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Can't get her over 45 mph after carb rebuild
Hello to all,
So I don't know if this should go in the Carb or performance forum. Here's the deal. I did a rebuild of the carbs using Randakk's kit. "Liberty" is an 84' Aspy with 78,000. The reason for the rebuild was the fact that the wife complained of the stink and Liberty was shooting out alot of carbon on exceleration with a wopping 29 mpg however, she did have some getup and go. I used the Haynes work shop manual and the Honda 1200 Carburetor repair guide by Howard (also purchased from Randakks). During the cleaning process, I followed the instructions to the letter, cleaning one carb at a time so as not to get any parts mixed up and to use the assembled dirty carb as a reference. I used the boiling method with distilled water and some use of brake parts cleaner. I also used an piece of E-string from my son's guitar to push through the jets to make sure they were clear, q-tips and a rag to clean surfaces on the inside and out, and my air compressor to blow carbs dry and blow anything that was stuck in a port or jet hole. The kit was awesome by the way. I had no leftover parts once rebuilt. I replaced all fuel and vaccum lines. The fuel filter was replaced with Randakk's high perfomance filter.

After installation on the bike I did a compression test with the following results: Cylinder #1@175 psi, #2@165, #3@175, and #4@160. I don't know what they were before teardown. I didn't think to do a compression test. I have my idle speed set between 1000 and 1050 rpm when in neutral on center stand. I had a devil of a time getting syncronized, it's not perfect but pretty dang close. I put the plastics back on and went out for a test ride. Here are the results of the test ride: Stalled in 1st gear, wasn't a problem before. I had to give a good twist on the trottle to get her up and moving. Before rebuild I could get up to atleast 30 before I had to shift to 2nd. Throttle was full and I was bearly getting 15mph. I shifted up to 2nd and she wanted to quit on me around 25 mph, throttle was full open, I shifted to 3rd only got up to 35 mph, eventually I got up to 45 mph but I thought I was going to have to get off and push to keep it at 45 mph I didn't pay attention to the rpms. Before rebuild I could get up to atleast 50 with rpms around 3k in 3rd gear. So there you have it gentlemen and ladies, if there are any out there. Does anyone have a clue of where I screwed up. I know it's gotta be something that I missed. Liberty has been good to me since I bought her over a year ago.
- Sean.
#1 07-30-2012, 03:06 PM,
Check all of your CV slides to be certain that the rubber diagphram is installed correctly in each carb and have no leaks and make certain that the slides can move freely with not sticking or resistance at all. You didn't mention black or brown smoke but if there is any the floats might be set wrong and causing a flooding condition. Also, are the throttle valves opening fully when you twist the throttle wide open? If not then maybe it's a linkage or cable problem. You'll need to do some inspecting and then maybe we can help you more from there.
Ed (Vic) Belanger - 1954-2015
Founder of

#2 07-30-2012, 06:44 PM,
Thank you,
Unfortunately I will not be able to work on the bike again until Wednessday. I will follow your recomendations. I know I should tackle one issue at a time, but, do you think my compression readings would have anything to do with the problem. I'm concerned with the low readings for carbs 2 & 4.
#3 07-30-2012, 09:36 PM,
Your readings are higher than mine were after rebuild.. And I'm having no issues (not with compression, still waiting on my fuel pump)
Vegetarian: Old Indian word for Bad Hunter

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#4 07-30-2012, 10:08 PM,
Fresh air filter and plugs to go along with those fresh carbs? Have a look at the choke cable and verify its adjustment. However, I agree with Vic. More than likely the carbs will have to back out to look everything over as he mentioned. The tell-tale sign is that you said the carbs were very difficult to synchronize.
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'96 ST1100
Brewerton, NY
#5 07-31-2012, 02:04 AM,
As Vic mentioned, the throttle needles need to float up and down in synch for the engine to operate correctly. If you took the top of the carburetors apart, you undoubtedly saw these diaphragms attached to the throttle needles. What causes them to raise is a difference of air pressure, the air passing through the carburetor and the air trapped in the top of the carburetor. What causes them to close is that large, seemingly soft spring.
I believe the top of number 4 carburetor can be removed without removing the entire carburetor assembly. If you want to take a peek, remove this one and see what is involved. Eventually the carburetors will need to be removed, but you can at least sooth your curiosity by looking inside number 4.

The four small screws come off and the cap will be pushed off by the large spring. Under the spring is the throttle needle which is attached to the throttle piston and the diaphragm.
Several items to note:
- was the spring seated correctly in both the throttle piston and in the carburetor top? If not, the spring may be pushing down harder than it should, making it more difficult for the throttle piston to float up, thus not allowing an increase of fuel flow with an increase of engine rpm
- was the diaphragm seated properly in its groove? If not, a difference of air pressure will not develop and the throttle piston will not float up, thus not allowing an increase of fuel flow with an increase of engine rpm
- there is a small hole which passes through the throttle piston. This hole must not have any blockage
- the wall surfaces of the throttle needle piston and the cylinder in which the piston moves are of a close tolerance. Any kind of gas residue, or other debris, will not allow the piston to glide seamlessly up or down
recall, the throttle needle is tapered. As it is raised it effectively causes the jet to get larger, thus allowing more gas to pass from the bowl to the carburetor and ultimately, to the engine as demand dictates. All four carburetors need to work in synch in order for the engine to make a smooth transition throughout its power band.
Imagine if one carburetor couldn’t supply the gas the engine demanded. The engine would bog down. Imagine if all four carburetors couldn’t supply the gas the engine demanded!

As was suggested, you will need to make sure all four throttle needles open and close without any resistance or you will experience the problems you've described.

Since the carburetors are designed to operate with gas, I used gas to clean the walls of the throttle pistons and the walls of the cylinders those throttle pistons slide through. Once clean, simply insert the throttle piston into the cylinder it came from and it should simply slide down to rest. Caution should be used when handling these throttle needles because they are soft and easily bent.
Once you are satisfied with the sliding action of the throttle needle piston within its cylinder, carefully and meticulously seat the diaphragm into its groove. Again use caution as you don’t want to fold or tear the diaphragm. Although aftermarket replacements are recently available, they are expensive. Next is the return spring. It needs to sit in the throttle needle piston body and gets seated in the underside of the carburetor top. Seat it correctly before placing the top on the carburetor, holding it down with one hand, placing a screw in one of the holes with the other hand, and tightening it with the other hand. (Yes, I know, three hands!) Just be careful. Tighten the screws enough to hold the top on and test the throttle needle piston movement. Using your finger, slide the piston up, noting any sort of resistance. Remove your finger and the piston should come down with a ‘click’. Do this repeatedly until you are convinced it is operating as it should.
One down, three more to go.
When all of the throttle needles have been disassembled, inspected, cleaned and reassembled, test the butterfly movement. Open the butterflies with the throttle linkage and feel for resistance. Let go of the linkage and the butterflies should close with a ‘snap’. Clean and lubricate the linkage accordingly until you are satisfied with their performance.
Give similar attention to the enriching circuit (it is not a choke, but the effect is the same) on each carburetor. Make sure the enriching pistons open and close without undue resistance. They will be tough to open and close, but they shouldn’t require going to the gym. This circuit is cable actuated.

When reinstalling the carburetor assembly, make sure to route the throttle and enriching cables so they don’t bind. Test this with the handlebars facing forward, to the extreme left and the extreme right.
Make sure the intake o rings are seated in the intake manifold groove prior to tightening the bolts and be careful the rings don’t fall and get pinched before the manifold is placed on the head.
Make sure all four carburetor-to-intake manifold clamps are tight.
Make sure the vacuum hose on number four carburetor is attached.
Test the throttle response at the right hand grip, it should still ‘snap’ shut and open with ease.
Test the enriching lever at the left hand grip, it should operate smoothly.
Make appropriate adjustments.

Now it is time to start the engine and eventually synch the carburetors.

Once the engine will idle without the enriching circuit, slowly open the throttle and listen (and watch the tachometer) as the rpm increases. Is there any hesitation of the rpm as the throttle is slowly opened? If so, this can also be addressed. Slight hesitation can be acceptable/tolerated, some can’t.

It is a lot of work, but if you are game, the rewards are fantastic.
I will confess to having my carburetors out 8 times before I got it right. Just reading and thinking, thinking and reading and I was able to bring the bike back to life after it sat for two years.

Good Luck.

-Ride On
enjoying the view from the saddle....... due mainly to the people and information found within this site
#6 07-31-2012, 01:59 PM,
I should also mention some difficulties in getting a smooth running engine can be attributed to aftermarket, chrome carburetor caps. If you have those, eliminate them as a source of air leak. Some dont seal as well as the factory.
enjoying the view from the saddle....... due mainly to the people and information found within this site
#7 07-31-2012, 02:03 PM,
Greetings all,

My appologies that it took longer than anticipated for me to give and update on my performance issue. Liberty is now running better than expected. It appears that when I cut new fuel lines, I cut the line going to carbs 1 & 3 to short and the 90 degree bend in the fuel line cut the fuel flow to the carbs. Fortunately, and with the help of a retired Ford Mechanic, the line was discovered before I pulled the carbs out. I might also add, the color tune device was pretty dang awesome. Using the tool and following the directions, I was able to acurately tune each carburator. Which made it possible to acurately sync the carbs. My fuel mileage increased from 29 mpg to 35 mpg. Thats with two up and me running high on the rpms between gear changes. No more stinky bike. I expect that if I drive prudently I may be able to get upwards of 40-42 mpg. So, thank you to everyone that chimed in with advice and thank you to all the other 106 members that read this post and did not reply. Remember, Keep the rubber on the road and the leather up top. Dress for the slide not for the ride. God Bless you all and see you on the next post.

#8 08-07-2012, 08:17 PM,
Where are you seeing "color tune" advice? My Wing is only getting 30 mph riding single, so there moght be something more I need to do here.
Vegetarian: Old Indian word for Bad Hunter

[Image: VisitedStatesMap.jpg]
#9 08-08-2012, 03:42 AM,
I use my bike as a commuter, one up, light luggage, light traffic going to work (65-ish mph) and on and off traffic going home (55-75-ish mph) and I average 39 mpg. If I can average 65 mph, I will get 41/42 mpg, so you may have some more tweaking to do.

Good luck.
enjoying the view from the saddle....... due mainly to the people and information found within this site
#10 08-08-2012, 03:33 PM,
Wild Horse,
I read about the color tune device (Made by Gunson) on the Steve Saunder's Goldwing forum. Basically, looks like a short 12mm spark plug with a glass top. It allows the user to look into the combustion chamber as the engine is running to see if you have good fuel/air mixture. White flame -to lean, yellow flame - to rich, blue bunson flame - proper mixture achieved. It's a device that is used in Europe, to tune cars. I guess it never took in the U.S. It's pretty easy to use. I bought mine from a distributor in Florida at a cost of about $65.00 bucks. It's made of some nylon composite meterial so it looks pretty cheap, but it does the job very well. After tuning, I used the SyncPro 08-0411 by Motion Pro cost about $88.00 to syncronize my carbs. Other than that, I just made sure that I cleaned the Carbs really good. I stayed away from using Sea foam cuz I read that long term use could damage the rubber diaphram. I just knuckled down and cleaned them manually. I burn 87 octane which is the low grade fuel for Washington. That's about the jist of it.

Question for bs175dths, what's your compression readings? I'm thinking that if you are getting in the ball park of 180 psi on all cylinders then that could be why your mpg is so good. I was thinking that I may do some work on mine this winter, the shop manual reads that my readings on 2 and 4 are on the low end of the spectrum. Well, gents, it's about my bed time I will speak at you later.
- Sean.
#11 08-08-2012, 09:55 PM,
Your compression is great, cylinders psi should be with in 10% too run smooth. A different gauge, a warm engine, and a hot battery numbers could be entirely different .
#12 08-09-2012, 09:07 PM,

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