anyone good with carburetors?

[Invigor]

i've got a 1987 dodge ram van with a 318 2bbl holley carb, it idles fine, but runs very very very rich (like $20 fuel in 3 days, city driving about 20minutes a day). exhaust smells like a skidoo's..

i've so far replaced the choke vacuum pull off, that didn't help. would it be recommended to take it apart and check the float, needle and seat? if it's choke related, how do I go about it?

I ran it home today with the engine cover off, air cleaner box off, and just the bare carb exposed so I could watch it..when I was driving at about 50kmph and stomp on it, it backfires, once it even backfired off two pistons.

i've checked vacuum lines, but there are only about 3 and they all seem to be ok.

can anyone recommend anything?

thank you!

[andestang]

Sounds like you may have a engine timing problem. Try and get the base and full advance timing checked. Also maybe timing chain slack if engine mileage is high. If your choke (electric I'm guessing) is working properly the flap should be almost straight up (vertical) after engine warm-up. Just some idea's.

[Invigor]

thanks for the reply.

someone came over and had a look at it, figures if it's in the carb, the jet's aren't set properly..he didn't mention timing, although you're the 2nd person that has.

I'm not too familiar with how to adjust the timing, but I've got someone I can go to, that can help me out.

Thank you again!

I'm not sure of the milage sitting infront of my computer, but I know it's over 200k

[BMW Rider]

Another problem common to the Dodge small block V8s was carbon build up in the exhaust crossover passage in the intake manifold. It results in the fuel not being properly vapourized due to the lack of heat under the carb. this would produce simptoms similar to what you describe. basuically you have backfireing beacause the fuel mixture is essentially lean since much of it is in liquid and un burnable form. This liquid fuel is then pumped duirectly through the engine out the exhaust resulting in a rich exhauast smell. It also tends to wash down the cylinder wall and cause excess oil consumption as well. The only cure is to remove the intake and clean out the carbon blockage.

[Invigor]

Originally Posted by BMW Rider

Another problem common to the Dodge small block V8s was carbon build up in the exhaust crossover passage in the intake manifold. It results in the fuel not being properly vapourized due to the lack of heat under the carb. this would produce simptoms similar to what you describe. basuically you have backfireing beacause the fuel mixture is essentially lean since much of it is in liquid and un burnable form. This liquid fuel is then pumped duirectly through the engine out the exhaust resulting in a rich exhauast smell. It also tends to wash down the cylinder wall and cause excess oil consumption as well. The only cure is to remove the intake and clean out the carbon blockage.

it does sound probable. the beast sounds ok when it idles, very hesitant when you give it gas..sounds like it's working really hard to get air...loss of power. I will add "possibly clean intake" to my list.

I've got, carb kit, set timing, and clean intake...whee! glad it's only a 2bbl

[StirCrazy]

sounds like timing to me, how is it starting? and did this happen all of a sudden or has it slowly been getting worse?

Steve

[BMW Rider]

Originally Posted by Invigor

it does sound probable. the beast sounds ok when it idles, very hesitant when you give it gas..sounds like it's working really hard to get air...loss of power. I will add "possibly clean intake" to my list.

I've got, carb kit, set timing, and clean intake...whee! glad it's only a 2bbl

It so hard to make a determination without seeing it first hand.

Check the ignition timing, if it is way off, then it is possible that the timing chain has jumped a tooth. It will be retarded since when the chain skips, the momentum of the crank will jump it ahead of the cam leaving the cam and distributor retarded. Usually when they go, they go to the point that the engine will not run, but it can just skip one tooth initially allowing the engine to still run sort of. Usually it won't be too long before it jumps another tooth or more and the engine will no longer run at all. Generally though, for timing to be the cause of backfireing, it will have to be too far advanced.

As for the carb jets being not set right, that is highly unlikely. The main jets are fixed orfaces and would have had to have been replaced to change them. The idle screws will only affect the idle mixture, and that does not seem to be your problem. It is possible that the float level is too high in the carb. This will have the effect of richening the mixture. this can be the result of a leaky needle valve or a float that has become too heavy, usually because it has absorbed fuel. But the backfiring is not a symptom of a too rich condition, but rather a too lean condition. If the only time it backfires is when you accelerate, it could be the accelerator pump not working properly and causing a lean out when the throttle is opened. Once the engine reaches the increased rpms, it will again run fine. Of course this means a thorough cleaning and overhaul of the carb is required.

Of course as is usually the case, there are multiple cuases combining to create the overall poor running. The timing may be slightly retarded due to timing chain stretch, the intake is cold due to carbon build up (almost a guarantee on that engine at that mileage if it has never been cleaned) and the carb is not in peak condition. There may be other factors such as the condition of the ignition system too. Check for bad wires, plugs, cap, rotor, etc. It may not be any one problem that is the major cause. And to top it off there may be more serious mechanical issues such as bad valves, camshaft, or other valve train component wear.

Like I said, so hard to diagnose whithout seeing it firsthand.

[Invigor]

Originally Posted by StirCrazy

sounds like timing to me, how is it starting? and did this happen all of a sudden or has it slowly been getting worse?

Steve

it starts wonderfully..pump twice and crank and over it goes, even when it's cold out! (I run castrol syntech 5-40w in it for winter)

i've noticed it's starting to idle a little rougher now, but could be because it's dropped 10 degrees, and I was fiddling around with the idle speed..I don't have a tach but I presume it's around 1000 to be smooth.

when you're driving it it sounds almost like you've got a rag over the top of the carb causing it to really struggle for air..sounds like it's working really hard to be smooth..it's not smooth at all accelerating from idle to probably 4000rpm + then it's too loud (don't have the engine cover on right now) to really hear how it's running. I think it does have a sticky lifter, the engine has a fast tick tick tick to it that gets faster the higher the revs..I think that's the lifters that cause the tick.

I popped off the rotor cap today, it doesn't look very new to me, the piece that spins around to each of the plugs looks ok, but the contacts it hits look a little worn.. I've asked my dad to drop off his ohmmeter so I can test the wires, and I plan on taking a look at the plugs today too..I'm sure they're due for replacement.

as for the cold intake, the engine doesn't run any better even after about an hour of driving it..it takes longer to warm up than I remember it too as well. not sure if that helps

I have a digital camera that takes movies, maybe I'll try to capture the sound of it accelerating (boy does it sound bad)..not sure if that'll help with anything.

is there anyway to "test" the accelerator pump? are they mechanical or vacuum operated?

thanks for the help!

[Robw]

To check the accelerator pump,with the engine off , look down the carb and hit the gas. You should see a jet of fuel squirt into the primary barrel. If the engine isn't warming up you might have a stuck thermostat.

[BMW Rider]

Another possible cause may be a restricted exhaust system.