VM33 smootbores

i run a kz1200cc , on the street and at track days.
Larry ported the head. it has 37.5mm intakes and .424" lift cams. i had vm33" on it with a 1135cc, and 1327cc build(same head). the low end bog is not a problem for the track, since u dont run that low in rpm's anyways.imo u need to go by feel until u figure it out. that way it will make scene in your head.if it feels better when u make an adjustment, u know u are going in the right direction, and u keep going until it feels right(smooth, no issues) and then keep going until it starts to feel bad again. at that point u have learned your boundaries.
just work on 1 section at a time. i mark off my throttle in graduations. that way i can be positive i am working on the circuit i want to be working on.if u are close on all circuits , then focus on wot,then mid then cruise. since these are of most importance to racing.
just remember, as u work down to the next circuit it will have a slight affect on the previous circuit, so u may need to revisit those later.

Cool Pic's, but some more would be great!
Let me say that I don't have and have never had those carb's on anything, so mine is just some basic thoughts.
You said high EGT but I never saw a #. Also what Plugs are you running?
Then since it's going to be different for your set up in the car, what sort of pressure fuel system? Have you a gauge to monitor WOT pressure? Then whats the Needle valve size for the float valve? Different between a gravity, larger, than a pressure system, smaller. Have you balanced those carb's for fuel level, and Vacuum?
Have you given any thoughts to making a Ram Air system, instead of just open pods? A box feed by a snorkel system would stabilize the air flow to the carb's and gain some CFM at speed.
I would jet for WOT to be correct, then work down to the mid range, then low, as you should have a high % of time there. Different again than a street machine, with all the Idle, start-stop. Just the weight and gearing can affect the jets you need. Higher weight, taller gears will require more torque, richer, light weight, low gears will like it a bit leaner.
By the way that looks like way to much Fun!!!!

Interesting thread, good reading, and lots of information.

Hopefully someone out there can answer a question I have about 33mm Smoothbores.

I currently run 29mm carbs on my engine and have decided to rework the engine and move up to 33mm carbs.

I purchased a set of 33's that "needed rebuilding". The carbs are a set of "diamonds in the rough" all the parts are there and nothing is damaged, they're dirty but in great condition. They just need a good cleaning, o-rings and gaskets and they're ready to go...

Now my question.....Has anyone out there ever ran across a situation where the pilot jet access port (on the bottom of the carb body) was intentionally plugged up?

On this set of carbs someone tapped the upper part of the pilot jet access port and then threaded a screw into the port using loctite to ensure gas could not get to the pilot jet. The pilot jets were in place but not being used.

It was not a problem removing the plugs but I'm just curious as to why someone would do this?

Any ideas?

Thanks,

Buzz

KruZer wrote:

Interesting thread, good reading, and lots of information.

Hopefully someone out there can answer a question I have about 33mm Smoothbores.

I currently run 29mm carbs on my engine and have decided to rework the engine and move up to 33mm carbs.

I purchased a set of 33's that "needed rebuilding". The carbs are a set of "diamonds in the rough" all the parts are there and nothing is damaged, they're dirty but in great condition. They just need a good cleaning, o-rings and gaskets and they're ready to go...

Now my question.....Has anyone out there ever ran across a situation where the pilot jet access port (on the bottom of the carb body) was intentionally plugged up?

On this set of carbs someone tapped the upper part of the pilot jet access port and then threaded a screw into the port using loctite to ensure gas could not get to the pilot jet. The pilot jets were in place but not being used.

It was not a problem removing the plugs but I'm just curious as to why someone would do this?

Any ideas?

Thanks,

Buzz

the only reason i could think of would be for a drag race ap. but that doesn't even make sense, so i dont know.
as for there use on your build. i would strongly recommend u keep the vm29's and try them and the 33's to see which u like best.
they have dif characteristics, and u may find that u prefer 1 over the other.
what size motor are u building and whats being done to the head? what lift cams? what characteristic are u looking for MOST in your build. the carb selection must match this characteristic. is this for street or track?

legrandemk18 wrote:

Is there a fuel pump of some sort to feed those 33s ?

If there is, call Sudco and see if they want a different fuel needle and seat.

Fuel pump is a good question!

Is there a fuel pump regulater, if so what is the fuel pressure? That would have a big affect on your mixture.

Mark 1122,

The engine is a 10.5 to 1 998cc KZ. I'm running 410 lift Engle cams with shims on top buckets.

I'm running gravity feed to the carbs.

I'm accually in the process of sending the head to Larry C. and will go with his recommendations regarding what the head needs for my application.

The engine is build for top end only so I'm not concerned about the drivability of the 33s.

As to my original post, I was just curious if anyone had ever run into a set of carbs that had the pilot jet access plugged.

Thanks,

Buzz

KruZer wrote:

Mark 1122,

The engine is a 10.5 to 1 998cc KZ. I'm running 410 lift Engle cams with shims on top buckets.

I'm running gravity feed to the carbs.

I'm accually in the process of sending the head to Larry C. and will go with his recommendations regarding what the head needs for my application.

The engine is build for top end only so I'm not concerned about the drivability of the 33s.

As to my original post, I was just curious if anyone had ever run into a set of carbs that had the pilot jet access plugged.

Thanks,

Buzz

my recomendation still stands. try booth.
33's favour bigger motors.
the 33's will give u more top, 29 more bottom, without loosing much up top.
u may prefer the 29's. with a 410 cam.and small cc's. I would.
Larry will advise u well. he did a great job on my head. he also has some 33's so he can tell u what u can expect from them.

Regarding the closed off pilot jet feed well.

Some CV carbs were done like that. They had a hole drilled between the pilot jet well and the well for the main & needle jet. Rubber plugs were used to seal off the pilot jet wells.

Pilots sill functioned....just drew fuel from the adjacent well rather than from the bottom.

I can't see where it made one bit of difference in the way the bikes ran. Never really inquired as to why they were manufactured that way. It may have been to prevent fuel slosh from affecting the pilot circuit.

Thanks Larry,

In this case the pilot wells do not have a port to the main jet well????

It seems that the pilot jets were intentionally blocked off and no fuel could get to them.

Anyway not a big deal,I fixed it and was just wondering why someone would have made this modification...

Thanks to everyone.

Buzz

Mark1122,

Thanks for the advise.

I will try both sets of carbs once I get the head back from Larry. Since I'm only looking for increased top end I would think the 33s might give me a little more help in that area.

Thanks again,

Buzz

i must say i used to think that so long as the carbs where not sucking the bowl dry on top end all would be good.

I think i now have a better understanding, let me know if this statement is correct:

the higher the fuel level in the bowl the more air holes are cover up on the needle jet and pilot jet resulting in a richer mixture ?

I do run a fule pump and regulator, it was set at 2.5 psi,
turning it up to 3.5 richened up the mixture to 14.3 afr from 14.7, and had no effect after that, so i assume that at that point the bowls are full and operating off of the floats.

so currently i have 22.5 pilots, 140 mains and 3.5 psi with an afr of 14.3 am pretty happy with that and it runs great, egt's still running 1400, dont like that.

i got my other pilots in yesterday and swapped out the 22.5 pilot with a 30 expecting to go a little richer and the afr actually went leaner went to 14.6, so im a little confused about that, will play with fuel pressure some more and if that has no effect i guess ill try the 22.7 and 17.5 pilots again.

Thanks