New GL1100 and suspected carb issues

[thesteve]

Just bought a 1983 GL1100 Interstate this weekend and am having some issues getting it running well. The previous owner gave up on it after a shop told him the pulse generator was bad. I tested the pulse generator with a multimeter (seems ok) and noted that it doesn't seem like an ignition problem to me. The engine is firing on all four, hot or cold. My vacuum advance is in good shape and does not leak.

The issue I'm having is I can barely get it to free-rev over 3500 RPM. It sounds like its running lean but I have no way of verifying that. The carbs were apparently just gone through, but from the workmanship I've seen I can't really put a lot of faith into that. If I stay light on the throttle I can eventually get it to rev up to around 7000 RPM, but it definitely doesn't want to. 3500 is about as high as it'll rev "normally".

What should I be checking first? I've rebuilt motorcycle carbs before but none with as many extra bits as these (accel pump, etc). Google is turning up all sorts of possibilities but nothing for this exact issue.

 

[kerryb]

Have you inspected the air intake area? Can it get all the air that it wants? New/clean filter? Does it run smooth or rough, is a carb sync in order?

 

[dan filipi]

Sounds like it's not getting gas or its flodding from too much gas?

Could be float levels are too high or too low, vacuum slides are hanging up not moving freely, partially clogged primary jets?

Could be as simple as a clogged fuel or air filter, maybe fuel pump not keeping up with demand.

 

[dan filipi]

Try loosening the gas cap to the first stop. Could be a vacuum preventing gas flow.

 

[thesteve]

Air intake is good. Clean UNI air filter. Looks to be almost brand new. It'll idle very smoothly at just below 1000 RPM. I can sort of putt around the neighborhood on it too as long as I stay below 3500RPM.

To me it feels like it's starved for gas. I say this because if you get it into the "problem area" and gun it, it falls on its face and nearly stalls. So it seems the rush of air leans it out too much.

I have not checked the float levels, but the slides seem to move freely. Have not inspected the jets due to the previous owner's note that it's been recently serviced, but I think that's the next step.

Fuel filter is brand new with receipt. The filter and fuel lines are translucent so I can see the fuel flowing through them. There doesn't appear to be any obstruction, and cranking it with the fuel line disconnected makes a nice mess so I think the pump is ok.

Thanks for the quick replies!

 

[joedrum]

hmmm its carbs most likely need good cleaning first ...but im sure if its running like that ..if carbs were done ..it wasnt even close to good .

 

[thesteve]

Gas cap is the first thing I thought of. It did seem to be "vacuum locked" and I heard a nice whoosh of air when I initially took off the cap. Unfortunately, it runs the same with the cap off. I plan on finding a new cap before I actually ride it.

 

[thesteve]

Yeah, I think the carbs need to be fully gone through. Going by the previous owner's comments, that shop didn't seem to want to work on this much and the work they did do seems halfassed. Is there anything specific that would cause it to lean out so drastically at that RPM? Or should I just do a top-to-bottom cleaning and hope none of the O rings tear? I'd really like to not have to spend the $220 on the full overhaul kit if I can avoid it.

 

[slabghost]

All good suggestions. Try running some Seafoam or ATF in the fuel and rev it . Hold it at highest you can and choke the intakes several times. Covering airbox inlets with a rag. This may force open some partly plugged passages.

 

[thesteve]

I've heard of that working but have never tried it myself. The carbs are currently off the bike (getting pretty good at removing them already) but I'll give that a shot upon reassembly.

Thanks

 

[joedrum]

if i had to guess id say idle circuits are pluged seems they all are ..also the pasages get cloged up the 90degree turns in some passages ..gas an air ...get all that and float set and try ....just have to dig and check everything got to be rather bad to run like that ..shops today at this old carb stuff as not eben worthy to fix or learn

 

[slabghost]

While they are off be sure to clean every passage. Be certain not to get carb cleaner on any of the rubber bits. Good idea to do a bench synch and check float levels while you are in there.

 

[thesteve]

Thanks guys. I'm off to the garage, I'll report back in a bit.

 

[dan filipi]

If any of the other work by that shop looks half assed, can be pretty certain they didn't spend the time and effort needed to get the carbs clean.
Roady's carb thread is a good place to start...viewtopic.php?f=11&t=261

 

[zman]

When it is cold fire it up a few seconds and feel each of all 4 exhaust pipes and check for differences, may need a few seconds longer to heat, cold indicates non firing or flooded cylinders. Plugs look like? If you pull the carbs follow the tutorial and look for any mistakes might have been made by others.

 

[thesteve]

Alright, I've gone through all four carbs per the walkthrough posted above. Annoyingly enough, the carbs were all pretty much spotless with only one exception. The choke plates on 1 and 3 were pretty much stuck in place and would not close without directly turning the shaft. Other than that, there wasn't a speck of dirt or any clogs anywhere. So I guess the shop did actually clean them properly and the carbs are unlikely to be the issue. The only other noteworthy thing was that the throttle linkages were not quite correct, they didn't have the washers in the correct order.

It's too late to continue messing with it tonight, but the carbs are back together. All that's left to do is check/adjust the float height. Following that, I guess I'll put them back on the engine unless there's anything else I should check while they're out. What would be next? Fuel pump?

Also, is there any chance the shop's diagnosis of a failing pulse generator is correct? I don't think it matches the symptoms and it does check out with a multimeter, but is it a possibility it's dropping out exactly in that RPM range but working above and below perfectly?

 

[thesteve]

zman » Today, 7:48 pm[/url]":4faf4jq5]
When it is cold fire it up a few seconds and feel each of all 4 exhaust pipes and check for differences, may need a few seconds longer to heat, cold indicates non firing or flooded cylinders. Plugs look like? If you pull the carbs follow the tutorial and look for any mistakes might have been made by others.

I can do one better than that, I've got one of those little IR thermometers and can check the exhaust temperatures that way. Not expecting much of interest there, it idles perfectly smooth and is definitely running on all four.

Will check plugs tomorrow.

 

[slabghost]

While you have them out you should bench synchronize them and once floats are set. Hang a gas can or bottle at least 5 ft up and feed fuel to the carbs. The height will simulate the pressure from the fuel pump. If there are any leaks they need found and fixed.

 

[zman]

Yea for sure get them close to sync like slab suggested, might want to check the cut off valves, at least the 2 you can get at and see if they are still good(don't miss the little oring inside with the cutoff valve), if not good chances are the others are bad as well as the accelerator pump to make sure all 4 squirt fuel, really helps low speed to have a working accelerator pump.After checking float level I bench fill the carbs,check the squirters then drain each bowl and measure right around 52CC`s each bowl.

 

[thesteve]

I'm at work right now and can't look at it, but I've been thinking this over. The perfect idle indicates the pilot circuits are OK, but the lack of power is likely the main jets not opening. Would the aftermarket air filter cause this? On a previous carbed bike, running anything other than the OEM filter would cause the diaphragms to not lift properly.

Pardon my ignorance, but what exactly does the accel pump do? I assume it fills in the gap between opening the throttle and the vacuum slides lifting?

What about the air cutoffs on the sides of the carbs? Those were all clean, but what are they there for? The carbs I've worked on (90s+ sportbikes) haven't had either of these parts.