Not getting enough fuel to one cylinder at idle. Did all the normal tricks:

* checked idle jet (clean)
* ran idle mixture screw in and out
* removed idle jet and mixture screw and blew out
* removed idle jet and "plugged the hole" with finger (this should give me a *very* rich mixture, only got down to 15:1 or so)

So, it's time to pull the carb. I suspect something is blocking the mixture screw area... Of course I have a race this weekend.

Sigh.

Just for giggles and because it's cheep anyway...for just the cyl that isn't firing, put a new spark plug in it and see what happens. Could be nothing.

I've had a few sets of carbs over the years that when gummed up (one barrel), I'd do the same thing, pull screws, try to blow out passages etc. Every once in a while, it'd need to be done it seemed on one barrel or another.

Occasionally, I wouldn't set that barrel as good as I could while fiddling and fouled that plug in short order.

Just a thought, can't hurt.

Check your valve settings on that cylinder and do a compression test..
OR.
Flip the carbs from one side to the other...

Carbs dont care if you have a spark, they are only controlled by the airpump...some evacuation will affect it..but not unless you have built the motor for that...

Flipping carbs sucks, but its an hour...

Rich

I second trying a new spark plug or even just cleaning your current one before trying other things.

Zach

It's got a Mallory 6AL, Bosch Blue Coil, and fairly new plugs. Plus it was fine when I "put it away"... Something changed as it sat.

Sounds like trash. PUll the carbs off and take the tops off, Clean out the carbs really good with water and purple. Make sure you blow out all the passages with compressed air. That shouldn't take but a couple of hours. Also check the valve adjust and check plug wires. If it has Bosch Plugs, that is part of the problem.

Vacuum leak?

Not questioning your ability to inspect the Jets, but have they been ultrasonic cleaned? If the car has sat for a period of time it is normal to run into fuel sediments and or debris/deposits that settle and clog these up. They often will appear to be clean when you look through them in the light and what not but you magnify them and it becomes clear .. or unclear for that matter. I had replaced these all the time when I ran dirt cars... No matter what kind of filtration I used it seemed to haunt me. So I feel your pain.

Also, while your in there do a quick look over your emulsion tubes for any sediments, deposits or debris. These can often cause issues as well, not often but it happens.

I hope this helps. Please do post what happened when you figure it out though, I am curious as to what it is. I will add it to my notes for further reference.

T

OK. Popped the carb off and R&R'ed the idle mixture screw and it's bits and pieces, verified my plugs (damn... they look good! Light brown! A testament to an LM-1), and put it all back together. Re-sync'ed the carbs and it ran great in the driveway. As soon as I pulled away it was stumbling all over the place.

FML

So, I need to verify my fuel pressure (CB's rotary pump) and then if that checks out it's down to a full rebuild of the carbs.

I should mention that I also checked the screen at the fuel inlet of the carb and it was pristine. I run a FI style fuel filter before the rotary pump. Still wondering about bad gas though...

Stuck a flash light down in the tank and the gas level is at the top of the fuel screen and it looks clean down there. I'll check the fuel pressure tomorrow.

How long did the car sit? If it had pump gas and was not run at least weekly to get good and hot then the additives that we now have to put up with in pump gas has turned to snot. Generally it is in places you can not see and needs boiling to clean out. There are two ways to cure this, and in your case just one and that is a complete rebuild including a good tank cleaning with carb solution. Use new rebuild kits and THEN the second thing is to run the car at least weekly until good and hot so the carbs will self clean. You can add some Marvel Mystery Oil to the gas to slow things down but it will happen eventually. If the car is mainly a racer then race gas will help but even 100 octane unleaded has some goop in it now and leaded is even worse. I learned this about 10 years ago when my vintage race car was sitting for weeks at a time and ran crappy when started and my mentor straightened me out about Webers.

Check you timing too.
I have been fighting a stumble that I tried to tune out with carbs ad it ended up all being ignition. Make sure that you are getting consistant spark.

Zach

Not the fuel pump. Steady 2.5 psi no matter what... Damn. I guess it's time to pull the carb tops off ant take a peak.

I think we have a winner....

john rogers - step right up!

Took the top off the drivers side carb and at first glance it was spotless. No seidiment or anything. Upon closer inspection there was some gelled gas in the bowl and in one of the passages in the bottom of the bowl.

Any recommendations on *great* carb cleaner in a spray can? I don't want to dunk them because Dell's used sealed bearings (like a skateboard) and I have new ones in these carbs. They are a pain in the butt to remove...

-Aaron

You can try spray cleaner BUT you'll end up being unhappy with it since you have the snot in the carbs.

if it has not been mentioned earlier, fill tank with fresh fuel and add seafoam. works wonders. gasoline goes bad in three years. here it goes bad in three months.

I have a 914 with the same prob, runs on all 4 for 5 min. then just 3. Pulled plugs, changed wires, still a miss! Bob