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Engine timing problems

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A vacuum leak might be the problem. There are two drain tubes on the bottom of the intake manifold - one up front and one in the rear. After some engine work, my BJ7 wouldn't idle below 2,000 rpm. Rear drain tube was completely missing. Putting one on solved the problem.
Bob
 
If it is running 40-60 seconds at 2000 rpm and stopping, it is a fuel problem not an electrical. It is either getting too much or too little fuel. So, it is a process of elimination. Two quick questions first, when it starts to die, does pulling the choke on do anything? When you turn the key on, but not to start, does the fuel pump make a few ticka tickas then stop and stay stopped or more tickas after a bit. That would indicate the float valve is not sealing and it is flooding out.

I'm thinking float valve or floats that don't float. Sounds like it is just running off the gas in the float or flooding out. These need to be checked.

I know you think the fuel system is good but there could still be something off in the fuel system such as:
- a clogged gas cap vent,
- a crack in the pick up line allowing it to suck air with gas (happened to me)
- a pump with too much fuel pressure
- a pump that flows when tested under no pressure but doesn't flow well against pressure
- clogged filters, new ones that clogged again, a filter you don't know about
- crud in the line
- partly blocked pickup tube in the tank.
- loose fuel line clamp somewhere
- fuel pump problem
To eliminate all of the preceding, take a small container of gas and run it directly to the carbs. Make sure the gas container is above the carbs so it will gravity flow. Use good gas. Make sure the screens in the carbs are clean.

If it still dies after 40 seconds, other possibilities are water in the carb, an obstruction in the carb. Won't hurt to spray some carb cleaner in the main jet and in the low valve.

Tell us more history. Was it running okay? Come on suddenly? Anything been changed on the car?
 
Andy,

thanks for your input.

What you suggest makes sense but Im not convinced its anything to do with the fuel feed before the carb. I have checked the pump and it stops ticking when the system is primed. Also I have checked the float bowls after the car stops running and they are always full. The car is almost impossible to start even with full float bowls.
Must be something to do with the carb? Its had new jets and needles?

As for history, its all in this post. Not much else for me to replace or look into?
 
Jeepster

Have you got the timing right now, I was a cylinder out when I first tried to start mine after a rebuild, with banging in the silencer etc. released the clamps and rotated the dizzy until she picked up, took a while so sort that out.

Go back to first principles, the minute the engine dies on you, check for sparks on all the plugs. I have bought 6 spark plug testers that fit between plug and leads so that you can see what is happening on each plug as you try and start it up, great for fault finding on the plugs / dizzy.

Check to see if they are wet after trying to start it up again - petrol getting through. If they are dry after several attempts then the carbs may be at fault.

My car never ran right, from the day I bought it and I found that the lead from the coil to the dizzy was partially to blame. Replaced it and it did help. However it was still not running properly and some where down the line the LT wire in the dizzy was possibly causing problems as the insulation was cloth and looked very dodgy, and the earth wire from the fixed plate to the condenser used to part company as the top plate moved and further more the star spring under the fixed plate had a leg broken off. I suggest that you check all these items out.

:cheers:

Bob
 
I re-read your posts. Key points: It got worse gradually. This sounds like the fuel sealer again. The step technique with the carb jets improved it from running a few seconds to 40 seconds or so. Sounds like the jet adjustment is compensating but not enough. I still don't see where the screens in the carb have been cleaned or that the passage behind the screens has been spayed with carb cleaner. The screens are under the banjo bolt. Have you found them?
- If the float is full, is the passage from the bottom of the float bowl to the jet absolutely clean and clear? When you take the piston off and lift the jet, does it squirt fuel as it should?
- Get some starter fluid, take the air filters off, and before it starts to die, spray some in. If it recovers for a moment then it is a fuel problem. It is sounding like an obstructed passage way between the float bowl and the jet or the jet itself.
- Consider putting the old jet and needles back in.

- Just to be safe, replace the fuel filter even though you just did. Blow though it compared with a new one.
Is it possible some more sealant is obstructing somewhere?
Electronic ignitions are funny. It may prevent the engine from revving over 2000 rpm but I can't think of why it would run for a minute then stop.

The starter fluid (spray ether) should narrow down the problem.
 
Andy65 said:
I re-read your posts. Key points: It got worse gradually. This sounds like the fuel sealer again. The step technique with the carb jets improved it from running a few seconds to 40 seconds or so. Sounds like the jet adjustment is compensating but not enough. I still don't see where the screens in the carb have been cleaned or that the passage behind the screens has been spayed with carb cleaner. The screens are under the banjo bolt. Have you found them?
- If the float is full, is the passage from the bottom of the float bowl to the jet absolutely clean and clear? When you take the piston off and lift the jet, does it squirt fuel as it should?
- Get some starter fluid, take the air filters off, and before it starts to die, spray some in. If it recovers for a moment then it is a fuel problem. It is sounding like an obstructed passage way between the float bowl and the jet or the jet itself.
- Consider putting the old jet and needles back in.

- Just to be safe, replace the fuel filter even though you just did. Blow though it compared with a new one.
Is it possible some more sealant is obstructing somewhere?
Electronic ignitions are funny. It may prevent the engine from revving over 2000 rpm but I can't think of why it would run for a minute then stop.

The starter fluid (spray ether) should narrow down the problem.
Click to expand...

Yesterday afternoon my mechanic and I spent five hours trying to sort the problem. We are both at a dead end.
Carbs were removed and re cleaned. All passages cleaned and ok.
Tank, filter pump, fuel lines cleaned and checked. ( can't be this as we always have a full float bowl).
The engine fault does seem like fuel starvation but we can't see what is causing this.

It must be something to do with the new jets or needles. I cant put the original jets in as they were the cause of the initial problem as they were perished. I am going to re fit the original needles today to see if there is any improvement. I checked the size and they are both UH ( std on old and new).
 
The old original needles are in and no improvement.

I just dont understand how fuel can be getting to the jets but not into the cyclinders?
 
I'll suggest what I (and several others) have suggested before: a vacuum leak. The car runs fine until things begin to heat up and expand, which opens up a crack somewhere. It's kind of a long shot, but it sounds like you've exhausted most other possibilities.
 
Keith_M said:
I'll suggest what I (and several others) have suggested before: a vacuum leak. The car runs fine until things begin to heat up and expand, which opens up a crack somewhere. It's kind of a long shot, but it sounds like you've exhausted most other possibilities.
Click to expand...

I wish it were that simple.
The car doesn't run fine until it warms up, it won't start for ages and then when it fires i get about 40 seconds of running.
Not much difference with it hot or cold. Tried looking for leaks by spraying around manifold etc.
it is fuel related as the plugs are dry when it struggles to start. Fuel at the jets and squirts out when you apply choke?
Its as if the fuel can't get past the jets and into the cylinders? But no blockages anywhere.
 
Jeepster said:
I wish it were that simple.
The car doesn't run fine until it warms up, it won't start for ages and then when it fires i get about 40 seconds of running.
Not much difference with it hot or cold. Tried looking for leaks by spraying around manifold etc.
it is fuel related as the plugs are dry when it struggles to start. Fuel at the jets and squirts out when you apply choke?
Its as if the fuel can't get past the jets and into the cylinders? But no blockages anywhere.
Click to expand...
I had a starvation problem several years ago and it wasn't until I diconnected ALL of the fuel lines and blew them out with an aircompressor did the problem get fixed. Dirt in the lines plus the fuel tank sealer decided to try and travel up stream to the carbs(I had to cut out a section of fuel line to remove that blockage!). Just a thought since you've done just about everything else. Yes, I spent a small fortune on replacing parts that were not bad.
 
Did you try spraying the starter fluid into the carb? Result? Spray some in and see if it starts better and runs a few seconds longer. Full float bowls don't really confirm a lot. Just because they are full doesn't mean they are working. A stuck float will leave a full carb. A float that that has a leak and doesn't float fully will leave a full bowel. The engine could be using fuel in the bowl then starving then bowles refilling when the float drops. However, I think it is unlikely both carbs would have float problems at the same time unless they were disassembled and reassembled wrong. (I've seen floats put back wrong way). At this point I only see two actions to isolate the problem. Starter fluid because it bypasses the jet entirely by going straight to the engine. Connect an alternate fuel supply directly to the carb gravity feed. You may not think the gravity feed is necessary but you can't skip in the process of elimination. For example, I had a pump that filled the jar just fine so it couldn't be the pump. Wrong. The aftermarket pump put out too much pressure. You must do both these tests to isolate the problem to determine for sure if it is between the float and the jet. After you do these tests take a tube and blow fuel or gravity and watch it go into float and out the jet. It should flow continuously. Don't let too much raw gas into the cylinders though. Moving the level and see gas is good but this tests if it flows unaided.
 
Another idea:
The float bowls need venting and have overflow tubes. Have you tried running the car with the float bowl lids off ? Disable the electric fuel pump and fill the bowls manually if and when fuel is needed, once it gets started.
Bob
 
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