Good afternoon guys, first time poster. I have a 1968 Corvette. In 1984 a crate 350 was put in and than it sat. I managed to pull it from a sea box and got it running. Long story short it appears the person who assembled the top end didnt use self aligning rockers and also didnt set the rockers up properly...a rocker arm went sideways taking out the pushrod and wallowed out the pushrod hole a few weeks afer i got it going. So i decided to do a full edlebrock top end...650 avs, performer and a set of e street heads. I did a xri igntion swap to ditch the points and replaced both front harnesses to make the car safer.

So here we are today with starting issues. The car is very very diffcult to start. Most cases itll turn over...stumble, then spin backwards and push vapor and smoke out of the carb. However..sometimes, itll get past this problem and idle low but spit and pop through the exhaust. Throttle, gas, choke appears to do nothing to this condition at which point it will die (and sometimes do its vapor spout) or just shut off. However sometimes it will get past this issue, and run just fine. No smoke out of the exhaust or anything like that. Very rarely will it ever just fire right up and run. It appears the condition is erractic but mostly worse when cold starting.

When i do it get it going, i set timing to around 16 base, 38 all in at 2500. Idle vaccum is a steady 16, revs fine, feels fine when driving it down the block.

At this point ive really tried everything i could think of. Most lean towards timing (which i tend to side with as well). So i checked tdc, looked fine, rocked the crank both directions and watched the rotor button, appears to be little, if any slack. I tried loosening the valves slightly. I havent tried a compression test which i know i should have done. Ill do it this weekend. All the ignition is new, the whole fuel system is new. The problem persists between the original carb vs the avs2. No metal in the oil filter.

Im sure i forgot some stuff, sorry for the long post but this problem is driving me insane.

 

JMPO but 38 deg timing all in is too much with those heads, pull it back to 34 and see how it starts with 12 deg initial. 36 deg seems to be generally accepted full advance on this site but that is with older heads not newer tech versions - once again JMPO This is of course idle advance with the vac advance disconnected.

 

Thank you for your reply. I have tried anywhere from 8-16 initial with the same results. However i will try it again this weekend ans report back with accurate, up to date answers.

 

I also want to add that the motor was a 9:1 with smogger heads and now it should be 10:1 as i ran the pistons and came out with their numbers of 10:1 with 64cc heads.

 

So what carburetor is on it now and what kind of choke does it have?
What rpm is the choke fast idle set to?

 

currently it has an edelbrock 650 avs2. It had a carter afb before, jetting slightly richer irrc and it had the same issue. It has an electric joke which i have messed with for cold starts to little progress. It has the fast idle set to around 2k initially out of the box. I lowered it to around 1500 but it rarely ever actually fast idles. When it does attempt to start it almost sounds like its lean as itll sit there and chug at like 400rpm. Any throttle will make it sound like its about to stall and spit and pop hardcore through the exhaust (as if it were lean).

if it doesnt do the above...it will crank, sputter, rougg idle for a second, spin backwards and throw smoke out of the carb.

 

I'm no expert on 68's. However I have read they run high 12V. Power to the coil for starting, once running, power goes through a resistor, cutting it down. Could it be your aftermarket electronic ignition convertion doesn't like this?
Problem is pretty much the same over 2 carbs. Once running it runs well you say. Seems to rule out a mechanical issue. I'm running 36 degrees total timing with Edelbrock heads. 20 Degrees initial. No issues. Perhaps borrow a distributor from a friend and just try it.

 

this is what i was reluctantly leaning towards as well. The points can be reinstalled. The XRi states that with a resistance wire it should be installed as is. I just find it weird that it would run and drive under load and rpm with no issue vs simply starting.

 

You mentioned performing a compression test, and I think that is a good idea. I get the feeling that your problem is related to valves. Either they are not sealing correctly, or the cam timing gear is off one tooth. You could also check your valve clearance/preload, based on whether you have solid or hydraulic valve lifters. If not set correctly, one or more valves could be held open.

 

So an older gentlemen mentioned that hes only really ever seen a car blast fuel vapor and smoke out of the car when its jumped time. I appears from the limited information i can gain from checking tdc and movement of the rotor button that the chain seems to be ok. However we are also talking about an 80s crate engine that had the rocker arm nuts upside down so i wouldnt be surprised. Im just confused as to why it would pretty much after the headswap. The ignition thing would make sense but im def doing a compression test first. I will give the results. Someone also mentioned to pull the coil wire off and junk crank it to see if the ignition is causing it to spin backwards etc

i will report back

 

You might consider pulling the timing gear cover to make sure your timing dots are lined up properly.
If they are set up 180 degrees off, so is your distributor.
You may need to set the timing marks correctly or pull and rotate your distributor 180.
It will run fine if the timing marks are 180 off, but you just have to set everything else up with this in mind.
There have been many threads where the timing marks were 180 off and corrected one way or the other.

 

*double post on my part* see below.

 

i did try rotating it and it was fighting to turn over etc. I did a compression test, 190 across the board and it turns over freely without the coil attached.

 

There are numerous experts on the forum who can help you better than I can, who are professionals in the field.
A couple have responded here already.
To get more interest from them, you may want to start a new thread asking specific questions that will spark their interest with a challenge.
If you have fuel and spark, it sounds like a set up problem, but that is as far as my limited knowledge can take you.
Good luck and I will be following.

 

What's an XRI ignition, and which harnesses (i'm assuming wiring, but which ones?) Ignition wiring? headlight harness? What distributor? MSD? Mallory? Is there an external ignition box added?
Lets figure this thing out

 

you guys are great i appreciate it. Engine and headlight harness are both new as is the starter, alternator etc. I ran large gauge cables to the battery and starter and ran additional large grounds to the block and frame to ensure the car was electrically sound. Stock distributor with the points replaced with a fast xri module wired to their coil..new cap rotor plugs and wires.

so last night i did the compression test, 190 across the board. I also rewired the choke off the 12v wire on the alternator (ign on 12v, not constant) and then reset the choke to its mid setting. Additionally i checked the coil, had good resistance values, put a spark tester on the coil and had what appeared to be good spark. Checked it at #3, had what appeared to be good spark at #3 plug. So i turned it over and all it did was crank, no sputter or resistance to spinning. Packed it in for the night.

Today i came out. Pumped the throttle a few times. Got the normal issues of idling low, stumble, shut down, little smoke out of the carb. Turne it over again and it idled low but enough for it to catch and idle up to 1500 via the fast idle screw. Then it ran fine. So i lowered the timing to 13 base, raised the idle to about 825 via the idle screw and shut it down. Tried to fire it immediately and it ran. Let it sit for 10 mins and it had turn it over 2 separate times to get to idle.

 

Maybe that XRI module is sending an erratic signal to the coil. Do you have any way to put a scanner on the primary ignition circuit? Or at least look at it with an analog volt meter while cranking the engine to see if the pulses are uniform?

 

Check your oil, and see if it smells like gasoline.
I think I know whats wrong

 

no smell of gas in the oil. Or taste for that matter. I thought it was a flooding condition as well bc the plugs would get wet and sometimes look carbon fouled.

 

Are the bearings for the distributor shaft worn so badly that you can wiggle it back and forth? That will adversely affect the signal that the XRI module sends to the ignition coil.