Question about jets sizes - Honda Rebel Forum
 
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post #1 of 7 Old 03-04-2019, 07:25 PM Thread Starter
 
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Question about jets sizes

I have a modified air intake. It is a filter intake, and I was wondering what do I have to do to the bike so it can be compatible with the filter? Do I get bigger jets? If I do, what sizes? Do I mess with the fuel/air screw?

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post #2 of 7 Old 03-06-2019, 07:00 AM
 
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Not much information there. What year and size bike. What kind of intake (they all have filters) Do you still have a stock exhaust? Got a picture of your setup?
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post #3 of 7 Old 03-06-2019, 10:27 AM Thread Starter
 
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(they all have filters) Do you still have a stock exhaust? Got a picture of your setup?
hahah of course Bike is an 85, 250. Yes on exhaust. At the moment I can just put a picture of what kind of filter it is but a cone with a BIT of extra tubing between it and the carb
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post #4 of 7 Old 03-06-2019, 12:53 PM
 
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Ok. It's a K&N or K&N copy. I would suggest a foam UNI filter, since they filter a lot better, but I'm assuming you're going for looks. Yes, you will likely have to go up one size on both the main and pilot jets, and turn the pilot air screw out a bit more. Without an emissions analyzer, the only real way to check it is by the way it runs and by the color of the spark plug insulators. Put 2 new plugs in it, and run it with stock jetting first. put 100-200 or so miles on it, city and highway riding. Pull the plugs and check them. If they are a dark tan, you are ok. If they are a light tan, you are too lean, but not in the danger zone. If they are white, you definitely need to richen up the jetting ASAP. Go up one size at the time until you get a dark tan color, putting new plugs in it every time. Don't throw away any of the plugs, they are all still good, and can be used as long as any new plug, once you get the jetting right.

I would advise not trying to run straight pipes with that filter. That would create more air flow that the carburetor can be tuned for. You can put home made baffles in straight pipes that will help create back pressure, bu8t if you decide to use aftermarket mufflers, I suggest the Emgo shorty ones like BCB sells.
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post #5 of 7 Old 03-06-2019, 01:42 PM
 
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You may do fine with original jets as 85 came with larger #135 main..
85-87 has a 25.2mm throttle bore.. book states 86-87 came with #128 main jet, which is what my bike has...

2nd Gen has a slightly larger 26mm throttle bore and smaller #108 main jet..
All designed to provide lower carbon emissions..

comparison of 1st and 2nd gen carburetor specs as published in oem shop manuals..

I'll agree with @JerryH read your plug color and adjust if needed..
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post #6 of 7 Old 03-08-2019, 03:57 PM Thread Starter
 
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Originally Posted by JerryH View Post
Ok. but I'm assuming you're going for looks.
Well it's actually how I got it from the PO, and mostly how the PO got it from the PO. Needed some work but other than that it came that way.

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post #7 of 7 Old 03-11-2019, 08:30 AM
 
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No you don't have to change the slow/idle jet. When the throttle plate is closed, the free-ness of air flow in the filter is irrelevant, and the slow jet siphons fuel based on the trickle of air around/past the throttle plate.

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HRF Answer #1 You should take the MSF Rider Course
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