Can't get over 4,500rpm in gear-Valkyrie help


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Morse
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Joined: Mon Jan 06, 2020 12:28 pm
Location: Mesa, AZ
Motorcycle: 98 Honda GL1500C Valkyrie, 83 Yamaha Venture, 08 Kawasaki KLR650

Can't get over 4,500rpm in gear-Valkyrie help

Post by Morse » Mon Jan 06, 2020 2:37 pm



Hello all. This is a question regarding a 98 GL1500C Valkyrie STD 34,000 miles, everything stock as far as I know but is desmogged. I've been posting in the Valkyrie forums on this but so far, although I've gotten a lot of help and good suggestions, we haven't been able to figure anything out. This is the link to that discussion: http://www.valkyrieforum.com/bbs/index. ... 080.0.html

I figure the bikes are alike in a lot of ways and maybe someone here has experienced something similar or has some suggestions.

So the problem is the bike won't go over 4,500 rpms in gear, and at each higher gear it gets worse with 5th not going much over 3,000. It idles nicely and starts right up with very little need for choke. Has good power until 4,500 rpm then feels like it hit a rev limiter and won't go any higher. All cylinders are firing and seemingly equally (tested by hand). It does rev just fine up to redline in neutral. No noticeable backfires at the moment.

I bought the bike 6 months ago in pieces and know almost nothing about it. It is in bad shape, looks beat up but not laid down (more like an angry girlfriend's revenge, valve cover keyed, purposeful looking scratches, tach and speedo glass and needles broken out) probably was stored outside and had not been run for years.

So far
-I've checked compression (all good)
-cleaned and rebuilt carbs twice (the second being full tear down, carb soak, lemon juice boil, compressed air blow out all holes, replace all rubber components except diaphragms[but did check them for holes])
-tried 3 separate petcocks (one being high flow non-vacuum)
-checked for air obstruction in airbox, put in new filter and o rings
-eliminated all vacuum leaks
-changed all fluids
-swapped ecms
-changed temp sensor
-tried wider i/d fuel line and T
-ensured no dips or high spots in fuel line
-removed fuel filter (just using tank screen now)
-checked the timing for a skipped tooth but have not yet checked with a timing light
-ensured tank vents not clogged
-synced the carbs
-changed all spark plugs, wires, and coils. Ensured they are going to the correct plugs
-new alternator
-checked all fuses
-new battery
-no rust in the tank, cleaned it out, no particles floating around in there
-the jets are stock 100 mains, 35 slows
-I have also messed with the mixture screws to see if it had any effect on the issue

I'm probably forgetting some things but nothing else is coming to mind right now. Has anyone heard of a similar issue on a wing or valkyrie? Any ideas are welcome and much appreciated. Thank you.



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virgilmobile
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Re: Can't get over 4,500rpm in gear-Valkyrie help

Post by virgilmobile » Tue Jan 07, 2020 1:40 pm

I'll take a poke at this.
Your engine can red line with no load.
It gets progressively worse as more load is demanded.
The 3 basics..
Spark..compression...fuel mixture.
Ok.Compression not a problem.
Sounds like the spark (may) be ok...altho a weak spark can cause this.Is the voltage at the coils ok and if you lift a plug wire does it have a good healthy snapping?
Fuel mixture...
This is a few things involved...It has to"breath" unobstructed...and exhale the same way.(obstruction in the exhaust.)Dirt dobbers?Mouse nest?
The slides must work properly to get the air flow and fuel needed to keep the mixture correct.slide movement can be checked by using a shop vac to simulate the engine or actually looking at them with a mirror while revving the engine..Are the spark plugs showing signs of a lean condition?

Just a few points to ponder.Hope it puts you on track to solving this.
Keep us posted please.

Morse
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Joined: Mon Jan 06, 2020 12:28 pm
Location: Mesa, AZ
Motorcycle: 98 Honda GL1500C Valkyrie, 83 Yamaha Venture, 08 Kawasaki KLR650

Re: Can't get over 4,500rpm in gear-Valkyrie help

Post by Morse » Thu Jan 09, 2020 12:57 pm

Thanks Virgilmobile for the response. I've checked most of these things. Spark seems strong, very snappy. The plugs look normal (might not have driven enough to tell and have 3/4 can of seafoam in there right now, so that might be messing with them) but I think you are on to something with the slide movement.

I took it out for it's first real ride last night (had a shrader valve held together with what looked like rtv until I replaced it yesterday. Didn't want to go too far on that)

What I found was that my throttle is limited. Over around 1/4 throttle I have absolutely no power, it starts engine braking if I go over 1/4. I think that is what's limiting my rpms. Until 1/4 throttle I have plenty of power.

This sounds like possibly some clogged mains but they are new (stock 100s) and the carbs were spotless when I put them back together. My thought is that my diaphragms might be too stiff, not allowing for the slides to move the needles up. I had one that was like hard plastic that cracked when I pushed the slide up. That was months ago and i replaced it. The replaced one is definitely softer than the other ones. They all move fine and the slides seem to return and move freely enough (and hold vacuum enough that the slide doesn't immediately click back into place). But it still seems possible they are too hard.

I'll be testing this over the next couple days, either by shop vac, mirror, or endoscope.

If this does turn out to be the issue does anybody know a trick for softening diaphragm rubber? I've heard people suggest soaking in wintergreen oil/alcohol mixtures, dot 3, non-ethanol gas, and lemon-juice but I'm concerned about swelling (and have heard lemon juice only works until the plastic dries). If anyone has experience or other suggestions it would be greatly appreciated. Thanks.

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CrystalPistol
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Re: Can't get over 4,500rpm in gear-Valkyrie help

Post by CrystalPistol » Thu Jan 09, 2020 1:35 pm

Have known some who owned a Valkyrie, no one I know seems to keep them due to poor mileage or rapidly deteriorating performance.

Stiff diaphragms might be too stiff, one already replaced due to hole when flexed? ... time to replace the other 5 as well.

Ru-Glyde is a soap like rubber conditioner, used for installing tires, makes a good dressing that will not harm the rubber. Ask NAPA. Any benefit is likely short term in the carbs.

Check throttle cable adjustment too.
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ct1500
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Re: Can't get over 4,500rpm in gear-Valkyrie help

Post by ct1500 » Thu Jan 09, 2020 5:02 pm

Morse wrote:
Thu Jan 09, 2020 12:57 pm
What I found was that my throttle is limited. Over around 1/4 throttle I have absolutely no power, it starts engine braking if I go over 1/4. I think that is what's limiting my rpms. Until 1/4 throttle I have plenty of power.
Being able to rev an engine in neutral is fairly meaningless as a no load condition taxes the engine systems very little. I have been around a Valk once or twice and with six carbs, running problems are usually associated with them. You have replaced a lot of parts so time to try something new as I think the engine is being fuel starved.

Get yourself a can of cyclo carb clean with a straw nozzle. Find some small diameter windshield washer hose or vacuum hose that you can insert the straw into. You are going to insert one end of the hose a few inches into the air box air intake and tape into place. The other end of hose is going to be up around the seat area. You are going to crotch the carb clean spray with the straw inserted into hose for a road test. Get the machine up to your 1/4 throttle top end and give the spray a good press. If fuel starved the RPM and power will climb. 8-)

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ka4yqi
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Re: Can't get over 4,500rpm in gear-Valkyrie help

Post by ka4yqi » Fri Jan 10, 2020 6:34 am

Never had the problem with a motorcycle doing that, but did with a Suzuki samurai. Motor ran well at low rpms but lost it in the higher rpms. Drove me nuts. I check everything I could think. I found that when they built the engine the cam was 1 tooth retarded on the cam timing belt. Before it top out about 48 to 50 mph, after setting it right it do 90 mph. So check the timing belts for correct timing. I notice you check everything else and someone may have been 1 tooth off.

It a idea,



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