carb mods

hi , i am new to this bike stuff . i'm not new to engines as i have built many mucle car motors . i am asking why there are so guys changing to a single carb . from seeing the photos of these single carbs it seems to me that cly. 1 and 4 are going to run lean becuase the is not enough runner lenght in the desing . i may be off base and if i am please tell me . thank you

 

I am with you on this one but, its gonna be fun watching someone try to do it.

The dual carb set up is totally doable.

 

Hi This is what it is all about. When some say why others say why not.
When some one comes up with an idea like this the people on the forum that are interested come alive and offer there help and encouragment. They think of all the things that may go wrong and all
the things that may go right and post there ideas up. Some have been down the trail before and can offer some practicle advice. Others
look on from the side lines interested but not involved. It all goes to
make a forum community that is interesting and exciting. I have often
wondered if it would be possible to fit a single carb on a 4cylinder bike
and here is someone trying to do it with pictures. How lucky is that.

 

spr- i can only speak for myself, but i am trying the single carb because i hate having to synch the carbs and check 4 different mixtures. i am taking my ideas from the auto side, so im sure you can relate when i say that a 455 rocket doesnt have 8 carbs, why should my I4 have 4 carbs?

you may be right, it might be more work than its worth, but before i look into my rack of 4 to see WTF is going on i am going to try to rid my life of them

"keep it simple" is whats driving me to try it out, but i havent thrown out the 4cv poop-o-matics yet just in case the warm weather arrives before i get it running right.

 

look at old jolly ollies (olivers), john deere, old cars, and some modern ish cars, they all have one carb or throttle body fueling the cylinders.

not everyone is doing it, just a handful.

but everyone does have opinions, and you know what they say about those

 

hi , thats for the input here . belive me i have done some things on race cars everyone said wouldn't work . it just made me thats much more to do it. after reading what has been posted here i now understand why you are trying this.

with it being true older cars and some of todays cars run with what would be a single carb or throttle body . i see it can be done but think that just the straight runner design would only work at or near full throttle . i would think you would have to make some type of plemtum to mix the air at low rpms . just my thoghts . i would never tell someone not to try things heck thats how we got here . hope it all works . be looking for posts on it .

 

throttle bodies don't fuel, injectors do. On each cylinder has one if not more.

 

Not always. Early GM cars (and probably still some cheaper cars) have a single "throttle body" injector. Effectively making it like a carb, but more complex.

 

In the auto world the early fuel injection is known as TBI (Throttle Body Injection) Most current Vehicles are PI (Port Injection) as fitz stated. I personally would be interested to see how going from the 4 carbies to a single carbie works out. After working as an auto mechanic for ten years I am delving into the motorcycle world for mechanicl experience there as well

 

Single carb mod i believe is not going to work. Unless you can make a duel plane intake. Your cyl pressures will be fighting each other down low. Your factory carbs suck thru a very short 1.25 tube carb to intake valve roughly 3 inches. With a single carb set up it will have to be ad least 6 to 8 inches probably more. That is an awful lot of air to flow before you will see the throttle response. Thats 1 of the reasons cars with long intake runners or tunnel rams have no vacuum . They use big accelerator pumps to flood it when you push the gas pedal.It actually puddles on the intake runners thats with the carb on top let alone on the side.
You can get away with it on a v twin the runners are much shorter. Plus Each cyl has so much more volume. You can anyone that has went to single carb set up they do not run as well as a multi carb set up unless their carbs were really out of adjustment. And when your comparing it to a 350 chevy the 350 runners are smaller then the bikes 1.25 diameter the bike 188 cc piston pumping each piston in the car is 713 cc thats almost as much as the whole bike thru 1 runner smaller then the bikes. My race car ia 8.2 litre 1025 cc per runner and they are still smaller Hope i make sense the gear heads will get it.
Now if you could port fuel inject it and mount the throttle body at the end of the intake where the single carb would go it would work much better

 

This is the reason why in concept, I believe it will work.



Because its been done before.

 

I would dump my carbs in a second if there was a reasonable priced fuel injection setup available.

MN

 

Yes darkfibre that did work , but that inline six would still suck as far as motorcycle throttle response etc. Throttle body, direct injection is a whole different animal. Can't be compared to trying a single carb mod. JMO

 

I totally agree, that post was just to answer the people who seem to think unequal length paths can not be made to work at all.

My XJ is in the middle of an EFI conversion, which is my preference.

 

The XJ motor is a high performance engine, if you want it to run like a stock Ford escort, go the single carb route. My 2c........