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

[BigD_83]

I'm still thinking fuel starvation, but I'm not sure how to prove it...it's pouring rain, I don't have the bike insured right now, and it's very difficult to keep it puttering around the city at 2500 rpm to do a plug chop.

One thing I haven't tried is just cranking the main idle speed adjuster to the stumble point. If it runs nicely there (no stumble), then it would suggest that it is the rate of change in the opening of the butterflies that is causing the problem, which would be more indicative of a vacuum leak/inconsistent vacuum/mixture ratio problem rather than a frank lack of fuel.

How high SHOULD the rpms go on these 650s with full choke, at startup?

 

[bccap]

I don't usually use full choke. But I just tried it, 3800 rpm, on my bike.

 

[BigD_83]

I don't usually use full choke. But I just tried it, 3800 rpm, on my bike.

Thanks, Garth...

When I got home tonight I flipped the petcock over to PRIME and fired it up. First time it scared me a bit so I killed it. I then left it on full choke to see where the RPMs got to. The final number was 4200. Boy, that seems awfully fast for a bike that hasn't warmed up yet.

 

[BigD_83]

Replicating a problem...

Replicating a problem...

Don't you hate it when you try to replicate a problem and can't do it?

That was ALMOST the case tonight. After starting the bike up tonight on PRIME and letting it run there for awhilie, I switched to ON again, and had no problems running it up and down through to about 1/2 throttle (6000 rpm?) It remained that way for a few minutes (up to maybe 5) at which point the stumble came back at very small throttle turns (less than 1/8th). EDIT-I did not take it to full throttle.

The engine died, and I fired it right back up again with no choke but on PRIME and it started like a trooper. No complaints whatsoever...after a short time, I switched it back to ON for a second time, and this time around I couldn't get it to bog or stumble at all.

I ran it for a minute or so at 3000rpm and chopped the engine. The plugs were all a little sooty with the exception of #2, which was a little on the lean (whitish) side. Cleaned them up, put them back in the bike, and it started up again with no hesitation. Again, I couldn't reproduce the stumble.

It would be presumptuous of me to call this a victory, but I'm finally to the point where I'm not worried the engine is going to cut out on me at lower rpms. I'm ready to take it the street on the next dry spell to see how it performs through the various throttle positions/rpms and gears.

If all goes well, I can start thinking about another oil and filter change, replacing the brake lines and pads, and getting all of the luggage racks mounted.

 

[tom203]

Thanks, Garth...

When I got home tonight I flipped the petcock over to PRIME and fired it up. First time it scared me a bit so I killed it. I then left it on full choke to see where the RPMs got to. The final number was 4200. Boy, that seems awfully fast for a bike that hasn't warmed up yet.

I don't let it go over 3000 and try to keep it under 2000, though it's very erratic for 15 seconds- it's better to wait for oil to get pumping then let it scream.
Anyways,sounds better, so maybe you just need to run it awhile to refresh its memory. keep your eye on the petcock, take a peek at #2 plug after a ride.

 

[BigD_83]

I don't let it go over 3000 and try to keep it under 2000, though it's very erratic for 15 seconds- it's better to wait for oil to get pumping then let it scream.
Anyways,sounds better, so maybe you just need to run it awhile to refresh its memory. keep your eye on the petcock, take a peek at #2 plug after a ride.

GSJim's post this morning has me reinvigorated. Seeing my bike twin in such nice shape has motivated me to get more done. The PO is going to be blown away by how easily it starts up and how strong the engine is now.

My girlfriend asked this morning where we would go for a ride. I don't think heading north this weekend is the answer she wanted to hear, and I don't think she wants to take car and motorcycle to SoCal this Christmas.

I think I can keep the revs around 2500 if I only use 1/2 choke at startup. Could the higher RPMs be an indication of richness in the pilot circuit, or is that completely separate from the choke circuit? Would leaning out the mixture screws help with that, or should I just leave well enough alone until I can get some miles on the bike?

 

[bccap]

That's pretty much what I do. I try to set the choke so it will fire around 2000, but often its 2500. Then set it around 2000 for a few seconds,then down to 1500 and let it warm up, or just go if I'm in a hurry. Maybe stick some oil down the cable, and make sure that there is a little play to make sure the choke is off, when you turn it to off. I'm not sure that 5000 is unreasonable, but one of the carb guru's would have to verify that.

 

[BigD_83]

That's pretty much what I do. I try to set the choke so it will fire around 2000, but often its 2500. Then set it around 2000 for a few seconds,then down to 1500 and let it warm up, or just go if I'm in a hurry. Maybe stick some oil down the cable, and make sure that there is a little play to make sure the choke is off, when you turn it to off. I'm not sure that 5000 is unreasonable, but one of the carb guru's would have to verify that.

Cap,

Yup, there's definitely enough free play in the choke, maybe a bit too much, but not enough to affect it's action.

We'll have to get out for a ride next weekend if the weather is favourable

 

[tom203]

Put some miles on this thing- getting it up to high temp might wake it up! As far as I can see, the "choke" circuit all by itself is able to add fuel and air in enuff quantity to let revs go way up. I take off with choke on about 1/4, but when I pull out on main street and apply throttle, I've noticed hesitation till choke is fully off, so the choke circuit definitely interferes with vacuum slide operation.

 

[BigD_83]

grip it and rip it!

grip it and rip it!

Put some miles on this thing- getting it up to high temp might wake it up! As far as I can see, the "choke" circuit all by itself is able to add fuel and air in enuff quantity to let revs go way up. I take off with choke on about 1/4, but when I pull out on main street and apply throttle, I've noticed hesitation till choke is fully off, so the choke circuit definitely interferes with vacuum slide operation.

...will do. Then we'll see if the high-heat gremlins come out of their hiding spots and start messing with the coils :-#

 

[bccap]

Cap,

Yup, there's definitely enough free play in the choke, maybe a bit too much, but not enough to affect it's action.

We'll have to get out for a ride next weekend if the weather is favourable

Derrick, you forget I just renewed my insurance. It's gonna RAIN for three months straight. But if it doesn't I'm in.

 

[tom203]

...will do. Then we'll see if the high-heat gremlins come out of their hiding spots and start messing with the coils :-#

I trust you have reviewed the charging situation. At the very least , make sure you have good ground from R/R ground to battery negative- do not rely on the factory hook up, unless you plan to have a rescue vehicle follow you around! I found the ignition system very reliable- worked even with poor charging/weak battery.

 

[BigD_83]

I trust you have reviewed the charging situation. At the very least , make sure you have good ground from R/R ground to battery negative- do not rely on the factory hook up, unless you plan to have a rescue vehicle follow you around! I found the ignition system very reliable- worked even with poor charging/weak battery.

Hi Tom,

Yes. I had a bit of a charging/starting issue when I first got the bike so I pulled the wiring had cleaned everything up nicely, especially the rusty ground points. At the time my multimeter was ok, but since then was destroyed in a flood so I've been without. BCCap was nice enough to drop his digital mm off and we've retested the charging of the battery and that was good. The coils (still factory AFAIK) have been giving inconsistent readings, but so far have been within spec.

So far there haven't been any hiccups I can't attribute to fuel, so fingers crossed the electrical will hold up. Winter is coming fast, which just means cold rain/sleet/slush here most of the time, but in the last couple of years we've had extensive periods (up to 10 weeks) of snow and ice on the ground. That's not much compared to what happens in the Rockies and to the east, but it'll provide plenty of time to pull the harness and do some of the mods if necessary

 

[BigD_83]

So much for mods over the winter. A trip down south and a bunch of other commitments kept me away from the bike. Apart from winterizing it (fogging oil in cylinders, Stabil in gas), I didn't get much done until the last few weeks when I pulled the engine with BCCap's assistance, got the header bolts drilled out, new helicoils in, and a BUB 4 into 1 header installed (minus the pop rivet). New tires on. New SGP petcock. New Rotella.

Nothing else has changed since I adjusted the valves in the fall. There are no miles on the engine since.

New eurobars on and waiting on new control cables.

I had the battery on the charger/tender (low amperage with a maintenance mode) and everything is reinstalled. Primed it, and I expected the bike to fire up like it had before Christmas...no fire at all, not even a chuff. It turns over strongly, I have compression (cold #1-4: 155 135, 140, 155) and spark (all four plugs evidenced by a nice blue spark outside the combustion chamber). There is fuel in the bowls, and it smells like there is some gas getting to the cylinders (at least #1 and 4), but not flooding with repeated cranking. The plugs are dry though. This is different than in the fall when the cylinders were flooding and pulling the plugs showed them to be very wet.

I checked the fuel flow from the petcock and it flowed fine on Prime when not attached to the carbs and didn't flow with the petcock in the ON or RES position.

Tapped around on the float bowls with the pommel end of a screwdriver to see if the floats were stuck closed with no difference.

What might I be missing here?

 

[tom203]

Make sure "choke" is operating fully at carbs. You've done all the right testing. Me, I'd restrict air cleaner element or block opening somehow and then crank it to see if you can get some more fuel up into carb throats.

 

[BassCliff]

Hi,

There is fuel in the bowls, and it smells like there is some gas getting to the cylinders (at least #1 and 4), but not flooding with repeated cranking. The plugs are dry though.

Even though there was Sabil in the gas tank, I suppose it's possible that the carbs got gummed up while sitting over the winter. I don't know if you'd want to try and clean them out with a couple of cans of carb cleaner or just go for the full strip and dip.


Thank you for your indulgence,

BassCliff

 

[BigD_83]

I'm not averse to stripping and dipping, but I am surprised at the change, based on other GSers experience with Stabil and "winter" storage. I wonder if storage effects could be worsened in warmer climates, with higher rates of fuel evaporation?

Is there a special tool one may use to drop the fuel bowls with the carbs attached? I guess a ratchet with a JIS driver would be just the ticket.

 

[Steve]

To clarify, I was using the tank like an auxiliary, with it set on the bench and the petcock on PRIME, with an inline filter just before the carbs, and the vacuum line plugged.

What was the height difference between the bench and the "normal" height when on the bike? :-k

.

 

[BigD_83]

What was the height difference between the bench and the "normal" height when on the bike? :-k

.

I just went out to measure, and the height difference on the bench is + 5.5" over normal. With that setup the fuel line dipped a little lower than, then rested on the left turn signal before connecting to the fuel intake on the carburetor. It seemed that fuel would flow back up hill just enough with the line set that way so there was a little air bubble where the line went back up, and the fuel line wouldn't go dry.

I'm back to having the tank installed.

On a positive note, I did manage to get the bike started tonight, and ran it for about 5 minutes in the breeze at the front of the garage with the fan blowing cold air on the engine. Shut off, start up, shut off, start up. I let it sit for a while as I worked on a couple of other things, and about a half hour later, it wouldn't start.

I'm calling that progress.

I've put the battery back on the charger, and I'll be able to check out its numbers later tomorrow.

 

[tom203]

I have had good luck with Stabil- with bike and outboards. Over months of sitting, the fuel is bound to evaporate and drop float bowl level- this likely keeps float needle shutoff from sticking closed. The choke system picks up from that liitle hole in bottom of fuel bowl - hopefully you got that poked open during cleaning. Even after just 1 hour of sitting off, my bike likes a little choke applied despite engine being too hot to touch.