Two problems solved, only to have two more pop up??? HELLLLP

[CruxGNZ]

What's your timing set at?

 

!M!

[Guest bastaad525]

Right now it's set at 13 degs. BTDC, I tried retarding it all the way to 6 degs., but it still dieseled and it also seemed to have a lot less pep.

[Guest Anonymous]

The backfiring should be due to being lean as you pointed out. An engine being a pump, pumps air, more duration on the cam means pumping (stuffing actually) more air through the engine, without changing the mixture it would follow that it very probably would be leaner. Just a little theory, but I'm sure thats the case. Fatten it up and it should go away. Not sure on the dieseling, but if your running more compression, what octane gas are you using and are you getting any detonation when your running it? Also are you sure the distributor is not a tooth off and your reading on the dampener is inaccurate? Just some idea's.

 

Regards,

 

Lone

[Guest bastaad525]

I'm running the finest in CA gas, a.k.a. 91 octane No pinging at all... and as I pointed out, after swapping the carbs for some rebuilt Ztherapy carbs, the dieseling had gone away completely... It only started back up after reinstalling the new head and cam. so I don't think it's the gas, unless the cam has also changed my octane requirements? I'm pretty sure the distributor isn't off... at any rate it hasn't been removed since the engine was rebuilt 2 years ago.

 

Anyways, today I went and retuned the carbs (using the Ztherapy method) and got the mixtures just about where they should be (highest, smoothest idle) then ran it on the freeway for about 50 miles and pulled the plugs and they looked just about right. I sprayed around the manifold and carbs with the engine running but didn't hear the engine RPM change... so if there's a vacuum leak I can't find it. So, carbs tuned, no vacuum leaks, timing adjusted from everything to 6 degrees BTDC to 13, valves adjusted (hot) and idle at the lowest it will run decently, about 800RPM, and still dieseling every time I shut off. SOMEONE HELP!

[Guest bastaad525]

Okay.. got my N42 head back from the machine shop, and had it installed with the new cam (.480 lift 270 duration). Luckily it turns out it WAS a valve seal that was leaking, hence my burning oil, and there was one bent valve, hence my persistent unfixable valve tap noise. So those two problems are down, but now... With everything back together the car seems to run good... kinda bogs a little at low revs, almost like its running rich, but i"m guessing this is due to the cam and my power band being moved higher in the rev range? Anyways... that's not really a 'problem', the two new problems are:

 

A)occasionall backfire thru the carbs... which means I'm running lean right? I know this is probably a stupid question, but does a hotter cam require richening the mixture?

 

B)DIESELING!!! I HATE it when it does this and now it ALWAYS does it, every time I turn the car off!!! I had this problem before with my old carbs... I ended up swapping them out for rebuilt Ztherapy ones. After the swap the engine NEVER dieseled on shut off. The ZT carbs are only 2 mos. old, so I'm assuming that's not the problem, unless it's because I"m now running too lean. I'm gonna check all over for vacuum leaks today.. but if that's not it, why would a cam upgrade cause my car to diesel... and I mean diesel BADLY??

 

As always, any tips or insight would be greatly appreciated!

[Guest bastaad525]

Something else I've noticed... the engine is running warmer now. Not dramatically so, maybe just 1/8th more than usual... it used to always run right around the halfway mark on the gauge, a little below or a little above, which was fine because I had installed the hotter thermostat (180 or 190 degrees, I forget). No it stays constantly at about 5/8's or 2/3's of the way up... too warm for my taste. Why hotter with the new cam?

[Tim240z]

Check all your vaccuum lines and fittings. MAybe one of the lines are split or cracked. The increase in temp. is likely a symptom of the lean mixture. Check all the bolts on the inlet manifold (manifold to head, carbs to manifold etc.)

I am assuming that you used all new gaskets!

If there are no vaccuum leaks, then richen up the mixtures in small increments until it's better.

Tim

[Guest bastaad525]

All hoses check out A-OK. All new gaskets were used. All the bolts are torqued tight. I did richen up the mixture quite a bit, judging by the plugs and the ZT tuning method it should be just about spot on. It didn't really seem to do any good

[DAW]

Set your idle as low as possible to get rid of dieselling, without going so low as to load up at idle.

 

So what's going on with the cooling system? You're running hot since the top-end rebuild...is there now a lot of pressure in the system? Is a cylinder leaking compression into a water passage (at head gasket seal)? Is there a hairline crack in the reworked head?

 

Assuming you increased compression with the head work, you have a new set of mixture requirements (richer), and timing parameters. Either or both of these being off will cause detonation and/or dieselling. Until you get it sorted out, don't let it run-on, hold with the brake and engage the clutch on shut down, and decrease idle speed. DAW

[Guest bastaad525]

well.. I inspected the head before having it reinstalled and it looked perfect. I don't think I"m having any kind of head gasket leak, did another compression test and they're all about even, only about a 10psi spread. Again, my idle is set at 800RPM, which is about as low as this new cam will let it idle decently. I was able to get it down to about 650rpm, but it was very rough and gave me a hard time when I am trying to start it. And yes, even idling at 650RPM it will STILL diesel on shutoff.

[Guest Anonymous]

I am no carb genius. But I think if that you know how to run wires and solder, running a cut off switch from the ignition to a pressure toggle in your fuel line close to the carbs would fix it maybe easier than rebuilding or fixing the carbs. But it just depends on how much your problem pisses you off, and how much time it takes you to fix it!

[Guest Anonymous]

Oh yes, and I gaurantee a few well placed sledgehammer hits to the carb will solve all your problems, lol.

[Guest bastaad525]

Heheh Tim you read my mind... well I got fed up with the guessing game so I decided to let a 'pro' tune it. Took it to my friends shop and hooked it up on the exhaust gas sniffer... turns out I had it tuned pretty much spot on, though it also turned out SM needles may be the wrong needles for my setup. Anyways, we had to settle for a bit of a compromise. If tuned to run 'perfect' at idle, it would actually run a bit lean under load at high revs. So we fattened it back up about to where I had it, runs good throughout (there are some rich and lean 'spots' however)the rev range but runs a bit rich at idle.

 

we tried both these setups and still the car diesels like mad when shut off.....

[Tim240z]

Dude,

I work in Chatsworth (near the mall), where are you?

Tim

[Guest bastaad525]

Northridge, pretty dern close what you have in mind?

[Tim240z]

Nutin' kinky

[Guest bastaad525]

ROFL ummm okay???

[Guest bastaad525]

Well I found out why it was running warm, too much coolant to water mix. So I forcefed some water in there and now the temp is right where it should be... still dieseling though

[Tim240z]

What is you schedule like on Friday? Maybe can meet up and I can have a look. I'm no expert, but sometimes a new set of eyes/ears can find something

Drop me an email and let me know.

Closest cross street to my workplace is Plummer/Tampa (actually Plummer/Oakdale)

Tim

[Tim240z]

Dude...take it to a shop with a exhaust gas analyser and check it out once and for all!!

Tim