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I don,t know what it is this year....but my bike seems to be requiring more care and attention, that ever. First it is the problem with the front wheel requiring change out, and now I seem to have developed a flat spot when accelerating in 3rd/ 4th and overdrive. This mainly occurs whenopening the throttle from around 2000- 3000rpm, and there is definite hesitation in acceleration untill 3000rpm is reached. After that the bike behaves as normal.

My thoughts are that the carbs require balancing. Any other ideas? Can cracked vacuum hoses; slack timing belts; dirty air/ fuel filter be the cause? I will be getting the bike dealer serviced again soon, however my particular dealer requires that you list all work needing done or they will not necesarily check out these faults.

Joe
 

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Hi Joe, thethings on your list that won't cause your problem are the timing belts and a dirty air or fuel filter, and carb balance.

Usually hesitation like you describe is caused by either a too lean condition caused by the carbs or a problem with the timing advance. A dirtyair or fuelfilter would cause increasing problems as the rpms increase, they wouldn't get better at higher revs. Carb balancing won't help with this one, it will make the bike idle smooth and pick up better from idle but that's about it. A vacuum leak should affect the engine at lower rpms but it could possibly cause problems with the ignition timing advance. One possible electrical problem could be the gear position switch. If memory serves the ignition timing is partially controlled in the top two gears by this switch.

I'd pick on the carbs first, possible accelerator pump or dirty jets. You might try running some carburetor cleaner with the gas to see if that will help at all before you start having any mechanical work done. The next thing I'd take a look at would be the spark plugs to make sure they aren't marginal. Try putting on a little choke and see if the problem gets better or worse, if a bit of choke helps it's likely the carbs are the culprits and need a good cleaning.
 

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Thanks for the reply Exadavid. I have tried running MMO in the fuel, but things seem to be getting marginally worse. Another thing I have noticed, that when starting from cold, and choke on the engine initially starts ok. When I reduce the choke or remove it completely when the engine is heating up it sounds as though the bike is not running on all cylinders, and does not idle smoothly. It gradually dies, even thougfh the temperature gauge is moving. On the last couple of occasions I have switched the engine off and then restarted, and funnily enough the bike idle revs finally smooth out. After running for a couple of miles, all seems to be ok, apart from the accelleration problem. From what you say this might indeed be carb problems. Is this a major job for a mechanic?

Joe
 

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Joe, The carb sliders in the early GL1500s have been known to stick. If you pull the air filter and spray some WD40 onto them and work them back and forth by hand a few times, it should cure the flat spot for a while. This is assuming the carbs are balanced of course, you should do this first.

GL1500 Carburettor Balancing

 

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I have the same bike 1989 wine berry and have sort of the same problem. Mostly mine is flat right as I open the throttle. Balancing the carbs is what everyone says to do. I have never done this before and am a little nervous about taking this on- Suggestions guys??



Mike
 

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After you check the slides for sticking, check the middle plug on the right side (Right as you sit on the bike)

I know this is a strange request, but if the vacuum petcock diaphragm is leaking you could be drawing fuel into the vacuum line and it goes into the middle cylinder. At lower rpm's the vacuum is highest, when you try and accelerate, you probably have a fuel fouled plug, if the leak is small the plug will clean itself as you increase rpm's.

Have you noticed any fuel smell in the garage after you shut it down ?
 

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mjohnson, same questions for you.

I know people here are in favor of balancing the carbs every 15 minutes, but in reality, carbs rarely need to be balanced and usually have another problem misdiagnosed as a balance issue.

If you find that you need to work on or balance the carbs more than every three or four years (unless you live in a third world country with unregulated gas) you probably missed the real problem.
 

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Not to just throw parts at it, but when were the plugs last changed? I note that Honda lists plugs as a first thing to check for many problems on the SE-i, and it fixed acceleration stumble on mine. I'm also surprised to see that they list plugs to be changed at twice the frequency of oil! Pluga are fairly cheap and easy to change, just remember to gap properly, apply anti-sieze to the threads, and use a torque wrench to tighten.
 

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All very good suggestions lads...Thanks. I have the bike dealer serviced every year, which includes fluid changes; filters oil/ air and spark plugs (generally every 2nd year). I usually average around 6-7k miles per year. Up untill this year, the bike has always ran very well and idled very smoothly. It is only within the last 2-3 months where I have noticed this problem, especially as mentioned earlier regarding the difficult starting from cold. I will be asking the dealer mechanic to check the carb sliders; lube / adjust throttle cables; tune / synchronise the carbs and of course check/ change the plugs. I think it may also be wise to inspect the vacuum hoses.

I will post back once the bike has been serviced.

Thanks to all again
 

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scotwing wrote:
...especially as mentioned earlier regarding the difficult starting from cold.
This is another sign of the vacuum petcock diaphragm leak, the available vacuum at cranking speeds isn't enough to open the fuel petcock with a diaphragm leak. Have your mechanic check this before he spends a lot of time ($$$) diagnosing the problem.
 

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Definitelycheckhoses. Also, does your engine speed drop, when you shift to first gear, coasting with clutch in? You might check timing in all gears, with bike on center stand, and front wheel up against a wall (strong wall) It shouldn't be any different except in first gear. Maintain 1200 rpm. Also, in neutral, check timing variation, by using mity-vac at vacuum advance unit (electronic) You might have to free up the idle adjuster, to do these steps, or use a throttle lock.
 

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I do 1500 carb work on the side. What I've learned is that once one or more of the holes in the jets get clogged, running a cleaner through the fuel usually won't clear them out.

I'd suspect a clogged accellerator pump outlet. Easy to check, though. Remove the radio shelter and the air filter /cover. Twist the throttle and see if fuel is shot into both carbs.

You can also check the slides while you're at it. With the engine running, goose the throttle and see if both slides pull in and then out in unison.

One precaution. NEVER spray carb cleaner into the carbs without taking them apart. If you get carb cleaner into the large half moon inlet, it will destroy the slide diaphragm. And they aren't cheap, around $80 eash USA.

You might also want to check the Secondary Air System. Sometimes the filter will flake apart and get sucked up into the vacuum valves and the carbs. Those valves actuate around 2000 rpm. So, if the engine runs good on one side or the other of 2000 rpm, the Secondary Air System could be at fault.

A friend of mine found that his vacuum valves were not operating properly, as one of them was constantly clicking open and closed. He had to replace the ECM.

There are a lot of systems that contribute to a smooth running engine. The factory Service Manual has a great troubleshooting section to check the various systems.

Dave DeWinter
Georgia, USA
 
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