Two Dead Cylinders on Cold Start

[Anonymous]

My 79 GS 1000 jus developed an illness. The bike when fired up on cold has been running on only two cylinders. The darnedest thing is its running on 1 and 2. It's been running super up until recently. I did a plug chop on the dead cylinders and the plugs are wet with gas. So starvation isn't the issue. If it was coils, wouldn't it be either 1 and 4 and 2 and 3? Plugs have less than 6000 kms. I think I'll start by getting new caps and plugs and see, but any ideas out there?

[Jay Swan]

gs1000 running on 2 cylinders

Hey, Total Recall

I have sort of the same problem, but on mine cylinders 2 & 3 are dead. I was hoping a carb clean up and synch would resolve it but, it did not. Takes 2-3 minutes before they start firing. I can pull on the choke and get all 4 to fire, but when I push off the choke it goes back to just 1 & 4. I will have to keep looking.
If your plugs are wet on those dead cylinders could it be caused by a bad
petc**k diaphram leaking gas into the vaccuum line? That would account for cylinder #2.

Jay

[KEITH KRAUSE]

Did the bike just start doing it? Did you do anything to the bike before the 3/4 firing problem started? Carb work/air/pilot screw adjustments, etc? Any other symptoms...fuel leaking, black exhaust, rust in tank, etc?

[Anonymous]

Two dead cylinders...

I also have the same problem. Starting from cold, the bike fires on two cylinders (1 and 2). A plug chop shows 3 and 4 are getting fuel, so my original thought of fuel starvation/wrong float levels went out of the window...

If I use full choke, I can get it to fire on all four, but pushing the choke in just makes it go back to 1 and 2. Mine doesn't have a vacuum petcock.

So far, I've replaced the plugs, points, condensers and plug leads, and had a carb rebuild/synch. I even re-wired the ignition circuits, suspecting bad connections (yes, I know, but I was running out of ideas). Nothing has made a difference.

Once it has started running on all four, I can kill the engine and it will restart immediately, running on all four. If I leave it to cool down and then try to restart, it's back to being a twin.

I'm out of ideas now, so any help/advice/WAG's would be much appreciated.

[scarr]

My '81 GS650E does the same thing. Two cylinders, not on the same coil, just don't fire right. I've checked everything without success. Using a timing light on the spark plug wires shows a terrible miss on these plugs. If you ever find out what causes this, please email me at faith@frankford.net.

[arveejay]

Sound like carb probs if all will run on choke and not with choke off. Time to tear down the carbs and try cleaning them a little better.

[Jay Swan]

GS 1000 cold start on 2 cylinders

Keith,

My cold start problem has developed over time, I didnt change anything untill the engine started running on 2 cylinders fully warmed up. It would take 30 minutes on the road before it would start doing that. That is when I decided to tear down the carbs and do a clean up. the carb boot o-rings were bad, cracked apart. I thought, wow this is the problem. After the rebuild and repacing o-rings I did a sync, ands the 2/3 cyl not firing still there, choke pulled on, all 4, pull off, only 1 and 4. But after a few minutes started firing ok. I havent done a test drive yet, had a flat front tire, had taken it off because the bead had broken off the rim moving the bike to a better location to remove the tire. Then! I snapped off the fork end cap stud when attempting to loosen the nut. Rats, time to replace all four if one will break off. Waiting on the parts now.

Jay

[KEITH KRAUSE]

Jay, a dirty/varnished carb, pilot circuit especially, fits your problem exactly. I'm assuming you have the VM carbs??? Some following info is for the VM's only.
An intake leak could cause it too, but you've already taken care of that possibility. So it's most likely the pilot circuit. Since you haven't touched the air or pilot fuel screws and the bike ran fine before, we can't blame the screws settings either. But the screws could be adjusted wrong and it could gradually start fouling some cylinders. Without knowing what the PO did, this is a possibility.
With the pilot circuit not flowing fuel correctly, the choke will help, as it does in your case. As it warms up, conditions become richer and this helps your bike, which is running lean, run better, plus the fact that you're running more on the needle circuit as you cruise around and there's less effect from the dirty pilot circuit.
First, be sure you don't have any broken pilot fuel screw tips stuck in the carb bodies. If OK, you need to clean the carbs inside well. Carb cleaner and at least 100 psi compressed air. Keep exact records of how far out your pilot fuel screws are before removal. They may be set at different points too. If any o-rings are hard/bad, I suggest buying the o-ring kits from Robert Barr, a member here. Check/adjust float levels while you have them off. Check/replace vacuum line. By the way, you mentioned #2 carb as the vacuum , not so on VM carbs. #3 is vacuum, #2 and #4 are float bowl vents. #2 is vacuum on CV carbs.
Be sure in any case, to set the side air screws using the highest rpm method. (Use a good fitting tool on the air and pilot fuel screws, they can be tight and the heads easily stripped.) Start with them set at 1 1/2 turns out. Then warm up the bike on the centerstand. Set idle to about 1,000 rpm's. Starting at any carb, slowly turn the side air screw in either direction until you hear the rpm's max out. When they stop rising, stop turning. Find the sweet spot. They generally end up between 1 1/2 and 1 3/4 turns out. Now re-set the idle to 1,000 rpm by adjusting the idle adjuster knob. Repeat until all 4 carbs are set.

[KEITH KRAUSE]

By the way, the fork leg nuts MUST be loosened and tightened uniformly, or breaking the stud is easy. Loosen and tighten in small degrees as you begin loosening or near final torque. To minimize breaking the studs...
The gap between the axle holder and fork leg bottom must be the same after final torquing. The "gap", meaning the space in front and the rear of the axle between holder and fork leg. The axle holder must be very parallel with the bottom of the fork leg body.
Be sure to use blue Loc-tite or equivalent on new studs before inserting into fork leg body. A little anti-sieze for the nuts will help in the future too. Make sure you have lock nuts and washers under the nuts.

[Jay Swan]

VM26 carb adjustment.

Keith, Your are correct, I thought Total Recall had an 1980 GS 1000 with cv carbs.
Mine does have the vacuum port on carb #3.
As for the fork studs, I will get them loctite(ed) in, thanks for the info.
By the way, when I had the VM carbs apart for a clean up, the pilot fuel screws were set to 1/4 turn out from closed. I read in another place in the forum that they should be 5/8 turn, so that is where I set them. That may be one problem with fuel starvation on cyls 2 & 3. You mentioned how to adjust the pilot air screws by rpm, but how do you do a fine adjustment on the pilot fuel screws? And are they 1 1/2 to 1 3/4 out too? Thanks in advance,

Jay

1979 GS1000 E

[KEITH KRAUSE]

Jay, if your problem got worse over time, I doubt the pilot fuel screws are your problem. Sure, if their springs are missing they could move but I really doubt it.
However, 1/4 turn out doesn't sound right. Too lean. There is no set point for these screws. They're the fine tuning for each cylinder and commonly end up set at different points. From the factory, stock intake/exhaust, they're generally from 1/2 to 1 1/4 turns out, with 1 turn out being a good place to start/test. I test/take plug reads for the pilot circuit by cruising around at minimal throttle position (such as cruising in 4th gear at about 35 mph) and of course, focusing on how it starts and warms up. There's some jet needle overlap at this throttle position but it's the best you can do. The pilot fuel screws are very sensitive to adjustments. Keep a record of adjustments and their results. AFTER setting them at the 1 turn out, adjust the side air screws using the highest rpm method. Remember, a vacuum synch is a must to get accurate plug reads/best performance.
I'm not sure what else you've done to fix your problem, but if it continues, your coil feeding 2/3 may have a weaker spark. As a basic check, in a dark area, the spark should be blueish/white and all 4 equal. Be sure the conections at the plug cap and lead are clean and solid. Check for clean/tight terminal connections at the coil. Check the plug wires in a dark area for any arching caused by old wires/cracks. Check plug gap too.

[Anonymous]

Teo dead cylinders

Thought I would give an update on my attempts to cure my starting problems.

My Haynes manual lists the settings for the pilot fuel screws as 5/8 of a turn out, but I agree with Keith, this is far too lean. As a starting point, I set mine to 1 1/2 turns out, which improved the starting immediately. I managed to dig out a Colourtune plug, something I haven't used in 20-odd years, and used this to set the individual pilot fuel screws until all cylinders were registering the same. For folks who haven't heard of a Colourtune, it's a transparent spark plug which you use in place of the normal plug, but being made of glass, it allows you to see the colour of the ignition process. You can vary the pilot fuel settings and see the results.

As Keith suggests, each pilot fuel screw ended up turned out a different amount. In my case, this varied between 1 1/4 turns and almost two full turns. Once the pilot fuel screws are set, then those of you with pilot air screws can adjust them using the highest rpm method as described by Keith.

Something else I'm trying is the use of a carb/engine cleaner additive that you put in the fuel tank. This stuff, made in the UK by Redex, claims to clean the carb internals as you drive. I think that a similar product is marketed by STP in the US. I'll let you know if it makes a difference.

Short version: my poor starting, firing only on two cylinders bike now starts fully and easily. No more running on two cylinders. I'm happy! Many thanks to you all for sharing your thoughts and ideas.

[Jay Swan]

2 cylinders dead on cold start.

Well, I know it's been a few weeks, I got the fork studs in and the front tire back on. The carb clean up and setting the pilot fuel screws to 1 1/2 turns out solved the cold start problem.
Afterwards, a 5 to 10 mile run cylinders 1 and 4 (not 2 and 3 like I thought!) would start to miss for 5 minutes, then completely quit while running on the other two cylinders 2 & 3. It was traced to a bad set of points and condenser for cylinders 1 & 4. Go figure, the set was cleaned at least 2 times, gapped checked 3 times and still was the problem. That was the original problem, now solved. The bike starts up without any choke, idles great. When the weather cools off a bit I will attempt to fine tune the pilot fuel screws, adjust the pilot air screws, and re-synch. Thanks for all the help guys, and you too Keith.

Jay

1979 GS1000E

[KEITH KRAUSE]

Glad the bike's running well!