Intermittent miss on F80TLRA

[JRad]

I'm getting ever closer to fixing an F80TLRA that died on the water 2 seasons ago and wouldn't start at all last season. So far I have done the following...

1 Replaced all of the fuel lines on the tank side of fuel pump
2 Pumped out all old gas and replaced with Startron treated gas
3 Replaced the 10 micron in-line filter
4 Cleaned the on-engine fuel filter
5 Dissembled and cleaned the fuel pump
6 Removed carb/intake manifold assembly
7 Cleaned float bowls / jets with carb cleaner
8 Replaced in-line filter at each carb
9 Installed carb/intake manifold assembly w/new gasket
10 Confirmed all bowls receiving fuel by opening bowl drains

At this point I was able to get the motor to start by pumping the throttle before cranking. The engine would only run rough at about 1/2 throttle, but not idle at all.

11 Pulled all 4 plugs & inspected. Plug 2 & 3 electrodes are black.

I suspect an ignition problem w/clys 2 & 3 so I made up a spark test jig to hold two grounded plugs. Unfortunately I couldn't see spark in the bright sun. I even tried one of the suspected good wires, & still couldn't see spark.

12 Disconnected & reconnected connector on hot side of both coils.
13 Swapped the two black end plugs to cyls 1 & 4 & clean plugs in 2 & 3

At this point the motor started, but again only after pumping the throttle. I was able to get it to run near 600RPM and it seem pretty smooth. After about 10 minutes of run time it coughed (backfire?) and then started to run rough again, requiring more throttle to keep it running.

As it runs at fast throttle, it seems like the missing cylinder wants to fire, but it won't keep firing - kind of intermittent. The intermittent part makes me pretty sure this is an ignition problem, not a fuel problem. It's very possibly a loose connection somewhere.

Next I will pull and clean the grounds at the coil packs. If that doesn't work I need to pull of some covers so I can find the other connectors on the ignition system.

If anyone has other ideas what might cause the intermittent fire please comment.

[jrdonicht]

I had an f80. Great motor but those orifices in the carbs are super small. Just spraying them will not clean them. They need to be soaked and then blowed out. The ticket to keep them carb motors running good is good gas with stable or seafoam in evey tank. Those carbs are finicky.

[JRad]

I had an f80. Great motor but those orifices in the carbs are super small. Just spraying them will not clean them. They need to be soaked and then blowed out. The ticket to keep them carb motors running good is good gas with stable or seafoam in evey tank. Those carbs are finicky.

Thanks. Without dissembling the carbs, I filled the float bowls with cleaner several times and let it soak for an hour or so each time before draining and blowing the cleaner out with air. I'm not saying that this did fully clean everything, but the fact that it wants to run sometimes makes me think that the problem is not fuel. Could an orifice clear for a while, then plug again? It was doing this the day it died too.

If I can't find a loose electrical connection, I'll take it for professional help since I don't have the tools to sync the carbs.

BTW - this motor has had complete carb rebuilds twice. The last time was about 2-3 engine hours prior to the last failure. It did sit for over a month with no stabilizer in it just before the day it died

[jrdonicht]

To bad you do not live closer. I went and bought a carb sync tool just so I could use it on that F80. Makes a big difference. Mine started and ran just as good as any efi. It may not be the carbs but most of the people around here that has had running issues has been those finicky carbs. They need to stay clean.

[jrdonicht]

I also forgot to mention that the factory puts in aluminum plugs where your idle mixture screws are behind.{ they do this so guys like us do not mess with them Mine were way out of adjustment] Do you know if these have been removed so you can adjust them. They would be a slotted head screw by where the lingage is at on each carb.

[JRad]

I also forgot to mention that the factory puts in aluminum plugs where your idle mixture screws are behind.{ they do this so guys like us do not mess with them Mine were way out of adjustment] Do you know if these have been removed so you can adjust them. They would be a slotted head screw by where the lingage is at on each carb.

I know the spot you are talking about and the plugs are there, either original, or replaced by my dealer (not likely).

Would you want to sell the sync tool (I assume its multiple vacuum gauges), or do you still need it ?

[jrdonicht]

I really don't want to sell it. May at some time use it again. Here is the one I bought. It comes with eveything you need.http://www.carbtune.com/

[99yam40]

Dried up fuel and trash will come out of the tank,lines, and pump and plug jets/passages even right after you clean the carbs, so it is a good idea to clean everything and install a 10 micron filter/water separator. Sounds like you need them cleaned again

[JRad]

Dried up fuel and trash will come out of the tank,lines, and pump and plug jets/passages even right after you clean the carbs, so it is a good idea to clean everything and install a 10 micron filter/water separator. Sounds like you need them cleaned again

I do have a 10 micron filter installed. It is about 3 feet upstream of the motor. Before I tried starting, I let fuel shock treated with Startron sit in the lines ahead of the fuel pump for a week, then flushed them good with more fuel. Unfortunately I did not do the same with the carb lines after the pump.

I think its time to by the sync gauges and do a complete carb tear-down / rebuild.

[JRad]

I really don't want to sell it. May at some time use it again. Here is the one I bought. It comes with eveything you need.http://www.carbtune.com/

Thanks for the link.