SINGLE CARB MOD

Hey Zookie, Just to note, if you didn't get the point of that particular experimentation on the blog, is that the bike gets great mileage. Over 100mpg on gasoline (depending on source derived and driving conditions etc) and well over that with diesel. There is much to understand in the propagation of the materials I described in my first reply. I was just trying to point out your going in the right direction and there is plenty of information to help lessen the trial and error part and to be hopefully encouraging. The point of the turbo on my bike was less about power and more about enhancing stratification although there is always a benefit to volumetric efficiency. You will have great bottom end torque and good mid range with the smaller diameter inlet. Good luck and keep the pursuit!

 

Zookie, I'll have to say you are obviously a very patient man, and quite a fabricator. Cool idea and interesting to watch you conquer this.

 

havent conquered it yet! i am still prepared for total failure

our good forum friend dwcopple gave me a great deal on his crabraider and shipped it. THANKS DUDE!

this project will take an intermission because:
a) i am back out on long island in a hotel for the rest of the week, 50 feet off the highway, 75 feet from the 4 train tracks, and directly under the takeoff line of a runway closeby.
b) this weekend i have to participate in a complete body swap on a 80's f-150, and while the rest of the guys are attacking the frame with wire wheels and POR-15, i and the trucks owner will be stripping the engine and reassembling with fancy Offenhauser/Holley 390 4bbl intake, GM hei style one wire ignition, full exhaust, and new seals and gaskets all around.

so.......stay tuned

 

Very interesting to say the least. It would be nice if someone could come up with a single carb application which actually worked while not loosing performance. With the price of carb re-build kits and time down a single carb could be very desireable on the 750XJ seca. After repairing a lot of other things on this 81' XJ750R Seca which I recently purchased I thought I was finally ready to see if the old gal had any fire left in her and prepared to try starting her? She fired about 5 times and then died! At this time I noticed that I had gas leaking all over the place! What was leaking was the pipes which run from carb to carb for the gas flow. The O-Rings must be shot in all of them$%^&%&^%^&!!! grunt007, Mi.

 

How is this going?

 

Hi ya Ravenz07,
Well, hows it coming eh? Like a TURD to say the least. Turns out that the ideot that I purchased this bike from should have never been allowed to put a wrench to it. The two outside carbs look like someone took a ballpeen hammer to them. The one appears to have a crack through the float bowl from top to bottom. In all of the bikes I have worked on over the years I have never ran into something like this at least not in the bikes which I have purchased. I noticed the carbs looked bad when I bought it but until I took all of them off I never dreamed that they were this bad. This Sunday in NOvi Mi. there is a large motorcycle swap meet that I am going to. Hope I can find some carbs there for a reasonable price? Some people now days should just not be allowed to have a motorcycle and this guy is one of them. Just no respect for a quality piece of equipment. I'm now looking at what new boots (carb to cylinder) carb kits, and who knows what else and to top it off I have to put up with a crotchity friend of mine which Is a THROUGHBREED Harley man rubbing it in. His last comment was just sell it for what every you can get and buy a Harley. Well, being a disabled VietNam Vet that is not an alternative. I never had a bike in parts or other wise that I did not finish and I don't plan on this XJ750R Yamaha being the first. And he can take his Harley's and shove them where the sun doesn't shine!
this old Yamaha will live to PUFF some smoke again one day one way or another. grunt007, Larry-Mi. I must admit though if it wasn't for this little web site(XJ Bikes) to read I would probably consider sending this gal to the great beyond! Take care for now bud! Ex-Marines just don't like to give up I guess, we sort of see ourselves and our survival in the things we work on and the hope we can build into them.

 

No such thing as an Ex Marine, once a Marine, ALWAYS a Marine (including that idiot Lonetree). Semper Fidelis!

 

sorry guys i havent had a minute to spare for the poor thing, my boss bought another truck and told me i have 5 weekends to make it a race truck. i guess one hill climber wasnt enough.

i should have some time on it tomorrow or sunday though.

 

just to tease you guys a little.....

i really havent had a chance to work on it. i did take about 10 minutes today, bolted the new manifold and carb up, and tried to start it.

1) i know the jetting is way to lean, but i figured i would run it as is and see for sure how it acted.

2) it started on choke, and would run strong for about 10 seconds, no fuel smoke out the tailpipes, no fouled plugs!

3) i need a different throttle cable, my current cable doesnt have enough throw to allow the slide to go lower than about 1/4 throttle......so any attempt at tuning would be difficult right now.

i have been too busy, because along with normal work, my boss (and friend) decided to buy a flare side f-150, and told me to "make it a hill climber" using donor drivetrain from the baja truck. so.......its been a busy past few days. i am NOT complaining, race vehicle work is always welcome.

as for my bike, tomorrow we are leaving CT again for LI, and i will be ordering my throttle cable, hopefully it will arrive in time for me to fiddle with it this weekend.

so although its not a bike, and not related to single carb mods......here is a pic.

 

Zookie, That is definitely not a bike! By the way, I have a 1990 Toyota 4-Runner with rust around the fenders, about 137,000 miles on her, V-6 3 liter, sun roof, front crash bar, never been 4-wheeled, good rubber, bet she would still make a good hill climber! I bought her new in 1990. She now has a bad fuel pump but interior is great shape and clean. All good glass, all power windows work fine and tail gate power window. Can't seem to part with her since she was always great to me. Never burned a drop of oil. 3,000 miles per oil change and the oil at 3,000 miles was still always right up to the full mark on the dipstick. Bet she would make a great hill climber! Driving her down to Florida I would get up to 28 miles per gallon with the stock I think 15x31.5 tires. AC still worked fine also when I parked her. Believe it or not, one year in the winter here on our back roads I was going to a job and one of our roads with a hill on it coated in ice there was a County double gravel train stuck and couldn't get up the hill. They had a 4-wheel drive road grader (diesel) hooked up to it with about 10 men throwing gravel on the icey road and it couldn,t mover it. I told the driver I thought I might be able to get him up the hill. He just laughed at me. I drove off the road and went through a field with snow over 1 1/2 foot deep and came out in front of the gravel train, backed up to it and hooked a 20ft. tow rope to the front, put her in 4-wheel drive, in CREEPER, told the driver to just give the power slowly. Long story short I pulled that bugger up that hill and when I got him up the hill his comment was, Well, now I guess you are going to tell everyone about this-I said, you better believe it-he wasn't laughing. Wish I would have had a video of that. Toyota would have probably given me a new 4-Runner to use that one for advertising! I use to swear that if she could get traction in CREEPER I bet I could pull a house down with her.
First Foreign car I ever owned and best car I ever owned. grunt007, 81'XJ750 Seca still in process of re-building! Mi. (newbie) but not a dumbie? ))))

 

dont worry, its on the back burner but the burner is still lit!!! i just havent had the time (when i am in state) to fuss with it.

i have been riding my sisters kz440 because she wants to sell it so i havent broken down and put the craprack-o-carbs back on for the season.

 

IT RUNS!!!

i only spent about 15 minutes tinkering with it but i drilled the jets larger (purposely went too rich) and it started without aid, and idled rough but without fouling and without "user input" to keep it alive. also although it was rough it would have idled indefinitely, idled for about 5 minutes straight before i shut it off.

it didnt want to take throttle when i first started it, but once it had a little heat in it i was able to rev it and although its not jetted perfectly it was close enough to make me want to button it up and ride

i need to get my jets and spend some time dialing it in!

side note: the manifold gets COLD!!! i might make a heated spacer for it, but first i want to try riding it. i think the heat from the air cooled engine may warm it in real world riding conditions. if it stays cold while i am on the road i think it would help to have a heated spacer or probe of some type. oil fed
will probably be the easiest for this application.

 

yep, them manifolds get icy cold...it is awesome for HP #'s too. dense charge of air=nice burn. Is that using the carb I sold ya?

 

yes sir! tiny little booger but it should work well! definitely going to choke out up top, but i rarely break 6k anyway.

i will grab a pic of it all bolted up when i work on it again.

we are working like crazy trying to get the second race truck ready by next saturday, so bike is not getting much attention.

 

awesome. glad to hear it.

 

ok fellas, i have good news and bad news....

the good:

i rode it, was only able to get up to 45 because of traffic but it went just fine. still needs a little tweaking on the mid range but its ridable. the idle speed is a little high, even with the screw turned down. perhaps a little machining would allow the slide to close more so it could be set a few hundred lower. its not terrible, about 1200 though.

the bad (for followers of this thread, but still good for me):

i have had some serious offers on parts off the bike, i never liked this bike, and the KZ gets 10mpg better than my xj. with that being said i will be parting the xj out and i officially own a 81 KZ 440 LTD in MINT stock condition. i would have loved to see this one to the end but i just do not have the time, and as diesel approaches $5 per gallon i need to make the wallet friendly decision to abort this project and move on. my time needs to be spent on the race vehicles rather than side projects.

i would love to see someone try this, and spend the time i didnt to get it dialed in perfectly and log some hours on it.

 

Been reading this thread with interest.
Here's a single carb setup I made 20+ years ago on a GS850 Suzuki. Still got it, running fine to this day.
I was driven to it by the cost of rebuilding the original carbs and on two bikes, at that. So I fell back on my own experience of SU carbs and how they function.
The manifold came off a four-banger car, cut and shut to match the port spacing of the engine, the port flanges were part of the Suzuki inlet rubbers and the whole thing welded up by a local ally welder, for the price of a case of beer. I think I underpaid him, to be honest.
The carb was originally a 44mm, which ran up to 115mph, but did show signs of struggling a bit at the top end - I suspect that was the limit of airflow on this manifold. A couple of years ago, I replaced that one with a 38mm and concentrated on getting the jetting right.
It goes like shit off a shovel, up to around 90mph, then gets a bit lean, so more work is needed.
Thing is, this bike is perfect for hauling stuff around and being a general duty tug, and now I've got an unmolested XJ900F, I don't need the GS to go any faster than 90mph anyway


And with a better diy K&N element for better air flow than that horrible pancake cheapy filter in the first pic.


Technical details:
The first carb was an HIF44, now it's an HIF38. Yellow spring, ADK needle.

 

Interesting one carburettor and a manifold, how difficult is it to make a manifold for the XJ 900f and what carburettor is suitable?

 

I've glanced at with this in mind, and I'd use the same procedure, as far as possible. 20+ years on the alloy Sunbeam / Avenger manifold is in much shorter supply that it was back then, but I've no doubt something suitable can still be found. The original Suzuki carb mounting rubbers contained alloy plates that mated to the cylinder head, and if the XJ ones are the same, then the game's on. If not, then something can be made from scratch - they're just simple flanges, after all.
The Sunbeam / Avenger manifold was cut by me and handed to the welder with the plates attached to the spare head I had, so all he had to do was stitch it up.
I'd use another SU carb, definitely an HIF 38 to start with and maybe a 44, depending. Jetting will not be too different from the Suzuki settings.
Fortunately, SU carbs are still plentiful, and I've been buying spares.

 

Did the welded up manifold fit into the Suzuki intake stubs? It would eliminate the need to balance carburettors too. Be interested to see what you do with the XJ could be a great modification.

 

The Suzuki inlet stubs have an alloy flange moulded into them. I liberated those flanges and they got welded on to the cut and shut manifold.
Those original inlet stubs were toast, and damn near thirty quid each at the time, so it went towards the overall cost of doing a rebuild. Plus the cost of airbox rubbers and the cost of new carb internals. On two bikes.
Eff that. I refused to bend over and let myself be shafted by the Suzuki Dealer Network.

 

I do the same Dave as costs mount up quickly. It's great how you made that manifold and as they work on cars why not. I would like to make one for my own bike now. You got me thinking about this single carburettor conversion. Mabe you can post a few pictures once you make one for your XJ and advise on the best parts to use and jetting etc?

 

Well, the XJ is a relative youngster with a mere 111K miles on it, as compared to the GSs which were considerably more than that, and everything that could be vibrated to death, was, including carbs. Allied to that, if the internet had been around back in the day, I'd probably have just picked up a replacement rack or two of carbs from somewhere and just got on with that more conventional route.
What I'm saying is, the XJ might not need a single-carb made for it, but if parts dry up or become pricey, then it might get one. Even carb diaphragms are available cheaply now, unlike 25 years ago.

 

...and, to update, things are afoot.
A recent descent into bad running had me examining the carbs, and by the time I buy new rubbers (hard and broken/leaky) front and rear and new diaphragms, plus the basic cost of a minor carb refresh kit for the float chamber, it all adds up to more than I feel like paying.
A Weber is the weapon of choice, this time.
I had a close look at the room available and Yamaha having moved the alternator and starter inboard and upwards means there's no real room for an SU in there unless I have it poking out the right hand side, meaning there's going to be a torturous passage for fuel/air mix, so rough measuring up revealed just about enough room for a simple branch manifold with a downdraught Weber sitting directly on top and it can poke up between the two frame rails. Hopefully there will be enough space above it to allow a smooth flattened elbow to get air into the top of it and a cool air hose can be run to the front of the bike, with a filter cone on the intake end (details to be finalised).
I've scored a Weber 32 DIR, which is a close relative of the DGV and even though it's a production-line carb originally fitted to small Volvos, the jetting in it is changeable enough to allow proper running on a 900. I'm fairly sure it will be an improvement on the SU, as the first choke is 23mm, the second choke is 24 mm, and there are a couple of extra enrichment circuits that might (or might not) help out.
To start with, the manifold will be roughed out using 1.5" mild steel thin-wall tube going into each port stub (I'll use the original port stubs for fitting, then replace them with a set of the cheapies from China), The feed tubes will be welded onto a short section of 2" square box , mounted longitudinally, centred on the rear of the head. Cylinders 1 and 4 will be fed via slightly longer curved elbows and cyls 2 and 3 via shorter elbows.
This is to attempt in some way to give each cylinder a chance of getting an even feed, both from the primary choke and the secondary choke in turn.
It won't be be perfect, but it will work.
I expect I will drop some power, but the mere fact of having a decent choke area I might not lose too much - I foresee a loss of at least 10hp and likely 15.
However, it it gets to 115 and can sit there without being too rich or too lean, I'll be happy enough.