Carb modification question

[Ryan140]

I was working in my buddys machine shop today and I noticed that the set of carbs I was working on (removing a striped jet) has some real nasty casting lines on them. I asked him if he thought it would be worth cleaning them up with a file and he stared at them a bit. He said I could make a cutting wheel on the lathe and open up the carb body throat so it was the same size all the way through. He also said to remove the washer and cut the screw holding the butterflys on and I could probably get away with thinning the shaft and use button head screws instead of stock and grind down the head. He also told me not to open the venteri because I would probably make the motor bog real bad. I wanted to hear everyones ideas and opinions (and experiences) on this project before I waste a whole days work for nothing. I was also going to remove of the little bumps in the carbs and stacks with 400 grind sand paper, going front to back to follow the path of the fuel. BUt then I got thinging maybe it needs the turbulance.

[half fast]

The step or venturi must be there or no fuel goes in da motta.I am not an experienced typest so
I will just say do not chase your caruretors around with a lathe or they will soon be book stops on a shelf. hf...

[Markus]

A carburetor which has the same diameter all the way through is no longer a carburetor.

However, increasing the venturi diameter without taking the venturi away will give more flow and thus better top-end, but will make the carburator react slower.

This is a quite popular modification on Yamahas, but since the casting quality is low, I assume that you have an American engine. ;) . It is rarely done on 2.5l Mercs. Don't know about OMCs, but I know of one very bad performance shop that does it.

[Ryan140]

Ive noticed that the step is different on different carbs. On my set of wh15s there is almost none but on wh22s it is twice as large. Can the edge of the step be blended so it is not so abrupt or does it need to be that way? Also you failed to comment about grinding down the screws and thinning the shaft.

[T-REX]

Ryan, I did all that crap to a set of 22's...cut down shafts, button head screws, cut off screws to shaft, sharpened butterflies...and I git the same results when I painted them pink!!!...I have a set ov 31's that have been opened up, have a set of 15's that have no venturi, have a set of31's that are polished inside, and the best ones I have run are the wh-20's that have had a lil progressiopn work and everthang else iz stock!!!...Common sense tells U that sanding down shafts and cutting off screwz and gettin rid of the big headed screws will increase air flow(or at least cut down on resistance), and it's true...BUT, U won't see anything on a clock or a radar gun, at least not enuff(if any) to warrant all that work...I spent the biggest part of 14hours doing my carbs, and I should have been waxing my bote so I could have seen a lil differnce!!!...Juss my 2 centz!!...REX :cool:

[Ryan140]

define progression work and what motor do wh 31 come off of?

[Ryan140]

What do you mean by progression work and what motor do wh31 s come off of? Oh what year and make were wh20s

[T-REX]

These are holes that are located under that cover on top ov the carbs...If U take off that cover, U kan see the small holes...then with further inspection, U'll see that when the butterflies are shut. 1 hole iz behind the butterfly(supplying gas), move throttle open and you'll see that anuther hole cumz open(supply'in mo gas for off idle) then anuther...These are reel small holes and before U plan on fooling wit them, have sum other carbs, are either have a set U don't mind mess'in up...cuz them lil holes can make U or break U az far az hole shot iz concerned...I have redrilled them in differnt places and differnt sizes, wit differnt outcumz, but I kan't tell ya which is what...it's kinna a trial and error thang....wh-31's came on a 88-89 200 2.4.......Wh-20's came on tha ole 225's and mod v-p's...REX:cool:

[Ryan140]

Rex. Ive got a few sets of 22s, a set of 15s, a set of 14s and a set of 28s. The 28s are suppost to be off a modvp. They came on a xdrilled intake. Any experience with them (28s)? I'll keep an eye out for some cheap 20s. Did you say that blending in the sharp ridge is a no-no or its ok but just doesnt do anything?

[T-REX]

The sharpening and flatning of the shafts won't hurt...well, lets clerify befo I got jumped by tha perfectionest...The thinner the shafts, the more likely the will break...theyz iz a lot ov vibration, so U know what I meen....What O meant wuz it's too much work for practally NO gain...Juss ain't worth tha trouble......I'm not familiar wit tha 28's at all...REX:cool:

[sosmerc]

Rex.......from your experience, what color makes the most power on "tuners"?:D

[T-REX]

ORANGE

[sosmerc]

Got a few carbs for sale for anyone wanting to practice carving, slicing, drilling, and, oh yea, painting!!
XR4 Set
WH3 set (s)
WH6 Set
Some others...

[Boz]

What are your thoughts on boring my stock carbs from 34 mm to 36 or something? I have a stock 1993 200 Yamaha Pro-V that I'm changing heads on(220) and porting. So far, that's it. Thoughts?
It's on an HST. :confused:

[Wayne Worthy]

Changing the 34mm to 36mm will not gain you anything that is measurerable! Be sure to re-jet the 34mm with the porting and higher compression heads that you are going to!www.hydrotecmarine.com

[Boz]

I'm curious what you would have to say about a place to start regarding modifying my 1993 Pro-V 200 Yamaha.
I have done the exhaust work by installing a tuner, removing the liner, and drilling four, 3/8 inch holes on either side of the just above the cav plate. Should we re-install the liner to increase back pressure or do you feel I'm ok with it removed? With what i've done to date, i.e. above mentioned exhaust work, I think my engine is sitting somewhere near 240 hp or so as this Yamaha shares the same powerhead as a 225 Yamaha. I want 270 plus...

[Wayne Worthy]

Which tuner did you use? The PROV200 tuner needs replacing for sure! Removing the liner does help with throttle response and I suggest removing it. Which tuner you use dictates back pressure.
What boat are you using with this Yamaha? What prop, pitch, and RPM? I thought that you said you were using 220 heads and if so, how much have you cut them?

[Boz]

I have yanked that choked down tuner and installed what appears to be Yamaha piece but is cut and staggered. G-5 I've been told by one person??
I have an 89 HST spinning a 29 SRX at 6300 RPM. We have yet to put the 220 heads on but will be doing so and I think they'll be cut to 50 thou. Timing wil be advanced to, I believe 25 degrees, with the new heads and port work that is being done. We're matching the bottom two ports with the top four. (or is it the other way around? I have it in my "boat file" at work)
I'm running 12" set back. We were going to throw the liner back in but that maybe not the way to go? Should the relief holes be drilled bigger above cav plate or are they ok? I don't mind a loud engine. As a matter of fact, I woudln't mind it louder. Is there an air box/silencer we can remove? I guess I'm one of guys that likes the sound of meaty sounding, straight piped two stroke. That sound makes me weak at the knees!!!:D

[Markus]

If you have an airbox, it is the black plastic + aluminum piece in front of your carbs. If it is still there, take it away, go for a test run and see what happens.

To see if you have anything to gain from big bore carbs, I would suggest testing the engine with the choke butterflies removed. If that gives a noticable performance increase, I would use a priming pump instead of the chokes and go up from 34 to 36.3 if it can be done at a reasonable cost.

As to the exhaust silencer, if you do not mind the noise, do not use it. On the other hand, I am not sure that you will notice any difference from not having it there.

The key to all performance mods, though, is to do them one at a time. I know it is tempting to do lots of things when the engine is torn down, but in the end, you do not know what worked and what did not work.

[Wayne Worthy]

Re-installing the liner is counter-productive! The liner actually is a muffler and by putting it back you will block your holes in the cav plate! When you install the heads cut at .050 you will need to richen your jets to 174mm. A stock P200 is 154mm. Also you can gain HP by modifying the intake (cross-milling) similar to the merc mod. If you remove the airbox (which is Plastic , not plastic and alum) you will need to watch the burn on your plugs. Keep in mind that you are leaning the motor by allowing more air in the intake!! See www.hydrotecmarine.com / Phase kits HT3250[URL=www.hydrotecmarine.com]

[Markus]

Wayne, it has been a long time since I removed one, but I believe there were two parts. In the front, there was a black piece of plastic on which it said Yamaha with white letters. Behind it was an aluminum piece with holes in it for the carbs and "runners" that went back towards the sides of the carbs for a few inches. I do not have a service manual around here to have a look at, but I am quite sure that is what it looked like.

This was on an old engine, though. Maybe things have changed since.

Anyway, if there is something in front of the carbs, remove it.

[Wayne Worthy]

Pre-1990 had the metal and plastic. A1993 p200 will be all plastic!

[Boz]

and I appreciate all of your input on my questions. Since i've got you Wayne, would you recommend losing my stock upper and lower cowl to shed some weight? You do sell them? It's on an HST which is a weight sensitive boat. I realize this is off topic of carbs; feel free to email me at [email protected] if you like:cool: