Can't get over 4,500rpm in gear

[Morse]

A few months back I picked up a 98 STD with 34,000 miles.  I got it in pieces (Carbs, airbox, exhaust, all lights and wiring separate from bike) and have no idea about the history of the bike.  I put it together after doing a thorough cleaning of the carbs and it won't go over 4,500 rpm  in 1st and even less in higher gears. It revs fine up to redline when in neutral.  It also has some serious backfires at about the 2k range.  Choke does not make any difference to this problem.  It starts just fine and idles ok, a little rough but nothing too bad.  it does fire on all cylinders.  It has fresh gas, al fluids have been changed.

So far I've rebuilt the carbs twice, replacing all rubber pieces, float valves, pilot screws, slow and main jets on the second rebuild.
I've tried 3 petcocks, one being the high volume non-vacuum style.
Ensured there are no high-spots in the fuel line.
Checked and sealed any vacuum leaks in carbs or airbox
Desmogged (stealth desmog)
Checked all diaphragms for holes.
synced the carbs twice
adjusted pilot screws from 1 7/8 to 2 3/8 turns out(from what I've read this should be fairly rich for these machines)

All this resulted in absolutely no change to the issue.

To me it seems like it's not getting gas, but after the carb cleanings and rebuild as well as petcock, fuel line, and pilot screw changes that doesn't seem to be the case.

I have not done a compression test.  The PO said he did one just before I bought it and it checked out fine but who knows.  I'll be doing one myself in the next few days.

I'm pretty stumped here...so far I've been thinking it could be electrical, bad coils, bad ICM maybe but really I don't know. 

Any ideas or help would be greatly appreciated. Thanks.

[Jims99]

Sounds like a fuel problem to me. But from what you’ve done, may be electrical. I would swap the icm with someone’s to test. Could be timing, maybe not advancing like it should. Also when you first start when cold, check all pipes are getting equally hot. Then you’ll know if it could be a coil. Make sure all connections and grounds are clean. Good luck.

[Skinhead]

Check the cam timing and trigger wheel as well, and does it have a stock ignition system?

[Chrisj CMA]

How is it running at 4500 rpms?  Smooth or like it’s starving for fuel?

[vanagon40]

Probably not the solution, but it will act the same way if starved for air. I had a Honda 360 in the 80s with a similar problem. Turned out I put a pair of gloves directly over the air intakes.

Welcome to the forum.

[Morse]

I'll check the timing and trigger wheel today, come to think of it that might explain both my backfires and poor acceleration...I think the ignition system is stock although I'm not positive. I'll look into how to figure that out here in the forums.

The pipes do all heat up, don't know about equally, I'll check that today too.  At any rate I have a replacement set of coils and wires coming in today so I'll figure out if that was the issue.  I have been considering snagging a used ICM somewhere if nothing else helps.

At 4500 rpms and lower it's pretty smooth.  I've never ridden a Valk before but to me it seems smooth.  As soon as I give it more gas in 4500ish rev range it feels like it's starving, will sort of sputter with no go. As I ease off it feels like it catches again and resumes smooth operation. if I really get on it it doesn't want to go either, I have to sort of ease it up to 4500.

I also considered air starvation...doesn't seem likely to me though, if anything for a while it was getting too much air, PO drilled a hole in the box and one of the filter seals was missing. I've since taped over the hole and gotten a new seal, filter is pretty dirty so I have a new one coming too.

A little more info on this bike: When Idling I occasionally hear a clunk and can hear it from the brake side, seemingly from the front most cylinder (#1, I think). I also do think this bike sat outside for a few years in somewhere cold.  When I got it the coolant overflow had burst (from freezing I assume) and the air box was pretty full of dust and dirt, bike was very dirty.  The glass on the gauges is broken out and the ends of needles snapped off, although they still respond to the bike, accurately it seems.  It was definitely not taken good care of, many nicks and brake fluid bubbling. It seems pretty possible that water and grime could have gotten anywhere in the bike.  Don't know if any of this info might spark someone's intuition but figured I'd put it out there.  Thanks

[Ricky-D]

Just the fact that you can get it to 4500 rpms would indicate there is no problem with the ignition.

***

[Warlock]

I'll check the timing and trigger wheel today, come to think of it that might explain both my backfires and poor acceleration...I think the ignition system is stock although I'm not positive. I'll look into how to figure that out here in the forums.

The pipes do all heat up, don't know about equally, I'll check that today too.  At any rate I have a replacement set of coils and wires coming in today so I'll figure out if that was the issue.  I have been considering snagging a used ICM somewhere if nothing else helps.

At 4500 rpms and lower it's pretty smooth.  I've never ridden a Valk before but to me it seems smooth.  As soon as I give it more gas in 4500ish rev range it feels like it's starving, will sort of sputter with no go. As I ease off it feels like it catches again and resumes smooth operation. if I really get on it it doesn't want to go either, I have to sort of ease it up to 4500.

I also considered air starvation...doesn't seem likely to me though, if anything for a while it was getting too much air, PO drilled a hole in the box and one of the filter seals was missing. I've since taped over the hole and gotten a new seal, filter is pretty dirty so I have a new one coming too.

A little more info on this bike: When Idling I occasionally hear a clunk and can hear it from the brake side, seemingly from the front most cylinder (#1, I think). I also do think this bike sat outside for a few years in somewhere cold.  When I got it the coolant overflow had burst (from freezing I assume) and the air box was pretty full of dust and dirt, bike was very dirty.  The glass on the gauges is broken out and the ends of needles snapped off, although they still respond to the bike, accurately it seems.  It was definitely not taken good care of, many nicks and brake fluid bubbling. It seems pretty possible that water and grime could have gotten anywhere in the bike.  Don't know if any of this info might spark someone's intuition but figured I'd put it out there.  Thanks

Have you tried with the gas cap loose. It could be not enough air to the tank. These are gravity feed and this will cause a big problem. JAT
David

[John Schmidt]

Just the fact that you can get it to 4500 rpms would indicate there is no problem with the ignition.

***

+1....sounds like an airflow issue or timing advance comes into play when under load, just a thought. Might want to check the temp sensor. Will be interesting to hear what you find.

[da prez]

Air intake system must be fully installed or the carbs will not work. BTW ,did you check the petcock function.  I have had them partially to fully plugged.

       da prez

[Forge]

Let us know how it runs after you install the clean air filter.

[Toovalks]

My first Valkyrie purchase... also was a "lean-to Queen"...rust from the Tank has repeatedly plugged up everything... it has taken a complete acid wash to clear it up.

[Chrisj CMA]

When you rebuilt the carbs did you make sure the little vent passages were clear. If partially plugged they may cause the filling of the float bowls to be slower than the consumption rate at higher rpms

[h13man]

Mine had same issue 6 yrs./24,000 mi. ago. Full tank mixed with a half a can of Seafoam fixed the issue within 3.5 miles.

[Morse]

Thanks for the replies everyone, I'm going to be heading down the list of suggestions you guys left over the next few days.  I'll keep updating the forum as I make progress.

So far I can say that I did check petcock function.  The OEM one leaked, instead of rebuilding I replaced it with a knockoff vacuum petcock, then replaced that one with a high volume free-flow petcock meant for harleys that fit, I checked the fuel flow from it and it seemed really good.

As far as vent tubes go, those are the joiner tubes and the 3-way air joint pictured on 5-16 of the manual, right? They lead to the hose that connects under the airbox. I replaced the o-rings on those tubes and cleaned them out as well as the holes they go into while I was in there.  If those are the vent tubes then I'm pretty certain they're clear.

I've tried B-12 and seafoam a few times with no luck so far but I'm still putting it in there.

I will definitely check the temp sensor out, I'm getting backfires but can't find any vacuum leaks, exhaust leaks, etc... Leads me to believe I might have a timing advance issue or even had the belt slip a tooth. 

Otherwise I did a compression test last night, it was getting dark so I ended up doing it on a cold engine, I know that won't give me an accurate reading (should read way low if I'm not mistaken) I got a solid 90 on each cylinder, at least they're consistent. I think I read it should be close to 170 when hot, hopefully I can get to that and check some other things out today.

[Willow]

For what it's worth (probably not much) that sounds like what occurred when I experimented with a Dyna 3000 aggressive curve on an Interstate.  Too much advance was what I decided happened under load and higher RPM.

[Chrisj CMA]

The vents I am talking about are inside the carbs. There’s three little towers. Two are the jets and one is just a hole that vents the bowl so a vacuum doesn’t build and more fuel can flow into the bowl

[Morse]

Ah, I see.  I did spray everything out with compressed air, carb cleaner, and used wires and a carb cleaning kit on all the holes and remember doing it to those three towers. That was a few months ago on the original cleaning though so I don't remember it all that well.  If the timing and other things all check out ok I'll go back in and check those towers, particularly the the hole one, out again, just have to wait for it to stop raining out here so I can get on it.

[9Ball]

Did you test the air cut valves and replace the plug and short rubber tube on each carburetor?  Also, is there an inline fuel filter between peacock and carbs?

[Morse]

9Ball, i haven't tested the air cut valves.  All I've done is spray them with starter fluid to check for vacuum leaks.  The original o-rings are still in there, something I should have replaced when I separated the carbs for the joiner tube o-rings but didn't have the parts at that time.  I have replaced all the rubber tubes but not sure what the plug you asked about is.

I did have an in-line filter in at one time but I removed it and just rely on the screen over the petcock for now.  In or out the bike runs about the same at the moment.

I am curious though what bad air cut valves would do.  From my understanding they cut off some air under hard decel to stop popping but beyond that I know nothing about them.  If they went bad in a certain way could they cause issue with acceleration?

[9Ball]

I don’t believe so.  They could be a source of air in leakage and you are correct about their function.  Just trying to see where you could be having air leaks.

Do you have adjustable needles?  Severe popping can also be due to too lean of a mixture.  That’s what I was getting at with your possible lean condition.  Some have had trouble with fuel filters, me included. Are you running a K&N air filter?  There could be a another source of air leakage and also a lean condition if improperly installed.

[Morse]

I haven't messed with the needles, i suspect they're stock and in the stock position but I don't really know.  Everything else in the carbs was stock when I pulled them apart.  I do have new needles. If the other things I'm trying right now don't fix the issue I'll be pulling the carbs to check the vent tubes.  At that point I'll probably put the new needles in and then I'll know the position for sure.

I have been suspecting a possible lean mixture.  I've been checking for vacuum leaks with starter fluid but when I think I've found one I can never re-create the rise in idle speed when I spray the same place.  After some frustrating hours I concluded that some fumes are probably just making it up to the airbox intake.  Also when I sync the carbs all manometer fluids stay pretty level.  In my experience with other bikes when there is an air leak the cylinder with the leak will wander and I won't be able to sync it.

I have the stock air filter and have a new one that just came in.  I'll be putting that one in and checking the ect tomorrow.  Hoping ect is bad and I'm having timing advance/retarding issues from it, making pops and giving accel trouble. We'll see.

[9Ball]

I haven't messed with the needles, i suspect they're stock and in the stock position but I don't really know.  Everything else in the carbs was stock when I pulled them apart.  I do have new needles. If the other things I'm trying right now don't fix the issue I'll be pulling the carbs to check the vent tubes.  At that point I'll probably put the new needles in and then I'll know the position for sure.

I have been suspecting a possible lean mixture.  I've been checking for vacuum leaks with starter fluid but when I think I've found one I can never re-create the rise in idle speed when I spray the same place.  After some frustrating hours I concluded that some fumes are probably just making it up to the airbox intake.  Also when I sync the carbs all manometer fluids stay pretty level.  In my experience with other bikes when there is an air leak the cylinder with the leak will wander and I won't be able to sync it.

I have the stock air filter and have a new one that just came in.  I'll be putting that one in and checking the ect tomorrow.  Hoping ect is bad and I'm having timing advance/retarding issues from it, making pops and giving accel trouble. We'll see.

Before you tear everything apart again, check a few things.

Take the carb covers off and check that you have either stock needles or aftermarket adjustable needles and how many shim washers are on each needle.  If all stock, inspect the diaphragms for holes or tears and if good then make sure they are seated completely when putting the covers back on .  Inspect that the enrichners are properly engaged in the sliding bracket.

Let us know what you find.

[tonybluegoat]

You guys are smarter than me on this stuff. But I have an 81 xj650 (4 carb) that had this same problem.  It would "bog down" at a certain rpm under load.. would rev up fine in neutral. The problem was particularly bad on hills.  I put bigger jets in the carb and fixed the problem right up. Everyone on the forums screamed that I didn't really "fix the problem." But they said that about my putting a bigger battery in it too. I'm a knucklehead but I have a running 1981 xj650 that has been on the road for years at this point... I've never even cleaned the carbs because I know if I take them apart the bike may never run again.

My point?  Check the jet size. (but my bike didn't pop or backfire... and ag'in... knuckhead.)

[Morse]

Thanks Bluegoat, sounds like we've got some similarities.  My daily driver is an 83 yama venture and it is all sorts of jerry-riged to get it going right.  So long as it runs, I don't care how it got there.

[CoreyP]

. Everyone on the forums screamed that I didn't really "fix the problem." But they said that about my putting a bigger battery in it too. I'm a knucklehead but I have a running 1981 xj650 that has been on the road for years at this point... I've never even cleaned the carbs because I know if I take them apart the bike may never run again.

No you didn't really fix the problem, you found a work around. LOL. With an 1981 bike I really won't care just as long as it worked. LOL.

[tonybluegoat]

Thanks Bluegoat, sounds like we've got some similarities.  My daily driver is an 83 yama venture and it is all sorts of jerry-riged to get it going right.  So long as it runs, I don't care how it got there.

 



This was a fun one. Some exhaust bolts snapped. So we built an “outrigger” that uses the frame to push the manifold to the engine.

[Morse]

Just giving an update on my issue.  I feel pretty certain I can rule out a carb problem.  just spent this last week pulling them all the way apart, soaking each seperate carb in a berryman's carb dip overnight then boiling them in lemon juice and water and finally blowing out each hole with compressed air.  I also soaked and boiled the jets and blew them out, cleaned all the remaining parts too.  Everything was spotless and I could get air through all the holes.  I also changed the o-rings in the air-cut offs. 

I changed the etc sensor and put in a new oem air filter.

After all that I put it all back together and...no change at all, not one additional rpm.  Also still getting some backfires.

Anyhow, now I'm thinking I'll pick up a used ecm, maybe an I/S one so if ecm is not the problem I'll still get something out of it.  One other thing, the fuel line I'm using is 8mm or 5/16.  The bike didn't come with the oem one and I'm not sure how big the I/D is supposed to be.  I doubt the line itself would be a problem but the T I'm using is a thick plastic one, I'm thinking maybe it's so thick that it's slowing down fuel delivery.  It's easy enough to change.  I'll probably just get some 10mm hose with 10mm T and see if that helps.

One last note, the rpm that the bike stops at is different in every gear, 4,500 is just in first with each higher gear having a lower top possible rpm, 5th is close to just 3,000.  it also seems that the top rpm in each gear is always exactly the same.  I would think that if it were fuel or air that it would vary some, especially with a carb clean or when switching between petcocks.

[Hook#3287]

One other thing, the fuel line I'm using is 8mm or 5/16.  The bike didn't come with the oem one and I'm not sure how big the I/D is supposed to be.  I doubt the line itself would be a problem but the T I'm using is a thick plastic one, I'm thinking maybe it's so thick that it's slowing down fuel delivery.  It's easy enough to change.  I'll probably just get some 10mm hose with 10mm T and see if that helps.

Are you talking about #15 ?

https://www.partzilla.com/catalog/honda/motorcycle/1998/gl1500c-a-valkyrie/fuel-tank

or # 10 & 12 here?

https://www.partzilla.com/catalog/honda/motorcycle/1998/gl1500c-a-valkyrie/carburetor-tubing

Or all?

It doesn't sound like a fuel issue, the way it cuts out at the same every time.  I agree to the thinking a fuel issue would be variable, depending on throttle twisting.

But I wouldn't run 5/16 in place of those hoses either.  I'd get larger "T's" also.  I would think highway riding would cause fuel starvation with that size hose.

I did this on my Bobber and it's done well.  Being a Bobber, it's around town riding, so I've never tested her on the highway for long periods of time and fuel starvation.

http://www.valkyrieforum.com/bbs/index.php/topic,93131.0.html

[Ricky-D]

Thinking that you could sign up for a photo hosting site so that you could post some pictures. It would be a great help, and I feel positive you can get some suggestions about a good site to employ, from members right here on this forum.

Here's a thought. I think having a single carburetor not helping could possibly drag the performance down to what you are experiencing. What I am suggesting is that it doesn't have to be all six carburetors necessarily (in unison) to be causing  the problem you are experiencing.

Still no information on a question that was asked about the slides and needles. Especially the needles about whether they are stock, or not.

I also agree with your thought about getting another ECM, although they are not generally know to be a problem. Did you ever say your's is a stock Honda ECM?

Good luck buddy.

[franco6]

 If the bike was outside and rusty ,has anyone put tank liner inside the tank? often the air vent is plugged and limits the flow of fuel!

[Morse]

Hey Everyone, I was gone for the holidays and didn't get a chance to respond. 

For the fuel line I was talking about 15, 10, and 12 but I've replaced them all with 3/8 line and a brass T, made sure no high spots and all that but it didn't change anything.

I put in the I/S ecm, that seemed to change things a little bit but it's still not getting much over 4500. The popping now stops totally if the choke is left on though, so that's some progress.

As far as the needles go I believe they are stock, they have just the one washer that the manual shows, so no shimming as far as I can tell.

I also have moved the pilot screws out to about 3 1/4 for the front two carbs, the rest are at 2 3/8 turns out. I read the front two carbs sometimes struggle to get gas.  It didn't seem to change much.  Might run them all a little richer, see if that helps any.

My plan right now is to try and drive it a hundred or so miles with either some tc w3 2 stroke marine oil in the gas or some b-12, maybe there is some carbon buildup somewhere and I can clean it out of there with a long ride. 

[Morse]

One more thing. The backfires are almost exclusively from the clutch side and get worse as I rev it.  At 6000rpm (in neutral it revs fine) they are so frequent it sounds like a bag of popcorn, at idle it is probably every 4 or five seconds.  It runs worse with the choke on but the backfires disappear.

[Morse]

As far as the tank vent goes too, I've tried it with the gas cap open and it didn't change anything.  Fortunately the tank was stored empty and doesn't have any rust.  I've rinsed it out and didn't find any material floating around in there.

[Ricky-D]

Seems to me, I remember a fellow having similar kinda problem with his Valkyrie and it turned out he had switched a couple of spark plug wires, that still let the engine run, however not really well.

I'm not saying this is your fix, but it wouldn't hurt to ascertain the wires from the coils are connected to the proper cylinders.

***

[gordonv]

With the addition of the IS ecm, isn't there another mod, the addition of a second temp sensor?

Doesn't the IS ecm change the dwell after the bike warms up? Wouldn't this also keep a "cold" engine from running too high of an rpm to avoid damage.

[Morse]

Gordonv - I haven't heard about the second temp sensor.  I was under the impression the I/S ecm was plug and play with an STD but I could easily be wrong.  I've done a little searching on these boards and haven't seen anything on the second temp sensor.   Do you know where I could find some info on it?

Ricky D - I am pretty certain the wires are going right.  I did replace the coils and wires and followed the diagram on the parts microphiche to make sure they were going to the proper cylinders.  I'll double check though.

I have narrowed down the backfire to just cylinder 4(Middle clutch side if I'm not mistaken).  With no choke I am getting lots of backfiring from cylinder 4.  When I unplug the plug wire for cyl 4 - with the choke off - all the backfires stop at both idle and when revving.  Also the idle does not change at all when I unplug it, but I know the cylinder does fire because the exhaust gets hot just as quickly as the others.

 With the choke fully on and the bike warm the idle starts to get weird (like you might expect from it drowning in fuel with the choke being on) but cylinder #4 stops backfiring at all rpms.  Also the idle will change, like it does for the other cylinders, when I remove the plug wire.

I have swapped plugs and the problem doesn't follow the plug.

I have sprayed two full cans of stater fluid looking for vacuum leaks and haven't found any. 

As far as I can tell cyl 4 seems to not be getting enough gas or has an air leak that I can't find.  I am going to try turning out the mixture screw tomorrow but I feel like even if that solves the issue it isn't the root of the problem, it is set at 2 3/8 turns out right now.

Is there anything else that would keep enough fuel from getting to the cylinder at all rpms that the enrichening circuit somehow circumnavigates?

Also if anyone has some good fuel additive suggestions to clear carbon from the valves, cyl chamber etc... that would be much appreciated.  I've thought about berryman's b-60, a beefed up b-12 as far as I can see.  Does anyone know about this stuff or have a different good suggestion?

Thanks all.

 

[Valker]

Have you tested the compression on Cylinder 4?

[h13man]

1/2 can of Seafoam to a fresh tank of gas. Worked on mine and that was 6 yrs. ago with no more issues.

[wirral_biker]

Seafoam.    I drained the float bowl on carb 2 (  that was causing a spitting/missing on start up )....back filled the float bowl with seafoam and ran her.  Better, so did it again, much better...so as soon as spring arrives ( roads covered in salt over here in Blighty ) I'll bung the rest of the can in the tank and take her for a run  

I'd done a lot of what you have, even removed exhaust and put new gaskets in etc
new plugs/checked leads etc.......but it looks like it is just a blocked carb.
Good luck !