I am in the process of tuning my car after a rebuild. I have dual weber 40's. My engine is a 2.27L. Everything is going pretty well. I am slowly getting the jetting closer and closer. I was driving around at about 60mph yesterday. The head were hotter than I like (325 degrees). I checked the spark plugs and they were bone white. The main jets were at 160. I increased them to 170 (above 160 I only have increments of 10). With the increase to 170, the car is running very well and the temp at around 60mph cruising is around 275. I sped home, tuned off the car and took out the plugs- bone white. I was quite surprised.

The main jet size sounds high too me. Does it sound high to everyone else? Is it possible that I am needing a high main jet size because of the float level? I have my floats set at 10.5 with the gasket.

Any opinions would be greatly appreciated

What size venturis?
40s are quite small for a 2270

What size idles? At least 60 or 65's. You should be running at least 44 webers or better yet 45 dells to feed that puppy. If you can't, then run bigger vents, at least 30's or 32's. You probably have 28's on it.

Just for clarity, are you sure you changed the main jet and not the air correction jet?

In the picture below, the main jet is shown away from the emulsion tube on the right. The air correction jet is still attached to the emulsion tube on the left.

BTW, I have 40's on my 2270 but changed out to the largest venturis (36mm) that would fit. John at Aircooled.net can hook you up.

I'm running 135 mains and 180 air correction. It's run great for close to 8 years now. Head temps are always low, but Jake's DTM shroud has a lot to do with that. (gratuitous plug for ya Jake )

Jetting is different on every engine. Don't use mine as gospel.

My idf's have 32 vents. I am definitely changing the main jets and not the AC jets. My idles are 65. Idle seems to be fine. I think that I have the mixture screws out about 2 full turns.

I also have a set of 34 vents. I stayed with the 32 vents because I thought they would be easier to tune. Is this correct? Should I just change to the set of 34's? I do have a metal lathe so I could shave them down to 36mm if needed. How can I tell if I need bigger vents?

I would like a set of 44 idfs but I don't want to spend the money (my wife is getting fed up with my hobbies).

If anyone is interested in trading a set of 40 idf's for 44 idfs let me know

The venturi's sound a bit too small as you surmise the 34's would probably be better. I used to use the website here: http://members.rennlist.com/webercarbs/
to do the venturi calculations.

Several other things I would check, what is fuel pressure when running, not idle and it should be 3.5 to 4#. What fuel pump are you running? I hope it is NOT one of those little Facet pumps as they tend to not have enough capacity for a hot rodded engine and the hard pulses they produce can cause needle/seat problems on Webers. Do you have an O2 sensor in the exhaust? If not I would suggest one to help save the engine from overcooking itsself. Finally, I would set the float levels on the high side especially since you have a lot of time and $$$$$ in this and it is better if the engine is too rich as opposed to too lean! Good luck

The larger vents would send a weaker signal to the mains meaning you'll need to increase jet size to get the same AF ratio. The larger vents would flow more air and increase your top end performance.

What exhaust are you running?

Another thing you might want to look at is your ET selection. The F11 is leaner by design at higher velocities, especially with AC jets over 2.00. With your 32 vents and larger displacement you have high flows at low RPM.

The F7 is designed for low velocity enrichment and it's richer than the F11 throughout the entire range. With the low velocity enrichment you might even be able to step down on your idle jets. The F7 seems to prefer AC jets in the 180 to 190 range.

You have not stated ....what AIR correction jet size you have......Before you continue to go up in main jet size, which you will shurely have to do with bigger VENTURIS.......It seems to me that you should sort out what you have /and are using FIRST....this is the principal of one change at a time, get data, before changing /altering again/some more.....many factors are involved in getting your particular engine running /jetted perfectly., as "tomeric914" has stated.... It is my opinion that if we knew the AIR correction JET size , feed back from these posts could have more validity, and be of more use to you.

Right now I have AC jets at 220. The reason for that size is that I only had 220 and 190. I received more in the mail just s few minutes ago. I now have 200 and 210.

For some reason I can only get my fuel pressure up to 3. I have a CB rotary. I have it mounted up front.

.................Great.....fuel pressure of 3 psi,(measured at the carburator) is as high as you should go..........Go lower on the air correction jets. if you now have 220, drop down to the next smallest size you have....210....drive and check plugs again., (if still lean on the plugs) drop down to 200...drive and check...same for the 190s......until you get some color on the plug tip, and oil and head temperatures are resonable......The AIR correction jet has a very significant change to the air fuel ratio, much more so than a single main jet step change...something like a 2 -3 main jet size change...and the smaller air correction jet will enhance the upper rpm range, by making it richer, far more than a main jet change/ or even two.(sizes larger)...."crawl "up on your solution one jet change at a time. you want that "lean burn" maximum horsepower, but not so lean as to cause other problems.excessive head or oil temperatures...after you get it sorted with the correct jetting.....then go to larger venturis, and repeat the process...the larger venturis will make the bottom end "soggy", and help the mid range and top end rpm,s.(more top end H.P.) The bigger venturis will also NOT atomize the fuel at low rpm,s as well as a smaller venturi. your plugs may look rich, but unless you use the WOT shutdown procedure you will have a difficult time diagosing plug color.

The rule of thumb I learned when racing which should also apply to street use is that with Webers set the starting fuel pressure at 4# and if you need to make a quick change at the track then changing pressure by 0.5# is the same as changing jet size by a full step I.E. drop pressure to 3.5# and it is like going from 160 to 150 in jet size. The BMW racers also used this and the folks at the Weber repair shop in Gilroy CA agreed. With your pump at that pressure you might be running out of fuel so I would suggest doing a capacity check to see what the flow rate is and why pressure can not get any higher and then solve the jet issues. Also as I mentioned earlier I would really think about installing an O2 sensor to watch things. Good luck with this.

I haven't found the changes quite as significant. The 220 AC jet will definately lean your mixture up at higher velocities. As I stated earlier you'll see those velocities at lower RPM due to your vent/engine size.

Here is an update. I drove my car to work today. I have 180 mains and 220 AC jets. The car ran well and the CHT cruising was around 275. The plugs were bone white. Before heading home, I changed to 190 AC jets. The car ran well and the CHT when cruising was around 275, maybe a little less. Plugs were still bone white.

I changed a few things. I changed the fuel filter (which only had 100 miles or so). The fuel pressure now can reach around 3.5. I changed to the 34mm venturis. I kept the mains at 180 and AC at 190. I adjusted the float heights to 10mm with the gasket (the floats were previously at 11 with the gasket-i thought they were at 10.5).

I drove the car around. I drove it quite hard. There was a noticeable increase in power however if I floored it, it seemed a little sluggish. Something that I was not expecting was that there was a deeper, throatier sound from the exhaust. It sounded great. I sped around and then did a quick shut down. Of coarse, when I pulled the plugs they were carbon fouled. I was quite pleased. I was afraid that I was going to be super lean still with the increase in vent size. I was quite happy to see the carbon fouling. I can work with this.

Does this sound reasonable- I plan on putting 210 AC jets and leaving the 180 mains. Drive around- if still fouled then start lowering the mains one step at a time until I get it right.

To address a few posts saying that I should get a o2 sensor and A/F gauge. I would love to however my wife is a bit pissed off at me for spending so much money. I have put one on my Christmas list (I can't wait 4 months!!!)

You will need to become the master of the trade off my young friend! There MUST be something your wife really wants (not needs) and with the argument that the O2 sensor will prevent a VERY costly engine melt down the outcome can easily be predicted...............

...............making progress....but you apparently made multiple changes and therefore dont really know any more than the engine is rich to the point of fouling plugs....consider this...when you raised the float level you may have gotten to the point that the carbs are flooding.(the float needles are almost always off the seats).....this problem will override any other adjustments you will ever make, and create an "artifical"fuel enrichment. This overrich condition will continue to show "carbon fouling" especially at idle, or low rpm,s...basicially I,m saying ....you have created a problem for which their is no solution....except to go back and reset the float levels to the "stock height"....I suggest you use the 190 air correction jets. these will give you the richest fuel mixture, (which is necessary for your increased displacement engine and especially necessary for higher rpm,s with your displacement.THEN start making the main jets smaller one full jet size at a time....Now ...you probably do not have the jets necessary. you are just going to have to acquire them. If you continue to try to only use the jets you have I do not think you will ever get the jetting perfect....I suspect that ..190 air corrections...and ....170 or 160 or 150 main jets will be what you need. The deeper rumble and noticable H.P. improvement is from getting the engine "rich",and it ran ok, but was sluggish at low rpm,s...thats from being "over rich" at low rpm,s..The float level being a component of this richness,..bigger venturis, and too big a main jet for the air correction jet size, all contributing to the problem...the fuel is not being atomized properly(too much of it), and fuel droplets are burning IN the exhaust pipes...it may sound great but the air fuel ratio is a mess...Running your engine in this rich condition can "wash down the cylinder walls" with raw fuel resulting in unseated rings,,glazed cylinders,smoking, and an unnecessary engine failure.

I think that I need clarification of the stock float height. I have seen people say that the float should be set at 11mm from the top of the gasket. I also saw in in my haynes weber manual that you should set the floats at 10mm NOT including the gasket. I was told by someone at aircooled.net that I was to set the floats at 10.5mm (gasket or not?). I have it set at 10 mm off the top of the gasket which would be 11 mm off the metal. What is the correct float height. It seems that I should be around the correct area.

The nice thing is that I have a large amount of main jets. I have everything from about 130 to 160 in increments of 5. Above that I have increments of 10. I have AC jets of 190, 200, 210 and 200.

Also, to clarify, last night when I was driving, I had the sluggish feeling when was driving above 2000 or so rpms. Below that everything was fine.

.........put the float level back where it was....reread your previous comments...reread my previous comments.

Murray is correct in that changing multiple things at once isn't the correct way to troubleshoot. You have no idea what had the most profound effect.

Increase fuel pressure = rich
Increase float height = rich
Decrease AC jet size = rich

I suggest you set a new base line with the below info and make changes from there one at a time. Note what each change does from here on out and then adjust accordingly.

#1 - Change AC jets to 2.00 - Assuming you have the F11, you never said what ET you have. 2.00 is base AC jet for the F11. Above 2.00 you lean the mixture at high velocity, below you enrichen.

#2 - Float height = 10mm w/ gasket 11mm w/out. I suspect this was the main reason you were lean with the huge main jets. At 11mm with the gasket your main fuel wells were a low.

#3 - That bogging at 2000 RPM is because your pig rich. Reduce your main jet size. I'd suggest 160's and go from there.

#4 - That new sound your hearing is a result of the larger vents. I personally love the sound.

#1 I have F11 ET tubes. I also have a set of f7 that I could use. I changed the AC to 2.00. Things ran better but still rich. I did not notice any bogging.
#2 Thank you.
#3 I went down to 170 so far and things feel pretty good however I have not had a chance to check the plugs.

Increasing the float height will not change the mixture unless you mess up and allow the bowl to overfill. The float work JUST like the one in your toilet tank.

When setting the float closed height (10mm or 11mm) make sure you don't compress the ball spring on the needle valve. You want the needle valve seated/closed, but not compressing the ball. If you do this wrong, your bowl will be too empty.

Fuel pressure will also not affect mixture, unless you set it too high and it blows the needle valve off it's seat. But there will be NO general mixture change between 2psi and 3psi.

Be careful. There is a LOT of misinformation about carbs out there.

You aren't kidding about misinformation.

As you increase or decrease float height you change the height of the fuel column inside the main fuel wells. The emulsion tube sits in that column of fuel. Air is sucked in through the AC jet and pulled through the center of the ET. This emulsifies the mixure which then enters the carb through the center of the venturi. The higher the column the richer the emulsified mixture.

As far as fuel pressure, the float has to fight the needle against fuel pressure to close it. The higher the pressure the harder it has to fight. With higher pressure what you actually end up with is a float that sinks a bit before it can shut of the flow. That gives you a higher float level. See above why that affects your mixture.

The rate at which fuel is admitted to the emulsion chamber is controlled by the main jet, not the fuel bowl level. The float height has nothing to do with that. To get nitty-gritty about it, a higher fuel level in the wells (due to a higher float setting) will provide a SLIGHTLY richer mixture just as the main jets come into play. But soon after that the emulsion tube situation stabilizes and you simply have fuel flowing at the rate allowed by the main jet and air flowing at the rate allowed by the AC jet and E-Tube.

You can't seriously be arguing that the level of the fuel being pushed by atmospheric pressure from the fuel bowl, is GREATER than the vacuum influence from the chokes?

I'm saying float level does have an effect on the mixture. I agree that it's effect is most apparent at transition where 1.5mm is the difference between blowing off your air cleaners or not.

I'll tell Bob Tomlinson to get this corrected ASAP.

I guess I read that paragraph a completely different way. If the fuel level is too high, it will spill into the throat, causing a rich condition. If the fuel level is too low, the carb can run out of fuel under hard acceleration, thereby causing a lean condition. The page you posted says nothing about the fuel level inside the emulsion tube. It makes a general statement that you assume applies to the entire RPM range. Bob is correct that a high float level can cause a rich condition, and a low float level can cause a lean condition. But that's not the same as changing the mixture overall.

From several of the posts here I seem to read that many think that the float raises up and at a certain level shuts off the fuel flow and acts like the float in a toilet tank. The guys at Pierce Manifolds (Weber repair masters) explained it to me this way as did several old German Porsche mechanics: The float and it's attached needle valve is bouncing like mad inside that carb body and on a race/street car with stiff springs and shocks it is worse than the carb was ever designed for. That is one of the items that PMO rectified with their design but unfortunately they do not make a 4 cylinder version. Anyways, since the needle does not actually shut tight and stay that way when you raise fuel pressure at the bowl it causes some spill over due to the increased force against the needle valve. I was not sure of this but when notable racers such as Wayne Baker and others said to bump up pressure by 1/2 to a full pound on a track such as CA Speedway or Willow Springs Big Track where you are at full throttle a very long time and this will provide some insurance against running out of pump capacity and going too lean. Sure enough, when at full throttle the O2 mixture would go rich by 1 full number, usually from 13.51 mixture to 12.5:1 mixture. On short tracks I would lower fuel pressure to about 3.5# and the car was very happy.

Of course this bouncing also affects the set float level and is one of the reasons why it changes over time. As a matter of fact the guys at Pierce Manifolds strongly suggest that float levels NOT be set until the car has been towed to the track as the vibration of the trip can affect the float settings!

I am new to carbs. I am a human mechanic and not a car mechanic. I am trying to learn and I appreciate everyones help.

Last night I only made three changes. The changes were that I increased the venturi size which should have leaned the mixture. I slightly increased the fuel pressure and I raised the float level from 11mm with the gasket to 10mm with the gasket. I then had a super rich mixture.

Today, I drove around quite a bit and played with the mains. I had AC jets of 190 the entire time. I tried 180, 170 and 160 and all were rich however 160 didn't seem too bad. I didn't have a 155 with me so I tried 150 and Now the mixture is lean. I am trying to find my 155's and i think that I should be dead on.

So what is the cheapest way to get a o2 sensor, a/f fuel gauge setup? I think that my wife will just have to be pissed for a little while.

PLX is $269, here.
Innovate Motorsports is $209, here.

A smaller choke will create vacuum in the main jet circuit at a lower RPM. The small diameter makes the air move faster. Faster air = larger pressure drop. The opposite is also true, a larger choke will slow down the air and delay the main jet activating. If your car were perfect at idle and perfect at mid RPM, but went rich in between (cruizing down the road for example) it's because the idle jets and the main jets are working at the same time. Going to a larger choke would move the main jet up the RPM band and keep them from overlapping.

...................terriffic......your jetting is in the range I suspected it might need to be in...., continue to keep an eye on the OIL temperature and Cylinder Head Temperature. Try a little longer trip after you get the 155,s in and see how it goes....Murray.

This is some of the most insightful carb tuning talk i have seen. And I am just getting started on optimizing my set-up, so its damn timely info.

Keep it coming.

I would suggest that for optimizing a carb setup to do it the following way. I learned this the hard (very hard) way when I tried messing with the race car when I went from a 2.2L four to a 2.8L four and then into a 2.2L six.
1. Start at the front, I.E. make sure the tank is clean and rust and junk free.
2. Install a fuel filter at pump suction.
3. Make sure you have the correct fuel pump, those little Facet "cube" shakers are bad for the float settings due to pulses.
4. Make sure fuel lines are large enough, 1/2 inch are great.
5. In the engine compt. do not let the fuel lines touch anything that generates heat and even covering them with fire sleeve is a good idea.
6. Add a pressure gauge just before the carbs so you will know what pressure is acting on the needle and seats.
7. Try to either add an O2 sensor/meter in your exhaust or borrow a meter so the car can be tuned to correct mixture.
8. Make sure to use the insulating spacers under the intake runners to keep heat away from the carbs.
9. Set float heights to the middle to start with and adjust as necessary if needed. Make sure to have the Weber repair books handy and refer to then often.
10. If the jet sizes seem a bit too far out of what normal should be, look for something wrong with the engine setup such as wrong venturi size, weak spark, etc.
11. When starting out, make sure ALL other items are in like new shape such as plugs, points (if used), valve adjustment, etc is not going to have a negative and masking effect on the carb tuning.
12. Do not ever try to sync the carbs by ear, use one of the professional synchrometers and make sure they are sync'd when starting.
13. Run the car ofter, especially in CA where the gas is crap and will let lots of junk settle into the bottom of the carbs.

Hope this helps some.

....................I would make the following observation and comment on your recommendations......add( 1A.) always add and install a seperate fuel pump cut off switch....this will allow you to run the engine,and shut off fuel supply, which empties the float boals. Then you can transport the race car without fear of flooding it,causing a hydrolic-lockup,...naturally this assumes you installed the fuel lines in such a manner as to NOT have a syphon effect going on...Your # (3) facet pumps generally are not used on race cars as most racers want a higher level of quality, fuel pump. They are fine for street cars.the pulsation effect is absorbed in the fuel line and pressure regulator. the float needles are bouncing anyway and are not going to be affected by the pump...Your # (4) 1/2/inch fuel lines is just nuts., unless you have a fuel/blown /dragster. that rediculious large size is just a larger heat sink,far more difficult to install in a protected manner,the fuel pumps and regulators do not have that inlet/or outlet size threads.(unless your going to specially made ultra high volume drag racer stuff)...Your #5...covering the fuel lines with "fire sleeve"... will just trap and hold heat against the fuel lines, obscure any ABRASIONS/or cuts that might occur and is a VERY BAD idea...Your #7... an o2 meter is ok, except that for almost the same money an EXHAUST gas temperature guage is far more accurate, and useful. (and it,s what you see in race cars not an o2 guage.)......hope this helps.

If the overlap is minimal or the mains come on just a tad late you can try and correct it with an ET change.

F11 = leaner transition - holes are placed higher, diameter of the tube leaves less room for fuel in the main fuel wells.

F7 = richer transition - holes are placed lower, smaller diameter to hold more fuel in the fuel wells.