I think it's a carb problem

R

ron3865

New member
A while back the ranch I work at picked up a used, home made water truck made out of an International truck frame with a 304 engine.
For the last couple of years it had been running pretty good up until last month.
It's always been easy to start and very smooth running right up until it quit on me.
I could smell partially burned gas through the holes in the cab floor, it started running rough, backfired a couple of times and slowly shut down. It would start, run poorly and shut down and after that it wouldn't start anymore.
The next day I replaced worn points, a cracked dist. Cap, capacitor and a coil that was right on the edge of failing an ohms test. It started, ran well and slowly died not to start again.
Checked the plugs and all were wet with gas. Took the carb off and checked the float and needle and seemed ok.
Started it again a couple days later, it ran and slowly died. I thought somehow gas was being forced into the engine due to stuck float but the gas was right at the bottom of the inspection hole.
I didn't have a timing light but I was able to get #8 tdc and the pointer was near enough the marks to run.
IH 304 cid
holly 2barrel/ manual choke
problems: 1. Starts, runs for a minute and slowly dies.
2. Strong smell of unburned/partially burned gas.
3. Wet plugs.
New coil, points, condenser, cap and rotor. Carb was disassembled, blew air through passages, checked float level and could see gas shoot out from accel. Pump when throttle moved.
I've never had a simple v8 stump me like this. I wonder if something internal to the carb. Gave way? Something I couldn't see or just missed?
 
You mention a sight hole, so that would indicate the carb model is a 2300, but confirmation should be made. Protect your vision while you look inside the carb for fuel drool both while the engine is at idle and immediately after it is switched off or dies. Are there any fuel filters in place? Are they clean? How old is the fuel in the tank? Your fuel pump should also be checked for proper function.
 
The fuel is fresh, tank is clean, pump is a year old and quickly fills up the new plastic fuel filter.
After being away from it for 2 weeks I tried it again today. Fired up right away, ran very rough, backfired a few times and quit with a smell of unburned fuel from the exhaust.
I have checked for fuel leakage into the carb and I can't see any at idle or after shut down.
What I can't figure out is how the problem, whatever it May be, started as I've never experienced the symptoms before....
Last month the truck started quickly, idled very smoothly and the first couple of loads of water went well. Then I noticed my eyes burning a bit and the smell of partially burned fuel. Over a period of about 10 minutes it started to run worse and lose power. Then a few backfires and it slowly quit. If I dry off the plugs and wait a day or so it'll start, run rough, won't idle on its own, backfire a few times and then quit and that's it for the day. Won't even fire after that.
Seems to me that if the dist. Jumped a few teeth or the timing chain went slack the problem would have been immediate but this developed over about 10 minutes.
 
Sometimes a backfire will blow a power valve. Try putting a rebuild kit in the carb and see if it fixes it.
 
IH engines don't have timing chains. Pretty difficult and damn near unheard of for any part of the timing gear set to "jump" teeth without human manipulation. Yes, teeth can be damaged, but that's generally the result of murder-death-kill lubrication issues prior to catastrophic engine failure. I don't think that's what you have going on. We still don't know for fact what carb you have. Maybe post some good pics if you're unable to id it yourself.
Backfire at the carb is usually indicative of a lean condition or combustion that is either happening out of time or not at all on some cylinders. With the raw fuel smells and wet spark plugs, I'm leaning more towards the latter than the former. Any way that you could have gotten the spark plug wires out of sequence? Is it firing on all 8?
 
scoutboy74 said:
IH engines don't have timing chains. Pretty difficult and damn near unheard of for any part of the timing gear set to "jump" teeth without human manipulation. Yes, teeth can be damaged, but that's generally the result of murder-death-kill lubrication issues prior to catastrophic engine failure. I don't think that's what you have going on. We still don't know for fact what carb you have. Maybe post some good pics if you're unable to id it yourself.
Backfire at the carb is usually indicative of a lean condition or combustion that is either happening out of time or not at all on some cylinders. With the raw fuel smells and wet spark plugs, I'm leaning more towards the latter than the former. Any way that you could have gotten the spark plug wires out of sequence? Is it firing on all 8?
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Carb is a 2300 holly and the backfire was through the exhaust. I know the plug wires are correct and that it was firing on all 8 as it ran fine when I started it up and ran it for about 30 minutes on the day that it quit.
The fact that the plugs are wet after it quits should mean way too much fuel, failed spark or a mistimed spark. Like I said, about everything related to the spark (plugs, wires, points, condenser, rotor, cap and coil) are new or almost new.
Re the "timing chain"....felt kinda dumb when I read that as I helped a guy install a new cam a few years ago:icon_rolleyes:
the gears were in good shape.
 
ron3865 said:
would a blown power valve cause an excessive amount of fuel to be dumped into the intake manifold?
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Yes indeed. A hole in the diaphragm will allow fuel to pass straight from the bowl and into the manifold. You probably won't notice the fuel because the passage is below the throttle plate.
 
Robert kenney said:
yes indeed. A hole in the diaphragm will allow fuel to pass straight from the bowl and into the manifold. You probably won't notice the fuel because the passage is below the throttle plate.
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That's the best news I've gotten on the truck so far:icon_lol:
later on this week I'll pull the carb and take a look. I'll let you know.
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Robert kenney said:
yes indeed. A hole in the diaphragm will allow fuel to pass straight from the bowl and into the manifold. You probably won't notice the fuel because the passage is below the throttle plate.
Click to expand...

Well, you called that one right! I replaced the power valve and dried off all the plugs. Started it up and it ran but really rough with a stink of unburned gas. I kept it going and it started to run smoother after a couple of minutes. In less than 5 minutes it was running like it should. There must have been a lot of fuel in that intake that took a while to burn off.
Thanks again.
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