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funky decel...

Old 10-18-2007, 11:14 PM
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Question Odd Problems With My VTR...

Problem -
-When I rev my VTR, upon returning to idle it will pause at 2,200 rpm before settling down at 1,200 rpm. If I set the idle at 1,700 rpm it will pause at 2,700... and so on.
-When it gets warm (200 degrees) it will idle down then die.
-Excessive gas consumption, I'm getting 34mpg when I should be getting 40.
-When warming up with the choke completely out it will only stay running for 60 seconds or so.
-Seems to be lacking bottom end power.

Remedies -
-Sonic carb clean X3.
-Pilot screw adjustment(2:3/4 turns out).
-New o-rings for air cut off valve.
-Carb sync X3.
-Swapped entire carburetor assembly off a good running VTR - same results.
-Checked petcock vacuum - good.
-Fuel delivery - good.
-Checked for intake leaks - none found.
-Tested wiring to tps - good.
-Tested tps - good
-Checked valve clearance - in spec.
-Changed spark plugs.
-Compression test - 150psi.
-Leak down test ~5% front and rear
-Pinched fuel line to each carb to get it to run on each cylinder individually, both have the same issue.
-Checked cam timing - good.
-Swapped coils with spark plug cap and wire from another vtr... same issue.
-Swapped converter unit and ICM with known working units.
-Checked for continuity from coil connection to plug at converter unit - good.
-Found choke housing was separated, snapped it back together.
-Rejetted, but still has the same issue (although, running a 42 pilot jet cures the "idle down and die" it creates a lean surge.
-Rebuilt the heads. Found bent valves and hammered valve seats. (same issue remains)


Tech. Info.
- Elevation 5,200'.
-Pair system removed.
-Yoshimura slip-on's (problem occurred before pair removal & slip-on's).
-10,500 miles on the clock. (Had the same problem at 4,500 miles when I purchased it)
-Stock jetting (175/178/45). (UPDATE - currently running FPJK RM180/FM178/PJ45/NC middle)


I'm pretty sure I've ruled out almost every possible mechanical issue...


Last edited by inderocker; 05-14-2008 at 08:10 PM. Reason: UPDATE!!
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Old 10-18-2007, 11:28 PM
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I know very little about carburetors and I won't lie about that...I'm an EFI guy. So, speaking from an EFI point of view...everything you've done has been basically carb-related. Have you checked TPS voltage? Not sure how it works on bikes but on many efi cars, a hanging rev *can* be caused by an overly high tps reading. Or a lean mixture, which youre obviously already looking for.

Last edited by SuperHawkins; 10-18-2007 at 11:31 PM.
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Old 10-19-2007, 05:55 AM
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assuming everything else is stock? And also assuming you had the bike at this elevation in the past and it ran fine? Check the choke cables and mechanisms as they insert into the carbs: they should expand/retract and seat well. The times I've had idles hang up like that it has always been the fuel mixture screw or an air leak somewhere. Do you have a 90 degree tool to adjust while the carbs are on the bike? If so, just turn in till you just get a drop in idle then back out 1/2 turn. They are a pain to reach/adjust on the bike.
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Old 10-19-2007, 06:47 AM
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.. sorry, But i love your avatar Cliby...
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Old 10-19-2007, 08:31 AM
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hanging idle normally means your running lean. but at elevation 5'2 & your at 3 3/4 out ( which is normally way rich ) i'd say you have an air leak or a little blockage in the pilot jets.

air leaks are easy to find with wd-40. spray it all around the carbs & listen for the engine to spead up.

tim
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Old 10-19-2007, 10:16 PM
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By chance have you pulled your plugs to look at their condition? I'm with trinc in that the mixture screws are too far out for your elevation. Check to make sure there is no vacuum leak in the rear cylinder vacuum tube to the petcock. Then check to see if the carbs are fully seated in their boots. Last, check the hose clamps snug.
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Old 10-20-2007, 05:40 AM
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Originally Posted by SuperHawkins View Post
I know very little about carburetors and I won't lie about that...I'm an EFI guy. So, speaking from an EFI point of view...everything you've done has been basically carb-related. Have you checked TPS voltage? Not sure how it works on bikes but on many efi cars, a hanging rev *can* be caused by an overly high tps reading. Or a lean mixture, which youre obviously already looking for.
I second this, TPS got to be way off, too much advance, the bike got to be a dog at accel around 3K rpm
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Old 10-20-2007, 09:08 AM
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Well... I ruled out carburetion. I swaped the carbs from my buddy's '98 and got the same results. This also rules out the tps itself.
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Old 10-20-2007, 09:36 AM
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Originally Posted by inderocker View Post
Well... I ruled out carburetion. I swaped the carbs from my buddy's '98 and got the same results. This also rules out the tps itself.
How long an amount of time does the idle hang? Are we talking half-second, 1, 2, 5 seconds?

Also, when's the last time you checked the condition of your throttle cables? And the throttle itself (without the cables attached)?


Last one, but it's more for the more carb-knowledgeable here - what was the set up on the carbs you swapped? Just because you swapped the entire assembly doesn't mean much if you still set it up the same.
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Old 10-20-2007, 09:37 AM
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I,ve had good results by performing the idle drop procedure. page 5-21
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Old 10-20-2007, 01:26 PM
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Check the TPS wiring, make sure the IM recieve the signal, otherwise I'm clueless
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Old 10-20-2007, 02:43 PM
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usually hangs for about 1-2 seconds, and it's always at 2k rpm.
the throttle cables are still basically brand new and move freely
the carbs i swapped were using stock jetting but a different pilot screw adjustment.


Originally Posted by Slim View Post
How long an amount of time does the idle hang? Are we talking half-second, 1, 2, 5 seconds?

Also, when's the last time you checked the condition of your throttle cables? And the throttle itself (without the cables attached)?


Last one, but it's more for the more carb-knowledgeable here - what was the set up on the carbs you swapped? Just because you swapped the entire assembly doesn't mean much if you still set it up the same.

Last edited by inderocker; 10-23-2007 at 11:38 PM.
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Old 10-22-2007, 05:23 PM
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Check your carb boots. Do a vacuum drop test on the petcock and it's tubing.
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Old 10-23-2007, 12:56 AM
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I called the Honda tech line today... they were as much help as they've ever been...
"wow... I don't know what to tell ya..."

Last edited by inderocker; 10-23-2007 at 01:44 AM.
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Old 10-23-2007, 01:47 AM
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updated original post!
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Old 10-26-2007, 12:01 AM
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There's only so many things that could be wrong... As far as TPS goes....factory spec range is pretty wide, has it ever been adjusted? Given your fuel economy and how much fuel you're throwing at it, I'd say it still sounds like mis-routed vacuum lines or a leak and after a second or two the bike is accomodating itself but still not right. Hows throttle response on a hard, unloaded off-idle rev? In my experience tuning cars, a lean condition produces a high, hanging idle and a sharp quick rev with occasional pinging, more noticeable under load....whereas a rich condition produces a lower, more stumbling idle, with a much slower, softer feel on rev plus hesitation, in addition to a drop and raise in idle upon decel.

But like Greg said, which is a huge point and I havent seen a reply mentioned....pull your plugs! That might tell you if the problem is isolated in a particular cylinder, and also give you an idea on your mixture.
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Old 10-26-2007, 04:39 AM
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If the TPS test failed, check your harness, it may be unplugged all the time, pulling timing and messing up your mileage (burning in the exhaust, heating up valves)
Get a multimeter and measure the resistance between the yellow/black and green/black wire from the unplugged timing module connector, you should have between 4000 and 6000 ohms. At the TPS connector, ignition ON you should have close to 5 V.

Last edited by gboezio; 10-26-2007 at 04:45 AM.
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Old 10-26-2007, 01:37 PM
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Originally Posted by SuperHawkins View Post
There's only so many things that could be wrong... As far as TPS goes....factory spec range is pretty wide, has it ever been adjusted? Given your fuel economy and how much fuel you're throwing at it, I'd say it still sounds like mis-routed vacuum lines or a leak and after a second or two the bike is accomodating itself but still not right. Hows throttle response on a hard, unloaded off-idle rev? In my experience tuning cars, a lean condition produces a high, hanging idle and a sharp quick rev with occasional pinging, more noticeable under load....whereas a rich condition produces a lower, more stumbling idle, with a much slower, softer feel on rev plus hesitation, in addition to a drop and raise in idle upon decel.

But like Greg said, which is a huge point and I havent seen a reply mentioned....pull your plugs! That might tell you if the problem is isolated in a particular cylinder, and also give you an idea on your mixture.
The only vacuum line that bike has is the vacuum for the petcock... well that and the lines that go from the acv's to the cabs. Taps on both my cabs and the cabs i had swapped out had never been adjusted. all signs about the hanging rev point to a lean mixture... no doubt. All other signs point to a rich condition (excessive fuel consumption, blubbering when throttle is snapped). Plugs have already been pulled, they were darker than they should of been, but they weren't black. new plugs were installed. I updated the original post a few days ago to show what has been done already
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Old 10-26-2007, 01:39 PM
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Originally Posted by gboezio View Post
If the TPS test failed, check your harness, it may be unplugged all the time, pulling timing and messing up your mileage (burning in the exhaust, heating up valves)
Get a multimeter and measure the resistance between the yellow/black and green/black wire from the unplugged timing module connector, you should have between 4000 and 6000 ohms. At the TPS connector, ignition ON you should have close to 5 V.
Original post has been updated. All electrical checked out ok.
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Old 10-26-2007, 03:06 PM
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Ok then, well I'll dump all my thoughts and do what you feel that is good.
Try a leakdown test, the compression test can't tell it all. Homemade LT by me
Get a timing gun and check spark all across the rpm range, specially around the problem RPM.
The problem can be caused by a malfunction that affect low idle, idle adjust could be 2000 RPM, then the trouble kicks in and the RPM drops. You probably have adjusted it so it can run, thus raising the idle speed.
Bad plug type could cause such a thing, tight gaps and incorrect length threads, specially the exotic metals, that "replace" OEM
Is the voltage dropping low at idle. ??
Is the idle irregular ?? Quits sometime ??
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Old 10-26-2007, 03:32 PM
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Have you done any airbox mods?
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Old 10-26-2007, 03:55 PM
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Originally Posted by gboezio View Post
Ok then, well I'll dump all my thoughts and do what you feel that is good.
Try a leakdown test, the compression test can't tell it all. Homemade LT by me
Get a timing gun and check spark all across the rpm range, specially around the problem RPM.
The problem can be caused by a malfunction that affect low idle, idle adjust could be 2000 RPM, then the trouble kicks in and the RPM drops. You probably have adjusted it so it can run, thus raising the idle speed.
Bad plug type could cause such a thing, tight gaps and incorrect length threads, specially the exotic metals, that "replace" OEM
Is the voltage dropping low at idle. ??
Is the idle irregular ?? Quits sometime ??
Whoops.. forgot to add the rear spark situation to the first post - hooked up a timing light to the front coil, and had good constant spark throughout the rpm range... hooked it up to the rear and lost spark around and lost spark intermittently throughout the rpm range, most noticeably at 5k rpm. I swapped the rear coil (plug wire and cap) with my buddies super hawk.... same problem. continuity test from coil connection to converter unit came - good. idle is irregular once the bike has warmed up... it will die at every stop light by the time i get to town. I'm using NGK DPR9EVX-9 spark plugs. Voltage is great at idle and upper rpm's.

Last edited by inderocker; 10-26-2007 at 03:58 PM.
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Old 10-26-2007, 04:09 PM
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Try swapping the ICM from one of your Buddy's bike to see if it make a difference. If it's still there I'll call a bad plug (defect), or a bad wires, they may test ok, but sometimes under load or vibration, voltage drops. There is continuity, or the rear would not run at all, it' a matter of how good is it. It could come from the pulse sensor, but unlikely, loose screw could affect how it pick the signal, I think the front is first tooth and the rear is first missing.

Last edited by gboezio; 10-26-2007 at 04:12 PM.
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Old 10-26-2007, 06:04 PM
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unfortunetly... his is a '98 so I can't switch icm's.
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Old 10-27-2007, 07:09 PM
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I got my new ICM and Converter Unit in today.... unfortunetly... niether did the trick.
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Old 10-27-2007, 07:11 PM
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Originally Posted by gboezio View Post
Try swapping the ICM from one of your Buddy's bike to see if it make a difference. If it's still there I'll call a bad plug (defect), or a bad wires, they may test ok, but sometimes under load or vibration, voltage drops. There is continuity, or the rear would not run at all, it' a matter of how good is it. It could come from the pulse sensor, but unlikely, loose screw could affect how it pick the signal, I think the front is first tooth and the rear is first missing.
If it was the pulse sensor wouldn't the front cylinder cut out as well?
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Old 10-28-2007, 12:56 AM
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It's the least resort check, but I really suspect wiring issues for now, you pretty went around everything except wiring under load, I think it's scope material, I'd hook a scope to the coil input to check for correct dwell and good signal, if the signal is good, that leaves spark plugs and coil. Then hook up to ICM output, check signal, then hook up to CPS to check the signal. You can check the Pulse genwith a multimeter with a peak hold on it, 0,7 V peak if I remember right.
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Old 10-28-2007, 06:41 AM
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0.7 peak is correct
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Old 01-03-2008, 09:35 PM
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When I first tore into my VTR I found that the choke junction housing was not snapped together properly. Judging by the previous owner and the low miles, I have to assume that the gas tank has never been lifted before. Theoretically the choke has been on for 4,500 miles. obviously this explains the excessive carbon build-up.

Since then, I have removed the heads and found almost every valve is shot in one way or another. Some are slightly bent, some have grooves, and a few looked decent at best... not what you'd expect from a bike with only 4,500 miles.

I've placed an order for all new valves, seals, gaskets, keepers, etc.. , ended up costing me $550 in parts. Hopefully this cures the problem. :unsure:
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Old 05-14-2008, 08:11 PM
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Video added.
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