Starts just fine but needs full choke to idle, smooth above 5k rpm

[nezzer]

I am having a problem with my bike and was hoping some could give me some advice on where to start troubleshooting.

I just finished my annual maintenance- did valve shims, adjust cam chain tension, cleaned air filter (K&N), replaced spark plugs, and changed the oil.

I took it for a test drive and all was well at first. It took a few seconds to start but it was the first ride of the season and about 45 degrees. The choke was all the way open and the bike was running fine as it warmed up. Then it started hesitating badly when I tried to accelerate. If I give it throttle while in gear it bogs down and accelerates at snail speed. If I let off the throttle it goes back to idle and smooths out like nothing was ever wrong.

If I close the choke half way the bike dies, even though by this point its warmed up.

Strangely enough, if I patiently accelerate past 5k RPM the bike feels smooth again and seems to accelerate just fine. Below that though and its dangerously slow and feels incredibly rough.

I have felt this symptom before. For probably the last 2 years the bike has sometimes exibited this behavior when warming up. On a cold day while the bike is warming up and with the choke all the way open, on very rare occasion I give it gas and it just bogs down and refuses to go anywhere. In the past all I had to do was let off on the throttle and let it back down to idle, then reapply the throttle and it was fine. This had only ever occured while the bike was warming up and never occured with the choke closed.

I am sure there are a mutlitude of things to start checking. I just wanted to get some guidance on what to check first.

My gut says its a fuel problem however the fact that it runs fine above 5k rpm boggles my mind. I would think the carbs need cleaning but the bike has been in constant use for at least 5 years, as long as I have owned the bike, and I always put stabile in the fuel and run it for a bit before putting it away for the season.

Now I am rambling. Any thoughts?

Thanks.

[CatatonicBug]

I'm just guessing here, but how about the pilot jets? The enricher ports in the carb throat or the idle circuit may also need a cleaning. I agree that it sounds like a fuel issue. The main jets don't kick in until you reach the higher RPMs, but it's not usually as high as 5k (more like 3k or so), so I'm not sure about it...

Mine was having a similar issue, when starting cold, but once it was warm and the choke was pushed in, it ran fine. Once I cleaned out the jets in the bottom of the float bowls, it starts up instantly, no matter how cold it is.

[bikerphil]

If I close the choke half way the bike dies, even though by this point its warmed up.

Sounds like plugged pilot circuits (idle to 4K) to me. Hate to say it, but it looks like the carbs need a good cleaning. I'd check all 4 for spark first to rule out electrical.

[Ken Talbot]

I am sure there are a mutlitude of things to start checking. I just wanted to get some guidance on what to check first.

4 things to check - carb #1, carb #2, carb #3, carb #4. More specifically, look for all the low-speed cirruits that got gummed up while it was sitting over winter. You might get real lucky and get by with just running some seafoam through, but you might also want to start lining up your tools.

[fredintoon]

Hi Nezzer,
consider that at ~5,000 rpm & above the engine is mostly running on the main jets.
Compared to the sizes of the fuel passages in the slow and mid-rage carb systems the main jet has a hole you could toss a brick through so it won't crud up as easily as the rest of the carb.
So yeah, once you coax the engine up to 5,000 rpm it's quite possible that she'll run great even if the carbs' slower speed circuits are all bunged up with crud.

[nezzer]

Well it unanimous, I should start troubleshooting at the carbs.

I will start pulling them apart this weekend and report back what I find. Thanks for the help.

[dbeardslee]

Might be able to get by with a good dose of Seafoam in the gas (1/2 can). Run it at low speeds for most of the tank to insure thorough cleaning. Then take her out and blow the cobwebs out. JAT

[nezzer]

==== short version =====

Well I didn't bother with spray carb cleaner or seafoam. I went right to a full cleaning of the carbs. The short story is that I am still having a problem, though maybe not the exact same one.

I went to balance the carbs and noticed that the #4 cylinder was not pulling much vacuum, regardless of how much I tweaked the balance screws. The engine is also burning off oil near the top of the #3 and #4 exhaust headers. There is no visible oil leak, its like it is seeping out everywhere. The oil is on the #3 and #4 carb boots and the exhaust headers. The oil flow is very slow but consistent. The exhuast fumes are fine, they are not white so I dont think its burning oil.

I did a compression check and came up with these numbers;
1=120,
2=100,
3=120
4=150

Any thoughts on why the compression on #4 would be higher yet the vacuum is almost non existent?


==== long version ====

I figured it was time I really dug into the carbs since I had never cleaned them in the 5 or 6 years I have owned the bike. As soon as I started taking my carbs off I noticed a problem, carb boot #3 had no screws securing it to the block! Now I just replaced the carb boots a couple years ago. Either I forgot the tighten the screws on #3 all the way and they later fell out, or gremlins took them. I am leaning towards gremlins.


I also noted a strange gunk build-up in the #1 carb. It was slightly in the #2 carb as well. It definatly came from the intake side. The carb boot and into the block looks clean. Maybe it was excess K&N air filter recharger oil. Thats all I can think of anyways. Regardless it cleaned up just fine.


I followed the advice in other posts and picked up a cheapy ultrasonic cleaner, big enough to fit 1 carb at a time.

I first tried it with just plain water. The results were spectacular. As soon as I hit the button clouds of grim drifted off my carb. After about 15 minutes the carb was much cleaner, but the water was not strong enough to get all the gunk off, especially in small nooks. I figured I would give simple green a shot but I read it was harmful to aluminum. I had another degreaser that would straight up eat aluminum. There is a aircraft grade simple green that would do the task but I would have to special order it. As long as I was going to wait for shipping I decided to buy a special built ultrasonic carb cleaning solution. I dunked my carb and 15 minutes later had a carb you could eat off of. I was amazed how clean it was. The water + cleaning agent mixture would start out clear, then after cleaning a carb it would be pitch black from all the grim! After doing all 4 carbs I decided to try cleaning other parts on the ultrasonic. I dunked the bars that hold all 4 carbs together. Again dirt just flew off it. I am now a big believer in the power of an ultrasonic cleaner. I didnt pull all my jets out, just the easy stuff, all the stuff you get in a standard rebuild kit. You might be able to get away with dunking the fully assembled carb in the ultra sonic cleaner. But it doesnt take that long to pull out the floats and such.





Here you can see the difference between a cleaned and reassembled carb and one that has not been cleaned.


Once they were all clean I checked the float level which was fine, no adjustment. I installed new clear fuel line, with new fuel filters, and quick disconnect fittings (I hate disconnecting the fuel line at the petcock, its a pain). All this work and material goes towards my hope that I can avoid cleaning the carbs again for many years to come.

Next I moved on to balancing the carbs since I had never done that before. I picked up a 4 carb balancer. I know there are ones you can make on your own for cheap, but I opted to spend the $ on a commercial unit so as to save my time (and frustration) for troubleshooting the bike.

It was when I was trying to balance the carbs I noticed that cylinder #4 has almost no vacuum. Hmm.



More photos

[dbeardslee]

When you were synching your carbs did you adjust the dampers? When I do mine I usually adjust them so the needles are bouncing a tiny bit so I'm sure I don't have them shut off all the way. What happens if you connect one of the other vacuum gauges to number 4?

[nezzer]

I did adjust the dampeners so the needle was still moving slightly. I didnt think to try the #4 guage on a different cylinder. I will try that next.

[TopCatGr58]

Hey Nezzer,

Others have also suggested that you put each vacuum gauge on just the same clyinder first to see how they measure, there can be slight variations in their readings. I think you can use the dampener screw to adjust how much vacuum is actually being drawn from each gauge, and so you can set each one using the same cylinder to the same level/amount first, THEN you can connect the gauges to the 4 synch ports and do the synch.

I only have/use the single gauge with the dampening chamber, so haven't used one with a dampening thumbscrew.

You'll want to check the port on #4 to make sure that it's NOT CLOGGED, the cylinder is probably pulling plenty of vacuum, but 5 years of running could have caused some crud to get into the synch port and clogged it up!

Also, hate to ask, but how did you do the compression test, engine warmed up, gas/petcocks OFF, throttle wide open, all 4 plugs out??
T.C.

[nezzer]

I did the compression test with bike luke warm, not cold, fuel petcocks to off, spark plugs in (except one being tested of course), and no throttle applied.

[TopCatGr58]

AHA,

You want all plugs out so that the engine spins more easily, and the throttle wide open so the air flow is very easy thru the carbs. I would suggest a repeat test with those changes.

ALso, you didn't mention that you took out the PILOT jets when you did your wonderful ultrasound cleaning?? The aeration ports in them are very small and easily gummed up. Having to use the choke/enrichener points to a clogged pilot jet/idle circuit!
T.C.

[nezzer]

I will redo the compression test as described. I did attempt to take the pilot jet out of the first carb... I think it must be welded in place. I had always just completely dissasembled and dunked the carbs in carb cleaner but at that moment I decided to give the ultrasonic a try. From what I read on the internet, many shops just dunk the carb in the ultrasonic cleaner without dissambling it first.

After the cleaning and reassembly, the bike does not seem to have any problems idling with the choke closed. I would like to see how the bike behaves when accelerating in gear while under 5k rpm since that is what gave me the most problems before. Until I get this oil issue squared away I am not taking the bike for any test drives. I am nervous a oil passage way may be clogged or something and I dont want to ruin the top end.

[TopCatGr58]

These engines are pretty tough, and the top end gets its oil supply from that large metal hose that is banjo bolted to the back of the head.

Just like your intake manifold nuts working loose, same thing can happen to the valve cover bolts, as well as shrinking of the gasket, etc.

Most of the time, oil around the head is either a leak from the valve cover gasket surface, check and retighten the cover bolts, wouldn't be surprised if you found some rather loose! Also, check your cam chain adjuster, it likes to leak there also, and while running in the wind, oil easily blows backwards towards the intake side, there are cooling and rain drainage ports in the heads around the plug cavities. It can actually leak on the inside edge of the valve cover/plug cavity and then drip/drain down thru those rain ports. Also the rubber coated half moons on the right side like to shrink and leak as well!
T.C.