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gl1200 carb size please help

6K views 29 replies 6 participants last post by  ekvh 
#1 ·
Hi guys.. just had a question on carbs on gl1200 what us the venturi bore size is it 32mm?
 
#3 ·
...'cause the answer's are here.
 
#6 ·
MY TURN>>>MY TURN>>> NO, a single carb will not make the same HP as the original set up
 
#9 ·
...how do you know that?
 
#7 ·
I said what I said because I see his conversation on another forum relating to this...
1200 carbs on a 1000, or something like that.
I thought we had a similar thread here?
It's not about a single carb conversion...
 
#10 ·
I'd have to research that stuff. I'm not too strong on factory carb spec's.
 
#11 ·
captain might be a clever one...anyhow hes partially right... and the reason im asking is would there be any power difference from using early 1000 carbs vs 1200 carbs

this is for my 76 with my 86 1200 in it, and we can toss around the idea of 1000 heads or 1200 heads on it
 
#12 ·
Like I said, I think we have a thread on it here somewhere. I'll look for it.
 
#13 ·
sorry if this is just a repeat im on my phone and its a bit harder and i had a lot "technical difficulties" joining this site awhile back and havent used it much

that azgl1800 helped me get all fixed by the way... thanks again
 
#16 ·
thanks captain.. well from what i understand now is that the 1200 was advertised as 32mm kehin carbs but this was the throttle bore, and the venturi bore was 30mm

and im taking it as gl1000 early carbs were 32mm throttle and venturi bores

i hadnt been thinking about this lately but i was before.. im just rebuiliding my 1200s now and a different question on a forum sparked my interest again..

and between throttle bore and venturi bire... the smaller one will be the limiting one?
 
#17 ·
this was from awhile its my 76 with the 86 fuel injected that i put carbs on... ill be going with 1200s first... this was just meant to be a power wing.. i fitted 1200 rear and front wheels onto it, but i bought some gsxr 1300 forks in plans of swapping them on
 

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#18 ·
Yeah, I can't find what I was thinking of. I may be thinking of something from another forum. I've been bouncing around the forums lately. I use to be able to keep track of it all. Not so much anymore.

I think your thinking is on the right track. Some very interesting thinking has been happening lately, in my opinion.
You with carburetor's and how you're looking at going about them, and another with the elbow manifolds.
Will there be any noticeable gains? I don't know. I kind of doubt it unless combined with other things. I am one that believes the penny's do add up into dollars though. The 1200 w/1000 heads seems to be popular now. A fella here is pretty strong on that swap and may have some answer's for you; SuperSkyPilot, I think his username is..
Anyway, Good Luck on trudging forward. You're in somewhat uncharted territory with the carb thinking imo..
I'll be watching, as I find it interesting ...even without having interest in factory carbs. I like the innovation of something new and different. If I can help, I will, but don't hold your breath. I'm just not experienced enough in actually using the factory carburetor's.
...there has to be someone having gone down this road you're on.
Work with Eric. I think he's probably the strongest on what you're looking to do that I'm aware of. He runs those factory carbs. I don't know if he's at where you're thinking though. I think his carb experience is with swapping factory racks versus modding the racks on his engine. I ain't sure.
Again, Good Luck..
CM
 
#19 ·
I just consider myself an idiot, with a lot to figure out and learn.. so ... let the knowledge flow in, sometimes i feel like i spend hours and hours trying to figure out something, and end up more confused

I'm aware of a few of 1200 into 1000 builds.... but not how many people dove into the carb question, I know 1 person who's played around with a bunch of carb set ups (Eric) as you mentioned, and was told super sky pilot steve.. probably got that wrong? Is pretty knowledgeable in the 1200 > 1000 swap

I was set on the 1200 would be a better carb set up regardless of 1200/1000 heads, but now finding out the "32 mm" 1200 carbs actually have a 30mm venturi bore have me wondering.. but then there's also the angle of 1200 carbs, and the runners,
 
#20 ·
Yeah, I saw that about the 1000 carbs using 1200 elbows to reduce the radius. I don't think it'll work well due to the float bowl's.

I always like the V-Max idea. I forget where that thread is. V-Max carbs on each side, in Randakk's fashion. That idea I always liked. Certainly other carbs out there that would work in this way as well, I would think. V-65? Again, I'm limited to only what I know through experience. I'm pretty strong on the single carburetor conversion's, but that's about it for induction.
 
#21 ·
Why are you trying to put 1000 heads on a 1200 motor?

If you want my advice, the 1200 motor makes plenty of power and changing the heads and carburetors will probably lose some of that power.
Believe it or not, those Honda engineers design some pretty good stuff.

I like what you have done so far, but getting the fuel tank back in and designing an air intake system would be enough. And I definitely wouldn't mess with the forks.
 
#22 ·
captain - i see your point on the elbows / float bowls and yes im pretty sure it was v65... as for that.. i dont have those.. but i do have sets of 1200s and 1000s so i was just going to work between the 2

dennis - well 2 reasons mainly, 1 being i like the look of the 1000 valve covers the most, and a potential power increase of the 75-77 cams, i say potential because as far as i know only "butt dynos" exist no real dynos comparing thr 2, some people that have done it say they are sure... but again..butt dyno

and i am with you on Honda... i have both cx turbos but unfortunatrly bo NR750

but if i do remember correctly the first head swap was done by a honda employee, so the story goes

other than the piston notch its just a head swap which is pretty easy on these, and to swap it back id suffer no loss, indo want to dyno them though

my main wing is a 77 that i put an 1100 in it because it was seized, i also fitted 78 cams and ignition on it which people said i couldnt do

i have modified the 1200 15 inch rear wheel so i can still swap it out with the 17 stock or my 16/18 inch lesters, with no issues

as for the fork swap thats not too big of a deal to me either, i dont have another 1000 fork brace and i like the brass/gold forks of the busa, i was going to put the 1200 forks on it, still might, but probably go with the busa forks with wing front wheel
 
#23 ·
If you do the swap, revisit Steves posts. Use the oil ferrule, spigot, I can't remember what it's called but gets two orings on each side of the head gasket---use the ones from the 1200. First glance, they look alike, but the 1200 has a much larger hole in it to flow more oil to the cams.

It's going to be really hard to compare all these possible carb/cam/head changes. No two motors are alike. One guy might have one with 190psi and another might only have 140psi compression. The only way would be to use the same block, but still varying engine conditions may influence results.
 
#27 ·
Bore diameter's from the book, though Ken already answered it...
 

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#29 ·
Trying to add pics, now it's upside down. Can't make this work on my phone. 77 left, 1200 center, v65 right shows inlets. The 85 years got rid of the choke and have a wide bell going down rapidly to the Venturi diameter. The 77's go straight in beyond the choke plate before a fairly steep radius end venturi. The newer versions must breathe better without the choke in the way.
 

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#30 · (Edited)
Last shows the differences with my calipers. My calipers are about as reliable as my head because they both have been dropped a time or three. I was surprised at how big the inlets were on the newer carbs. These are geometric measurements and some visual cues, but the only sure way to know which is best is to flow them or dyno them. For the majority of riding, I'm guessing the stock 1200's are best. They might start giving a little away only when you start pushing your 40 year old motor above say 7500 rpm.

My v65 experiment is very close to the same venturi and inlet/exit dimensions as the 77 carbs. They should flow better because of no chokes in the stream, but it's limited because the only intake elbows I've found to fit are 1200's which are smaller, same as 1200 carb exit. I hope to get something else figured by summer.
 

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