:

Here is my #38 slow jet:


Here is the #150 main jet:

The main jet looks really weird, and the top looks like someone just took a file to and ground it down!

The #130 jet that came with the Keyster Carb rebuild kit looks like the ones shown below. I figure I should look for ones that match up this look rather than the mystery #150's
 

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Discussion Starter · #7 ·
Here are the plugs:


Looks like I am running rich
 

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krukster86 said:
Here are the plugs:

Looks like I am running rich
Yep, that's no surprise - assuming you have good compression, you probably need to jet smaller.

Unfortunately, finding smaller jets will be problematic, expecially the slow jet.
Maybe the guys here have sources for them, but I really don't.
There are probably sources out there somewhere.

If you know a machinist, you can always solder the old ones closed, then have the machinist drill them out with precision drills.
Not that complicated, a 100 jet has a 1mm hole, 85 has a 0.85mm hole, 135 is 1.35mm, etc......

Anyway, if your plug photos are from the 150 jets, try the 130's you have in hand - that's not going to address the low speed thing, but one step at a time.....
Clean the plugs first and take off on it - if it acts up at speed, try slipping in a little choke - if it runs better, that tells you it's too lean.
Then look at the plugs again.

I'm interested in how this turns out - could be a lifesaver for a lot of 360 guys with bad diaphragm carbs.
 

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Discussion Starter · #9 ·
OK so correct me if I am wrong:
Increase size of the Slow jet?
Decrease size of the Main jet?
 

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Discussion Starter · #10 ·
If I need to go smaller on the slow and main jets, I see that the Keyster carb kit for the CB360 has #100 main jet and #35 slow jet...in the same size/style as the ones that I have. If I need to go down in size I am wondering if I should splurge on those
http://cgi.ebay.com/ebaymotors/HONDA-CB ... 510005r527
 

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krukster86 said:
OK so correct me if I am wrong:
Increase size of the Slow jet?
Decrease size of the Main jet?
No, you'll most likely have to make both smaller - just work on higher rpm first - the slow speed jet is only in the equation for a small amount of riding situations.
We'll worry about that later......

Your plugs show incomplete combustion.
Again assuming you have good compression, which also causes incomplete combustion (as does bad timing), you need to go smaller.
That's no surprise, as the carbs are for a bigger engine.
 

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krukster86 said:
If I need to go smaller on the slow and main jets, I see that the Keyster carb kit for the CB360 has #100 main jet and #35 slow jet...in the same size/style as the ones that I have. If I need to go down in size I am wondering if I should splurge on those
http://cgi.ebay.com/ebaymotors/HONDA-CB ... 510005r527
You know, I'm not sure if the jets are the same or not.

I'll bet Steve knows.......

I think a drop to 100 might be a bit much - try the 130 first, best to be careful.
The 35 sounds good, if it will actually fit.
 

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Discussion Starter · #13 ·
OK so I put in the #130 main jets this afternoon and since it was raining outside, I messed around with the bike in the garage. I want to say that there was a slight improvement, but I already forgot the performance of the #150 jets from the other day :roll:
Anyway...Initial rolling on of the throttle to 1/8 seems to be ok and anything above that I am greeted with the same symptoms (sounds like surging, random backfiring, inconsistency), Keep going down in main jet size no?
 

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krukster86 said:
I don't have a compression tester :oops:

Then borrow one and do the test.
It's beginning to sound suspicious to me............
If your compression is low, you're just chasing your tail around.
 

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Discussion Starter · #18 ·
K will do...might be a while before ya hear back about this I am gonna be busy next couple weekends.
 

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Discussion Starter · #19 ·
Just wanted to post this:
"CB360 Carb Kit Jet Sizes:
Main jets are Keihin Large Rounds… about 8mm high and 8mm dia on the top and 4.8mm dia by the threads. The slow jets are about 21mm long 4 mm dia at the top, 3.3mm dia at the threads and 2mm dia at the bottom.
-Andrew"
 

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Discussion Starter · #20 ·
Picked up a compression tester and an impact driver today on my lunch break...my tool collection is growing, slowly but surely :D
 
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