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L6 running bad need help


Guest SpudZ

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Guest SpudZ

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 2thumbs.gif

 

I already missed one autocross this season and don't want to miss

another one.

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Guest SpudZ

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 :(

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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.

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Guest SpudZ

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.

 

:confused:

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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

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Guest SpudZ

Thanks everyone for your help 2thumbs.gif

 

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.

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Guest SpudZ

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 !

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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

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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

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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

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Guest SpudZ

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 !!

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Guest 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 smile.gif

 

Does remind me to put them on my to do list though.

 

Thanks !

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  • 1 month later...
Guest SpudZ

I fixed it and she rins like a top smile.gif

 

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 smile.gif

 

Thanks to all who helped out 2thumbs.gif

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Guest bang847
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 smile.gif

 

Does remind me to put them on my to do list though.

 

Thanks !

2thumbs.gif 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..

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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.

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