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

[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!!!)

[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.