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Old 03-06-2013, 08:28 AM   #1
jonfrabitoy
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Default Single Carburetor and Manifold Solution for GL1100

Part 3 of my Calculation process is to properly size for a single carb intake system. The GL1000 and GL1100 motorcycles are old, the engines and frames outlast the fuel metering systems.

New carbs for these cycles are not available anymore I understand. You might find NOS on the shelve somewhere if your lucky, but the old, rebuilt 45 times, carbs on your cycle are getting old, worn out, they are pitted and sometimes just hard to synchronize. I woke up one morning and thought, would it be nice just to have one carb to tune, no more troubles, less working parts, and I could have a new carb? I just cruise anyway 55-60 mph.

So I was researching and found two fellas that were making single carb manifolds. Cool. When I asked these fellas for there engineering sheets and heat balances, they said, they just trial and error it. So, I sharpened my pencil and in two previous threads, I calculated 162.3 CFM as a required min air flow requirement for 100% power and I know how much fuel I need to meter, 44.5 Lbm of Gasoline at 100% power. This way I have designed for the full power band.

Jets are designed to deliver grams of fuel per minute according to the factory guys at Mikuni. so we can use dimensional analysis to figure jet size requirements as well, later. There are a few carbs on the market that will suit our designs, the weber two barrel carb, the rochester 2 barrel carb and of course the solex Pict 34 carb. There might be others, but for now, these will do.

Now, this is why I needed to know CFM. If the weber carb can not deliver 162.43 CFM, it will not be a good candidate. And if jet sizes can not be installed to deliver the liquid fuel, then it will not work as well.

The weber carb can deliver 190 CFM before the mach number is comprimized. The solex can deliver 124 CFM and the rochester 215 CFM.

The final item to discuss is location of the carb for identical response. This will be another thread later.
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Old 03-06-2013, 12:11 PM   #2
JK McDonald
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Default Carb Project -

Hey Jonfrabitoy, If you are not set on reinventing the wheel - there have been several nice sets of 1100 carbs on Ebay and there are plenty of motorcycle salvage yards that would probably be tickled to hook you up with some parts.

I am sure your project is possible but wouldn’t a single carb setup require that the fuel/air mixture make a lot more twists and turns before entering the combustion chamber ? The added length would sling the heavier fuel particles against the intake wall with every turn which typically requires a richer mixture to compensate for the loss in flow efficiency. Most designs then must add heat to the intake tube surfaces to try and smooth the air/fuel mixtures around the corners.

The only reason I mention some of the problems you may run in to when trying to install a single carb on a flat four cylinder engine is because I was involved in a similar project one time. A buddy spent a ton of money changing over from fuel injection to a single carb setup on one of the old air-cooled fast back VW’s that was a family free-be. The engine actually ran great but he decided it would be simpler to maintain if he ditched the FI. We first tired a intake/carb setup that stood straight up - but was too noisy inside the car. Because the rear interior had a flat panel directly over engine the aftermarket intake and carburetor had to lay on it’s side. Both intake/carb designs - along with all the above mentioned fueling/ducting issues, made that thing unbelievably temperamental and burn fuel like 12 cylinder Ferrari.

It is not that you probably can not design an intake/carb setup but Honda would more than likely have saved the production cost of those 4 carbs if it was reasonably feasible.

Good Luck, Michael

Last edited by JK McDonald; 03-06-2013 at 12:43 PM.
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Old 03-06-2013, 12:47 PM   #3
jonfrabitoy
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Quote:
Originally Posted by JK McDonald View Post
Hey Jonfrabitoy, If you are not set on reinventing the wheel - there have been several nice sets of 1100 carbs on Ebay and there are plenty of motorcycle salvage yards that would probably be tickled to hook you up with some parts.

I am sure your project is possible but wouldnt a single carb setup require that the fuel/air mixture make a lot more twists and turns before entering the combustion chamber ? The added length would sling the heavier fuel particles against the intake wall with every turn which typically requires a richer mixture to compensate for the loss in flow efficiency. Most designs then must add heat to the intake tube surfaces to try and smooth the air/fuel mixtures around the corners.

The only reason I mention some of the problems you may run in to when trying to install a single carb on a flat four cylinder engine is because I was involved in a similar project one time. A buddy spent a ton of money changing over from fuel injection to a single carb setup on one of the old air-cooled fast back VWs that was a family free-be. The engine actually ran great but he decided it would be simpler to maintain if he ditched the FI. We first tired a intake/carb setup that stood straight up - but was too noisy inside the car. Because the rear interior had a flat panel directly over engine the aftermarket intake and carburetor had to lay on its side. With all the above mentioned fueling/ducting issues, that thing turned unbelievably temperamental and burned fuel like 12 cylinder Ferrari.

It is not that you probably can not design an intake/carb setup but Honda would more than likely have saved the production cost of those 4 carbs if it was feasible.

Good Luck, Michael
Of course, both your suggestions, carb distance from the valves and performance of the engine are very valid. The manufacturer (Honda) installs or positions the carbs, a design intent, 6 inches by linear measurement from the head port. The carbs meter the fuel another 2 inches back, to make the distance just to the head, 8 inches. The Goldwing engine is very forgiving, on other inline 4 cylinder bikes, the throat of the carbs are only 3 inches from the head port.

now, carbs respond faster when they are closer to the valve. the velocity of the air/fuel mixture is important as well, sometimes racers restrict or install smaller bore carbs to increase air/fuel velocity into the head port for better faster response. The goldwing is not balanced for racing, just cruising, so performance is important, but not paramount.

Next you mention air/fuel charge turbicity. Yes, there are more turns and a longer distance for the air/fuel mixture to travel before the head port. and this can be a concern for performance. will it cause the fuel mixture to richen??? Hum, I dont think that can happen.

If i install an orifice that can only allow a max flow rate through it, and nothing more, then it is fixed.

Heating? it might be desireable to atomize the fuel early, heating the manifold will cause the fuel to atomize or vaporize sooner, before it reaches the head port. it could help performance, good questions ??
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Old 03-06-2013, 01:51 PM   #4
budoka
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I think I could have used your brains when I was racing sleds jon. Reckon you could have saved me a whole lot of grief while I was re-designing my intake tract for the old Blizzard!
This is an very interesting post, looking forward to your results! Not sure, but I think there were some 2 barrel modifications for the 1200 engines years back; kind of neat when you figure the 1500 came out with pretty much that set-up in '88.
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Old 03-06-2013, 07:37 PM   #5
JK McDonald
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Default Heated Intake -

Hey Jonfraitoy, On the project I mentioned above, we found that with both the vertical/horizontal intake/carb setups the idle fuel mixture adjustment and the primary jets had to be sized much richer than expected. Initially, the air/fuel charge was just too lean by the time it reached the combustion chambers because of the length of the runners. In order to have any throttle response with no dead spot we finally had to also max out the acceleration pump/valve and use heated incoming air at all times.

By the way - all this drama was using straight gasoline. With 10% - 15% Ethonal gasoline there may even be additional issues.

Good Luck, Michael

Last edited by JK McDonald; 03-06-2013 at 07:45 PM.
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Old 03-07-2013, 08:15 AM   #6
jonfrabitoy
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Quote:
Originally Posted by JK McDonald View Post
Hey Jonfraitoy, On the project I mentioned above, we found that with both the vertical/horizontal intake/carb setups the idle fuel mixture adjustment and the primary jets had to be sized much richer than expected. Initially, the air/fuel charge was just too lean by the time it reached the combustion chambers because of the length of the runners. In order to have any throttle response with no dead spot we finally had to also max out the acceleration pump/valve and use heated incoming air at all times.

By the way - all this drama was using straight gasoline. With 10% - 15% Ethonal gasoline there may even be additional issues.

Good Luck, Michael
Hum, I want to thank you for your input. its seems a lot of your findings are serious issues. perhaps a single carb solution might not be the answer? maybe a two carb solution is the natural conclusion, that way, we can position the carb the distance from the head port as the original equipment. Someone else wrote, that is the solution Honda made for the GL1500 and now is standard for the GL1800?
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Old 03-07-2013, 09:27 AM   #7
6adan
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jonfrabitoy if you are new to old Goldwings go to Randakks.com and you will find all you want to know about the carbs both single and duel setups.
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