potential fuel starvation after start-up??

[ridingrambling]

Brief context:  1989 Itasca Suncruiser, 454, P30.Recently installed alternator - seems to work great. Recently installed carb - see the problem below:
Disclaimer: I am not a mechanic; but usually can figure stuff out by sorting through hours on Youtube, in forums, reading, etc.

The Problem: Installed rebuilt Quadrajet carb and new associated vacuum lines. Now starts and immediately stalls, accompanied by intake backfire/popping. 

Diagnosis?: From my naive perspective seems to be a fuel starvation/extreme lean mixture issue. So I am trying to diagnose/check potential causes of such.

More background: Engine was running "OK" prior to new carb. I.e., would get me down the road; but could not resolve extremely high idle so figured replacing old/grubby carb/choke prior to heading out for NH-CA journey a good idea. Looked easy enough, and for most part went as expected.
One issue/caveat - had to cut fuel intake to remove old carb. Now finding it difficult to find something to make the U-turn into the fuel intake filter without kinking. Currently using about a foot of flexible 3/8 spectra fuel line; but not super pleased with set up.
-I have capped vacuum ports to try to isolate possible cause lean mixture.
-New idle mixture screws seem set in midrange (3-4 turns out).
-Have tweaked new choke adjustment to start at point just begins to open.
-Have confirmed accelerator pump pushing strong stream of fuel into both primaries with engine off.

Again, my best naive guess is something is causing fuel starvation right after startup. This was not an issue prior to new carb, so not sure what think. Am looking for list of what to investigate. Any logical suggestions appreciated. Thank you.

[Rickf1985]

Did you clean the gasket mounting surface on the intake manifold clean and use a new carburetor mounting gasket? Same with base of carb, cleaned of all old gasket? Sounds like a vacuum leak. 4 turns out is probably pretty rich but that will not make it stall instantly. Did you reset the float level? Did you put the fuel filter in the carb inlet in the right direction? It can be installed backwards.

[RockwoodMike]

The only thing I can think of is the seal between the intake manifold and the base of the new carb..If there is gap or a bad seal between..that would let in plenty of air..causing the problems you are having

Rick..you type fast!! You beat me!!

[ridingrambling]

Did you clean the gasket mounting surface on the intake manifold clean and use a new carburetor mounting gasket? Same with base of carb, cleaned of all old gasket? Sounds like a vacuum leak. 4 turns out is probably pretty rich but that will not make it stall instantly. Did you reset the float level? Did you put the fuel filter in the carb inlet in the right direction? It can be installed backwards.

Thank you for your quick reply.
I did clean mounting surface and used new gasket.  I did not reset float level. Presumed it was set properly by carb rebuilder (I purchased rebuilt quadrajet). I have not yet confirmed fuel filter is in correct direction; but it was on my list of today's todo's.

I also am suspicious of vacuum leak. Given that I have blocked off ports, I will probably unmount carb and double check gasket/surface. I thought I was careful mounting.

Was tempted to attempt to id vacuum leak via carb cleaner spray outside; BUT, the backfire through intake makes me nervous as I would not want vaporized spray outside intake/carb to explode :-(.

[ridingrambling]

The only thing I can think of is the seal between the intake manifold and the base of the new carb..If there is gap or a bad seal between..that would let in plenty of air..causing the problems you are having

Rick..you type fast!! You beat me!!

Thank you. Seems it is worth a double check. Is it possible to tighten on gasket too much? I thought I was careful; I did not ream on it; but something clearly not right.

[Rickf1985]

It is VERY possible to over tighten it! Especially on a quadrajet where the two bolts got through the entire carb. You say you blocked off vacuum ports, let me ask you this, do you still have all of the emissions equipment on this engine? There are several vacuum sources going on here.

[Rickf1985]

You say you bought this as a rebuilt carb? So you did not rebuild your old carb? I would not get into the carb but I would take it back. There could be major issues and you could void any warranty by taking it apart and then you are stuck with it and I am guessing you had to turn in your old carb as a core so that would leave you with nothing.

[ridingrambling]

It is VERY possible to over tighten it! Especially on a quadrajet where the two bolts got through the entire carb. You say you blocked off vacuum ports, let me ask you this, do you still have all of the emissions equipment on this engine? There are several vacuum sources going on here.

Good question.The original emissions equip appears still in place. (I also recently replaced all four belts, fun times...) The vacuum lines do make up a bit of a spider web :-(. I capped the ports on the carb, presuming that would be most effective way of making sure no leaks.

[ridingrambling]

You say you bought this as a rebuilt carb? So you did not rebuild your old carb? I would not get into the carb but I would take it back. There could be major issues and you could void any warranty by taking it apart and then you are stuck with it and I am guessing you had to turn in your old carb as a core so that would leave you with nothing.

Yes, I bought rebuild online from seemingly reputable shop. At time, I just thought more likely to get it right, and with quick shipping it was time efficient (so I thought).

I was supposed to depart for NH to CA this week (I am spending winter in Death Valley, volunteering for national park service. Did same gig in this rig two years ago.). I am supposed to be in CA in a week. Not likely now. Which means I will not arrive for my winter gig on time. Big bummer.

I still have the old carb. They give me a couple weeks to return core... Also have thought about re-installing it to see if having same issue...

[Rickf1985]

Reinstall old carb, Solving a high idle is much easier than diagnosing a quick stall/ fuel issue on an unknown carb. You probably only need a new choke pot on the old carb.  Where are you located?

[Rickf1985]

One thing you can try is to plug all of the open vacuum lines also and try to start it.

[ridingrambling]

Reinstall old carb, Solving a high idle is much easier than diagnosing a quick stall/ fuel issue on an unknown carb. You probably only need a new choke pot on the old carb.  Where are you located?

Ironically, I originally presumed it was choke (still think it was); but I thought I was being extra proactive by replacing entire carb, including new choke.

My concern now is that I have accidentally changed something. OR, maybe my jury-rigged fuel intake line is creating supply issue. It "looks" ok; but I wish I had been more persistent at getting line separated from old carb without cutting it. I eventually got the fuel line stub apart from the fuel filter housing once off the engine, but it was very difficult.

But yes, I am having some remorse about trying to be extra proactive, when I might have been able to just resolve high idle more simply. I will spend afternoon re-installing and  hoping it returns to that problem... but something in my gut says it might not... :-(
I am currently sitting about 20 miles from Keene, NH, at my folks.

[ridingrambling]

One thing you can try is to plug all of the open vacuum lines also and try to start it.

Never thought of that... can open lines, not ports, impact what is happening inside carb? Certainly willing to try anything that simple at this point. thx.

[Rickf1985]

While cutting the line was not optimal it is not a disaster. Use high quality fuel injection line that will slide tightly over the original line and clamp it with quality clamps. That will not cause an issue.You can use some Permatex #3 gasket sealer on the base gasket since it is going to be reused and that will make sure it seals. Do not use too much, a thin layer is good. Keep this stuff around as it is a good all around sealer. I use it in all paper type gaskets in addition to all radiator and heater hoses. It not only seals the hoses but it prevents the inevitable corrosion on the water neck of the thermostat housing. It also makes it a LOT easier to remove the hoses when the time comes.

[Rickf1985]

Any vacuum leak on the engine will impact the mixture coming into the intake manifold

[Rickf1985]

I was just thinking of something, is the choke closing on the new carb? Is it staying shut when you start it and is it stalling with it shut?  That is an indication of not enough gas in the float chamber. Either bad fuel pump, clogged filter, bad float setting, etc. Since you had none of these issues with the old carb I am going to say it is the carb that is the issue as long as the choke is closing when you get the stalling.

[ridingrambling]

I was just thinking of something, is the choke closing on the new carb? Is it staying shut when you start it and is it stalling with it shut?  That is an indication of not enough gas in the float chamber. Either bad fuel pump, clogged filter, bad float setting, etc. Since you had none of these issues with the old carb I am going to say it is the carb that is the issue as long as the choke is closing when you get the stalling.

All of your comments are helping me think through things. Thank you. I ordered a new gasket; but cannot pick it up until tomorrow. Will pick up some of the sealer you advise.

choke looks closed. in fact I can only open it part way via manually operating choke, so was wondering if after I resolve lean start issue, if I am going to have a problem when it is supposed to be wide open... 

My issue with the fuel line is getting something to flex around the necessary U-turn heading  into the fuel filter housing. Everything wants to kink. I tried bending some copper line; but both tries failed. The current spectra is my second hose attempt; Going to see what results from re-installing old carb... If I have this new issue then I created it...
after I first try starting with lines capped... 

[Rickf1985]

The rubber line should not kink if you give it enough room, you will have to cut the metal line back further . I am assuming you cut it close to the carb so go back about 6 inches or so and cut that much more off towards the fuel pump and then bridge that with the rubber line. If you find a junkyard in your travels just scrounge a new line off of any big block with a carb and a fuel pump. If you are trying to make your own line you need a tubing bender to prevent the kinking.

[BamBam]

[/q][/q]

-I have capped vacuum ports to try to isolate possible cause lean mixture.
-New idle mixture screws seem set in midrange (3-4 turns out).




If your mixture screws are that far out, your running a rich condition! The screws should be unscrewed between 1-1/2 to 2 turn from fully seated for ideal fuel mixture.

[ridingrambling]

yea, I kinked it even using a tubing bender...  ... I like the junkyard option, eventually... good suggesting to cut the l back more on the fuel pump end. That should give hose some more room. Of course, getting to it deeper in will be fun... more goodies to remove/reinstall :-).

[ridingrambling]

[/q][/q][/q]

-I have capped vacuum ports to try to isolate possible cause lean mixture.
-New idle mixture screws seem set in midrange (3-4 turns out).




If your mixture screws are that far out, your running a rich condition! The screws should be unscrewed between 1-1/2 to 2 turn from fully seated for ideal fuel mixture.

Yes; I do not disagree. But my symptoms seems to be too lean, so guessing not the idle screws...

[Rickf1985]

The fuel injection line should be a bear to slide over the metal line but try to get at least a few inches of it on there. Use that sealer as a lubricant if you have to and I suggest using double clamps even though there is only 5 psi of pressure mainly because it is a gas line and the ends are not bulged out to hold it on. This is massive overkill but better that having it slide off.


By the way, A tip, wear mechanics gloves or nitrile or latex gloves when using that sealer because for some reason no matter how careful you are it WILL get on you and your tools. I don't care if the tools are across the room, it is magic, the sealer will find them! :)rotflmao  Once on your skin there are only a couple ways to get it off. Carburetor cleaner, which is rough on the skin or it will wear off in a month or so.   That stuff is one step above pine sap when it comes to sticking to skin!

[Rickf1985]

Do not cut off more than you think you will need because contrary to popular belief metal line will not vapor lock as fast as rubber line. The black soft surface absorbs engine heat so try to keep it to a minimum.

[ridingrambling]

The fuel injection line should be a bear to slide over the metal line but try to get at least a few inches of it on there. Use that sealer as a lubricant if you have to and I suggest using double clamps even though there is only 5 psi of pressure mainly because it is a gas line and the ends are not bulged out to hold it on. This is massive overkill but better that having it slide off.


By the way, A tip, wear mechanics gloves or nitrile or latex gloves when using that sealer because for some reason no matter how careful you are it WILL get on you and your tools. I don't care if the tools are across the room, it is magic, the sealer will find them! :)rotflmao  Once on your skin there are only a couple ways to get it off. Carburetor cleaner, which is rough on the skin or it will wear off in a month or so.   That stuff is one step above pine sap when it comes to sticking to skin!

LOL... yea, my first attempt at a hose over metal line ended up gushing fuel. second attempt of slightly flaring end of tube, then double clamping worked better. Also, the rubber tube inside the spectra line (current setup) was MUCH tighter, and the clamps held - no leak. I am paranoid about fuel leaking, so I will get it... Orielly's had a bunch of Permatex choices, but no #3... I picked up some fuel resistant, but will see if I can find #3 elsewhere... oh, I still have some blue oil-based enamel under my fingernails from paint job a month ago... so I have also learned my lesson about gloves.  :-)... good suggestion!... I had read about risk of rubber line vapor locking, so was another reason I was hoping to resolve using as little rubber as possible. Again, thank you for heads up.

Well, busy afternoon ahead. Hoping I make some diagnostic progress to my "I'll just drop a new carb in and hit the road" project...  ha...

[ridingrambling]

  potential dumb question... is there a top/bottom orientation to the mounting gasket? Obviously there is a front/rear; but I did not carefully inspect/think about potential differences in gasket surfaces and mating to carb?...
Removed my new carb and compared new gasket to old and I do not see obvious differences in alignment, depth of grooves created, etc. But I also am not 100% what I am looking for.

I have a new gasket to pick up in morning; but re-installing old carb w old gasket tonight to see if I can get engine actually running again instead of immediate fuel starvation upon start up.  (UPDATE: decided to wait for new gasket in morning)

On the bright side, removing/dropping in new carb process getting familiar. Too bad doing so seems to make me immobile :-(...