Spark-check...Compression-check...Fuel-oh Yes...no ignition on #3/4

[BigD_83]

Vacuum leak diagnosis using CarbTune

I found another use for the CarbTune. It is amazingly sensitive to vacuum leaks. As I wrote previously, I was getting good readings from 3 of 4 cylinders, but nothing from #2.

Thinking it might be caused by a partially plugged petcock vacuum line, I removed the hose and plugged it with my thumb...no change.

I then took out the port adaptor, wrapped the threads with plumber's teflon tape and put it back...no change


I got thinking about things and tried cranking the engine with WOT. No movement on the CarbTune from any of the cylinders.

Aha! Perhaps the bench synch had gone off as I had not torqued down the locknuts. I started playing with the synch screw on #2. By massively adjusting it so the butterfly was relatively CLOSED, I was able to get the metal tube to bounce a little when cranking the engine, but nowhere near the same draw as #s 1,3 and 4.

So I started thinking there must be a massive leak around a boot, but I really couldn't see anything jumping out at me except for a very slight difference in the distance from the front of the #2 airbox boot to the little tab on the left side of the carb. Not much, but just a little larger gap than on the rest of the carbs.

I figured I had nothing to lose, so I loosened off all the boot clamps and the main breather/filter clamp and pulled the carbs back a bit while pushing the breather forward. Then while grabbing the carbs and breather box I tightened the #2 boot clamp back down.

Once I got everything back in place...I had a strong reading from the CarbTune on all 4 cylinders. There must have been a slight gap at the bottom of the #2 airbox boot that I couldn't see.

Now I just hope that when I get the exhaust back on tomorrow (different story), my mysterious air/gas ratio problem will be solved on #3/4, and AliGS will run on all four cylinders.

[tom203]

Well, I don't see how leaky airbox boot to carb intake affects vacuum of a cranking engine, but I will think about it while I watch the snowmelt.Gravity feeding the carbs shows no overflow, so where is this surplus fuel in 3 and 4 coming from when 1 and 2 are working? Maybe the choke circuit lines are passing too much in these carbs 3 and 4. Could you temporarily cap off that copper feed tube in bowl and see what happens? I'm grasping at straws, but excess fuel is being suppied somewhere.

[BigD_83]

too much fuel or not enough air?

It could be a leaking choke plunger...there was an unfortunate marriage of the #4 plunger seal with carb dip, and the thing swelled like you wouldn't believe, but rebounded to it's original size and shape. BUT, that was only the #4 plunger. Chef says he has a replacement for me if needed.

I also pulled the exhaust off yesterday to seal some leaks at the joints, and noticed the same oily/sludgy/watery-carbon-gas wetness right where the header pipe mated to the head, but only on the #3 cylinder.

I suppose I could pull the carbs again and swap the plunger to see if the condition follows it. I'm starting to get pretty efficient at reinstalling them

First things first. I have to replace the exhaust and fire the bike up with the carbs remounted and sealed, and see what the newest changes tell me.

You just have to KNOW that the carbs are coming off again though...not a biggie. It's all part of the learning process.

[BigD_83]

Well, I don't see how leaky airbox boot to carb intake affects vacuum of a cranking engine, but I will think about it while I watch the snowmelt.Gravity feeding the carbs shows no overflow, so where is this surplus fuel in 3 and 4 coming from when 1 and 2 are working? Maybe the choke circuit lines are passing too much in these carbs 3 and 4. Could you temporarily cap off that copper feed tube in bowl and see what happens? I'm grasping at straws, but excess fuel is being suppied somewhere.

Tom, I don't want to influence your pondering too much but,

Does this logic work?

1. Vacuum is constantly read, but should be at maximum when the intake valves are open and the exhaust valves are closed and the piston is on a downward stroke.

Assuming 1 is correct then

2. If the butterfly was open too much, then airflow through that carburetor would be unimpeded and airspeed through the carb lower than the other cylinders. If there was a leak at the boot then there would be less resistance to air draw. I see this as the difference between pulling a syringe back with (no leak) and without (leak at the boot) your finger covering the tip.

[tom203]

Remember that an intake stroke comes every other crank revolution which is pretty slow at cranking speed- the colortune liquid has to have decent viscosity or you'd get dizzy watching the intake pulses. But yes, your #1 is correct, but I'm unsure of its significance. My bike will start/idle fine with a blatant airbox boot to carb leak- no filter in place; the almost fully closed throttle plate seems to restrict airflow( this is why it's stressed not to use throttle during startup).
You are pretty cheerful about pulling the carbs ( I'm not looking forward to doing mine) and I think you have no choice,as somewhere somehow fuel is flowing where it should not.

[BigD_83]

Fire in all four pots!

...and the drum roll please.

Exhaust back on, but not fully sealed against the head (darn you broken bolts; not by me been that way for at least a couple of POs) at the moment. It will be a winter project to get those bolts out.

I have combustion on all four cylinders again, and pretty decent readings on the vacuum synch to start. I'm going to assume that raising the float height has helped the situation, because nothing else I have done specifically targets the #3/4 cylinders. They are still running colder than 1/2, but for now I'm just going to revel in their mysterious reappearance.

Maybe I have a in the garage. After all...

HAPPY HALLOWEEN!

[tom203]

Hooray for progress! Maybe it just craved your attention- or was intimidated by your carb removal threats.

[Carter Turk]

Did replacement of the float needle or careful inspection of the seat on 3 & 4 happen? Just a random thought.

[BigD_83]

Did replacement of the float needle or careful inspection of the seat on 3 & 4 happen? Just a random thought.

I had a quick look at the seats when I was in there and blew a bit of compressed air around them but I didn't see anything fly out. I had a really close look at the needles and seats when I cleaned the carbs in the summer and nothing looked awry compared to the ones in #s 1 and 2. If I do have to pull the carbs yet again, I'll take some good high resolution photographs to see if I've missed anything.

Tom...don't let my girlfriend hear you say that. I've spent far too much time with the motorcycle this past week, and she's the one craving attention (..as he veers into Off-Topic Forum)

[tom203]

Tom...don't let my girlfriend hear you say that. I've spent far too much time with the motorcycle this past week, and she's the one craving attention (..as he veers into Off-Topic Forum)

Get her involved! maybe she could remove those broken exhaust bolts for you. Remember, no EZ outs, no screw extractors- get some quality left hand drill bits and a decent penetrant, along with patience.

[BigD_83]

EZ outs and header bolts

She, um...doesn't like getting greasy, and HER bike is pretty much all taken care of for the moment. I'm probably going the welding route to build up a bead and get a nut on the end to help turn those out. It looks like someone may have already snapped an ez out off in one of the bolts

[BigD_83]

NEW info regarding idle jets...

Carter Turk...

in a fit of frustration at the bike firing up but then flooding #s 3/4, I pulled the carbs off the bike yet again, and had a real close look at the differences between the setup of 1/2 and 3/4.

Summary:

Float levels were all the same but my gauge was off, reading closer to 19.4 mm rather than 22.4mm. I reset them all to 22.4mm

The needles and seats all looked fine with no apparent damage to #3/4 and no debris at the seats

All passages were free to air movement

The slides lifted with air pressure

Here's the NEW INFORMATION

While blowing air through the carb, I managed to blow out the rubber plugs over the pilot jets, and along with them the pilot jets from #3/4 carbs. Do you think this might have contributed to too much fuel being dumped into the cylinders?

They either backed themselves off, or more likely, I never tightened them down properly. I checked #1/2 and they were tight, so as far as I could tell that was the only difference.

Got them all back together, resynched, in the bike, and fired it up again. Couldn't run it for long as I was getting a racing throttle due to (I think) binding throttle cable; I definitely have all four cylinders firing, and the plugs are staying dry. A little popping and backfiring from #s 3/4, but I'll take that at this point as I still have a bit of an exhaust leak at the joint where #3 header goes into the muffler receiver. At least I have a better starting point

Time for highest idle and another vacuum synch...

[BigD_83]

now it stumbles off idle...

Fixed binding throttle and set highest idle done and settling in around 2 turns. No time for plug chops but the plugs were fairly sooty running at idle. Tightened up the joints so there was less leaking at the receivers.

Vacuum synch not perfect, but all within 1 of each other (Morgan Carbtune). Note that the pipes are 4 into 2 with no cross-over/collector.

Here's the strange part:

it was running well with the tank off the bike (on PRIME, inline fuel filter installed), with no hesitations anywhere, but as soon as I started running the engine with the tank in place (petcock ON, inline fuel filter removed), it would stumble and die as the rpms hit about 2000-2500rpm. I thought it was due to the vacuum line being disconnected starving the engine of fuel, but hooking it back up hasn't fully rectified the situation. It will go through that rpm, but I really have to goose it. Feathering the throttle kills the engine.

FYI: I have previously tested for it, and the petcock does not leak in the ON position

I am going to switch it over to PRIME to see if it helps, and I think that is the next logical step.

Any thoughts?

[sedelen]

There's a itty bitty vent hole in the filler neck of the tank, make sure it isn't plugged as it will create vacuum inside the tank and not allow fuel to flow as easily as it should.

[BigD_83]

There's a itty bitty vent hole in the filler neck of the tank, make sure it isn't plugged as it will create vacuum inside the tank and not allow fuel to flow as easily as it should.

Thanks, wouldn't that also affect the fuel flow on PRIME?