Hard Starting Hot & Intermittent missing / hesitation
 

350 SBC rebuilt to stock with a "mild cam" and has about 300~400 miles on it. QJet 4BB (matching number for 72 from uscarburetors). It has a Top Street Performance HEI (has a stock look to it, with external coil).

When starting up in the morning or when has sit a rather long time, turn key and boom starts right up.

Drive around a good 5~10 miles to get good and hot/warmed up. Say I stop at the gas station, fill up, go into store to get a drink. I have to put the gas pedal to the floor to get it to startup and after which a bit of rough idle then clears up.

Timing was rechecked today, well because it ended up not being locked down! Also the fuel pump was replaced today (only part that was reused from before rebuild). Set to 12 degrees and has just shy of 16 for vacuum.

Re: Hard Starting Hot
 

Could be fuel percolating causing a little flooding.
Did you touch the gas pedal?
Some motors don’t like you to even think about touching the pedal.
Or the new pump is putting out too much pressure.
Look in the carb when you shut it down hot. Look for any raw fuel.

Re: Hard Starting Hot
 

when I don't touch the pedal I am sure it will not start, crank and crank until I so hit the pedal.

I had to google percolating. My brother actually suggested a wooden clothespin. I thought he was pulling my leg. Non ethanol gas and most of the other things on Mike's Carburetor Parts percolating, I am not sure about being able to do.

I am not sure its the pump, since it did this with the old pump too. I'll check for raw fuel to get that off (or on) the list.

Thanks.

Re: Hard Starting Hot
 

My truck had that problem. I installed an Edelbrock Heat Insulator Gasket and now it starts right up after sitting a little while when hot.

Re: Hard Starting Hot
 

Clothespin only works on Studes! And some Fords!
Quadrajets normally don’t have fuel percolation problems.
If you have a hot slot intake and the wrong base gasket they might.
What choke you got?
Post a pic of your carb.
Could see something amiss.

Info here on the ‘infamous’ hot slot intake.


https://www.corvetteforum.com/forums...d-problem.html

Re: Hard Starting Hot
 

But I have a QJet, are those generic to any carburetor?

Getting photos.

Re: Hard Starting Hot
 

If you’re talking heat spacer every carb is different.
Quadrajet doesn’t need one. Normally. Hot slot intake does.
Eddy carbs do. Usually made from aluminum, phenolic resin (think plastic) or wood.
Holley uses a shield that deflects heat from the bowls.
The position of the float bowl determines the device needed.
Quadrajet bowl in a low heat zone above the plenum.
Eddy has two bowls. Each out on the high heat sides.
Holley bowls out front and back.

Another consideration on your starting problem is your choke setting. Too rich can act like yours.

Re: Hard Starting Hot
 

Choke, interesting. I think my brother talked about some choke problems or something. I poke him about that. He'll be up in about a hour.

I have photos but the form is giving me some error (security token was missing.). I'll keep at it.

Edit: uploaded forgot to resize them - doh.

Dead cold from overnight, gas pumped once. I am thinking I should have one after running it 10 miles or so and then stopped ... but it is just now 6am LOL

Re: Hard Starting Hot
 

Make your pics smaller.

Re: Hard Starting Hot
 

For the record, I do not have that “hot slot” aka smiley face intake. I have the one exactly for my 72 SBC - got a NOS from North West (350ci V8 Intake Manifold 6268751). My Carb is matching for 72 SBC C10 Truck, exactly (7042208 1972 CHEVY GMC TRUCK).

Edit: While the sticker on the intake is not 7042208, it's a crossable number back to mine (this intake part number is for a Chevy/GMC boat that was made past '72). I had to get a new one because my stock one had a crack in it :(

Re: Hard Starting Hot
 

Is this choke plate is opened up and sitting vertical when you try to start it again after it is warmed up?

Re: Hard Starting Hot
 

as soon as it's light, I'll give a good 10 mile drive and get a quick photo of the carb. Currently, I do not know. I am learning (and my brother says Qjets are not like carbs on a 30 Ford LOL - so he is learning too).

Re: Hard Starting Hot
 

I hate to mix things in but kind of on topic I think. With my mild RV Cam we are set to straight up stock 12 degrees. What is recommended for a RV Cam (generally), we are thinking to bumping it up to 15 and perhaps that will bring up vacuum closer to 17 or a bit more?

Re: Hard Starting Hot
 

I see something I hope your brother didn’t do on your carb.
We can blame him anyway! LOL!
That nut you’ve got holding the air cleaner rod in place can hang up on the secondary rods.

Re: Hard Starting Hot
 

How can that nut hang anything but brother said - easy take it off LOL

Re: Hard Starting Hot
 

Poke the secondary door wide open and watch the rod hanger. It might hit that nut.
Rod hanger goes straight up towards it.

Re: Hard Starting Hot
 

It did tap the leavers / hangers. Just a bit. Removed.

That would’ve caused my hot starting problem, right? Though I imagine it would cause problems with the hanger getting worn being banged up against that nut. Best I could tell it just slightly wouldn’t allow the secondaries to open 100%, hardly noticeable.

Re: Hard Starting Hot
 

Look down the carb when it is running. Make sure you don't have fuel dribbling out of the primary boosters. This can cause a rich condition and when it's hot and you shut it off it essentially acts like an engine that has been flooded, hence having to open the butterflies open with your foot tp start.

This can happen because of various circumstances, not all that are obvious. Float level and non functioning needle and seat are an example but can also happen if the primary butterflies are open too much with the idle screw (improper tuning) which leads to too much carb signal.

I've worked on a handful of engines that have had this issue. Let me know what you find! If it is this I can tell you things to check and ways to fix it

Re: Hard Starting Hot
 

Some photos hot

Re: Hard Starting Hot
 

When I wrenched for far too many years we would get cars/trucks in with QJ carbs that would have that issue. What I found a lot was the lead plugs on the bottom of the carb for the main jet passages leaked gas and then flooded the
engine. Which caused a hard start to the point you have to hold your foot to the floor to clean it out then it would start. I fixed them by takin the carb off cleaning the spots and then JB Weld over the plugs. Not sure of this is your issue but it sounded fimilar so thought I would throw that out there.

Re: Hard Starting Hot
 

I hope that’s not it, I paid some nice coin for this carb! But if / when I have to take it off I will double check that LNP. Thank you for your post!

Re: Hard Starting Hot
 

Okay a worse problem that we had hoped we had solved when the distributor nut was loose and new fuel pump was replaced (yesterday morning). Not sure if this is related to "Hot starting".

Intermittent severe missing or hesitation which dmjlambert reported and fixed when he had his carb sent off to National Carburetor. His posting seemed very similar to my issue I am fighting now. Though he didn't report any "Hot Starting" issues.

This morning we also went from 12 to 16 timing, for the record.

After we finish the work above we did nice early evening/dusk test drive (6:30pm or so). Some good highway speeds, 50~70 with a little bit of 80mph. Then city driving (lots of stops and goes). We stopped at the Kilgore Chevy/GM house since they had a C10 in the showroom (but it seemed a bit frankensteined to me). We left the truck idling for at least 15 minutes while peaking into the showroom. Then the last bit of our drive back to my brother's house was farm roads (no more than 50mph but lots of 30s). So this trip was roughly 50 miles. No problems. Personally I think it was because my brother was in the truck.

This morning as I said a bit ago, we went with a 16 degree timing. I also needed to fix my left turn canceling (silly spring needed adjustment) but that let me get my steering wheel sorted as it was a few teeth off to the right and it was really getting on my nerves LOL

Soooo, I decided okay let me drive home to Austin, 11am I get no more than 8 miles after getting to 60 and I started getting missing or hesitation. This is actually what it was doing to me my first two tries going home yesterday but a lot worse (yesterday). But the common between yesterday and today is it was hot sun barreling down on my hood, where-as last nights perfect drive was no sun dusky cool.

When my brother gets back from a little trip he wants to put back on the Carter Qjet that the previous owner put on (parts store sold him a 78 Chevy Truck carb). He thought it had a flooding problem early on this rebuild and I bought that matching numbers 72 Chevy Carb from uscarburetors. I have yet to send the core back.

To anyone that took the time to read all that rambing - ideas?

Could this also be related to percolating / vapor lock / fuel boiling? The hard fuel lines to really close the the passenger's ram head. Then the hard line gets close to the block too when it comes up from the fuel pump.

Re: Hard Starting Hot
 

Could be fuel.
Did you check the timing first. It moved before. Coulda moved again.
They slowly move retarded (cw).

Re: Hard Starting Hot
 

I checked the timing again after this mornings attempt. It’s solid 16 degrees.

Re: Hard Starting Hot
 

btw, I did not miss your posting j_cst_10 - we are not seeing anything pour/dribble out of the primaries. Not sure if my photo from the top was of any use but that was a photo right after stopping the engine.

Re: Hard Starting Hot
 

Ok let's not worry about the timing. It is a mechanical setting that isn't going to change if the truck is hot. It might be able to mask the symptom but it isn't the solution to the problem. And a quick check of spark quality when the engine has hot soaked should reveal weakness in the ignition system.

Your initial post indicates a flooding situation. There are several common causes for that.

The choke being closed. Your pictures show the choke being completely open.

The float may be set on the edge of being too high. The fuel level in the bowl is okay when the fuel is cool, but after the engine has stopped there no longer is cool fuel entering the carburetor. The fuel that is in the bowl will heat up and expand until it flows over into the intake manifold. The cure would be to lower the float a small amount.

And the well plug(s) could be leaking. To determine if this is in fact happening you can check the fuel level in the bowl when the carburetor is cold and then again after it has set for 20 minutes when hot. I will say that if this is happening you would also experience the need to crank the starter a bunch to start a cold engine, as there would be no fuel in the bowl and the fuel pump would have to refill the bowl so the accelerator pump would work. It has been my experience that well plugs generally leak when the carb is cold and seal when hot. That being said I have run across carburetor bodies that have cracked and when cold they don't leak, but leak when hot. Hard to check for other than pull the carburetor off when hot and put a clean cloth underneath it and set back on the intake to hot soak. When it has set for 20 minutes check the cloth for signs of fuel.

I hope I have helped with solving your problem. All of this is my opinion so Good Luck!

Re: Hard Starting Hot
 

Thank you HO455 for you reply.

Okay, we turned off the engine and I hopped up on the engine real fast and looked down into the primaries. We are seeing fuel still flow in... I'd think that would be bad?

Also, when we were giving it WOT real fast the back larger butterflies are not opening, not even trying (no idea what is happen under them). This leads me to share a observation when driving it and where I would give it a good pedal for max power. I get nothing or at least I don't "hear a thing". About 20 years ago I had a big block 78 Suburban and you went for max power, not other did you feel it you heard it kick in (like a big vacuum sound). I justed assumed that was a big block thing but now reading / looking at a YouTube or to my C10 350 should too. My bad for ignoring that observation until now.

Seem I keep digging myself a hole here on this $400 QJet.

Re: Hard Starting Hot
 

Float level too high or crap in the needle/seat.

The secondary air door won’t move just on a free rev.
I noticed in your picture that the choke stove cover is close to the secondary lock out lever and tang. That might cause the no feel/sound of those big secondaries opening.

Re: Hard Starting Hot
 

Geezer's right the secondary butterfly will not open on a free rev. If you looked into the venturi after shutting off the engine and fuel is running out of the discharge nozzle then I would start with excessive float level, bad float, or too much fuel pressue. Even after shutting off the engine it takes a moment for the pressure to drop. If the fuel bowl level is to high it will leak fuel out the discharge nozzle until the level is more normal. These issues will cause hard starts on quick trips to the store but will go unnoticed overnight.

Re: Hard Starting Hot
 

I just checked the choke stove, it’s tight but no touching - complete free movement.

One thing my brother thought was happing before replacing the carter was pressure was building up and I needed a vented cap. But my 72 has that emissions canister by/under the battery - which we unhooked at the canister because it seemed it was clogged.

Re: Hard Starting Hot
 

How do you mean clogged? I know that this is taking away from the main thrust of the thread, but there is a filter on the bottom of that canister. This will not be something that causes fuel to drip into the primaries, whether it is clogged or not. You can find a complete downloadable service manual for your truck here:

http://67-72chevytrucks.com/vboard/showthread.php?t=558016&highlight=hatzie"]http://67-72chevytrucks.com/vboard/showthread.php?t=558016&highlight=hatzie

Just copy and paste that in a new tab. :chevy:

Re: Hard Starting Hot
 

hi Steeveedee - I hear what you are saying, thank you for then link.

He blew air from the line at the fuel tank vent and nothing went through until he disconnected it from the canister...... this "seemed" to pressurize the tank or that was my brother's thought process. But this was over a month ago with the Carter QJet.

I actually just tried to take it out but got stopped by needing to take the battery tray out, which has cooling lines mounts under it and a bolt blocked by the radiator. So it was a bigger job than I thought it would be. I was running out of sunlight and mosquitoes were eating me alive - so I couldn't think about trying a different removal method :(

I want to see what was causing the clog myself (I have the service, overhaul, and assembly original non-reprint manuals). But it surely is not causing a problem now as it is disconnected and there is a clear path from the EEC Tank connection to the engine bay for venting.

Edit: forgot about bad luck. when putting the negative back on, it seems to be stripped/won't tighten. Fun times!

Re: Hard Starting Hot
 

Had a good chat with US Carb and we are going to send it back. It was great they offered a voice call.

One thing I learned from my brother is the Carter 17058213 QJet did not have any problems starting cold or hot- the hot starting started with the US Carb 7042208. She always started fine, its main issue was idle was crap. It is also the one that dumped enough fuel into the engine when stopped that the oil had to be changed (which really kicked off getting the proper matching C10 72 7042208 from US Carb Ebay). Though the fuel dumping we feel was some kind of a EEC Vent line issue.

Re: Hard Starting Hot
 

another oddity after looking at my 72 Chevy Service Manager, section 8 pg 9 is the hard line. It looks like the line are supposed to hug the frame, which makes total sense once I look at the manaual. My lines have popped away from the frame right where the ram horns bolt up to the exhaust. One line was about 1/2 ~ 1 inch from the exhaust and the over right behind it.

I'd image that there is a bit of radiated heat getting to the line(s) from the exhaust and the lines are not getting any cooling effect from the frame. Again, I am just assuming the frame would act like a temperature stabilizer.

From the manual there should be some clips to keep the lines to the frame, guess I need to look for some but for now I used some tie wraps to two holes in the frame. The lines are not much further away but not completely tucked into the frame (but are now touching it pretty good).

Re: Hard Starting Hot
 

New update, the Carter after popping up off the top, first reaction "wow look at all that crap in there". Brother saids it looks like someone dumped cinnamon in the bowl.

Removing tank and having it lined (brother has a shop for that, will be less and faster than new tank) and adding a inline filter is now a high priority. I guess the QJet filter in the carb sucks....

Re: Hard Starting Hot
 

Test drive update:

Hot Starting: Corrected even with A/C left on (though it was a wee bit harder to start)
Intermittent missing / hesitation: Also appears solved
Testing WOT at idle: Back butterflies just a bit engage and open and suck in air. I would not say I hear or feel them kick in when driving. But going up a very nice long upwards grade I can go from 60 to 80.

I think our reasoning for replacing the Carter (other than I really wanted the proper numbered Rochester and not Carter) was due to trash and I am guessing my brother was mistaken about the EEC Canister too (that's my gut telling me that).

Re: Hard Starting Hot
 

Oh and I am buying a replacement for one of these from Ecklers Automotive for my driver's side visor :-D

That takes the guesswork out of pedal pushing LOL


Full Size Chevy Engine Starting Procedure Decal, 1972 40-164566-1

Re: Hard Starting Hot
 

You do know that whether it says carter, Rochester, Weber or Edelbrock on it the carb is exactly the same.
So when you break down in Resume Speed Texas the nearest parts place will know it’s just a quadrajet.

Re: Hard Starting Hot
 

They *both* have Quadrajet stamped on them. But the the one that came on the car came from AutoZone/O'Riley's (don't recall the store) was manufactured by Carter in 1978 (17058213) - previous owner did that - not me. He was rather proud of letting me know it had a new carb on it ;-)

The one that is called out for my 72 C10 350 that came from US Carb has Rochester stamped on it (7042208).


Please see Lars Grimard Tech Bulletin on these two Carbs.

Re: Hard Starting Hot
 

Oh, I think I miss read what you what you were saying, that they are the same. quadrajet is a quadrajet ... I thought you were asking if I was sure a Carter was really a quadrajet.