4.3LX & Weber Carb Service

[Lou C]

Repeat the comp test with a hot engine ignition disabled and throttle valve & choke wide open. Mine has always been between 160-170 psi. If yours tests lower on 1 or more cyls you have to find out where the loss of compression is. A common cause is sticking or burned valves.

 

[dubs283]

The video linked in post #1 shows what I would say is close to normal operation for your engine with a weber carb and choke stove

The stove cover for the choke coil spring appears missing which accounts for the extended period choke operation along with running the engine on muffs at an idle (no load). Takes a long time under these conditions for the engine to fully heat up to spec temp. Not to mention weber carbs are basically toilet bowls and run pretty rich at startup with no load

The choke stove assy, when fully operational is designed to open faster than you recorded when under a load. The engine assy heats up faster and the stove cover keeps heat surrounding the spring

For your latest post with compression numbers seeing 95, 120, 140 and 160 doesn't mean much for a cold engine not run for six months especially if it was fogged at layup. The 95 might be concerning but it's best to get the engine running under a load for 10- 15 mins to clear it out. Then do a compression test with warm engine.

As far as getting the engine running it sounds like the carb is flooding out. Can't say as to where you're at with it but it's an indicator of wrong float height, bad needle/seat, plugged idle circuits, too high fuel pressure (9-10 psi sounds high but is probably okay with a sound carb), incorrect timing, etc...Probably means going through the carb again and setting up with quality parts

 

[Swedefj40]

Compression is way off
Seeing 95 to 167 is to much of a span. How your doing the test and accuracy of gauge can have a bearing but my also be engine problems

It use to fire up and run rough but not hardly fires and when it does there is backfire. So check spark and timing

Spark is there and I checked the timing. It hasn't fired at all this spring, just backfires. I disconnected the12v to the fuel pump when I checked the compression and no backfire then.

 

[Swedefj40]

Repeat the comp test with a hot engine ignition disabled and throttle valve & choke wide open. Mine has always been between 160-170 psi. If yours tests lower on 1 or more cyls you have to find out where the loss of compression is. A common cause is sticking or burned valves.

I did all that you said minus the hot engine due to it not being ale to start. I'm suspecting the valve in cylinder #3.

 

[Swedefj40]

The video linked in post #1 shows what I would say is close to normal operation for your engine with a weber carb and choke stove

The stove cover for the choke coil spring appears missing which accounts for the extended period choke operation along with running the engine on muffs at an idle (no load). Takes a long time under these conditions for the engine to fully heat up to spec temp. Not to mention weber carbs are basically toilet bowls and run pretty rich at startup with no load

The choke stove assy, when fully operational is designed to open faster than you recorded when under a load. The engine assy heats up faster and the stove cover keeps heat surrounding the spring

For your latest post with compression numbers seeing 95, 120, 140 and 160 doesn't mean much for a cold engine not run for six months especially if it was fogged at layup. The 95 might be concerning but it's best to get the engine running under a load for 10- 15 mins to clear it out. Then do a compression test with warm engine.

As far as getting the engine running it sounds like the carb is flooding out. Can't say as to where you're at with it but it's an indicator of wrong float height, bad needle/seat, plugged idle circuits, too high fuel pressure (9-10 psi sounds high but is probably okay with a sound carb), incorrect timing, etc...Probably means going through the carb again and setting up with quality parts

Yeah, the carb is the only thing changed from last year, and it ran pretty good then. It's likely the issue... I hope. Thanks for the info.

 

[Scott06]

I did all that you said minus the hot engine due to it not being ale to start. I'm suspecting the valve in cylinder #3.

Yes if you checked timing and backfire would do a leakdown test . You also can just put compressed air into cylinders and see if it leaks back to intake.

 

[Lou C]

Any leakage around the joint between the manifold & elbow? That can cause sticking valves.

 

[Swedefj40]

Update... Well I pulled the new carb off the engine. I then put the old carb back together with the divorced choke and reinstalled it on the engine without the 1/2" phenolic spacer and Vroom!!! She fired up right away! I let it run up to normal operating temp then shut it down and checked the compression again. Much better readings this time:

Cyl #2 & #6 - 180 PSI
Cyl #1 @ 165 PSI
Cyl #3 @ 135 PSI
Cyl #4 @ 140 PSI
Cyl #5 @ 155 PSI

I still want to switch to electric choke and put the spacer back in. I may just run the old carb this season and consider switching to the Holley Marine Sniper EFI in the future. I dunno. The top plate air horn assembly is cracked along the divider between the primary barrels and I'm a little worried that it may break off and get sucked into the engine. That's my only concern.

 

[Scott06]

Update... Well I pulled the new carb off the engine. I then put the old carb back together with the divorced choke and reinstalled it on the engine without the 1/2" phenolic spacer and Vroom!!! She fired up right away! I let it run up to normal operating temp then shut it down and checked the compression again. Much better readings this time:

Cyl #2 & #6 - 180 PSI
Cyl #1 @ 165 PSI
Cyl #3 @ 135 PSI
Cyl #4 @ 140 PSI
Cyl #5 @ 155 PSI

I still want to switch to electric choke and put the spacer back in. I may just run the old carb this season and consider switching to the Holley Marine Sniper EFI in the future. I dunno. The top plate air horn assembly is cracked along the divider between the primary barrels and I'm a little worried that it may break off and get sucked into the engine. That's my only concern.

The spacer was probably creating a vacuum leak. Why are you hung up on using it? If its working I wouldn’t bother converting the choke and spending money on the sniper, too many mixed reviews

 

[Swedefj40]

The spacer was probably creating a vacuum leak. Why are you hung up on using it? If its working I wouldn’t bother converting the choke and spending money on the sniper, too many mixed reviews

Just trying to lessen the heat soak. Maybe it'll be better with the floats adjusted properly and the rebuild done on it. We'll see.

 

[Swedefj40]

One other thing... when I was having the issues, I had removed the divorced choke's heater and just left the mounting point on the manifold as I assumed it was just a spot for the heater to mount too. There is a small hole (pilot?) that the heater lines up on, in it. Is this just a hole to align the heater or is it open to the manifold runner and I just created a vacuum leak by not covering it?

 

[Scott06]

One other thing... when I was having the issues, I had removed the divorced choke's heater and just left the mounting point on the manifold as I assumed it was just a spot for the heater to mount too. There is a small hole (pilot?) that the heater lines up on, in it. Is this just a hole to align the heater or is it open to the manifold runner and I just created a vacuum leak by not covering it?

I believe this is mounted in the exhaust cross over so would not affect vacuum (intake) side of manifold. There could be an exhaust leak depending on how it is set up. On older cars that had an integral choke with heat tubes coming up from the crossover there was a air tube inside the cross over, unless this rotted out there would be no leak. Would assume there is some separation between the divorced choke thermostat and the exhaust passage but could be wrong

I believe there is a vacuum pull off on these carbs that could leak if tubing is cracked etc

 

[Swedefj40]

Well I was planning on launching the boat today and while I was checking the oil level in the driveway I found the oil level was slightly over filled and chocolaty in colour. I unscrewed the filter a bit and this what came out.

 

[Swedefj40]

The old girl is really fighting me this year

 

[alldodge]

It's has water in the oil

 

[Swedefj40]

Yup

 

[cyclops222]

Weber carbs ARE A DIFFICULT / IMPOSSIBLE carburator for American DIY people to play with or get right. Especially if on the wrong sized engine.

 

[Scott06]

Weber carbs ARE A DIFFICULT / IMPOSSIBLE carburator for American DIY people to play with or get right. Especially if on the wrong sized engine.

Why do you say that ? The AFB/weber/ edlebrock carbs are generally regarded as easy to tune. I have certainly found that on both my boat and 65 GTO

 

[cyclops222]

If nobody pulls it apart and starts changing fuel and air metering tubes for 5 stages of metering tubes? NO problem.

 

[nola mike]

Weber carbs ARE A DIFFICULT / IMPOSSIBLE carburator for American DIY people to play with or get right. Especially if on the wrong sized engine.

Edelbrock has a whole handbook dedicated to tuning it. And you could say this for any carb.