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

[BigD_83]

I've been chasing my tail for the better part of a week and no amount of reading has me any closer to firing up all four cylinders

Here's the situation:

Compression (#1-4) 160 150 145 155

Tank off and vacuum line plugged with a golf tee

Valves adjusted to midrange clearances

Carbs cleaned per tutorial, all o-rings replaced, float heights set and bench-synch done

Mixture screws out 2 1/2 turns

No timing adjustments by me

Spark on all 4 plugs when grounded to head. Nice fat blue sparks all around

New gas with Seafoam

Freshly charged battery and good charging numbers at idle and 5,000rpm

Starts readily on #s 1/2, but there is absolutely nothing happening in cylinders #3/4.

There is NO gasoline in the airbox (with clean air filter installed).

I can watch the gas being sucked down the line into the carbs at a horrendous rate, and there is a swimming pool flooding #3/4 cylinders, but nothing coming out the overflow onto the engine. Even if I turn the mixture screws in all the way it will not give me ignition on #3/4. I believe I am getting fuel dripping on the ground at the header/muffler connection of #4 (not stock pipes)

Could this be caused by stuck floats? Any other ideas I should pursue?

 

[BassCliff]

Hi,

Forgive the silly questions.

Are the spark plug cables in the right place? Normally the left coil fires #1 and #4, the right coil fires #2 and #3. Have you tried new spark plug caps?


Thank you for your indulgence,

BassCliff

 

[Guest]

You could switch around the input leads to the coils at the bullet connectors (at least on my GS1000), then switch around the plug wires from 1 and 2, and 3 and 4. I have done this on my bike and it's still set up this way (one day I'll have to change them back). Then you can see if anything changes. But check to see that you got your plug wires correct first.
It's unusual to have those two cylinders not working especially when they get two different timing inputs, unless you got your plug wires crossed, like maybe 3 & 4. Do 1 & 2 fire at the same time?
1 & 4 fire at the same time as do 2 & 3, but 1 & 4 are on different timing from 2 & 3.

 

[SqDancerLynn1]

As Cliff mentioned sounds like crossed plug wires !!!

 

[BigD_83]

Basscliff and Steve,

I should have put that info out there in the original post. Yes, the left coil is hooked up to #1 and #4 and the right coil to #2/3. I have not tried it the other way around.

I have swapped both the leads (1 to 4 and vice versa AND 2 to 3 and v.v.) and the plugs side to side, with no change in the pattern; #s 1 and 2 continue to combust with nada from 3/4. With the plugs out, 3/4 are firing at different times when the engine is cranked, but I have not tried the igniter test yet.

The plugs are new. I cleaved 1/2" off the leads and put the caps back on in case there was some corrosion in the wires at the caps. The primary and secondary resistance of the coils came in spec, although the primary is a little high (4.5 Ohm vs 3.0), but is the same for both coils. There is very little resistance across the isolated caps

Steve (sedelen): I hadn't thought of doing that. I don't understand which bullet connectors you mean. Do you mean the spade +/- connectors at the coils, or something at the igniter?

I do have new caps on the way, but the pattern suggests to me this is more likely a carburetor issue. My gut feeling is that the new caps are not going to be the answer, but I'm very new to all of this, and open to any ideas.

 

[BigD_83]

As Cliff mentioned sounds like crossed plug wires !!!

It does sound like it, so I'm going to have another look right now. I swear if that's what it is I'm hanging up my wrench for the night.

 

[BigD_83]

It does sound like it, so I'm going to have another look right now. I swear if that's what it is I'm hanging up my wrench for the night.

Nope,

all the wires were hooked up correctly. For laughs I tried swapping them around (left coil onto 2 and 3, right to 1 and 4). Nothing at all...that's good, because that says they are hooked up correctly

 

[BigD_83]

So, if all the leads are hooked up properly and I'm getting good spark and compression, then I guess I should be looking internally.

Hypothetically, could a maladjusted float lead to this kind of fuel dumping into the carbs?

I tapped the bowls and couldn't effect a change. Still flooding #3/4.

Which is more likely, a stuck float, or some POC (technical microscopy term here- piece of crap) in the needle valve seat?

Is there anything else I could be missing before I pull the carbs off yet again?

 

[tom203]

There is NO gasoline in the airbox (with clean air filter installed).

I can watch the gas being sucked down the line into the carbs at a horrendous rate, and there is a swimming pool flooding #3/4 cylinders, but nothing coming out the overflow onto the engine. Even if I turn the mixture screws in all the way it will not give me ignition on #3/4. I believe I am getting fuel dripping on the ground at the header/muffler connection of #4 (not stock pipes)

Could this be caused by stuck floats? Any other ideas I should pursue?

This amount of gas suggests carb float problem. It looks to me that that on this model, the carbs are tipped slighty to engine, so overflowing gas would run first towards there and not to airbox. Remove the carb sync port screws and see if gas pours out when petcock is in prime spot.

 

[BigD_83]

This amount of gas suggests carb float problem. It looks to me that that on this model, the carbs are tipped slighty to engine, so overflowing gas would run first towards there and not to airbox. Remove the carb sync port screws and see if gas pours out when petcock is in prime spot.

Will do. Tom203...can you clarify what you mean by the carb synch port screws?

 

[bccap]

I think he means the screws you take out to put your synch tubes in ?

 

[BigD_83]

runs with vacuum port OPEN

runs with vacuum port OPEN

Here's the update:

Took the screw out of the carb synch port with a fuel line gravity feeding the carbs and no fuel dripped out. Drained the bowls and there seems to be the right amount of fuel in the bowl.

Couldn't get my fuel level gauge screwed in with the bowls in place...there doesn't seem to be enough room under the carb for the tool (Suzuki part)

Here's the strange part:

I got combustion on #4 by starting the engine with the vacuum port OPEN. This is just screaming carburetor (too much fuel) issue. Stranger still, I was getting combustion in #3 as well. Perhaps tapping around with the screwdriver DID do something there.


I know a vacuum synch MIGHT help here, but I can't get it running well enough on all four cylinders to do it. Unless anybody has any suggestions, it looks like it's time to pull the carbs, check the float on #4 and bench synch it again.

 

[BassCliff]

Hi,

OK, it seems you've eliminated spark as the issue. I think you are correct in taking a closer look at the carbs. Perhaps you have a float that's not actually floating? Do you have wet plugs in #3 and #4?

With the vacuum sync port open you are drawing more air into that cylinder. Since it started firing I would suspect too much fuel going into that cylinder. I think you're on to something. Check the carbs to be sure everything was reassembled and adjusted properly.

Did you use aftermarket float bowl gaskets? Sometimes you have to remove a punch-out or two in order to make them the same as the OEM gaskets. All four float bowl gaskets might not be exactly the same.

Thank you for your indulgence,

BassCliff

 

[BigD_83]

Thanks for the headsup on the gasket BassCliff. I have an OEM gasket installed that still works.

I pulled the carbs and had a look at everything and nothing appears out of place. Readjusted the float heights in #s 3 and 4 as they were around 19.5mm. I really do not understand that one as I reset the float heights back in the summer.

Put it all back together with a new bench synch, and managed to get it going, but again, no combustion in #s 3 and 4, and plenty of gas making it into the cylinders. VERY wet plugs. I do not want to run it for very long in that condition as I'm afraid that much gas in the cylinder and exhaust will cause some damage, and if it ever does catch it could be disastrous...

That being said, I was able to get the CarbTune on to attempt a vacuum synch. Let's just say that's going okay, but I'm terrified that something explosive might happen.

 

[BigD_83]

got a little backfiring and popping...but no vacuum reading on #2

got a little backfiring and popping...but no vacuum reading on #2

Went back out for attempt #2 on the vacuum synch, and I'm getting good readings on 3 of 4 cylinders, plus a little backfiring and popping on #s 3 and 4, so I'm getting closer to resolving this combustion issue.

I am getting no reading on cylinder #2 with the Morgan Carbtune. I changed the line over with #1 and the problem followed it, so I know it is not the instrument.

I wonder how this is possible? Could the bench sync be so badly off that I wouldn't be able to get a vacuum reading on one of the two working cylinders, and still have it running? If I am getting no reading, does that mean no air is being sucked past the butterfly into the cylinder (i.e. not open enough)? There's obviously enough to get combustion as the #2 header is getting hot to touch, but that must mean the fuel mix is a little lean.

I guess there could be a leak in the line itself. Will hit it again in the morning.

 

[BigD_83]

Vacuum leak diagnosis using CarbTune

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?

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.