Weber service, Backfiring through the carbs |
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Weber service, Backfiring through the carbs |
wjpierce |
Jul 31 2010, 11:03 PM
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#1
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Newbie Group: Members Posts: 15 Joined: 2-December 07 From: Lompoc, ca Member No.: 8,407 |
I have a '74 1.8 converted to 2.0 with dual 44IDF Weber carbs. There is lots of backfiring through the carb on the left at neutral throttle, and it tends to run on three cylinders unless I am on the gas. Does anyone know of a place to send the carbs for service? I did the rebuild kits to no avail. Thanks
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IronHillRestorations |
Aug 1 2010, 07:13 AM
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#2
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I. I. R. C. Group: Members Posts: 6,719 Joined: 18-March 03 From: West TN Member No.: 439 Region Association: None |
Tuning and correct balance would probably help.
Here's my carb tuning proceedure. Remember "Search" is your friend! >>>> IMPORTANT >>>>Assumptions: the carbs have the optimum jet and venturi package (good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good. Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist. Start and warm up the engine. Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin igntion wrench to snap them off. Turn the mixture screws all the way in and then 5 half turns out. Turn the air bypass screws all the way in. Turn the idle speed screws out til it just touches, and then in 5 half turns. Put on your hearing protection and start the car. Use your STE and find the barrel that pulls the most. We'll call this one baseline. Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter) Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels. Go to the other carb and do the same thing. Snug the jamb nuts on the air bypass screws. All six barrels should pull the same amount of air at this point, if not repeat air adjustment proceedure. Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance. Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm. Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest rpm, then turn it in 1/4 turn. Do the same with the five other mixture screws. If you have to turn the mixture screws more than two turns either way, you've got the wrong jets. Recheck side to side and individual air balance, adjust as needed. Road test the car. If you get snapping and poping out the intake, it's generally a lean condition. If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich. If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets. That's a rough, five minute draft of my carb tuning proceedure, hope it helps! If it goes good it should take about 45 minutes, if not about three years. Another good tip: If you think you have a lean cylinder (idle jet plugged) you can back out the jet carrier a half to one full turn and the engine should stumble, if it doesn't change theres a good chance the jet is clogged. This primarily applies to the 3 barrel carbs, as the 2 barrel IDF's have a different type idle jet set up |
Silverstreak |
Aug 1 2010, 09:23 AM
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#3
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Edmund J. Fournier #36 Group: Members Posts: 117 Joined: 2-April 10 From: Pensacola Member No.: 11,552 Region Association: South East States |
To be fair, the Search engine on this site kinda blows. JMO. Then again, maybe I don't use it right.
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DBCooper |
Aug 1 2010, 01:28 PM
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#4
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14's in the 13's with ATTITUDE Group: Members Posts: 3,079 Joined: 25-August 04 From: Dazed and Confused Member No.: 2,618 Region Association: Northern California |
Clean the idle jet that side that cylinder.
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jmill |
Aug 1 2010, 01:42 PM
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#5
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Green Hornet Group: Members Posts: 2,449 Joined: 9-May 08 From: Racine, Wisconsin Member No.: 9,038 Region Association: Upper MidWest |
If you can't maintain your own carbs it's going to get expensive fast. Buy the Weber Tech Manual and read it 5 times. Soon you'll troubleshoot and repair your carbs yourself.
I agree it sounds like a clogged idle jet. |
gothspeed |
Aug 1 2010, 03:07 PM
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#6
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Senior Member Group: Members Posts: 1,539 Joined: 3-February 09 From: SoCal Member No.: 10,019 Region Association: None |
Sounds lean. If they were fine before, then something is clogged or lost adjustment.
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wjpierce |
Aug 2 2010, 07:13 PM
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#7
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Newbie Group: Members Posts: 15 Joined: 2-December 07 From: Lompoc, ca Member No.: 8,407 |
Tuning and correct balance would probably help. Here's my carb tuning proceedure. Remember "Search" is your friend! >>>> IMPORTANT >>>>Assumptions: the carbs have the optimum jet and venturi package (good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good. Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist. Start and warm up the engine. Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin igntion wrench to snap them off. Turn the mixture screws all the way in and then 5 half turns out. Turn the air bypass screws all the way in. Turn the idle speed screws out til it just touches, and then in 5 half turns. Put on your hearing protection and start the car. Use your STE and find the barrel that pulls the most. We'll call this one baseline. Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter) Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels. Go to the other carb and do the same thing. Snug the jamb nuts on the air bypass screws. All six barrels should pull the same amount of air at this point, if not repeat air adjustment proceedure. Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance. Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm. Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest rpm, then turn it in 1/4 turn. Do the same with the five other mixture screws. If you have to turn the mixture screws more than two turns either way, you've got the wrong jets. Recheck side to side and individual air balance, adjust as needed. Road test the car. If you get snapping and poping out the intake, it's generally a lean condition. If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich. If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets. That's a rough, five minute draft of my carb tuning proceedure, hope it helps! If it goes good it should take about 45 minutes, if not about three years. Another good tip: If you think you have a lean cylinder (idle jet plugged) you can back out the jet carrier a half to one full turn and the engine should stumble, if it doesn't change theres a good chance the jet is clogged. This primarily applies to the 3 barrel carbs, as the 2 barrel IDF's have a different type idle jet set up Thanks much I will try it. Appreciate the thoughtful reply |
IronHillRestorations |
Aug 2 2010, 08:36 PM
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#8
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I. I. R. C. Group: Members Posts: 6,719 Joined: 18-March 03 From: West TN Member No.: 439 Region Association: None |
BTW 44's are really too big for your engine, you need 40's with probably 34mm venturis.
The "search is your friend" comment was from the original post, I don't know what happened but the older search feature was better. |
tomeric914 |
Aug 2 2010, 10:39 PM
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#9
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One Lap of America in a 914! Group: Members Posts: 1,259 Joined: 25-May 08 From: Syracuse, NY Member No.: 9,101 Region Association: North East States |
Also check to make sure your valves are adjusted correctly. If one is too tight, you'll get rough running at idle and possible popping back through the carbs.
I don't use the site search function anymore. Use the Google advanced search function and put in www.914world.com as the website. Much better. http://www.google.com/advanced_search?hl=en |
Root_Werks |
Aug 3 2010, 09:04 AM
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#10
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Village Idiot Group: Members Posts: 8,321 Joined: 25-May 04 From: About 5NM from Canada Member No.: 2,105 Region Association: Pacific Northwest |
The ethonanol they are putting in the gas around here durring the sumer months causes the fuel to turn into a slimey goo inside the carbs pretty quickly. I was constantly cleaning my jets out until I started using a little of that Stable product every couple of fill ups. Much better now.
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