Request for help

[indymachinist]

At the risk of sounding desperate....

Would anybody temporarily loan a complete stranger such as myself a known working Rochester Monojet carb?

I know that is an odd request but I am pretty much stumped on why mine will not work and am wanting to either confirm that something is wrong with my carb, or maybe wrong with me.

I have had carb savy friends come over and try to help with this thing and we just can not get it up and running to save our lives.

The truck in question is a 68 250 online 6 with a Monojet #7029021

[57larry]

I don't have a carb for a 6 cyl but would suggest that you tow your truck to 3D Carb shop on the southside. they'll get it running

[Orange Crate]

if you are willing to describe your problem it might make it easier for someone to help out. Also there are a lot of experts on this forum and you might be surprised to find an answer from one of them, or another member that has done the same mod.

[Tom Vogel]

I will bet this problem has nothing to do with the carb.

[Grumpy old man]

Will it start or at least try to fire using carb cleaner ?
Posted via Mobile Device

[indymachinist]

I can't post a detailed story at the moment but I will when I get on lunch break.

Long story short it will generally start after a couple seconds of cranking and will idle shakily for maybe 5 to 10 seconds and then die. It stinks of fuel from the exhaust and if you give it throttle it dies immediately. A couple of times it has idled nice and smooth for a brief time. Looking down the carb throat, puddled fuel can be seen on the floor of the intake.

[snipescastle2]

Couple of things to check, I'm sure others will add to this. If you still have a point type ignition, try changing the points and condenser. You may have a bad coil too.is the accelerator pump in the carb shooting gas when you pump th pedal or move the throttle blades? There could be lots of small issues causing this condition. Fuel filter clogged, accelerator pump in the carb is bad, fuel pump going bad,etc...
If you disconnect the fuel line from the carb and direct the fuel discharge into a bucket/bottle, is there adequate fuel flow and volume? If your plugs are wet and fuel puddling in the intake, sounds like a weak spark or ignition issue.

How does the spark appear from the plug wires to ground? Is it blue/purple? A faint spark will usually indicate a bad coil. Could be bad wires too.just a few things to check.
Ben

[Grumpy old man]

Clean the carb , check for crud in needle seat , check float level is correct , change filters and check the fuel pickup in the tank . This all sounds like a flooding problem , when you get it to start can you run the engine at fast idle ,1500 rpm ?
Posted via Mobile Device

[indymachinist]

Ok I am going to try to get out as much as I know about this thing.

I bought this truck with this no run condition already existing. The previous owner was a middle man that got it from someone else on a trade and he didn't have any luck getting it to run.

Things previous owner replaced:

Reman carb (not sure who did it, but P.O. messed with it a lot)
Fuel filter
Fuel pump,
Distributor (all new distributor not just cap and rotor, still points style)
Plug wires

Things I have done:

Carb rebuild kit including brass float
Ignition coil
Spark plugs

When I bought the truck the previous owner told me he thought a piece was missing from the carburetor. He had taken it apart and put it back together a bunch of times with his helpers trying to get the truck running. So the first thing I did was get a full carb rebuilt kit from the guy "Mike's Carburetors" that does the rebuild videos on youtube. I fully tore it down a piece at a time, cleaned everything, and rebuilt the carb to the specs that I was provided with the rebuild kit. I did not notice anything missing from the carb based on looking at the exploded views seen online, but that doesn't mean it isn't missing something.

I just had a couple buddies come over yesterday that have a lot more experience with carbed engines than I do. The first thing they wanted to check was the spark so the distributor was checked, timing was set as best as possible with a non running engine, and the spark was looked at and considered good. We replaced the ignition coil just because it was the last old part of the system left and it was fairly inexpensive.

After checking over the ignition side of things they wanted to take a look at the float side of things under the top cover of the carb. Checked the needle and seat, made sure the inside of the carb wasn't dirty and everything looked ok visually. Made sure the accelerator pump was working which it was. Then we set out trying to get it running.

The truck will start without too much trouble, but runs kind of rough. The exhaust smokes a bit and smells like gas. It will stall out after around 5 or 10 seconds. If you pump the throttle at all it dies. Even just cracking the throttle a bit will kill it. My helpers think it is dumping in way more fuel than it should be. We adjusted the float down considerably lower than it is supposed to be set and that seemed to help a bit, but it still doesn't want to run right. Adjusting the float down is when we were able to get it to idle best though. The idle mixture adjuster seems happiest around 1 1/2 to 2 turns out, but we can't get it to idle long enough to really get any kind of set on it. Occasionally when it stalls out after running a few seconds it will huff raw fuel spray back up out of the carb.

[indymachinist]

Also spark plugs come out sooty and black, but not wet.

[hamjet]

Sounds like its just a stuck, maladjusted choke...

[saltynuke]

Please confirm that the PO has the spark plug wires connected correctly and in the correct order.

[indymachinist]

It is not the choke that is wide open and not hooked up. Using the choke pretty much immediately floods it and it won't run at all.

Plug wire order is correct. That was the very first thing I looked at.

[RichardJ]

I assume with all those people looking at it, someone shook the float to make sure it isn't full of fuel from a leak.

>> timing was set as best as possible with a non running engine,<<

Has anyone tried "static timing" the distributor? If done properly, that will get it to within a couple degrees and will start and run easily.
If it won't static time, the distributor could be 180-out or there could be a problem with the points or their installation.

[RichardJ]

With that many people looking at it, there is one other, but really remote possibility.
Double check that TDC is where you think it is.
There are at least two different timing tab locations on different timing chain covers.

[Gromit]

I'm not able to help on the carb; but if it were me I would try the following:

If the motor has not been running consistently for a long time it is possible the volatiles in the existing gasoline have all evaporated and what is left is just plain too old. So changing out the gas with fresh gas may help. I have read some say that today's gas is only good for a few months - but in my own experience I have stored it and used it for at least a year.

A compression check on all cylinders.

A harmonic balancer ring TDC mark check against true TDC on the compression stroke to make sure the rubber ring has not been spun out of alignment with its cast iron hub.

I have used a borescope fiber optic USB camera (less than $25 on Ebay - see photo) and an old laptop - with the camera in the spark plug hole to verify true TDC on Cylinder #1 with the timing cover marks (as the previous poster wisely mentioned) - and since this is such a critical need to know item when you have an unfamiliar motor.

I assume the initial timing must be advanced before TDC at least 5 crankshaft degrees and someone didn't install a timing tape on the harmonic balancer backwards - and your timing light is set at zero if you are using the factory timing marks.

Finally; the throttle plate or butterfly bushings don't generally get replaced in a carb rebuild kit and if you have a leak there from worn bushings it could cause symptoms like you describe and the play is so small it is pretty subtle upon casual inspection.

[Gromit]

I just noticed you wrote in your original post that you had a remanufactured carb - hopefully they checked for and/or replaced the throttle plate arm bushings but it is still worth a look - with no return spring load on the linkage the play between the throttle plate arm and the bushing should be just a few thousandths - you can barely feel that when wiggling the throttle plate arm or bolt against its bushing. If it is ten thou of play that is way too much and you will get a big vacuum and fuel leak and the motor will barely run and die when you try to further open the throttle.

[70STOVEBOLT]

I have one I could "rent" you. I would need a deposit into my paypal account that I would refund to you after I receive the carb back. It is a manual choke type from my '70 250.

[Acorn]

Originally Posted by 70STOVEBOLT

I have one I could "rent" you. I would need a deposit into my paypal account that I would refund to you after I receive the carb back. It is a manual choke type from my '70 250.

^^people like that are the reason I love this site so much.
I would jump on an opportunity like that. Check and double check all the things everyone has mentioned here then get a 'known to be good' carb from 70stovebolt and slap that sucker on and go from there. It could save you hours of staring at your engine and scratching your head. My .02

[indymachinist]

Originally Posted by 70STOVEBOLT

I have one I could "rent" you. I would need a deposit into my paypal account that I would refund to you after I receive the carb back. It is a manual choke type from my '70 250.

Sent you a PM

[70STOVEBOLT]

Hi Curt,

PM returned. This carb is on a 250 that I took out of my truck in favor of a 402 last fall. The engine ran fine when removed. Good luck, I hope it helps to solve your problem.

Thanks,
Mark

[indymachinist]

70STOVEBOLT loaned me his carb which I put on the engine and tried.* It did start right up on choke and idle for a while.* It smelled different while running, more like proper combustion, not stinking of tons of excess fuel like it had, but it still won't run right. It still won't rev up. It tries to now but there must be more to the problem than just the carb.

I really wanted to be able to drive this truck a bit as it was but I just don't want to sink any more money into the engine that is in it now when my plan is to put a V8 in it. So with that in mind, I am going to let this go.

Thank you to all who helped, especially 70STOVEBOLT who trusted me with his carb.

[70STOVEBOLT]

Curt, that sucks to hear. Good luck with your build in the future.

[Gromit]

That new V8 will be fine but that conversion is not completely painless or cheap either; as far as I know nobody makes a kit with every single thing you need to replace that 250 with a 350 and there is an awful lot of fiddling around and wasted? life there as well (though as someone once pointed out on this site it is always good to remind oneself we do all of this out of love, right)?

Fortunately Jegs and Summit with their price matching policies work in our favor and we all have access to those pristine GM Performance Mexican long blocks in seemingly endless supply for less than $1.75K

But if it were me for peace of mind I would still do a compression check on all cylinders on your 250. Because if you have good compression that means it is down to your cam/pushrods/lifters/rockers (assuming your new distributor/vacuum advance was good), okay maybe fuel pump - but that is a $200 problem.. better to have than going to a complete new motor in my opinion.

So even if you did still go to replacing the motor at least you would be doing so knowing that you really, really needed to do it.

That known good carb from 70Stovebolt is worth its weight in gold; as would be a known good distributor and known good fuel pump..(all of which would fit in one of those Home Depot 5 gallon Homer buckets)..hmmm

[indymachinist]

Want to see a bad idea in the making?