The Stovebolt Site Forums The Shop Area Engine Shop More Questions for the CarbKing!

Hey Jon, I have a couple more Monojet questions. Back when I first bought my truck the carb was trashed, so I bought a NAPA rebuild with manual choke. It actually worked pretty good and I'm thinking of putting it back on when I do my rebuild. The one complaint I had was the time it took to warm up enough to get decent drivability. The engine had to get up to about 170 or so before it would run good under a load. And it always stuttered a little just above an idle. My heat riser is not working due to missing parts and I'm wondering if fixing it would cure those problems?

Next question; the number on this carb is 7040012. According to the info on your web site this carb never came stock on a 250. It is for a 292. What is the difference, and does this explain why I did not gain any performance improvement when I converted to the Holley/Weber 5200?

Thanks in advance,
Boo

You have a Rochester carb? A working heat riser will make a big difference, much quicker warm up.

Boo - For a street engine to warm rapidly in a colder climate, the heat riser should function.

Your next question requires a tactful answer, so I am searching for wording. ..... Well, after trying several times to write a tactful answer concerning the Holley Weber, I am afraid I cannot come up with one, so please forgive me for not answering the comparison question. We don't sell them.

Jon.

HEY BOO!! the carb is just set up a lil larger on jets and discharge nozzles for the larger cid...your not going to automaticly pick up performance with a lil larger carb...you might have a fuel prob. on the plugs if there is to much gas. which would also not help with the lil stumble you have ..i would get the heat on it working for the better warm up though and keep an eye on the plugs for to much gas ...(loading up)blackish !! the plug should run a light tan color to be correct..you might even think about a lil carb spacer 1"..this will take a lil low end off but should help lean the carb out some...hope that this helps....regards.....gary

With the calibration for the 292, you're too lean, not too rich. Larger engines pull more air through the venturi, raising the venturi vacuum for any specific RPM. Generally, a carb for a larger engine will have a lower float level, and leaner jetting to prevent an over-rich condition. You could probably cure some of the cold-run problems by raising the float level slightly, and going to a little richer jet, but the heat riser needs to be fixed first! Spark plug condition and color is a good indicator. A tan to chocolate-brown color is about right, black is too rich, white is too lean.
Jerry

This is an interesting post,I'll stick in my two cents on carburation. While searching through many Holley model 1904 single barrels for a matched set of 3, I found one consistant thing.All the carbs identified for truck use had far larger power valve jets, like .020 larger for high load operation than the carbs used for cars.The main jets were the same, but the truck model carbs had bigger air bleeds.The larger air bleed jets will tend to lean the mixture during part throttle operation.That would mean the truck carb was designed to operate mostly at full throttle. The air bleed change is necessary cause the truck engine spins more rpm,more venturi vacuum,the bleed change prevents over richening at part throttle high rpm conditions.
The above is true on Rochester carbs, except the Roch usually has a slightly larger main jet on truck models. So this kinda backs up what Hot Rod Lincoln says.
The Holley Weber is an extremely ugly but well designed unit.At wide open throttle,the HW flows around 20-30 percent more air than the typical one barrel carb.The HW has a small primary barrel,too small for decent power on a large inline six,some guys report reduced part throttle power but more when the secondary is opened on full throttle.I think Holley Webers are not the cure all and are somewhat over rated.I do know from personal experience,2 or 3 Holley Webers on a inline can make for good power and sharp throttle response.
It obivious Carbking doesn't like Holleys

Truckedup - your last statement is not totally true. The Holley 847 series (single barrel); 852 series and 885 series (two barrel); 2140 series and 4000 series (4 barrel) carburetors were very good to excellent.

Jon.

Just poking at ya Like you say,a carb designed for the application is always best,otherwise it make take some tuning that may or may not work out well.

Tony

Three H/W on a 302!!!!

Homemade(?) manifold.....lumpy pistons?

After all this you'll complain that GMC's are nothing special.

No Holley Webers on the 302,I tried em once on the 261, they carbureted nice , but they were uglier than dead cats mounted on the intake.And a single 4 bbl worked just as well,less complicated and for sure less fugly
A big port GMC 4bbl intake just fell into my lap, have the 390 Holley 4bbl and linkage off the 261,don't wanna be fussing with tuning carbs on a fresh engine, build the intake later on.

Truckedup - are the three dead cats what happened to the "tiger(s) in your tank"?

I like the analogy to the H/W 5200.

Jon.

TREE DEAD CATS !!!!!!!!!!!LOL......YUP..THIS TURNED OUT TO BE A VERY INTERESTING POST FUR SHURE!!!......9I GOT MY EARS ON FUR THIS ONE !!! ......GARY

This post was addressed to a specific person.
Only one of you is CarbKing! The rest are
somewhat irritating, as well us somewhat misinformed.
Boo :p
Now I don't know about dead cats, but a live cat peeing in the manifold would probably make my engine idle as smoothly as any of the Holley / Webers I've tried.

BOO..no pun intended..( ....( can't we all just get along)it is good for a lil humor ..it is not meant to harm anyone ...i just learned alot from reading this post...it really turned out to be a very educational post, for i bet alot of us reading it, that really care ....regards..gary

GaryS -- that's a fake fit in my last post; just popping for the sake of popping off! Now the thing about the cat peeing in the manifold, that is my honest opinion.

Now here's a dead cat with a different smell:
The Monojet came in 3 sizes. The smallest has a 1-7/16" throttle bore and 1 7/32" venturi. It was used on 4 cylinder engines. The second largest and most common has a 1-11/16" throttle bore and a 1-5/16" venturi. This is the 250 carb. The largest has a 1-11/16 throttle bore and 1-1/2" venturi. It was used on the 292 in heavy duty applications. The throttle bores are the same on the 250 and 292 carbs but the 292 has a larger venturi. The small carb flows 160cfm - 250 carb flows 210cfm and 292 carb flows 250cfm. The fact that I already had a carb that flows at 250 cfm explains why I didnt' notice any improvement in performance when I installed the weber that flows at only 20 cfm more.

Boo

Hey Boo, in this place there's no such thing as a post to a specific person,we're all buddies here,like family,don't ya think?
Mis informed? oh come on,you put a Pinto carb on your Chevy

Yep! A pinto carburetor with an air cleaner made out of hub caps. Actually I think I may jet it up, enlarge the idle circuit, modify my manifold so it fits with out the strangulation adapter, and keep using it. However, when stated so bluntly, "You put a pinto carburetor on a chevy," it is rather a shock to the system!
Boo

Well guys, without regard to dead cats, not matter how smelly, I'm committed. I just bought $54.00 worth of parts I'm hoping will make the Holley/Weber work good. It's not bad now except for the rough idle. I read an article that tells how to cure that.

I'm also gonna work the manifold over so it will receive the weber without any adapter. I think that strangulation adapter is a real problem.

My engine will have a lot more scoot in the giddy-up when I'm done, so I'm going to try 170 and 190 main jets with 190 and 200 air corrector jets. Along with the manifold mods this should make a BIG difference.

Boo