Honda Twins banner

1 - 20 of 31 Posts

·
Registered
Joined
·
76 Posts
Discussion Starter · #1 · (Edited)
Good day everyone!

I am posting this because i am having a crap shoot trying to tune my carburetors. I am running stock air boxes and filters with a custom exhaust. The right side is running rich while the left is running pretty perfect. I had 155 main jets in both sides with #38 pilots but I am going to try putting a 150 in the right side to see if it balances out.
I am running with the Fuel/Air screw at 1/4 turn out from all the way in on both sides.

Also, I can't get it to go faster than 50 miles an hour without sputtering. The manual says this bike at one time went 120 but even before i tuned the carbs i could never get it to go faster than 70-75mph.

Has anyone ever had to run unbalanced carbs like this and why?

Thanks!
20170620_144013.jpg
 

·
Registered
Joined
·
13,085 Posts
Many factors could be in play, like a small difference in cylinder compression between the two sides or one carb not quite as clean as the other, probably others as well. How are you checking the level of richness?
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #3 ·
I am looking at spark plug color to check richness.
The right side insulator was black. The left side was white.
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #4 ·
So...I heard a rumor that the stock setup on a CB500T enging is #38 pilot and 145 main jets? Can anybody verify this?
Also, I'm thinking about installing different air filters. I heard their is a model of K&N that works well. Anybody know which ones?
 

·
Registered
Joined
·
526 Posts
As above, I'd start with compression check, valve clearances first. Try and get it running properly as is while it's basically stock before changing things over and messing things?
Have you pulled the carbs and cleaned everything yet, or just adjusting settings?
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #6 ·
I cleaned the carbs at the end of last season and did a full tune up which included timing and valve clearances.
 

·
Registered
Joined
·
4,458 Posts
Have you checked your ignition recently?
Are you sure you'r even getting sparks and consistently on right side?
Have you vacuum sync'd the carbs? If not then this is also a must do item on the list.
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #8 ·
Yes i did static ignition timing.
Whats the best way to check for spark?
I do not have the tool to vacuum sync the carbs nor do i know how to do it. Which tool do you recommend? They are bench synced though.
 

·
Registered
Joined
·
4,458 Posts
Take the right plug out but leave it connected to the spark plug wire. Hold it and rest the tip against the engine, turn on the ignition and press the start button. As the engine turns over watch for sparks from the plug.
Is it a strong spark or is it weak? Or is there any spark at all?

As for a vacuum sync, I'd use something like this

AlphaMoto Honda Vacuum Carburetor Synchronizer Carb Sync Gauge Cylinder Bike

Connect each to the carb's vacuum port and start up the bike. The idea is to adjust the carbs so that both will read, rise and fall the same.
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #12 ·
Spark was good. Thanks for the recommendation on the vacuum gage.
Here are some photos with two possibilities for the vacuum port...let me know if I am close.
20170624_115941 - Copy.jpg 20170624_115746 - Copy.jpg 20170624_115022 - Copy.jpg
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #13 ·
Sorry 76TWIN. Didnt see your photo till I replied.
Based on your photo, which looks a little different than mine, it looks like what my manual calls a plug screw is the vacuum port. It also appears to connect to 2 small holes in the throttle body. Does this sound right?
 

·
Registered
Joined
·
6,495 Posts
Semi-stupid question...where is the vacuum port on a Keihin 14H carb?
The red bike in the photo of your original post is not a 500T, it looks to be a CB450 K6 or K7.
There are no vacuum ports on a 14H carb.
14H carbs were stock on CB450 K1-K4, not on K5-7 or 500T.
If you do have 14H's on a 450, they usually have 130 or 135 main jets.
 

·
Registered
Joined
·
4,458 Posts
Yeah those are definitely not CB500T carbs for sure. Unfortunately the CB450 carbs do not have vacuum ports built in.
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #16 · (Edited)
You guys know your stuff (not that i ever doubted it). I blew the original 450 motor and swapped it with a 500T. These are the carbs that were on the bike when i bought it. I thought they were original, but according to tbtmusic these werent on a K7... So...there is no way to vacuum sync these carbs? Should i get new carbs?
 

·
Registered
Joined
·
76 Posts
Discussion Starter · #17 ·
What is the nipple for on the right side carb? I went and looked at my bike and there isn't one on the left from what I can see...
 

·
Registered
Joined
·
6,495 Posts
What is the nipple for on the right side carb? I went and looked at my bike and there isn't one on the left from what I can see...
It's not a vacuum port.
Some of us here have drilled and tapped for vacuum ports in our 450's - I put them in the aluminum intake, not in the rubber manifolds. It's a little hard to see in the photo because of the black engine, but it's the thing with the orange washer. Commonly called a "barb", plugged with a rubber cap when not in use - I forget where I got them (maybe MotionPro), but the rubber caps are very common parts with Jap auto engines.
A search here should yield some threads and photos of the topic.
The 14H's should work fine on a 500T (better than the original 500T carbs in fact), but 130/135 might not be big enough for the increased displacement of a 500 engine. Drop to 140/145 and see how it runs and what the plug color looks like. Then work with it to get the right size figured out.
14H carbs are very tolerant of exhaust and air cleaner mods, so I don't think that will affect you as long as they're not too radical........
 

Attachments

·
Registered
Joined
·
76 Posts
Discussion Starter · #19 · (Edited)
Thanks for the great picture!
I did a search for vacuum port install and these are the things I came up with:
TwinMax Synchronizer Adapter :: Aerostich Motorcycle Jackets, Suits, Clothing, & Gear
TwinMax Synchronizer :: Aerostich Motorcycle Jackets, Suits, Clothing, & Gear
https://www.motionpro.com/product/08-0218

Will that synchronizer work better than the one suggested in the previous post?
http://www.ebay.com/itm/382126876557?rmvSB=true
Anyone know if advance or autozone sells one that will work?
I am running unbalanced main jets right now. I think i will drop down to 145 on both because i heard somewhere that that was the original jet size on the 500T? I'll also put in new plugs.

I am a little hesitant to start drilling holes in my intake manifold...but I am always up for a challenge...
Also, another noob question...when I actually have a vacuum port, which screws/settings do i tweak to balance the vacuum?

Thanks!
 
1 - 20 of 31 Posts
Top