Hard to start after 2 days, fuel drain is possible. Why?

I don't run chokes on mine, and all parts are removed.

Many times after sitting, it is common for the fuel to evaporate and/or drain back. Several short cranks fills the bowl from mechanical pump and it will start.

Mine became harder to start recently, and in fact, hasn't started now for several months. It will crank and has fuel.

Business has been great, and that keeps me from working on my own cars for fun, but I do suspect I have a spark issue. Possibly MSD box bad. I haven't pulled the plugs, but I suspect the harder to start issue could have been from plugs. I haven't changed them in a few years. There was several times it acted like it wasn't going to start at all, and leave me stranded, but then it would start up. It got me home and won't start since. This all occurred over a couple month period, when it started becoming harder to start, and now asleep in garage.

Yours may be similar if not completely carb related. You may have checked your plugs or they may be fresh, but that is where I am starting, to see if I have any spark now.

 

I would say that a combination of lower ambient temps making any engine harder to start, along with the seasonal change to winter blend gasoline, which is has a higher RVP and as such, evaporates faster, are conspiring together to make your car harder to start.

Conversely, if you still have a tank of summer gas, the RVP is too low for the ambient temp...

Of course check all other possible sources.

I would pre-prime the carb like Larry does, to see if there is a difference. This will lead you toward or away from a fuel issue.

JW

 

You can adjust the high idle speed down to where you like it. I usually crank mine over with out setting the choke until the oil pressure builds. then i stab it once and it starts with oil pressure.

there should be almost no fuel coming out of the primary jets at an idle. the rods are pulled in tight for one. I can't get behind your "jetted up" theory. if you read cliff's book, he states that even with the most radical builds that the stock jets and rods are the best starting point for tuning. If you're jetted up enough to enrich the carb enough to act like it has a choke on then you are seriously running pig rich and leaving a lot on the table. i get that bigger jets let more fuel through, but they should still be appropriately sized for your engine.

 

thats a good idea. Im gonna start doing that.

 

Step one - look for a good pump shot after sitting for 2 days.

 

Larry, you mentioned you weren't running a choke. so therefore no fast idle cam, no high idle and no closed choke creating a wicked vacuum in the throttle bores. You are talking about 2 different carbs here. I'm talking specifically about a q-jet with no choke.

As far as cliff's recipes, I did my own q-jet. I own the book and read it thoroughly. you might be surprised to find out that most of the modifications are to the idle circuit. his recipes don't get into jetting. as I mentioned before- most engine combos, even much more radical than stock, don't require very much if any changes to the jets and rods. I believe he even states in the book that the number one mistake he finds is unnecessary jet changes. that being said, your Q-jet from JW is probably jetted near stock. you certainly didn't jump 5 sizes up. maybe one or two at the most. My point is, your worked carb can't really offer any huge starting advantage simply because you might be up one jet size over a stock carb.


on a side note- for a warm weather only car, I've often thought about running a choke system without the choke blade. that way a fella could still get a high idle for a few minutes. but I've since learned to really fine tune a choke.

also, it only cranks about 8 seconds before it builds oil pressure. it can't be any worse than having the motor kick and half fire a few times before it lights up..

 

FYI on the carb,

Its a 750 cfm Buick front inlet that was originally done by Osborne years ago. I have worked on it over the years for Mike in search of better ET and driveability/performance. (no problem with Osbornes build, it ran good, but engine combo changed) It is now set up identical to a Stage 1 factory carb as far as jetting, rods and hanger in an effort to improve starting and driveability. It has a non slotted .130 or .135 needle and seat. Mike has the build sheet I did on it, so I cant remember all of the measurements on the idle system etc, but it is one of the recipes in Cliffs book.

I also drilled and tapped both front and rear wells, installed screw in plugs and then Marine Epoxied them per Cliffs book. They are not leaking.

I am interested to hear if it has pump shot today prior to cranking it. I know the check ball can allow the pump cavity to leak down and I suspect that could be a problem as I didn't check it the last few times it was apart.

I am certainly not ruling out a carb issue, as admittedly I am no carb expert, and I have suggested he send it out to Mark for a rebuild. I had Mark do a qjet for me that has the absolute best manners of any qjet I have had on my race car. He is doing another for me now that is more set up for stabbing and steering.

 

My car did nearly the same thing. I installed an electric fuel pump that only works when the key is on but the engine isn't running. Maybe that's a possible solution?

 

If the fuel is indeed draining back, a simple solution is to remove the little wire hanger that hangs the needle onto the float. When the fuel begins to evaporate, the "front door" will remain closed when the float starts to drop.

 

OK. 2 nights after I last drove the car. I removed the air cleaner. Climbed above the carb and squirt away. There was fuel at the pump. I then checked for spark and I saw spark, but don't know the quality.

I put the air cleaner back on and proceeded to start the car it fired off quicker than expected, after about 5-6 seconds and another depress of the gas pedal. Not I know tha motor was not flooded and the idle was quite irrational and jumping around 150-200 rpm jumps and required my constant attention to keep it running. I understood before that possible flooding may be a culprit and my idle was rough. These plugs were replaced the last time I had the car to the track and are NGK UR4, I believe (I went a colder plug as my compression is 9:1 or less). The car eventually clears up and runs what I feel is good. I am concerned that maybe the coil or Crane XRI module is acting odd.

I think I will start with a new cap and rotor. I will find a brass post cap. I need to check the resistance of my coil to balance it with the Crane specs.


More to work on.


Thanks all

Mike

 

Do you know how to check for vacuum leaks?

 

I wonder about the accelerator pump check ball sealing? That will allow accelerator pump to drain back if it sits. I always take a a punch and use the old ball and seat it with a couple smacks with a hammer.

 

what state are you located? what was the temperature outside? sounds like a normal cold start without a choke to me.

 

I had a similar issue awhile back with my Q-Jet, the accelerator pump lip seal was poopoo, sometimes it would pump, sometimes it would just dribble the fuel, VERY cantankerous to start cold:rant:

 

did it sometimes hesitate from a stop sign?