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Carby Backfire and Valve timing - Need Help!

oshi16

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Hey All,

First I'd like to say that I love this site; and the vast majority of the time I find all the info I need on existing posts and help where I can. But this time I'm in dire need of a complicated problem.

I have an 85' VK commo, black 202 6 cyl. I have Scraped the EST and am running an after market Bosch Remake of the VH dizzy; and an HEI coil. I've also got 9.5m ignition leads and platinum IX plugs. I've changed out the basics, such as a new radiator, thermostat, water pump, starter motor and a hell of other little things.

About 5 Weeks ago I broke down on the freeway. The symptoms at first was of a blown head gasket! However, I later found out that one of my Push rod cover gaskets blew and the 5th cyl rocker saddle/bridge snapped.

In this event I took it upon myself to do a rebuild of the engine (not going further then the head), with all the basics of gasket swapping, fluid flushes and a ****load of cleaning. I also replaced the head bolts with an ARP head stud kit; and also did a Weber 34ADM carby conversion (fyi, I installed a proper conversion kit and the weber is second hand, but came of a running XE).

So all is going well except for how long it took; I hit many small walls and delays, and I mainly only had a couple of hours a night and the weekends to work on it (also this being my first rebuild I learned a lot the hard way), In all it took me a month. However, just under a week ago I had it finished, and I crosschecked as much as I could; until I was going around in circles. So I turned her over to be presented with nothing more then a large carby (flamed) backfire! (p.s. this scared the hell out of me and I though I blew up the carby). I tried once more, and had the same event! Tried twice more, thinking the system may need to get crap out of it or something and two more backfires happened, this time it did not ignite and it was purely made up of fuel air mixture.

Well **** now the trouble shooting begins! My first discrepancy I found is that I had the dizzy cap and lead 180 degrees the wrong way (FAIL OF EPIC PROPORTIONS)...but yeah fixed that quite easy, and tried again; No difference; Fuel air mix backfire (no flame). Next thing I found was that the weber that I got was missing the Idle solenoid, and I did my homework and got the right one (fyi the weber 34ADM used of the XE and XF had two types of Idle Solenoid, XE with a 12v switch type, and the XF with a vacuum operated one, that included a jet I believe). Anyway, I installed it, got a 12v wire running to it and had not change, except for an actual exhaust backfire...against the shed door at half a foot that scared the hell out of me and had my ears ringing for about 10 minutes.

So now this is where I stand; the only other thing I can think of is Valve/cam timing. However I've looked, read, asked and questioned everything to do with this topic 'How do you time the cam in a vk 6 cyl?' 9 times out of 10 I get the response of the EST will handle it, you're not supposed to do it yourself...(*slap*) and the other 1 is time it using the harmonic balancer and timing cover with a timing light (+ get cyl 1 to TDC and the Dizzy rotor button aiming at lead 1). Ok that's all well and good, but how the hell do you get at the timing cover without removing the engine, or dropping the Trans? It is on the back of the block right?

I'm sorry about this essay, I applaud you for reading to the end (*CLAP CLAP CLAP*). And I selfishly ask for any good advice on this; I'm in a desperate situation; as I want to get the girl running asap!

Thanks Heaps Everyone!

Brendan
 

oshi16

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Oh and just i side note, I've scrapped a fair bit of the tacked on emission control garbage that seizes up and causes nothing but trouble. However the Air pump and Injectors are still hooked up; and Also I've only half hooked up the egr....It is on the intake as before, with one hose going to he vac switch on the head and the other is hanging lose....for the moment I have no clue on how to set it up properly. Do I put the other vac hose into the carby?...should I just scrap the piece of crap? ...

Also a person message to whoever is ready this....."YOU ROCK! Thank's for reading my windbagged post!"
 

vkberlina

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finally we get another good problem, woohoo :)

ok when you did the rebuild in the engine what cam did you use? did you alter the cam timing?

timing cover is on the front it covers the timing chain hence the name :)

You need to get #1 on TDC on the compression stroke then time it off the timing marks on the timing cover on the drivers side of the timing cover above the harmonic balencer., good to do it with dizzy cap off so you can make sure you have #1 right on it then redo your leads on the dizzy cap so you dont have leads backwards as that will give the same result.

scott
 

bogan_vk

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im trying to understand what your trying to say i think its how do you get no1 at tdc on the compression stroke you can put a screwdriver in no1 sparkplug hole and you will feel when the piston reaches the top the timing marks on the front pulley must line up, to turn the engine over by hand pull on the fanbelt when you put the dizzy in make sure you put it in with the rotor button pointing at the mark on the dizzy top edge theres where no1 lead goes if i forgotton something someone will fill in the rest.
 

the_boozer

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The symptoms at first was of a blown head gasket! However, I later found out that one of my Push rod cover gaskets blew and the 5th cyl rocker saddle/bridge snapped.
upon myself to do a rebuild of the engine (not going further then the head)?
So from what your saying old mate you ve done up the head and changed to weber carby?
What do the spark plugs look like now you've tried to start it and it wont go?
How about the diaphragm in the webber carby did they break during back fire (personaly think efi conversion is better than webber but that means sfa) did it burst the rocker gasket when it stopped?
from what you ve written I gather you didn't touch the bottom end and the new and disturber is turning in the correct place making blue spark.
Did you have the cam out? and not line up the timeing gear like said above?
 

Guzzoline addict

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Compression test it to make sure your head gasket sealed properly.Also when you snaped the rocker saddle did you check that valve wasnt bent.(compression test should show)
 

oshi16

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Madness! Thanks for getting back to me guys.

First of all - Scott (VKBerlina), I didn't touch the cam at all, so I guess you could call it a partial rebuild in a sense. And wow! that's sweet that the timing cover is on the front; I'll attack that asap and get this thing timed up! I'll let you all know how it goes.

Thanks for the Tip too VKBogan!

Hey Boozer, yeah I only messed with the head and carby, only a partial rebuild as I said above. And to be honest I haven't looked at the plugs, they're still pretty new (under 2000K's) and I didn't feel the need to check after the carby backfire. Also No, nothing broke from he backfire (thankfully...*phew*) I checked that pretty well. Rocker cover (and gasket) and the weber are still in top condition, just got lightly saturated in fuel... And also as I'm saying in this post, no I didn't touch the cam at all. (probably should of in hindsight, but when I started this I knew crap all about my engine, except for a few little bits an pieces; but now I've done a crap load of research and learned by doing...and failing many times...hahaha).

Hey Guzzoline Addict! Yeah I probably should have mentioned this; I actually checked the compression before the leads (forgot to write it); every cylinder seems good. Cyl 1 is a little low...about 90...but I shot up when I topped up some oil. the others ranged from 105 - 120. Because yeah, my first thought was that the new rocker saddle/bridge was holding the 5th valves open at the same time and was stuck in that position. But I quickly found that that was not the case.

Anyway Guys, Cheers heaps for all the advice and super fast replies! I'm going to attack the timing with Scott's and Bogan's advice this weekend (if not earlier) and I'll hopefully get back to you with some good news! Is there anything I should know about doing this that can be a trap for the inexperienced? or should I just go at it and it's pretty straight forward. From what has been explained it seems to be striaght forward...But I guess I'm going to have to take off all the belts yeah? (after the radd, shroud and fan of course) or can I get away with just the alternator one, and any other lower ones that run on the H-Balancer.

Thanks Again Guys! I'd shout you all a drink if we ever met!

Brendan
 

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As you say it poped the side plates when it stopped I reckon you may have broken a ring do a comp test. The reason I asked what the plugs look like now are any oiled up?
 

oshi16

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Oh Right, Sorry Boozer I misunderstood. The plugs looked like they were a bit black from carbon or something (which came off when I cleaned them); but definiatlly not covered in any oil. And I did a comp test and everything seems ok.

Cheers!
 

ari666

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significant vac leaks can cause back firing and flames from the carb.

personally i check for number 1 TDC by taking off the rocker cover. the harmonic balancer and piston goes around twice for each cycle (once on power, once on induction) so even sticking a screwdriver in the hole you still have a 50% chance of getting it wrong. not to mention you have just stuck a screw driver in your engine. the thought of that makes me shudder.

with the rocker cover off you can watch the #1 intake valve close which means you are on the correct stroke. and sticking a bit of thin wire in the spark plug hole is less likely to damage anything.

once you are sure the intake valve has just closed and you are on top dead with your piece of wire, the mark on your harmonic balancer should be lined up with the 0 mark on your timing cover. if not your blanacer has spun or your cam timing is out.

so lets say the balancer lines up with your piece of wire and the timing mark, and your intake valve has just closed. you can safely guess your at #1TDC. move to your dizzy. pop off the cap and look where the rotor button is pointed. you can proceed in 2 ways.
1. switch all your leads to suit where the rotor button is pointed
2. undo the retaining bolt, lift the dizzy about 4 inches and rotate the rotor button to suit your cap.

either way works fine, but switching your leads may mean the shorter ones cant reach your sparkplugs.

drop the cap back on, tighten everything back up and fire her up.

dont forget to check that your rotor button is going CLOCK WISE. and your firing order is [insert correct firing order here]
 
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