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Weber IDA Troubleshooting
I have a 347 with new IDAs from Pierce Manifolds. The carbs were jetted and syncronized on the dyno. Ran like a champ. Now that the motor is in the car is runs excessively rich at idle (All plugs are wet with fuel) Ignition is good and the motor idles with backfire in the exhaust.
I checked the fuel system (Carter pump, -6 AN lines, return line, 2.5lbs pressure) and all seems OK. I pulled the fuel supply line and started the car with existing fuel in the bowls. Car ran the same (wet plugs) I've not touched any of the carb settings since the dyno. They were taken off the motor when it was installed. It's almost as if the primary circuit is open at idle. Any thoughts as to what I should look at? http://home.comcast.net/~lemanswinne.../Mar22_012.jpg |
Check the float levels. If the floats are high in an IDA everything goes super rich at idle.
Also, did you add air filters to the carbs? They also mess things up prett quick. Do you have an exhaust leak? IR intakes and carbs do not like exhaust leaks. Will cause popping through the exhaust. Good luck BRent |
Float level, using a depth gauge, measuring with the float out of the carb from the bottom of the arm to the bottom of the tang should be around .165. Check your idle jets to see what size they are, as well as the corresponding holder.
Are all the plugs wet or just some of them? Brent makes a good point. Any kind of restriction, such as foam type cleaner over the carbs will pooch everything. Throw that stuff away. |
The idle mixture has almost nothing to do with the idle jets. Yeah, I know...anyway, you set the idle mixture with the screws that are located at the base of each barrel. Turn each screw in until the cylinder "dies" and then back it out until it is firing again. I have no idea why they would have changed from the dyno. I can see how one or two could have gotten bumped, but all eight? Even the floats don't seem right, as all four would have had to change. All of this makes me think the fuel pressure may be too high.
Rob Bond |
While tuning on mine we had the same problem as you describe. Turned out my engine builder had put too cold of spark plugs in ( which is probably good on a new engine being broken in on the dyno ). It dyno'd great, but over time would foul out the plugs. We went up two heat ratings on the spark plugs and all is good. We used a chassis dyno to get the air/fuel correct from idle to 6000 rpm.
David |
Is the exhaust on the dyno different from the side pipes on the car? There may be a back pressure change.
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1. This may sound strange but is the Dyno at the same (within reason) elevation???
Rick |
I have to agree with David and Rick. Both the plugs and the elevation will cause serious changes to the setup of the car. On the setting on the float you really can't say what is normal..well you can but whats normal for every car and not everyone will touch the tang in the same place...as well you have to remember that on a 289 vs a 427 the carbs are angled at 10deg and that means that the fuel will overflow at a higher setting...we had a car this weekend that because of the vibration and the floats it was spewing fuel out the pump jet..this was causing the car to load up at the stop lights and then when he took off from about 1500-2000 it jumped and stumbled like mad...adjusted the floats WAY UP and no more problem...now thats not recommended if you are going to be racing but hell he can drive a mile after turnin off his fuel pump before the carbs run out of gas....trust me he knows :)
The elevation will cause problems because obviously you are moving a different density of air...if you had this engine built at a higher elevation than you buy a significant amount then you are going to have to jet it way back down.. Matt |
NealM
Thanks for the feedback. Elevation (about sea level) is the same. Only difference in the exhaust is that I have Borla mufflers, straight through. Although this may have a slight impact the fact that the plugs are so far off must mean it's something bigger. Noted an exhaust leak after installation but corrected it with a new gasket. No leaks now.
I'll check the float levels for consistency. As I said the carbs did come off and all seem to exhibit this issue. I suspect whatever the issue is that it is consistent from carb to carb. Keep in mind, I removed the fuel supply line, started the car and it still has excessive fuel. I'm running Champion RC9YC plugs. Looked great on the dyno after several checks. I'll go at it this weekend. |
That is a relatively cold plug RC9YC, if memory serves.
As Aggie said, the .165 is a baseline for the floats--it is actually the setting that comes from the Factory plus or minus .003. In almost all cases, it is acceptable. Again, street use and set up doesn't equate to track use. The levels are invariably different. For example, on a set we did for Ernie Nagamatsu's Cobra (Le Mans Top), we set them as high as we could, using a paper clip to check for float buoyancy as close to the top as could. We also enlarged the float chamber by milling out the circular casting that lies in the housing, giving us a few extra cc's of fuel. Not something that one would do for the street, obviously. |
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