Honda Rebel Forum banner

1 - 20 of 27 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
converting the single to a dual carb. I have done this but now my throttle cable is very loose and my choke cable doesn't really fit well with the new setup. I'm lacking in knowledge of this sort of work my granddad is helping me. Also most importantly the bike doesn't want to stay idled it seems that after it warms up it cuts off and won't start back up easily. I replaced the spark plugs as well. Thanks for any help in advance!
 

·
Premium Member
Joined
·
11,902 Posts
Do you have it connected to the air box or are you running pod filters? It's best to acquire the Y-connector from eBay that goes between the carbs and air box, pod filters are just too cantankerous.

Those look like the same ones I acquired but they leaked, I am currently going with a CB250 Nighthawk carb until I can find time to futz with the duallies.

 

·
Premium Member
Joined
·
11,902 Posts
Mine were FUBAR'd from the get-go, the jet seats were upside down and the diaphragms were not seated either. After addressing both issues they leaked upon start-up.

You probably need to get yours synchronized.
 

·
Banned
Joined
·
765 Posts
This may seem like a silly question, but why would you want to make it more complicated? I seriously considered converting a dual carb Kawasaki Vulcan 750 to a single carb, and a 4 carb Goldwing to a single carb. Honda only used 2 carbs on their 1500 6 cylinder Goldwing. My Rebel and Sportster both work fine with one carb.
 

·
Premium Member
Joined
·
11,902 Posts
Once upon a time before the 1800 Wings debuted there was an aftermarket company that offered four banger Gold Wing manifolds that accepted a common automotive four barrel or two barrel carburetor (you had a choice) along with the old school air cleaner that was secured with a single wing nut (re: dirt cheap automotive filters).

As far as why convert to a dual carb, it's been long accepted that multi-carbs outperform single carbs. Case in point: the 5HP difference between a 88-98 dual carb 600 Shadow and the 99-07 single carb 600 Shadow, or the same spread between the dual carb 1500A Vulcan and single carb 1500 Vulcan Classic (the latter of which was further hindered with an extra 140 pounds heft). Note the motors did not change between intake changes on either bike. All the inline four MC motors back then had four carbs, the inline sixes had six...none of them had one. C'mon...an old school motorhead like you had to ask that? ;)
 

·
Banned
Joined
·
765 Posts
Once upon a time before the 1800 Wings debuted there was an aftermarket company that offered four banger Gold Wing manifolds that accepted a common automotive four barrel or two barrel carburetor (you had a choice) along with the old school air cleaner that was secured with a single wing nut (re: dirt cheap automotive filters).

As far as why convert to a dual carb, it's been long accepted that multi-carbs outperform single carbs. Case in point: the 5HP difference between a 88-98 dual carb 600 Shadow and the 99-07 single carb 600 Shadow, or the same spread between the dual carb 1500A Vulcan and single carb 1500 Vulcan Classic (the latter of which was further hindered with an extra 140 pounds heft). Note the motors did not change between intake changes on either bike. All the inline four MC motors back then had four carbs, the inline sixes had six...none of them had one. C'mon...an old school motorhead like you had to ask that? ;)


Performance? On a Rebel? I doubt there is anything you could do to make a noticeable gain in performance on the Rebel. And even if you could, it would be matched by a decrease in engine longevity and reliability. The best way to get more performance on almost all motorcycles is simply to get a bigger motorcycle, or, in the case of a 250, The Ninja 250 makes a lot more power than the Rebel, but can still last 100,000 miles. IF you can handle the riding position.

I once considered a 600 Shadow, because Twisted Throttle made a centerstand for it, making it possible to repair a flat tire on the road. But I was dead set on the single carb version, mainly for simplicity. It's a cruiser. Looks and comfort are what matter, not sportbike performance. I actually liked the looks of the older model better. But having dealt with 2 carbs on a Vulcan 750, I never want to go through that again.
 

·
Premium Member
Joined
·
11,902 Posts
Touché on noticeable gains on the Rebel, although nobody has actually provided before & after dyno runs when switching from one to two carbs so until that happens, it;s purely theory at this point. Even if it did make a noticeable change I don't see why it would decrease longevity or reliability, more so considering how the Asian & Australian models came from the factory with twins.

My dual carb 600 Shadow (came from the factory as such from 1988-98 ) has 136K miles on it. Granted it caught on fire last year (fuel pump) and is suffering from other electrical gremlins since I got it back on the road, but that had absolutely nothing to do with having an extra carburetor on the bike. It was a faulty design on the fuel pump, I've had four out of six VLX pumps go bad including that one. Honda silently replaced it with a new version somewhere in the past few years as the part number has changed.
 

·
Registered
Joined
·
13,264 Posts
I have always wondered why 2 carbs would theoretically be any better than one on a 360 degree twin like the Rebel. Each cylinder pulls an air charge on one stroke out of 4 of each piston, and these charging strokes are offset from each other by one full revolution of the crank. It seems that the peak air flow through a single carb should be about the same as for each twin carb. The difference, of course, is that on a single carb, you get a pulse of air flow on every crank revolution as opposed to every second revolution for twin carbs. If anything, I would think that a steadier air flow would make for better carb performance on the single, since there is less stop and start pulsation of air through the carb throat.
maybe someone who knows more about it than me could explain why 2 carbs should give at least a little bit more performance than a single.
 

·
Super Moderator
Joined
·
7,829 Posts
In a single carb engine you get air turbulence in manifold and week suction pulses because of area and size of runners. And they are delivering your air fuel mixture in a lazy way
With twin carbs as on a rebel you have short runners direct in to the engine that give strong suction pulses that fill the combustion chamber faster and easier ie they are more efficient and less turbulence is created
Is similar with exhaust manifolds and pipes the better the flow the more HP you get
 

·
Registered
Joined
·
13,264 Posts
That makes sense..You eliminate the inefficiency of a manifold. In theory that should flow more air due to reduced pressure drop in induction system downstream of the carbs.
 

·
Banned
Joined
·
765 Posts
My 1964 Ford Fairlane with a straight six and a one barrel carb runs just fine. It doesn't look like it would, since the length of the runners for the middle 2 cylinders are significantly shorter than the runners for the 2 end cylinders, then you have the other 2 cylinders in between. Yes, inline 6 cylinder car engines have been built with a carb for each cylinder. I'm sure they make more power. And that's fine for a sports car, but for a car made for basic transportation, it is unnecessary. If the Rebel were a sport bike, I can see it. But it's a cruiser. And cruisers these days tend to be pretty slow. Back in the good old days, Japanese manufacturers made some very fast cruisers. My 1980 Yamaha XS1100 Special was one of them. Four cylinders, four carbs, DOHC, 1100cc. It was very fast in a straight line, but handled curves like a wheelbarrow. However that is not what it was designed for. If you wanted handling and power, you could buy a Honda CB1100F.



Back during the '90s, the 1500cc six cylinder Goldwing had 2 carburetors. When they put that engine into the Valkyrie, they used six carburetors. I'm not sure whether it was for performance or looks or both. They also switched from maintenance free hydraulic valves to mechanical valves you had to adjust. 6 carbs to keep synchronized, 6 cylinders to adjust the valves on. You have to wonder if it was worth it.
 

·
Premium Member
Joined
·
11,902 Posts
Back during the '90s, the 1500cc six cylinder Goldwing had 2 carburetors. When they put that engine into the Valkyrie, they used six carburetors. I'm not sure whether it was for performance or looks or both.
https://web.archive.org/web/20170712142627/http://www.mcnews.com/mcn/articles/2015_01PerfIndex.pdf

GL1500 Valkyrie top speed: 131mph, 0-60: 3.8 seconds, ¼mile: 12.02sec @ 110.70mph
GL1500 Gold Wing top speed: 120mph 0-60: 5.26 seconds, ¼mile: 13.28sec @ 99.96mph

Safe to say it benefited both. Granted the Valk is also nearly 200 pounds lighter, all in all the difference is quite noticeable. ;)
 

·
Registered
Joined
·
13,264 Posts
I am a little sympathetic to Jerry's position on this one. Single carb and manifold setups were standard on autos back in the day, and of course they all did the job just fine. Certainly multicarb setups make more peak power at the expense of complexity and perhaps rougher running in the low to mid range due to low flow velocity through each carb.
My Norton Commando has twin Amal carbs. A popular mod for these bikes was the conversion to a single Mikuni carburetor. The Mikuni is a more modern precise carb than the relatively crude Amal concentrics, and every day idle and midrange operation was vastly improved with the Mikuni with very little penalty on top end power which on a big bike like the Norton is not an area that was explored very often anyway. All old British bikes with twin carbs require nearly constant tweaking of the idle settings to maintain decent idling perofrmance.
Certainly the gain from 2 carbs on a Rebel would not make the complication and expense of a conversion worthwhile for me.
 

·
Super Moderator
Joined
·
7,829 Posts
Not so I tuned my carbys when I rebuilt my engine and is still running the same as it was done more than 4 years ago :)
 

·
Registered
Joined
·
7 Posts
Discussion Starter #20
The choke cable went from being inserted into the carb to latching on. It doesn't seem to fit anymore without being modified. Has anyone else ran into this or other problems doing this conversion?
 
1 - 20 of 27 Posts
Top