My van ('84 e150, 351w and c6 trans) started running really rough after sitting for 3 weeks. I figure the secondary float seemed to have stuck, flooding it with fuel (tapping the secondary float bowl cleared it up fairly quick). I am getting it running better again but it is backfiring now under cruising and light-medium throttle. I will be putting new spark plugs in this afternoon hopefully but I'm wanting to make sure a few other things are set correctly. I checked some ofthe plugs after running around the block a few times and idling for a bit, cylinder 8 plug was the richest and they got leaner towards cyl 5 plug. plugs 5 and 6 had white straps, 7 and 8 had black straps. plug 7 had wet threads. Correct me if i am wrong but the rear seems too rich and the front too lean? i am under the impression the straps should be tan or brown, not white or black, please correct me if i am wrong.

2 things i want to verify.

1. idle screw settings. the idle screw anti-tamper plugs have been drilled out and i don't know where the screws are set, nor do i know where they are supposed to be from the factory. Has anyone here removed the anti-tamper plugs and verified where the idle screws are set from factory?

2. float height. I tried to adjust the float height based on a holley video on youtube. It involves making adjustments while the engine is running and checking to see if fuel is coming out of the float level plugs. The whole engine shakes enough when idling that fuel sloshes out even though the float is pretty near bottomed out. I am going to check fuel level after work today but assuming that is not too high, i need to figure out: a) if the fuel level is still high even when the float is adjusted to almost bottoming out, and b) if the needle valve is functioning properly.

Has anyone found a clever way to check fuel level without the engine shaking the fuel out of the level plugs? or any other pointers?

 

I've seen clear circular "windows" on some holleys but it was years ago and for 650 and 750s
can't say if they have then for yours

 

yes, some newer holleys come with sight windows like you describe, rather than plugs I have. In my mind that wouldn't help me much, I would see the fuel sloshing around rather than see it sloshing out the plug hole. I could be wrong on that though.

 

It's important to check fuel pump output for both volume and pressure before carburetor setup and tuning. If in doubt replace needle and seat as a pair. If the fuel delivery is not within spec it will be impossible to get proper fuel height in the bowl. Once that's squared away a mechanic's vacuum gauge is useful for setting idle mixture. Lean it out to maximum indicated vacuum reading at factory idle RPM.

The clear sight windows are slick but some have reported they can shear off and present a fire hazard.

 

i have read that the rear 2 idle screws are 1 turn out from factory. Can anyone confirm that and/or confirm what the fronts are supposed to be?

Also i can see from the main "1968-2013 Full Size Vans" forum page and my email that Tedster9 has posted in this thread but his post doesn't show up for me when i open the thread. Is it just me or can anyone else not see his post?

 

Keep in mind those are just bench settings or "ballpark" adjustments to ensure the engine will start initially and idle so the carburetor can be final tuned. Every engine is going to be a bit different depending on compression and ignition timing, valve overlap, outside air temperature etc.

The idle mixture screws should be leaned out as far as practicable consistent with a smooth idle. A vacuum gauge works good for this, but setting by ear is acceptable when ya get the hang of it.

 

thanks Tedster, i see your posts now. I am planning to check fuel pressure tonight. I'm not sure how a person checks fuel flow though. There certainly is no lack of fuel flow though.

As for benchmarks, i do realise that. My intent is to see how far off of factory the carb is set to now, hopefully it will give me some indication of what else is going on.

anyone have input on the backfiring and the plug colors?

 

Post pics of the plugs if you can, close up and high res. There are some good webpages on plug reading, each part of the plug indicates different things. Porcelain color is just a part of it, and not really all that useful anymore because of oxygenated fuels. Ground strap color indicates heat range and also the amount of ignition advance. Wide open throttle or load/power mixture is read by the color of the "fire ring" deep inside the plug, right where it transitions to the metal shell.

The base ring and first couple threads color and deposits indicate whether steady cruise jetting is lean or rich. But, that can really only be read accurately after a bit of a steady speed highway run, killing the engine coasting to a stop, then reading the plug. Idling or driving around the block or whatever will color the plug up and a false indication. Wideband O2 sensors have become popular in recent years since the price has come down, they make carb tuning, power circuit adjustment and jetting very accurate.

 

I just tested fuel pressure, i removed the carb and put a pressure gauge in fuel line and cranked the engine. The pump developed 10psi of fuel pressure. Holley states a maximum of 7 if i recall correctly.

 

Right, you mentioned earlier that the carb float was bottomed out, yet still having problems with flooding or excess fuel, so I wondered about that. It's important that both fuel pressure and volume is just right at all times under all conditions or carb will flood or be starved for fuel at higher speeds etc.

Just keep hammering on each of the individual specs and adjustments outlined in the manual one at a time and things will start to drop in place tuning wise. If there's a single carb adjustment that's most important though, fuel height is probably it.

 

Thanks Tedster9. I picked up a new fuel pump and put it on, fuel pressure went down to 7.5 psi. I replaced the spark plugs and it runs quite well now. I still need to check float level though. While ih had the carb off i popped the float bowls off to physically look at were the floats were set. They were set to close just before the flat edge of the float is level. I think the level could be raised a hair but will verify that.

i checked the idle screws, back ones are set to 1 turn out, front ones are set to 2-1/4 turns out. They may get turned out a hair more id the fuel level doesn't need to be raised.

i think the van is on its way to running great, thanks guys for your help.

 

Good deal. Helps if the engine is at normal operating temperature for final check, the fuel volume probably expands some. Level ground.

Remember the idle mixture screws are turned in for tuning from those initial bench settings, the idle afr mixture will be absolutely pig rich otherwise. Excessively rich mixtures tends to load up the plugs. Each idle pair should end up at the same number of turns. The idea is to lean out the idle mixture as far as possible consistent with a smooth idle, this helps with off idle transition. The engine spends a lot of time in this zone so it's important to get it right. A vacuum gauge is instructive on what the engine likes, after that you can ear-ball it real close. I found when using an O2 sensor for tuning that just a small 1/16 turn of the mixture screws say, alters the idle AFR by a full point, if the engine is tuned pretty good it's very responsive.

 

I am still working through this issue. i drove the van this past weekend on a camping trip. it ran okay but needed tweaking still. The problem was that if i slooowly rolled on the throttle, and held it just above idle it would want to stumble and almost die. If i stabbed the throttle it was much better. Also at large throttle openings it wouldn't make much power, and would accelerate faster if I let off the throttle some. This was all pointing to a lean condition to me so i decided to check the float/fuel level since i never actually verified after installing the new pump.

The new fuel pump regulates much better and I can actually set the float levels now. When I checked i found I had them set so low that when I removed the fuel level plugs no fuel would come out. So (with engine running) i adjusted them up until fuel showed up at the sight plugs.

I took it for a test drive after this and the same issues persist (off-idle and large throttle) just not as bad. I would just use the idle screws to make it happy in the off-idle area, but that won't help the large throttle issue will it? (I am trying to learn about carbs still, have had fuel injected vehicles until this one). I am thinking i can adjust the float levels up just a bit more (1/4 turn maybe) and see how that affects things, and go from there. I can double check my work at setting the float heights too, then if the large throttle issue keeps up there is probably another issue.

thoughts?

 

I raised the float levels 1/4 turn and took it for another drive. That seems to have cleared up the off-idle issue and it seems much better at large throttle openings as well. I still need to tune the idle mixture screws with vacuum but it runs real well as is. Thanks to all who helped!