I have been working on my motor it seems for 3 months now. Had everything going last month and was having trouble getting it tuned right after I thought I had a successful break-in completed. Well, I had pulled the carb to rebuild it as the solution to my problems. While I had the engine down I decided to also check the lift of the valves, etc to make sure everything else was ok. That was when I found my cam had a wiped #8 exh lobe. So, I tore down everything to install a new cam. Mind you the carb was still sitting there in a re-built but untuned state but all things on the carb were put back to their original state.

Now I'm back to doing break-in #2 with a new cam and a re-built but untuned carb. I started this afternoon to do the break-in and first time out had a flame thrower. In addition I could WOT the thing but only get to 2200 rpm (that's all before I noticed the flame thrower effects). So, only about 3 minutes of break-in and then I had to turn it off or else burn my car up! I did two things: advanced the timing about 6 degress and also checked the carb float level. I noticed that the air-horn was a little saturated with gas was why I looked at the float. A flame thrower can come from either re-tarded timing or a really rich mixture is why I did both. I checked the float level and it seemed to be too high. I had gas in the bowl up to about 3/4 of the way in the bowl. So I lowered the float to about 0.5" measured from the back of the float to the top of the bowl.

Fire it up again and now the flame thrower is gone but when I get it to 2200rpm to keep it there for the remaining 20 minutes of break-in I get a miss, a little blow back out the carb and occassionally a little flame. I can recover it by letting off the throttle and then bring it back and then about 2 seconds of 2200 rpm it does it again. So, it's not a one off problem it keeps repeating. I stopped one more time, retarded the timing about half way in between, I'm guessing at 12* BTDC, and repeat with the same results. The vac advance is disconnected.

Where to look next for this situation?

 

Could be a vacuum leak, perhaps carb to intake gasket?

 

Just curious...and I'm almost afraid to ask...but what brand of cam had the wiped lobe?

Dep

 

Carb gasket is brand new from the kit and snug and tight. It matched the shape of the old gasket perfectly as well.

 

I almost feel sheepish in saying the letters X & E followed by 268H Our beloved Comp Cams.

 

ACK!

I had a feeling

Dep

 

Checked the plugs? The #8 might be fouled if the exhaust valve was whacked for a while. Just a thought about why it might be missing.

 

They are all fouled and strong gas smell. I also pulled the carb and it was a STRONG gas smell in it and along the runners in the intake. Looks like to me I have a serious issue with the carb. I'm leaning to replacing it with a Holley 4160 and move on. I'll put the Q-jet back on the original motor I'm storing away since they are both original.

 

Uh oh. I'm no expert, but I like to try one thing at a time rather than multiple fixes. My personal next steps would be to (1) clean the plugs and do a quick gap check on them while they're out, (2) readvance the timing to the previous setting, and (3) lean the mixture further.

Fouled plugs can, of course, be from running too rich. 12* seems to be a pretty hefty timing adjustment to me, so I would turn to the carb.

Hope this gives you some ideas. Let me know how it goes.

-Ben

 

I checked over the carb multiple times. Remember I did a rebuild on it as well. One of the reasons I did the rebuild to begin with was that the air horn gasket always seemed damp from fuel. During the rebuild I replaced the float and needle and it still did it. I adjusted the float level down to 0.5" and it's still saturating the air horn gasket. I think there's a problem where the needle isn't seating or the pressure is overcoming the force of the float trying to seat the needle and then floading the bowl, etc. The fuel pump is bone stock and brand new so I don't think that's it.

It's for those reasons that I'm going down the carb route. I did clean and check the plug gap. All ok. 12* may be a little too far advanced but it shouldn't make the car do all this weirdness at 2200 rpm and blowing gas out the air horn like it's someone is poring it downt the throat. I've seen carb back fires before and generally speaking you see the mist but you don't get wet. I literally have drops of gas flying back. Gasoline is not one my preferred colognes.

 

Maybe I missed something, but if you are getting blow-back thru the carb, you may be pressurizing the intake via a open intake valve (stuck guide or weak valve spring). Put a vacuum gauge on the intake and rev to 2-2500 rpm and see if there is any fluctuation . A jittery pointer on the vacuum gauge indicates a valve issue....

 

You put a new motor in your vette and put the Q-jet from the old motor on it? Geez, get a real carb...like a Holley!!

Brett

 

 

It's your engine timing nothing else.

 

are you sure your coil is good? It's a cheap part, but has thrown me a time or two. Also, how tight is the distributor? Now I like Q-Jets. It's debatable, but Holleys are good for straight line cars, but my opinion is that a Q-jet will not dump raw fuel like a holley on the tilt.

 

Would you say the same thing if the Q-jet was a Lars rebuild?

 

 

Well I owe you all an update. Started out frustrating but ended well. Here's the story:

* Got the new Holley 4160 installed. That was a lot more work than I expected because of the need to setup the linkages with an Edelbrock linkage kit. Got everything on and ok, took about 2 hours of adjustments.

* Checked the timing again. Set the timing to 12 BTDC just as before with the XE268H cam before it wiped.

* Start her up and it's running like poop. Can't even get it to 2000 rpm without serious blowback through the carb.

* Pull out a different set of plug wires and put those on. No difference, still poop.

* Pull the plugs themselves since they were fouled and cleaned and put in new Autolite plugs. No difference, still poop.

So at this point I'm pulling my hair out, beating on the car and then I thought to see how the main BAT going into the distributor looked. With just the key engaged I was getting a decent 12V at the clip going into the dist. So, here's what I did:

* I was able to jam the negative lead to my meter into the throttle bracket and wedge the positive lead into the underside of the BAT clip to the dis and then set the meter so I could see it through the windshield.

* Try firing it up and it's running like poop for about 2 seconds, the meter is twitching around from 8V to 12V and all over the place, and then all of a sudden smooth as silk running at 2500 rpm. The meter is showing a solid 14V and it's looking good.

* Running for about 2 minutes and I'm smelling the headers getting too hot again (you know you're getting too good when you can tell a problem by it's smell! ). Shut it off quickly and look underneath and the headers are a dull red at the collector. I let that cool off and advance the dist to 16 BTDC.

* Hop in and start it up again. Now it's running right out of the gate and up at 2200 rpm almost instantly. Let that run for 5 minutes. Shut it down quickly and look at the headers. The glow is gone and the headers are not overheating dramatically.

* Hop back in and it starts up just fine again and I run it to 2200 rpm and vary it every few minutes from 2000-2500 rpm for the next 15 minutes. Everything is solid. Water temp good, oil pressure good, the meter showing a solid 14V on the BAT terminal to the dist.

* At the end I run it up to 2500 rpm, 3000 rpm each for 1 minute and then back down in 500 rpm increments to 1500 rpm each for 1 minute. THis is procedure in the Lunati install instructions.

Shut her down and everything looks good. What a freakin' mess though getting all those issues untangled. Looks like a compounded problem of too rich carb, electrical problems, fouled plugs, and 4* BTDC more advance. But it's worth it now that I have the motor running. What a week!

 

Uhhhh, yeah.

 

Congrats!! More kudos for the forum.

Brett