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Rebiult L20B gutless and won't rev


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#1 Guest_///FiveOneOh_*

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Posted 06 July 2005 - 03:03 PM

Ok go ahead say it.. the timing is off! right? Thats what it would seem but the car is acting sooo strange..

Heres the info.

1972 510, rebiult L20B, L18 pistons, shaved A87 closed chamber head, shadbolt cam (stamped 510 on the back), Stock L20B carb till its runing right the webbers come later, fireball optronic ignition.

Eveything was set to exactly what the OEM manuel says. Timing marks all line up, dizzy drive is set to 11:20.

Problem is the car revs as if it has a 5000 pound flywheel! To me that would say its way to retarded... but when you shut it off it runs on horribly and under any load it pings... so then its to advanced at the same time?

This is my friends car BTW.. I'm fighting with a KA swap in my 510 right now.

Any help would be greatly appreciated.

#2 PeterZ

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Posted 06 July 2005 - 05:12 PM

I would recommend verify your cam timing. Retarded cam timing will drop intake manifold vacuum and show lower than expected compression readings. Your run-on may be due to the throttle position. I'll bet you raised the idle to kep it running because it had a very low idle. Too much fuel/air with the key off can cause run-on (Just like a poorly set pair of S.U.s). Your ignition turns off with the key so ignition advance would not likely effect run-on unless it was causing high idle speeds or very hot combustion chamber temps.

#3 Supra510

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Posted 06 July 2005 - 07:04 PM

When I bought my 510 it ran like a pig. The timing chain was off a tooth or two. I fixed it and it ran great.

Anthony

#4 Here comes trouble

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Posted 06 July 2005 - 07:27 PM

The timing chain maybe off a tooth or two.... run #1 piston up TDC and see where your timing mark is. if it is on Zero,,,,,,,, A stock carb can make the L20 run like crap of which I could not throw away fast enuff for a single DGV Weber replacement......If your timing chain was installed precisely and you got a good carb ...then this proceedure will get the L 20 running correctly and only if the timing chain is dead on.....disconnect vaccum advance from distribitor..... hook up a vaccum gauge to the manifod and dial in your carb air idle screw to get the highest vaccum reading.... at highest vaccum if idle is way too fast...reduce idle speed....check timing and readjust....,. check vaccum and adjust for highest vaccum.......keep readjusting vaccum, idle speed and timing until it runs right I have been tuning these engines for years with this method and do not let anyone tell you they can tune a car by ear... I cannot do it....I have yet to meet anyone who can tune an L 4 cylinder better than I can. My biased opinion..A vaccum guage is most often a very under utilized tool. I would choose it over a timing light.

#5 Guest_///FiveOneOh_*

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Posted 06 July 2005 - 08:40 PM

the carb came off my runing driving 510. the timeign is perfect, he biult the engien with his auto teacher, then he rechecked the timing with me and its perfect. Idle was turned up and right back to where it was because the car wont; idle unless your flooring the piss outa it. So I can't even mess with the carb to try and tune it....

#6 JMortensen

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Posted 07 July 2005 - 07:05 AM

So you're saying that nothing is wrong, that the timing is perfect, and you're just wondering why the engine sucks so bad? Tough to answer that one since it defies logic. If the teacher and the student did manage to screw up the cam timing or the ignition timing that would definitely explain the situation. Since you've ruled out timing problems it looks like they're stuck with a crappy engine. ;-)

Just triple check the timing. It's obvious that something is wrong, right? So your job if you want to help your friend is to figure out what it is. If you truly believe that the engine is assembled correctly you wouldn't be posting here, would you?

I think based on your description you can pretty much rule out the carb. Sounds to me like maybe the distributor shaft is in a tooth off. That is a very easy mistake to make. Done it myself. Try going full advance or full retard with the distributor. If either helps at all, then pull the oil pump and turn the distributor drive in the direction to make the timing better. Takes a while, but that might be your answer. You can have the timing pretty far off and the car will still run, but only at high rpms just like you're describing.
Jon Mortensen

#7 Here comes trouble

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Posted 07 July 2005 - 10:37 AM

JON: looks like a strong case of denial in the engine

#8 SleeperZ

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Posted 07 July 2005 - 11:12 AM

How are your plugs and wires? Or your coil? It sounds a lot like an ignition problem I had where it was a pig, and took forever to rev up under load. I had some bad plug wires.

1978 280Z -->  L28ET, MS3, T3/T4 (V1/V2), 440cc injectors, Spearco IC, BW T5

 

Otherwise all stock.


#9 PeterZ

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Posted 07 July 2005 - 04:53 PM

Again, have you checked camshaft timing? The cam cam be in backwards and still have correct ignition timing unless I've got the wrong engine then I'm sorry for the confusion. Like the Ol' Timer says: go to TDC and check the camshaft timing marks. Check at the piston 'cuz you can't believe the pulley at this point. I had a dampener pulley once that was slipping on the rubber dampener. Every fifteen seconds at idle the ignition timing marks would slip into alignment and then rotate away. Totally weird. Just from the pulley load from the alternator. Verify piston TDC, the camshaft timing marks and also for split overlap between the intake and exhaust valves if you want to go nuts. Then go check for things like the shop rag stuck in the downpipe. You can tell that by feeling for a pulse at the tailpipe. Plugges exhausts have a real smooth air flow. That's another story...

#10 Guest_///FiveOneOh_*

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Posted 09 July 2005 - 11:30 AM

Ok so we turned the engien by hand..this took forever! but the timing marks lined up correctly agian on both the crank and the cam. Right smack on the little timing marks. manualy checked for TDC with a screw driver in #1. Came up correct.

We backed the mechanical timing off one tooth and tried agian, it started better but still wouldnt rev, one more tooth and it won;t run. So at the moment the mechanical timing is at one tooth retarded.

Turning the dizzy doesn't make much of a difference. it just verys how badly the car back fires out the carb. However it does the same thing in both directions. I have all the screws out fo the dizzy so I can rotate it 180 degrees. At all settings the car runs on..and on...and on.. it has to clutch killed.

the coil is sort of unknown.. but the spark seems to be very strong, plugs and wire are all brand new.

I'm wondering. is it possible due to the shaved head that the timing has been thrown out of wack?

#11 Guest_///FiveOneOh_*

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Posted 09 July 2005 - 11:32 AM

According to the books the dizzy drive should be at 11:20. Does this sound correct or should we move it to 12:00?

#12 JMortensen

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Posted 09 July 2005 - 09:17 PM

[quote name='///FiveOneOhWe backed the mechanical timing off one tooth and tried agian, it started better but still wouldnt rev, one more tooth and it won;t run. So at the moment the mechanical timing is at one tooth retarded.[/quote]
I wouldn't get too crazy with changing the cam timing, on a shaved head with a cam you can run the valves into the pistons pretty easily. If you wanted to try and screw with the valve timing, try using the other holes in the cam gear instead of rotating the cam a full tooth and putting the chain back on. Those other cam gear holes advance and retard the cam 4º.
[QUOTE=///FiveOneOh
Turning the dizzy doesn't make much of a difference. it just verys how badly the car back fires out the carb. However it does the same thing in both directions. I have all the screws out fo the dizzy so I can rotate it 180 degrees. At all settings the car runs on..and on...and on.. it has to clutch killed.[/QUOTE]
That doesn't make any sense. Even if the ignition timing weren't the problem, turning it 180º off should make a difference (should make it run horrible). If it was the problem, turning it 180º should also make a difference (make it run a lot better). Makes me think that the firing order is screwed up.
[QUOTE=///FiveOneOh
the coil is sort of unknown.. but the spark seems to be very strong, plugs and wire are all brand new.
[color=#0000ff]

[color=#0000ff]I'm wondering. is it possible due to the shaved head that the timing has been thrown out of wack?
[/QUOTE]
This really doesn't sound like a coil issue to me. Shaving the head does retard the cam timing a couple degrees, which usually gives a little more top end power. Unless it was shaved a whole bunch I don't think that's your issue.

I'm now CONVINCED that your ignition timing is screwy. Something, either the firing order or the distributor shaft or both is not right. What you said above just doesn't make any sense at all.

Sorry, can't help with the 11:20 bit. Never did it that way, just put the thing to TDC and pointed the rotor at the #1 terminal on the cap.
Jon Mortensen

#13 Guest_///FiveOneOh_*

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Posted 09 July 2005 - 10:14 PM

Cam is # 2 right now.. we tried to move it to #1 but the cam wont; turn that far and we didnt; want to force it. I'm sure we did something wrong there...

head is shaved enough that you can no longer read A87. looks more like /O7

Firing order is set 1342.

#14 JMortensen

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Posted 14 July 2005 - 09:32 PM

So did your friend give up yet or did he figure out what was wrong?
Jon Mortensen

#15 fastzcars

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Posted 15 July 2005 - 06:44 AM

Well it sounds you did everything right. I got one more thing to add , how about restricted muffler or kinked exhaust? unbolt the whole exhaust system from the manifold and start it up uncorked.
Keep the rubber side down.

#16 Here comes trouble

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Posted 18 July 2005 - 10:55 PM

Some basics> L 20 B (and L 6) .. Most manuals show the blade or spade of the timimg shaft located at TDC at what is considered "11:25 AM".. the top of the blade is just right of the top distribitor mounting bolt hole and the bottom of the spade is just left of the bottom distribitor bolt hole ...ie 11:25 AM... At TDC your distribitor rotar's horizontal electrical blade should point towards the radiator and be under or near the distribitor cap's # 1 spark plug wire. The distribitor rotates counter-clockwise....and firing order is :1-3-4-2.. Your timing chain bright links should be aligned with sprocket timing mark (round indentation) at crankshaft and at the marked #1 indentation on the cam shaft sproket. Just a slight deviation from the above will cause problems........re-check all






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