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Discussion Starter · #1 ·
Hi,
might be interesting for you what I've done 'cause not much about that on this forum. I was tired of my unstable DellOrto so I dicided to make an experiment with motorcycle carbs. My choice: four Mikuni carbs Yamaha 1300 ccm for $80 in perfect condition. The home made airbox fits perfect. The rest you can see on the pics.
Foam mold:



Glassfiber body



Ready to install




And here we are



Not tuned carbs: easy engine start, idle perfect, car pulls good at low rpm and has fantastic low gas mileage 7,5 l/100 km touring at 100/110 km/h but poor dynamic and poor max speed. So could be cheap driving her daily in the city. We like to step on gas pedal sometime and we don't care of gas, isn't it? So I tuned the carbs in three steps:
1. Main fuel jet 107.5 changed to 112.5; result slighlty better but still no enough power and lean mixture at higher revs.
2. Main fuel jet changed to 122.5; yes that was probably what was needed. I tryed to stay with as low gas mileage as possible so dicided to take just one last step to improve dynamic at middle revs
3. The needle gone up; clip one groove down and one shim under the needle.

I'm very happy with the result. The carbs are extremely easy to tune, adjusting and sync. I feel that they got much more potentaial and power that can be awaked but I don't want to visit gas station more often. The airbox killed carbs noise and now it is very nice throaty deep sound from the back pipe only.
And one thing: that set-up when tuned and adjusted you can disconnect from the engine intake and put it on again not loosing synchronization; just plug and play ! :)

Now it's time to do some serious set-up for having more fun. I have bought FCR set-up for $400 on ebay. After first test; friend of mine in TR6 with supercharger smells my back pipe :) and the carbs are not even tuned yet, sorry dude. Don't aske me about gas mileage. Now time to play with tuning. Any time I can change set-up one to another within an hour; just eight bolts.

 

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it is obviously a really nice job you have done there, but with such a superbly clean engine bay as you have there in the photos, why not just go with twin Weber 40 DCOE's - surely a lot simpler
(My S4 also gets 7.5 to 7.8 l/100 km from standard - which is good over here as gas is as expensive as single malt over your side of the Atlantic:))
 

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Very nice work! You make it sound all too simple! What's the FCR setup, for a larger displacement motorcycle?
 

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I can say having tuned on many motorcycles that those carbs are simple to tune. My current fj1200 has a set of keihen cr37's and they are simple to adjust and do jet changes. I have never had to deal with webbers but from what I have seen from other postings they are not as easy as this motorcycle set up. I for one like the inginuity involved with this set up but if drivabilty issues are at play now the fcr carbs would seem to me to be be more likely to be tempermental. I have to say that my kehein's when jetted correctly work great just a little tiring on the wrist on long rides. Good work and keep us posted on the developments with the fcr's. Now you have me thinking how clean my engine bay would be without all the FI components and how often do I realy ride the fj anyway hmmm!
 

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You may experience some tuning problems because of how the carbs were mounted on the bike. They were not horizontal. They were mounted at about a 45 degree angle for a semi-downdraft system. If you look at the float bowls you'll see that they are angled for the bike application, thus possibly causing either flooding or starvation at different rpm's. I suggest you visit a Yamaha dealer to see the original installation.
 

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Discussion Starter · #7 ·
it is obviously a really nice job you have done there, but with such a superbly clean engine bay as you have there in the photos, why not just go with twin Weber 40 DCOE's - surely a lot simpler
(My S4 also gets 7.5 to 7.8 l/100 km from standard - which is good over here as gas is as expensive as single malt over your side of the Atlantic:))
Thank you. Well, the point was not to go back to DelOrtos or Webers and in my opinion I have achieved a very good drivabilty for very low cost. That set-up is much better that my DelOrto. All problems gone.
 

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You may experience some tuning problems because of how the carbs were mounted on the bike. They were not horizontal. They were mounted at about a 45 degree angle for a semi-downdraft system. If you look at the float bowls you'll see that they are angled for the bike application, thus possibly causing either flooding or starvation at different rpm's. I suggest you visit a Yamaha dealer to see the original installation.
Agree with rocket but I thought you would account for that, but if you look at the cv carbs off of the 1300 they look side draft certainly not like the FCr's bowls and as with my FJ1200 you can get side draft cr carbs. The fj motors were used alot on legend cars so there are carbs out there to be had hopefully not for more than you spent on the fcr's. My keheins new were in the 900+ $ range so $400 seems like a bargain to me.
 

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Discussion Starter · #9 ·
Very nice work! You make it sound all too simple! What's the FCR setup, for a larger displacement motorcycle?
FCR setup was used for one mile racer bike lately

You may experience some tuning problems because of how the carbs were mounted on the bike. They were not horizontal. They were mounted at about a 45 degree angle for a semi-downdraft system. If you look at the float bowls you'll see that they are angled for the bike application, thus possibly causing either flooding or starvation at different rpm's. I suggest you visit a Yamaha dealer to see the original installation.
Rocket, I had no tuning problems at all. It is common to take few steps to find the best jets configuration. The float bowls are in the same position as in Yamaha xjr. Before I do anything I try to find and read almost everything about that including shop manuals. As you see I welded different inox intakes for different carbs taking the proper bowls level under consideration. FCR carbs could be tilted in some pretty wide angle range.
 

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Discussion Starter · #10 ·
Agree with rocket but I thought you would account for that, but if you look at the cv carbs off of the 1300 they look side draft certainly not like the FCr's bowls and as with my FJ1200 you can get side draft cr carbs. The fj motors were used alot on legend cars so there are carbs out there to be had hopefully not for more than you spent on the fcr's. My keheins new were in the 900+ $ range so $400 seems like a bargain to me.
It was accounted with alfa engine tilt degree. Believe me that the bowls level are perfectly horizontal.

 

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Motorcycle carb size for 1974 GTV 2000

Hi,

I live in Montreal, Canada and am the recent owner of a US spec 1974 GTV 2000 with Spica FI. I am interested in converting it to carburetors and I am very intrigued by your creative use of motorcycle carburetors.

What size engine does your spider have? My car has the stock original 2000 cc engine.What size of throttle bores would I need for my engine? What carburetors would you recommend?

Please PM me your email address so I can contact you off line, if I need advice or mor information.

Thany you,
Richard
 

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Discussion Starter · #14 ·
Hi,

I live in Montreal, Canada and am the recent owner of a US spec 1974 GTV 2000 with Spica FI. I am interested in converting it to carburetors and I am very intrigued by your creative use of motorcycle carburetors.

What size engine does your spider have? My car has the stock original 2000 cc engine.What size of throttle bores would I need for my engine? What carburetors would you recommend?

Please PM me your email address so I can contact you off line, if I need advice or mor information.

Thany you,
Richard
Hi Richard,
email address sent.
My Spider originaly was 2000 cc engine with Spica.
The bigest throttle bores the better result. But you can't find a bike with 2L engine with carbs so try to find carbs for 1300 cc engine or go for FCR 39 or biger if you gonna build a rocket :)
 

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How did/are the fcr carbs working out V. the cv carbs?
 

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Hi,

I live in Montreal, Canada and am the recent owner of a US spec 1974 GTV 2000 with Spica FI. I am interested in converting it to carburetors...
Every time a SPICA car is converted to carbs, the Alfa Gods cry...
 
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