Latest motor build.

[DAM shop]

Just finished with our latest motor. Bored, stroked camed 110 motor running with this real cool ( never before seen) Mac pipe. We are just now in the tuning stages and need a little advise as to the direction we should start. We are running a mikuni 22 mm carb main jet 100. The trike starts, idles and has good response to 3/4 throttle. 3/4-wot it surge's. Tried a bigger main but the only one on hand was much bigger than the 100 and the surge worsened. Dropped the needle 1 clip down, no difference. I am assuming I'm not pushing enough air the reason I think that is because our other 110 (bored only) is running a 24mm mikuni.
Would removing my air filter give me a clue as to if I'm
Starving for air. Should I just start with a 24mm carb?
I've also considered putting a 185 carb on if it will fit with the shorty intake we are running. I also have a flat side carb size around 30 without measuring it
Anybody have any thoughts here? Again I've just started testing and tuning just looking for somewhat of a starting point.

[barnett468]

A carb that is smaller than the optimum size will not cause an engine to surge, providing it is properly jetted. It will merely act as a restricter and reduce power and peak rpm.

Since you have not tried to jet it with jets that are close to the 100 you have, it would seem logical to try jets closer to that before simply trying different carbs, unless you happen to have one that will bolt right on, in which case, it will likely need to be jetted too.

Also make sure the float level is the correct height.

.

[El Camexican]

.... and that it’s not starving for fuel.

[DAM shop]

Well maybe the surging I noticed is a restriction. Obviously to small of a carb wouldn't make any difference regardless of how big you jet it because you also need the correct amount of air flow correct?

Also where can I find the proper float height for a mikuni? Or how do I know that the float height is not correct? Can I do that with a clear rubber tube ?

[DAM shop]

And furthermore wouldn't I be better off shoving as much air in ( within reason) and adjusting with the main jet?

[barnett468]

And furthermore wouldn't I be better off shoving as much air in ( within reason) and adjusting with the main jet?

oh my...that is a very complicated question, but to vastly simplify it. the 24 is too big for your stock 110 and it would be better off with a 20 max since the stock carb was only a 16mm. Going from a 16 to a 20 is a 25% increase.

Shortline10 would have a better idea than I would on the best carb size for a built 110, but it depends on a few factors with one of them being needing to know what the projected max rpm will be, but my guess is that it would be around a 22, and if it is a high revver and you plan to run it in the high rpm range most often, then a 24.

[El Camexican]

Without knowing anything about these motors, if your carb throat is much larger that the rest of the passage to the valve it won’t run worth a s**t. For lack of better words, the main jet needs to be emersed in negative pressure to draw fuel.

[yaegerb]

Just finished with our latest motor. Bored, stroked camed 110 motor running with this real cool ( never before seen) Mac pipe. We are just now in the tuning stages and need a little advise as to the direction we should start. We are running a mikuni 22 mm carb main jet 100. The trike starts, idles and has good response to 3/4 throttle. 3/4-wot it surge's. Tried a bigger main but the only one on hand was much bigger than the 100 and the surge worsened. Dropped the needle 1 clip down, no difference. I am assuming I'm not pushing enough air the reason I think that is because our other 110 (bored only) is running a 24mm mikuni.
Would removing my air filter give me a clue as to if I'm
Starving for air. Should I just start with a 24mm carb?
I've also considered putting a 185 carb on if it will fit with the shorty intake we are running. I also have a flat side carb size around 30 without measuring it
Anybody have any thoughts here? Again I've just started testing and tuning just looking for somewhat of a starting point.

Flip the choke on while warm and idling. Does it get better or worse?

[DAM shop]

Flip the choke on while warm and idling. Does it get better or worse?

Yes will give that a try..

[Gabriel]

If only given two options...I'd rather have a carb a little too small than a little too big. You can jet and tune a smaller carb to run fine but a bigger one will always give a big vacuum drop that's hard/impossible to deal with.


I built an FE Ford many years ago. 390 with a 428 bore. That makes a 406. I ran a Holley 600cfm vacuum secondary. Yes, the engine could have benefitted from MORE air but the jetting was spot on and the throttle response was amazing. You could stomp it and the engine would ALWAYS take it immediately. Different animals I know but the theory is the same. The RIGHT thing to do is calculate the air flow needed and get the proper sized carb though.

[shortline10]

Assuming your using a VM22 mikuni ? Which is a good size for your application .
They can be a PITA to tune , you could try a 90 main but it should be anywhere from 90-120 ish , moving the needle is only needed for mid range tuning . I have also seen where the shorty manifolds had hiccups that I couldn’t get out and a long style cured everything

Also make sure the mechanical advancer is working properly and the points are set correctly .

[DAM shop]

Assuming your using a VM22 mikuni ? Which is a good size for your application .
They can be a PITA to tune , you could try a 90 main but it should be anywhere from 90-120 ish , moving the needle is only needed for mid range tuning . I have also seen where the shorty manifolds had hiccups that I couldn’t get out and a long style cured everything

Also make sure the mechanical advancer is working properly and the points are set correctly .

Yes I agree with the longer intake Mike, unfortunetley for us the two we have are already mounted on other trikes. I also heard that a short intake is good for low end torque as the longer intakes are good for top end speed. I know that there are many factors that also need to be considered when using this logic.
Maybe at this point I should leave well enough alone, not to many times that we go balls out most of the playing around is under 3/4 throttle. I suppose one needs to keep this in mind when it comes to tuning of any sorts, (carbs and cams come to mind) is ones riding style.
As you have said before Mike it's hard to have the both of both worlds either you are tuning for wide open throttle type racing or tuning on the lower end of the power curve and right now the lower end of our tuning is spot on..

[barnett468]

Just finished with our latest motor. Bored, stroked camed 110 motor

What bore, stroke (displacement), and cam?

Any cylinder head mods?

What intake manifold?

running with this real cool ( never before seen) Mac pipe.

Can you post a photo?

Maybe at this point I should leave well enough alone,

I for one wouldn't stroke, cam, and pipe an engine etc and then just leave it as is if it is running noticeable poorly under any riding condition or throttle position etc. Also, if the jetting is far enough off, it can cause some issues like premature ring wear, or even seizing etc.

Would removing my air filter give me a clue as to if I'm
Starving for air.

What type of filter is it?

The simple and shortest answer, is try it with and without it and see if you can tell a difference, however, in general, a carb will work better if it has a "velocity stack" attached to the inlet side of it, and some clamp on air filters have the inlet boot shaped this way to some degree.


..............................

[DAM shop]

I hear what you are saying Barns the jetting isn't that far off really it's all main jet at this point. Air filter is a k and n, and I actually think they restrict air flow, vIMO. I think at this point a rejet of the main both ways and see what I get.
I have a 185 carb I may try if the height will allow it.
I can't try a longer intake without robbing Peter to pay Paul.
It's just a matter of trying different combos at this point.

[DAM shop]

I hear what you are saying Barns the jetting isn't that far off really it's all main jet at this point. Air filter is a k and n, and I actually think they restrict air flow, vIMO. I think at this point a rejet of the main both ways and see what I get.
I have a 185 carb I may try if the height will allow it.
I can't try a longer intake without robbing Peter to pay Paul.
It's just a matter of trying different combos at this point.

Mac pipes is still in business. I sent them a pic of this pipe. They said they made them for the 90/110 and 185 in the day..