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1998 SE Gas Cap Small Orange Rubber Diaphragm and Other Issues

677 views 2 replies 3 participants last post by  Bike...and Dennis 
#1 ·
Hi, I'm still having issues getting the bike working properly. Here's a current list of problems:

*Bike RPMs dip at idle and dies often (restarts just fine usually, sometimes requires a little choke), runs fine under power. I think this may be related to the small orange rubber diaphragm in the gas cap, as it's a vented cap. I had issues with the petcock, so I rebuilt it and while it did fix the leaking fuel, it seems like the tank may not be pressurized properly? I looked at the gas cap and tried to "clean it out" and found that the little orange rubber diaphragm was torn and not seated properly. Is there a place I could order this piece specifically without replacing the entire gas cap? Alternately, could this be due to a weak fuel pump? I don't have the equipment to test that. I also changed the fuel filter.

*There is minor surging at idle. I had the carbs cleaned right before my trip and it seemed to fix the problem, but that only lasted a week or two; same issue. It's generally not more than +/- 100rpm variation. I already replaced as many vacuum lines as I could find, including the ones under the carb, with silicone lines. I don't think I missed any, but could be wrong. The carbs are sync'd. Yes, I've run seafoam through it.

*While I was on my trip, the bike seemed to lose power at high speeds, 70mph+. It wouldn't have the power to climb hills, almost like half of the cylinders weren't firing or something. The exhaust made a very strange sound, I don't know how to describe it besides..."airy" sounding...sort of like a weird blowoff valve? I found that using the killswitch and immediately restarting was generally a good fix for a while when still on the highway, but it would inevitably do it again. This only happened on the highway.

*Whenever it rains, it idles around 2500-3500rpm. This is clearly not correct and it only seems to do it when it rains.

*When decelerating, the exhaust pops a decent bit. I never feel like I have any hesitation on acceleration. Spark plugs have been changed, I'm thinking either coils or spark plug wires, maybe? Both are likely original.

Can anyone offer any advice or throw any more troubleshooting steps at me? I'm getting used to working on the bike and can do most things, but if this is going to get intensive or require specialty tools, I'll probably have to take it into a shop, but I'd rather avoid the labor charges. Hopefully this will be enough to put together a full picture of what may be interconnected problems.
 
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#2 ·
Just a couple thoughts: When the carbs were cleaned, did they check the rubber on the vacuum pistons for tears, cracks (even very small cracks etc.)...?? That can cause loss of power at speed. Also the spark plug wires can cause loss of power when riding in the rain. Both of these issues caused problems on my friends 1989 Wing....!!

If you accelerate very hard does the engine tend to bog down..?? I mean a pretty hard acceleration from idle....!!

Have you checked the auto fuel "shut-off" valve...??
 
#3 ·
To get the fuel cap gasket, go to your local Honda dealer. Surprisingly, they sell parts for Honda motorcycles!

Once I had a guy clean and rebuild a set of eBay carbs for me. The bike ran okay until conditions required power. (passing, uphill, fleeing from police) When I looked into it, the problem was he had set the floats to GL11 specs. I was running out of fuel.
 
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