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#1 _77TUFF_

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Posted 26 July 2016 - 11:32 AM

Gday

 

I have got a problem with my lx 308 vn headed motor

 

SO

i had BPR6EF vn ngk spark plugs in for a while and they seemed to keep gunking up!!! once it started no problem. sick of ripping them out and cleaning 

its only a once , twice monthly driver 

 

i was going to put iridium in but i was  told to use wb plugs BPR5FS-15 which i tried and worked well straight away.

Went for a drive about 30km and had lunch cooled right down and restarted no problem but while driving it kept backfiring through the carby when you put your foot down and lost power like the timing was out??? so ive been turning the dizzy bit by bit to see if any different BUT nothing im going to check timing soon with light 

its weird that it was working perfect then Boom totally different 

float levels are good

air /fuel mix Same

 

 

any info would be great

 

cheers

 



#2 Redslur

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Posted 26 July 2016 - 12:00 PM

Try going to a hotter range spark plug.  Think I run the same plug as you and they are only good if you tend to drive the car hard. They will gum up if you stop and start a lot.



#3 _77TUFF_

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Posted 26 July 2016 - 12:03 PM

vn plugs or wb



#4 _77TUFF_

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Posted 26 July 2016 - 02:40 PM

Yeah I will try that hotter range vn plug the wb wouldn't be sparking in the camber to short I reckon


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#5 76lxhatch

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Posted 26 July 2016 - 03:48 PM

What is the gunk? Maybe you've got issues with your PCV valve/oil breather and its sucking in too much? Or perhaps the coil is on its way out and having trouble producing spark?



#6 EunUCh

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Posted 26 July 2016 - 08:50 PM

If the plugs are an oily wet type fouling then it will be getting oil from somewhere , if the fouling is a sooty (dryish)  black deposit ...check the jetting of carb. , carbon has a bad tendency to conduct electrons into the wrong place at times.

 

Pull a plug from the modern daily driver and have a look at the porcelain insulator , if they are not at least on the light tan side or almost 

white then a tuning procedure might be needed?

 

 

 

 



#7 _77TUFF_

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Posted 27 July 2016 - 07:50 AM

thanks 

 

pcv valve is old and the hose going into carby is pretty wet /oily think shes due for a change so might be coming from there ?????

 

 

 

i did notice when i checked timing it was out a bit and the dizzy bolt is very tight but the dizzy can still be moved with a bit of force so maybe over high reving it moves ever so slighty, so moved back to 36 degrees @4500 where she runs the best from the start of all this  then went for a cruise and only back fired once but still didnt feel like all the power was there. 

so im going work out the bolt on dizzy ?? and change plugs back first to vn (deeper long tread than the wb) and pcv valve then  test

 

 

hopefully get this done today ill keep in touch 



#8 Redslur

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Posted 27 July 2016 - 12:01 PM

That is a lot of total timing for a 308.  They normally don't like much more than 28 degrees.



#9 _77TUFF_

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Posted 27 July 2016 - 03:08 PM

The dude that built my motor said between 34 and 36 degrees adv @4500  for peak performance with cam etc

286 cam vn heads  and all the rest of the gear 

any under 34 run like a dog 

36 wheel spin all gears  with no pinging 

starts pinging  above 40 degrees adv

 

 

with the spark problem

dizzy spring was shot so with a bit of mods, the dizzy isn't moving!!! went for cruise and no backfiring went well. SO must have been moving and retarding  which caused backfire im guessing ????  and causing richer fuel to gum up plugs??????

 

 

 

so next is jets and fine adjustment  i think  



#10 mick_in_oz

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Posted 27 July 2016 - 07:36 PM

I'm not throwing stones, but any Holden V8 that needs that much timing doesn't have a good set of heads. If the bowl and seat and throat are average, they will want the extra timing but as mentioned above, a good set of heads will see the engine unhappy about the 28deg mentioned. A sweet set of heads and a good combo might not want any more than 25deg. That much timing with nice heads will see pushed out head gaskets, and very quickly.

 

How much timing does it have at idle? It may have way too much advance in the dizzy, so to have a good amount at idle it ends up with way too much total, and visa versa.

 

Rough starting point knowing zip about the engine, I'd be happy to see it starting at maybe 15deg at idle and max at 28. If the heads are average, then maybe 34 -36, but I'd be cautious till I was sure it needed that much. If it's got plenty of cam in it maybe 20deg at idle and 28 max.

 

I'd also run a standard heat range plug and only go colder if it really needs it, but unlikely.

 

A lack of initial timing could also be a source of fouled plugs. 



#11 _Mint_

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Posted 27 July 2016 - 08:03 PM

my 2 cents ..the plug gap is too big the 15 bit on the end of the plug number means its gapped to 1.5mm that's huge

the 'ol 253/308 plugs ran 0.9mm...so even with a ramped up ignition 1.1mm would be plenty

I personally think you got too much fuel and the carb needs to be rejetted I recently went 4 jet sizes down front and rear on my Holley 650 dp with great results clean plugs and no surging if its a Holley/Quickfuel they are set up "fat" straight outta the box

#12 EunUCh

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Posted 27 July 2016 - 08:46 PM

^ yep , that's what i sort of meant about pulling a plug from a "modern" daily driver and compare it to the plug color to of current set up.

 

Most carbs "out of the box" are set on the fat side so that they "cover their arse" for a lean burn out so that there is no "come back" on

carb. maker for a lean burn , better off with fouled sooty plugs and sort the jets out  or at worst washing the the oil off the bore , so they don't really win either way".

 

Don't be frightened by leaning the thing out a step at a time and driving , carbs have been around a lot longer than efi and the AFR has not changed all that much since the conception of petrochemical internal combustion engines.

Light tan insulator or at worst almost white , more like grey , might even be able to get out of shed without killing the chooks and choking the bloke next door on washed out rich mix. ?

 

 

 

 

 



#13 IMORAL

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Posted 27 July 2016 - 09:23 PM

My dizzy moved once. 3 cracked pistons in the shed for my troubles

As others said that seems an awful amount of timing

Mines happiest around the 28 mark

#14 gtrboyy

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Posted 27 July 2016 - 09:54 PM

Wow sounds like it's got lots of timing in it.

 

Bigggish cam low compression ratio?

 

Fit up catchcan asap that should help out heaps

If pedantic do sealed setup pcv on top of catchcan then hose to aircleaner should stop majority oil from getting into carby.

 

Then see if some improvement.



#15 76lxhatch

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Posted 28 July 2016 - 07:29 AM

34 degrees total advance is pretty common and works well for engines that want it. 1.5mm plug gaps are standard for HEI



#16 _77TUFF_

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Posted 28 July 2016 - 08:54 AM

The Timing at idle is 15degrees

 

i tested the vac at idle 11 hg 

 

so std from holley i think?

 

front 67 rear 76 PV 6.5

 

at the moment ive got in 

 

front 70 rear 79 PV 6.5



#17 Dr Terry

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Posted 28 July 2016 - 09:46 AM

The BPR5FS plugs won't work for very long in VN heads, they are too short.

 

For VN Heads you must use the long thread type plugs. I would use BPR6EF.

 

Dr Terry



#18 _77TUFF_

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Posted 28 July 2016 - 10:22 AM

yeah mate that whats back inn



#19 mick_in_oz

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Posted 28 July 2016 - 08:03 PM

Maybe some engine specs?

 

But I doubt I'd be running 6's in it, I'd start with 5's, even if they are the wrong choice they should cope with the current state of tune or trouble better.

 

For a hottie engine on the street, I'd run as hot a heat range plug as you can get away with without unwanted trouble, forget about what everyone says about plug heat range and give the engine what it needs, if you can't keep them clean with tune then approach the trouble from another direction, or tuning aid, and put a hotter plug in that will take on enough heat to burn off the contaminants and keep the plugs clean.

 

Lets say it makes best power on a dyno with 6's or 7's, that's fine, but how often do you drive around at wide open throttle making 400HP or whatever it is, almost never, but it will spend most of its time nannaing about town, and its this driving that will benefit from or need the hotter plug.

 

Passing thought, whats up with the popping, missing? is it ignition related? or lean carb trouble?



#20 _77TUFF_

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Posted 29 July 2016 - 10:47 AM

308 block  mach 0.25

vn headed mach 57cc

10.5:1 comp

Torque power hi rise single plane manifold

650 Holley vac sec

flat tops

Crane H286 cam

Crane lifters and roller rockers

straight cut gears (sounds mean)

modified T5 gearbox to suit the shifter position  in original floor tunnel  

borg warner diff 3.7 gears

 

could be to lean??? i have been told on the Holley throttle lever there is different colour springs ive got the std one its green ive been told get the pink one this allows more fuel into the bowl or something???? when you really give it some

 

any thoughts cheers 



#21 Redslur

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Posted 29 July 2016 - 12:07 PM

Still think that the amount of timing you are running for that combo is way too much.  The manifold is too much too. A dual plain would much better suit your application especially with a Crane 286 cam.  I am starting to wonder if your dizzy is not healthy hence it not running right and you fowling plugs etc.

 

I have run similar 308 combos with a dual plane running both a Crane 286 and Crane 304 hydraulic and both engines ran at 26 degrees total timing. Using a dual plain manifold I was getting around 350 flywheel HP.  Both these combos were dyno tuned correctly too.  I would suggest running your car up on a dyno and getting it set up properly.

 

My experiences anyway!



#22 _Mint_

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Posted 29 July 2016 - 12:57 PM

the lighter secondary spring wont put more fuel in the bowl it will open the secondary throttle blades earlier since toranas are a light car you can have quite a light spring...the 600 vac sec I had on my 253 I had the lightest one available

but that's not why your plugs are fouling

Edited by Mint Julip, 29 July 2016 - 12:57 PM.


#23 mick_in_oz

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Posted 29 July 2016 - 08:15 PM

The coloured "spring" he is referring to is the accelerator pump cam, these come in different colours, standard would normally be natural (a whiteish colour) and the pink cam is standard on some HP series carbs. Yes the Pink cam will give you a bit more accelerator pump shot and for a longer period of time methinks.

 

I've just reread your opening post and it might be worth trying a pink cam.

 

Another thought is if the pink cam helps but doesn't fix the trouble, it might need a 50cc pump kit. The thinking being its a standard stroke motor with the large single plane, it could be that the combo is on the edge of not enough fuel from the standard acc pump.

 

Are there any carb spacers being used? Open or 4 hole, thickness???



#24 mick_in_oz

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Posted 30 July 2016 - 07:24 AM

The "spring" mentioned, I guess someone was probably referring to the vac diaphragm spring, I didn't go this way due to there not being a Pink Spring, but there is a pink pump cam that will add more fuel.

 

Anyways, another thought was if the small ball bearing is still in the Vacuum Diaphragm housing? If its missing it can account for sags in acceleration and even backfires as the secondaries come open too quickly causing a lean condition. 






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