1975 Goldwing Bogs down at 5,000 rpms

[ISRAELI]

Hello All,

I have a 75 that I rebuilt and put some Webber Carbs on it. The problem with the bike is that when I try to go at high speeds at around 5-6K rpms, it just bogs down and feels like it is lacking energy. Also, when I ease on the throttle at that time, I get backfires a plenty. Any idea what this could be? I have tried rejetting my carbs, changed the regulator and spark plugs but I don't think that the problem is there. Something tells me that the problem is with the fuel combusting. Anyone had this problem before? I am thinking of rebuilding the old carburetors and testing to see if they will perform better. Also, my compression test reads 110 for all 4 cylinders. Could that be the problem given that I read that a good engine should read at least 150-170?
Thanks.

[ISRAELI]

Other than the bike bogging down at the high rpms, it performs pretty well when on the first three gears. It is only when you want to get to the 4th gear that all the energy drains from her and she starts riding really bad.

[Whiskerfish]

I know nothing about the webber carb setup but on a regular bike I would check the timing advancer first.

Was it like this before the webbers?

[wingrider]

Might need to jet down.

[ericheath]

Check fuel pressure. Others have had issues with a gas cap one way valve not working. Soaking it in vinegar can help it. Quick check is to loosen the cap enough to ride and repeat your test. Easier check than the first, but entirely possible suggestions.

[robin1731]

What do the plugs look like? Ride it where it will run good then stop and pull one or two plugs to see what they look like. Then try riding it as best you can where it acts up for a good mile or two, more if possible, then stop and pull a couple plugs and see what they look like. Do both without letting it idle or riding it more. Along side the road where it is safe to pull over and pull the plugs. That will tell you much more of what is going on. Without reading the plugs you just guessing.

[ISRAELI]

Thank you everyone who has responded so far. The power of crowd knowledge is awesome and I appreciate it. Here is where I am. First, I checked the timing belt and the belts are pretty new. I lined up the timing marks at T1 and like I said the belt and everything seems to be lined up on the timing marks. So it seems that we can rule out that it skipped a tooth or something. The previous owner installed a DYNA S ignition system, and I am using the DYNA 3ohm coil packs. I am using spark plug wires that don't have resistor caps. I put in new OEM spark plugs. I set the static timing on the electronic ignition system but the problem still persists. Is it possible that the DYNA S module can somehow seize or require lubrication and is causing problems at high RPMs? And if so, should I apply grease and remove the bolt holding on to the DYNA S module?
As for the gas tank, the gas tank seems to pressurize and there is a pressure relief even after the bike has been sitting overnight when I open the tank. It is like pressure builds in the gas tank? Is that supposed to be so.
Now, I never tried it with the original carbs because the bike was dead when I got it. It hadn't run for ten years or so. And I brought it back to life with the webbers. Am trying to see if I can rebuild the old carbs and try them out.

[ISRAELI]

I am running Randaaks recommending jet sizes on the webbers. Am running 110 on the jets. Maybe might try to see if I can find smaller sizes.

[ob1quixote]

Your fuel tank should not pressurize.

[ob1quixote]

Seems like the fuel cap is standard Honda Civic from the '70's, IIRC.

[Whiskerfish]

The fuel tanks do pressurize just a bit. Often when on a gas stop after a good run you will pop the cap and feel it lift a hair as it vents out. the problem is if it does not vent inward, you do not want it to hold a vacuum. Typically a tank that is holding a vacuum will get you just a mile or 2 down the road then die. Easiest way to check that is make a run with it cracked open.

[Track T 2411]

viewtopic.php?f=47&t=64814
Here's a link from the unique carburetion forum, and several others in the related topics section below it...

[ISRAELI]

Solution found. the Webers that I had were the problem. I fixed the stock carbs and the bike fires up and rides much better. I think that she still has some problems here and there and that she is still not performing to her potential, but she sounds and rides much better and the revs for all the way up. Thanks to all who helped with suggestions!