3 cylinder woes.

martylove · 06-18-2005, 03:58 AM

so i had this new motor built up for my 914, 96mm pistons, 40mm dellortos (new out of box) lots of head work, a big cam, crane x700 ignition, all polished balanced and lightened.

when i first got the car back it ran fine while running in, then started to run on 3 pots. we couldnt work out why.... we have spark, we have fuel, we have compression. i think its #4 thats off.

when running the motor removing the lead makes no difference, but if any of the other 3 are taken off it dies. im guessing if it was a timing problem then the others would be off / misfiring as well which is not the case.

any ideas cos we are lost

martin

John Rogers · 06-18-2005, 10:04 AM

If you pull a plug wire and nothing happens, that means either that cylinder is getting no spark or no fuel. Pull the spark plug and crank it to see if the plug is firing. Pull the cylinder next to it to see if they look the same (roughly). It could be a failed plug, failed wire or bad contact inside the distrib cap. If that looks okay, check the carb on that side to see if the cylinder is getting any fuel. I'd suspect it's a spark issue though.

NoEcm · 06-18-2005, 12:45 PM

1. Check as suggested above

2. Check the valve springs for the cylinder in question

3. With the ignition coil disconnected turn the engine over with the starter and have someone observe that both the intake and exhaust valves are fully opening.

martylove · 06-19-2005, 02:04 AM

valves operating fine (just set spaces)

getting fuel (plug is wet)

getting a big fat spark

compresion is fine

still wont run

you know those days where you think about giving up and selling the car.......

martylove · 06-19-2005, 06:19 AM

so i just picked the car up from the mechanic and took it back to my lock up to think about what to do next......

it runs really rough, i got white smoke coming out the back, more under load.

a small chink of light though.... when gunning it the very flat 3 pot power seems to surge intermitently as if #4 cylinder is trying to fire....

please help

mikey · 06-19-2005, 09:31 AM

plugged idle jet on #4???? Especially if it is kicking in when throttle is applied.

Mike

mikey · 06-19-2005, 09:32 AM

try squirting some fuel into #4 when engine is idling to see if it makes it come alive.

John Rogers · 06-19-2005, 03:55 PM

If you have a spark and the plug is wet, then the spark may not be in the right time? Look inside the distributor cap for cracks or arcs that can cause the spark to occur at the wrong time. Also switch the plug wires between the plugs on one side and at the distributor to see if the miss moves to the other cylinder. Finally after you have run it some, do a compression test (hot and allplugs out) to see what you have. The worst case could be broken rings, cracked piston, cracked head so as not to have any compression then the fuel will not ignite.

Type 4 Unleashed · 06-26-2005, 09:47 PM

Quote:

Originally posted by mikey
plugged idle jet on #4???? Especially if it is kicking in when throttle is applied.

Mike

Did you get it figured out? If, you havn't, I, agree, #4 idle jet is cloged, it doesn't take much, pull it out, blow it clear.

mattr_914 · 06-26-2005, 11:53 PM

I was chasing a 3 cyl problem on my 912 for quite a while and i found it to be the float levels. I guess just because the dells are freash out of the box doesnt mean they're all adjusted right. I'd go through and double check everything. If the plug is wet, thats confusing though unless its running on 3 at idle only.

martylove · 06-27-2005, 12:29 AM

aint fixed it yet guys,

thanks for the concern though

to recap - #4 is down, at idle and up to about 4500+ revs (it tried to kick in a bit above this i think at least last time i drove it).

i have fuel
i have spark
i have compression
valves opening and closing fine
i have white smoke

just one small note..... on closer inspection my new carbs are webers (which i am really angry about - why do these guys lie to you? the quote is as follows "hey one of your throttle shafts is bent so we need order new carbs" "we will get new dellortto 40's, no problem" then after i noticed... "oh yeah they dont make em anymore" this is made even more annoying by me having 2 sets of webers sitting on a shelf anyway dammit)

(if anyone wants some 40 dellorto or some 45 weber drop me a line)

we dont get much summer here in the uk so i need to fix this quick!

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Just because the carbs are new doesn't mean they're in perfect shape. Take 'em apart and clean 'em up. Blow out the jets--especially the idle jets--and check the float levels and all of that. Sounds like you may be getting too much fuel on #4.l

--DD