Hard Starting Hot

[RustyPile]

Originally Posted by Carl Spangler

Was the engine completely warmed up for the 'stumbly take off' test?

Here's another easy test:
Crack the thottle about half open and see how much side-play is in the throttle shaft. i.e. clearance between the shaft and casting. A proper rebuild would include drilling out the housing and pressing in a brass insert. If rebuilt properly there should be an 'interference fit' between the shaft and brass bushings. If not done properly this could be a source of air leak and whistle.

With all the QC issues, I don't doubt that's a possibility one bit... A stiff return spring is the number one cause of throttle shaft wear..

[Rich72C10]

Originally Posted by Carl Spangler

Was the engine completely warmed up for the 'stumbly take off' test?

Here's another easy test:
Crack the thottle about half open and see how much side-play is in the throttle shaft. i.e. clearance between the shaft and casting. A proper rebuild would include drilling out the housing and pressing in a brass insert. If rebuilt properly there should be an 'interference fit' between the shaft and brass bushings. If not done properly this could be a source of air leak and whistle.

I don't know if they did the brass inserts or not.

I put the throttle half way and I can move the throttle side to side. Not sure if that is what you mean but I can move it laterally. When I pull the throttle out from the body, I can get almost a penny wedged in.

Yes, she was full warmed up real good.

What do you mean by QC ... to me that means quality control.

[Carl Spangler]

Originally Posted by Rich72C10

I don't know if they did the brass inserts or not.

I put the throttle half way and I can move the throttle side to side. Not sure if that is what you mean but I can move it laterally. When I pull the throttle out from the body, I can get almost a penny wedged in.

Yes, she was full warmed up real good.

What do you mean by QC ... to me that means quality control.

The throttle shaft should have absolutely zero 'play' side-side (tangent to the shaft) and almost zero play along the axis of the shaft. Take the throttle spring off so you can freely move the throttle.

Quadrajet parts sells a special stepped drill and the bushings: https://quadrajetparts.com/carbureto...uad-p-886.html
Available in 3/8" and 5/16" This is the tool I used to fix my worn out carb.

[Rich72C10]

Yes, I have seen that kit (that is where I got my standard rebuild kit for my original carb). I suppose I had it in my mind that QuadraJet Power would do this - I see this in their YouTube. Not sure how to "spy" for the bushings.

https://www.youtube.com/watch?v=Nz46xrO_I-o

I have the carb off the truck again, so no spring is attached but I did pour gas all over me (which pissed off everyone in the house and I was made to take a bath and change LOL).

[Rich72C10]

here is a vid of it moving side to side.

https://drive.google.com/file/d/1EBH...ew?usp=sharing

[Carl Spangler]

hmmmmmmm................ that's more longitudinal play than I'm used to seeing. I'm not sure if that's a show-stopper. ???

Since this carb was rebuilt by the folks that make the shaft bushings/tool it would seem unlikely that the bushings weren't properly installed. ??? Again, if the shaft bushings are new there should be virtually zero clearance between the shaft and bushing.

[Rich72C10]

while holding the throttle good and closed (so it isn't moving longitudinally), it does wiggle.

[Carl Spangler]

Originally Posted by Rich72C10

while holding the throttle good and closed (so it isn't moving longitudinally), it does wiggle.

Well, that would be a big thumbs down then. Don't waste money buying any lottery tickets for a while.

[Rich72C10]

To be honest, it doesn't wiggle much at all but it does move.

Anyways, filled out the form to return the carb and its already on its way from the Kyle Post Office.

Mark from QuadraJet Power did tell me this morning the bushing were installed - that was part of the rebuild process on my carb. Not sure what that means, if after installing these bushing there isn't suppose to be any movement. Though most definitely there wasn't anything done to stop any lateral movement.

[HO455]

Throttle shaft bushings on a new Qjet (NOS) will allow the shaft to wiggle. 002 to .004. As the carburetor goes through it's life the base plate holes will wear as will the throttle shaft. An extremely worn carburetor will have 3/16 of fore and aft play in the shaft.
The majority of the wear occurs in the base plate due to it being a softer material than the steel throttle shaft. The result being that when new bushings are installed there may be play than in a brand new carburetor due to the wear on the throttle shaft. This additional play would be measured in thousands of an inch not fractions of an inch. I speculate that you are feeling this amount of play and it should not be a problem.
This small amount of play is allowing a small amount of air into the intake below the carburetor metering circuits. This type of air leakage was designed to be compensated by the idle mixture screws. Thus over the designed life span of vehicle proper idle characteristics could be maintained.
Can you give us a measurement of the play you can feel? The average human can easlly detect .010 of play but, most don't know how to communicate that amount. I suggest you compare the amount of play you have to a feeler guage and let us know your findings.

[Rich72C10]

The carb has already gone back to QuadraJet Power. Either they'll tell me I'm a idiot (very possible) or there is something wrong with the carb (I hope this option).

[HO455]

I am suspicious that the carb may have issue in the main body or possibly a mismatch with the base plate.
What kind of shape was the carburetor in when you received it?
I have seen lots of frankenjets over the years. Different year carburetor sections bolted together or a Chevrolet main body bolted to a Buick base plate. In almost every case this causes problems for the vehicle operation. Sometimes it is just some one trying to solve a problem other times it is an unscrupulous seller looking to sell an incomplete carburetor for more money.
I do wonder too about your quote from QP: From Mark @QP
Quote:

Carb can idle with them closed. It has bypass air built in and we richened the mixture based on your engine descriptions.

This essentially means they physically modified the idle circuit in the main body of the carb which is may not be problem but they did it before the carburetor was on the vehicle and driven. If I am not mistaken you have a basically stock engine with the correct carburetor on it. If that statement is correct then such a modification should not be necessary. I have modified the idle circuits on my Burban's Qjet but it is off of a 1978 400 cu engine. The idle circuits were designed for emissions and as a result too lean for my engine. By modifying the circuits we were able to get the idle mixture screws to work properly. Scroll to post 455 in the link below for more info on what was done.
A common problem these days comes from corrosion. Most people seem to think that letting a carburetor sit out in the weather is not a problem. This is far from the truth. The metering circuits in the carburetor are machined to very exact specifications that are matched to the specific engine it is going to be installed on, whether or not it has to meet California emissions, and if it was going to be shipped to a high altitude dealership. When one of these precision machined passages become corroded they become larger and now will no longer meter correctly resulting in driveablity issues that are difficult if not impossible to solve. Folks who drag carburetors from swap meet to swap meet and let them sit in the rain time after time deserve a special place in he11. Photo below is a good example. Not a Qjet but a reasonable looking carburetor on the exterior but corroded badly on the inside to the point that rebuilding it may not be possible. Not something a person who spent $600 for a correct carburetor wants to hear.
One other problem that comes to mind which is rare ( We've only seen it twice that we know of over the years) is you may have a crack in the main body that only causes problems when the carburetor is hot. This is a hard to troubleshoot problem that many people have never run across.
Good luck and keep us posted.

https://67-72chevytrucks.com/vboard/...698377&page=19

[Rich72C10]

The carb that I sent them, came to me looking from the outside very clean (I wasn't about to open it up, what would I know anyways if I did). It was actually a carb I got in a outfit from Chicago that sells rebuilt carbs. So I bought it for fairly good money and then didn't mind having it rebuilt again to have it perfect.

This is what they said about it when they got to it before the rebuild:

Hi, we have disassembled and evaluated your 7042208 for your level 2 performance build for you 72 C10. Carb was clean, but had several calibration errors typical from a commercial remanufacturer as they try to make all carbs generic. We will correct the calibration specific for your build and replace all of the serviceable parts.

That is pretty much all they said, then a few weeks later it shows up. I had no idea when they worked on it that it would be expected (likely?) to idle when throttle was all the way off - that seems unnecessary. I use and intend to keep using, the anti-dieseling stop solenoid - I have told them this in the email and in my RMA.

When I reached out to them, I told them about my engine being rebuilt to stock with a mild RV Cam. I asked about getting them to do my carb, I told them I really wanted them to be sure the secondaries kicked and were adjusted properly. They told me I needed their "level 2 performance build" for that adjustment. Even if I thought that was a bit odd for that one adjustment, I did not argue the point. I don't mind paying proper money for proper work, ever. If I can't pay for something, well then I don't get the work done.

Not sure if I answered all your questions, I think I did. The carb showed up in their PO Box today... now more waiting I am sure.

[Rich72C10]

Carb is on its way back!

Man, getting information from these guys is like pulling teeth - I really don’t get that. Even if everything is perfect, I won’t recommend them because of that.

So after 3 requests for information (after I got a email it had shipped back) this is what I got.

Internal adjustments made to help you with the tune

I was like WTF?!?!? Then after more or less begging for additional details I finally got today:

Hi, We went to 72 jets with 36B primary rods. We restricted the bypass air, so idle can be lowered. We checked and adjusted throttle linkages to verify the secondaries won’t open any at idle to let air through. We removed the clip on the needle/seat to let it set when fuel is not flowing to prevent back flow. This should provide easier start up. The vacuum brake was replaced. It had a slight leak and is probably the source of the whistle.
Thank you.

[Steeveedee]

I remember that Mark had a pretty good name with Q-Jets. Hopefully it runs well when you get it back, and was a one-off with the problems.

[body bolt]

The implied relationship between empty fuel lines and hard starting is odd. You're using fuel in the bowl for starting.

[Carl Spangler]

Now that I think about it ............... I've never used that little clip on the float 'needle'. Things that make you go hmmmmmmm.

[Rich72C10]

It’s mostly Greek to me.

[Rich72C10]

Well, I know now what “remove clip on the needle/seat” means after some searching. Not really sure why they did that, since my current carb doesnt have a issue. My understanding is if you let your Vehicle sit to long the needle can get stuck and the only why to fix that is to take the carb apart.

Great, something to worry about.

[Carl Spangler]

Originally Posted by Rich72C10

Well, I know now what “remove clip on the needle/seat” means after some searching. Not really sure why they did that, since my current carb doesnt have a issue. My understanding is if you let your Vehicle sit to long the needle can get stuck and the only why to fix that is to take the carb apart.

Great, something to worry about.

Only way that could possibly happen is if the rubber seal on the 'needle' completely disintegrates and glues itself to the seat. At that point it's game over for that needle/seat anyway.

Like I mentioned above I've never used that clip and I've been rebuilding carbs since the early 70's. Carbs today are a problematic due to the high volatility fuels we are saddled with. It is what it is..................

[Rich72C10]

Ah, thank you for that input <3

[Steeveedee]

I could see the needle sticking in the seat if the fuel was gummy and then the bowl dried out. But the bowl goes dry on my truck all the time, as I drive it maybe every few weeks. I have an electric fuel pump to feed the mechanical pump, so I run that for a bit, to avoid cranking too much.

[LNP]

If you're still having issues and you suspect fuel delivery, or no fuel in bowl, or
you just want to eliminate fuel in the bowl before trying to start it. Heres a link to show how to check the float level with the vehicle running. This would insure the fuel level in the bowl is correct and you can use the same gauge to see if theres fuel in the bowl after the truck has set for a while.

http://ww2.justanswer.com/uploads/ca...ajet_Dodge.pdf

Heres where you can order the gauge

https://www.summitracing.com/parts/smp-ct10

I used this style of gauge when I use to work on the computer controlled quadrajets. Hope this helps

[body bolt]

Originally Posted by Carl Spangler

Carbs today are a problematic due to the high volatility fuels we are saddled with. It is what it is..................

This. With the high temperatures we've been having I believe I have a nasty vapor lock problem.

[Rich72C10]

I got the returned carburetor installed this morning. I have to say, it's much easier to get her to run down the road without her falling flat on her face. I think I got her dial in okay, though on Tuesday I'll have my shop take a look (she is going in to relook at my rear end leak). The difference is night and day but it is apparent I am no carburetor tuner. This is even with my fancy timing light (to watch for max idle) and vacuum gauge (to watch for max vacuum)!

With that said, I still have these problems:

1. Can't get the anti dieseling solenoid to do its job, still idles ~500 RPMs when solenoid is disengaged.
2. The above is with the throttle closed, of course, and the high pitched whistling is still there. The whistling goes away once I adjust above 600~650 RPMs.
3. The left (passenger) adjustment screw is still really loose, lots of wiggling. The right (driver) seems okay, especially compared to the left. I haven't any idea what issue this could cause, if anything - other than perhaps being able to fine turn the mixture on that side of the carburetor.

Seems the "whistling" would be a air leak, which in turn allows the engine to still idle, even though the throttle is fully closed.

Edit:

From Mark @QuadraJet Power

It is idling at 500 now? That is so low that the anti dieseling solenoid would not be effective. I thought that solenoid was primarily utilized to kick up the idle speed when the ac was turned on.

With throttle blades closed and low idle speed, the carb is pulling air through every possible point. Throttle blades are typically open slightly to get proper idle speed and allow the flow through the primary blades. Your carb, as with most, has a bypass air system to allow some air with throttle blades mostly closed. Might have a sound if you try to force all the air through the bypass.

Idle adjustment screws often wiggle. No problem.

I am a bit disappointed that it seems they haven't any clue as to the operation of the GM Stop Solenoid / Anti-Dieseling Solenoid.