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Discussion Starter · #1 ·
ok guys, getting the bike all back together, took it for a quick spin before I put all the bodywork back on, when I notice an issue. it doesnt seem to matter what gear I'm in, if I've got the throttle wide open, the engine bogs out at about 4500 RPM, it will come back at about 3800RPM, but will never hit the red line if I mash the throttle wide open. HOWEVER, if I roll up on the throttle gently, I can get up and past the redline.

pulled the top off the air filter box and it seems to walk right up to the redline without issue, but when the air filter is re-installed and top of the box back on, the problem returns.

a little history, I just had the entire engine out of the bike due to a shifting issue (shifts just fine now) and had the carbs off. when I had the engine out, I changed the timing belts (have a small chirping noise coming from the front of the engine at idle too) new fuel filter, new air filter.

I seem to remember the engine bogging down on a ride before I took everything apart, so I dont think that anything I did could be causing the problem.

pretty sure I put the filter in right, going to check on that now and while I'm at it, will check the fuel pump pressure
 

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Don't know bout the air box thing, but a chirp in the front of the engine after a re-belt, would most likely be a tensioner that is too tight. Just my guess. jimsjinx
 

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Just a shot in the dark here... One time I installed a brand new fuel filter and within 2 weeks my bike began bogging down. I troubleshot the heck out of that thing ignoring the fuel filter because "its was new". Anyway I got back to basics and pulled the filter and tried to blow through it. A lot of resistance. You should be able to blow through a nice clean filter like blowing through a straw. No resistance. Good luck on that. Bobby
 

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Discussion Starter · #4 ·
didn't think to blow through the filter, I've got it installed in the right direction, full tank of gas, fuel pressure just over 2 PSI. haven't tried again with air filter off, but on the center stand, in neutral, dumping the throttle wide open the engine runs up to just under 5000 RPM then the RPM's are up and down, I guess I'd describe it as a 'flutter' almost.

I'm stumped
 

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Recheck the vacuum lines, you may have gotten something switched, or you may have gotten the cam timing off a tooth. And did you check the idler pulleys when changing the belts?
 

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Discussion Starter · #6 ·
ok, no resistance blowing thru the air filter, vacuum gage on the automatic fuel valve shows total loss of vacuum when at wide open throttle, RPM's no higher than 4750. applied external vacuum to the automatic valve, same result. looks like time to double check vacuum lines and timing belts

:headbanger:

this project has felt like one step forward and two steps back for the last couple weeks now!!!
 

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Sounds fuel related so now we check to see if rich or lean.

Get a can of carb clean the good stuff that burns and is non foaming like Cyclo. Unsure if it burns shoot a little on your lighter or a match held with pliers.;)

Remove plastic intake snorkel from front of air box and plug that vacuum line.

Take a short length of vacuum hose that just fits over the straw of carb clean and tape one end of it to the outside of box near the opening so just a couple of inches of hose is inside box pointing towards middle of the box above air cleaner.

Tape your can of carb clean down to top of box, make sure the can is near full and it will spray the juice out lying on its side.

Shove the straw into other end of hose and tape good so it leaks as little as possible.

Take it for a ride and when it breaks down mash on the spray button sort of like nitrous:ROFL:

If it wants to take off lean if it bogs down it is rich. Be careful if it is lean with one hand on the bar it will want to go like all get out if in a lower gear.
 

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The fuel valve does operate off manifold vacuum and will show less vacuum at WOT. If you applied external vacuum source to valve and same symptom valve is likely not the problem but not impossible if innards are falling apart.

BTW the valve should hold vacuum rock steady if it doesn't it should be on the list for a freshen up.
 

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Discussion Starter · #9 ·
valve holds vacuum rock solid, all good there, going to do some spraying around the carbs to see if I have a vacuum leak, got some sealing grease for the boots, I have a feeling those are the issue
 

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Another less precise way to check for lean while riding or stationary is use your fingers as a shutter in front of air box opening with differing amounts of blockage.

You are not adding fuel just limiting air making what mixture you do have a little richer. If it picks up a little same thing lean.
 

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Check the operation of the hot air riser valve located in the air horn (snorkel) at front of air box. Check cold and hot to see that it's opening properly. There's a temp sensor inside the airbox left side that signals vacuum to the valve to open or close as needed. Make sure there's nothing obstructing air flow thru that snorkel.
 

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Discussion Starter · #12 ·
ok, now I'm really getting frustrated. fired bike back up, ran the RPMs up to the "trouble zone" and blocked off airflow with my hands, RPM's dropped even further, so I tried spraying carb cleaner in the throats at idle, RPM's dropped again. I think that I can then assume that I have no vacuum leaks. I sprayed carb cleaner around all the vacuum connections with no increase in RPMs again, so I think vacuum leaks are not the problem (damn)

pulled the timing belt cover off, found the right belt a bit tighter than the left belt, but timing marks lined up perfectly. re-tensioned the belts, fired it back up, now I get up to about 5000 RPMs before we start losing RPM's again.

the heat riser snorkel is operating correctly, although for most tests the cover and the air filter were removed from the air filter box, so for the most part we've eliminated that as well.

I'm beginning to wonder about a couple things. First, the carbs were off for a few weeks, wondering if the floats are hanging up somewhere due to being dry for so long. on second thought, the fact that I can gently roll up to redline but a sudden opening of the carbs gives me the RPM loss doesn't seem to make sense either.

I thought that the Idle Airshot System might be malfunctioning, but I would assume that would give me a lean condition at high RPM's and partially blocking the airflow would give me a rise in RPMs rather than a drop?

any other thoughts?
 

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ok, now I'm really getting frustrated. fired bike back up, ran the RPMs up to the "trouble zone" and blocked off airflow with my hands, RPM's dropped even further, so I tried spraying carb cleaner in the throats at idle, RPM's dropped again. I think that I can then assume that I have no vacuum leaks. I sprayed carb cleaner around all the vacuum connections with no increase in RPMs again, so I think vacuum leaks are not the problem (damn)
I'm beginning to wonder about a couple things. First, the carbs were off for a few weeks, wondering if the floats are hanging up somewhere due to being dry for so long. on second thought, the fact that I can gently roll up to redline but a sudden opening of the carbs gives me the RPM loss doesn't seem to make sense either.
I thought that the Idle Airshot System might be malfunctioning, but I would assume that would give me a lean condition at high RPM's and partially blocking the airflow would give me a rise in RPMs rather than a drop?

any other thoughts?[/QUOTE

The plot thickens, covering up the intake with your hand can also be a little dicey as you are now putting a vacuum situation on the numerous air bleeds at the top of the carb and it can do funky things.

Is everything your doing in neutral and if not is the OD light coming on. Could be one carb is cutting out (fuel) look down the throats at trouble zone you should see a nice cloud of fuel vapor being sucked in from slide needle area with the slides open equal distance, your manometer might catch that too with very different readings.

When using the spray you start off with a little dribble and increase until change noted. Do the spray thing at trouble zone into intake and note any change. And then for kicks put your finger over the hole in bottom of air box at right front under air cleaner at trouble zone and note any change. And for more kicks clamp off hose going from air valves to sub cleaner case on right side at trouble zone and note any change.
 

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Discussion Starter · #14 ·
true, very true.

just for kicks, I tested the Idle Airshot system according to the service manual and it passed.

also for kicks, I took off the air box entirely from the carbs and rapped on the tops of the carbs with a screwdriver handle, just in case anything was hung up, figuring the vibration would help knock things loose.

interestingly enough, when I put it back together, it seems to rev higher without cutting out.

I'm going to put the timing belt covers back on tomorrow and take it out for another quick ride and see if things behave, or if I still have gremlins plaguing me (I even put the bells back on today too :p )
 

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Discussion Starter · #15 ·
tried taking it out for a ride again today, same problem :(

"just to see what would happen", i closed the choke when it was cutting out, and...........nothing happened, no rise, no drop, no effect.

I tried rolling gently up to 6k when the engine began to miss!!! I started pulling plug wires, noticed that the front left cylinder (#2?) was not firing, but after a moment or two, began to fire again. :wtf:
I'm pretty sure the gear selection switch is working because I get a neutral light and the OD light comes on in 5th, so I don't think thats an issue either.


looks like I'm gonna pull the carbs (again) and apply grease to the boots, just in case they are leaking and double check all my vacuum lines, I also have a small water leak down at the pump that will require a new hose, so gonna do that as well. Also gonna replace spark plugs tomorrow.

I'm wondering if the ECU on the 1500 needs to be reset?? does it hold any settings that might be limiting the revs?? gonna disconnect the battery while I'm working on the rest and see if that makes any difference.

has anyone else ran into this kind of issue on their 1500?
 

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They do have a rev limiter set at 5.5k at redline IIRC.
 

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Discussion Starter · #17 ·
interesting, is that 5.5k in neutral and 6.5k in gear? I've never hit any sort of rev limiter before.

I do have a different hear indicator switch in the engine (I broke the old one, this one is used), wonder if I need to jump some of the pins (making the bike think it's in 2nd or 3rd gear) and see if I still hit the limiter. I have the same RPM falloff in every gear.
 

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5.5k limiter anytime and will definitely start missing at 6k. Mine cuts out at exactly 5.5k.

How about holes in the carb slide diaphrams?
 

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Discussion Starter · #19 ·
mine is cutting out at about 4.5k, sorry if I mislead anyone thinking it was a 5.5k, if I dump the throttle open, it cuts out at about 4.5k, if I ease into the throttle, it will go up to redline.

before I tore into the bike, it would go over 100mph no problem, now it has a hard time doing 75

also, before the repair, first gear acceleration was neck-snapping and I loved it!, would run right up to 5.5-6k now it seems to be way more sedate, I know it's not the gearing, clutch isnt slipping, all power is gone at about 4750 rpm, if I keep the throttle open, it will lose RPM's down to about 4200 before picking back up, going up to about 4500rpm but not running well at all.

Both slides appear to be working correctly, they are open about 1/2 way before the engine starts cutting out. I tried manually holding the slides open all the way, and still have the same RPM issue
 

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Discussion Starter · #20 ·
took carbs off, greased the boots, put it all back together, same thing, cutting out at about 4750rpm, bogging down to 4200 then coming back up.

I dont have a timing light to check if the timing is advancing/retarding correctly, is it possible that is the problem?

I also noticed today (don't ask me why it took so long to notice), that I smell unburned gas from the exhaust when it is cutting out.

Soooooo, I'm now thinking its something in the ignition system, will replace plugs tomorrow and get a timing light to check it per the service manual.

any other input would be most appreciated!!

Kaz
 
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