Using carbs as throttle bodies?

[TheFieryMan]

I've been reading through many of the threads and I saw a comment that I can't find now. Someone mentioned converting their actual carbs for use as throttle bodies in an efi conversion. It's the first I had heard about that possibility. Is there any information on that or has someone done it with good results? If there is a thread on it already I apologize. Searching the forum for anything related to carbs or throttle bodies is not very effective as you can imagine.

[redglbx]

When I built my hot rod 1100 carbs for my 76 1000 I considered doing a set of 1000’s up as throttle body injectors. But as I got into it initially with a set of 1000 carbs and then with the 1100’s I soon realized that they are pretty thin and intricate castings that would make adding injectors really difficult w/o welding some bungs in for them. And I’ll add that welding on these carbs particularly after years of use would be difficult at best, you’d have to TIG them by the way.

I have a number of 1100 carb bodies that are junk from the different things I tried and will say that most body modification imho is a waste of time and will most likely trash the body.

So what can you do ? In my opinion and something I keep considering is to use a single carb manifold, the one that was cast aluminum & used to add the magna supercharger not the one that used the VW carb, that’s a terrible design. And once you get the correct manifold (rare !) I’ve been thinking of adding a Holley or similar stand alone throttle body system, they make one that’s around 300cfm and will support around 350hp which should be more than enough, you don’t want to go to big because it’ll make the performance pretty soft down low.

So why haven’t I done this ? I have a manifold which is the hard part. But my very modified 1100’s work so very well I’d be hard pressed to improve on them. I will add that normally I’m not a 1100 carb proponent as the stockers will not improve a 1000’s performance and will probably decrease it quite a bit, past the slightly improved throttle response due to the accelerator pump, they really kill the top rpm’s performance. A lot of people will tell you that they will improve you mpg’s , give you the ability to pop power wheelies on demand (pure bs) , give you whiter teeth and a much improved sex life. But in my opinion none of that is remotely true.

That’s my take on that, if you decide to pursue a fuel injection path please keep us in the loop.

[TheFieryMan]

Thanks for that insight. For the purpose of this question I'm not thinking about the fuel part of it. I'm mostly wondering what would be required to make the carbs function as standalone throttle bodies. What modifications would need to be done? Obviously some things could be removed but what else would need to be done?

I should also clarify that I'm talking specifically about the GL1100 and that fuel would be delivered via injectors close to each cylinder head.

[Rednaxs60]

This is a good read: https://ngwclub.com/forum/viewtopic.php?f=47&t=25983

As for 1000/1100/1200, parts/components required is the same. How these are installed/mounted is the interesting part because there is always more than one way to do things.

Using carb throttle bodies in a fuel injected system/conversion can be done, but the carb throttle body is necked to get a Venturi effect. FI throttle bodies are straight. This means that for the same throttle body size, there is more air flow through the throttle body, something that is a key element in an FI system.

You would be using the throttle body for the injector placement. Look into the injector holder(s) from an '85/'86 Gold Wing CFI system. This injector holder design works well.

Agree with redglbx in that FI benefits are not as expected. May get better fuel economy, may not, depends on your tuning skills. More HP, no. FI gives can give you better reliability regarding starting and normal riding, I prefer FI over carbs. This is because you now get to tune a variety of parameters to enhance engine operation, not just RPM and air mass.

You could also consider picking up a second 1100 that has been converted to FI. If this worked out, maybe then convert an 1100 to FI. You can get an '85/'86 GW FI model as well. The Honda CFI system was state of the art in the day and the CFI system design formed the basis for Honda's PGM-FI system that is still used today.

Keep looking, gathering information. Most FI conversions never come to fruition because it requires a lot of work, time, effort, research, collecting parts/components, choosing an appropriate aftermarket ECU, and not to mention expense.

Good luck with your quest.

[redglbx]

I had a 86 Sei that had the CFI fuel injection, loved that bike and should have never sold it but fear of parts availability pushed me in that direction. It was a good bike once I got all the previous owners problems fixed.

Getting to ride that 86 Sei back to back to my 76 with the hot rodded 1100 carbs quite frankly there was no real performance advantage in the FI’d 1200 other than cold starting where no matter how long the Sei sat it always just started immediately, whereas the 1000 would crank a bit more, not a huge difference but a little difference.

In all honesty the 1100 carbs have great throttle response no matter what rpm but so did the CFI system on my 86. There just isn’t in my opinion enough or any real advantage in the FI to justify spending the money of converting my 76 to FI, but if I was going to do that, like I said above I’d buy an aftermarket stand alone setup, truthfully I’ve been giving thought to doing a Holley 500 cfm 2 barrel carb on my aluminum single carb manifold,,,,, but the 1100 carbs work so well !

One of the things I do to see how well my carbs/tune work on my bikes is to run it in high gear (usually 5th) down to idle rpm and then see how easily it will pull back to normal running rpm. I do-not just whack the throttle open but I want to be able to smoothly accelerate back up to speed with no bucking or chattering just smoothly accelerate. If it’ll do that then the tune is pretty good. My .02

[TheFieryMan]

In all honesty the 1100 carbs have great throttle response no matter what rpm but so did the CFI system on my 86. There just isn’t in my opinion enough or any real advantage in the FI to justify spending the money of converting my 76 to FI, but if I was going to do that, like I said above I’d buy an aftermarket stand alone setup, truthfully I’ve been giving thought to doing a Holley 500 cfm 2 barrel carb on my aluminum single carb manifold,,,,, but the 1100 carbs work so well !

That's very helpful experience. For me it's not necessarily about whether it's significantly better or not. Of course I want to take advantage of the benefits of efi but it's more about figuring it out. It's the puzzle and experience gained through figuring it out and completing something unique.

Initially when I started thinking about the build I was going to go the route that most others do by just swapping in throttle bodies from other bikes or doing a single throttle body but when I heard it might be possible to use the original carbs as throttle bodies instead, it really appealed to me for a few reasons. First, it's exactly because the stock carbs are so efficient as you mentioned. Trying to fabricate a new manifold or plenum might really hurt the performance. Secondly, I like the idea of keeping the look of the engine as close to stock as I can while still modernizing the whole system.

So I guess the question is somewhat more technical than philosophical.

If fuel wasn't part of the equation, is it feasible to turn the 1100 carbs into throttle bodies? Had anyone done it? And what needs to be changed on the carbs themselves to achieve it?

[joecoolsuncle]

how would one tune a DIY efi system on an gl? does someone build a tuneer that would connect to a ecm? if going with a standalone efi system, why not just use all their components and neck down the throttle body?

[ericheath]

There are a few builds in here from years ago. It’s pretty complex, but some include the parts they used.

There was a company making injectors that dropped into the opening for the slide. It hid the injector and retained stock appearance. It is a little farther away from the intake valve than most efi setups. The ones I saw were advertised for VMax bikes of the 80’s/90’s. I don’t recall reading anyone who tried it, but lots of newer retro styled bikes use this to give the appearance of carbureted versions of yore.

[TheFieryMan]

how would one tune a DIY efi system on an gl? does someone build a tuneer that would connect to a ecm? if going with a standalone efi system, why not just use all their components and neck down the throttle body?

Planning to use the Mega Squirt ECU for both ignition and fuel so it would all be tuned by laptop.

[joecoolsuncle]

how would one tune a DIY efi system on an gl? does someone build a tuneer that would connect to a ecm? if going with a standalone efi system, why not just use all their components and neck down the throttle body?

Planning to use the Mega Squirt ECU for both ignition and fuel so it would all be tuned by laptop.

thanks. does megasquirt offer base maps for that particular make/model/year? are you an accomplished tuner?

[TheFieryMan]

how would one tune a DIY efi system on an gl? does someone build a tuneer that would connect to a ecm? if going with a standalone efi system, why not just use all their components and neck down the throttle body?

Planning to use the Mega Squirt ECU for both ignition and fuel so it would all be tuned by laptop.

thanks. does megasquirt offer base maps for that particular make/model/year? are you an accomplished tuner?

I have no idea. And no. Thankfully the MegaSquirt community is massive, super responsive and very encouraging. Also, my ability to do things I've never done before has a pretty significant track record.

[joecoolsuncle]

Planning to use the Mega Squirt ECU for both ignition and fuel so it would all be tuned by laptop.

thanks. does megasquirt offer base maps for that particular make/model/year? are you an accomplished tuner?

I have no idea. And no. Thankfully the MegaSquirt community is massive, super responsive and very encouraging. Also, my ability to do things I've never done before has a pretty significant track record.

if no one has taken the many many hours and $$$$$ to create a base map, and you do not have a dyno with a 5 gas sniffer, you are in for a real ride.
do you have a weather station and data logging capabilities?
my first thoughts are : is the megasquirt even capable of being tuned to the point to create a better runing gl1200 than the oem carb setup?

[TheFieryMan]

thanks. does megasquirt offer base maps for that particular make/model/year? are you an accomplished tuner?

I have no idea. And no. Thankfully the MegaSquirt community is massive, super responsive and very encouraging. Also, my ability to do things I've never done before has a pretty significant track record.

if no one has taken the many many hours and $$$$$ to create a base map, and you do not have a dyno with a 5 gas sniffer, you are in for a real ride.
do you have a weather station and data logging capabilities?
my first thoughts are : is the megasquirt even capable of being tuned to the point to create a better runing gl1200 than the oem carb setup?

I will be doing the conversion to my 82 GL1100 Aspencade. There are at least two members here who have already made this conversion but there are tons of variables that will affect the tune of couse.

viewtopic.php?f=47&t=25983
viewtopic.php?f=47&t=59774

I have read every post of these two threads at least three times as I plan this build. So I know it can be done.

[TheFieryMan]

As for the topic of this thread, I've actually decided against using the carbs as throttle bodies. At this point I plan to use a single throttle body and replace the carbs with fabricated runners from the main plenum to the runners I found used on eBay from an 86 efi model. I am also planning some experiments to try and achieve some better flow through the plenum and runners.

[Rednaxs60]

Don't know about the Megasquirt family, but there are various examples of FI installs on motorcycles on the Speeduino forum. May be worth a look. I'm doing an OEM ECU replacement/upgrade project using the Speeduino Project.