Moto Guzzi Sport 1100 Keihin FCR specs

[Guzzi07]

Hi:

 

Just thought I would post the setup specs for my Moto Guzzi Sport 1100 fitted with Keihin FCR39 carburettors, just in case someone else is trying to tune a bike with this setup (I could not find any specs for FCRs fitted to an MG 1100 Sport online). I have posted the specifications here for both FCR41s (advice from Keihin & Sudco) & FCR 39s (based on experience with my bike) as fitted to a Sport 1100. You take this advice at your own risk.

 

When I bought the bike it was running quite poorly (too lean from off idle to 1/2 throttle [surging] and too rich at idle etc), I found that the jetting was way out. After jetting them to FCR41 specs it did run better but was still surging and not idling properly (too rich). I belatedly went back to basics and measured up the carburettor dimensions and found that were not actually FCR 41s as I had assumed (the only FCR kit for Sport 1100s), rather they are FCR 39s. Also unlike the kit, these FCR39s do not feature a ram air pressurised float bowl.

 

After a fair bit of playing, the Keihin FCR 39s now run pretty well with the following setup. I think the bike is still running a little lean off idle (I think I will screw in the slow air jet ¼ turn and lean up the idle accordingly) and perhaps a little rich on the needle (might try a leaner needle, EMP or EMQ needles). I have deliberately kept the ½ to full throttle specifications quite rich to compensate for any ram air effect leaning the mixture (the FCR39s I have not allow for pressurising the float bowls unlike the proper FCR41 kit) and just to err on the side of caution (i.e. for engine longevity it is always better to err on the rich side). The bike is standard apart from a K&N air filter (with standard air box) and mistral crossover and cans (without DB killers).

 

If I keep the bike long term I might go to FCR41s, as I would imagine that the FCR39s are restricting top end performance.

 

Keihin FCR39 Specs (based on my bike):

#155 main jet, #200 main air, #50 slow fuel jet (pilot jet), slow air screw 1 & ½ turns out, fuel screw (idle mixture) 1 & ¾ turns out, EMN needle (5th groove from the top).

 

Keihin FCR41 Specs (from Keihin for a standard bike):

#155 main jet, #200 main air, #55 slow fuel jet (pilot jet), slow air screw 2 turns out, fuel screw (idle mixture) 1 & ¼ turns out, ELS needle (4th groove from the top).

 

Keihin FCR41 Specs (from Sudco for a standard bike):

#155 main jet, #200 main air, #55 slow fuel jet (pilot jet), slow air screw 1 turn out, fuel screw (idle mixture) 1 turn out, ELS needle (4th groove from the top).

 

Hope this helps someone.

 

After rebuilding the gearbox (with a clutch replacement), giving the bike a full service and fixing a few odd issues and playing around with jetting the last 4 weeks, I am hoping now to start riding the bike and enjoying it!

 

Thanks,

 

Jason

[GuzziMoto]

I would think all you need to do to "pressurize the float bowls" is to run the vent lines into the airbox. That way the float bowl and the airbox would be at the same pressure. Do your carbs not have nipples on the vents where you can put a hose on? That would be unusual in my experience.

As you are probably already aware, a smaller carb typically needs slightly leaner jetting for the same motor then the larger carbs do. Sounds like you are going in the right direction.

How did you end up with 39's?

[Guzzi07]

There are no nipples on the carbs to pressurise the float bowls unfortunately. There appears to be a type of FCR for bikes with pressurised air boxes (Kawasaki ZXR, Guzzi Sport 1100 etc) which has a vent nipple for the float bowl (just like the original 40mm dellortos that would have originally come with the bike) which can then be linked up to the airbox, however the carbs I have are not of this type and do not have this vent. There does not appear to be any obvious way (without a fair bit of drilling and taping of the carb body) to add a vent nipple. I understand the ram air effect really only makes a difference above 160 km/hr (100 mph), which I will not be doing very often (at least not on public roads anyway).

 

I am going to check the fuel consumption, but suspect that the needle is probably too rich (it is richer than the FCR 41 spec). The bike runs well now, so the plan is to bring it back to my place (about 3 hours ride from where the bike is now) and play with it from there. As you say, all things being equal, the FCR39s should be jetted leaner than the FCR41s for the same bike. If I could just have access to a dyno and exhaust gas analyser for 1 hour, I am pretty sure I could make it run spot on. Maybe when I have a bit more money I might splash out with a dyno tune.....

 

The carbs came with the bike. I thought they were FCR41s when I bought the bike (that’s what the owner thought as well and I don't think he was lying). As far as I know there are no external markings apart from the part number that distinguish an FCR39 from an FCR41. The carbs have the right bellmouth adaptors to connect up to the Guzzi airbox and the the rubber intake manifolds.

 

Anyway I am pretty pleased with how it runs now and it has been a good learning experience, none of this tuning with a laptop like my MG 1200 Sport, but the old fashioned way with needles and jets and using the old seat of the pants dyno! When I bought the bike (for a good price admittedly), when starting from cold you really had to keep pumping the accelerator pumps constantly to keep it running and even then it was spitting and carrying on, and even when hot the bike would not idle and be spitting and surging when running below 5k. Now it runs really well with only a little surging when cold (which I would expect as the bike would be running lean).

[GuzziMoto]

I do not recall ever seeing a carb that did not have vents for the float bowl. It is pretty much standard to vent the area above the fuel in the float bowl. Not all of them have had nipples for the vent lines, many CV carbs have internal venting back to the intake bell. That is pretty much the same as venting to the airbox. Where do your carbs vent the float bowls? On the FCR's I have seen the float bowl vents were about halfway up the main carb body on both sides of the slide area.

Here is a link to an exploded view of one.

http://www.pbase.com/jdjetting1/image/53264343

You can see the nipples for the vents about half way up the sides of the carb body.

It has been a while since I have played with a 39 FCR but last one I saw I was pretty sure it had vents. That was on a supermoto.

Either way, unless you spend a good bit of your riding above 100 mph I would not worry about it and just jet it correctly.

Typically you should be running leaner jets and needles in a 39 FCR then you would in a 41 FCR for the same motor. Something to do with the increase in intake vacumn that results from the reduction in carb size.

[Guzzi07]

I should have been a bit clearer, the carbs do not have male "nipple" vents (that I was expecting to find), however the carbs do of course have float bowl vents (I blew the vents out with compressed air when I cleaned each carb). The FCR link you provided is quite different from my carbs (though the basic workings are the same), this exploded view shows the design of my FCR39s: http://www.showandgo.com.au/carbie/fcrexp.htm

 

Looking at it more carefully, I now realise that male pipes are all that is needed, they are inserted into the receptacle holes, with a rubber hose then used to connect the vents to the airbox. As I recall both ends of the vents are open, so I guess a rubber bung would be needed to block one end from atmospheric pressure. There would however be a problem with the R/H carb as some idiot has managed to break the round part off the vent receptacle casting (how someone would do this I don't know), though I could probably use some Devcon F to build up this receptacle again.

 

In the end, even if I had looked a bit deeper and worked this out, with the broken receptacle on the R/H carb it would be too much hassle to setup for moderate gains at the top end of the range. If I eventually go to a proper FCR41 kit, I'll make sure I set up the pressurised float bowls properly.

 

I plan to take a few pics of the bike when I pick it up in a few weeks (next to my 1200 Sport), I'll take a close up of the R/H carb with the broken vent receptacle. Apart from the carbs and someone using red locktite on the drive shaft clamps (the bolts were an absolute b**tard to remove), the rest of the bike is in great condition with no evidence that anyone has mucked around with it (i.e. missing parts, incorrectly assembled bits, stripped threads etc).

[boogla]

Hi. Pls excuse my ignorance but I just bought a carb sport that has pod-filters and a full staintune system. i'd love to get the 41fcr's but in reading your info am concerned it will present probs as I dont have a pressurized airbox any more. I'm very interested in how things go with your set-up and any info people can provide, I'm also after some thoughts on how to improve the front-end m1r forks(spring upgrades etc) Sorry if that causes a slight thread drift

Cheers

[Guzzi07]

My problems were really related to some idiot in the past bolting on a set of FCRs to the bike without setting up the jetting. I think if you buy a proper kit, they really should just be a bolt on arrangement. After having worked on the carbs for a while (and learning a lot), I really began to appreciate they are a beautiful bit of engineering.

 

From what I understand the ram air effect only really comes in to play above 160km/hr, unless you are going racing, I don't think the missing ram air setup will make much difference on the road. To my way of thinking, you actually should have no problems at all buying a standard FCR41 kit for the Sport 1100 with pod filters. The pod filters may flow a bit better, so you might need to richen things up a little. My setup is a bit of a problem as I am running a pressurised airbox without pressurising the float bowls, given you will not be using a pressurised airbox and just running the float bowls at atmospheric pressure, it should not be much of an issue (apart from the slight loss of top end performance without the ram air setup and maybe a little leanness due to the higher flowing pod filters).

 

GuzziMoto seems to know a lot about these carbs, so hopefully he might add some advice.

 

Having pod filters makes it much easier to work on the carbs and make preload adjustments to the rear shock (as well as sounding great), however at this stage I don't want to spend any money on the bike.

 

Haven't played with suspension yet, plan to ride the bike over the Australian summer and then start working on the front forks next winter.

 

I live in Canberra but have been working on the bike at my parent's place in Sydney. I plan to take the bike for a long run up the putty road on a weekend in late September / early October before taking the bike to Canberra, if you wanted to join me and have a look at the setup. Let me know via a PM if you want to meet up.

 

Jason

[Skeeve]

Hi. Pls excuse my ignorance but I just bought a carb sport that has pod-filters and a full staintune system. i'd love to get the 41fcr's but in reading your info am concerned it will present probs as I dont have a pressurized airbox any more.

 

Don't worry about that: somewhere in the archives is a post by Greg Field (iirc) to the effect that someone once measured the amount of airbox pressurization achieved by the Spot/Sporti's airbox, and it only amounted to about 1/2 psi @ 100mph. Obviously, it would go higher as speed goes up, but it can't really be called "pressurization" so much as "compensating for sheer-induced vacuum in the airbox at speed."

 

You've much bigger problems than that running pods, as any side-breeze will affect your jetting. [Airboxes are faster; pods look better. Que sera sera! ]

[GuzziMoto]

My experience with those carbs is from Ducati Roadracers and Supermoto's. I have not put them on a Guzzi, yet.

They are really nice carbs, that make all the right noises and work really well once set up correctly. About the only negative aspect to them is the cost of parts like jets tends to be relativelyhigh. But once you have them jetted correctly that should no longer be an issue.

I agree that not having a pressurized airbox makes it easier, not harder, to use and set up these carbs. And I don't think the lack of ram air is an issue on a Guzzi.

I would not hesitate to switch to the FCR's if I had a carbed big block. But the only carbed Guzzi at my house is a Lario. I think even the 39's might be too big for that one.

As for forks, when I needed to upgrade/fix the conventional forks on my Daytona I swapped them to a set of late model GSXR1000 forks. The lighter front wheel, better brakes, and changes to the geometry (steeper rake and more trail), all contributed to a large improvement. Much more then I could have ever gotten out of the stock forks. And it set me back $600 for the front end including the wheels along with $350 for a high end Brembo master(that was just a cherry on the sundae).

I am sure you could spend less on upgrading the stock forks on your bike. I would send them to your preferred suspension guy for that.

[boogla]

Thanks Guys

I appreciate the replies and info

The way the bike is currently jetted is pretty rich, so hopefully cross-winds etc won't lean it out too far

 

I own a Thruxton with pods too and the FCR's will probably find their way onto it too if they work well on the Guzzi. unfotunately I got hit by a car and fractured my leg in 2 places so until the financial compensation rolls in, the dellorto's stay. Here's hoping the cash rolls in soon and I can report back on how the development of the bike goes.

 

As for the forks, it will be the same - wait for the cash then get serious with the mods, so I'm just collecting whatever advice or information I can gather prior to commencing works.

 

Cheers