Steve Saunders Goldwing Forums - View Single Post - 1997 Goldwing GL1500 Jerks under 2,000 RPM

View Single Post
post #40 of (permalink) Old 06-10-2018, 08:23 PM Thread Starter
GoldwingA1500's Avatar
Join Date: Jun 2018
Location: Sumter, SC
Year: 1997
Make: Honda
Model: Goldwing GL1500 Aspencade
Posts: 281

So this evening I performed a compression test (dry) to see if any valves might be suspect. All four cylinders on the left side averages about 190 +/-. I'm sure it would have been higher had I squirted a little bit of oil, but overall I'm pleased with the results. So this pretty much eliminates sticking valves.

I also disconnected both vacuum hoses on the left side and plugged both ports. Of course, the bike stalled (as I suspected) since the IASA Valve opened during throttle deceleration just from a stand still. So I had to remove the cooling fan and isolate the valve by plugging the three lines. Then the bike was able to run but as a very rich state. The rear vacuum port controls the PAIR Valves, and I believe the cruise control, so it was not an issue unplugging. So with the IASA valve isolated, and the two ports plugged, there was no change. The bike still jerked under 2,000 RPM. So I believe we can safely assume that there is no vacuum leak.

HOWEVER, this is what I did notice. When I reconnected the IASA Valve, and the aft vacuum port, and took the bike around the block, the damn thing ran beautiful. Absolutely little to no JERKING! Guys I'm stumped! Is it possible that the IASA Valve is not function correctly? I just replaced that damn thing although it was a used one. I checked it according to the book and it worked fine. It opens and closes as it is supposed to, and there are not vacuum leaks on the valve. Remember the bike stalled at first attempt because the valve opened when I had the vacuum line disconnected. So I had to isolate it. Yet with the valve taken out of the picture, the bike still jerked. When I reconnected the valve, the damn thing ran great with no jerking under 2,000 RPM.

Could someone with more thorough knowledge please explain to me how the IASA valve is controlled (opened/closed)? I know that a small vacuum hose is connected to the right side of the valve, and a larger free-flowing hose connected to the bottom port. And a larger hose is connected to the left side of the vacuum which has a strong vacuum.

I know when testing the valve, vacuum pressure is applied to the lower large port and there should be no vacuum leak; this passed. Vacuum is applied to the smaller port, while about 5psi is pushed on the lower larger port. When the small vacuum hose suction is reduced, this causes the valve to open momentarily and the larger vacuum hose on the left side (forward side towards the radiator) pulls air from the larger hose on the lower right side. This all happens during deceleration under high intake vacuum. As soon as you are at a stop and returned to idle, the valve closes but I do not know how or why.

Now I only ran the bike twice around the block after the two tests, and as I've stated, it ran fairly well with only minor jerky, very little at that and below 2,000 RPM. No doubt tomorrow (or even now) when I take the bike out, it will jerk again.

What's freaking weird is when I isolated the IASA valve (taking it out of the picture), the bike still jerked. So I'm confused fella's. LOL Now I cannot be sure that the bike ran perfect since I did not exceed 30mph in the neighborhood, so I'm going to call it a flue test. Thus at this point, there was no change with eliminating possible vacuum leaks, and the valves appeared to be good based on the compression test results. So I think next is removing the carburetors again and inspecting the IASA hoses that go to the left and right intake manifolds; you cannot change those unless the carbs are least to the best of my knowledge. I'm also going to examine the CV boots to make sure there is no hole. Might as well replace all the seals and hoses on the carbs again while I am at it.

I am officially stumped beyond stumphood.

GoldwingA1500 is offline  
For the best viewing experience please update your browser to Google Chrome