Weber IDF Main jet help Options

[tornik550]

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

[Jake Raby]

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

[type2man]

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.

[tomeric914]

The main jets were at 160.

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.

(IMG:http://www.914world.com/bbs2/uploads_offsite/uploads.turbosport.co.uk-9101-1281581607.1.jpg)

[tomeric914]

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 (IMG:style_emoticons/default/biggrin.gif))

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

[tornik550]

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 (IMG:style_emoticons/default/w00t.gif)

[john rogers]

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

[jmill]

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?

[jmill]

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.

[ME733]

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 (IMG:style_emoticons/default/w00t.gif)

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.

[tornik550]

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.

[ME733]

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.

[john rogers]

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.

[jmill]

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

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.

[tornik550]

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!!!)

[john rogers]

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

[ME733]

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!!!)

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

[tornik550]

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.

[ME733]

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

[jmill]

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.