have an issue with 3.0 SC with high hydrocarbons on one side...

[Karnak]

hi,

i am currently working on a 1980 911 3.0 SC engine (in a 914) that has been sitting for a long time 15 yrs or so. the case has never been opened.

the compression is sitting on all cylinders at about 120psi except for one that is 127psi.
the engine has 40 ida3c carbs on it. mains =125 idles =45 air =180 and in the main body (looking in) i see "36".

the motor's hydrocarbons are high on one side and nothing can be done to lower them.

so far, the carbs have been rebuilt (by a shop)
i have sync'd them up to the best of my ability and they are very equal.
idle is smoothest at 1000 to 1100 rpm. below that it labours (sounds like it wants to die)
the psi feeding the carbs is 3.5psi and i have tried lower and higher perssures
the plugs are "hot" and the gap is set to .040" in an attempt to 'burn' the fuel
premium grade fuel is in the car
the distributor has also been curved for the full range of advance (since there is no longer any vacuum hoses...)


the car is easy to get going at an idle (drive) but as i add gas, it is non responsive. there is a dead spot so i have to play with the accelerator to bring the revs up before letting out the clutch. once i get going, it runs in a very erratic way with not a lot of torque. until i open it right up...then it smooths out

at 3000 rpm i had experienced missing and misfire and immediately replaced the spark plug wires with new Bosch ones.

after the leads were installed, i double checked the carb sync and attempted to furhter lean out the mixture. popping in the exhaust can be heard. i leaned out the mixture until either popping occured in the carb, or the engine performance degraded. the process of leaning and syncing took about 90 mins, as i listened and adjusted and looked at my synchrometer.

the next road test revealed the missfiring was 'gone' or at least has taken a different form. the car is better as i start but is still lacking power (torque) and the 'hole' is still there. the car at 3000 rpm (2nd gear) is surging and is not smooth at all.

during my long sync of the carbs, i would rev up the motor to see how it settles and i noticed 2 things

the motor's rpm would remain high 1300 rpm or so, for a time before coming back down to 1000, where is had it set
and
the sound coming from the side of the motor that poped in the exhaust (even with the mixture as lean as i could go) thru the 3 barrels was

louder and more 'open' sounding than that on the other side.

soooo...

is this valve gaps? could it need its cam timing looked into?

i have played with the carbs and wires and plugs so much that i feel there is nothing left to try there and think it may be elsewhere in the motor...

any insight would be very much appreciated...

thanks,
Gary

[Karnak]

hi, me again,

no body has any thoughts...?



i pulled the plugs and before the wires and last sync adjustment they were lean looking, except for a couple which were likely the miss firing ones, not they are silver with bone white insulators...definitely too lean. the pop in the exhaust is still there though.

i have started to check the valve lash and the feeler gauge is impossible to insert, although, the rocker, when i work it with my fingers, i can detect lash.

i was forced to re-set the gaps in order to check them.

am i on the right track?

thanks,
Gary

[Karnak]

ok...i am back.

i had done somee reading (here on the forum) and a couple of test drives, and went out and bought some NGK plugs (copper core) and put them in at 0.028 gap.

pop pop...pop...bang..the noise in the exhaust is setting off alarms.

i have since re-gapped the plugs to 0.035 and it is better. i have a plan to go wider still.

i also understand that the distributor timing should be set when the engine is running at 6000 rpm (to 30 deg) then expect the idle to be ok. (if idle is not ok then i have an advance issue)

can someeone validate this please?


i have been setting the timing at idle and then noticing that i do not get enough advance at higher rpms...

is that why i have a hole between 1000 and 3000 rpm?

should i move the distributor a tooth to get more access to advance...does it work that way?

the valve adjustments did not help what so ever

the high hydrocarbons one one side might just have been the spark plug wires.

[914efi]

Assuming the carbs are correct and identical, the only other thing that could different from side to side is cam timing, or maybe vacuum leaks. Is the exhaust system good on both sides?

[Karnak]

yes, the exhaust is new and quite symmetrical.

this is a project that my brother started about 20 yrs ago and i have purchased it from him. his ride is a GT3 now.

i will double check all other things related to timing before is pull the engine to check the overlap.

thanks for your response!


Gary