Guest SpudZ Posted April 27, 2002 Share Posted April 27, 2002 I have been having a heck of a time troubleshooting my L6. The engine is running rough and backfiring through the tail pipe and also through the front carb. I have been messing with it for weeks now when I get the time. I have done the following to see if I could cure the problem : Replaced wires, cap, rotor, points, condensor, coil. Adjusted valves, timing, carbs as much I could with a bad running motor. I have checked the compression and it is even numbers straight across the engine. The fuel flow seems good across the board, and there is no oil in water or water in oil. I had someone suggest it could be a vaccum leak and I checked for that also. I might have missed it if it was a small leak. They also suggested it could be a bad valve. The engine was rebuilt less then 5k miles ago, but I am not ruling the bad valve out. Any other suggestions would be greatly appreciated I already missed one autocross this season and don't want to miss another one. Quote Link to comment Share on other sites More sharing options...
DAW Posted April 29, 2002 Share Posted April 29, 2002 Run a compression test. DAW Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted April 29, 2002 Share Posted April 29, 2002 DAW, I have already done a compression check . It was on list of things that were completed. Thanks for the suggestion ! It is really bugging me now. It is probably something simple Quote Link to comment Share on other sites More sharing options...
johnc Posted April 29, 2002 Share Posted April 29, 2002 Latest issue of Grassroots Motorsports has an article describing how to tune SU carbs. Most important is to get the timiing right, valves adjusted, and make sure there are no vacume leaks. Only then can you start tuning the carbs. Seems that you've covered all of the above. Try tuning the carbs per that article or one of the Z Therapy videos. Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted April 29, 2002 Share Posted April 29, 2002 Thanks for the help John !! I have that issue of Grassroots Motorsports sitting right here and I will read through that article and also Julians web site on SU's. I need to find that gremlin before I start replacing my bushings and other suspension stuff. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted April 29, 2002 Share Posted April 29, 2002 I would start from scratch again with all the settings. Get the #1 piston to TDC on compression. Check that the valve timing is correct (hasn't jumped the chain a tooth).Check your valve lash. With the piston at tdc, put a loose spark plug on #1 wire and switch the ignition on. Turn the distrib. back and forward until you see the plug firing. Lock down the dizzy at the point where the plug fires. Be sure the spark is nice and strong. This way you know your cam timing is right and your ign. timing will be at 0deg, enough that it should run ok. If it is still crappy, then it's most likely a fuel/air issue. HTH, Tim Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted April 29, 2002 Share Posted April 29, 2002 Thanks everyone for your help Here is a couple of things I haven't checked. It is still on the same tank of gas I put it away with last year. I did add fuel additive last year before I put it away for winter, however, it was starting to run rough before I put it away. I did drain the fuel bowls thinking it might be water in the gas. The symptoms are like that of having bad gas ( the car not me ). I am going to put some fresh gas in it and put my glass inline filters back in to see if I collect any water. You guys are getting me closer to whats wrong. I also dumped the oil out of the carbs when checking the needles. After reading the article in GRM like John suggested that was a no no. I will take all of your advise and start from the beginning and work make way forward. I feel much better now thinking it isn't a burn't valve. I just put this motor in last Summer. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 29, 2002 Share Posted April 29, 2002 a leakdown might help Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted April 30, 2002 Share Posted April 30, 2002 A leakdown test was suggested by a friend. I just don't have a leakdown tester here. If I can't get it to run better by this weekend I will borrow one to give it a check. Thanks ! Quote Link to comment Share on other sites More sharing options...
DAW Posted April 30, 2002 Share Posted April 30, 2002 Last time I raced autocross, my Zcar sputtered and backfired and performance was poor and erratic. Turns out the linkage to the front of the three carbs was intermittantly slipping where it clamps to the linkage rod. DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted April 30, 2002 Share Posted April 30, 2002 Sorry, I missed compression test on your list but you shouldn't be still concerned re a bad/bent valve; your compression test ruled it out. DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted April 30, 2002 Share Posted April 30, 2002 Man, I'm not paying attention...I thought I read "SK" carbs, forget the tri-power reference. Start with simple things first before you start tearing into your SUs. Reach in with your finger into the SU airhorn and lift each piston in turn. If they feel about the same and return to down position when you let go, then rule out other things before going further with them. What about the quality of the gas? Has the car been sitting? Each SU fuel bowl has a little drain plug. You could drain these, top off with a full tank of fresh gas and use some gas treatment to get rid of water which may have collected with condensation. DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted April 30, 2002 Share Posted April 30, 2002 A leakdown test is a good test and is what's used on aircraft engines. However, you've already done a compression test and you said it was fine. With an intact compression test, any findings on a leakdown test would be subtle and not significant enough to make the car undriveable. DAW Quote Link to comment Share on other sites More sharing options...
johnc Posted April 30, 2002 Share Posted April 30, 2002 Drain the tank and put in new gas. Also, if the problem occurs when the motor is real hot, check to see if the fuel in the float boals is boiling. Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted April 30, 2002 Share Posted April 30, 2002 I will empty the tank this weekend and put fresh fuel in it. I think there is only about 4 gallons left in there anyway. That way I can start fresh with the trouble shooting. I am getting to think it is more of a fuel related issue by the replies I have been getting and the symptoms. Thanks guys !! Quote Link to comment Share on other sites More sharing options...
Guest bang847 Posted April 30, 2002 Share Posted April 30, 2002 maybe try venting your gas tank when it is running and take the belt off your smog pump... Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted April 30, 2002 Share Posted April 30, 2002 Smog Pump whats that ? In Idaho all the car has to have is windshield wipers. You can run without a windshield , but not without wipers. We have no smog checks here at all. DWV take less then 10 minutes to get tags for your car. I am thinking it isn't venting to the tank. Heck I have enough leaks in my houses back by the tank to keep it well vented Does remind me to put them on my to do list though. Thanks ! Quote Link to comment Share on other sites More sharing options...
Guest SpudZ Posted June 17, 2002 Share Posted June 17, 2002 I fixed it and she rins like a top Well after all the trouble shooting work I did it was just a spark plug. I thought it was the front carb and ignition that was giving me problems when all along it was the rear cylinders. I through in new plugs and she fired up and ran smooth. I used plugs from another car I had the first time I checked it out and they might have been bad to start with. Now I just through the old plugs away Thanks to all who helped out Quote Link to comment Share on other sites More sharing options...
Guest bang847 Posted June 17, 2002 Share Posted June 17, 2002 Originally posted by SpudZ:Smog Pump whats that ? In Idaho all the car has to have is windshield wipers. You can run without a windshield , but not without wipers. We have no smog checks here at all. DWV take less then 10 minutes to get tags for your car. I am thinking it isn't venting to the tank. Heck I have enough leaks in my houses back by the tank to keep it well vented Does remind me to put them on my to do list though. Thanks ! good to hear it is running good...I wonder if anyone is willing to register a 280 for me in idaho so i can drive it here.. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted June 17, 2002 Share Posted June 17, 2002 That is pretty funny, have to have windshield wipers even if you don't have a windshield. Sounds like a good ol' alabama law to me. We don't have those stinking smog checks either, thank goodness. Glad you got your car running. Good plugs mae a big difference. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.