This has just started happening lately. The car idles smooth and runs smooth for the most part. The only problem is at WOT off idle, the car backfires. Well...maybe not a backfire but more like a POP out of the carburator. It only does it off idle, when I WOT it from a roll it's fine. Any ideas as to what could cause this?
Setup- Holley 600 e-choke w/6.5 power valve; Vaccum adv distributor set at 10* base; stock exhaust except for the muffler and gutted cat

BTW...I un-screwed the sight plug on the secondary fuel bowl and quite alot of fuel came out- could this be the problem? Also the car has been very difficult to start in the morning(just trying to let you guys know all of the symptoms).

 

I'd say its either your timing is too high, or you are leaning out when you stomp on it. Try backing down the timing a few degrees and see if anything changes. If not, then try richening up the idle mixture screws to see if it gets any better. This isn't the proper way to do it, but it will help to diagnose it. If it is leaning out, you'll want to richen up the pump shot a bit.

 

Don't bother doing anything else until you set the floats correctly. Do that then report back what if any changes are made from that.

 

When you take out the sight plugs, fuel should just barely dribble out of the hole.

Make sure you do this with the car on a level surface.

 

How do you know when the floats are set correctly? I think the floats are not set right because sometimes when I come to a steady stop, the car will start dying out, then when I am fully stopped, it slowly builds back up to a solid idle speed.

 

Look at Air Adam's post just above your last post. Do it while the engine is at ilde. You loosen the flathead set screw on top of the bowl and then with a wrench turn the nut underneath the set screw to adjust the float up and down. You'll want to loosen the set screw a little at a time, turn the nut, loosen set screw a little more...etc. Make sure that after you adjust the nut some that you let the engine idle for a bit to verify the new fuel level. I just got started with Holley's not too long ago so I can tell you that the first time can be a bit frustrating until you get the hang of it. Make sure you have a few rags around for picking up spilled fuel. Once you have the fuel level just at the bottom of the sight plug threads just use the wrench to hold the nut while you tighten up that set screw again. You'll probably want to buy a book on Holley carbs at some point or there might be some helpful info online somewhere too. Good luck.

 

So...from the symptoms I have described, does it sound like I need to raise or lower the float levels?

 

I had the same problem with the back floats on a trip i had with my holley. the float needle stuck open a little bit and it completely flooded the car out. and it would die. sounds like your problem is a little less severe, but adjust the float level to the correct point and things should work a bit better for you. Also a nice thing to use now are the clear sight hole plugs for the holley carb. makes it alot less messy and fuel does not go all over.

 

So the fuel should just barely trickle out while the car is running?

 

Yeah with the car level that should be fine, that or just slightly lower and you should be good.

To comment on the clear sight plugs, they will save some fuel spilling, but when I was starting out I had more fuel lost from the set screw up top than the sight hole. I have also heard some bad stories of those plugs melting causing fuel leaks and even fires. Unlikely, but I prefer the old fashioned way.

 

Update: I tried to set the float levels with little success. The primary fuel bowl the fuel was up to about halfway in the sight hole. When I unscrewed the sight plug for the secondaries, fuel came gushing out- the level was above the plugs. Which way should I turn the screw to bring these levels down?

 

Yeah with the engine off loosen the set screw then turn the nut underneath counter clockwise a few turns. It is much easier to have it too low and then work your way up, so give that a try.

 

Agreed... if it comes gushing out when you loosen off a site plug, put the plug back in and lower the float a bunch, and try again... if it doesnt come gushing out, then the float level is below the plug - a good thing. Now leave the plug out, and slowly adjust the float level untill you see the fuel come up to the level of the site plug, so it just barely trickles out. Once you have it there, tighten up the float adjustment screw (hold the nut with the wrench though, so it does not turn), look again to make sure the level did not move, and then put the plug back in. Done. Now do the same for the secondary side.

 

I took both fuel bowls off and cleaned the whole float assembly and checked for/removed debris. Installed the floats back in teh fuel bowl, and adjusted the float levels in both the primary and secondary fuel bowls.
So far, the car doesn't stumble anymore when I come to a stop.
I've got the primary fuel bowl perfect, but the secondary fuel bowl does not seem to respond to any adjustments of the float level. Is the level in the secondaries always supposed to be high?

 

no. it shold be identicle to the lvl in the primary fuel bowl. you may have to replace the needles in the float bowls. or the float itself. If you have a needle that is not seating properly, or gets stuck open, your fuel bowl will flood with fuel and you will not get the performance you are looking for out of it.

 

Just a side note on your timing question.

I have spent the last few weekend fine tuning my timing and have came up with these rules of thumb.

My motor is happy @ 15 deg base.

The more you advance the timing, the easier the car is to crank. However, go to far and the car will stumble or die under WOT.

The more you redtard timing the harder it will be to crank. And it will give the same result you described before....a backfire or "puff" back through the carb when let off the gas after you rev it up.

That's just my 2 cents

 

Is this "pop" something that could damage my car/carburator?

 

Just a side note on your timing question.

I have spent the last few weekend fine tuning my timing and have came up with these rules of thumb.

My motor is happy @ 15 deg base.

The more you advance the timing, the easier the car is to crank. However, go to far and the car will stumble or die under WOT.

The more you redtard timing the harder it will be to crank. And it will give the same result you described before....a backfire or "puff" back through the carb when let off the gas after you rev it up.

That's just my 2 cents



The above is backward. More timing is harder to start. Less timing will make the car die off idle. Retard is to go backward advance is to go forward. Turn the distributer counter clockwise to advance the timing.

From reading the post the stumble coming to a stop is the fuel splaching out of the secondaries and fluding the engine. Fixing the rear float will take care of this. If it does not respond to adjustments change the needel and seat.

Based on what I have read in the posts;but not seeing the car I would guess that the pop off idle going to WOT, this is due to too little initial timing not too much.

When you ease on it and it takes the throttle it is because your timing is advancing to compensate.

 

Unlike the primaries, there isn't a constant draw of fuel on the secondaries. So, if it is set high, adjusting down won't appear to make the level go down. You have to run some of it out by opening the secondaries - you can do this by just holding the secondary shaft open, although it won't open much. That's why it was said it's easier to have them too low at first and adjust them up.

 

After I tried to adjust the secondary fuel bowl, I drove the car around a little and gave it alot of WOT to try to clear the secondaries out.