Twin Weber 40s on a GL1200?

[RazMan]

Hi guys, I am new here so be gentle with me on my first post
I am currently building a custom GL1200 bobber, stripping everything back to basics except for the carbs. I am on a tight budget so I intend to put a pair of 'clone' Weber 40 IDFs on custom made manifolds. As far as I know, no one has done this before - quite a few on GL1000 & 1100 but not a 1200 in sight. I will post pictures of the project as I go and would welcome your comments and suggestions.

 

[Dusterdude]

Welcome,interesting project

 

[RazMan]

Can I ask a favour of you guys? I am told that the Randakk Weber conversion manifolds for the GL1000 wont work on the 1200 because the intake ports are too small.


Quote from Randakk's website

"Note: These Weber manifolds are not marketed for GL1200s even though they bolt up fine. The problem is GL1200 heads have much smaller ports, so that creates a "step" that adversely affects flow. Some customers have overcome this by installing machined "transition" spacers between these manifolds and the GL1200 cylinder heads. A better path is to put GL1000 heads ('75-'77 preferred) onto the GL1200 engine. That gives you hotter cams, better breathing combined with the larger displacement engine and results in a very powerful combination. It usually means converting to a GL1000-style ignition driven off the left cam in the usual GL1000 fashion."

I have measured my ports at 32mm dia and I wondered what the 1000 & 1100 ports are - any chance that somebody can tell me?
I don't really want to re-invent the wheel so maybe I can modify the Randakk ones to fit."

Can someone tell me what size the ports are on the 1000 & 1100?

 

[zman]

I cant answer your question but 1000 heads sounds like a good solution, you can get rid of the electronic ignition, as for the 1200 heads I dont see why they cant be opened up to match the manifolds.

 

[julimike54]

Welcome to The Forum and enjoy! Might also need to check the center to center dimension.....

 

[RazMan]

@zman When I contacted Randakks, they told me that their stock has been withdrawn due to a problem or fault. So I can't even get their set and bung on some 1000 heads as suggested. Interesting that you say to get rid of the electronic ignition - is it not better than the points system?

​

@julimike54 I'm pretty sure that the centre to centre measurement is the same as Randakks say that it will bolt up to the 1200 heads and just have a smaller port to adapt to.

 

[zman]

you will have to adjust the points from time to time but better then pulling an engine to get at the electronic ignition., they have a kit to put an electronic ignition on the head but when an ignition control module or pickup sensor fails your stuck on the road, not so with points, heck..you can even carry an extra set of points with you

 

[RazMan]

Having had a 70s GL1000 which had points, I was never happy with the timing - it seemed to drift after a few thousand miles and I was always tinkering with it. When I upgraded to the GL1200 I never had to do anything - just ride it This my 4th GL now after a break of 20 years or so and I think will stick to the (IMO) reliable electronic system .......... oooohh I hope I haven't jinxed things now

 

[pidjones]

OEM GL1200 electronic ignition and aftermarket kits for the GL1000 are quite different in reliability. Still, the points are dead simple and compact, plus easily accessible on the back of the left head and the arcing wear can be eliminated by using an easiy bypassed electronic device to operate the coils (switched by low current through the points). I tried that on a '79 successfully until a failed regulator let the system voltage go to over 17 volts. But, would the GL1000 mechanical fuel pump supply enough fuel for your carbs? I have GL1000 heads in a box in the shed, but not going out there today (too hot!)

 

[RazMan]

"But, would the GL1000 mechanical fuel pump supply enough fuel for your carbs?" - another good reason to stick with my 1200 kit methinks


After further investigation it appears that my GL1200 might be fitted with GL1000 heads (32mm inlet ports) and the Randakk kit will indeed fit!
If only they had any for sale!

 

[joedrum]

Hmmm ..ok I basically have a bike set up like yours ...except no twin Weber set set up ...but do use the 1200 short block ...actually 1100 heads ...with early 75-77 cams ...my ignition is the out of business c 5 programmable ignition ..the best ignition ever made for early oldwings ...the problems with the early points ignition is they use springs for timing advance that are small old and very unreliable and no adjusting ..this also true with electronic set ups made to replace them ...the dyna set ups made this problem even worse as there adjustment to adapt was worse than the points ...one of the best things and worse things about oldwing 4s is they use 2 trimming belts ...in reality this is like 2 motors in one ..if the belts are perfectly in sync in tension you can never time the motor a tighter belt and a looser belt motor is impossible to time with the ignition set ups out there for 1000 head bikes ...even 1200 and 1100 ignition fall prey to the belt situation ...in oldwings ..plus they are totally non adjustable ...and the number one cause why Fuel injection never seems to work right on these motors cause FI needs to be able to control timing as well as fuel to work good ..so on my bike with its progressive Weber 2 barrel carb and it's programmable timing advance ..witch I can tell you is huge over stock setup is the biggest reason my bike has tons of power ..as long as I get the belt timing tension equal on both sides the bike is a monster ...I had the choices of the electronic ignitions on the 1200 motor I use but it was set up way to mild to operate the second barrel kicking in ...I don't know what going on top of manifolds you got but my guess is the 1200 ignition is mild and not adjustable in any way ...my vote would be to switch to the 1000 set up ..and probably points as you could tweak the advance and my guess is the 78-79 points set up would be the desired one to work with cause they actually advanced more than the 75-77 set up ...as said C5 is nest ever but you would need programmable set up to with is about impossible I'd say ...I am sure if something ever happens to my c5 the bike is dead lol...good luck with your bike the potential in that set up of 1000 heads and 1200 short block is huge my bike been set up that way about a decade now ..I don't ride it much anymore ..but it seems too fire right up even after long sits of not running ..stock carbs would never do that ...

 

[RazMan]

Hmmm ..ok I basically have a bike set up like yours ...except no twin Weber set set up ...but do use the 1200 short block ...actually 1100 heads ...with early 75-77 cams ...my ignition is the out of business c 5 programmable ignition ..the best ignition ever made for early oldwings ...the problems with the early points ignition is they use springs for timing advance that are small old and very unreliable and no adjusting ..this also true with electronic set ups made to replace them ...the dyna set ups made this problem even worse as there adjustment to adapt was worse than the points ...one of the best things and worse things about oldwing 4s is they use 2 trimming belts ...in reality this is like 2 motors in one ..if the belts are perfectly in sync in tension you can never time the motor a tighter belt and a looser belt motor is impossible to time with the ignition set ups out there for 1000 head bikes ...even 1200 and 1100 ignition fall prey to the belt situation ...in oldwings ..plus they are totally non adjustable ...and the number one cause why Fuel injection never seems to work right on these motors cause FI needs to be able to control timing as well as fuel to work good ..so on my bike with its progressive Weber 2 barrel carb and it's programmable timing advance ..witch I can tell you is huge over stock setup is the biggest reason my bike has tons of power ..as long as I get the belt timing tension equal on both sides the bike is a monster ...I had the choices of the electronic ignitions on the 1200 motor I use but it was set up way to mild to operate the second barrel kicking in ...I don't know what going on top of manifolds you got but my guess is the 1200 ignition is mild and not adjustable in any way ...my vote would be to switch to the 1000 set up ..and probably points as you could tweak the advance and my guess is the 78-79 points set up would be the desired one to work with cause they actually advanced more than the 75-77 set up ...as said C5 is nest ever but you would need programmable set up to with is about impossible I'd say ...I am sure if something ever happens to my c5 the bike is dead lol...good luck with your bike the potential in that set up of 1000 heads and 1200 short block is huge my bike been set up that way about a decade now ..I don't ride it much anymore ..but it seems too fire right up even after long sits of not running ..stock carbs would never do that ...

Thanks very much for your comments Joe - I really appreciate it. While I've got the engine out (waiting for the frame to be powder coated) I will look into the pointy setup as you suggest - the ability to tweak the timing might indeed prove to be invaluable for my setup and it was something that I had not considered but it makes perfect sense after your detailed explanation. I have a million other things to sort out before getting the engine running but I have now ordered the kit from Randakks and I am now like a kid waiting for Christmas!
I will report back with pictures as my project progresses

 

[pidjones]

Sure sign of the GL1000 heads would be the points (or at least a cover for them) at the aft end of the left head and the fuel pump/tach drive on the right. Or at least a plate covering the ports, in which case the cams have probably been altered.

 

[RazMan]

Like these?, although there are just a black plastic bungs under the plates so no ports as such - not sure which cams I have until I take the cam covers off to paint later

 

[pidjones]

No. GL1000 heads have no port aft of the intakes like yours do. This is a GL1000 left head. The 1000s can actually be reversed to the other side, I believe (you have to swap some things).

 

[RazMan]

So it looks as though I have 1200 heads after all as I have those extra ports next to the intakes (anti backfire thingies I think?) ...... Ah now I am a bit confused. The Randakk blurb say that the GL1200 has 'much smaller ports' but I measured mine as 32mm which is the same as the carbs that I removed. The Weber carbs are 40mm dia (duh) so I am hoping that their manifolds taper down to 32mm or I am going to have some issues setting them up on the 1200.

 

[joedrum]

Hmmmm if I were you ...and was going to use 1200 heads and the randakks Weber set up so to speak ..you have to use the 1200 cams and 1200 igntion and leave the small head ports the way they are ...1200s are the mildest setup in oldwing fours ...basically Honda had to shrink the head ports going to the carbs so it could pull enough velocity for the carbs to work ...also 1200 carbs are the smallest carbs ever made for old wing fours ...this is what they did to make hydro lash heads work ..very mild cam ..smaller head port ..and smaller carbs ...with the Weber setup witch is huge carb setup in comparison ..you certainly wouldn't want to make the head port bigger ...leave it small like it is or it will never create the air speed to operate the carbs good ...especially with the carbs sitting right on top of the head's ...looks cool ...but this type of setup will bog like HELL untill the rpm got high enough to work the carbs but the mild cam would come into play not sure how much rpm you could get ...there was a guy who modded a propane powered 1200 and got 10ooo RPM out of his build easy with 1200 heads and mild cam setup ...that's over 3000 rpm increase over stock ..sadly he past away ...yrs ago ...

In my opinion parts mixing is very hard things to succeed at ...bolt and go just doesn't happen much ..in my opinion the dual Weber setup as was pushed by randakks was a completely over carb setup ..and really difficult to dial in or run very strong ..my bike for instance is carb just short of one of your Webers ...and it took me awhile and many mods to get it to work right .

In my option the 1300 head's and dual Weber stands no chance of working good without several mods to the carbs heck they don't even work good on 1000 bikes with bigger heads and hotter cams ...your thread bump my interest when you posted 1200 motor ..early cams ...I was thinking the best thing you got going is the extra 200cc that might make the randakks Weber setup work ....but I don't see it working good with 1200 heads and cams

 

[RazMan]

Hmmm ,,, it certainly looks like I've got a can of worms about to be unleashed, and all that will be at the very end of this custom build. I have potentially got a few months of design, fabbing and painting on the rest of the bike before I even think about getting the engine properly sorted. That said, I couldn't resist getting the carbs and manifolds ordered at this stage and it looks like a pair of 1000 heads will be on my shopping list now - ah well, I do like a challenge

Its worth pointing out that I am not after getting maximum performance out of my ageing beauty (I've got a Rocket 3 for that) and I just want something that is rideable and pleasing to look at - something interesting. I build my bikes as a kind of therapy and when I sell them I rarely make any money on them - I just love the building process, transforming an unloved pile of parts into something that doesn't look out of place in this century !

 

[RazMan]

Ok so now that I am definitely going to swap the heads, what should I look for? GL1000 or GL1100? Any particular years to avoid? etc etc.

Reverting to points will certainly simplify the wiring as there is no need for the ECU/ignitor and I can change the timing more easily to suit the enormous carbs if necessary. I will have to make some kind of a cover for the redundant fuel pump drive.

As you can see, I have quite a long way to go

 

[D-50Dave]

JoeDrum's bike, Hooch, is the standard of Oldwing 4-cylinder modification on this forum. Here's the link to the build.
https://classicgoldwings.com/threads/the-full-story-of-the-hooch-build.5313/It's an interesting read, even for those of us who are not so inclined. Good luck, Dave