gl1200 won't rev-up without the choke

[OrWingRider]

What a great site. I've been doing lost of reading but I can't find a discussion of the problem I'm having.

I picked up a project bike a week ago, an 84gl1200 interstate. The odometer shows 34K. It hasn't been on the road in at least 13 years. The previous owner started taking all the body panels off to repaint....and well....All the body work is off so I have easy access to the engine! I'm trying to get it running right before jumping into the rest of the restoration.

The previous owner did say he attempted to rebuild the carbs and then found another set that were supposedly off a running bike and went that direction. So I have two sets of carbs, some shiny jets and new o-rings. I decided to rebuild the set that were off the bike(original) as the internals looked cleaner.

The slides and needles were slightly stuck. The choke plungers were also a little stuck. The jets and emulsion tubes needed cleaning but in the end everything cleaned up great. Lots of carb cleaner, simple green and compressed air and it's looks pretty respectful in there. I did set the float heights at 7.5mm and verified that I got the same 1.5oz out of each float bowl when draining them. I set all the fuel screws at 3.5 turns out.

I did compression test and I'm getting 160-170.

Today it will start right up and idle great. I only need the choke for 30 seconds or so. While it was idling I synced the carbs. The idle is smooth and sounds pretty good.

The problem I'm having is that it will only rev up to about 3000rpm(no tac so an estimate) before it starts to stumble and backfire and won't rev any further. If I put the choke back on it will rev up much higher. It doesn't sound super smooth at the higher revs but it's much better. So my conclusion is it's running lean at higher rpms.

I've had the carbs off a couple times now double checking everything and checking for a plugged main jet. I'm at a bit of a loss as to where to look next. Any thoughts on what might be going on here?

[Whiskerfish]

Let start with a disclaimer. I don't know much about 1200's but one thing comes to mind. I think the 1200 advance is vacuum controlled?? Seems like I have read on here about ways to test it's operation. I would try a search for that and check it out.

Welcome to the club!

[OrWingRider]

I don't know much about 1200's either....but I'm learning. I think I read that the vacuum advance only kicks in when your in 3rd or 4th gear. But I'll still look up the ignition testing procedure.

[robin1731]

A lot of hoses on the 1200 carbs. Did you replace them? Did you eliminate them? Some do. Also make sure you look at the diaphragms closely. They can have holes in the rubber.

"So I have two sets of carbs, some shiny jets and new o-rings." Are these aftermarket or Honda parts?

One last thing. While you're testing this do you have the air filter housing, air filter, and lid on?

.

[salukispeed]

The ignition advance feature only comes into play in 4th and 5th so not likely that. The diaphragms/slides could be related somehow. they only start to come into play around 1/4 throttle but meter most of the fuel from there up. they must float freely and do get torn and it is critical that they are sitting in the groove with the little "O" ring projection in the correct place when the caps and return springs are reinstalled. No vacuum leaks allowed at the cap to body allowed, or you will get little to nothing above 1/4 throttle. Starting with the unmolested carbs will give you the best chance of success since it ran correctly with them at some time.

[OrWingRider]

Thanks for the input. Let me see if I can answer the questions....

All the hoses are still on the carbs. The air cutoff valve is still there and checks out. And the anti afterburn system is there and also checks out. I used a vacuum pump to check for vac leaks in the connecting hoses. No leaks, but they are the originals.

I'm not sure on the rebuild kit. I only used the o-rings. The jets cleaned up good so didn't use the ones from the kit.

I visually looked over the diaphragms and didn't see any holes or problems. But a problem there seemed like a likely cause of my problems. I pulled the carbs again tonight and did a shop vac test on them. All the slides went up smoothly as the butterfly was opened. Operation seemed smooth and consistent across all 4 carbs. Bummer as I was hoping that was it.

There was question about the air filter...I'm just running the air filter on top of the intake without the surround or lid. It's an EMGO brand filter. Could it be getting too much air?

[jdvorchak]

There was question about the air filter...I'm just running the air filter on top of the intake without the surround or lid. It's an EMGO brand filter. Could it be getting too much air?

For sure the OEM paper air filter is the best bet for success. To fully test and sync the air cleaner box has to be assembled and tightened down.

The one vacuum hose that must be hooked correctly and often missed is the hose from the #4 intake ( most rearward left side) to the ignition module located on the upper frame, left side. Those hoses will be right up next to the ignition module. In an unmolested state it will have a Tee fitting where one end is plugged and the other goes to the #4 intake port. That port is located toward the inside of the engine and some times overlooked.

One further note. When reviving an old bike that hasn't run in years and I've pulled and cleaned the carbs, I don't get in a hurry to sync the carbs, other than bench sync. I'll let it make a couple of heat cycles and ride it a couple of miles before final sync.

You didn't mention it but it is THE MOST IMPORTANT PART AND DO NOT DELAY! You have to change the timing belts preferably before you even hit the starter again. Check out the crossover parts list for NAPA or GATES belts. They are under $30 for both. Easy to change, especially since you have the plastic off the bike. What most folks don't realize is that the belts will most likely break at idle and will destroy the engine.

[robin1731]

snip..................
There was question about the air filter...I'm just running the air filter on top of the intake without the surround or lid. It's an EMGO brand filter. Could it be getting too much air?

Yes it could be getting too much air. CV carbs are pretty picky. They don't run very well without the stock air filter housing installed. This is true of all CV carbs. Any brand, not just Honda or GL's. Put the air filter housing and lid back on. Then try running it again. That may be all it needs.

.

[OrWingRider]

I've got some timing belts coming. Should be here in a couple days.

Once the new belts are on I'll try again with the full air box installed and report back.

[OrWingRider]

The new timing belts came in and went on just fine.

I reinstalled the full airbox and fired it up. Not much difference, if any.

After a while I reasoned that it's probably not all the carbs that are going lean and requiring the choke. So I warmed up the bike and then disconnected the choke linkage. Then one by one I added some choke to try to determine which carb was having issues. Strangely, it ran better without the choke linkage connected. A test ride confirmed that it's much better. Far from great, but better. So now I'm thinking it's something in the enricher circuit....maybe the spring loaded plungers weren't or aren't sealing well or maybe the linkage was holding one slightly open.

The plan now is to pull the carbs and go through them again, this time paying close attention to the choke plungers to see if I can find fault there.

It really doesn't seem to fit the symptoms I was seeing. But maybe if one of those plungers wasn't fully sealing a bit of vacuum might be delivered to the underside of the main diaphragm and that might be keeping the needle lower than it should be. Not sure that makes sense either. Just my latest theory

[OrWingRider]

I can't believe it's been this long since I've posted on this forum. The bike project got pushed aside for a couple years.

But now it's back on the front burner and I'm making progress! The plan was to build a bobber out of this bike so I worked on the frame for a bit trusting that the engine issue could be resolved.

The major frame modifications are done and I hooked up minimal wiring to fire it up. What I found was the plug wires for cylinders 3 and 4 were unscrewed from the resistor plug caps. The wires were held in place by the rubber boots but not actually connecting to the plug cap. If that makes sense. I didn't realize the wires could be disassembled from the end caps like that.

But let me say, it runs much better when all 4 plug wires are connected and not just two!

Here is a video of it running.

https://youtu.be/TyOuN8oHJPI

If I would have followed the full ignition trouble shooting section of the manual the first time I would have found this sooner. Thanks for the help!! I'll post more once it's riding around.

[CYBORG]

sounds pretty good. What are the plans for a fuel tank?

[Track T 2411]

Yum! Looks like some significant fabrication going on there. I'd love to see more...

[OrWingRider]

For the tank I found a Kawasaki, 750 ltd tank that fit the top rails really nice. Had to fabricate some mounts for it, but I think it will work great.

The underside of the tank is hollowed out quite a bit....just as a lot of stock tanks are. At first I was disappointed because I liked the outside shape but wanted more fuel capacity. I think it's rated at 3.25 gallons. But now I'm realizing I can hide all the electronics under the tank! Coils, voltage regulator, and ignition module, fuse box, it's all going to fit under and get plenty of airflow to stay cool.

This is the only picture I have of the tank now.

IMG_20200102_211557924~2.jpg (100.5 KiB) Viewed 158 times

[Track T 2411]

The tank has a nice 'flow' with the frame...
You should really start a build thread and add lots more pics!