15 replies to this topic

[WickedClown]

anyone actually tinkered around with drilling out the stock jets and potentially making more power from the stock carby. we all know that eldos mod will bring on the secondaries earlier but what about more fuel delivery??
whats your opinions??
cheers
marcus

[Surestick]

More fuel without more air will give you nothing (other than emmisions & bad mileage).

As it is stock the carb provides a lean mixture for emissions up until close to WOT at which point it will enrichen the mixture to best power.

[Fennec]

Well I know Eldo himself drilled the jets in the stock carb for his turbo setup. Your gonna need some really small drill bits for that job though...

[Wagovan4WD]

anyone actually tinkered around with drilling out the stock jets and potentially making more power from the stock carby.

<{POST_SNAPBACK}>

I will be drilling out the stock jets in the near future to convert my Wagovan 4WD from gasoline to ethanol. I'll be starting at a 20% oversize, then increasing in 5% steps until I get it right. All of the books I've read say that carbs need to be modified between 20% and 60%, depending on the overall system, generally ending around 35% to 45% when completed.

For gasoline, I'm not sure what else you could do. You'd have to adjust the second barrel to open in conjunction with the first one by modifying the restrictor cam on the throttle assembly. That might give you what you're after, though without proper vacuum you'll just be pushing unburned fuel through.

- Rick C. Hodgin

[Kurt]

When I put yamaha r1 carbs on my civic I had to drill the jets out from 1.3 mm to 2 mm because it ran to lean. If you are just drilling main jets the drill bits are not that small. If its pilot and air jets then you will need some very small drills.

[WickedClown]

surestik

i cant see how over fueling the car will be a bad thing .. after all that is essentially what dual webers do .. over fuel the car more fuel and more air : more power

[Omega Mugen]

I didn't drill the stock carb, but I drilled Weber jets with a round tapered file and also a very small triangular file.

[Surestick]

surestik

i cant see how over fueling the car will be a bad thing .. after all that is essentially what dual webers do .. over fuel the car more fuel and more air : more power

The stock carb already meters the correct amount of fuel for the amount of air it can flow.

More fuel without more air = bad
More air without more fuel = bad
More fuel & more air in the correct ratio = good.

Getting more fuel through pretty much any carb or intake is not a problem, never has been (some boosted set-ups aside). It's easy to open up the jets on a carb. The hard part is getting the extra air in there so that it's not running rich & costing you power and money. How do you plan on getting more air through the carb to go with the extra fuel? That's where the skill lies.

Sidedraft carbs (such as the Weber DCOE) if properly set-up should deliver fuel & air in exactly the same ratio as the stock carb. They are able to deliver more of this mixture due to a less restrictive intake path. They do not overfuel the motor (which implies running rich) they let it breath better. Eldo's mod does the same thing - it allows the secondary ventury to fully open earlier allowing a slightly higher manifold pressure at a lower RPM. Unlike a set of sidedrafts though it will not improve breathing at higher RPM where the secondaries would be fully open anyway and consequently does not give extra peak horsepower, only extra midrange (which the sidedrafts also provide).

[Omega Mugen]

This is true to a point. Maximum fuel efficiency is acheived with an air/fuel ratio in the high 15s. For the most power, on the other hand, the optimum A/F is in the high 12s, but in my EW, I've found it to be in the high 13s with the power dropping below that. Depending on how the stock carb is jetted (and I really don't know how it is) it maybe jetted for fuel efficiency rather than maximum power. So, you can richen up the mixture a bit for more power, but there comes a point where you will start to loose power. Engine, exhaust, and intake modifications also alter fuel curves, which require rejetting/modifying the jets, if you want a really good tune. And a really good tune is what you want.

Edited by Omega Mugen, 05 September 2006 - 06:12 PM.

[Surestick]

Generally the carb is tuned to provide a lean mixture at part thottle & a richer (best power) mixture at WOT.

I don't disagree with the need to make changes to the carb to compensate for other changes in the intake/engine/exhaust system but Wickedclown's initial post made it sound like he believed more power was available simply by drilling the jets.

If he has modifications that would require a change to the carb it might be worth posting them. Maybe another member has already been through this & can suggest appropriate jet sizes or other mods that will help him with his goal of more power without wasting extra time experimenting.

[Omega Mugen]

OK. I see.

Bigger is not always better also. I reduced the size of the pump jet in my Weber an unleashed a few extra horses. It was spraying too much fuel.

[WickedClown]

sorry i didnt explain myself properly guys,
my ew2 has extractors k&n filter and a cold air ram tube to fll my engine bay with cold fresh air , i understand that this set up will have no effect on drilled jets .. however i am soon to be getting a stage 2 cam grind and port and polished head ... i figured with these mods a lil extra fuel delivery wouldnt hurt .. providing i advance my ignition timing a lil.
since ill have a high flowing head and bigger lifting cam i figured the motor could handle a richer mix being that the valves will be opened for longer and the head will flow better.
back to my initial question .. has anyone actually drilled the stock carb jets and what size where they drilled to .. as a matter of fact does anyone know the stock carby jet size???
thanks in advance guys
cheers
marcus

[eldo]

sorry i didnt explain myself properly guys,
my ew2 has extractors k&n filter and a cold air ram tube to fll my engine bay with cold fresh air , i understand that this set up will have no effect on drilled jets .. however i am soon to be getting a stage 2 cam grind and port and polished head ... i figured with these mods a lil extra fuel delivery wouldnt hurt .. providing i advance my ignition timing a lil.
since ill have a high flowing head and bigger lifting cam i figured the motor could handle a richer mix being that the valves will be opened for longer and the head will flow better.
back to my initial question .. has anyone actually drilled the stock carb jets and what size where they drilled to .. as a matter of fact does anyone know the stock carby jet size???
thanks in advance guys
cheers
marcus

<{POST_SNAPBACK}>

With a stage 2 Colt Cam, ported heads and headers, i found leaving the primary jets alone and raising the float bowl adjusting screw by 1 turn and richening the idle mixture screw by 1/2 to 1 turn worked good. The secondaries ran fine but i think drilling them out 10 thou. will probably net a little more power(I never played much with the secondarie jet as i added a lot of extra fuel when i ran it with a 116 shot of nitrous with it.)

I know the Can. keihin carb has 120 primary jets and 180 secondary jets(The USDM carb i have had a 100 primary and 180 secondaries-double check that because it's been awhile and those numbers could be the airbleeds- I have the diameters of the jet holes somewhere but seeing as i have gotten divorced and moved 3 months ago ,i cannot find anything anymore!) Either way, get a drill set to get a reference of what the jet sizes originally are .

[WickedClown]

With a stage 2 Colt Cam, ported heads and headers, i found leaving the primary jets alone and raising the float bowl adjusting screw by 1 turn and richening the idle mixture screw by 1/2 to 1 turn worked good. The secondaries ran fine but i think drilling them out 10 thou. will probably net a little more power(I never played much with the secondarie jet as i added a lot of extra fuel when i ran it with a 116 shot of nitrous with it.)

I know the Can. keihin carb has 120 primary jets and 180 secondary jets(The USDM carb i have had a 100 primary and 180 secondaries-double check that because it's been awhile and those numbers could be the airbleeds- I have the diameters of the jet holes somewhere but seeing as i have gotten divorced and moved 3 months ago ,i cannot find anything anymore!) Either way, get a drill set to get a reference of what the jet sizes originally are .

<{POST_SNAPBACK}>

ill note that information down thanks for the help your knowledge is priceless.
im really surprised you didnt blow the head off the block when you ran nitrous lol ive seen that been done many times over here in aus. my car was built in japan so i would say its running the jap spec carby whatever that may be. you seem to know a lot about the old 86's what do you do for a living if you dont mind me asking it seems like you do this stuff all day

cheers
marcus

[Doodson]

I too drilled out the secondary jet on the canadian Carb on my racecar but am unsure of the size? I also had a colt cam Stage2. The car would idle fine and I only drilled the secondary out a WEEE bit to take advantage of the cam. I did this about 5 years ago and cant tell you much more.